An Improved Grid Voltage Feedforward Strategy for LCL-type Grid-connected Inverters in Weak Grid

doi:10.11985/2019.02.014

Abstract

Abstract:

Grid-connected inverters often use grid voltage feedforward control to improve the suppression capability and startup performance of the system. When the grid behaves a weak grid, the direct proportional feedforward control of the grid voltage will weaken the stability margin of the grid-connected inverter control system. Based on the comparative analysis of the open-loop frequency characteristics of no feedforward and direct proportional feedforward control under weak grids, an improved feedforward scheme is proposed with a lag transfer function for frequency selective in the voltage feedforward channel. Thus the system stability margin improves obviously. Finally, the verification is carried out on a set of LCL-type grid-connected inverter experimental platform. The experimental results demonstrate that the adaptability of improved voltage feedforward strategy under weak grid is more stronger.

Key words: LCL-type grid-connected inverter, weak grid, grid voltage feedforward control, system stability

CLC Number:

TM561

YU Wenqian,TONG Xiangqian,YAN Cong,JIAO Pan. An Improved Grid Voltage Feedforward Strategy for LCL-type Grid-connected Inverters in Weak Grid[J]. Journal of Electrical Engineering, 2019, 14(2): 79-85.

Figures/Tables 13

References 17

[1]	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 Transactions on Power Electronics, 2006,21(1):263-272.
[2]	李小强, 伍小杰, 耿乙文 , 等. 感性电网阻抗下三相光伏逆变器稳定性分析[J]. 中国电机工程学报, 2014,34(18):2906-2916. doi: 10.13334/j.0258-8013.pcsee.2014.18.006
	Li Xiaoqiang, Wu Xiaojie, Geng Yiwen , et al. Stability analysis of three-phase photovoltaic inverter under inductive grid impedance[J]. Proceedings of the CSEE, 2014,34(18):2906-2916. doi: 10.13334/j.0258-8013.pcsee.2014.18.006
[3]	周林, 张密, 居秀丽 , 等. 电网阻抗对大型并网光伏系统稳定性影响分析[J]. 中国电机工程学报, 2013,33(34):34-41.
	Zhou Lin, Zhang Mi, Ju Xiuli , et al. Analysis of the influence of grid impedance on the stability of large-scale grid-connected photovoltaic system[J]. Proceedings of the CSEE, 2013,33(34):34-41.
[4]	潘冬华, 阮新波, 王学华 , 等. 增强LCL型并网逆变器对电网阻抗鲁棒性的控制参数设计[J]. 中国电机工程学报, 2015,35(10):2558-2556. doi: 10.13334/j.0258-8013.pcsee.2015.10.023
	Pan Donghua, Ruan Xinbo, Wang Xuehua , et al. Control parameter design of enhanced LCL grid-connected inverter for grid impedance robustness[J]. Proceedings of the CSEE, 2015,35(10):2558-2556. doi: 10.13334/j.0258-8013.pcsee.2015.10.023
[5]	Wang X, Ruan X, Liu S , et al. Full feedforward of grid voltage for grid-connected inverter with LCL filter to suppress current distortion due to grid voltage harmonics[J]. IEEE Transactions on Power Electronics, 2011,25(12):3119-3127.
[6]	许津铭, 谢少军, 唐婷 . 弱电网下LCL滤波并网逆变器自适应电流控制[J]. 中国电机工程学报, 2014,34(24):4031-4039. doi: 10.13334/j.0258-8013.pcsee.2014.24.006
	Xu Jinming, Xie Shaojun, Tang Ting . Adaptive current control of LCL filtered grid-connected inverter under weak power grid[J]. Proceedings of the CSEE, 2014,34(24):4031-4039. doi: 10.13334/j.0258-8013.pcsee.2014.24.006
[7]	滕宇, 王学华, 余辉 , 等. 提高LCL型并网逆变器对电网阻抗鲁棒性的阻抗调节方法[J]. 中国电机工程学报, 2015,35(S1):197-204.
	Teng Yu, Wang Xuehua, Yu Hui , et al. Impedance adjustment method for improving the robustness of LCL grid-connected inverters to grid impedance[J]. Proceedings of the CSEE, 2015,35(S1):197-204.
[8]	杨东升, 阮新波, 吴恒 . 提高LCL型并网逆变器对弱电网适应能力的虚拟阻抗方法[J]. 中国电机工程学报, 2014,34(15):2327-2335. doi: 10.13334/j.0258-8013.pcsee.2014.15.001
	Yang Dongsheng, Ruan Xinbo, Wu Heng . Virtual impedance method for improving the adaptability of LCL grid-connected inverter to weak grid[J]. Proceedings of the CSEE, 2014,34(15):2327-2335. doi: 10.13334/j.0258-8013.pcsee.2014.15.001
[9]	马兴, 徐瑞林, 陈民铀 , 等. 弱电网下并网逆变器自适应H_∞控制方法[J]. 电力系统自化, 2018,42(13):189-195.
	Ma Xing, Xu Ruilin, Chen Minyou , et al. Adaptive H_∞ control method for grid-connected inverters in weak grids[J]. Automation of Electric Power System, 2018,42(13):189-195.
[10]	钱强, 谢少军, 季林 , 等. 一种提升逆变器对电网适应能力的电流控制策略[J]. 中国电机工程学报, 2016,36(22):6193-6201.
	Qian Qiang, Xie Shaojun, Ji Lin , et al. A current control strategy for improving the adaptability of inverters to power grids[J]. Proceedings of the CSEE, 2016,36(22):6193-6201.
[11]	刘乐, 同向前, 杨树德 . 提高弱电网下并网逆变器鲁棒稳定性的电网电压部分前馈控制策略[C]. 第十一届中国高校电力电子与电力传动学术会议,湖南, 2017.
[12]	徐飞, 汤雨, 谷伟 . 弱电网条件下LCL型并网逆变器谐振前馈控制策略研究[J]. 中国电机工程学报, 2016,36(18):4970-4979.
	Xu Fei, Tang Yu, Gu Wei . Research on resonant feedforward control strategy of LCL grid-connected inverter under weak grid conditions[J]. Proceedings of the CSEE, 2016,36(18):4970-4979.
[13]	杨树德, 同向前, 尹军 , 等. 增强并网逆变器对电网阻抗鲁棒稳定性的改进前馈控制方法[J]. 电工技术学报, 2017,32(10):222-230.
	Yang Shude, Tong Xiangqian, Yin Jun , et al. Improved feedforward control method for enhanced robust stability of grid-connected inverters to grid impedance[J]. Transactions of China Electrotechnical Society, 2017,32(10):222-230.
[14]	李巍巍 . 三相LCL型并网逆变器中电网电压引起的谐波和不平衡电流抑制研究[D]. 武汉:华中科技大学, 2014.
[15]	国家电网. Q/GDW 480 分布式电源接入电网技术规定[S]. 北京:国家电网, 2010.
[16]	Parker S G, Mcgrath B P, Holmes D G . Regions of active damping control for LCL filters[J]. IEEE Transactions on Industry Applications, 2014,50(1):424-432. doi: 10.1109/TIA.2013.2266892
[17]	胡寿松 . 自动控制原理[M]. 5版. 北京: 科学出版社, 2007.

参数	数值	参数	数值
额定容量/(kV·A)	2.2	调制方式	倍频
额定电压/V	220	逆变侧电感/mH	0.99
额定电流/A	10	滤波电容/μF	1
开关频率/kHz	50	网侧电感/mH	0.44
采样频率/kHz	50	谐振频率/kHz	9.1

	直接比例	带通滤波	滞后选频
稳定裕度	小	大	较大
截止频率	高	较低	较高
低频增益	大	小(50 Hz大)	较大
相位滞后	大	小	较大