Robust digital controller design for three-phase inverter using CRA method

This paper proposes a CRA based robust digital controller for three-phase PWM VSI inverter. To regulate the inverter output voltage with constant voltage and constant frequency, the usual inverter controller consists of double looped PI controllers. Those are an outer voltage controller and an inner current controller, then the order of system characteristic polynomial is high and so the gain tuning of the controllers is difficult. Considering the limited switching frequency of the devices and sampling frequency of the digital controller, the gain tuning is practically dependent on the engineering experiences with the try and error method. In this paper, the error-space approach is used to get the system model including the controller with low order, and the characteristic ratio assignment (CRA) method is proposed for the design of robust controller which has the advantage to design the optimal gain to meet the referenced response and overshoot within the limit range. The validity of the proposed controller is verified through the PSiM simulation and experimental results.