The Capacitor Voltage Balancing Problem in FS-PTC for Induction Motor fed by 3L-NPC Inverter

The requirement of capacitor voltage balancing occupies an important position in controlling Three-Level Neutral Point Clamped (3L-NPC) inverter. It becomes even more important when 3L-NPC inverter is applied to drives system. In the past ten-year, Finite State Predictive Torque Control (FS-PTC) for Induction Motor (IM) is gaining huge attention from researchers in the field of electric drive system. The use of 3L-NPC inverter for FS-PTC is extremely complex because in addition to controlling torque and stator flux, FS-PTC also maintain capacitor voltage balancing. This problem can be solved by using the cost function with three optimal components: optimal component of torque error, optimal component of stator flux error and optimal component capacitor voltage error. However, choosing 2 weighting factors for this cost function is difficult because there is not basis to choose. This paper build a new method to remove the optimal component of capacitor voltage error from the cost function. It is done by selecting the appropriate vectors for the capacitor voltage balancing before calculating the predicted values of torque and stator flux and after finding the optimal voltage vector. This selection is made through output of a hysteresis controller.