Constant frequency torque controller–based direct torque control (CFTC-DTC) is emerging as a powerful control strategy for a high-performance
control of alternating-current motor drives. Compared to DTC, the CFTC-DTC has less torque and flux ripples with a fixed switching frequency.
Nevertheless, it has a limitation of the torque-loop bandwidth, as it uses the sampling frequency from a digital signal processor (DSP) to generate
a triangular-based carrier. The switching frequency of the control system is determined by the carrier frequency of the CFTC. The frequency limitation
of CFTC leads to sector-flux droop, which causes a distortion in the motor phase current and aggravation in the torque and speed waveforms at low
speed regions. In this paper, we propose a modification of the frequency carriers of the CFTC-DTC of induction motors to increase the switching
frequency and torque loop bandwidth by replacing the triangular-carrier-based waveform with a ramp-carrier-based waveform. The proposed method
is verified by simulation and experimental results showing its excellent performances in steady- and transient-state operations.
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