Cancellation Predictive Control for Three-Phase PWM Rectifiers under Harmonic and Unbalanced Input Conditions
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This paper presents an intuitive and simple-to-implement control scheme to improve the performance of three-phase boost-type PWM rectifiers under harmonic and unbalanced input conditions. Unlike most other control strategies, the proposed method does not need to extract either the harmonic or the negative-sequence components in the supply voltages and currents. A near-synchronous reference frame is used to determine the positive-sequence fundamental-frequency component in the input voltages. Utilizing only the extracted component, the DC-link voltage control and power factor control are implemented independently to determine the phase angle and magnitude of the PWM reference voltage. The commanded rectifier voltage adjustments are superimposed upon the grid voltages in such a way that the distortions (both harmonic and negative sequence components) are effectively cancelled. By employing a near-synchronous reference frame, no line-synchronization algorithm or hardware PLL is needed, so very little computational effort is required for its implementation. Simulation results show that the proposed method performs very well under extreme harmonic and unbalanced conditions such as when one or even two phases of the grid voltages are zero. In order to further verify its effectiveness, a laboratory hardware platform has been developed