A Novel Protection Method to Enhance the Grid-Connected Capability of DFIG based on Wind Turbines

Abstract

This paper proposes a robust protection technology to enhance the grid-connected capability of the doubly fed induction generator (DFIG) based on wind turbines (WTs) under low voltage ride through (LVRT) conditions. The proposed method to control the rotor side converter (RSC) and grid side converter (GSC) uses proportional–integral (PI) controllers. The protection devices are the static compensator (STATCOM), crowbar, series dynamic resistor (SDR), and DC-chopper, with the proposed method to control STATCOM using proportional–integral (PI) controllers and the proposed method to control the rest of the protection devices based on the allowable threshold values of rotor current and DC-link voltage. The protection coordination strategy between them is proposed to avoid the disconnection between the rotor circuit and grid, maintain the DC-link at constant voltage, enhance the dynamic response of WT, and improve the voltage response at the point of common coupling (PCC) of WT. The DFIG-WT of 2 MW-575 V connecting to the 34-bus IEEE network is carried out to verify the effectiveness of the proposed method under the conditions of symmetrical and asymmetrical faults, and the LVRT requirements of the Spanish grid code are considered. The obtained simulation results using the PSCAD/EMTDC software show that the rotor current, DC-link voltage, voltage PCC, and power oscillation damping are significantly improved compared to not using it or applying the conventional method based on passivity theory. Therefore, the LVRT capability of the proposed DFIG-WT system is significantly enhanced, and it has enough ability to continue to provide electrical energy to the power network. Abbreviation DFIG, Doubly Fed Induction Generator; DVR, Dynamic Voltage Restorer; FACTS, Flexible AC Transmission System; FRT, Fault Ride Through; FS-WT, Fixed-Speed Wind Turbine; GSC, Grid Side Converter; LVRT, Low Voltage Ride Through; PCC, Point of Common Coupling; PI, Proportional–Integral; PMSG, Permanent Magnet Synchronous Generator; PWM, Pulse Width Modulated; RSC, Rotor Side Converter; SDR, Series Dynamic Resistor; STATCOM, Static Compensator; SVC, Static Var Compensator; UPFC, Unified Power Flow Controller; VS-WT, Variable-Speed Wind Turbine; SLG, Single Line-to-Ground; LL, Line-to-Line; LLG, Double Line-to-Ground; WT, Wind Turbine