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This paper aims to tackle the general problem of increasing the performances of small permanent-magnet (PM) machines, through the use of bonded magnets instead of the more diffused ferrite magnets. In particular, the study is developed for a fractional-slot concentrated winding PM machines for automotive applications. Neodymium bonded magnets with different and unconventional resins are realized in the internal laboratories. The rotors with the different magnet technologies are experimentally characterized, and the experimental values are compared with the simulation ones. The obtained results allow to define the possible performance increment. Finally, this paper analyzes the possible improvement of the rotor magnetic circuit for a better exploitation of the bonded magnets, without altering the stator structure and the motor housing.

In the field of the renewable energy exploitation, it is often at disposal the possibility to obtain electric power along small waterways, with values between 10 and 150 kW (micro hydro). For such cases one of the most suitable solution is the one which provides as hydromechanics turbine a cochlea, which was used in the past mainly for water pumping plants; the described solution is often indicated as Archimedes Screw Generator (ASG). Such a technical solution is more and more frequently adopted for economical reasons, and present a very large application field, with the possibility to exploit situations otherwise not convenient; an ASG provides normally an induction generator directly connected to the mains. After a short description of the mentioned systems and of their working principle, the proposal of the adoption of a frequency converter drive between the induction generator and the mains is discussed under both the technical and economical point of view.

We compare two recent extensions of the answer set (stable model) semantics of logic programs. One of them, due to Lifschitz, Tang and Turner, allows the bodies and heads of rules to contain nested expressions. The other, due to Niemela and Simons, uses weight constraints. We show that there is a simple, modular translation from the language of weight constraints into the language of nested expressions that preserves the program's answer sets. Nested expressions can be eliminated from the result of this translation in favor of additional atoms. The translation makes it possible to compute answer sets for some programs with weight constraints using satisfiability solvers, and to prove the strong equivalence of programs with weight constraints using the logic of here-and there., Comment: To appear in Theory and Practice of Logic Programming

The principle of the universal field oriented (UFO) controller, operating in an arbitrary reference frame, is applied to a CRPWM inverter. Due to its high degree of generality,the UFO controller is compatible with rotor, stator, and air-gap flux field oriented control. The authors compare the stability regions and the steady state performance of these three types of controllers applied to the same machine. The rotor flux based controller has been selected as the basic reference. Digital simulation results are carried out to show that the performance of the complete UFO system, i.e., combined direct and indirect UFO, in a nonrotor flux based reference frame leads to a robust high performance drive with no dependency on machine parameters in steady state. >

Permanent magnets are frequently adopted in small brushless machines for automotive applications. Normally anisotropic ferrites, but some research on bonded magnets is being carried on. Several types of magnetization can be proposed, involving different levels of complexity in the magnetization process. In the paper a comparison between parallel and radial magnetization is described, taking into account on one side the major complexity of the radial process and on the other the small power derating of the parallel.

The adoption of Permanent Magnets in small brushless machines for automotive applications is becoming frequent. Some research on bonded magnets is being carried on to substitute the ferrites. In the paper the parallel and radial magnetizations are considered: the different process complexity levels are analyzed and the effects on the iron losses and the energetic performances are evaluated by means of a simulation analysis and its experimental validation.

In PM machines with curve shaped magnets the magnetization can have parallel or radial direction. The paper aims to evaluate the impact on the motor characteristics of magnetization direction, by means of simulation and experimental results. The proposed analysis is based on two different magnets technologies: one technology is industrially well established (anisotropic ferrite), while the other one is unconventional (rare-earth powder with phenolic resin bonded magnets). The case study is based on fractional horse power motor for electro-fan automotive applications: a concentrated windings fractional slots PM machine with external rotor.

In the paper the problems related to the adoption of cast copper squirrel cages are faced, and self-produced prototypes of small induction motor are analyzed. A theoretical analysis to get the expected values of the parameters, and their experimental comparison is conducted for aluminium and copper cages. Particular care is devoted to the casting of melted materials, and the obtained structures have been deeply studied by means of electronic microscope analysis obtaining interesting information about the motor parameter estimation.

The possibility to obtain water through the use of PV energy is analyzed; the approach provides the use of thermoelectric devices for bringing the ambient humidity under the dew temperature. A second prototype has been realized after an analysis performed through a suitable modelling activity. In order to improve the system a larger number of thermoelectric devices has been adopted. The obtained results are presented, and show that the choices adopted are in the right direction. Many information have been collected about the ambient conditions in which the system can be utilized. More work has still to be done to investigate the aspects concerning to surface properties, in particular for the so called "wettability", that is the possibility for the water to drop. The results are also very useful for carrying out information useful to implement a closed loop control choosing the best working point with respect to the environmental conditions.

Given two classes of logic programs, we may be interested in modular translations from one class into the other that are sound with respect to the answer set semantics. The main theorem of this paper characterizes the existence of such a translation in terms of strong equivalence. The theorem is used to study the expressiveness of several classes of programs, including the comparison of cardinality constraints with monotone cardinality atoms.

In the paper the iron loss change, due to the modulation technique, in soft magnetic materials, supplied by single phase PWM (Pulse Width Modulated) inverters, is analyzed. Experimental tests on non oriented, oriented and amorphous materials are reported. The specific iron losses vs the flux density, for the two modulation techniques which are practically used in industrial converters, are presented for each analysed material.

The activity carried out and presented in this paper deals with the opportunity of utilizing high quality magnetic materials, such as amorphous, microcristalline or cubic texture materials for the magnetic structure of medium size induction motors. In order to evaluate the benefits introduced by these materials for reducing the iron losses in a.c. motors, digital preliminary computations have been carried out considering the characteristic of such materials (Induction versus specific losses) and the obtained results for each solution have been compared. At the present, however, the; above mentioned materials are costly, not easy to handle and to assemble and therefore a practical solution with grain oriented steel in a crossed structure obtained alternating sheets with orthogonal grain orientation, in order to simulate the cubic texture material (i-oriented material) has been proposed. To verify the obtained theoretical results with the digital computations, a prototype of 20 Hp, 380 V, three pha...

The energetic behavior of several samples of soft magnetic materials excited by inverter voltage supplies has been analyzed. The iron losses increasing due to nonconventional voltage supply such as inverter-fed induction motors have been considered. Square wave and pulse-width-modulated (PWM) inverter voltages have been selected as the excitation waveforms for the samples under test. Extensive experimental results on medium- and high-quality grain oriented silicon steel and amorphous alloy wound cores are presented. A detailed description of the testing procedure is also reported. The results allow one to estimate the percentage of the iron losses increasing the nonsinusoidal supply. Comparison with the results obtained with sinusoidal supply gives useful indications to electromagnetic device designers about the derating factor to be used in devices fed by static power sources. >

In the last ten years, the new power electronic devices and the new control techniques have allowed to open new application fields for adjustable speed/torque electrical drives. Although the traditional dc drives keep still the market supremacy, the new ac drives have performance really attractive and some additional benefits due to the machine structure and to the maintenance costs. Usually, ac drives use induction or brushless motors and the power amplifiers are driven by variable voltage/frequency in order to obtain variable speed. The authors deal with induction motors fed by non conventional supplies at very high frequency. In order to evaluate the total motor losses and the single items, a test bench with a synchronous machine capable to work up to 2 kHz with sinusoidal output voltage has been set up. As a consequence, an induction motor equivalent circuit with parameters depending on the frequency has been proposed. Today, the empirical procedure is that to use for high frequency applicati...

This paper deals with a direct vector control induction motor drive, for electrical vehicle (EV) applications, that, in order to get high peak torque value over a wide frequency range, employ an induction motor with winding commutation. The stator windings are series connected at low speed and parallel connected at high speed, thus a constant voltage supply region of 1:n is reached from the point of view of the whole drive, while 1:(n/2) constant voltage supply region is reached from the point of view of the motor. The motor characteristics, both with series and parallel windings, are analyzed and experimentally verified. The winding changeover procedure, with direct field oriented control, is presented with experimental results.

In this paper, the authors deal with the effects of inverter characteristics on iron losses in induction motors fed by pulsewidth modulation (PWM) controlled power converters. Laboratory tests based on no-load input power measurements were carried out and in order to avoid the influence of mechanical losses and rotor copper losses, which are difficult to be measured or computed, a special test bench with an unconventional test device was employed. In particular, the influence of the following inverter parameters are considered: modulation index; modulation waveform; and switching frequency. Complete experimental results are presented and discussed.

In the paper change in iron losses due to the switching frequency in soft magnetic materials supplied by PWM inverter, is analyzed. Experimental tests with several samples of material and switching frequency from 1 kHz up to about 20 kHz, are reported. Values of iron losses vs switching frequency, for different values of the fundamental flux density and assigned modulation parameters, are presented for the materials investigated.

In the paper the authors deal with induction motors design criteria for electrical spindles fed Current Regulated PWM (CRPWM) inverters controlled by field oriented technique In particular, the flux weakening operation is the main feature considered. The design target concerns the possibility of having a wide flux weakening region avoiding or limiting, at the same time, to oversize the motor and the inverter. In the paper, the design stages are analyzed in detail and a 7.5 kW and a 22 kW spindles motors performance are shown and compared with the behaviour of similar standard design motors.

A complete analysis of induction-motor losses increasing due to the inverter supply is made. The study is based on the analysis of no-load and short-circuit tests performed with sinusoidal, square wave, and PWM (pulse width modulated) inverter supplies. For the PWM supply the effects of the modulation index on the iron losses are considered. Comparisons of experimental results are made to analyze the motors' energetic behavior. To verify the limits of the no-load and the short-circuit tests in the analysis of the loss increases due to inverter supply, a complete set of load tests have been performed using a test bench equipped with speed and torque transducers. >

In the paper the authors deal with induction motors used in electrical spindles and fed by high frequency inverters. The design problems of high frequency machines are analyzed by the electromagnetic, the mechanical and the thermal points of view. The possibility to use the classical relations adopted to calculate the equivalent circuit parameters for standard motors at 50 Hz is carried out and the results are compared with the experimental ones. A brief overview of problems related to the mechanical design (bearings, lubrication, shaft stiffness) and to the thermal design is reported. Finally, starting from both the simulation and the experimental results, some specific criteria for the electromagnetic design are well focused.

At present time, induction motors are widely supplied from several types of solid-state adjustable voltage-frequency controllers with a wide range of operating features. However, in any case, the motor has to be derated for the harmonic effects due to the non-sinusoidal nature of the supply voltage. The authors propose a simple method based on the no-load and short circuit test in order to get the useful machine parameters to adopt in equivalent circuit model for the losses evaluation. Complete experimental results are reported and the comparison between six-step and sinusoidal supplies are summarized.

The energetic behavior of several samples od soft magnetic materials excited by inverter have been analyzed. The authors dealt with the iron loss increase due to the nonconventional voltage supply such as inverter-fed induction motors. Square-wave and PWM inverter voltages have been selected as the excitation waveforms for the samples under test. Extensive experimental results on good-quality nonoriented silicon steel, medium and high-quality grain-oriented silicon steel, and amorphous alloy would cores are presented. Furthermore, a detailed description of the testing procedure is reported. The results allow one to estimate the percentage of the iron loss increase with the nonsinusoidal supply. The comparison with the results obtained with the sinusoidal supply gives useful indications to the electromagnetic device designers about the «derating factor» to be used for devices fed by static power sources

In the paper an investigation technique is described useful for studying steady state and dynamic performances of convertor-fed AC drives, by way of hybrid computer and with the opportunity of directly supplying the machine model with the convertor's voltage waveforms. Starting from some general considerations concerning the possibility of describing a quite general supply voltage system by way of an opportune space vector, it is pointed out that the opportune knowledge of such vector in module and position is sufficient to define the input voltages valid for any two-phase equivalent rotating machine model. It is shown that for an inverter-fed machine the module and argument space vector determination and the input model voltages are deducible from the real inverter voltages, for any reference frame, with an opportune hybrid technique. A natural hybrid simulation technique is deducible. Some examples are reported concerning the method application to the case of an inverter-fed variable speed synchronous drive when different modulation techniques are utilized.