不平衡运行工况下并网逆变器的阻抗建模及稳定性分析
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摘要
实际运行中,并网逆变器常工作在电网电压、电网阻抗和逆变器滤波电感均不平衡的复杂工况下。文中研究了在此复杂不平衡工况下并网逆变器的阻抗模型及其和电网互联系统稳定性分析策略。在并网逆变器公共耦合点电压不平衡和逆变器滤波电感不平衡运行工况下,推导了电压不平衡分量及滤波电感不平衡和各谐波分量之间的关系,建立了并网逆变器在正、负序坐标下的输出导纳模型,得出了导纳矩阵的解析表达式,并分析了正、负序及耦合导纳的特性。依据广义奈奎斯特判据和逆变器不平衡导纳表达式,给出并网逆变器在不平衡运行工况下也适用的阻抗稳定性运行判定方法。最后,对不平衡工况下所研究的系统稳定性判据的有效性进行了实验验证。
As it is,the grid-connected inverter usually works under the condition of unbalanced grid voltage,unbalanced grid impedance and unbalanced filter inductance.This paper studies impedance modeling and stability analysis of grid-connected inverters under the unbalanced operation conditions.Firstly,under the conditions of unbalanced voltage at the point of common coupling and unbalanced inverter filter inductance,the relationships between the voltage imbalance component,the filter inductance and the harmonic component are derived.Then the output admittance model of the grid-connected inverter in the positive sequence and negative sequence coordinates are developed.Thus the analytical expression of the admittance matrix is obtained,and the characteristics of the positive-sequence,the negative-sequence and the coupling admittances are analyzed.Based on the generalized Nyquist stability criterion and the unbalanced admittance expression of the inverter,the stability analysing criterion of the inverter in the unbalanced situation is given.Finally,experimental results are given to verify the stability criterion.
As it is,the grid-connected inverter usually works under the condition of unbalanced grid voltage,unbalanced grid impedance and unbalanced filter inductance.This paper studies impedance modeling and stability analysis of grid-connected inverters under the unbalanced operation conditions.Firstly,under the conditions of unbalanced voltage at the point of common coupling and unbalanced inverter filter inductance,the relationships between the voltage imbalance component,the filter inductance and the harmonic component are derived.Then the output admittance model of the grid-connected inverter in the positive sequence and negative sequence coordinates are developed.Thus the analytical expression of the admittance matrix is obtained,and the characteristics of the positive-sequence,the negative-sequence and the coupling admittances are analyzed.Based on the generalized Nyquist stability criterion and the unbalanced admittance expression of the inverter,the stability analysing criterion of the inverter in the unbalanced situation is given.Finally,experimental results are given to verify the stability criterion.
引文
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[3]赵争鸣,雷一,贺凡波,等.大容量并网光伏电站技术综述[J].电力系统自动化,2011,35(12):101-107.ZHAO Zhengming,LEI Yi,HE Fanbo,et al.Overview of large-scale grid-connected photovoltaic power plants[J].Automation of Electric Power Systems,2011,35(12):101-107.
[4]BLAABJERG F,TEODORESCU R,LISERRE M,et al.Overview of control and grid synchronization for distributed power generation systems[J].IEEE Trans on Industrial Electronics,2006,53(5):1398-1409.
[5]赵强松,叶永强,徐国峰.分布式发电系统中并网逆变器的新型有源阻尼策略[J].电力系统自动化,2015,39(14):140-144.DOI:10.7500/AEPS20141208009.ZHAO Qiangsong,YE Yongqiang,XU Guofeng.A novel active damping control scheme for grid-connected inverter in distributed power generation systems[J].Automation of Electric Power Systems,2015,39(14):140-144.DOI:10.7500/AEPS20141208009.
[6]刘振亚,张启平.国家电网发展模式研究[J].中国电机工程学报,2013,33(7):1-10.LIU Zhenya,ZHANG Qiping.Study on the development mode of national power grid of China[J].Proceedings of the CSEE,2013,33(7):1-10.
[7]CHENG P,NIAN H.Enhanced operation for DFIG-based WECS using resonant feedback compensators under grid unbalance[C]//IEEE Energy Conversion Congress and Exposition(ECCE),September 15-19,2013,Denver,USA:2283-2288.
[8]LISERRE M,TEODORESCU R,BLAABJERG F.Stability of photovoltaic and wind turbine grid-connected inverters for a large set of grid impedance values[J].IEEE Trans on Power Electronics,2006,21(1):263-272.
[9]NIAN H,ZENG R.Improved control strategy for stand-alone distributed generation system under unbalanced and non-linear loads[J].IET Renewable Power Generation,2011,5(5):323-331.
[10]SUN J.Small-signal methods for AC distributed power systems-a review[J].IEEE Trans on Power Electronics,2009,24(11):2545-2554.
[11]TIMBUS A,LISERRE M,TEODORESCU R,et al.Evaluation of current controllers for distributed power generation systems[J].IEEE Trans on Power Electronics,2009,24(3):654-664.
[12]MIDTSUND T,SUUL J A,UNDELAND T.Evaluation of current controller performance and stability for voltage source converters connected to a weak grid[C]//2nd IEEEInternational Symposium on Power Electronics for Distributed Generation Systems(PEDG),June 16-18,2010,Hefei,China:382-388.
[13]MIDDLEBROOK R D.Input filter considerations in design and application of switching regulators[R].1976.
[14]FENG X,LIU J,LEE F C.Impedance specifications for stable DC distributed power systems[J].IEEE Trans on Power Electronics,2002,17(2):157-162.
[15]ZHANG J M,XIE X G,JIAO D Z,et al.Stability problems and input impedance improvement for cascaded power electronic systems[C]//Nineteenth Annual IEEE Applied Power Electronics Conference and Exposition,February 22-26,2004,Anaheim,USA:1018-1024.
[16]BELKHAYAT M.Stability criteria for AC power systems with regulated loads[R].1997.
[17]HARNEFORS L,BONGIORNO M,LUNDBERG S.Inputadmittance calculation and shaping for controlled voltage-source converters[J].IEEE Trans on Industrial Electronics,2007,54(6):3323-3334.
[18]CESPEDES M,SUN J.Impedance modeling and analysis of grid-connected voltage-source converters[J].IEEE Trans on Power Electronics,2014,29(3):1254-1261.
[19]CESPEDES M,SUN J.Methods for stability analysis of unbalanced three-phase systems[C]//IEEE Energy Conversion Congress and Exposition(ECCE),September15-20,2012,Raleigh,USA:3090-3097.
[20]HU J,HE Y,XU L,et al.Improved control of DFIG systems during network unbalance using PI-R current regulators[J].IEEE Trans on Industrial Electronics,2009,56(2):439-451.
[21]SUN J.Impedance-based stability criterion for grid-connected inverters[J].IEEE Trans on Power Electronics,2011,26(11):3075-3078.