- Email: [email protected]
An enhanced premium power park configuration using active power and voltage conditioning devices
Control Engineering Practice 21 (2013) 1542–1552
Contents lists available at ScienceDirect
Control Engineering Practice journal homepage: www.elsevier.com/locate/conengprac
An enhanced premium power park configuration using active power and voltage conditioning devices Masoud Farhoodnea n, Azah Mohamed, Hussain Shareef, Hadi Zayandehroodi Department of Electrical, Electronic and Systems Engineering, University Kebangsaan, Malaysia
art ic l e i nf o
a b s t r a c t
Article history: Received 7 February 2013 Accepted 25 July 2013 Available online 22 August 2013
In this paper, an enhanced premium power park (PPP) configuration is proposed to effectively mitigate power quality disturbances using a combination of active power and voltage conditioning devices in a spot-configuration-based distribution system. Furthermore, a new coordination algorithm is proposed to achieve full-range coordination between the controllers, thus ensuring the maximum reliability of the proposed configuration. To prove the enhancement of the proposed PPP configuration in terms of improved power quality and investigate the performance of the system under different types of power quality disturbances, several scenarios are simulated using the Matlab/Simulink software. & 2013 Elsevier Ltd. All rights reserved.
Keywords: Custom power park Premium power Premium power park Power quality improvement Power quality park
1. Introduction Power quality disturbances such as voltage sag/swell and harmonic distortion are known as the most intricate issues among power engineers in the last three decades, which eventually may cause severe and costly interruptions in industrial plants (Bollen, 1995; Farhoodnea, Mohamed, Shareef, & 2010; Madtharad, Sorndit, Premrudeepreechacharn, & McGranaghan, 2007). Based on the traditional energy-providing policy, power suppliers tend to deliver energy to their customers through one-size-fits-all grades of power quality, which may be unacceptable and unreliable for most of the sensitive industrial customers (Edinger & Kaul, 2000; Farhoodnea, Mohamed, Shareef, & Mohamedet, 2012; Mansoor & Sundaram, 2000). The key solution to the economic improvement of overall quality, reliability, and availability (QRA) of the delivered power is to offer different levels of QRA based on the sensitivity degree and requirements of the loads using a more reliable distribution configuration and/or a combination of stateof-the-art power electronic-based devices called custom power devices (CPDs). This combination, which is called a premium power park (PPP), can efficiently mitigate power quality disturbances, such as harmonic distortion, voltage sags/swells, and voltage variations within pre-specified limits (Nara & Hasegawa, 1999; Nara, Mishima, & Hasegawa, 2000). Over the past two decades, various studies have focused on the concept of PPP, which led to the design and implementation of several practical PPP plans worldwide. In 1999, the world's first
n
Tel.: +60 1112800403. E-mail address: [email protected] (M. Farhoodnea).
0967-0661/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conengprac.2013.07.006
premium power park was designed and implemented in an existing industrial park in Delaware, Ohio by Electric Power Research Institute (EPRI) to provide both technical and financial satisfaction for utility and customers (Domijan, Montenegro, Keri, & Mattern, 2005; Domijan et al., 2000). The Delaware PPP consists of a combination of Dynamic Voltage Restorer (DVR), Static Transfer Switch (STS), and Static Var Compensator (SVC) to protect the sensitive loads against voltage sags/swells and voltage variation. The Hsinchu and Tainan Science-Based Industrial Parks (HSIP&TSIP) are another practical example of implemented PPP, which was designed and developed between 1999 and 2002 by the Taiwan Power Company (TPC) (Tzong-Yih, Chiung-Yi, ChingYun, & Ching-Junget, 2003). The HSIP&TSIP received the benefits of DVR and several power quality monitoring devices to provide enhanced power quality and better services for customers. In 2005, Weixing proposed a multi-terminal high voltage DC systembased PPP to ensure uninterrupted quality power to sensitive loads using IGBT Voltage Source Converters (VSCs) (Weixing & Boon-Teck, 2005). Considering the concept of PPP and due to the network reconfiguration requirements of the proposed method, this configuration is very costly and cannot offer different levels of power quality to the loads. An inverter-interfaced distributed generation (DG)-based PPP was applied to provide reliable power and improved power quality (Yop et al., 2005). The proposed configuration consists of a series and shunt-connected inverters, a DG set, an inter-tie Solid State Breaker (SSB), and a large capacitance at the DC-link that acts as an energy buffer between the DG and the inverters. In this configuration, various functions such as harmonics and voltage events mitigation can be achieved by controlling the series and shunt units of the inverter. Nonetheless, this configuration is unable to provide different levels of QRA and
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
should be installed for individual customers, which is very costly. An extended custom power park (CPP) was proposed by Meral to improve current and voltage profile of linear and nonlinear loads using DVR, active power filter (APF), STS, and DG (Meral, Teke, Bayindir, & Tumay, 2009). In the proposed CPP, STS transfers the loads from the preferred feeder to the alternative one to protect sensitive loads against voltage sags, swells, and interruptions. In addition, APF compensates harmonic current and the reactive power of the loads, whereas the DVR and DG protect sensitive loads against voltage sag/swell and interruption with 5–10 s of delay. Nonetheless, this configuration is unable to provide power at the time of voltage interruption when the DG is at the warmingup mode that lasts for first 5–10 s. Moreover, the limitation of the DC-link of the DVR hinders the proposed scheme from compensating long-duration voltage sags. Recently, an improved PPP configuration has been proposed to mitigate voltage sags/swells and voltage variations using STS, DVR, and D-STATCOM (Chiumeo & Gandolfi, 2010). In this configuration, the voltage sag/swell is mitigated using DVR and STS, whereas D-STATCOM compensates voltage variations attributed to motor starting. The weakness of this system is the lack of a backup supply and the limitation of the DC-link of the DVR, which prevents the provision of power for the sensitive loads at the time of power interruptions or long-duration voltage sags. In addition, another enhanced PPP configuration has been proposed using Solid State Circuit Breakers (SSCB), DVR, D-STATCOM, and renewable energy-based DG with a backup battery in close electrical proximity to provide voltage sags/swells and voltage variations compensation (Farhoodnea, Mohamed, Shareef, & Zayandehroodi, 2012). The proposed configuration requires a large backup battery and DC-link capacitor bank which are very costly and causes operational limitations. In this paper, a novel PPP configuration is proposed based on the spot network configuration and a combination of active power and voltage conditioning devices, SSCB, and a grid-connected DG in close electrical proximity. The proposed configuration is able to mitigate voltage sags/swells, voltage variations, harmonic distortions, and power interruptions. The proposed scheme also provides three levels of QRA for standard, sensitive, and critical loads. An administrative algorithm is presented to ensure the maximum coordination between the utilized devices in the proposed PPP. In comparison with conventional PPPs, the proposed configuration has superior performance because the distributed loads of the park are fed through three spot network-based feeders to provide more reliable power than the conventional secondary-selective feeder configuration. In addition, during voltage interruptions, the grid-connected DG can supply the required power for sensitive and critical loads as an emergency power supply. To investigate the performance of the proposed configuration under different power quality events, four scenarios are simulated using Matlab/ Simulink software, and the results show the capability of the system to improve power QRA.
1543
For the sake of convenience, the acronyms used in this paper are given in Table A1, Appendix A.
2. Proposed premium power park configuration The proposed PPP configuration offers an improved and multilevel QRA to meet the load requirements. Fig. 1 demonstrates a simplified single-line diagram of the proposed configuration, which consists of a combination of SSCBs, Active Power Conditioner (APC), Active Voltage Conditioner (AVC), Circuit Breakers (CBs), and a grid-connected DG set. In the figure, the proposed configuration is fed through three feeders with spot configuration. Fig. 2 shows a typical spot network configuration, which is known as a more reliable network than the conventional one and is able to protect the customer loads from long- and short-duration interruptions (Behnke et al., 2005; Cutler-Hammer, August 1999). To show different levels of the required QRA, the loads in Fig. 1 are divided into three categories, namely, standard load (L1), sensitive load (L2), and critical load (L3), as follows: (i) Load L1, which is a balanced induction motor load, requires almost a voltage sag/swell and harmonic free power. (ii) Load L2, which is a sensitive inverter-based harmonic polluting load, requires almost a voltage sag/swell, harmonic, and interruption-free power. (iii) Load L3, which is a critical load, cannot tolerate any disturbances. In the proposed configuration shown in Fig. 1, all incoming feeders are fed through SSCBs that are able to disconnect the faulty feeders for protecting customer loads from voltage sag with a depth of 40% or more and power interruptions. In addition, the APC can provide regulated voltage, correct power factor, and mitigate current harmonics for all loads at the Point of Common Coupling (PCC). When all SSCBs trip due to an upstream fault or deep voltage sag, the load side becomes isolated from the faulty feeders, and grid-connected DG provides the required power without interruption for sensitive and critical loads. Note that an
Fig. 2. Typical spot network.
Fig. 1. Single-line diagram of the proposed premium power park.
1544
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Table 1 Summary of improved QRA levels. QRA level
QRA-L1 QRA-L2 QRA-L3
Custom power device
Protection
SSCB
APC
DG
AVC
40% and more sag/swell
Harmonics
Voltage variations
Interruptions
10–40% sag/swell
Voltage imbalances
√ √ √
√ √ √
√ √
√
√ √ √
√ √ √
√ √ √
√ √
√
√
automatic make-before-break operation is considered to transfer power between the DG and the system in the emergency situation to meet IEEE Std 1547 requirements (IEEE, 2009). Finally, AVC is able to protect critical load voltage sags with a depth of 10–40%. Note that in the proposed configuration, only voltage sags/swells caused by upstream faults are considered; however, protecting the system against downstream faults requires protection coordination between DG and CPDs, which is outside the scope of this paper. 2.1. Proposed QRA levels Fig. 3. Block diagram of PLL for calculating the voltage magnitude.
The proposed PPP configuration offers three different QRA levels based on the requirements of customer loads, as follows: (i) Level QRA-L1: This level can provide the required power for all loads with sag-free or voltage sag with a depth of less than 40%. In other words, each SSCB can disconnect its respective faulty feeder when voltage sag with a depth of 40% or more has occurred. In this situation, all loads can be fed through other healthy feeders. In addition, APC can compensate voltage variation due to the inrush or motor starting currents, and provide harmonic free current for all loads at normal operation conditions to meet IEEE Std 519 requirements (Halpin, 2006). Note that in case of voltage sag with a depth of 40% or more in all incoming feeders, momentary voltage interruption may occur in this level due to the opening of all SSCBs. Furthermore, this level is not protected against voltage sag with a depth of 10–40%, voltage imbalances, and longduration interruptions. (ii) Level QRA-L2: This level can provide superior QRA level than the previous level by receiving the benefit of grid-connected DG as a continuous emergency power supply in addition to the advantages of SSCB and APC, which are essential for sensitive and critical loads. Notably, this level is unprotected against voltage sag with a depth of 10–40% and voltage imbalances. (iii) Level QRA-L3: This level, which is over QRA-L2 level, can receive the benefits of AVC to protect critical load against voltage sags with a depth of 10–40% and voltage imbalances, in addition to the advantages of SSCB, APC, and DG. Table 1 summarizes the described QRA levels for the proposed PPP configuration.
Fig. 4. Block diagram of the solid state circuit breakers controller.
3.1. The SSCB controller To reduce the sensitivity of the loads to upstream faults and consequently voltage sags/swells and power interruptions, each feeder is energized through a high-speed silicon-controlled rectifier (SCR) based SSCB, which is able to disconnect the faulty feeder in 4–8 ms (Hingorani, 1998), and meet IEEE Std 1100-1999 requirements (IEEE, 2006). The required local voltage control function is achieved using the phase-locked loop (PLL) based on the amplitude detector shown in Fig. 3 (Karimi & Iravani, 2002). In the figure, v(t) is the line-to-line voltage of each feeder, which is considered as the input signal, whereas vmag(t) is the obtained voltage magnitude. In the SSCB controller, the computed voltage magnitude by PLL is subjected to a hysteresis comparator, where the output is identified as the sag/swell detection signal and used to generate on–off commands of the SSCBs. The sag detection signal equals to one during normal operating conditions (SSCB is switched on and energizes its respective feeder), and zero under sag/swell conditions (SSCB is switched off and disconnects its respective feeder). Fig. 4 shows the block diagram of the SSCB controller, which is used in the proposed configuration (Smith et al., 1993).
3. Controllers and coordination methodology 3.2. The APC controller In this paper, a true combination of state-of-the-art power electronic-based devices, including SSCB, APC, and AVC in close electrical proximity, is used to mitigate multiple power quality disturbances simultaneously. Furthermore, the customer loads are planned to feed through the three-feeder spot network configuration to increase the reliability and availability of power for the proposed PPP.
The APC with Voltage Source Inverter (VSI) topology is used in the proposed PPP to regulate voltage variation at the PCC due to motor starting condition or inrush current, power factor correction, and mitigate current harmonic distortions by injecting the required compensation current. The instantaneous load current, iLoad(t), and the PCC voltage, vpcc(t), can be expressed as (Jain,
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1545
Agrawal, & Guptaet, 2002): n
iLoad ðtÞ ¼ I 1 sin ðωt þ φ1 Þ þ ∑ I h sin ðhωt þ φh Þ
ð1Þ
vpcc ðtÞ ¼ V m sin ðωtÞ
ð2Þ
h¼2
where ω, h, and φ are radial frequency, harmonic order, and phase angles of the load current and the PCC voltage, respectively. Then, the instantaneous load power, PLoad(t), can be expressed as P Load ðtÞ ¼ vpcc ðtÞniLoad ðtÞ ¼ V m I 1 sin 2 ðωtÞn cos ðφ1 Þ þ V m I 1 sin ðωtÞn cos ðωtÞn sin ðφ1 Þ
h¼2
ð3Þ
where pf (t), pr (t), and ph (t) are the fundamental components of power, reactive power, and harmonic power, respectively. The source current supplied by the PCC, i'pcc(t), after compensation should be sinusoidal as 0 ipcc ðtÞ ¼ pf ðtÞ=vpcc ðtÞ ¼ I 1 cos ðφ1 Þ sin ðωtÞ
ð4Þ
If the APC compensates the total reactive and harmonic power, then PCC current, i'pcc(t), can be in phase with the PCC voltage and purely sinusoidal. Therefore, the injected compensation current, icomp(t), can be expressed as 0 icomp ðtÞ ¼ iLoad ðtÞipcc ðtÞ
ð5Þ
The APF control consists of a Low Pass Filter (LPF), PID controller, PLL unit, and hysteresis comparator to estimate the required compensation current, as shown in Fig. 5 (Karuppanan & Mahapatra, 2011; Vechiu & Munteanu, 2011). In the figure, the DC-link voltage of the APC is sensed and compared with the reference voltage to generate the DC voltage error. Then, LPF with cut-off frequency of 50 Hz smooths the error signal and proceeds to the PID block. The PID block estimates the magnitude of the source current, i'pcc(t), which is considered as the magnitude of the reference current, Is-ref. At the same time, the phase of the PCC voltage, φ, is extracted using the PLL unit to compute the reference current, Ins-ref. Then, the error between the generated Ins-ref and the line current is passed through a hysteresis comparator to independently generate the gating signals for each phase of the APC. 3.3. The AVC controller In the proposed configuration, IGBT-based AVC is used to mitigate 10–40% voltage sag and imbalance for critical loads with a very fast response, and meet IEEE Std 1100-1999 requirements (IEEE, 2006). The AVC structure is based on direct ac/ac converter with dc-link energy storage elements, which allow AVC to provide long-duration compensation (Babaei, Kangarlu, & Sabahiet, 2010). The control of AVC is based on the pulse width modulation (PWM) technique during a sampling period of Ts ¼ 1/fs, where fs is the
Fig. 5. Block diagram of the active power conditioner controller.
switching frequency. Therefore, the average of the output voltage of the converter should track the desired output voltage, which is generated by summing the sampled pieces of PCC voltage and zero voltage. Assuming that the switching frequency, fs, is large enough, the terminal voltage of the converter, vC (t), can be expressed as vC ðtÞ ¼
n
þV m sin ðωtÞn ∑ I h sin ðhωt þ φh Þ ¼ pf ðtÞ þ pr ðtÞ þ ph ðtÞ
Fig. 6. Block diagram of the of the AVC controller.
t 1 vPCC ðtÞ Ts
ð6Þ
where T s ¼ t1 þ t2
ð7Þ
where t1 and t2 are the sampling period time intervals between 0 and Ts, and vPCC(t) is the measured voltage at the PCC. To compensate voltage sags and swells, the nominal load voltage vL(t) can be expressed as vL ðtÞ ¼ vPCC ðtÞ þ vinj ðtÞ
ð8Þ
where vinj ðtÞ ¼
vC ðtÞ N
ð9Þ
where N is the turns ratio of the injection transformer. Fig. 6 shows the block diagram of the AVC. 3.4. The DG operation In the proposed scheme, a grid-connected gas turbine-based DG is used based on the IEEE Std 493 (IEEE, 2007) suggestions to inject its power to the system, and provide more reliable electric power with stable frequency and voltage as an independent power producer (IPP) under normal conditions (La Seta & Lerch, 2010; Zahedi, 2008). However, power flow from the DG to the system is prohibited under downstream abnormal conditions, and should be prevented using protection coordination techniques (Zayandehroodi, Mohamed, Shareef, & Mohammadjafari, 2011) to meet IEEE Std 1547 requirements. When all incoming feeders are lost due to the upstream fault, DG acts as an emergency power supply and immediately feeds sensitive and critical loads, whereas standard loads are disconnected. 3.5. Coordination algorithm To supervise different types of conditioning and controller devices and mitigate multiple disturbances simultaneously, a coordination system is required. Fig. 7 shows the proposed coordination algorithm to generate the on–off command for the PPP elements. Based on the proposed algorithm, under normal conditions or when voltages of the incoming feeders are over 60%, the feeders continue feeding the customer loads of the park through their respective SSCBs. However, when voltage sag with a depth of 40% or more occurs in an incoming feeder due to the upstream faults, the respective SSCB disconnects the faulty feeder, and all loads can be fed through other healthy feeders. This open/close logic ensures that all loads receive the required power within the pre-determined sag level based on the baseline offered by the utility, except at the time of sustained interruption when all SSCBs trip due to the occurrence of voltage sag with a depth of 40% and more in all incoming feeders. In this situation, the sensitive and critical loads can be fed through the DG, while the coordination center sends an open command to the circuit breaker of standard load. Furthermore,
1546
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Fig. 7. Proposed coordination algorithm.
Table 2 Test system parameters. Element
Description
Value
Feeders Z-feeder Brk, ncb DG APC SSCB AVC Z-l1 Z-l2 Non-liner part of L2 Z-L3
Incoming feeders Feeder impedances Normally close circuit breaker Grid-connected gas turbine Voltage source inverter Feeder disconnector Voltage source inverter Induction motor Load L2 impedance Current harmonic source Load L3 impedance
380VL–L Negligible – 380VL–L IGBT based six-pulse bridge inverter SCB based switch H-bridge inverter per phase P ¼750 kW, PF ¼0.7 165 Ω/ph Thyristor bridge rectifier 88 Ω/ph
when the sag level is between 10% and 40%, or the point of common coupling voltage is unbalanced, the AVC provides additional voltage compensation for the critical loads. Finally, under normal operation conditions, when the PCC voltage is between 90% and 110% of the nominal voltage, the APC mitigates voltage variation and harmonic distortion for all loads connected to the PCC by injecting the required compensating current to the PCC.
4. Simulation and results To test the performance and ability of the proposed PPP configuration under the different types of power quality disturbances
such as harmonic distortion, voltage sags/swells and interruptions, voltage imbalance, and voltage variations, a test system shown in Fig. 1 is simulated using the Matlab/Simulink software using the simulation parameters given in Table 2. To evaluate the performance of the proposed PPP, the following case studies are presented in achieving QRA improvement: (i) Occurrence of voltage sags with a depth of 60% due to a symmetrical three-phase fault at feeder 3, to evaluate the SSCB performance in protecting the quality of the PCC voltages against voltage sags with a depth of 40% or more. (ii) Occurrence of voltage sags with a depth of 30% with voltage imbalance due to an asymmetrical fault at feeder 1, to evaluate
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1547
Fig. 8. SSCB 3 controller signals: (A) rms voltage at feeder 3 and (B) on–off signal of SSCB3.
Fig. 9. Measured PCC voltages: (A) without SSCB 3 operation and (B) with SSCB 3 operation.
the AVC performance in protecting the quality of the L3 terminal voltages against voltage imbalances and voltage sags with a depth of less than 40%. (iii) Occurrence of interruption due to the simultaneous threephase to ground faults in all incoming feeders, to evaluate the DG performance as an emergency power supply for sensitive and critical loads, L2 and L3. (iv) Occurrence of voltage variation and harmonic distortion due to the motor starting effect of load, L1 and harmonic pollution of load, L2, to evaluate the APC performance for voltage regulation, power factor correction, and harmonic compensation.
PCC power is supplied by feeders 1 and 2 through SSCBs 1 and 2 to restore the PCC voltage to the pre-fault magnitude. Fig. 8 shows the detected voltage sag and generated open command of the SSCB3controller, whereas Fig. 9 shows the measured PCC voltage with and without the SSCB 3 operation. The figures show that the SSCB3 controller can successfully identify the occurred voltage sag at 100 ms and recover the PCC voltage to the pre-fault level by disconnecting feeder 3 using its respective SSCB within one cycle, thus giving fast power restoration. After clearing the fault at 300 ms, the SSCB3 restores feeder 3 to continue supplying the PCC power. 4.2. Voltage sag and voltage imbalance mitigation using AVC
4.1. General voltage sag mitigation at the PCC using SSCBs In this scenario, the feeder 3 voltage drops to 40% of nominal voltage due to an external symmetrical three-phase fault. In this situation, the PLL unit of the SSCB3 controller senses the voltage drop caused by the short-circuit resistance and transformer impedance at feeder 3, and the gating signal is generated by the hysteresis comparator unit of the controller to turn off the SSCB3. Consequently, the SSCB3 trips the faulty feeder, and the required
In this scenario, the PCC voltage drops to 70% of nominal voltage due to the occurrence of an external asymmetrical threephase fault at feeder 1. In this situation, the SSCB controllers, which are not sensitive to voltage sags with a depth of less than 40%, cannot detect the occurred voltage sag and imbalance. Therefore, the AVC should sense and restore the voltage magnitude to its pre-fault level at L3 terminal. Figs. 10 and 11 show the sag detection signal of the AVC, injected power and measured
1548
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Fig. 10. AVC controller signals: (A) the CL terminal voltage and (B) on–off signal of AVC.
Fig. 11. Injected power and CL terminal voltages: (A) AVC injected active and reactive powers, (B) CL terminal voltage without the AVC and (C) CL terminal voltage with the AVC.
voltage at L3 terminal, respectively. Fig. 11 demonstrates that the AVC can successfully balance and recover voltage up to 98% of its nominal voltage, and this proportion is within the acceptable voltage range. Given the use of direct ac/ac converter and lack of dc-link energy storage elements, the AVC is able to compensate voltage sag for an unlimited time interval, because it provides the required energy directly through the grid. This characteristic makes AVC a more efficient sag mitigation device for critical load, L3. Note that in the above-mentioned situation, APC and DG are disconnected by the coordination center to prevent the feeding of occurred external fault.
and voltage interruption is said to occur. The coordination center sends the command signal to open the circuit breaker, Brk1, and disconnect standard load, L1, from the PCC, and the DG continues to supply power to the sensitive and critical loads, L2 and L3, as a backup power supply. After clearing the external fault and returning the system to the normal condition by restoring the incoming feeders, DG keeps its power exchange mode with the network. Fig. 12 shows the injected power by DG into the network, and the measured voltages at the load terminals for this scenario. Based on the figure, the DG can deliver the required power for L2 and L3 when the main feeders are lost.
4.3. Voltage interruption mitigation at L2 and L3 using DG
4.4. General power quality improvement using APC
To test the performance of the grid-connected DG to recover the PCC voltage at the time of voltage interruption, three simultaneous external three-phase to ground faults in all incoming feeders are created that caused 60% voltage sag in each feeder. Based on the coordination logic, the SSCB controllers identify the occurred voltage drop, and each SSCB trips its respective feeder in a few milliseconds. Consequently, the PCC voltage drops to zero,
To approve the ability and effectiveness of the APC for performing voltage regulation at the PCC, an inrush current is simulated due to the induction motor starting. This inrush current causes an 8.5% voltage drop in the PCC voltage, as shown in Fig. 13. After identifying the voltage variation by the APC controller, the required current to compensate the PCC voltage is injected by APC. Fig. 14 illustrates the amount of injected active and reactive
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1549
Fig. 12. Injected power and measured voltages by DG at the PCC: (A) injected active and reactive powers, (B) SL terminal voltage, (C) SEL terminal voltage and (D) CL terminal voltage.
Fig. 13. Measured voltage and current without APC: (A) rms voltage at the point of common coupling and (B) Current at the SL connection point.
powers into the PCC and the PCC voltage after the APC voltage regulation action. To investigate the performance of the APC in harmonic compensation, the assumption is that load L2 injects harmonic current into the network and pollutes the PCC voltage with 26.84% THD. The APC controller estimates and injects the required harmonic current at the PCC and decreases the voltage THD to 1.56%, in which this THD is below the IEEE Std 519-1992 limitations. Therefore, non-harmonic polluting loads which are connected to the PCC can almost receive harmonic free power. Fig. 15 shows the measured voltage at the PCC before and after APC harmonic compensation. The results prove that the APC can precisely inject the required harmonic current with a 1801 phase difference to eliminate the harmonic distortion as much as possible at the PCC.
Additionally, the APC is able to provide general power factor correction for all loads by injecting a current in phase with the PCC voltage. Fig. 16 shows the normalized phase voltage and current waveforms at the load L1 terminal before and after power factor improvement. Based on the figure, it is clear that the phase current at the L1 terminal is almost in phase with the voltage after the APC action. The results of the simulated scenarios prove that the proposed PPP configuration is effective to provide superior QRA compared with the regular distribution systems. Moreover, the proposed PPP is able to offer three different levels of QRA for its distributed loads based on their requirements. To present a clear comparison of the proposed PPP with conventional PPPs (Chiumeo & Gandolfi, 2010; Meral, Teke, Bayindir, & Tumay, 2009; Weixing & Boon Teck, 2002;
1550
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Fig. 14. Performance of APC in voltage regulation: (A) injected powers by APC at the point of common coupling and (B) measured voltage at the point of common coupling when APC is switched on.
Fig. 15. The PCC voltage: (A) without APC and (B) with APC.
Fig. 16. Phase voltage and current waveforms at the SL terminal: (A) APC is off and (B) APC is on.
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1551
Table 3 Comparison between the functions of the proposed and conventional PPPs. Functions
Proposed PPP
Configuration in Yop et al. (2005)
Configuration in Meral, Teke, Bayindir, & Tumay (2009)
Configuration in Chiumeo & Gandolfi (2010)
Configuration in Weixing & Boon Teck (2002)
Configuration in Farhoodnea, Mohamed, Shareef, & Mohamedet (2012)
More reliable incoming feeder configuration Different QRA level Unlimited voltage sag compensation Unlimited voltage imbalance compensation Voltage regulation Harmonic mitigation Power factor correction Uninterrupted/ unlimited backup power supply
√
√
√
√ √
√
√
√
√
√ √
√
√
√
Not completely
√ √ √ √
√ √ √ Not completely
√ √ √ Not completely
√ √ √
√ √
√ √ √ Not completely
power quality disturbances, including voltage sag, imbalance, harmonic, voltage variation, and interruption.
Table A1 Lists of acronyms. Acronym
Description
APC APF AVC CB CL CPD CPP DG D-STATCOM DVR EPRI IPP LPF PCC PID PLL PPP PWM QRA rms SCR SEL SL SSB SSCB STS SVC TPC VSC VSI
Active power conditioner Active power filter Active voltage conditioner Circuit breaker Critical load Custom power device Custom power park Distributed generation Distribution static compensator Dynamic voltage restorer Electric power research institute Independent power producer Low pass filter Point of Common Coupling Proportional-integral-derivative Phase-locked loop Premium power park Pulse width modulation Quality, reliability, and availability Root mean square Silicon-controlled rectifier Sensitive load Standard load Solid state breaker Solid state circuit breaker Static transfer switch Static Var compensator Taiwan power company Voltage source converter Voltage source inverter
Yop et al., 2005), Table 3 is provided to summarize the advantageous functions of the proposed PPP.
5. Conclusion In this paper, an enhanced PPP configuration based on the active conditioning devices is presented. In the proposed configuration, the distributed customer loads are fed through three feeders with spot network structure, and each feeder is equipped with an SSCB to remove deep voltage sags and deliver more reliable power. In addition, the proper combination of active conditioning devices, including APC and AVC, is used to offer three improved levels of QRA for non-sensitive, sensitive, and critical loads. The proposed configuration is simulated using four scenarios to cover the most important power quality disturbances. Results prove that the proposed configuration is able to mitigate
Appendix A. Acronyms See Table A1. References Babaei, E., Kangarlu, M. F., & Sabahi, M. (2010). Compensation of voltage disturbances in distribution systems using single-phase dynamic voltage restorer. Electric Power Systems Research, 80(12), 1413–1420. Behnke, M., Erdman, W., Horgan, S., Dawson, D., Feero, W., Soudi, F., et al. (2005). Secondary network distribution systems background and issues related to the interconnection of distributed resources. Technical Report NREL/TP-560-38079. National Renewable Energy Laboratory. Bollen M. H. J. (1995). Fast assessment methods for voltage sags in distribution systems. In IEEE industry applications conference (pp. 2282–2289). Chiumeo, R., & Gandolfi, C. (2010). D-STATCOM control system and operation in a configuration of premium power park. In 14th International Conference on Harmonics and Quality of Power (ICHQP) (pp. 1–7). Cutler-Hammer (August 1999)). Spot network systems. TD.52.01A.T.E. Domijan, A., Jr., Montenegro, A., Keri, A. J. F., & Mattern, K. E. (2005). Simulation study of the world's first distributed premium power quality park. IEEE Transactions on Power Delivery, 20(2), 1483–1492. Domijan, A., Jr., Song, Z., Baptista, G. N., Montenegro, A., Wang, X., Gurlaskie, G. T., et al. (2000). Power quality monitoring and analysis in a customized power industrial area using the FRIENDS concept. In Ninth international conference on harmonics and quality of power (pp. 379–384). Edinger, R., & Kaul, S. (2000). Humankind's detour toward sustainability: Past, present, and future of renewable energies and electric power generation. Renewable and Sustainable Energy Reviews, 4(3), 295–313. Farhoodnea, M., Mohamed, A., & Shareef, H. (2010). Identification of multiple harmonic sources in power systems using independent component analysis and mutual information. International Journal of Enterprise Information Systems, 18(1), 51–63. Farhoodnea, M., Mohamed, A., Shareef, H., & Mohamed, R. (2012). Premium power park: A review of the concepts, definitions and applications. Advances in Natural and Applied Sciences, 6(2), 173–184. Farhoodnea, M., Mohamed, A., Shareef, H., & Zayandehroodi, H. (2012). A novel distributed Premium Power Park design for power quality improvement. International Review on Modelling and Simulations, 5(2), 672–679. Halpin, S. M. (2006). Revisions to IEEE Standard 519-1992. In IEEE PES transmission and distribution conference and exhibition (pp. 1149–1151). Hingorani, N. (1998). Overview of custom power applications. Technical panel session paper of IEEE/PES (SM'98). IEEE (2006). IEEE recommended practice for powering and grounding electronic equipment—Redline. IEEE Std 1100-2005 (Revision of IEEE Std 1100-1999)—Redline (pp. 1–703). IEEE (2007). IEEE recommended practice for the design of reliable industrial and commercial power systems—Redline. IEEE Std 493-2007 (Revision of IEEE Std 493–1997)—Redline (pp. 1–426). IEEE (2009). IEEE application guide for IEEE Std 1547. IEEE standard for interconnecting distributed resources with electric power systems. IEEE Std 15472–2008 (pp. 1–207). Jain, S. K., Agrawal, P., & Gupta, H. O. (2002). Fuzzy logic controlled shunt active power filter for power quality improvement. IEE Proceedings-Electric Power Applications, 149(5), 317–328.
1552
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Karimi, M., & Iravani, M. R. (2002). A nonlinear adaptive filter for online signal analysis in power systems: Applications. IEEE Transactions on Power Deliverery, 17(2), 617–622. Karuppanan, P., & Mahapatra, K. K. (2011). PLL synchronization with PID controller based shunt active power line conditioners. International Journal of Computers & Electrical Engineering, 3(1), 42–47. La Seta, P., & Lerch, E. (2010). Reliable operations of low voltage local energy systems with high presence of renewable energy sources. In International conference on power system technology (pp. 1–5). Madtharad, C., Sorndit, C., Premrudeepreechacharn, S., & McGranaghan, M. (2007). PEA's premium power service: Baseline and risk assessment. In 9th international conference on Electrical Power Quality and Utilisation (EPQU) (pp. 1–6). Mansoor, A., & Sundaram, A. (2000). Premium power grades. In International conference on Power System Technology (PowerCon) (pp. 933–939). Meral, M. E., Teke, A, Bayindir, K. C., & Tumay, M. (2009). Power quality improvement with an extended custom power park. Electric Power Systems Research, 79 (11), 1553–1560. Nara, K., & Hasegawa, J. (1999). Configuration of new power delivery system for reliable power supply. IEEE power engineering society summer meeting, 248–253. Nara, K., Mishima, Y., & Hasegawa, J. (2000). A new type power delivery system for reliable power supply—FRIENDS and its optimal network design. In International conference on Power System Technology (PowerCon) (pp. 649–654). Smith, R. K., Slade, P. G., Sarkozi, M., Stacey, E. J., Bonk, J. J., & Mehta, H. (1993). Solidstate distribution current limiter and circuit breaker: Application requirements and control strategies. IEEE Transactions on Power Delivery, 8(3), 1155–1164.
Tzong-Yih, G., Chiung-Yi, H., Ching-Yun, L., & Ching-Jung, L. (2003). Power quality task force of taipower: Experiences & results on PQ monitoring and mitigation. In Sixth international conference on Advances in Power System Control, Operation and Management (ASDCOM) (pp. 41–48). Vechiu, G. G. I., & Munteanu, T. (2011). Power quality improvement using renewable energy. In International Conference on Renewable Energies and Power Quality (ICREPQ) (pp. 1–6). Weixing, L., & Boon Teck, O. (2002). Multi-terminal HVDC as enabling technology of premium quality power park. IEEE power engineering society winter meeting, 719–724. Weixing, L., & Boon-Teck, O. (2005). Premium quality power park based on multiterminal HVDC. IEEE Transactions on Power Delivery, 20(2), 978–983. Yop, C., Sung-Woo, P., Hee-Jung, K., Seung-Il, M., Byung-Moon, H., Jae-Eon, K., et al. (2005). Operating strategy and control scheme of premium power supply interconnected with electric power systems. IEEE Transactions on Power Delivery 20(3), 2281–2288. Zahedi, A. (2008). Renewable energy-based power system to supply reliable electricity for remote applications. Australasian Universities power engineering conference, 1–4. Zayandehroodi, H., Mohamed, A., Shareef, H., & Mohammadjafari, M. (2011). A Comprehensive review of protection coordination methods in power distribution systems in the presence of DG. Electrical Review, 87(8), 142–148.
Contents lists available at ScienceDirect
Control Engineering Practice journal homepage: www.elsevier.com/locate/conengprac
An enhanced premium power park configuration using active power and voltage conditioning devices Masoud Farhoodnea n, Azah Mohamed, Hussain Shareef, Hadi Zayandehroodi Department of Electrical, Electronic and Systems Engineering, University Kebangsaan, Malaysia
art ic l e i nf o
a b s t r a c t
Article history: Received 7 February 2013 Accepted 25 July 2013 Available online 22 August 2013
In this paper, an enhanced premium power park (PPP) configuration is proposed to effectively mitigate power quality disturbances using a combination of active power and voltage conditioning devices in a spot-configuration-based distribution system. Furthermore, a new coordination algorithm is proposed to achieve full-range coordination between the controllers, thus ensuring the maximum reliability of the proposed configuration. To prove the enhancement of the proposed PPP configuration in terms of improved power quality and investigate the performance of the system under different types of power quality disturbances, several scenarios are simulated using the Matlab/Simulink software. & 2013 Elsevier Ltd. All rights reserved.
Keywords: Custom power park Premium power Premium power park Power quality improvement Power quality park
1. Introduction Power quality disturbances such as voltage sag/swell and harmonic distortion are known as the most intricate issues among power engineers in the last three decades, which eventually may cause severe and costly interruptions in industrial plants (Bollen, 1995; Farhoodnea, Mohamed, Shareef, & 2010; Madtharad, Sorndit, Premrudeepreechacharn, & McGranaghan, 2007). Based on the traditional energy-providing policy, power suppliers tend to deliver energy to their customers through one-size-fits-all grades of power quality, which may be unacceptable and unreliable for most of the sensitive industrial customers (Edinger & Kaul, 2000; Farhoodnea, Mohamed, Shareef, & Mohamedet, 2012; Mansoor & Sundaram, 2000). The key solution to the economic improvement of overall quality, reliability, and availability (QRA) of the delivered power is to offer different levels of QRA based on the sensitivity degree and requirements of the loads using a more reliable distribution configuration and/or a combination of stateof-the-art power electronic-based devices called custom power devices (CPDs). This combination, which is called a premium power park (PPP), can efficiently mitigate power quality disturbances, such as harmonic distortion, voltage sags/swells, and voltage variations within pre-specified limits (Nara & Hasegawa, 1999; Nara, Mishima, & Hasegawa, 2000). Over the past two decades, various studies have focused on the concept of PPP, which led to the design and implementation of several practical PPP plans worldwide. In 1999, the world's first
n
Tel.: +60 1112800403. E-mail address: [email protected] (M. Farhoodnea).
0967-0661/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conengprac.2013.07.006
premium power park was designed and implemented in an existing industrial park in Delaware, Ohio by Electric Power Research Institute (EPRI) to provide both technical and financial satisfaction for utility and customers (Domijan, Montenegro, Keri, & Mattern, 2005; Domijan et al., 2000). The Delaware PPP consists of a combination of Dynamic Voltage Restorer (DVR), Static Transfer Switch (STS), and Static Var Compensator (SVC) to protect the sensitive loads against voltage sags/swells and voltage variation. The Hsinchu and Tainan Science-Based Industrial Parks (HSIP&TSIP) are another practical example of implemented PPP, which was designed and developed between 1999 and 2002 by the Taiwan Power Company (TPC) (Tzong-Yih, Chiung-Yi, ChingYun, & Ching-Junget, 2003). The HSIP&TSIP received the benefits of DVR and several power quality monitoring devices to provide enhanced power quality and better services for customers. In 2005, Weixing proposed a multi-terminal high voltage DC systembased PPP to ensure uninterrupted quality power to sensitive loads using IGBT Voltage Source Converters (VSCs) (Weixing & Boon-Teck, 2005). Considering the concept of PPP and due to the network reconfiguration requirements of the proposed method, this configuration is very costly and cannot offer different levels of power quality to the loads. An inverter-interfaced distributed generation (DG)-based PPP was applied to provide reliable power and improved power quality (Yop et al., 2005). The proposed configuration consists of a series and shunt-connected inverters, a DG set, an inter-tie Solid State Breaker (SSB), and a large capacitance at the DC-link that acts as an energy buffer between the DG and the inverters. In this configuration, various functions such as harmonics and voltage events mitigation can be achieved by controlling the series and shunt units of the inverter. Nonetheless, this configuration is unable to provide different levels of QRA and
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
should be installed for individual customers, which is very costly. An extended custom power park (CPP) was proposed by Meral to improve current and voltage profile of linear and nonlinear loads using DVR, active power filter (APF), STS, and DG (Meral, Teke, Bayindir, & Tumay, 2009). In the proposed CPP, STS transfers the loads from the preferred feeder to the alternative one to protect sensitive loads against voltage sags, swells, and interruptions. In addition, APF compensates harmonic current and the reactive power of the loads, whereas the DVR and DG protect sensitive loads against voltage sag/swell and interruption with 5–10 s of delay. Nonetheless, this configuration is unable to provide power at the time of voltage interruption when the DG is at the warmingup mode that lasts for first 5–10 s. Moreover, the limitation of the DC-link of the DVR hinders the proposed scheme from compensating long-duration voltage sags. Recently, an improved PPP configuration has been proposed to mitigate voltage sags/swells and voltage variations using STS, DVR, and D-STATCOM (Chiumeo & Gandolfi, 2010). In this configuration, the voltage sag/swell is mitigated using DVR and STS, whereas D-STATCOM compensates voltage variations attributed to motor starting. The weakness of this system is the lack of a backup supply and the limitation of the DC-link of the DVR, which prevents the provision of power for the sensitive loads at the time of power interruptions or long-duration voltage sags. In addition, another enhanced PPP configuration has been proposed using Solid State Circuit Breakers (SSCB), DVR, D-STATCOM, and renewable energy-based DG with a backup battery in close electrical proximity to provide voltage sags/swells and voltage variations compensation (Farhoodnea, Mohamed, Shareef, & Zayandehroodi, 2012). The proposed configuration requires a large backup battery and DC-link capacitor bank which are very costly and causes operational limitations. In this paper, a novel PPP configuration is proposed based on the spot network configuration and a combination of active power and voltage conditioning devices, SSCB, and a grid-connected DG in close electrical proximity. The proposed configuration is able to mitigate voltage sags/swells, voltage variations, harmonic distortions, and power interruptions. The proposed scheme also provides three levels of QRA for standard, sensitive, and critical loads. An administrative algorithm is presented to ensure the maximum coordination between the utilized devices in the proposed PPP. In comparison with conventional PPPs, the proposed configuration has superior performance because the distributed loads of the park are fed through three spot network-based feeders to provide more reliable power than the conventional secondary-selective feeder configuration. In addition, during voltage interruptions, the grid-connected DG can supply the required power for sensitive and critical loads as an emergency power supply. To investigate the performance of the proposed configuration under different power quality events, four scenarios are simulated using Matlab/ Simulink software, and the results show the capability of the system to improve power QRA.
1543
For the sake of convenience, the acronyms used in this paper are given in Table A1, Appendix A.
2. Proposed premium power park configuration The proposed PPP configuration offers an improved and multilevel QRA to meet the load requirements. Fig. 1 demonstrates a simplified single-line diagram of the proposed configuration, which consists of a combination of SSCBs, Active Power Conditioner (APC), Active Voltage Conditioner (AVC), Circuit Breakers (CBs), and a grid-connected DG set. In the figure, the proposed configuration is fed through three feeders with spot configuration. Fig. 2 shows a typical spot network configuration, which is known as a more reliable network than the conventional one and is able to protect the customer loads from long- and short-duration interruptions (Behnke et al., 2005; Cutler-Hammer, August 1999). To show different levels of the required QRA, the loads in Fig. 1 are divided into three categories, namely, standard load (L1), sensitive load (L2), and critical load (L3), as follows: (i) Load L1, which is a balanced induction motor load, requires almost a voltage sag/swell and harmonic free power. (ii) Load L2, which is a sensitive inverter-based harmonic polluting load, requires almost a voltage sag/swell, harmonic, and interruption-free power. (iii) Load L3, which is a critical load, cannot tolerate any disturbances. In the proposed configuration shown in Fig. 1, all incoming feeders are fed through SSCBs that are able to disconnect the faulty feeders for protecting customer loads from voltage sag with a depth of 40% or more and power interruptions. In addition, the APC can provide regulated voltage, correct power factor, and mitigate current harmonics for all loads at the Point of Common Coupling (PCC). When all SSCBs trip due to an upstream fault or deep voltage sag, the load side becomes isolated from the faulty feeders, and grid-connected DG provides the required power without interruption for sensitive and critical loads. Note that an
Fig. 2. Typical spot network.
Fig. 1. Single-line diagram of the proposed premium power park.
1544
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Table 1 Summary of improved QRA levels. QRA level
QRA-L1 QRA-L2 QRA-L3
Custom power device
Protection
SSCB
APC
DG
AVC
40% and more sag/swell
Harmonics
Voltage variations
Interruptions
10–40% sag/swell
Voltage imbalances
√ √ √
√ √ √
√ √
√
√ √ √
√ √ √
√ √ √
√ √
√
√
automatic make-before-break operation is considered to transfer power between the DG and the system in the emergency situation to meet IEEE Std 1547 requirements (IEEE, 2009). Finally, AVC is able to protect critical load voltage sags with a depth of 10–40%. Note that in the proposed configuration, only voltage sags/swells caused by upstream faults are considered; however, protecting the system against downstream faults requires protection coordination between DG and CPDs, which is outside the scope of this paper. 2.1. Proposed QRA levels Fig. 3. Block diagram of PLL for calculating the voltage magnitude.
The proposed PPP configuration offers three different QRA levels based on the requirements of customer loads, as follows: (i) Level QRA-L1: This level can provide the required power for all loads with sag-free or voltage sag with a depth of less than 40%. In other words, each SSCB can disconnect its respective faulty feeder when voltage sag with a depth of 40% or more has occurred. In this situation, all loads can be fed through other healthy feeders. In addition, APC can compensate voltage variation due to the inrush or motor starting currents, and provide harmonic free current for all loads at normal operation conditions to meet IEEE Std 519 requirements (Halpin, 2006). Note that in case of voltage sag with a depth of 40% or more in all incoming feeders, momentary voltage interruption may occur in this level due to the opening of all SSCBs. Furthermore, this level is not protected against voltage sag with a depth of 10–40%, voltage imbalances, and longduration interruptions. (ii) Level QRA-L2: This level can provide superior QRA level than the previous level by receiving the benefit of grid-connected DG as a continuous emergency power supply in addition to the advantages of SSCB and APC, which are essential for sensitive and critical loads. Notably, this level is unprotected against voltage sag with a depth of 10–40% and voltage imbalances. (iii) Level QRA-L3: This level, which is over QRA-L2 level, can receive the benefits of AVC to protect critical load against voltage sags with a depth of 10–40% and voltage imbalances, in addition to the advantages of SSCB, APC, and DG. Table 1 summarizes the described QRA levels for the proposed PPP configuration.
Fig. 4. Block diagram of the solid state circuit breakers controller.
3.1. The SSCB controller To reduce the sensitivity of the loads to upstream faults and consequently voltage sags/swells and power interruptions, each feeder is energized through a high-speed silicon-controlled rectifier (SCR) based SSCB, which is able to disconnect the faulty feeder in 4–8 ms (Hingorani, 1998), and meet IEEE Std 1100-1999 requirements (IEEE, 2006). The required local voltage control function is achieved using the phase-locked loop (PLL) based on the amplitude detector shown in Fig. 3 (Karimi & Iravani, 2002). In the figure, v(t) is the line-to-line voltage of each feeder, which is considered as the input signal, whereas vmag(t) is the obtained voltage magnitude. In the SSCB controller, the computed voltage magnitude by PLL is subjected to a hysteresis comparator, where the output is identified as the sag/swell detection signal and used to generate on–off commands of the SSCBs. The sag detection signal equals to one during normal operating conditions (SSCB is switched on and energizes its respective feeder), and zero under sag/swell conditions (SSCB is switched off and disconnects its respective feeder). Fig. 4 shows the block diagram of the SSCB controller, which is used in the proposed configuration (Smith et al., 1993).
3. Controllers and coordination methodology 3.2. The APC controller In this paper, a true combination of state-of-the-art power electronic-based devices, including SSCB, APC, and AVC in close electrical proximity, is used to mitigate multiple power quality disturbances simultaneously. Furthermore, the customer loads are planned to feed through the three-feeder spot network configuration to increase the reliability and availability of power for the proposed PPP.
The APC with Voltage Source Inverter (VSI) topology is used in the proposed PPP to regulate voltage variation at the PCC due to motor starting condition or inrush current, power factor correction, and mitigate current harmonic distortions by injecting the required compensation current. The instantaneous load current, iLoad(t), and the PCC voltage, vpcc(t), can be expressed as (Jain,
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1545
Agrawal, & Guptaet, 2002): n
iLoad ðtÞ ¼ I 1 sin ðωt þ φ1 Þ þ ∑ I h sin ðhωt þ φh Þ
ð1Þ
vpcc ðtÞ ¼ V m sin ðωtÞ
ð2Þ
h¼2
where ω, h, and φ are radial frequency, harmonic order, and phase angles of the load current and the PCC voltage, respectively. Then, the instantaneous load power, PLoad(t), can be expressed as P Load ðtÞ ¼ vpcc ðtÞniLoad ðtÞ ¼ V m I 1 sin 2 ðωtÞn cos ðφ1 Þ þ V m I 1 sin ðωtÞn cos ðωtÞn sin ðφ1 Þ
h¼2
ð3Þ
where pf (t), pr (t), and ph (t) are the fundamental components of power, reactive power, and harmonic power, respectively. The source current supplied by the PCC, i'pcc(t), after compensation should be sinusoidal as 0 ipcc ðtÞ ¼ pf ðtÞ=vpcc ðtÞ ¼ I 1 cos ðφ1 Þ sin ðωtÞ
ð4Þ
If the APC compensates the total reactive and harmonic power, then PCC current, i'pcc(t), can be in phase with the PCC voltage and purely sinusoidal. Therefore, the injected compensation current, icomp(t), can be expressed as 0 icomp ðtÞ ¼ iLoad ðtÞipcc ðtÞ
ð5Þ
The APF control consists of a Low Pass Filter (LPF), PID controller, PLL unit, and hysteresis comparator to estimate the required compensation current, as shown in Fig. 5 (Karuppanan & Mahapatra, 2011; Vechiu & Munteanu, 2011). In the figure, the DC-link voltage of the APC is sensed and compared with the reference voltage to generate the DC voltage error. Then, LPF with cut-off frequency of 50 Hz smooths the error signal and proceeds to the PID block. The PID block estimates the magnitude of the source current, i'pcc(t), which is considered as the magnitude of the reference current, Is-ref. At the same time, the phase of the PCC voltage, φ, is extracted using the PLL unit to compute the reference current, Ins-ref. Then, the error between the generated Ins-ref and the line current is passed through a hysteresis comparator to independently generate the gating signals for each phase of the APC. 3.3. The AVC controller In the proposed configuration, IGBT-based AVC is used to mitigate 10–40% voltage sag and imbalance for critical loads with a very fast response, and meet IEEE Std 1100-1999 requirements (IEEE, 2006). The AVC structure is based on direct ac/ac converter with dc-link energy storage elements, which allow AVC to provide long-duration compensation (Babaei, Kangarlu, & Sabahiet, 2010). The control of AVC is based on the pulse width modulation (PWM) technique during a sampling period of Ts ¼ 1/fs, where fs is the
Fig. 5. Block diagram of the active power conditioner controller.
switching frequency. Therefore, the average of the output voltage of the converter should track the desired output voltage, which is generated by summing the sampled pieces of PCC voltage and zero voltage. Assuming that the switching frequency, fs, is large enough, the terminal voltage of the converter, vC (t), can be expressed as vC ðtÞ ¼
n
þV m sin ðωtÞn ∑ I h sin ðhωt þ φh Þ ¼ pf ðtÞ þ pr ðtÞ þ ph ðtÞ
Fig. 6. Block diagram of the of the AVC controller.
t 1 vPCC ðtÞ Ts
ð6Þ
where T s ¼ t1 þ t2
ð7Þ
where t1 and t2 are the sampling period time intervals between 0 and Ts, and vPCC(t) is the measured voltage at the PCC. To compensate voltage sags and swells, the nominal load voltage vL(t) can be expressed as vL ðtÞ ¼ vPCC ðtÞ þ vinj ðtÞ
ð8Þ
where vinj ðtÞ ¼
vC ðtÞ N
ð9Þ
where N is the turns ratio of the injection transformer. Fig. 6 shows the block diagram of the AVC. 3.4. The DG operation In the proposed scheme, a grid-connected gas turbine-based DG is used based on the IEEE Std 493 (IEEE, 2007) suggestions to inject its power to the system, and provide more reliable electric power with stable frequency and voltage as an independent power producer (IPP) under normal conditions (La Seta & Lerch, 2010; Zahedi, 2008). However, power flow from the DG to the system is prohibited under downstream abnormal conditions, and should be prevented using protection coordination techniques (Zayandehroodi, Mohamed, Shareef, & Mohammadjafari, 2011) to meet IEEE Std 1547 requirements. When all incoming feeders are lost due to the upstream fault, DG acts as an emergency power supply and immediately feeds sensitive and critical loads, whereas standard loads are disconnected. 3.5. Coordination algorithm To supervise different types of conditioning and controller devices and mitigate multiple disturbances simultaneously, a coordination system is required. Fig. 7 shows the proposed coordination algorithm to generate the on–off command for the PPP elements. Based on the proposed algorithm, under normal conditions or when voltages of the incoming feeders are over 60%, the feeders continue feeding the customer loads of the park through their respective SSCBs. However, when voltage sag with a depth of 40% or more occurs in an incoming feeder due to the upstream faults, the respective SSCB disconnects the faulty feeder, and all loads can be fed through other healthy feeders. This open/close logic ensures that all loads receive the required power within the pre-determined sag level based on the baseline offered by the utility, except at the time of sustained interruption when all SSCBs trip due to the occurrence of voltage sag with a depth of 40% and more in all incoming feeders. In this situation, the sensitive and critical loads can be fed through the DG, while the coordination center sends an open command to the circuit breaker of standard load. Furthermore,
1546
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Fig. 7. Proposed coordination algorithm.
Table 2 Test system parameters. Element
Description
Value
Feeders Z-feeder Brk, ncb DG APC SSCB AVC Z-l1 Z-l2 Non-liner part of L2 Z-L3
Incoming feeders Feeder impedances Normally close circuit breaker Grid-connected gas turbine Voltage source inverter Feeder disconnector Voltage source inverter Induction motor Load L2 impedance Current harmonic source Load L3 impedance
380VL–L Negligible – 380VL–L IGBT based six-pulse bridge inverter SCB based switch H-bridge inverter per phase P ¼750 kW, PF ¼0.7 165 Ω/ph Thyristor bridge rectifier 88 Ω/ph
when the sag level is between 10% and 40%, or the point of common coupling voltage is unbalanced, the AVC provides additional voltage compensation for the critical loads. Finally, under normal operation conditions, when the PCC voltage is between 90% and 110% of the nominal voltage, the APC mitigates voltage variation and harmonic distortion for all loads connected to the PCC by injecting the required compensating current to the PCC.
4. Simulation and results To test the performance and ability of the proposed PPP configuration under the different types of power quality disturbances
such as harmonic distortion, voltage sags/swells and interruptions, voltage imbalance, and voltage variations, a test system shown in Fig. 1 is simulated using the Matlab/Simulink software using the simulation parameters given in Table 2. To evaluate the performance of the proposed PPP, the following case studies are presented in achieving QRA improvement: (i) Occurrence of voltage sags with a depth of 60% due to a symmetrical three-phase fault at feeder 3, to evaluate the SSCB performance in protecting the quality of the PCC voltages against voltage sags with a depth of 40% or more. (ii) Occurrence of voltage sags with a depth of 30% with voltage imbalance due to an asymmetrical fault at feeder 1, to evaluate
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1547
Fig. 8. SSCB 3 controller signals: (A) rms voltage at feeder 3 and (B) on–off signal of SSCB3.
Fig. 9. Measured PCC voltages: (A) without SSCB 3 operation and (B) with SSCB 3 operation.
the AVC performance in protecting the quality of the L3 terminal voltages against voltage imbalances and voltage sags with a depth of less than 40%. (iii) Occurrence of interruption due to the simultaneous threephase to ground faults in all incoming feeders, to evaluate the DG performance as an emergency power supply for sensitive and critical loads, L2 and L3. (iv) Occurrence of voltage variation and harmonic distortion due to the motor starting effect of load, L1 and harmonic pollution of load, L2, to evaluate the APC performance for voltage regulation, power factor correction, and harmonic compensation.
PCC power is supplied by feeders 1 and 2 through SSCBs 1 and 2 to restore the PCC voltage to the pre-fault magnitude. Fig. 8 shows the detected voltage sag and generated open command of the SSCB3controller, whereas Fig. 9 shows the measured PCC voltage with and without the SSCB 3 operation. The figures show that the SSCB3 controller can successfully identify the occurred voltage sag at 100 ms and recover the PCC voltage to the pre-fault level by disconnecting feeder 3 using its respective SSCB within one cycle, thus giving fast power restoration. After clearing the fault at 300 ms, the SSCB3 restores feeder 3 to continue supplying the PCC power. 4.2. Voltage sag and voltage imbalance mitigation using AVC
4.1. General voltage sag mitigation at the PCC using SSCBs In this scenario, the feeder 3 voltage drops to 40% of nominal voltage due to an external symmetrical three-phase fault. In this situation, the PLL unit of the SSCB3 controller senses the voltage drop caused by the short-circuit resistance and transformer impedance at feeder 3, and the gating signal is generated by the hysteresis comparator unit of the controller to turn off the SSCB3. Consequently, the SSCB3 trips the faulty feeder, and the required
In this scenario, the PCC voltage drops to 70% of nominal voltage due to the occurrence of an external asymmetrical threephase fault at feeder 1. In this situation, the SSCB controllers, which are not sensitive to voltage sags with a depth of less than 40%, cannot detect the occurred voltage sag and imbalance. Therefore, the AVC should sense and restore the voltage magnitude to its pre-fault level at L3 terminal. Figs. 10 and 11 show the sag detection signal of the AVC, injected power and measured
1548
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Fig. 10. AVC controller signals: (A) the CL terminal voltage and (B) on–off signal of AVC.
Fig. 11. Injected power and CL terminal voltages: (A) AVC injected active and reactive powers, (B) CL terminal voltage without the AVC and (C) CL terminal voltage with the AVC.
voltage at L3 terminal, respectively. Fig. 11 demonstrates that the AVC can successfully balance and recover voltage up to 98% of its nominal voltage, and this proportion is within the acceptable voltage range. Given the use of direct ac/ac converter and lack of dc-link energy storage elements, the AVC is able to compensate voltage sag for an unlimited time interval, because it provides the required energy directly through the grid. This characteristic makes AVC a more efficient sag mitigation device for critical load, L3. Note that in the above-mentioned situation, APC and DG are disconnected by the coordination center to prevent the feeding of occurred external fault.
and voltage interruption is said to occur. The coordination center sends the command signal to open the circuit breaker, Brk1, and disconnect standard load, L1, from the PCC, and the DG continues to supply power to the sensitive and critical loads, L2 and L3, as a backup power supply. After clearing the external fault and returning the system to the normal condition by restoring the incoming feeders, DG keeps its power exchange mode with the network. Fig. 12 shows the injected power by DG into the network, and the measured voltages at the load terminals for this scenario. Based on the figure, the DG can deliver the required power for L2 and L3 when the main feeders are lost.
4.3. Voltage interruption mitigation at L2 and L3 using DG
4.4. General power quality improvement using APC
To test the performance of the grid-connected DG to recover the PCC voltage at the time of voltage interruption, three simultaneous external three-phase to ground faults in all incoming feeders are created that caused 60% voltage sag in each feeder. Based on the coordination logic, the SSCB controllers identify the occurred voltage drop, and each SSCB trips its respective feeder in a few milliseconds. Consequently, the PCC voltage drops to zero,
To approve the ability and effectiveness of the APC for performing voltage regulation at the PCC, an inrush current is simulated due to the induction motor starting. This inrush current causes an 8.5% voltage drop in the PCC voltage, as shown in Fig. 13. After identifying the voltage variation by the APC controller, the required current to compensate the PCC voltage is injected by APC. Fig. 14 illustrates the amount of injected active and reactive
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1549
Fig. 12. Injected power and measured voltages by DG at the PCC: (A) injected active and reactive powers, (B) SL terminal voltage, (C) SEL terminal voltage and (D) CL terminal voltage.
Fig. 13. Measured voltage and current without APC: (A) rms voltage at the point of common coupling and (B) Current at the SL connection point.
powers into the PCC and the PCC voltage after the APC voltage regulation action. To investigate the performance of the APC in harmonic compensation, the assumption is that load L2 injects harmonic current into the network and pollutes the PCC voltage with 26.84% THD. The APC controller estimates and injects the required harmonic current at the PCC and decreases the voltage THD to 1.56%, in which this THD is below the IEEE Std 519-1992 limitations. Therefore, non-harmonic polluting loads which are connected to the PCC can almost receive harmonic free power. Fig. 15 shows the measured voltage at the PCC before and after APC harmonic compensation. The results prove that the APC can precisely inject the required harmonic current with a 1801 phase difference to eliminate the harmonic distortion as much as possible at the PCC.
Additionally, the APC is able to provide general power factor correction for all loads by injecting a current in phase with the PCC voltage. Fig. 16 shows the normalized phase voltage and current waveforms at the load L1 terminal before and after power factor improvement. Based on the figure, it is clear that the phase current at the L1 terminal is almost in phase with the voltage after the APC action. The results of the simulated scenarios prove that the proposed PPP configuration is effective to provide superior QRA compared with the regular distribution systems. Moreover, the proposed PPP is able to offer three different levels of QRA for its distributed loads based on their requirements. To present a clear comparison of the proposed PPP with conventional PPPs (Chiumeo & Gandolfi, 2010; Meral, Teke, Bayindir, & Tumay, 2009; Weixing & Boon Teck, 2002;
1550
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Fig. 14. Performance of APC in voltage regulation: (A) injected powers by APC at the point of common coupling and (B) measured voltage at the point of common coupling when APC is switched on.
Fig. 15. The PCC voltage: (A) without APC and (B) with APC.
Fig. 16. Phase voltage and current waveforms at the SL terminal: (A) APC is off and (B) APC is on.
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
1551
Table 3 Comparison between the functions of the proposed and conventional PPPs. Functions
Proposed PPP
Configuration in Yop et al. (2005)
Configuration in Meral, Teke, Bayindir, & Tumay (2009)
Configuration in Chiumeo & Gandolfi (2010)
Configuration in Weixing & Boon Teck (2002)
Configuration in Farhoodnea, Mohamed, Shareef, & Mohamedet (2012)
More reliable incoming feeder configuration Different QRA level Unlimited voltage sag compensation Unlimited voltage imbalance compensation Voltage regulation Harmonic mitigation Power factor correction Uninterrupted/ unlimited backup power supply
√
√
√
√ √
√
√
√
√
√ √
√
√
√
Not completely
√ √ √ √
√ √ √ Not completely
√ √ √ Not completely
√ √ √
√ √
√ √ √ Not completely
power quality disturbances, including voltage sag, imbalance, harmonic, voltage variation, and interruption.
Table A1 Lists of acronyms. Acronym
Description
APC APF AVC CB CL CPD CPP DG D-STATCOM DVR EPRI IPP LPF PCC PID PLL PPP PWM QRA rms SCR SEL SL SSB SSCB STS SVC TPC VSC VSI
Active power conditioner Active power filter Active voltage conditioner Circuit breaker Critical load Custom power device Custom power park Distributed generation Distribution static compensator Dynamic voltage restorer Electric power research institute Independent power producer Low pass filter Point of Common Coupling Proportional-integral-derivative Phase-locked loop Premium power park Pulse width modulation Quality, reliability, and availability Root mean square Silicon-controlled rectifier Sensitive load Standard load Solid state breaker Solid state circuit breaker Static transfer switch Static Var compensator Taiwan power company Voltage source converter Voltage source inverter
Yop et al., 2005), Table 3 is provided to summarize the advantageous functions of the proposed PPP.
5. Conclusion In this paper, an enhanced PPP configuration based on the active conditioning devices is presented. In the proposed configuration, the distributed customer loads are fed through three feeders with spot network structure, and each feeder is equipped with an SSCB to remove deep voltage sags and deliver more reliable power. In addition, the proper combination of active conditioning devices, including APC and AVC, is used to offer three improved levels of QRA for non-sensitive, sensitive, and critical loads. The proposed configuration is simulated using four scenarios to cover the most important power quality disturbances. Results prove that the proposed configuration is able to mitigate
Appendix A. Acronyms See Table A1. References Babaei, E., Kangarlu, M. F., & Sabahi, M. (2010). Compensation of voltage disturbances in distribution systems using single-phase dynamic voltage restorer. Electric Power Systems Research, 80(12), 1413–1420. Behnke, M., Erdman, W., Horgan, S., Dawson, D., Feero, W., Soudi, F., et al. (2005). Secondary network distribution systems background and issues related to the interconnection of distributed resources. Technical Report NREL/TP-560-38079. National Renewable Energy Laboratory. Bollen M. H. J. (1995). Fast assessment methods for voltage sags in distribution systems. In IEEE industry applications conference (pp. 2282–2289). Chiumeo, R., & Gandolfi, C. (2010). D-STATCOM control system and operation in a configuration of premium power park. In 14th International Conference on Harmonics and Quality of Power (ICHQP) (pp. 1–7). Cutler-Hammer (August 1999)). Spot network systems. TD.52.01A.T.E. Domijan, A., Jr., Montenegro, A., Keri, A. J. F., & Mattern, K. E. (2005). Simulation study of the world's first distributed premium power quality park. IEEE Transactions on Power Delivery, 20(2), 1483–1492. Domijan, A., Jr., Song, Z., Baptista, G. N., Montenegro, A., Wang, X., Gurlaskie, G. T., et al. (2000). Power quality monitoring and analysis in a customized power industrial area using the FRIENDS concept. In Ninth international conference on harmonics and quality of power (pp. 379–384). Edinger, R., & Kaul, S. (2000). Humankind's detour toward sustainability: Past, present, and future of renewable energies and electric power generation. Renewable and Sustainable Energy Reviews, 4(3), 295–313. Farhoodnea, M., Mohamed, A., & Shareef, H. (2010). Identification of multiple harmonic sources in power systems using independent component analysis and mutual information. International Journal of Enterprise Information Systems, 18(1), 51–63. Farhoodnea, M., Mohamed, A., Shareef, H., & Mohamed, R. (2012). Premium power park: A review of the concepts, definitions and applications. Advances in Natural and Applied Sciences, 6(2), 173–184. Farhoodnea, M., Mohamed, A., Shareef, H., & Zayandehroodi, H. (2012). A novel distributed Premium Power Park design for power quality improvement. International Review on Modelling and Simulations, 5(2), 672–679. Halpin, S. M. (2006). Revisions to IEEE Standard 519-1992. In IEEE PES transmission and distribution conference and exhibition (pp. 1149–1151). Hingorani, N. (1998). Overview of custom power applications. Technical panel session paper of IEEE/PES (SM'98). IEEE (2006). IEEE recommended practice for powering and grounding electronic equipment—Redline. IEEE Std 1100-2005 (Revision of IEEE Std 1100-1999)—Redline (pp. 1–703). IEEE (2007). IEEE recommended practice for the design of reliable industrial and commercial power systems—Redline. IEEE Std 493-2007 (Revision of IEEE Std 493–1997)—Redline (pp. 1–426). IEEE (2009). IEEE application guide for IEEE Std 1547. IEEE standard for interconnecting distributed resources with electric power systems. IEEE Std 15472–2008 (pp. 1–207). Jain, S. K., Agrawal, P., & Gupta, H. O. (2002). Fuzzy logic controlled shunt active power filter for power quality improvement. IEE Proceedings-Electric Power Applications, 149(5), 317–328.
1552
M. Farhoodnea et al. / Control Engineering Practice 21 (2013) 1542–1552
Karimi, M., & Iravani, M. R. (2002). A nonlinear adaptive filter for online signal analysis in power systems: Applications. IEEE Transactions on Power Deliverery, 17(2), 617–622. Karuppanan, P., & Mahapatra, K. K. (2011). PLL synchronization with PID controller based shunt active power line conditioners. International Journal of Computers & Electrical Engineering, 3(1), 42–47. La Seta, P., & Lerch, E. (2010). Reliable operations of low voltage local energy systems with high presence of renewable energy sources. In International conference on power system technology (pp. 1–5). Madtharad, C., Sorndit, C., Premrudeepreechacharn, S., & McGranaghan, M. (2007). PEA's premium power service: Baseline and risk assessment. In 9th international conference on Electrical Power Quality and Utilisation (EPQU) (pp. 1–6). Mansoor, A., & Sundaram, A. (2000). Premium power grades. In International conference on Power System Technology (PowerCon) (pp. 933–939). Meral, M. E., Teke, A, Bayindir, K. C., & Tumay, M. (2009). Power quality improvement with an extended custom power park. Electric Power Systems Research, 79 (11), 1553–1560. Nara, K., & Hasegawa, J. (1999). Configuration of new power delivery system for reliable power supply. IEEE power engineering society summer meeting, 248–253. Nara, K., Mishima, Y., & Hasegawa, J. (2000). A new type power delivery system for reliable power supply—FRIENDS and its optimal network design. In International conference on Power System Technology (PowerCon) (pp. 649–654). Smith, R. K., Slade, P. G., Sarkozi, M., Stacey, E. J., Bonk, J. J., & Mehta, H. (1993). Solidstate distribution current limiter and circuit breaker: Application requirements and control strategies. IEEE Transactions on Power Delivery, 8(3), 1155–1164.
Tzong-Yih, G., Chiung-Yi, H., Ching-Yun, L., & Ching-Jung, L. (2003). Power quality task force of taipower: Experiences & results on PQ monitoring and mitigation. In Sixth international conference on Advances in Power System Control, Operation and Management (ASDCOM) (pp. 41–48). Vechiu, G. G. I., & Munteanu, T. (2011). Power quality improvement using renewable energy. In International Conference on Renewable Energies and Power Quality (ICREPQ) (pp. 1–6). Weixing, L., & Boon Teck, O. (2002). Multi-terminal HVDC as enabling technology of premium quality power park. IEEE power engineering society winter meeting, 719–724. Weixing, L., & Boon-Teck, O. (2005). Premium quality power park based on multiterminal HVDC. IEEE Transactions on Power Delivery, 20(2), 978–983. Yop, C., Sung-Woo, P., Hee-Jung, K., Seung-Il, M., Byung-Moon, H., Jae-Eon, K., et al. (2005). Operating strategy and control scheme of premium power supply interconnected with electric power systems. IEEE Transactions on Power Delivery 20(3), 2281–2288. Zahedi, A. (2008). Renewable energy-based power system to supply reliable electricity for remote applications. Australasian Universities power engineering conference, 1–4. Zayandehroodi, H., Mohamed, A., Shareef, H., & Mohammadjafari, M. (2011). A Comprehensive review of protection coordination methods in power distribution systems in the presence of DG. Electrical Review, 87(8), 142–148.