Harmonic Suppression Scheme of L-type New Energy Grid-connected Inverter Based on Harmonic Injection Method

As a new energy generation technology, photovoltaic power generation has been widely used. However, in the process of grid-connected photovoltaic power generation, due to the switching characteristics of the inverters, the output current usually contains low-order harmonics, of which the 5-order and 7-order low-order harmonics are the most serious. In order to restrain low-order harmonics in grid-connected current and reduce power loss in lines and loads, this paper proposes a modulation scheme based on SPWM harmonic injection, that is, to inject 5-order and 7-order harmonic compensation voltage into SPWM sinusoidal signal, so as to reduce the specific sub-harmonic content of output current and improve grid-connected power quality. The simulation and experiment of matlab/Simulink show that the scheme can effectively reduce the specific sub-harmonic content in grid-connected current, reduce the harmonic distortion rate and improve the power quality of grid-connected current of photovoltaic power generation.

I. Introduction

In the process of grid-connected photovoltaic power generation, the output current will be distorted due to the switching characteristics of the inverters, resulting in harmonics. The frequency of the harmonic current component is related to the number of pulses in the inverter. The higher the number of pulses in the inverter, the higher the lowest frequency of the harmonic component ^[1]–[2]. The emergence of harmonics, the use of electrical equipment in a non-ideal working environment, power system is a kind of interference and pollution^[3]–[4]. At present, the main measures for harmonic suppression of grid-connected photovoltaic inverters are active harmonic suppression and passive harmonic suppression^[5]–[6]. Active suppression starts from the electrical equipment itself, and reduces the harmonic generation of the electrical equipment by improving the PWM control technology^[7]–[8]; passive suppression compensates the harmonic of the electrical equipment by adding passive filter and active filter device to avoid the harmonic component entering the network^[8]–[9].