一种提高虚拟同步机电流质量的电压-电流级联闭环控制方案

doi:10.19595/j.cnki.1000-6753.tces.222327

Abstract
Figure/Table
References
Related Citation (15)

Download: PDF (8371 KB) HTML (1 KB)
Export: BibTeX | EndNote (RIS)

Abstract With the increasing amount of renewable energy sources and energy storage devices in the power grid, more power electronic inverters get tied to the grid as current sources. As a result, the overall grid rotary inertia and frequency stability will decrease. So Virtual Synchronous Generators (VSG) schemes are being implemented in grid-tied inverters. VSGs are inverters in voltage source control mode. Particularly, its output voltage vector instantaneous angle is obtained by the rotor dynamics equation of the virtual synchronous generator to provide inertia and frequency support to the grid, just as the rotary synchronous generators. However, when VSG is connected to the grid, even a slight amount of grid voltage distortion would induce significant harmonics currents. Therefore, various VSG harmonic current suppression schemes are introduced.
Existing VSG harmonic current suppression methods are mainly based on PCC voltage feedback, whose voltage harmonics get extracted and added to the VSG output voltage commands. Therefore, the line connecting VSG and PCC would have no net harmonic voltage across, and no harmonic current would be induced. However, the existing methods based on PCC voltage feedback have practical limitations. As the line impedances are usually small, it only takes a tiny amount of harmonic voltage difference to induce a significant amount of harmonic currents. Slight noises and nonlinearity in the feedback path will introduce harmonic voltage difference and large harmonic current. Therefore, some paper proposes adding extra inductors in series with the PCC connecting line, but extra volume and cost are incurred.
This paper introduces a VSG output harmonic current closed loop to receive the voltage harmonic signal feedback. Therefore, the noises and the nonlinearity in the previous open-loop PCC harmonic voltage feedbacks can be eliminated, and the VSG output voltage can accurately track the voltage harmonics at the PCC point. As a result, the output current harmonics suppression is more effective.
This paper first establishes the impedance model of VSG and analyzes the output current harmonics. To implement this closed-loop control scheme, the sum of all orders of the harmonics is first extracted from the VSG output current feedbacks by a first-order complex vector filter and fed through a proportional-resonant control loop to generate the VSG harmonic voltage reference. The enhancement of the harmonic loop impedance with the proposed method is analyzed in detail and compared with the existing methods. Moreover, this paper further analyzes the system stability of the proposed method for both fundamental frequency voltage control and harmonic current control, using the impedance-based stability criterion of the voltage-source inverter. Compared with the existing harmonic current suppression methods using virtual impedance, the proposed scheme can suppress the harmonic current with much larger loop gains than the virtual impedance-based method.
Finally, a 15 kW VSG prototype is built to verify the proposed method compared with the conventional VSG and two harmonic current suppression methods based on PCC voltage feedback and the virtual impedance, respectively. The method proposed in this paper significantly improves VSG output current THD. Besides, it is noted that the harmonic suppression effect of the proposed method is much less susceptible to the low impedance value of the PCC connection line than the PCC voltage feedback-based method. In addition, the best suppression effect can be realized using the maximum virtual impedance value without instability.

Key words： Virtual synchronous generators (VSG) harmonic suppression impedance reshaping power quality

Received: 17 December 2022

PACS:	TM464
	TM341
	TM762

	Service

	E-mail this article
	Add to my bookshelf
	Add to citation manager
	E-mail Alert
	RSS
	Articles by authors
	Xu Song
	Yang Bo
	Liu Hao
	Lu Shuai

Cite this article:

Xu Song,Yang Bo,Liu Hao等. A Cascaded Harmonic Voltage and Current Closed-Loop Control Method to Improve the Current Quality of Virtual Synchronous Generators[J]. Transactions of China Electrotechnical Society, 2024, 39(6): 1871-1885.

URL:

https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.222327 OR https://dgjsxb.ces-transaction.com/EN/Y2024/V39/I6/1871

[1] 王成山, 李琰, 彭克. 分布式电源并网逆变器典型控制方法综述[J]. 电力系统及其自动化学报, 2012, 24(2): 12-20.
Wang Chengshan, Li Yan, Peng Ke.Overview of typical control methods for grid-connected inverters of distributed generation[J]. Proceedings of the CSU- EPSA, 2012, 24(2): 12-20.
[2] Mohandes B, EI Moursi M S, Hatziargyriou N, et al. A review of power system flexibility with high penetration of renewables[J]. IEEE Transactions on Power Systems, 2019, 34(4): 3140-3155.
[3] Wang Baochao, Xu Yongxiang, Shen Zhaoyuan, et al.Current control of grid-connected inverter with LCL filter based on extended-state observer estimations using single sensor and achieving improved robust observation dynamics[J]. IEEE Transactions on Indu- strial Electronics, 2017, 64(7): 5428-5439.
[4] 詹长江, 吴恒, 王雄飞, 等. 构网型变流器稳定性研究综述[J]. 中国电机工程学报, 2023, 43(6): 2339-2359.
Zhan Changjiang, Wu Heng, Wang Xiongfei, et al.An overview of stability studies of grid-forming voltage- source converters[J]. Proceedings of the CSEE, 2023, 43(6): 2339-2359.
[5] 高海力, 谭建成. 大型光储联合虚拟同步发电机技术综述[J]. 电气技术, 2018, 19(1): 1-4, 9.
Gao Haili, Tan Jiancheng.The overview of the VSG technology of grid connected large-scale PV-storage hybrid system[J]. Electrical Engineering, 2018, 19(1): 1-4, 9.
[6] D'Arco S, Suul J A. Equivalence of virtual syn- chronous machines and frequency-droops for converter-based microgrids[J]. IEEE Transactions on Smart Grid, 2014, 5(1): 394-395.
[7] Shuai Zhikang, Shen Chao, Liu Xuan, et al.Transient angle stability of virtual synchronous generators using Lyapunov’s direct method[J]. IEEE Transactions on Smart Grid, 2019, 10(4): 4648-4661.
[8] 刘一锋, 周小平, 洪乐荣, 等. 虚拟惯性控制的负荷变换器接入弱电网的序阻抗建模与稳定性分析[J]. 电工技术学报, 2021, 36(4): 843-856.
Liu Yifeng, Zhou Xiaoping, Hong Lerong, et al.Sequence impedance modeling and stability analysis of load converter with virtual inertia control con- nected to weak grid[J]. Transactions of China Elec- trotechnical Society, 2021, 36(4): 843-856.
[9] 姜卫同, 胡鹏飞, 尹瑞, 等. 基于虚拟同步机的变流器暂态稳定分析及混合同步控制策略[J]. 电力系统自动化, 2021, 45(22): 124-133.
Jiang Weitong, Hu Pengfei, Yin Rui, et al.Transient stability analysis and hybrid synchronization control strategy of converter based on virtual synchronous generator[J]. Automation of Electric Power Systems, 2021, 45(22): 124-133.
[10] 颜湘武, 张伟超, 崔森, 等. 基于虚拟同步机的电压源逆变器频率响应时域特性和自适应参数设计[J].电工技术学报, 2021, 36(增刊1): 241-254.
Yan Xiangwu, Zhang Weichao, Cui Sen, et al.Frequency response characteristics and parameter tuning of voltage-sourced converters under VSG control[J]. Transactions of China Electrotechnical Society, 2021, 36(S1): 241-254.
[11] 于彦雪, 关万琳, 陈晓光, 等. 基于序阻抗的虚拟同步机同步频率谐振现象[J]. 电工技术学报, 2022, 37(10): 2584-2595.
Yu Yanxue, Guan Wanlin, Chen Xiaoguang, et al.Synchronous frequency resonance in virtual syn- chronous generator based on sequence-impedance[J]. Transactions of China Electrotechnical Society, 2022, 37(10): 2584-2595.
[12] 余裕璞, 顾煜炯, 和学豪. 逆变器电压电流双闭环控制系统设计[J]. 电力科学与工程, 2019, 35(3): 1-7.
Yu Yupu, Gu Yujiong, He Xuehao.Design of voltage and current double closed-loop control system for inverter[J]. Electric Power Science and Engineering, 2019, 35(3): 1-7.
[13] 吴恒, 阮新波, 杨东升, 等. 虚拟同步发电机功率环的建模与参数设计[J]. 中国电机工程学报, 2015, 35(24): 6508-6518.
Wu Heng, Ruan Xinbo, Yang Dongsheng, et al.Modeling of the power loop and parameter design of virtual synchronous generators[J]. Proceedings of the CSEE, 2015, 35(24): 6508-6518.
[14] Chen Xinran, Ruan Xinbo, Yang Dongsheng, et al.Step-by-step controller design of voltage closed-loop control for virtual synchronous generator[C]//7th Annual IEEE Energy Conversion Congress and Exposition, Montreal, QC, Canada, 2015: 3760-3765.
[15] 姜静雅, 王玮, 吴学智, 等. 基于自适应无功功率补偿的虚拟同步机功率解耦策略[J]. 电工技术学报, 2020, 35(13): 2747-2756.
Jiang Jingya, Wang Wei, Wu Xuezhi, et al.Power decoupling strategy in virtual synchronous generator based on adaptive reactive power compensation[J]. Transactions of China Electrotechnical Society, 2020, 35(13): 2747-2756.
[16] 葛平娟, 肖凡, 涂春鸣, 等. 考虑故障限流的下垂控制型逆变器暂态控制策略[J]. 电工技术学报, 2022, 37(14): 3676-3687.
Ge Pingjuan, Xiao Fan, Tu Chunming, et al.Transient control strategy of droop-controlled inverter con- sidering fault current limitation[J]. Transactions of China Electrotechnical Society, 2022, 37(14): 3676-3687.
[17] IEEEStd 519-2014 IEEE recommended practice and requirements for harmonic control in electric power systems[S]. IEEE, 2014.
[18] Liu Baojin, Liu Zeng, Liu Jinjun, et al.An adaptive virtual impedance control scheme based on small-AC- signal injection for unbalanced and harmonic power sharing in islanded microgrids[J]. IEEE Transactions on Power Electronics, 2019, 34(12): 12333-12355.
[19] Wu Wenhua, Zhou Leming, Chen Yandong, et al.Sequence-impedance-based stability comparison between VSGs and traditional grid-connected inverters[J]. IEEE Transactions on Power Electronics, 2019, 34(1): 46-52.
[20] 耿乙文, 田芳芳, 孙帅, 等. 一种基于虚拟同步发电机的电流谐波抑制方法[J]. 电工技术学报, 2018, 33(5): 1040-1050.
Geng Yiwen, Tian Fangfang, Sun Shuai, et al.A method of current harmonics suppression based on VSG[J]. Transactions of China Electrotechnical Society, 2018, 33(5): 1040-1050.
[21] 徐健, 曹鑫, 郝振洋, 等. 基于电网谐波电压前馈的虚拟同步整流器电流谐波抑制方法[J]. 电工技术学报, 2022, 37(8): 2018-2029.
Xu Jian, Cao Xin, Hao Zhenyang, et al.A harmonic- current suppression method for virtual synchronous rectifier based on feedforward of grid harmonic voltage[J]. Transactions of China Electrotechnical Society, 2022, 37(8): 2018-2029.
[22] He Jinwei, Li Yunwei, Munir M S.A flexible harmonic control approach through voltage-controlled DG-grid interfacing converters[J]. IEEE Transactions on Industrial Electronics, 2012, 59(1): 444-455.
[23] 冯伟, 孙凯, 关雅娟, 等. 孤立微电网中基于输出电压复合控制的电压源型并网逆变器谐波电流抑制策略[J]. 电工技术学报, 2016, 31(7): 72-80.
Feng Wei, Sun Kai, Guan Yajuan, et al.A harmonic current suppression strategy for voltage source grid- connected inverters based on output voltage hybrid control in islanded microgrids[J]. Transactions of China Electrotechnical Society, 2016, 31(7): 72-80.
[24] Zhao Xin, Meng Lexuan, Xie Chuan, et al.A unified voltage harmonic control strategy for coordinated compensation with VCM and CCM converters[J]. IEEE Transactions on Power Electronics, 2018, 33(8): 7132-7147.
[25] 周杰, 刘傲洋, 罗皓文, 等. 虚拟同步机接入弱电网的电能质量新问题及谐波抑制方法[J]. 智慧电力, 2021, 49(2): 83-90.
Zhou Jie, Liu Aoyang, Luo Haowen, et al.Power quality issues and harmonic suppression method of virtual synchronous generator connected to weak grid[J]. Smart Power, 2021, 49(2): 83-90.
[26] Liu Baojin, Liu Jinjun, Liu Zeng.Improvement of grid current quality for droop-controlled grid- connected inverters under distorted grid conditions[C]//11th IEEE Energy Conversion Congress and Expo- sition, Baltimore, MD, USA, 2019: 2560-2565.
[27] Savaghebi M, Jalilian A, Vasquez J C, et al.Secondary control for voltage quality enhancement in microgrids[J]. IEEE Transactions on Smart Grid, 2012, 3(4): 1893-1902.
[28] He Jinwei, Li Yunwei.Analysis, design, and imple- mentation of virtual impedance for power electronics interfaced distributed generation[J]. IEEE Transa- ctions on Industry Applications, 2011, 47(6): 2525-2538.
[29] 阮新波, 王学华, 潘冬华. LCL型并网逆变器的控制技术[M]. 北京: 科学出版社, 2015.
[30] Sun Jian.Impedance-based stability criterion for grid- connected inverters[J]. IEEE Transactions on Power Electronics, 2011, 26(11): 3075-3078.