A Control Strategy for Simultaneously Achieving SOC Balancing and Reducing Switching Loss in Hybrid Cascaded Energy Storage Converter

Cascaded H-bridge converter is favored in the high-voltage large-capacity electrochemical energy storage field for no need power frequency step-up transformer, lower costs and higher efficiency. However, the issue of high switching loss and the battery state of charge (SOC) balancing become increasingly prominent with the rising number of cascade units. To address these challenges, the hybrid cascade energy storage converter (HCESC) is developed, which is based on the cascaded H-bridge (CHB) architecture and incorporates a cascade-connected high-frequency two-level voltage source inverter (2L VSI). This configuration provides a viable solution for reducing the significant switching loss. A hybrid modulation scheme combining the nearest level modulation (NLM) and pulse width modulation (PWM) for the HCESC is proposed. Compared with the traditional phase shift pulse width modulation (PS-PWM), this scheme significantly reduces the switching loss. Additionally, a hierarchical control method is adopted to simultaneously implement active power control, reactive power compensation, and phase/inter-phase battery SOC balance. Finally, the simulation experiments results validate the efficacy of the proposed hybrid modulation scheme and control method.