Three-phase Grid Inverter for Combined Electric Power System with a Photovoltaic Solar Battery

Abstract

The purpose of the paper is providing with the compliance of the IEC standards for the harmonics composition of the grid current at the point of common coupling to grid the inverter and load in the maximum range of current values. Dependences for the amplitude of the pulsations of the inverter current and the error on the fundamental harmonic, when using PWM, according to the voltage at the input of the inverter, the modulation frequency and inductance of the output reactor are obtained. Based on this, the parameters of the inverter current control loop are determined. It has been established that with constant parameters of the current control loop and the use of a nonlinear reactor, the inductance of which depends on the amplitude of the inverter current, the energy losses in the inverter switches increase several times or the harmonics composition of the grid current deteriorates significantly. In accordance with this, it is proposed to change the coefficient of proportional link of the current control loop according to the amplitude of the inverter current reference. At low values of the grid current, the modulation frequency increasing is desirable. The structure of the control system with a corresponding change in the parameters of the current control loop in the case of using a non-linear reactor is proposed. The simulation of the “grid - inverter - load” system was performed with a linear and non-linear reactor with an estimate of the power losses in the inverter switches.