Predictive control of a three-phase neutral point clamped inverter

A new predictive strategy for current control of a three-phase neutral point clamped inverter is presented. It is based on a discrete-time model of the system, used to predict future values of the load current and voltage of the capacitors in the DC-link, for each possible switching state generated by the inverter. The state that minimizes a given quality function "g" is selected to be applied during the next sampling interval. Several compositions of g are proposed, including terms dedicated to achieve reference tracking, balance in the DC-link and reduction of the switching frequency. The algorithm uses the redundancy of switching states, typical of a three-level inverter, by means of a simple strategy. In comparison with classic PWM current control, the strategy presents a remarkable performance. The proposed method achieves comparable reference tracking with lower switching frequency per semiconductor and a slightly improved transitory behavior. It requires a greater sampling frequency, which should not be a problem, considering the present technologies available in digital signal processors. The main advantage of the method is that it does not require any kind of linear controller or modulation technique, achieving a different approach to control a power converter.