Soft Switching Modulation Strategy for Modular Multilevel Solid-State Transformer with Integrated Switching Pairs

This paper proposes a soft switching modulation strategy for a modular multilevel solid-state transformer with integrated switching pairs (ISP-MMCSST). In contrast to the current hybrid modulation strategy that adds a high-frequency sinusoidal signal to the fundamental-frequency modulation signal, this approach superimposes a high-frequency square wave modulation signal with the same frequency and phase as that of the carrier. The proposed hybrid modulation strategy enables soft switching for all switching devices on the secondary side of the high-frequency transformer and for half of the switching devices on the primary side. Furthermore, the power transmitted to the secondary side can be effectively decoupled within a limit phase shift angle. Simulation results in MATLAB/Simulink validate the effectiveness of the proposed soft switching modulation strategy.