A space-vector PWM algorithm with a hybrid switching sequence for regulated ac electric drives based on a three-level voltage inverter

This article proposes a new space-vector PWM with a hybrid switching sequence for a three-level neutral point clamped voltage source inverter. Based on the advantages of the five-stage and seven-stage switching sequences, a hybrid sequence was developed with to maintain the neutral point voltage balance at a predetermined level and to reduce the switching losses of power switches. The algorithm allows for the flexible adjustment of the specified criteria depending on the operating conditions of the system by changing the regulation coefficient. An approximated dependence is obtained that allows the determination of the optimal control coefficient for any values of a given frequency at the input of the inverter when operating on an asynchronous short-circuited motor with a control law U/f = const. The effectiveness of this algorithm was confirmed by computer simulation using MATLAB Simulink. The article gives experimental dependences of the static state spaces of the maximum neutral point voltage error and the number of switching pairs of power switches depending on the specified frequency at the input of the inverter and the control coefficient of the hybrid sequence of switches. The results showed that the proposed PWM algorithm with a hybrid switching sequence reduces the number of power switches by an average of 14.3 %, while maintaining a neutral point voltage balance close to the seven-level sequence (deviation does not exceed 0.75 %). Thus, the proposed algorithm is an effective tool for controlling a three-level voltage source inverter, which has a positive effect on its energy efficiency, size and weight characteristics, and operational reliability.