An analysis of the benefits of signal injection for low-speed sensorless control of induction motors

TL;DR

This paper explains the challenges of low-speed sensorless control of induction motors and demonstrates how signal injection and magnetic saturation improve observability, supported by simulations and experiments.

Contribution

It provides a control-theoretic analysis of observability in induction motors and shows how signal injection enhances sensorless control at low speeds.

Findings

Signal injection restores observability at zero speed.

Sensorless algorithms may perform poorly under certain conditions.

Experimental results validate the analysis.

Abstract

We analyze why low-speed sensorless control of the IM is intrinsically difficult, and what is gained by signal injection. The explanation relies on the control-theoretic concept of observability applied to a general model of the saturated IM. We show that the IM is not observable when the stator speed is zero in the absence of signal injection, but that observability is restored thanks to signal injection and magnetic saturation. The analysis also reveals that existing sensorless algorithms based on signal injection may perform poorly for some IMs under particular operating conditions. The approach is illustrated by simulations and experimental data.