Mario Lazzari

A comparison between the axial flux and the radial flux structures for PM synchronous motors

The aim of the paper is the comparison of the axial flux (AF) structures versus the conventional radial flux (RF) structures for PM synchronous motors. The comparison procedure is based on simple thermal considerations. Two motor typologies are chosen and compared in terms of delivered electromagnetic torque. The comparison is developed for different motor dimensions and the pole number influence is put into evidence. The paper reports the complete comparison procedure and the related results analysis. The obtained results show that, when the axial length is very short and the pole number is high, axial flux motors can be an attractive alternative to conventional radial flux solutions.

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.

Digital field-oriented control for dual three-phase induction motor drives

A direct rotor-field-oriented control of a dual-three phase induction motor drive is described in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The stator windings are fed by a current-controlled pulsewidth-modulation (PWM) six-phase voltage-source inverter. Three key issues are discussed: (1) the machine dynamic model is based on the vector space decomposition theory; (2) the PWM strategy uses the double zero-sequence injection modulation technique which gives good results with low computational and hardware requirements; and (3) to eliminate the inherent asymmetries of the drive power section, a new current control scheme is proposed. Experimental results are presented for a 10-kW dual three-phase induction motor drive prototype.

An improved estimation of iron losses in rotating electrical machines

Core losses in rotating electrical machines have been estimated through direct use of the standard Epstein loss data of the employed magnetic laminations, without introducing empirical correcting factors. The prediction is based on a numerical finite element approach to magnetic flux distribution, coupled to a physical model of losses in ferromagnetic laminations under generic flux waveform, which takes into account the specific role of the hysteresis and classical and excess loss components. An application has been made to the case of a 7.5-kW four-pole induction motor under no-load conditions. The predicted core losses turn out to be about 20% lower than the measured ones, a fact which points to an appreciable contribution of the rotor cage Joule losses and to the detrimental role played in the material properties by the residual and applied stresses introduced by lamination punching and core assemblage. >

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.

Computational Algorithms for Induction-Motor Equivalent Circuit Parameter Determination—Part I: Resistances and Leakage Reactances

This paper deals with methods and algorithms for the estimation of induction-motor equivalent circuit parameters starting from the geometrical and electrical data generally available after an electromagnetic design. The main aim of this paper is to help the readers pass from the theoretical analysis to the numerical code suitable to be included in its own design software. For this reason, the step-by-step algorithms are included in this paper. Some of the methods are based on well-known approaches while the other ones are original. For the latter ones, a complete discussion of the theoretical analysis is reported and discussed. The first part deals with the stator- and rotor-resistance computations and the determination of the leakage inductances based on an original flux classification. Finally, the skewing slot effects on the machine parameters are provided. The comparison between computed and measured values confirms the accuracy of the proposed computational algorithms.

Iron losses in magnetic materials with six-step and PWM inverter supply (induction motors)

The energetic behavior of two samples of soft magnetic materials fed by inverters has been studied. The authors dealt with the increase of the iron losses due to a nonconventional voltage supply. Six-step and PWM (pulse width modulated) inverter output voltages have been selected as the excitation waveforms for the samples under test. Extensive experimental results of high-quality grain-oriented silicon steel and amorphous-alloy-wound core samples are presented. A detailed description of the testing procedure is shown. The results are quite informative and quantify the iron-loss increase with nonsinusoidal supply in comparison with the results obtained by the standard tests (sinusoidal supply and Epstein method). The comparison can give useful indications to electromagnetic-device designers about the derating factors for the different magnetic materials that have to be used in designing devices fed by static power sources. >

Digital field oriented control for dual three-phase induction motor drives

A direct rotor field oriented control (DRFOC) of a dual-three phase induction motor drive is described in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The stator windings are fed by a current controlled PWM (CRPWM) six-phase voltage source inverter (VSI). Three key issues are discussed: (1) the machine dynamic model is based on the vector space decomposition theory; (2) the PWM strategy uses the double zero-sequence injection modulation technique which gives good results with low computational and hardware requirements; and (3) to eliminate the inherent asymmetries of the drive power section, a new current control scheme is proposed. Experimental results are presented for a 10 kW dual three-phase induction motor drive prototype.

About The Effects Of Different Modulation Index On The Iron Losses In Soft Magnetic Materials Supplied By Pwm Inverter

The increase in iron-loss in soft magnetic materials due to the modulation depth in pulse width modulation (PWM) inverters is analyzed. In particular, the specific loss variations with different modulation indexes are measured, both in wound cores realized with high quality grain oriented magnetic material, and in induction motors. >