虚拟同步机场景下OUF与OUV检测盲区分析
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摘要
目前,分析被动式孤岛检测方法性能时所考虑的分布式电源(distributedgenerator,DG)接口主要是基于PQ控制的逆变器。而随着虚拟同步机(virtual synchronous generator,VSG)的广泛应用,现有孤岛检测方法能否适应于VSG场景下的孤岛效应值得深入研究。基于PQ控制的逆变器具有电流源特性,且没有机械惯性;而VSG对外体现为电压源特性,并模拟惯性,导致两种DG孤岛后的系统特性差异显著。该文建立VSG孤岛后系统频率及公共连接点(pointof common coupling,PCC)电压的数学模型,并得到过/欠频检测盲区(non-detection zone,NDZ)关于VSG惯量、阻尼、调速器参数以及电磁功率变化的解析解;研究空载电动势、同步电抗、无功功率调节器与本地负载参数对过/欠压(over/under voltage,OUV)的NDZ的影响;同时,针对孤岛后VSG可能因电流饱和运行在电流源特性的情况,分析电流饱和情况下的OUV的检测盲区。利用仿真和实验验证分析结果的正确性。
The interface of distributed generator(DG) is mostly PQ controlled inverter, which the performances analysis of passive islanding detection methods are implemented based on. With the wide application of virtual synchronous generator(VSG), the reliability of the existing island detection methods applied to VSG is worth studying. The PQ controlled inverter has external characteristics of current source and has no mechanical inertia. However, the VSG based inverter behaves as a voltage source and emulates the mechanical inertia of the real synchronous generator, which leads to significant difference in system characteristics after islanding. This paper constructed mathematic models of system frequency and voltage at point of common coupling(PCC) in the islanding condition for VSG. Derived from the models, an explicit closed-form expression for non-detection zones(NDZ) of over/under frequency(OUF) detection method was developed with respect to VSG inertia, damping, governor parameters and variation of electromagnetic power. As to the over/under voltage(OUV) detection method, effects on the detection performances brought by the no-load electromotive force, synchronous reactance, the local load and the parameter of reactive power regulator were also analyzed. Taking into account that the VSG based inverter will turn into current source since its current saturates, the NDZ of OUV on the condition of current saturation was also analyzed. The analysis results were verified by simulation and experiments.
The interface of distributed generator(DG) is mostly PQ controlled inverter, which the performances analysis of passive islanding detection methods are implemented based on. With the wide application of virtual synchronous generator(VSG), the reliability of the existing island detection methods applied to VSG is worth studying. The PQ controlled inverter has external characteristics of current source and has no mechanical inertia. However, the VSG based inverter behaves as a voltage source and emulates the mechanical inertia of the real synchronous generator, which leads to significant difference in system characteristics after islanding. This paper constructed mathematic models of system frequency and voltage at point of common coupling(PCC) in the islanding condition for VSG. Derived from the models, an explicit closed-form expression for non-detection zones(NDZ) of over/under frequency(OUF) detection method was developed with respect to VSG inertia, damping, governor parameters and variation of electromagnetic power. As to the over/under voltage(OUV) detection method, effects on the detection performances brought by the no-load electromotive force, synchronous reactance, the local load and the parameter of reactive power regulator were also analyzed. Taking into account that the VSG based inverter will turn into current source since its current saturates, the NDZ of OUV on the condition of current saturation was also analyzed. The analysis results were verified by simulation and experiments.
引文
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[2]曾正,邵伟华,冉立,等.虚拟同步发电机的模型及储能单元优化配置[J].电力系统自动化,2015,39(13):22-31.Zeng Zheng,Shao Weihua,Ran Li,et al.Mathematical model and strategic energy storage selection of virtual sychronous generators[J].Automation of Electric Power System,2015,39(13):22-31(in Chinese).
[3]郑天文,陈来军,陈天一,等.虚拟同步发电机技术展望[J].电力系统自动化,2015,39(21):165-175.Zheng Tianwen,Chen laijun,Chen Tianyi,et al.Review and prospect of virtual synchronous generator technologies[J].Automation of Electric Power System,2015,39(21):165-175(in Chinese).
[4]Alipoor J,Miura Y,Ise T.Power system stabilization using virtual synchronous generator with alternating moment of inertia[J].IEEE Journal of Emerging and Selected Topics in Power Electronics,2015,3(2):451-8.
[5]European FP6 project workshop,VSYNC project workshop[EB/OL].Netherland:VSYNC Commission,2011[2013-3-15].http://www.vsync.eu/.
[6]Zhong Q C,Weiss G.Synchronverters:inverters that mimic synchronous generators[J].IEEE Transaction on Industrial Electronics,2011,58(4):1259-1267.
[7]Yong C,Hesse R,Turschner D,et al.Comparison of methods for implementing virtual synchronous machine on inverters[C]//International Conference on Renewable Energies and Power Quality.Santiago de Compostela,Spain.2012:1-6.
[8]D’Arco S,Suul J A,Fosso O B.A virtual synchronous machine implementation for distributed control of power converters in SmartGrids[J].Electric Power Systems Research,2015,122(6):180-197.
[9]杨向真,苏建徽,丁明,等.面向多逆变器的微电网电压控制策略[J].中国电机工程学报,2013,32(7):7-14.Yang Xiangzhen,Su Jianhui,DING Ming,et al.Voltage control strategies for microgrid with multiple inverters[J].Proceedings of the CSEE,2013,32(7):7-14(in Chinese).
[10]杜燕,苏建徽,张榴晨,等.一种模式自适应的微网调频控制方法[J].中国电机工程学报,2013,33(19):67-76.Du Yan,Su Jianhui,Zhang Liuchen,et al.A mode adaptive frequency controller for microgrid[J].Proceedings of the CSEE,2013,33(19):67-76(in Chinese).
[11]俞侃,雍静,梁仕斌,等.电力线信号技术的改进分布式发电系统孤岛检测方法[J].中国电机工程学报,2015,35(13):3283-3291.Yu Kan,Yong Jing,Liang Shibin,et al.An improved power line signaling technique based anti-islanding protection approach for distributed generation system[J].Proceedings of the CSEE,2015,35(13):3283-3251(in Chinese).
[12]刘思佳,庄圣贤,谢茂军.基于调制比定向偏移控制的孤岛检测方法[J].电力系统自动化,2015,39(3):132-139.Liu Sijia,Zhuang Shengxian,Xie Maojun.Islanding detection method based on modulation index directional shift control[J].Automation of Electric Power System,2015,39(3):132-139(in Chinese).
[13]Velasco D,Trujillo C L,Garcera G,et al.Review of anti-islanding techniques in distributed generators[J].Renewable And Sustainable Energy Reviews,2010,14(6):1608-1614.
[14]程启明,王映斐,程尹曼,等.分布式发电并网系统中孤岛检测方法的综述研究[J].电力系统保护与控制,2011,39(6):147-154.Cheng Qiming,Wang Yingfei,Cheng Yinman,et al.Overview study on islanding detecting methods for distributed generation grid-connected system[J].Power System Protection and Control,2011,39(6):147-154(in Chinese).
[15]徐华电,苏建徽,张军军,等.基于谐波特征与核Fisher判别分析的孤岛检测方法研究[J].电工技术学报,2016,31(03):25-30.Xu Huadian,Su Jianhui,Zhang Junjun,et al.Research of islanding detection based on harmonic characteristic and kernel fisher discriminant analysis[J].Transactions of China Electrotechnical Society,2016,31(3):25-30(in Chinese).
[16]Liu N,Aljankawey A,Diduch C,et al.Passive islanding detection approach based on tracking the frequencydependent impedance change[J].IEEE Transactions on Power Delivery,2015,30(6):2570-2580.
[17]Ye Z,Kolwalkar A,Zhang Y,et al.Evaluation of anti-islanding schemes based on nondetection zone concept[J].IEEE Transactions on power electronics,2004,19(5):1171-1176.
[18]张兴,曹仁贤.太阳能光伏并网发电及其逆变控制[M].北京:机械工业出版社,2011.Zhang Xing,Cao Renxian.Solar photovoltaic gridconnected power generation and its inverter control[M].Beijing:China Machine Press,2011(in Chinese).
[19]Kim B H,Sul S K.Comparison of non-detection zone of frequency drift anti-islanding with closed-loop power controlled distributed generators[C]//2015 IEEE 2nd International Future Energy Electronics Conference(IFEEC).IEEE,2015:1-5.
[20]Sun Q,Guerrero J M,Jing T,et al.An islanding detection method by using frequency positive feedback based on FLL for single-phase microgrid[J].IEEE Transactions on Smart Grid,2017,8(4):1821-1830.
[21]Zeineldin H H,Kirtley Jr J L.Performance of the OVP/UVP and OFP/UFP method with voltage and frequency dependent loads[J].IEEE Transactions on Power Delivery,2009,24(2):772-778.
[22]GB/T 19939-2005光伏系统并网技术要求[S].2005.GB/T 19939-2005 Technical requirements for photovoltaic systems to being connected into the grid[S].2005(in Chinese).
[23]石荣亮,张兴,徐海珍,等.基于虚拟同步发电机的多能互补孤立型微网运行控制策略[J].电力系统自动化,2016,40(18):32-40.Shi Rongliang,Zhang Xing,Xu Haizhen,et al.Operation control strategy for multi-energy complementary isolated microgrid based on virtual synchronous generator[J].Automation of Electric Power Systems,2016,40(18):32-40(in Chinese).
[24]徐海珍,张兴,刘芳,等.基于超前滞后环节虚拟惯性的VSG控制策略[J].中国电机工程学报,2017,37(7):1918-1926.Xu Haizhen,Zhang Xing,Liu Fang,et al.Virtual synchronous generator control strategy based on lead-lag link virtual inertia[J].Proceedings of CSEE,2017,37(7):1918-1926(in Chinese).
[25]Kundur P,Balu N J,Lauby M G.Power system stability and control[M].New York:McGraw-hill,1994.