I’m currently working on a simulation project based on DTC with Third Harmonic Injection PWM (DTC-THIPWM) for an induction motor drive.

Instead of using the classical DTC approach with hysteresis comparators and switching tables, I adopted a DTC-SVM-style architecture, but replaced the Space Vector Modulation stage with Third Harmonic Injection PWM (THIPWM).
The goal was to keep the fast dynamic response and decoupled torque/flux control advantages of DTC while using a PWM generation method that is simpler and computationally lighter than SVM.

The system behavior is actually good overall:

• Speed tracks the reference correctly
• Flux converges nicely to the reference
• Mean electromagnetic torque converges properly as well

However, the issue is with the instantaneous electromagnetic torque.
Even though the average torque is correct, the raw torque waveform contains a large ripple that I cannot fully explain.

Simulation setup

• Speed reference: step input at t = 0 s
• Reference speed: 150 rad/s
• Load torque: 5 N·m
• Sampling time: Ts = 1e-6
• Control period: Tol_Ts = 10*Ts
• PWM frequency: 2 kHz

What confuses me is that:

• The PI controllers seem validated since the mean values converge correctly
• Rotor speed is relatively stable
• Flux estimation looks fine
• But the electromagnetic torque ripple remains significant in steady state

At this point I suspect the ripple could be caused by:

• THIPWM harmonic content
• Low PWM frequency
• Torque estimation noise
• Flux estimation inaccuracies
• PI interaction
• Or maybe replacing SVM with THIPWM fundamentally changes the voltage vector quality

Has anyone worked on something similar or seen this kind of behavior in DTC-THIPWM structures?
I’d really appreciate any insight on where this ripple could realistically come from.