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Encoderless Control with Resistance Immunity

Azionamenti ElettriciCTENEXTElectrical drivesEncoderless controlInformatica Tsd EnSensorless controlSynchronous reluctance machineTemperature immunity


For cost and reliability reasons, the angular position encoder is replaced by an observer in electric motor drives for industry applications. The observer stability is susceptible to temperature dependent variation of the motor resistance. The novel Adaptive Projection vector for Position error estimation (APP) technique is resistance- (i.e. temperature-) independent, same as with the encoder on.

Technical features

This invention improves the performance of sensorless controlled Synchronous Reluctance motor (SyRM) drives. Such drives are the super-premium efficiency replacement of standard-efficiency induction motor (IM) drives. As IM drives do not need a rotary encoder, sensorless control is mandatory also for SyRMs. Moreover, the maximum torque per ampere (MTPA) control law makes SyRMs highly efficient at low load too, besides at nominal output power. Respect to existing sensorless techniques for SyRMs, the new approach relies on peculiar manipulation of the flux and position observer error signal called Adaptive Projection vector for Position error estimation (APP). The APP eliminates the need for inverter identification, mandatory for all existing techniques, and makes the control immune to motor temperature variations, which are inevitable during operation.

Possible Applications

  • Variable speed drives compliant to efficiency standards;
  • Industrial applications: pumps, fans, conveyors, presses, etc.;
  • Home applicances: vaccum cleaners, hair dryers;
  • Automotive industry: control accessories, safety redundancy.


  • Temperature-independent sensorless control;
  • Simplified inverter comissioning stage;
  • Accurate tracking of MTPA for high efficiency operation;
  • Supplementary resistance adaptation for accurate flux/torque estimation.