一种针对数字控制下光伏并网逆变器的陷波器滞后补偿方法
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摘要
由于数字控制中存在着延时环节和零阶保持器环节,使得光伏并网逆变器的运行极易发生不稳定的状况。为了研究数字控制下光伏并网逆变器的稳定性问题,首先针对逆变器建立了z域模型,并推导了其z域传递函数,然后通过严格的数学推证发现当逆变器谐振角频率 w res = π/(3Tsa)时,系统存在的两个开环不稳定极点和一次穿越-π线之间的矛盾导致了逆变器的谐振角频率在此点必不能稳定,同时指出了当逆变器的谐振角频率 w res在π/(3Tsa)附近处时系统亦难以稳定。针对此种情况,提出一种陷波器滞后补偿策略,在讨论了数字控制下陷波器特性和离散方法后,给出了滞后补偿的设计思路和方法。根据前述思路与方法搭建了一台功率为6.6kW的三相光伏并网逆变器,实验结果表明此方法简单有效,能够使逆变器在其谐振角频率 wres位于π/(3Tsa)及其附近处时皆能保持稳定状态,验证了理论分析的准确性。
Due to the existence of time-delay link and zero-order-holder link in digital control, the operation of PV grid-connected inverter is easily unstable. In order to study the stability of PV grid-connected inverter under digital control,the z-domain model was firstly established for the inverter,then the transfer function was derived. It can be found through strict mathematical evidence that when w res is equal to π/(3 Tsa),the contradiction between two open-loop unstable poles and one pass through -π line leads to a completely unstable case.Besides, the system is easily unstable if w res is near π/(3 Tsa). In this case, a lag compensation method based on notch filter was proposed. After studying the characteristic and the discrete method of notch filter, a design idea was given. And based on the design idea, a 6.6 kW experimental setup was established.Finally, the correctness of the theoretical analysis is verified by the experiment.
Due to the existence of time-delay link and zero-order-holder link in digital control, the operation of PV grid-connected inverter is easily unstable. In order to study the stability of PV grid-connected inverter under digital control,the z-domain model was firstly established for the inverter,then the transfer function was derived. It can be found through strict mathematical evidence that when w res is equal to π/(3 Tsa),the contradiction between two open-loop unstable poles and one pass through -π line leads to a completely unstable case.Besides, the system is easily unstable if w res is near π/(3 Tsa). In this case, a lag compensation method based on notch filter was proposed. After studying the characteristic and the discrete method of notch filter, a design idea was given. And based on the design idea, a 6.6 kW experimental setup was established.Finally, the correctness of the theoretical analysis is verified by the experiment.
引文
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[14]杨明.大型光伏电站逆变器并网控制策略及稳定性分析[D].重庆:重庆大学,2014.Yang Ming.Control strategy and stability analysis for grid-connected inverters in large-scale photovoltaic power plants[D].Chongqing:Chongqing University,2014(in Chinese).
[15]刘飞,查晓明,段善旭.三相并网逆变器LCL滤波器的参数设计与研究[J].电工技术学报,2010,25(3):110-116.Liu Fei,Zha Xiaoming,Duan Shanxu.Design and research on parameter of LCL filter in three-phase grid-connected inverter[J].Transactions of China Electrotechnical Society,2010,25(3):110-116(in Chinese).
[2]Zou Changyue,Liu Bangyin,Duan Shanxu,et al.Influence of delay on system stability and delay optimization of grid-connected inverters with LCLfilter[J].IEEE Transactions on Industrial Informatics,2014,10(3):1775-1784.
[3]盘宏斌,欧思程,刘林海,等.LCL型并网逆变器数字单环控制延时影响与稳定域分析设计[J].电力系统自动化,2016,40(6):85-90.Pan Hongbin,Ou Sicheng,Liu Linhai,et al.Influence of delay and stable domain analysis and design based on digital single-loop control of grid-connected inverter with LCL-filter[J].Automation of Electric Power Systems,2016,40(6):85-90(in Chinese).
[4]Parker S G,Mc Grath B P,Holmes D G.Regions of active damping control for LCL filters[J].IEEE Transactions on Industry Application,2014,50(1):424-432.
[5]谢文浩,刘一琦,王建赜,等.提高LCL型并网逆变器阻抗重塑控制鲁棒性的延时补偿方法[J].电工技术学报,2017,32(S1):178-185.Xie Wenhao,Liu Yiqi,Wang Jianze,et al.A delay compensation method of the grid-connected inverter with LCL filter to improve robustness of the impedance Shaping Control[J].Transactions of China Electrotechnical Society,2017,32(S1):178-185(in Chinese).
[6]周乐明,罗安,陈燕东,等.LCL型并网逆变器的鲁棒并网电流反馈有源阻尼控制方法[J].中国电机工程学报,2016,36(10):2742-2752.Zhou Leming,Luo An,Chen Yandong,et al.A robust grid-current-feedback-active-damping method for LCL-type grid-connected inverters[J].Proceedings of the CSEE,2016,36(10):2742-2752(in Chinese).
[7]Wang Jianguo,Yan Jiudun,Jiang Lin,et al.Delay-dependent stability of single-loop controlled grid-connected inverters with LCL filters[J].IEEETransactions on Power Electronics,2016,31(1):743-757.
[8]许津铭,季林,葛小伟,等.计及逆变器侧电流反馈影响的LCL滤波器参数优化设计[J].中国电机工程学报,2016,36(17):4656-4664.Xu Jinming,Ji Lin,Ge Xiaowei,et al.LCL-filter optimization design with consideration of inverter-side current feedback control impacts[J].Proceedings of the CSEE,2016,36(17):4656-4664(in Chinese).
[9]程红,王聪,王俊.开关变换器建模、控制及其控制器的数字实现[M].北京:清华大学出版社,2013:151-202.Cheng Hong,Wang Cong,Wang Jun.Modeling、control and digital controller implementation of switching power converters[M].Beijing:Tsinghua University Press,2013:151-202(in Chinese).
[10]Ogata K.离散时间控制系统[M].蔡涛,张娟,译.2版.北京:电子工业出版社,2014:75-83.Ogata K.Discrete-time control systems[M].Cai Tao,Zhang Juan,Trans.2nd ed.Beijing:Publishing House of Electronics Industry,2014:75-83(in Chinese).
[11]左为恒,周林.自动控制理论基础[M].北京:机械工业出版社,2007:123-123.Zuo Weiheng,Zhou Lin.Foundation of automatic control principle[M].Beijing:Machinery Industry Press,2007:123-123(in Chinese).
[12]Pan Donghua,Ruan Xinbo,Bao Chenlei,et al.Capacitor-current-feedback active damping with reduced computation delay for improving robustness of LCL-type grid-connected inverter[J].IEEE Transactions on Power Electronics,2014,29(7):3414-3427.
[13]Xin Zhen,Loh P C,Wang Xiongfei,et al.Highly accurate derivatives for LCL-filtered grid converter with capacitor voltage active damping[J].IEEE Transactions on Power Electronics,2016,31(5):3612-3625.
[14]杨明.大型光伏电站逆变器并网控制策略及稳定性分析[D].重庆:重庆大学,2014.Yang Ming.Control strategy and stability analysis for grid-connected inverters in large-scale photovoltaic power plants[D].Chongqing:Chongqing University,2014(in Chinese).
[15]刘飞,查晓明,段善旭.三相并网逆变器LCL滤波器的参数设计与研究[J].电工技术学报,2010,25(3):110-116.Liu Fei,Zha Xiaoming,Duan Shanxu.Design and research on parameter of LCL filter in three-phase grid-connected inverter[J].Transactions of China Electrotechnical Society,2010,25(3):110-116(in Chinese).