Active and Reactive Power Injection Strategies for Three-Phase Four-Wire Inverters During Symmetrical/Asymmetrical Voltage Sags

Electric grid codes are expected to change in near future to accommodate an increased number of distributed generation units in the distribution power system without impairing its power quality. It is desired that the generators remain connected during voltage sags and provide ancillary services, such as voltage and reactive power control, ensuring the operational stability of the power system. This paper explores how the existing strategies for active and reactive power injection impact the operation of grid-tied inverters in terms of required power, current flowing, and reduction of active power delivery during the voltage sags. Such inputs are relevant to properly size converters for operation under fault events. In addition, this paper contributes to devise: 1) constant peak current control, 2) constant active current control, and 3) constant average active power control strategies for three-phase four-wire grid-tied inverters considering the natural (abc) reference frame. The design and implementation of the investigated power injection strategies are discussed, and their effectiveness and technical viability are analyzed through dynamic computational simulations under symmetrical/asymmetrical voltage sags, and variation of the short-circuit ratio.