Predictive Optimal Control for Three-Phase Neutral Point Clamped Multilevel Converters

This research work presents the predictive optimal control of output ac currents and input dc capacitor voltage balancing in a three-level, three-phase neutral point clamped multilevel converter. The ac output currents and input dc capacitor voltages are sampled and predicted for the next sampling time, using linearized models and considering all the 27 output voltage vectors. A suitable quadratic weighed cost functional is used to choose the voltage vector minimizing both the ac current errors and the input dc capacitor voltage unbalancing. For a given ripple in the ac currents, the predictive optimal controller reduces the switching frequency in comparison with a sliding mode controller. Obtained simulations and experimental results show that the ac currents follow their references (with amplitude steps), without steady state error, and the capacitor voltages are well balanced.