PI Regulator-Based Duty Cycle Control to Reduce Torque and Flux Ripples in DTC of Six-Phase Induction Motor

In this paper, a proper duty cycle control method is proposed to reduce torque and flux ripples and harmonic loss in direct torque control (DTC) of six-phase induction machine (6PIM). Three different methods are proposed to improve the performance of switching table DTC for 6PIM. First, by the suitable selection of two vectors in each sampling period, the harmonic amplitude is significantly decreased, but the torque and flux ripples are still large. Then, the abovementioned method is combined with duty cycle control technique and the torque and flux ripples and current harmonics are significantly reduced. In addition, the switching frequency is also reduced by selecting the suitable voltage vector in each sampling period. Finally, a simple control method is suggested to calculate the duty ratio of voltage vectors independently of machine parameters. Although neglecting the one-step delay makes performance of the final technique similar to the previous one, considering this delay in real conditions shows the following advantages for the final method: less torque and flux ripples, less current harmonics, simplicity, and constant switching frequency. Despite these improvements, all duty cycle-based DTC approaches (duty-DTC and PI-duty-DTC) increase the inverter switching losses. The simulation and experimental results presented in this paper verify the performance advantages of the proposed methods.