Predictive current control for neutral-point voltage regulation and load balancing in three-level grid connected compensator

In recent years many studies have treated the neutral-point voltage regulation problem in the Neutral-Point-Clamped (NPC) converter. Besides, many works have proposed appropriate control strategies for these grid interfacing NPC converters to compensate the problem of load current unbalance and power factor correction. This paper addresses both problems. Therefore, a predictive current control method for a three-level NPC converter capable of simultaneously compensating the problems of: neutral-point voltage regulation, load balancing and power factor correction is presented. The discrete-time model of the system is used to predict the future value of the converter currents and the capacitors voltages for all possible voltage vectors. The voltage vector which minimizes a given cost function is chosen. Reference converter currents are generated using the instantaneous p-q theory. The simulation results of the proposed method are analyzed, and its good performance is verified compared with the traditional carrier-based PWM strategy using zero-sequence voltage injection.