A transformer-less static synchronous compensator employing a multi-level inverter

Abstract

This paper examines the application of a high voltage multi-level invertor in a 13.8 kV distribution system static synchronous compensator (SSC). Equations are developed for the component MVA of the multi-level inverter. Trends in component MVA as a function of the number of inverter voltage levels and the modulation strategy are identified. Control of the DC bus capacitor voltages during phase voltage imbalance is identified as a problem. A method is described whereby the multi-level inverter's DC bus capacitor voltages are actively controlled without using additional power components. The operation of the capacitor voltage control loop is demonstrated through EMTP simulations of an SSC responding to single phase and three phase load variations in a model distribution system.