Performance improvement of Predictive Direct Power Control of a PWM rectifier based on virtual flux under unbalanced grid voltage

摘要

Virtual Flux-based Predictive Direct Power Control (VF-PDPC) of three-phase PWM rectifiers using dead-beat control has several advantages like a constant switching frequency, near-sinusoidal input current waveform, and no need to PI-based active and reactive power control loops. However, under unbalanced grid voltage condition, the input currents become highly distorted and ripple in active and reactive powers increase significantly. This paper presents a simple method for improving Virtual Flux-based PDPC performance under unbalanced grid voltage by employing a new instantaneous active and reactive powers estimation technique using extension of the original instantaneous power theory. This method does not need the calculation of positiveegative sequence from the grid voltage/current. Compared to the existing VF-PDPC, using conventional instantaneous power estimation, the proposed method has better characteristics, such as smaller ripple in active and reactive powers and lower THD in grid current. The proposed method is simulated using MATLAB/SIMULINK on two-level three-phase PWM rectifier under balanced and unbalanced grid voltages. Results verification demonstrate effectiveness of the proposed method under both conditions.