直流电压含二次纹波条件下并网逆变器输出谐波抑制

单相并网逆变器及电网电压不对称情况下的三相并网逆变器，直流母线电压均含有明显的二倍工频纹波分量。受该纹波分量影响，逆变器交流侧输出含有明显的三次谐波，影响逆变器输出电能质量。针对上述问题，利用双重傅里叶变换和开关函数法对并网逆变器的输出谐波特性进行了分析，在此基础上提出了抑制单相和三相逆变器输出三次谐波的改进脉宽调制方法。该方法根据直流母线电压修正调制波，无需提取直流母线电压纹波分量信息，算法复杂度低，易于实现。通过开关函数法详细证明了新型调制方法的可行性，给出了基于该调制方法的单相及三相光伏逆变器的控制策略。仿真验证了所提调制方法可显著降低直流母线电压含二次纹波条件下并网逆变器的输出三次谐波成分。

Output harmonic suppression of a grid-connected inverter with secondary ripple in DC voltage

In a single-phase grid-connected inverter and three-phase grid-connected inverter with asymmetric grid voltage, the bus voltage on the DC side contains an obvious double power frequency ripple component. Affected by this ripple component, the AC output side of grid-connected inverter contains an obvious third harmonic, which affects the output power quality of the inverter. To solve the above problems, the output harmonic characteristics of grid-connected inverters are analyzed using a dual Fourier transform and switching function method. An improved pulse width modulation method is proposed to suppress the third harmonic output of single-phase and three-phase inverters. This method corrects the modulation wave according to the DC bus voltage, and does not need to extract the ripple component information of the DC bus voltage. The algorithm is low in complexity and easy to implement. The feasibility of the new modulation method is proved by the switching function method. The control strategies of single-phase and three-phase photovoltaic inverters based on this modulation method are given. Simulation results show that the proposed modulation method can significantly reduce the output third harmonic components of grid-connected inverters with secondary ripple in the DC bus voltage. This work is supported by the Key Science and Technology Project of Henan Province (No. 182102210333).