考虑死区与延时影响的LCL型并网逆变器谐波特性分析

Harmonic Characteristics Analysis of LCL Grid-connected Inverter Considering the Influence of Dead Zone and Time Delay

针对大规模逆变器接入弱电网易引起宽频带振荡,影响自身及系统的稳定运行的问题,结合PWM控制的三相桥式逆变电路,研究了脉冲宽度调制技术及死区效应下的逆变器并网口输出电压的谐波特性,以及LCL滤波器的固有谐振点以及控制延时对谐波的影响。通过在仿真平台搭建模型,实现了逆变器谐波特性的复现。结果表明,PWM调制技术会产生载波频率及其整数倍附近的高次谐波;死区效应增加了逆变器输出波形的低次谐波,且随着死区时间的增加,5次和7次谐波含量增加;控制延时将造成滤波器谐振频率的偏移。

Large-scale inverters connected to a weak grid can easily cause wide-band oscillations,which affect the stable operation of themselves and the system,by analysing a three-phase bridge inverter controlled by PWM,this paper studies the harmonic characteristics of the grid-connected inverter output voltage under the PWM modulation and the dead zone effect,and the impact on harmonics with the consideration of LCL filter natural resonance point and the control delay.The harmonic characteristics of the inverter are reproduced by modeling in the simulation platform.The results show that the PWM modulation produces high-order harmonics near the carrier frequency and its integer multiples.The dead zone effect increases low-order harmonics from the inverter output.In addition,the content of 5 th and 7 th harmonics increases with the increase of the dead time and the control delay causes the shift of the resonance frequency of the filter.