Design and Development of a High-Frequency Multiport Solid-State Transformer With Decoupled Control Scheme

In this article, a four-port solid-state transformer and a control scheme to control the power flow and output voltage are studied, developed, and tested. The converter consists of three ports with H-bridge converters and one port with a diode bridge rectifier. The ports with H-bridge converters are capable of bidirectional power routing as well as reactive power contribution in a volt/Var control scenario. The diode bridge rectifier provides a dc voltage for load connection. Different arrangements for the four transformer windings are analyzed, simulated, and compared to achieve an optimal design. A new control strategy, which uses a combination of phase-shift and duty cycle control, is employed to control the flow of power between the converter branches and to regulate the output voltage. While phase-shift control ensures the balance of power on each port based on a reference value, the duty cycle control keeps the load voltage at a desired voltage level. A high-level control scheme is employed to determine the power references for all ports according to the load demand, generation capacity of the distributed generation system, and state of charge of the energy storage. The performance of the proposed system is validated with simulation and experimental analysis. A prototype is designed and built with 10-kW power rating at each port. The operating frequency of the system is designed at 100 kHz to obtain a very compact size for the whole converter.