弱电网下并网逆变器多机并联系统稳定性研究

基于光伏和风电等可再生能源的分布式发电系统，是缓解能源危机和环境污染的有效途径。随着可再生能源在电网中渗透率的提高，电网越来越呈现弱电网的特点，基于可再生能源分布式发电系统接入电网后，存在并网逆变器和电网之间谐振、多台并联并网逆变器之间的谐波环流等稳定性问题。本项目针对基于可再生能源分布式发电系统，以提高弱电网下并网逆变器多机并联系统稳定性为目标，将提出适用于并网逆变器系统的稳定性判据，建立考虑锁相环和脉宽调制(PWM)边带效应影响的并网逆变器模型，在此基础上提出改善系统稳定性的方法和减小多台并网逆变器之间谐波环流的控制策略，最终将搭建由多台并网逆变器原理样机组成的三相并网系统，以验证理论分析的正确性和所提方法的有效性。本项目将为弱电网下并网逆变器系统稳定性分析提供理论基础，研究成果可以应用于基于新能源的分布式发电站和小型发电单元。

Distributed power generation system based on renewable energy such as wind and solar energy is an effective way to alleviate the problems of energy shortage and environmental pollution. With the continuously increasing penetration of renewable energy, the power grid exhibits more like a weak grid, which leads to stability problems such as resonance between the grid and the grid-connected inverters, harmonic circulating current among the paralleled grid-connected inverters. This project focuses on the renewable energy based distributed power generation system, and aims at improving the stability of the multi-paralleled grid-connected inverters system under weak grid. A stability criterion applicable to grid-connected inverter system will be proposed, and the phase-locked loop and the pulse-width modulation (PWM) sideband effect will be taken into consideration to establish the mathematical models of the grid-connected inverters. Then, the control strategies will be proposed to improve the system stability and suppress the harmonic circulating current among the paralleled grid-connected inverters. Finally, a three-phase grid-connected system consisting of multiple grid-connected inverters will be built to verify the correctness of the theoretical analysis and the effectiveness of the proposed methods. The outcomes of this project will provide a theoretical basis for the stability analysis of gird-connected inverter system under weak grid and can be widely used in distributed power generation stations and small power generation units based on renewable energy.