不平衡电压下VSG无锁相环并网及运行控制策略

Control strategies of grid-connection and operation based on virtual synchronous generator without phase-lock loop under unbalanced grids

针对并网逆变器在不平衡电压下电流畸变严重和锁相环节复杂等问题,文中设计了一种基于改进虚拟同步机(VSG)的逆变器无锁相环控制策略。重点研究了VSG在不平衡电网电压下的运行控制方法,设计了一种基于比例积分谐振(PIR)控制器的改进VSG控制策略,在不改变VSG外特性的基础上有效抑制了逆变器输出电流的不平衡分量。同时,提出一种基于虚拟功率的VSG预同步控制策略,保证VSG孤岛转并网模式的无缝切换。整个控制过程不依赖锁相环,避免了锁相环对系统控制精度以及响应速度的影响,降低了控制系统的复杂度。最后,基于RT-LAB的实时仿真平台对所提控制策略进行了验证。

In order to solve the problem of the current distortion under unbalanced voltage and the complexity of the phase-locked loop(PLL)of the grid-connected inverter,a strategy based on virtual synchronous generator(VSG)under unbalanced grid voltage without PLL is proposed.The control method of VSG under unbalanced grid voltage is detailed studied.An improved VSG control strategy based on PIR current control loop is designed to restrain current distortion effectively without changing output characteristics.Meanwhile,a VSG resynchronization control strategy based on virtual power is proposed to guarantee seamless switches between grid-connection mode and off-grid mode.The PLL is not used throughout the proposed strategy,which avoids the bad effect of PLL on control precision and response speed and makes the control system simplified in addition.Finally,a real-time simulation platform based on RT-LAB is built to verify the proposed control strategy.