Michele Angelo Pastorelli

A simplified thermal model for variable-speed self-cooled industrial induction motor

In this paper, a simplified thermal model for variable-speed self-cooled induction motors is proposed and experimentally verified. The thermal model is based on simple equations that are compared with more complex equations well known in the literature. The proposed thermal model allows one to predict the over temperature in the main parts of the motor, starting from the measured or the estimated losses in the machine. In the paper, the description of the thermal model setup is reported in detail. Finally, the model is used to define the correct power derating for a variable-speed pulsewidth-modulation induction motor drive.

Predicting iron losses in soft magnetic materials with arbitrary voltage supply: an engineering approach

We propose a new approach for predicting iron losses in soft magnetic materials with any voltage supply, starting from the knowledge of the iron losses with a sinusoidal or pulsewidth modulation supply. The model is based on the separation of the loss contributions due to hysteresis, eddy currents, and excess losses with the two supplies. Since any contribution depends on the voltage supply characteristics, it is possible to find a direct mathematical relationship between the iron loss contribution and the voltage supply characteristics. As a consequence, an iron loss prediction can be obtained with any voltage supply if it does not produce a hysteresis minor loop. The energetic model is based on coefficients that depend on the magnetic material characteristic. We performed an accurate analysis of the model on eight magnetic materials used for electrical machine construction, of different thicknesses and alloy compositions. In this way, we found the main coefficients for a large spread of magnetic materials. As a consequence, our approach can be a useful support for electrical machine designers when the energetic performance of a magnetic material has to be predicted for a voltage supply different from the sinusoidal one.

Cross-Saturation Effects in IPM Motors and Related Impact on Sensorless Control

Permanent-magnet-assisted synchronous reluctance motors are well suited to zero-speed sensorless control because of their inherently salient behavior. However, the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy. These errors are quantified in this paper as a function of the working point. The errors that are calculated are then found to be in good accordance with the purposely obtained experimental measurements

Design of low-torque-ripple synchronous reluctance motors

A design approach oriented to minimization of torque-ripple is presented, for synchronous reluctance motors of the transverse-laminated type. First, the possible types of rotors are classified and the more suited rotor structure is evidenced, to be matched to a given stator. Then, the inner rotor design is described, pointing-out the low-ripple measures. Last, experimental results are given, from three different rotors: they confirm the validity of the proposed approach.

Stator resistance tuning in a stator-flux field-oriented drive using an instantaneous hybrid flux estimator

A self-tuning control scheme for stator-flux field-oriented induction machine drives in electric vehicles operating over a wide speed range is discussed in this paper. The stator flux can be determined accurately from the terminal voltage when the machine is operating at high speed. However, at low speed, the stator resistance must be known to calculate the stator flux. The problem of calculating the stator flux accurately over the entire speed range is addressed. The rotor flux can be found from the machine speed and rotor time constant. The stator flux, at low speed, is then calculated directly from the rotor flux. By alternating between these two methods of determining the stator flux, a self-tuning operation is achieved, wherein the stator and rotor resistances are periodically updated. Since both methods of determining the stator flux are forced to track one another, a smooth transition between flux estimators is obtained. The torque and flux are then controlled in a deadbeat fashion. Good torque control over a wide speed range can therefore be obtained. With the proposed scheme, the advantages of direct torque control are obtained over the entire speed range with the addition of a speed sensor.

Impact of cross saturation in synchronous reluctance motors of the transverse-laminated type

The cross-saturation phenomenon in synchronous reluctance motors is extensively analyzed, with a main reference to motors of the transverse-laminated type. A mixed, theoretical and experimental approach is adopted, aiming at definition of motors behavior when large overload currents are driven, up to ten times the rated current. As a consequence, a special test and measuring procedure has been adopted. The obtained results are used to check the validity of the adopted model and to prove the unexpected overload performance of this motor. Finally, the tendential behavior at infinite current is discussed.

International standards for the induction motor efficiency evaluation: a critical analysis of the stray-load loss determination

The motor efficiency has to be measured or calculated in accordance to International Standards. The most important world references are the IEEE 112-B, the IEC 34-2 and the JEC 37 Standards. In this paper, a comparison of the measurement procedures defined by these International Standards is reported, together with some comments to the prescribed methodologies. The comparison is based on experimental results obtained by testing four general purpose three-phase induction motors. The stray-load loss measurement represents a critical key for the correct evaluation of the motor efficiency. For this reason, a critical analysis of this type of losses has been performed. In particular, the stray-load loss sensitivity to the measurement errors is analyzed in order to understand which are the most critical quantities that influence their evaluation. In the final part of the paper the temperature influence on the conventional iron losses is experimentally analyzed. The performed tests show that the temperature difference between the no-load test and the motor real operative conditions is not negligible.

Impact of cross-saturation in sensorless control of transverse-laminated synchronous reluctance motors

Synchronous reluctance (SyR) motors are well suited to a zero-speed sensorless control, because of their inherently salient behavior. However, the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy. These errors are quantified in the paper, as a function of the working point. The so-calculated errors are then found in good accordance with the purposely obtained experimental measurements. The impact of the amplitude of the carrier voltage is then pointed out, leading to a mixed (carrier injection plus electromotive force estimation) control scheme. Last, a scheme of this type is used, with a commercial transverse-laminated SyR motor. The robustness against cross-saturation is shown, in practice, and the obtained drive performance is pointed out proving to be effective for a general-purpose application.

Position-sensorless control of permanent-magnet-assisted synchronous reluctance motor

The sensorless control of permanent-magnet-assisted synchronous reluctance (PMASR) motors is investigated, in order to conjugate the advantages of the sensorless control with full exploitation of the allowed operating area, for a given inverter. An additional pulsating flux is injected in the d-axis direction at low and zero speed, while it is dropped out, at large speed, to save voltage and additional loss. A flux-observer-based control scheme is used, which includes an accurate knowledge of the motor magnetic behavior. This leads, in general, to good robustness against load variations, by counteracting the magnetic cross saturation effect. Moreover, it allows an easy and effective correspondence between the wanted torque and flux and the set values of the chosen control variables, that is d-axis flux and q-axis current. Experimental verification of the proposed method is given, both steady-state and dynamic performance are outlined. A prototype PMASR motor will be used to this aim, as part of a purposely assembled prototype drive, for light traction application (electric scooter).

Position-sensorless control of the transverse-laminated synchronous reluctance motor

The sensorless control of the transverse-laminated synchronous reluctance motor is introduced, pointing out the negative effect of cross saturation. Then, an observer-based sensorless control scheme is proposed which solves this problem. Thus, a very good robustness against load variations is achieved. Moreover, the working speed is extended from zero to maximum speed, including the flux-weakening feature. This is obtained by a combined method of rotor position estimation, making use of both electromotive-force-based estimation and signal injection, without any need of additional voltage. A prototype drive has been assembled, making use of a commercial motor, and the obtained experimental results are given. A dynamic performance is achieved which is near to that of a sensored control, in the whole speed range. Moreover, position-sensorless position control is feasible.