阻性逆变器并联环流分析及鲁棒下垂多环控制

Circulating Current Analysis and Robust Droop Multiple Loop Control Method for Parallel Inverters Using Resistive Output Impedance

对于独立微电网中的并联逆变器,其等效输出阻抗和线路阻抗差异对功率分配和环流抑制存在较大影响。从逆变器并联的功率传输特性出发,分析现有下垂控制对阻性逆变器并联功率分配的影响,并在分析阻性逆变器环流特性的基础上,提出一种鲁棒下垂多环控制方法,其由功率外环和电压电流内环构成。功率外环采用鲁棒下垂控制器,减小阻抗差异对功率精确分配的影响;通过引入含阻性分量和感性分量的虚拟复阻抗,将逆变器的等效输出阻抗设计呈阻性;采用准谐振PR控制实现在较宽频带内逆变器输出电压的零稳态误差控制,进而减少逆变器间输出电压偏差并抑制环流。采用输出电压前馈和电容电流比例控制提高系统暂态响应和电流抗扰动能力。深入对比分析控制方式和控制参数对等效输出阻抗的影响,并择优选取控制参数。仿真和实验结果验证了所提提方法的正确性和有效性。

For parallel multi-inverters in island microgrid,the difference of equivalent output impedance and line impedance affects greatly on power sharing and circulating current restraining.From power transmission characteristics of parallel inverters,the influence of power sharing among resistive inverters was analyzed in this paper,where the conventional droop control was applied.Based on the analysis of circulating current characteristics of resistive inverters,a robust droop multiple loop control method was proposed,which included the outer power loop and the inner voltage and current loop.In the outer power loop,a robust droop controller is adopted to reduce the effects on accurate power sharing due to the impedance difference.Introducing virtual complex impedance including resistive component and inductive component,the equivalent output impedance of inverters is redesigned as pure resistance.Quasi proportional-resonant（QPR） control is applied to realize zero steady-state errors control of the output voltage with wide bandwidth for parallel inverters,which will reduce further the deviation of output voltage and restrain circulating current.The output voltage feedforward control and the proportional control of the capacitor current are adopted to improve the transient response and current disturbance.The effects on the equivalent output impedance in the different control mode and parameters were analyzed comparatively, and the proper parameters were selected. Simulation and experimental results show the correctness and validity of the proposed control method.