Three-stage commutation failure suppression strategy based on safe commutation boundary and predictive control model

HVDC systems are vulnerable to commutation failure due to insufficient commutation margin during AC faults, which threatens system stability. Existing optimization strategies are often computationally complex and heavily reliant on simulation models, limiting their direct application in practical engineering. This work focuses on current control to rapidly suppress commutation failure while providing a theoretical explanation of the linear mechanism of the Voltage-Dependent Current Order Limiter (VDCOL). The dynamic response of DC current in HVDC systems exhibits nonlinear behavior and time delay, which precludes an accurate description by simple analytical models. To address this, a dual-input dual-output transfer function is established using least squares and piecewise nonlinear system identification to characterize the dynamic evolution of current and commutation angle under fault disturbances. By incorporating converter valve constraints and introducing an appropriate overshoot margin, the DC current drop is accelerated to suppress commutation failure. Once commutation failure is blocked, the original VDCOL control strategy is reinstated, with a controlled ramp-up rate of the DC current order to prevent overshoot-induced secondary commutation failure. © 2017 Elsevier Inc. All rights reserved.