Virtual Flux Direct Power Control for PWM Rectifiers Based on an Adaptive Sliding Mode Observer

In the traditional virtual flux estimation for a three-phase pulsewidth modulation rectifier, the integration element causes problems for the initial value and dc bias, and the unstable grid voltage induces a nonconstant flux amplitude. To address these issues, an improved direct power control scheme based on an adaptive sliding mode observer is proposed in this work. The observer employs a sigmoid function as switch function to estimate the grid-side source voltage. Meanwhile, an adaptive compensator instead of pure integral element is also designed to dynamically adjust compensation. The stability of this observer is proved by the Lyapunov function; moreover, simulations and experimental results indicate that this new virtual flux observer substantially improves the observation accuracy based on voltage sensorless control. The application of this strategy successfully suppresses the fluctuation of the dynamic voltage response in the dc bus, eliminating high-frequency noise from the grid side, while simultaneously boosting the power quality.