Research on the Soft-Switching Characteristics of Modular DC Solid State Transformer for DC Power Distribution Applications

Modular dc solid state transformer (MDCT), which plays an important role in the dc distribution system, can achieve electrical isolation, voltage conversion and power transmission between different dc voltage levels. The MDCT uses the high frequency transformer to transfer energy, which can reduce the size of the system, but this will generate more switching loss. The basic operation principle of the MDCT under quasi square wave modulation strategy was analyzed firstly. On this basis, this paper proposes a soft-switching operation scheme which can effectively reduce the switching loss for the system. The soft-switching condition and range of MDCT were analyzed and derived. Furthermore, a capacitor voltage-balancing strategy was presented in the MDCT, which can reduce the number of sensors and the cost of the system. Finally, the effectiveness of the theoretical analysis and the overall control strategy have been validated by the simulation results in MATLAB.