Coordinate Control of Grid Power, Battery SoC and LVRT Protection in Single VSC Tied DFIG

Abstract

This paper proposes a coordinate control scheme for the single VSC tieddoubly-fed induction generator (DFIG). In this control scheme, both the gridpower and battery SoC (State of Charge) are maintained to provide an un-interrupted power supply. During the continuous operation of DFIG in thesub synchronous region, there is scope for complete battery discharge. Henceto overcome this drawback, the coordinated control scheme maintains thebattery SoC level within the limits. If the SoC falls below the specified lowerlimit, then the proposed scheme curtails the grid power. Instead of dischargingthe battery, the control shifts the battery to charging mode until the safelimit of SoC is attained. During the continuous operation of DFIG in thesuper synchronous region, if the SoC reaches its upper limit, the proposedscheme discharges the extra power to the dump load. Further, this controlscheme also introduces the low voltage ride through (LVRT) aspect accordingto IEGC (Indian electricity grid code) of 15% of nominal voltage and also an enhanced rotor position computation is implemented for the effectiveestimation of rotor position for single VSC tied DFIG. This control makesthe topology more robust and improves the reliability of the system. Theproposed scheme is validated for a test system of 3.7 kW Wound RotorInduction Machine based DG unit and investigations are done in MATLABsimulation.