Power calculation algorithm for single-phase droop-operated inverters considering nonlinear loads

Abstract

The average active and reactive powers, Pav and Qav, are crucial parameters that have to be calculated when sharing common loads between parallelized droop-operated single-phase inverters. However, low-pass filters (LPF) with very low cut-off frequency should be used to minimize the distortion impact in the amplitude and frequency references provided by the droop equations. This forces the control to operate at a very low dynamic velocity, degrading the stability of the parallelized system. For this reason, different solutions had been proposed to increase the droop operation velocity in literature, but with the consideration of only sharing linear loads. The issues derived from the sharing of nonlinear loads had not been properly considered. This paper proposes a method to calculate Pav and Qav using second order generalized integrators (SOGI) that increase the velocity of the droop control algorithm considering nonlinear loads as the design worst case scenario. Then it is employed a double SOGI (DSOGI) approach to filter the current non-sinusoidal waveform and provide the fundamental component, which results in a faster transient response and improves the system's stability. The proposed calculation method shows to be faster than other approaches when considering nonlinear loads. Simulations are provided to validate the proposal.