A Reduced Switch Hybrid Multilevel Converter With Coordinated Control Method for Current Distortion Mitigation and Capacitor Voltages Balancing

This article presents a reduced switch hybrid multilevel converter (RSHMC). The proposed RSHMC is attractive for medium voltage industrial applications as it can work in a wide range of voltages, and lower switch count compared with other multilevel topologies. Nevertheless, the RSHMC faces challenges of neutral-point (NP) voltage, flying capacitor (FC) voltage balancing, and input current distortion mitigation. Therefore, a four-layer coordinated control (FLCC) method is presented for the RSHMC in this article. First, the relationship between the voltage vector and the current polarity of the RSHMC is analyzed in detail, and the improper vectors are removed. Second, calculate the reference voltage in the
$\alpha \beta $
orthogonal coordinates frame. The voltage vectors are rotated to the first sector to reduce the computational burden, and the optimal voltage vector is selected by cost function considering the current tracking. Third, the redundant switching states of the optimal voltage vector are restored to the original sector of the reference voltage. Fourth, the optimized switching state is selected for NP voltage and FC voltage balancing by the cost function considering voltage control. Through the aforementioned FLCC method, fast current tracking, input current distortion mitigation, NP voltage, and FC voltage balancing can be realized simultaneously for the RSHMC. Finally, experiments and simulations verify that the proposed FLCC can effectively balance capacitor voltages and mitigate current distortions. Compared to the conventional MPC method, the current THD value and the computational time are reduced by 45% and 83%, respectively.