Nonlinear adaptive control for position-sensorless permanent magnet synchronous motors with uncertainties

In this paper we show that, when the rotor position is not measured in (nonsalient-pole surface) PMSMs with unknown constant load torque and stator resistance (with the rotor speed being available along with the stator currents), it is possible to guarantee exponential rotor position tracking and-mainly-regulation without resorting to persistency of excitation conditions which involve a non-definitely zero rotor speed reference. A new output feedback control is accordingly designed, which relies on a novel adaptive observer. The only price to be paid is constituted by a non-constant reference for the stator current vector d-component.