非线性负载下逆变器并联系统控制策略研究

Research on Control Strategy of Inverter Parallel System under Nonlinear Load

微电网并联逆变器接入非线性负载时出现的谐波电流,会引起逆变器输出电压畸变严重。以两逆变器并联运行模型为研究对象,提出一种综合控制策略。首先,在电压外环采用比例积分控制和重复控制串联控制方法的同时,考虑下垂控制所引起的基波频率偏移会进一步恶化输出电压质量,改进重复控制方法,实现在频率变化时对电压谐波的有效抑制。其次,由于SOGI可以抑制输入信号的谐波,将基于SOGI的虚拟复阻抗引入到电流反馈环,抑制谐波电流对虚拟复阻抗影响,有效改善功率均分效果和抑制逆变器间环流。最后,对所提出的综合控制策略进行仿真研究,验证所提控制策略的正确性和可行性。

Harmonic current of parallel inverters in micro-grid will cause serious distortion of output voltage when they are connected to non-linear loads.In this paper,a comprehensive control strategy is proposed based on the parallel operation model of two inverters.Firstly,while adopting the proportional-integral control and repetitive control series control method in the outer voltage loop,considering the fundamental frequency offset caused by sag control will further deteriorate the output voltage quality,we improved the repetitive control method and achieved effective suppression of voltage harmonics when the frequency changed.Secondly,because SOGI can suppress the harmonics of the input signal,the virtual complex impedance based on SOGI was introduced into the current feedback loop to suppress the influence of harmonic current on the virtual complex impedance,which effectively improved the effect of power-sharing and restrained the circulation between inverters.Finally,the proposed integrated control strategy was simulated to verify the correctness and feasibility of the proposed control strategy.