Control Strategy Of Pfc Rectifiers For Pmsg Wind Generation System

Direct drive permanent magnet wind generation system is the research focus in current wind generation technique area. In this kind of system, the power of permanent magnet synchronous generator (PMSG) needs to be transformed from variable voltage variable frequency AC power into constant voltage DC power which is then fed to the grid or load by an inverter. In order to overcome the drawbacks in the two common rectification topologies, a novel scheme called PFC rectifier is proposed in the thesis, which employs one-phase power factor correction (PFC) circuit for each phase of the PMSG. Both steady DC output voltage and low THD of AC currents can be achieved by the proposed control technique. The current control techniques and its sensorless control strategy are advanced in this thesis.Based on the models of the PMSG and the PFC circuits in different coordinates systems, two current control strategies are developed, which are average current control and synchronous PI current control. In the average current control, the zero-crossing distortion and steady-state error of PI regulators are analyzed. Considering the specialties of the PFC circuits and the behavior of the PMSG, the current control is aimed to keep the stator phase current and voltage being in phase and the corresponding control structure is developed.Its sensorless control strategy is advanced, providing the rotor position for the current control strategies. The electromotive force of the PMSG is reconstructed based on the models of the PMSG and the PFC rectifier; the rotor flux linkage is observed by an equivalent integrator and the phase angle for current control of the PFC circuit is derived from the rotor flux linkage.Taking six-phase PMSG as an example, the PFC rectifier is appled to the rectification of multi-phase PMSG, both average current control and synchronous PI current control developed. Due to the characteristic of the generalized coordinate transformation theory in the synchronous PI current control, the different harmonics of the currents can be projected onto a set of subspaces and controlled independently.Results of experiments both on three-phase and six-phase PFC rectification platform verify that the PFC rectifier adopting the control strategy can effectively achieve sinusoidal AC currents, steady DC output voltage. Sensorless control strategy can provide rotor position for the current control.