Parallel operation of solid state transformer

This paper introduces a high performance controller for voltage source converter (VSC) used as front-end interface of solid state transformer (SST). The closed-loop controlled VSC is the core entity that enables the SST to work as both inverter and rectifier. Different from other converters that interface renewable energy source to microgrids, the SST can connect both dc load and energy sources. Based on the dc power balance, some SSTs out of a parallel array of SSTs can operate as inverters while others as rectifiers, which can be easily implemented if taut regulation of the VSCs is achieved using an outer control loop. A proportional+resonant (PR) controller with active damping is adopted to achieve the sought dynamic response and system stability. The effectiveness of the VSC controller and parallel scheme is verified both by experiments and simulations.