Modulated model predictive control (M2PC) with fixed switching frequency for an NPC converter

Advances in power electronic converters technology along with the wide range of applications require sophisticated digital control schemes. In the recent years Finite Control Set Model Predictive Control (FCS-MPC) has been successfully proposed as an alternative to the traditional control techniques, due to its fast dynamic response, easy inclusion of nonlinearities and constraints in the control algorithm and the ability of incorporate several control requirements in one cost function. However, FCS-MPC is characterized by a variable switching frequency which can cause a degradation in system performance, or demand higher output filtering. In this paper a Modulated Model Predictive Control (M²PC) strategy is proposed for constant switching frequency operation and verified with a neutral-point-clamped (NPC) converter for load current regulation and DC-link capacitor voltages balancing. The aim of this control technique is to obtain a modulated waveform at the output of the converter, whilst maintaining all the desired characteristics of FCS-MPC. The feasibility of this strategy is evaluated using simulation and compared to the classical FCS-MPC strategy.