A multi-featured single-phase utility interface with reduced DC link capacitor for distributed power sources

This paper discusses the operating principles and implementation of a multi-featured single-phase utility interface for distributed power sources. It controls the active power injected into the utility grid to keep the DC bus voltage regulated and compensates for the reactive power demanded and the current harmonics created by a local load. The DC bus voltage control loop includes a voltage ripple estimator so that the low order harmonics (2nd, 4th, 6th...) can be cancelled from the feedback signal. This way, one can use a small non-electrolytic capacitor in the dc bus without distorting the grid current despite of an increased dc bus voltage ripple. Besides, the loop bandwidth can be increased for a faster response. A three-level hysteresis current control scheme that presents reduced average switching frequency is used to impose a sinusoidal grid current in phase with the grid voltage. Experimental results in a scaled-down prototype demonstrate the feasibility of the proposed power electronic interface.