Unified Switching Frequency Minimized Harmonic Mitigation Technique for Asymmetric Cascaded H-Bridge Converters

To obtain the optimal switching pattern with low-order harmonic mitigation capability and the optimal switching angle distribution in asymmetric cascaded H-bridge (ACHB) converters with the lowest switching frequency, a unified switching frequency minimized harmonic mitigation (SFMHM) model for ACHB converters is proposed in this article. Based on PWM waveform discretization, the switching frequency of each H-bridge cell can be mathematically modeled as the state change of output levels. Then, the overall switching frequency of all cells is used as the objective function to be minimized in the proposed model, while the amplitude of fundamental and low-order harmonic components to be regulated are used as constraints. To achieve an optimal switching angle distribution with fewer switching losses, the well-designed weighting factors are assigned to the switching frequency functions of different cells in the proposed formulation. The model-solving algorithm based on mixed integer programming is introduced, and various numerical results are presented and compared with the conventional selective harmonic elimination PWM (SHE-PWM) and selective harmonic mitigation PWM (SHM-PWM) for ACHB converters. Simulation and experimental results verify the effectiveness of the proposed model.