Coordinate Control of Grid Power, Battery SoC and LVRT Protection in Single VSC Tied DFIG
This paper proposes a coordinate control scheme for the single VSC tied doubly-fed induction generator (DFIG). In this control scheme, both the grid power and battery SoC (State of Charge) are maintained to provide an un-interrupted power supply. During the continuous operation of DFIG in the sub synchronous region, there is scope for complete battery discharge. Hence to overcome this drawback, the coordinated control scheme maintains the battery SoC level within the limits. If the SoC falls below the specified lower limit, then the proposed scheme curtails the grid power. Instead of discharging the battery, the control shifts the battery to charging mode until the safe limit of SoC is attained. During the continuous operation of DFIG in the super synchronous region, if the SoC reaches its upper limit, the proposed scheme discharges the extra power to the dump load. Further, this control scheme also introduces the low voltage ride through (LVRT) aspect according to IEGC (Indian electricity grid code) of 15% of nominal voltage and also an enhanced rotor position computation is implemented for the effective estimation of rotor position for single VSC tied DFIG. This control makes the topology more robust and improves the reliability of the system. The proposed scheme is validated for a test system of 3.7 kW Wound Rotor Induction Machine based DG unit and investigations are done in MATLAB simulation.
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