Performance evaluation of three-phase, neutral-point clamped bi-directional rectifier for supply and load perturbations

In this study, an improved performance three-phase neutral-point clamped bidirectional rectifier with modified control scheme is proposed. The proposed control strategy takes into consideration the amount/degree of deviation of source voltage from desired rated value during supply perturbation and accordingly modifies the reference current template for each phase individually which is termed as compensated reference current. In other words, magnitude, shape and phase of compensated reference current waveform for each phase are different depending on amount of deviation of that phase. A complete mathematical model of rectifier using pulse width modulation technique is developed. The performance of the converter is evaluated in terms of near unity input power factor, low input current total harmonic distortion, reduced ripple factor of the regulated DC output voltage and particularly the neutral-point voltage balance under different load conditions both for rectification and inversion modes of operation. It is shown that the three-level AC to DC converter with the proposed control scheme displays better performance under source voltage perturbations such as voltage sag, swell, unbalance, harmonics, frequency variations as well as phase angle deviations which are regularly encountered in practical environment.