Comparison of oversampled current controllers for microgrid utility interface converters

This paper presents the comparison of three different fully digital, oversampled, large bandwidth inverter current controllers: a proportional integral controller, a predictive controller, and a non-linear hysteresis controller. The purpose is to determine which one allows to achieve the highest final performance when adopted as the inner current control loop in a microgrid utility interface converter. The utility interface operation in the microgrid, as either a voltage supporting or a voltage forming converter, needs a fast output voltage control loop. In order to achieve a large bandwidth voltage regulation, with effective load disturbance rejection, the inner current loop small-signal bandwidth needs to be maximized. To prevent saturation of the voltage loop, a fast large-signal response of the current controller is also beneficial. The paper analyzes the above current controllers and compares their small-signal bandwidths and large-signal reference tracking performance. The better performing controller is then used in a multi-loop voltage control for the utility interface converter. Experimental results are presented that allow to validate the analytical results and to illustrate the achievable performance of the utility interface voltage regulation loop in steady state and transient conditions.