Sensorless operation of a PWM rectifier for a distributed generation

This paper presents a power converter configuration interfaced with the distributed ac power generation system to regulate the dc bus voltage. It is composed of a pulsewidth modulation (PWM) rectifier directly tied to the generator's terminals without ac reactors. Hence terminal voltages are not useful due to the switched pulse of the PWM rectifier and also it is not the terminal voltages, but the generator's electromagnetic field voltages that are required for a synchronous angle of the PWM rectifier. This paper proposes a method for estimating the synchronous angle through only the measurement of the ac line currents, and is thus called the voltage sensorless control strategy. For a smooth startup of the PWM rectifier, a technique of setting the integrators' initial values in the proposed estimator is described. In this paper a commercial engine generator set is used as the distributed generation system. The feasibility of the overall system and algorithms has been verified by the experimental results. Index Terms--Distributed ac power generation, engine generator set (En-Gen set), pulsewidth modulation (PWM) rectifier, synchronous angle, voltage sensorless control.