LCL型逆变器并联系统母线电压质量改善方法  

Bus-voltage Quality Improvement Method for Parallel-connected LCL-type Inverters System in Islanded Micro-grid

作　　者：周乐明[1] 姜捷[1] 陈燕东[1] 伍文华[1] 周小平[1] 熊昊哲 刘思怡 ZHOU Leming;JIANG Jie;CHEN Yandong;WU Wenhua;ZHOU Xiaoping;XIONG Haozhe;LIU Siyi(National Electric Power Conversion and Control Engineering Technology Research Center(Hunan University),Changsha 410082,Hunan Province,China)

机构地区：[1]国家电能变换与控制工程技术研究中心(湖南大学)

出　　处：《中国电机工程学报》2019年第23期7000-7012,共13页Proceedings of the CSEE

基　　金：国家重点研发计划项目(2016YFE0123900);国家自然科学基金项目(51707061);湖南省自然科学基金项目(2018JJ3048)~~

摘　　要：非线性负荷接入微电网会造成其母线电压畸变严重,同时下垂控制所引起的基波频率偏移极有可能进一步恶化母线电压质量。为此,该文提出一种LCL型逆变器并联系统母线电压质量改善方法,主要包括小谐波阻抗重塑的输出电压直接控制、自适应快速鲁棒下垂控制和并联虚拟导纳控制。首先,输出电压直接控制采用比例–重复控制器,用以重塑逆变器的等效输出阻抗为小谐波阻抗。同时,采用自适应快速鲁棒下垂控制用以改善母线电压的动态响应速度。然而,研究发现当下垂频率偏移时,所提电压控制方法对母线电压畸变的抑制作用失效,其原因为受重复控制器带宽的制约,一旦下垂频率稍有偏移,逆变器的输出阻抗将大幅度增大,严重恶化母线电压质量。在此基础上,进一步提出并联虚拟导纳控制方法,使得逆变器的最大输出阻抗不超过所并联导纳的阻抗值,用以降低下垂频率偏移对逆变器输出阻抗的影响,保证频率偏移情况下的母线电压谐波抑制效果。其次,对所提并联虚拟导纳控制进行简化,使得其便于在控制器中实现。同时,搭建2台LCL型逆变器并联系统用以验证所提方法的有效性。High proportion of non-linear load in micro-grid will lead to severe distortion of the AC bus-voltage.Moreover,the droop-control will result in a shift in the fundamental frequency of output voltage,which probably further deteriorate the AC bus-voltage quality.To address this issue,a method was proposed for system of the paralleled LCL-type inverters to improve the AC bus-voltage quality.It mainly included the direct output-voltage control reshaping the small harmonic impedance,the adaptive fast robust droop control and parallel virtual admittance control method.Firstly,the output-voltage control can realize characteristic of small harmonic impedance for the inverter’s equivalent output impedance through proportion-repetitive controller.Meanwhile,the adaptive fast robust droop control was adopted to improve the dynamic response characteristic of the bus voltage.However,it was found that the proposed voltage control method would fail to suppress the AC bus-voltage distortion when the droop frequency slightly shifted.That was because the output impedance of the inverter would greatly increase with a slightly shifted droop frequency owing to the bandwidth limitation of the repetitive controller.Based on these,a parallel virtual admittance control method was further proposed to make the amplitude of inverter’s output-impedance less than the paralleled one,reducing the influence of droop-frequency deviation on the output-impedance and guaranteeing the efficiency of harmonic bus-voltage impression under frequency-offset conditions.Then the proposed parallel virtual-admittance control method was simplified,making it easy to implement in the controller.The effectiveness of the proposed method was verified by experiments on the parallel system consisting of two LCL-type inverters.

关 键 词：微电网 母线电压 重复控制 低畸变 小谐波阻抗 虚拟导纳 

分 类 号：TM464[电气工程—电器]