Adaptive Loss‐of‐Excitation Protection for Variable‐Speed Pumped Storage Units with Full‐Power Converters

ABSTRACT

For variable‐speed pumped‐storage units with full power converters (FPC‐VSPSUs), converter‐based decoupling control fundamentally reshapes the machine‐terminal measured impedance trajectory during a loss‐of‐excitation (LOE) fault in the excitation system (ES). Consequently, conventional machine‐terminal measured‐impedance‐based protection schemes may suffer from large blind zones and a high risk of failure to trip. To address this issue, this paper presents a comprehensive analysis of the post‐LOE impedance characteristics under two field‐orientated control (FOC) strategies: stator‐flux orientation (SFO) and rotor‐flux orientation (RFO). Under stator‐side unity‐power‐factor operation, it is revealed that, for both FOC strategies, the machine‐terminal measured impedance trajectory moves along or near the real axis during the early LOE stage. Based on this characteristic, an adaptive rectangular LOE protection scheme is proposed, in which the setting boundaries are dynamically adjusted by integrating multidimensional operating‐state information, including rotational speed, operating condition, and FOC strategy. PSCAD simulations and RTDS hardware‐in‐the‐loop (HIL) experiments with an industrial protection relay demonstrate rapid and reliable fault identification over a wide operating range, including low‐active‐power generation conditions, while avoiding maloperation during grid disturbances.