Hi Joel and community,
I'm building on Frank's PMSM model from this thread (A_model.slx / A_config.m) with the EMRAX 228 motor. The original model works perfectly in **Velocity Control mode** — Te tracks the reference, RPM follows the commanded speed, everything is consistent.
I'm now trying to convert it to **Torque Control mode** for a Formula SAE electric vehicle application, and I'm hitting a fundamental issue:
**Symptom:**
- Te (electromagnetic torque) tracks T_ref ≈ 190 Nm **perfectly** (see attached scope)
- RPM ≈ 0 (oscillates between -5 and +0.2 RPM — essentially locked)
- The FOC current loop works flawlessly, but the shaft doesn't rotate
**What I changed from the original model:**
1. FOC CtrlMode: 'Velocity control' → 'Torque control'
2. FOC Input 1: now receives torque_signal (from driving cycle) instead of omega_ref
3. Motor parameters corrected to EMRAX 228 MV: Ld=76µH, Lq=79µH, Rs=7mΩ, ψ_PM=0.0355 Wb, p=10
4. PI gains recalculated using Modulus Optimum: Kp_d=0.2027, Ki_d=18.67, Kp_q=0.2107, Ki_q=18.67
5. Added SHAFT Connection Port (PMIOPort) for future drivetrain connection
6. PMSM.J set to 0 (using external Inertia block J=0.0383 kg·m²)
**What I did NOT change (and I suspect is the problem):**
The original PMSM subsystem has a **Load block** (connected to the mechanical rotational network via Inport Tm). In velocity control mode, this block works fine as part of the control architecture. But in torque control mode, I believe this block may be imposing ω=0 as an algebraic constraint, absorbing all 190 Nm while keeping the shaft locked.
**The dilemma:**
- If I **keep** the Load block → Te=190 Nm perfect tracking, RPM=0 (shaft locked)
- If I **remove** the Load block → RPM becomes chaotic, Te loses tracking entirely
**My questions:**
1. In the original model's PMSM subsystem, is the Load block an Ideal Angular Velocity Source or an Ideal Torque Source? If it's a velocity source with input=0, that would explain ω=0 perfectly.
2. When converting from velocity to torque control, what should replace the Load block to provide proper mechanical loading without constraining velocity? Should I use an Ideal Torque Source with T_load = f(ω) instead?
3. Is there a recommended Simscape architecture for torque-controlled PMSM driving a mechanical load (gear + tire + vehicle body) where the FOC only controls torque and the mechanical dynamics determine speed naturally?
**System details:**
- EMRAX 228 MV CC (surface-mount PMSM, 10 pole pairs)
- Bamocar D3 inverter, Vdc=420V, fsw=8kHz
- FSAE vehicle: 300kg, gear ratio 8:1, wheel radius 0.23m
- Simscape Solver: BackwardEuler local solver @ 2µs, DoFixedCost=on
- MATLAB R2025b
I've attached screenshots of the PMSM subsystem, the Te tracking scope, and the RPM scope.
Thanks for any guidance!
