A Novel Loss-of-Excitation Protection Scheme for Variable-Speed Pumped Storage Units with Full-Size Converters Under Different Control Strategies

This paper presents an in-depth investigation into the loss-of-excitation (LOE) protection for variable-speed pumped storage units with full-size converters (FSC-VSPSUs). It elucidates the dynamic interaction between electromagnetic transients and converter control loops under various machine-side converter (MSC) control strategies. The study reveals that units employing voltage-oriented control face a fundamental risk of phase-locked loop (PLL) instability following an LOE event. Given the inadequacy of traditional impedance-based protection for FSC-VSPSUs, a novel LOE protection scheme is proposed. This scheme integrates a dynamically tuned main impedance criterion with an acceleration criterion based on the rate of change of the impedance’s real part, incorporating a speed compensation coefficient to accommodate variable-speed operations. Experimental validation on an RTDS platform demonstrates that the proposed strategy accurately identifies LOE faults across various turbine and pumping modes, offering superior response speeds compared to traditional methods and other techniques reported in the existing literature.