Stability Analysis and Controller Synthesis for Single-Loop Voltage-Controlled VSIs

This paper analyzes the stability of the digital single-loop voltage-controlled Voltage-Source Inverters (VSIs) using linear voltage regulators. It reveals that the phase lags caused by using the resonant controller and the time delay of digital control system can stabilize the voltage loop without damping of the LC-filter resonance. The stability region for the digital single-loop resonant voltage control is then identified considering the effects of the discretization methods applied to the resonant controller. An enhanced voltage control scheme with widened stability region is subsequently proposed, and a holistic design method of the controller is developed with the root contours in the discrete z-domain. Simulations and experimental tests for a 400-Hz VSI system validate the theoretical analysis and the performance of the proposed approach.