Dynamic performance improvement of three-phase voltage source inverter using capacitor charge balance control method

Conventional linear controllers (such as the voltage-mode and current-mode schemes) in dq rotating frame have been widely utilized to control three-phase VSI in uninterrupted power supply system (UPS). However, during the step change of load current due to switching ON/OFF of different utility equipments, a large amount of charge is removed from or absorbed by output filter capacitor so as to meet the output current requirement. It causes large voltage drop or overshoot on the filter capacitor and always requires a long settling time. This paper presents a new control structure with the combination of linear controller and non-linear controller to fully exploit their respective advantages. The concept of capacitor charge balance control method is introduced to improve dynamic response with reduced settling time and overshoot/undershoot for three-phase voltage source inverter (VSI) under rapid load change. The conventional linear controller is used to guarantee the steady-state performance such as error elimination. Simulation results verify that three-phase VSI with new control structure demonstrates the smallest possible voltage deviation and the shortest settling time under an arbitrary load transient.