Observer-Based Control Methods for Combined Source-Voltage Harmonics and Unbalance Disturbances in PWM Voltage-Source Converters

In this paper, computationally efficient sinusoidal-disturbance estimation and elimination methods are introduced into the control of an active front end (AFE) voltage-source converter (VSC) to achieve effective disturbance rejection in high power systems with slower pulsewidth-modulation switching frequencies (e.g., 5 kHz) and limited current-controller bandwidth. Since the active rectifier is in series with the source and the load, there is no need to add additional hardware for harmonic elimination. The input positive- and negative-sequence voltages are extracted using the new observer methods, and negative-sequence currents are injected to eliminate the dc-link 120-Hz ripple. The observer-based disturbance-rejection methods are proven to be very effective when all three types of disturbances (input-voltage harmonics, unbalance, and inductor unbalance) coexist simultaneously, even under input-inductance variations of 30%. Simulation results are verified experimentally using a 15-hp adjustable-speed-drive system that includes an AFE VSC coupled to a dSpace controller.