Unified Balancing Control Strategy for Cascaded PCSs Based on Third Harmonic Injection

To address the state-of-charge (SOC) imbalance and the limited convergence speed of conventional SOC balancing strategies in cascaded power conversion systems (PCSs) under practical grid-connected conditions, this paper investigates the control of cascaded H-bridge energy storage converters under multiple operating scenarios. The three-phase cascaded H-bridge topology is first reviewed, followed by the development of a hierarchical control framework for the cascaded PCSs. The corresponding overall control block diagram is then presented. Based on this, a unified power equalization control strategy based on the third harmonic injection is proposed, which ensures the effectiveness of power control, SOC equalization control, and fault-tolerant control by increasing the injection range, and it guarantees the normal operation of the cascaded PCSs. Considering the phase relationship of the PCS output voltage after the third harmonic injection, the maximum zero-sequence voltage injection range is found, and the constraints of zero-sequence voltage injection are derived. A MATLAB/Simulink simulation model and a real-time hardware-in-the-loop (HIL) platform based on the MT6016 are established to validate the effectiveness and practical feasibility of the proposed control strategy.