Direct Power Control of Doubly-Fed Induction Generator for Wind Turbines Based on Improved Sliding Mode Variable Structure

Direct Power Control (DPC) is widely recognised as an effective method of regulating the operating state of Doubly-Fed Induction Generators (DFIGs) by controlling the active and reactive power errors. In DPC, the instantaneous power values are used directly for control, providing advantages in terms of dynamic response speed and control accuracy. However, it should be noted that DPC is sensitive to model uncertainties and external disturbances, which can result in steady-state errors. Sliding Mode Control (SMC) is considered to be a robust nonlinear control strategy that is well suited for dealing with system uncertainties and external disturbances. As such, the introduction of SMC into the DPC framework for DFIGs can significantly improve system robustness. The resilience of SMC to uncertainties allows it to deal effectively with system nonlinearity, parameter variations and external disturbances. Nevertheless, the problem of chatter, characterised by high-frequency oscillations as the system state moves along the sliding surface, is often observed in SMC. To address this issue, this paper proposes an improved SMC strategy in which the conventional sign function is replaced by a reaching law based on the fal function. Simulation results show that, compared to the traditional approach, the improved SMC effectively reduces chatter, enables faster stabilisation under parameter variations, and improves both response speed and system robustness.