光伏电站多逆变器并网系统输出谐波研究

针对多台逆变器并联在同一公共连接点接入电网引起的谐波问题进行了研究。建立了多逆变器光伏并网系统的单台和多台逆变器小信号等效模型。推导出逆变器、PWM开关谐波源和电网的等效阻抗传递函数，通过Bode图分析逆变器、PWM开关谐波源的等效输出阻抗幅频特性和相频特性。应用Matlab/Simulink对35 kV光伏电站多逆变器并网系统在不同工况下进行谐波分析。仿真结果表明:并网逆变器台数越多，PCC处电流谐波畸变率越大，但主要为低次谐波，高次谐波含量较少，验证了建立的小信号模型的有效性。

Study on output harmonic of multi-inverter grid-connected in photovoltaic plant

The harmonic problem caused by the multi-inverters grid-connected to the power grid in point of common coupling is studied. Small-signal circuit model for single inverter and multi-inverters is established. The equivalent impedance of transfer function of the inverter, PWM switching harmonic source and power grid are derived. The equivalent output impedance of amplitude-frequency characteristic and phase frequency characteristics of the inverter and PWM switching harmonic source are analyzed by Bode diagram. The harmonic of 35 kV photovoltaic power station multi-inverters grid-connected system under the different conditions is analyzed in Matlab/Simulink. The simulation results show that if the grid-connected inverters are more, the current harmonic distortion rate of PCC will be greater. It mainly contains low-order harmonic but less high harmonic. The effectiveness of small-signal circuit model is verified.