Load-side Voltage Compensation of Small Hydropower Grid-connected System Using DVR based on PV Source

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 56 (2014) 610 – 620

11th Eco-Energy and Materials Science and Engineering (11th EMSES)

Load-side Voltage Compensation of Small Hydropower Grid-connected System using DVR based on PV Source Wuthikrai Chankhamriana, Chakrit Winitthama, Krischonme Bhumkittipichb,*, Sontaya Manmaib a Department of Electrical Technology, Faculty of Argo-Industrial Technology, Rajamangala University of Technology Tawan-Ok Chanthaburi Campus, 131 Moo 10 Pluang khao kitchagoot, Chanthaburi 22210, Thailand b Department of Electrical Engineering, Faculty of Engineering, Rajamangala University of Technology Thanyaburi, 39 Moo 1 Klong 6 Thanyburi, Pathumthani 12110, Thailand

Abstract Hydro turbine generator is one of the alternative renewable energy to replace the existing power supply sources in the remote settlement or to increase the efficiency in power distribution system. Small hydro turbine is connected to the grid for dividing current and power into the load. According to the power quality problem, the voltage amplitutde will be changed in power distribution system and directly effect to the electric load. Dynamic voltage restorer (DVR) is a custom power device used for compensating the voltage ampitude when power quality problem occurred. Therefore, this paper presents a simulation model of small hydro turbine generator connected to the grid and three-level diode-clamped converter DVR that using the photovoltaic (PV) system as alternative DC source. Low-pass filter is used for filter harmonics and reduction signal distortion from the DVR which is considering output voltage waveform of the converter. Simulations were carried out by using the MATLAB/Simulink program. The simulation results proved the capability of DVR based on PV system under the eliminating voltage sag distributed system. Improving of the voltage in power distribution system as an energy generator and stabilizing its voltage is the main result of this work. Keywords: photovoltaic, Small Hydro Turbine Generator, three-level diode-clamped converter, dynamic voltage restorer ;

1. Introduction Hydro turbine generator is one of the alternative renewable energy to replace the existing power supply sources in the remote settlement or to increase the efficiency in power distribution. Hydroelectricity is one of the most mature

* Corresponding author. Tel.: +662-549-3403 E-mail address: [email protected]

1876-6102 © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of COE of Sustainalble Energy System, Rajamangala University of Technology Thanyaburi (RMUTT) doi:10.1016/j.egypro.2014.07.200

611

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620

forms of renewable energy, providing more than 19% of the world’s electricity consumption from both large and small power plants [1]. One of the primary sources is considering is small hydro turbine generator, which is small scale hydroelectric system. The area is ideal for this energy source, as it is very mountainous, has heavy rainfall and is located next to a large river. Small hydro turbine generator as a device that receives hydro energy must work in special condition. For example the generators of turbine should have been stabilized. Thus the voltage and current of generator which connected to the grid should be steady. Voltage sag is currently the most severe power quality problem encountered because of its adverse financial impact on customers [2]. In order to eliminates voltage sag in the power distribution system. To achieve this, the device named dynamic voltage restorer (DVR) is used. This device controls the voltage of bus and removes the voltage sag through fault time. Thereby the power quality in generators is increased. DVR is series-connected in the grid for generating the compensation voltage. Control of DVR is required the high performance of detection method to detect the voltage magnitude and frequency [3]. The power system requirements are rapid operation for protecting the sensitive loads. The structure of DVR includes a DC source that can provide the power of injection. In this paper, instead of DC source connected to the DVR, the photovoltaic (PV) has been used. PV energy is derived from completely safe energy that is renewable and the cost is low in compare with other energies [4]. 2. Power Distribution System and Renewable Energy Model Study power system as shown in Fig. 1 includes a small hydro turbine and dynamic voltage restorer (DVR). Small hydro turbine has variable speed generator that is directly connect to the network with a converter and auto switch. DVR is one of the important tools of power electronics. It is to stabilize the amount of voltage in the bus of sensitive loads. DVR includes a DC source using PV. ZLine

VS ILine

Lf

Converter

VLoad

Load

DVR

Cf

Small Hydro Turbine Generator SW

G

ILoad

Rf Converter

PV

Energy Storage Fig. 1. Proposed System

Electrical power from hydro power is given by,

P where

gdQH P is electrical power from hydro power (W) Q is flow rate of water through turbine (m3/s) g is the acceleration of water (9.81 m/s2) d is the density of water (kg/m3) H is height of waterfall (m)

Electrical Energy is given by [5],

(1)

612

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620

W

(2)

Ptnƒ

where W is Electrical Energy (kW/hr) P is electrical power from hydro power (W) t is period of operation (hr) n is efficiency of the hydro turbine-generator (0.5-0.9) f is coefficient of variation of the water flow

2.1. Permanent Magnet Synchronous Generator (PMSG) The generator considered in this paper is a PMSG. The equations for modeling a PMSG, using the motor machine convention [6], are given by,

did dt

1 ªud  pZg Lq iq  Rd id º¼ Ld ¬

(3)

diq

1 ªuq  pZg  Ld id  Mi f  Rq iq º ¼ Lq ¬

(4)

dt

where

id ,iq are the stator currents ud ,uq are the stator voltages p is the number of pairs of poles

Ld ,Lq are the stator inductances Rd ,Rq are the stator resistances M is the mutual inductance i f is the equivalent rotor current

In order to avoid demagnetization of permanent magnet in the PMSG, a null stator current associated with the direct axis is imposed [7].

2.2. Converter for Grid Connected [8] The system has used the power converter for transferring the active and reactive power to grid system the flow diagram is shows in Fig. 2. The grid connected control flow diagram is shown in Fig. 2.

Fig. 2. Grid-connected flow diagram

613

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620

vd vq

Vdc*

id vd vd*   iq

id*  Vdc

Q*

3vd

Z L

id

ZL

 iq

DE dq

dq

DE vq*  

v v

DE abc

i DE

DE i



 id i q

iq* 

dq

ia

abc

ib

ic

Sa Sb Sc Vdc

vq

Fig. 3. Grid side converter controlled diagram

2.3. Grid connected control system The grid side converter has cascade connected from the PMSG side and control by current loop control. Clark’s transformation has used for transfer 3 phase to 2 phase coordination system, the equation are given by, xD

2  xa  0.5 xb  0.5 xc 3

(5)

xE

2  0 xa  0.866 xb  0.866 xc 3

(6)

Where x is variable parameter instead of voltage and current. Equations (7) and (8) are used for transferring D  E  0 to dq .

xd

xD cos T  xE sin T

(7)

xq

 xD sin T  xE cos T

(8)

2.4. Phase Lock Loop (PLL) PLL technique was applied to this research because this application will generate the grid angle for the grid side control. This technique is calculated by Equation (9).

T grid

§ vE · tan 1 ¨ ¸ © vD ¹

where T grid is grid phase angle.

(9)

614

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620

2.5. DVR design DVR is used to protect sensitive electrical loads like large semiconductors, auto switches in power electronic and etc. against power system disturbances. DVR is connected in series with the distribution system as shown in Fig. 4. The main components of a DVR are the control system, DC voltage source, and a three-level diode-clamped converter. In the proposed DVR design, a photovoltaic (PV) system is incorporated to function as a DC voltage source. The reason for using PV is that it does not need bright sunlight to operate, it does not produce noise, harmful emission or polluting gases and it is fuel free. Such a modular PV system can be quickly installed anywhere, requires minimal maintenance to keep the system running and also no moving parts to wear out or break down. The electric power produced by the PV system can be considered economically viable [9].

Grid

ZLine

VS

ILine

ILoad

VLoad

DVR

Load

Cf Detection and Controller

Rf

Lf

PV

Converter Energy Storage

Fig. 4. DVR Configuration

An LC filter is connected at the output side of the DVR, which is attenuating the DVR output signal and eliminating the harmonics on the distribution system.

2.6. Control of DVR [10] Operation of control systems starting in occurred voltage sag. Detector will verify it. When there are signs it, the reference voltage generator part is created reference voltage for comparison with the actual voltage in the system. After, the voltage in this comparison will sent to PWM in the compensating voltage generator & voltage injection part for drive the converter, so it will inject voltage into the system. Block diagram control as show in Fig. 5. VGrid Space Vector Transformation

VABC

VDE

Referance Voltage Generator

Vdq

Vdq

VABC

VDE

VABC,ref VABC,com

Start

Vdc,bus

VPWM Start Compensating Voltage Generator & Voltage Injection

Sag Signal

Sag Detector Fig. 5. Block diagram control of the DVR.

615

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620

2.7. PV Modeling [2] The PV is used to provide a DC source for the DVR by injecting active power into a distribution system. The PV is designed and modeled with a boost converter to charge the DVR capacitor with good efficiency as shown in Fig. 6. The capacitor is connected in parallel with the PV panel to limit the voltage undulation in the panel, as well as to ensure the availability of a voltage source.

Fig. 6. PV Modeling with Boost Converter

The boost converter is designed to boost the power that is generated from the PV and send it to the DVR capacitor. It consists of inductor, diode and capacitor. A continuous voltage of the converter output can be obtained by connecting a large capacitor between the cathode and ground such that when the capacitor value increases, the output voltage increases too. The output voltage of the converter must be greater than the source and it is given by, Vo

Vs

1 1 k

(10)

The voltage across the capacitor can be stepped up by varying the duty cycle, k. When k=0, the minimum output voltage becomes the source voltage, Vs. During the on state (switch close), inductor current rises and energy is stored in the inductor. The inductor voltage is given by, VL

L

di1 dt

(11)

In this situation the source energy is transferred to the inductor, and the peak-to-peak ripple inductor current is obtained as, 'I

Vs t L

(12)

The inductor current in this mode becomes, I1 t

Vs t  I1 L

(13)

During the off state (switch open), the stored energy in the inductor is transferred to the capacitor and the inductor current falls. Consider the energy supplied to the capacitor which is given by,

616

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620

1 2 2 C Vmax  Vmin 2

1 2 2 L  I max  I min 2

(14)

The capacitance is given by,

LI nom 'I Vnom 'V

C

(15)

Capacitor sizing plays an important role in the DVR. It acts as a dc source to provide reactive power to the load during fault conditions. The following equation is used to determine the sizing of the capacitor, Cdc, 1 Cdc ª¬VC2max  Vdc2 º¼ 2

1 Vs 'I LI T 2

(16)

where Vdc is preset lower limit voltage of energy storage capacitor.

'I LI is step increase of the peak value of the real fundamental component of the load current. T is period of the utility voltage source. From (16), the dc capacitor value for a three-phase system can be derived and given as,

Cdc

where Vdc

3

Vs 'I LT VC2max  Vdc2

(17)

3 3 Vs S

3. Simulation and Results

The simulation program is MATLAB/Simulink. The DVR and small hydro turbine generator are connected in series and parallel with transmission line, respectively as shown in Fig. 7. DVR is composed of a three-level diodeclamped converter for each phase that each converter has eight switches. Switching frequency is 20 kHz. Also we use an AC filter at DVR output for removing the harmonics of switching. In this case we used PV instead of batteries for feeding of DC link which is connected to the DC capacitor. Small hydro turbine generator used in this simulation consists of PMSG and back to back converter connected to the grid side 20 kW, 380 V 3 phase, 50 Hz. It is applied to the network at the time between 0.06 until 0.26 seconds. For making disturbance in the system we used a three phase to ground fault, which is applied to the network at the time between 0.12 until 0.2 seconds.

617

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620 A

Discrete , Ts = 3e-006 s.

t Clock

B

To Workspace 1

[Vabc ]

C Three -Phase Fault

B C

To Workspace3

C

t1

Three -Phase Series RLC Load

To Workspace 2 Scope 1

A Vabc Iabc B a b C c

A B C

A B C Three -Phase Series RLC Branch 2

A Vabc Iabc B a b C c

Three -Phase V-I Measurement

com A B C

Three -Phase Transformer (Three Windings )

t2

B

a

C

Three -Phase Source

A

A B C Three -Phase Series RLC Branch 1

b

B

Goto

A

A B C

c

A

a2 b2 c2 a3 b3 c3

Vdc

Vref 1

Vref

Vdc

Vref 2 +

Vdc

Vref 3

Vref

3 level inverter 1

A B C Three -Phase Three -Phase V-I Measurement 1 Series RLC Branch 3

Vref

+

3 level inverter

Timer

Scope

A B C

+

3 level inverter 2 Vdc1

Vref 1

Vref 1

Vref 2

Vref 2

Vref 3

Vref 3

Va Vdc2

[Vabc]

Vabc

Vb Vdc3

From 1

Vc

[Vabc ]

Voltage Generator by Small HydroTurbine

From

Vabc

Control DVR

Fig. 7. Circuit of Power Distribution System

The simulation begins with small hydro turbine generator connected to the grid side which is duration time between 0.06 and 0.26 seconds. Fig. 8 and Fig. 9 show voltage of supply and small hydro turbine generator are stabilities after synchronized small hydro turbine generator to the grid. Current and power of supply and small hydro turbine generator are dividing feed to the load shown in Fig. 10 to Fig. 13, respectively. 1.5

Magnitde (V)

1 0.5 0 -0.5 -1 -1.5 0

0.05

0.1

0.15

0.2

0.25

0.3

0.25

0.3

Time (s)

Fig. 8. Load-side Voltage 2

Magnitude (V)

1.5 1 0.5 0 -0.5 -1 -1.5 0

0.05

0.1

0.15

0.2

Time (s)

Fig. 9. Small Hydro Turbine Generator Voltage

618

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620 1.5

Magnitde (A)

1 0.5 0 -0.5 -1 -1.5 0

0.05

0.1

0.15

0.2

0.25

0.3

0.25

0.3

Time (s)

Fig. 10. Load-side Current 1.5

Magnitude (A)

1 0.5 0 -0.5 -1 -1.5 0

0.05

0.1

0.15

0.2

Time (s)

Fig. 11. Small Hydro Turbine Generator Current 0.6 P Q

Magnitude (P, Q)

0.5 0.4 0.3 0.2 0.1 0 -0.1 0

0.05

0.1

0.15

0.2

0.25

0.3

Time (s)

Fig. 12. Load-side Power 0.3 P Q

Magnitude (P, Q)

0.25 0.2 0.15 0.1 0.05 0 -0.05 0

0.05

0.1

0.15

0.2

0.25

0.3

Time (s)

Fig. 13. Small Hydro Turbine Generator Power

After applying fault in the network the time between 0.12 and 0.2 seconds it is seen that the network voltage sag shown in Fig. 8 and Fig.9. Power of supply and small hydro turbine generator are decreasing shown in Fig. 12 and Fig. 13. The DVR is injecting voltage to the network. The injection voltage and power of DVR are shown in Fig. 15 and Fig. 16, respectively.

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620

1.5

Magnitude (V)

1 0.5 0 -0.5 -1 -1.5 0

0.05

0.1

0.15

0.2

0.25

0.3

Time (s)

Fig. 14. Injection Voltage of DVR

P Q

Magnitude (P, Q)

0.25 0.2 0.15 0.1 0.05 0 -0.05 0

0.05

0.1

0.15

0.2

0.25

0.3

Time (s)

Fig. 15. Injection Power of DVR

During applying fault in the network, load voltage, current and power are remaining constant shown in Fig. 16 to Fig. 18, respectively. 1.5

Magnitude (V)

1 0.5 0 -0.5 -1 -1.5 0

0.05

0.1

0.15

0.2

0.25

0.3

Time (s)

Fig. 16. Load-side Voltage after compensation 1.5

Magnitude (A)

1 0.5 0 -0.5 -1 -1.5 0

0.05

0.1

0.15

0.2

0.25

Time (s)

Fig. 17. Load-side Current after compensation

0.3

619

620

Wuthikrai Chankhamrian et al. / Energy Procedia 56 (2014) 610 – 620 0.6

Magnitude (P, Q)

0.5 0.4 0.3

P Q

0.2 0.1 0 -0.1 0

0.05

0.1

0.15

0.2

0.25

0.3

Time (s)

Fig. 18. Load-side Power after compensation

4. Conclusion

This paper proposes the small hydro turbine generator connected to the grid and three-level diode-clamped converter DVR using photovoltaic (PV) for improving the power distribution system. The small hydro turbine generator can synchronize the grid system which is reducing supply power to the load. It is dividing power feed to the load. Thus load power is more stability. During power distribution system has voltage sag, DVR be able to compensate voltage sag in a power distribution system. The DVR output is filtered in order to mitigate the harmonics generated from switching. The PV is connected to a boost converter so as to achieve a higher output voltage for charging the DVR capacitor efficiency. Simulation results prove that the small hydro turbine generator and PV based DVR can be improving the power distribution system. References [1]

Van der Geer J, Hanraads JAJ, Lupton RA. Clean Energy Project Analysis: Retscreen® Engineering & Cases Textbook, Small Hydro Project Analysis Chapter. J Sci Commun 2000;163:51–9. [2] Ali O Al-Mathnani, Azah Mohamed, Mohd Alauddin Mohd Ali. Photovoltaic Based Dynamic Voltage Restorer For Voltage Sag Mitigation. The 5th Student Conference on Research and Development-SCOReD, 2007, p. 1-6. [3] Ghosh,A.,Jindal,A.K., & Joshi,A. Inverter control using output feedback for power compensating devices. TENCON. Conference on Convergent Technologies for Asia-Pacific Region, 2003. [4] M.Farsadi , A.Gara shahrak , F.Salehpour oskouyi. Photovoltaic based DVR for Improving the Operation of wind farm. 2011 7th International Conference on Electrical and Electronics Engineering (ELECO), 2011, p. I-298 – I-301. [5] Sontaya Manmai, Krischonme Bhumkittipich. Modeling of Grid-connected Permanent Magnet Synchronous Generator (PMSG) by Using Vector Control. Electrical Engineering Network of Rajamangala University of Technology (EENET), 2012, p. 64-67. [6] Ong, P.-M. Dynamic Simulation of Electric Machinery: Using Matlab/Simulink, PrenticeHall, ISBN: 0137237855, New Jersey, 1998. [7] Senjyu, T., Tamaki, S., Urasaki, N. and Uezato, K. Wind velocity and position sensorless operation for PMSG wind generator, Proceedings of 5th Int. Conference on Power Electronics and Drive Systems 2003, p. 787-792. [8] M. Edilson, D.Sergio, L.Fernando, M.Antunes and C.Cicero. Photovoltaic system for supply sublic illumination in electrical energy demand. In proc. 2004 Energy Processing and Control group, Electrical Engineering Department, 2004. [9] Nathabhat Phankong, Sonthaya Manmai, Krischonme Bhumkittipich and Poolkiat Nakawiwat. Modeling of Grid-connected with Permanent Magnet Synchronous Generator (PMSG) using Voltage Vector Control. Energy Procedia 34, 2013, p. 262 – 272. [10] W. Chankhamrian and K. Bhumkittipich. The Effect of Series-Connected Transformer in DVR Applications. 9th Eco-Energy and Materials Science and Engineering Symposium, 2011, p. 33.