Control of a Three-Phase Grid-Tied Inverter Designed for Discontinuous Current Mode Operation

This paper proposes to operate a particular circuit topology of the three-phase grid-tied inverter in a discontinuous current mode (DCM). A feed-forward current control method and some specific control techniques for the DCM operated three-phase topology are discussed. This paper shows that the feed-forward current control is suitable for the DCM operated grid-tied inverter due to the non-linear characteristics of the DCM operation and difficulties of the current sensing. Some additional controls for a DC voltage balancing and a phase voltage stabilization are proposed for the extension of the DCM operated single-phase grid-tied inverter to the three-phase topology. Moreover, a different approach of the third order harmonic voltage injection to increase output voltage, which is usually achieved by modifying the voltage reference in the conventional converters, is proposed. The feed-forward current control and the above additional control techniques were verified with a 1-kW laboratory prototype. The resulting total demand distortion of the grid currents in the experiments was 2.96%.