Closed-loop input current control strategy based on waveform similarity index for the emerging matrix converters with harmonic injection technique

Abstract

Harmonic injection matrix converter (HIMC) achieves direct AC-AC power conversion with maximum voltage transfer and reduced transistor capacity. However, the existing open-loop current control method for HIMC may bring in low-order harmonics if the injected harmonic current deviates from its desired value. To address this issue, this paper proposes a closed-loop input current control strategy based on the waveform similarity index (WSI) for these emerging MC topologies. The WSIs are defined as the ratios of the corresponding input currents against the maximum and minimum input voltages. Multi resonant controllers are adopted to regulate the WSI difference so that its low-order harmonics are eliminated, which generate an additional signal to correct the injected harmonic current. By adopting the proposed current control strategy, the 5th and 7th harmonics are suppressed to lower than 1.0% under the sinusoidal input voltages and nominal load scenario. Even with inaccuracies in the reference harmonic current generation, the proposed strategy enables the input currents to approach sinusoidal waveforms with significantly reduced WSIs difference, thus enhancing the input power factor over the conventional open-loop method. Besides, the proposed method is effective under unbalanced and distorted conditions through the experimental verification.