Design and comparison of various voltage control systems for distributed generators in electrical networks

The supply of ancillary services is now a new challenge to boost the development of distributed generators (DG). So far, a local DG may participate to the local voltage control. In this case the output voltage of the DG is required to be sinusoidal with minimum total harmonic distortion at the connection bus. The use of a second order filter enables this task and enables also the design of a precise control system of the capacitor voltage. So this paper investigates the suitability of various control strategies for a three-phase voltage-source inverter with a second-order filter. The general control scheme incorporates a capacitor voltage control, a fixed switching frequency, and a variable duty cycle modulation to produce sinusoidal output voltage with minimum harmonic distortion. Various control systems are presented. Their principle of operation and performances are compared.