Model Predictive Direct Current Control for multi-level converters

A model predictive current controller for multi-level inverter driving electrical machines is proposed that keeps the stator currents within given bounds around their respective references and balances the inverter´s neutral point potential around zero. The inverter switch positions are directly set by the controller thus avoiding the use of a modulator. Admissible switching sequences are enumerated and a state-space model of the drive is used to predict the drive´s response to each sequence. The predicted short-term switching losses are evaluated and minimized. The concept of extrapolation and the use of bounds achieve an effective prediction horizon of up to 100 time-steps despite the short switching horizon. When compared to classic modulation schemes such as pulse width modulation, for long prediction horizons, the switching losses and/or the harmonic distortion of the current are almost halved when operating at low pulse numbers, thus effectively resembling the steady-state performance of optimized pulse patterns. During transients the dynamic response time of the proposed controller is in the range of a few ms and thus very fast.