Model predictive direct current control strategy for three-level T-type rectifier under unbalanced grid voltage conditions

In order to reduce the total harmonic distortion (THD) of grid current and output power fluctuations under unbalanced grid voltages, a model predictive direct current control (MPDCC) strategy is proposed for three-level T-type rectifier. The reference current is used as the control objective and calculated by grid voltages and its 1/4 delaying value. Compared with the conventional method, computation of instantaneous active power and reactive power, extraction of positive and negative sequence, phase-locked loop (PLL), PWM modulation and inner current loop are avoided. In addition, the redundant P-type and N-type small vectors are selected to control the neutral-point balance simultaneously. The experimental results are presented to verify the feasibility and effectiveness of proposed MPDCC strategy.