The simulation study of the modulation method for PV grid-connected system

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Applied Energy Symposium and Forum, Renewable Energy Integration with Mini/Microgrids, Applied Energy Symposium and Forum, Energy Integration REM 2017, 18–20 Renewable October 2017, Tianjin, China with Mini/Microgrids, REM 2017, 18–20 October 2017, Tianjin, China

The simulation study of the modulation method for PV gridThe 15th International on Districtmethod Heating andfor Cooling The simulation study ofSymposium the modulation PV gridconnected system connected system Assessing of using the heat demand-outdoor a the feasibility Xiaonan.Caoa, Changzhi.Zhangaa, Yingtian.Zhangbb, Zhiyong.Ganaa, Haoran.Liaa, Xiaonan.Cao function , Changzhi.Zhang , Yingtian.Zhang , Zhiyong.Gan , Haoran.Li , temperature for a long-term district heat demand forecast a a

Weichen.Nia, Jianjun.Wanga*† *† Weichen.Ni a a , Jianjun.Wang b c c Andrić *, A. Pina , P. No.8 Ferrão , J. Fournier ., industrial B. Lacarrière O. Le Corre State Grid I. Tianjin Electric Power Research Institute, Haitaihuake 4th road, Hi-Tec Park,Xiqing ,district, Tianjin, 300384,China

a

a,b,c

b State Grid Tianjin Institute, No.8 Haitaihuake Hi-Tec industrial district, Tianjin, 300384,China TianjinElectric ElectricPower PowerResearch Technology Development co Ltd, No.4th 184road, Harbin Road, Heping Park,Xiqing district, Tianjin 300041, China a b IN+ Center for Electric Innovation, Technology andDevelopment Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Tianjin Power Technology co Ltd, No. 184 Harbin Road, Heping district, Tianjin 300041, China b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France

a

Abstract Abstract With the improvement of monocrystalline silicon material manufacturing technology, PV modules gradually reduce the With the improvement of monocrystalline silicondifficulties material manufacturing modules gradually reduce the manufacturing cost. However, the main technical for solar powertechnology, system are PV the optimization problems of gridAbstract manufacturing cost.This However, the main technical solar China power and system the optimization problemsPVofpower gridconnected system. paper firstly introduced the difficulties differences for between otherare countries in grid-connected connected system. This paper firstly introduced the differences between China method and other countries in system, grid-connectedmethods PV power generation area. Furthermore, paper alsoaddressed mainly researched the modulation of PV inverter District heating networks arethis commonly in the literature as one of the most effective solutionsasfortwo decreasing of the generation area. Furthermore, this paper also mainly researched the modulation method of PV inverter system,grid-connected as two methodsPV of SPWM and SVPWM modulation grid system modeling and then applied the methods to the three-phase greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat SPWM and SVPWM modulation system modeling and then applied the methods to the method three-phasebe grid-connected PV simulation to thegrid curve of voltage current output, advantages SVPWM verified. sales. Duesystem. to theAccording changed climate conditions andand building renovation policies,ofheat demand in thecanfuture could decrease, simulation system. According to the curve of voltage and current output, advantages of SVPWM method can be verified. prolonging the investment return period. Copyright ©scope 2018 Elsevier Ltd.isAll rights reserved. The main© thisAuthors. paper to assess the feasibility of using the heat demand – outdoor temperature function for heat demand Copyright 2018ofThe Published by Elsevier Ltd. Copyright © 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee the Applied Symposium and Forum, forecast. The district of Alvalade, located inofLisbon (Portugal), was used as a case study.Energy The district is consisted of 665 Selection and peer-review under responsibility the scientific committee of theof Applied Energy Symposium and Forum, Selection and peer-review under responsibility of the scientific committee of the Applied Energy Symposium Forum, Renewable Energy Integration with Mini/Microgrids, REM 2017. Renewable Energy with Mini/Microgrids, 2017 Three weather scenarios (low, medium, high) and and buildings that varyIntegration in both construction period andREM typology. three district Renewable Energy Integration with Mini/Microgrids, REM 2017. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Keywords: Grid-Connected PV power generation; Inverter; SPWM; SVPWM compared with results from a dynamic heat demand model, previously developed and validated by the authors. Keywords: Grid-Connected PV power generation; Inverter; SPWM; SVPWM The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation 1.scenarios, Introduction the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1.The Introduction value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the The researches aboutofgrid-connected PV22-139h power during of domestic and overseas which mainly on the inverting decrease in the number heating hours of the heating season (depending on thefocus combination of weather and The researches about grid-connected PV power of domestic andcan overseas which mainly focus oncurrent the inverting control technique andconsidered). grid-connect PV inverter be dividing into voltage and type on the renovation scenarios On optimization. the other hand,The function intercept increased for 7.8-12.7% per decade (depending control optimization. The PV inverterthecan be dividing into voltage and current type coupledtechnique scenarios).and Thegrid-connect values suggested could be used to modify function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. * Xiaonan Cao. Tel.: +86-15510886610; fax:+86-022-84304799. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and *E-mail Xiaonan Cao. Tel.: +86-15510886610; fax:+86-022-84304799. address: [email protected]. Cooling. E-mail address: [email protected]. Keywords: Heat demand; Forecast; Climate change 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the Applied Energy Symposium and Forum, Renewable Energy Selection and peer-review under responsibility the scientific Selection peer-review under responsibility Integrationand with Mini/Microgrids, REM 2017. of the scientific committee of the Applied Energy Symposium and Forum, Renewable Energy Integration with Mini/Microgrids, REM 2017. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 Copyright © 2018 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the scientific committee of the Applied Energy Symposium and Forum, Renewable Energy Integration with Mini/Microgrids, REM 2017 10.1016/j.egypro.2018.04.020

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inverter circuit, the current type inverter circuit can be controlled by two strategies which are the voltage based control and current based control. Zhou [1] indicates that, the PWM (Pulse Width Modulation) is the most common method of pulse modulation which mainly including sinusoidal Pulse Width Modulation method, space vector pulse width modulation, space harmonic elimination method and so on. This paper will be research the SPWM (Sinusoidal Pulse Width Modulation) and SVPWM (Space Vector Pulse Width Modulation) method for PV inverter and then the principle and application of those two methods can be introduced. The advantages and disadvantages of the SPWM and SPVWM were presented through the simulations. Nomenclature PWM SPWM SVPWM PV

Pulse Width Modulation Sinusoidal Pulse Width Modulation Space Vector Pulse Width Modulation Photovoltaic

2. The principles for SPWM and SVPWM modulation 2.1. The principle of SPWM modulation The method of SPWM can be applied base on the PWM principle which to change the pattern of the modulation pulse. The duty ratio of pulse width time is arranged by sine law, the output waveform through the wave filtering which can be used as sine wave output. With the development of full controlled power electronic devices and Highspeed microprocessor chips. The SPWM can be widely applied for PV system. 2.2. The principle of SVPWM modulation Dai [2] discovered that the SVPWM method that comes from the flux linkage analysis, which aims to control the trajectory of magnetic chain space vector of the motor to approximate the base circle, and then the torque ripple of the motor can be reduced, a better operating performance can be achieved in the final. From Yang’s [3] research, when the SVPWM method applied as the inverter controller which can effectively reduce the harmonic content of the out current and the inverter can also be protected. 3. Modeling implementation and simulation analysis 3.1. SPWM model The three-phase PV grid simulation model can be constructed by using the PWM module of the MATLAB/SIMULINK.

Fig. 1. Three-phase PV grid simulation model

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3

3.2. SVPWM model Firstly, the sector needs to be judged. The sector N can be judged base on the rest frame Uα and Uβ which from the reference voltageUref , the corresponding relation as the table 1 below.

Table 1 The corresponding relation for N with sector. Sector

Ⅰ

Ⅱ

Ⅲ

Ⅳ

Ⅴ

Ton1

Ta

Tb

Tc

Tc

Tb

Ta

Tc

Tc

Ta

Ta

Tb

Tb

Ton2 Ton3

Ta

Ta

Tb

Tb

Tc

Ⅵ Tc

Secondly, the action time of the two vectors T1 and T2 , which need to be calculated. The basic vector action time of T1 and T2 can be obtained through the calculation as the table 2 𝑋𝑋 = √3𝑉𝑉𝛽𝛽 𝑇𝑇/𝑢𝑢𝑎𝑎𝑎𝑎𝑎𝑎

(1)

{ 𝑌𝑌 = (3𝑉𝑉𝛼𝛼 + √3𝑉𝑉𝛽𝛽 )𝑇𝑇/2𝑢𝑢𝑎𝑎𝑎𝑎𝑎𝑎

𝑍𝑍 = (−3𝑉𝑉𝛼𝛼 + √3𝑉𝑉𝛽𝛽 )𝑇𝑇/2𝑢𝑢𝑎𝑎𝑎𝑎𝑎𝑎

Table 2 Assignment for T1 and T2 Sector

Ⅰ

Ⅱ

Ⅲ

Ⅳ

Ⅴ

Ⅵ

T1

-Z

Z

X

-X

-Y

Y

X

Y

-Y

Z

-Z

-X

T2

After the assignment, the T1 and T2 should be applied the saturated judgment. When T1 + T2 < T, the values of T1 and T2 will be kept remain, when T1 + T2 > T, T1 equal to T1 T/(T1 + T2 ), and T2 equal to T2 T/(T1 + T2 ). Thirdly, space voltage vectors need to be synthesized.

Fig. 2. The sector vectors switching point

The time switching point Ton1 , Ton2 , Ton3 of Leg switch for phase A,B,C, which should be calculated. The definition is Ta = (T − T1 − T2 )/2,Tb = Ta + T1 , Tc = Tb + T2 , the space vector switching point as showing as the bellowing table. Table 3 The corresponding switching point for sectors Sector Ton1 Ton2 Ton3

Ⅰ Ta Tb Tc

Ⅱ Tb Ta Tc

Ⅲ Tc Ta Tb

Ⅳ Tc Tb Ta

Ⅴ Tb Tc Ta

Ⅵ Ta Tc Tb

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By comparing the vector switching point with the triangular wave, the 6 channel pulse waves can be obtained that can control the on/off state for the 6 switches, and the SVPWM can be also achieved. According to the analysis, the following model can be constructed by using Simulink as figure 3 and figure4.

Fig. 3. Simulink model for SVPWM control module

Fig. 4. The vector switching point model

3.3. The results of simulation

Fig. 5. The response of grid-connected voltage and current for the SPWM method

Fig. 6. A phase grid-connected voltage and current of SPWM method

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Fig. 7. Grid-connected Voltage and current of SVPWM method

Fig. 8. A phase grid-connected voltage and current of SVPWM method

Figure 5 and figure 6 present the voltage and current of SPWM method, which shows the grid voltage remains constant. Because the PV array apply the infinite power as model, grid voltage has distortion within 0.1s, the harmonic analysis of current shows harmonic content as 5.46% which has a bigger harmonic rate. The figure 7 and figure 8 displays the voltage waveform as a stable three-phase sine wave, the gird current only fluctuates in a very short period of time, and then reaches to the stable soon. The harmonic analysis shows the harmonic rate which only 2.59%. Comparing the harmonic rate obtained by SPWM, the results from the SVPWM which are more consistent with the requirements for renewable energy generation in power system.

Fig. 9. Dual current error hysteresis loop

3.4. The control method of hysteresis current base on the SVPM Because of the instruction voltage signal 𝑉𝑉 ∗ has derivative term which can influent the stability for the system. There is a new dual hysteresis control technology. As the figure 9, the inside hysteresis as the switch valve of the switch device which directly control the opening and cutoff of the power electronic device, and the hysteresis loop state can be presented by (IBA, IBB, IBC). The outside hysteresis loop signal (OBA, OBB, OBC) decide the location of the instruction voltage 𝑉𝑉 ∗ . The figure 10 presents the relationship between current error signal and dual hysteresis at the space plane.

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Fig. 10. Dual hysteresis loop error behaviour

Under the normal state, the current error can be limited in the inside hysteresis. If the error current over the inside hysteresis loop, point A, and obtain the outside hysteresis loop, point B, which means the instruction voltage signal has been changed the area, so the state needs to be changed at the point B, and the area testing unit can influent the instruction signal that can lead to the current error back to the inside hysteresis loop. The relationship between reference voltage and current error changing rate can be presented as bellowing figure 11. The plane was divided as 6 parts. Each part presents the totally deferent switching criterion. From the figure 11, the instruction voltage signal is located at area Ⅱ. Because of the smallest derivative term, optimal voltage vector at this time are V1 , V2 , V3 and V0 . When the instruction voltage has been decided, the states can control the opening and cutoff behaviour. Therefore, the α − axis of changing rate dδ/dt should be negative, the other axes should be positive. The 𝑉𝑉1 is the optimal choice.

Fig.11. Relationship between reference voltage and current error changing rate.

4. Conclusion This paper was introduced the principles and methods for SPWM and SVPWM modulations which were also simulated by using MATLAB/Simulink. To sum up, SVPWM has a shorter distortion time compare to the SPWM modulation method, and the SVPWM also has a shorter harmonic rate which was only 2.59%. The SVPWM is more suitable for PV grid-connected devices. References [1] X S Zhou. Control strategy of PV grid-connected inverter. East China Electric Power; 2000. [2] L W Dai. Research on High-Power PV Array Simulator Based on the PWM Rectifler. Electric drive, 2013. [3] Y L Yang. Reasearch of PV grid-conneted inverter. Wuhan University of Technology, 2012.