Sliding Mode Control Strategy for Three-Phase Three-Level T-Type PWM Rectifiers with Capacitor Voltage Imbalance Compensation

This paper presents a sliding mode control (SMC) strategy for three-phase three-level T-type rectifiers with capacitor voltage imbalance compensation capability. The proposed SMC strategy which is formulated in the natural frame is based on generating a modulating signal from the difference of line currents and their references. The amplitude of line current references is generated by regulating the output voltage using a proportional-integral (PI) regulator. In order to satisfy the unity power factor requirement, the generated amplitude is multiplied by the corresponding unity sinusoidal waveforms for each phase. For the sake of eliminating the imbalance in the capacitor voltages, a compensation term involving the capacitor voltage feedback through a suitable gain is added into the line current reference obtained for each leg. The performance of the proposed control strategy is investigated by simulation study during steady-state, transients caused by load change, and unbalanced grid. It is shown that the dc output voltage is regulated at desired level and line currents track their references in all cases.