According to the second embodiment shown in Figure 5, the sensor-less torque/flux regulator system 114 may preferably comprise: a subtractor stage 120, a torque hysteresis control stage 121, a subtractor stage 122, a flux hysteresis control stage 123, a switching table stage 124 and a sensor-less torque/flux estimator stage 128. The sensor-less torque/flux estimator stage 128 may be configured to: receive in input the currents iu(t), iv(t), iw(t), receive in input the signals Uu(t), Uv(t), Uw(t), estimate a torque signal T based on the three-phase sensed currents iu(t), iv(t), iw(t), and signals Uu(t), Uv(t), Uw(t), and output the estimated torque signal T. The estimated torque signal T comprise a value indicative of the actual torque of the electric motor 2 during the rotation of the drum 104. Preferably, the estimated torque signal T comprise a value indicative of the actual torque on the motor shaft of the electric motor 2. 

The sensor-less torque/flux estimator stage 128 may be further configured to: estimate a flux signal Ψ based on the three-phase sensed currents iu(t), iv(t), iw(t), and signals Uu(t), Uv(t), Uw(t), and output the estimated flux signal Ψ . The estimated flux Ψ is indicative of the actual magnetic flux of the electric motor 2 during the rotation of the drum 104. 

It is understood that operations performed by the sensor-less torque/flux estimator stage 128 to estimate the actual magnetic flux Ψ and the actual torque T of the electric motor 6 based on the motor-currents iu(t), iv(t), iw(t), and signals Uu(t), Uv(t), Uw(t), are known and will not be further described. 

With reference to Figure 5, the subtractor stage 120 is configured to: receive in input the torque reference Tref and the estimated motor torque T, determine a torque error Te based on the difference between the torque reference Tref and the estimated motor torque T, and outputs the calculated torque error Te. 

The torque hysteresis control stage 121 is configured to receive the torque error Te and provides a torque control signal dTe. 

According to an exemplary embodiment, the torque hysteresis control stage 121 may comprise a plurality of level hysteresis controllers. For example, the torque hysteresis 

