采用共交直流母线并联的三相两电平光伏并网逆变器并采用相应的控制策略可以提高系统的效率,但是会带来模块间的环流问题.为了解决环流所引起的系统稳定性问题,针对两电平逆变器并联高频环流,首先提出一种基于共LCL滤波电容中点的滤波器方案,提高了零序环流传递函数的阶数,从而能够较好地抑制高频环流;其次对低频零序环流的主要谐波进行分析,设计合适的零序环流补偿器来抑制低频零序环流,与高频抑制方案组成环流复合抑制策略.最后基于该策略搭建Matlab/Simulink仿真平台,结果验证了环流理论分析的正确性和所提环流复合抑制策略的有效性.
The efficiency of the system can be improved though the three-phase two-level parallel photovoltaic grid-connected system,and the inter-module circulating current is caused by sharing positive,negative and AC buses.To solve the problem of the reduction of stabilization caused by the circulating current,firstly,a new scheme of LCL filter based on sharing neutral point of capacitances is proposed to suppress high frequency common-mode circulating current,because it improves the order of the zero-sequence circulating current transfer function.Secondly,the low frequency components of the zero-sequence circulating current are analyzed,and an appropriate harmonic compensator is designed to reduce them.A composite strategy of suppressing circulating current is proposed working with the new scheme of LCL and the harmonic compensator.Finally,a Matlab/Simulink based platform for simulation is constructed.The simulation results show that the theoretical analysis on the circulating current and the proposed control strategy are correct.