Mu synthesized robust controller for multi-SST islanded smart grid

Abstract

This paper introduces a robust controller design method for maintaining microgrid operation under grid islanded mode by solid state transformers (SST) using master-slave control strategy. In the grid islanded mode, the grid voltage controller of the master SST, designed using μ synthesis, ensures stable control of the microgrid voltage. This paper extends the uncertainty modeling to general grid impedance uncertainties, slave SST current command uncertainties and master SST DC link voltage uncertainties. Also, the proposed design method is general and flexible enough to be readily scaled for applications in larger power systems. A three-SST system is used to demonstrate the design method with twelve uncertainties modeled. The designed system stability and performance robustness are validated in μ analysis, PLECS simulation, and a controller-hardware-in-the-loop (CHIL) test bed with a Real-Time Digital Simulator (RTDS).