Enhanced Instantaneous Power Theory for Control of Grid Connected Voltage Sourced Converters Under Unbalanced Conditions

Undesirable power oscillations take place in grid-connected voltage sourced converters (VSC) during unbalanced conditions. This problem becomes more difficult and pronounced during transients which include zero sequence content flowing through the ac/dc interface. This paper introduces a method especially designed to control the instantaneous power in voltage sourced converters operating under unbalanced transient scenarios with positive, negative, and zero sequence content. The control is based on an adaptive transformation that instantaneously adjusts itself to the dynamic voltage conditions. The method allows control over constant and oscillating terms of the instantaneous three-phase power. It is applied to grounded three-wire and four-wire schemes, especially accommodating zero sequence unlike previous approaches. The technique expands the application of the p-q theory, which is attached to the αβ0 transformation. The effectiveness of the proposed control approach and the proposed power conditioning scheme was demonstrated using electromagnetic transient simulation of a VSC connected to an ac system.