Flux-Balancing Scheme for PD-Modulated Parallel-Interleaved Inverters

A simple scheme to realize Phase-Disposition carrier Pulse Width Modulation (PD PWM) for parallel Two-Level Voltage Source Converters (2L-VSCs) is presented in this paper. The proposed implementation only uses a single carrier signal and can easily be implemented using a digital signal processor. The operation of the parallel VSCs with the Coupled Inductor (CI), under the PD PWM is briefly discussed and the associated dc flux injection problem is investigated. A CI saturation issue during the band transition under the PD PWM scheme is also explored and the strategy to avoid this problem is presented. In addition, the proposed strategy also maintains a volt-sec balance to synthesize desired reference space voltage vector during the band transition. As a result, a smooth transition from one modulation band to the other is ensured without causing disturbances in the line-to-line voltage. The switching losses and the harmonic performance of the proposed implementation are also compared with the commonly used Phase-Shifted carrier Pulse Width Modulation (PS PWM). The implementation issues are discussed and the experimental results are also presented.