Inverter control loops in practice
Nested loops, sampling rates and what happens when a fault is detected.
- Explain inverter control loops in practice at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive system
Overview
A production inverter is a layered control system: a fast current loop inside a slower torque loop, all wrapped in protection logic that can shut everything down in microseconds if something goes wrong.
In depth
| Loop | Typical rate | Regulates |
|---|---|---|
| Current (Id/Iq) | 10–20 kHz | Phase current against FOC targets |
| Torque | 1–2 kHz | Torque against VCU request |
| Thermal derating | 10–100 Hz | Power limit against junction temperature |
| Diagnostics | Continuous | Overcurrent, overvoltage, desaturation faults |
DC to AC conversion simulator
Watch the inverter build a three-phase sine wave from a switched DC bus in real time.
The bridge never makes a real sine wave — it makes pulses whose moving average is a sine. Frequency sets motor speed; amplitude sets flux, and the two are usually raised together to keep volts-per-hertz constant.
Diagnose: inverter fault trip
A test bench inverter trips on start-up. Work through the clues to find the cause.
Inverter enable fails, no torque
The inverter accepts the enable command but immediately reports a fault code and disables gate drive.
Key takeaways
- Production inverters nest a fast current loop inside slower torque and thermal loops.
- Desaturation and insulation monitoring protect the power module from destructive faults.
- Diagnosing a trip means correlating the fault code with independent sensor evidence.
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