Optimal Predictive Control of Three-Phase NPC Multilevel Inverter: Comparison to Robust Sliding Mode Controller

This research work presents the optimal control of the 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. Obtained experimental results show that the output AC currents follow their references showing small ripple, total harmonic distortion less than 1%, harmonic contents 46dB below the fundamental, and no steady state error. The capacitor voltages are correctly balanced. Comparatively to a robust sliding mode controller the optimal controller reduces the total harmonic distortion of the AC currents, being a suitable controller for power quality applications.