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The paper concerns the dimensioning of “zero” emission power-train architecture of an urban electrical mini-bus fed by a hybrid power unit based on hydrogen fuel-cells and a flywheel energy storage system. Performance numerical analyses are carried out by using fuel-cell experimental data and by modeling the mini-bus running along a L'Aquila city (Italy) urban drive cycle, experimentally tested in real traffic conditions. The results are presented and discussed also in terms of hydrogen consumption

Coaxial magnetic gears with permanent magnets have a very simple structure and performance comparable to that of mechanical gears. The paper describes an analytical simplified approach for the analysis and design procedure. The mathematical model is one-dimensional: only the variation of electromagnetic quantities as function of angular position is considered and the permanent magnets are modeled by means of constant currents located at their edges. The resulting magnetomotive force generated by the two rotors is modulated by the distribution of the variable permeance due to the stationary ferromagnetic pole-pieces. The influence of the ratio between the width of the magnet and the pole pitch on the air-gap flux density is also considered. The analytical results are verified by means of a FEM considering the power losses and the torque ripple in order to obtain minimum volumes of the magnets and high torque densities.

The behavior of a magnetic gear which employs rare earth magnets is analyzed; the magnetic gear allows the power to be transmitted by transforming speed and torque. An analytical simplified approach for the analysis of the considered magnetic gear is used in this paper. The approach can be suitable for design aims. The mathematical model is one-dimensional: only the variation of electromagnetic quantities as function of angular position is considered, the permanent magnets are modeled by means of constant currents located at their edges. The resulting magnetomotive force generated by two rotors is modulated by the distribution of the variable permeance due to the difference of the magnetic permeability between the air of the slots and the magnetic material of the pole-pieces. The analytical results are verified by means of a finite element method.

The concept of reliability and safety is the foundation of every kind of system used in the aeronautical and aerospace applications and diagnostics contributes significantly to this goal. In the literature there are several methods (thermal, on test bench, etc...) that perform diagnostics of electric motors both in the production phase and in the test phase in the sample. These methods tend to test the electrical and mechanical parameters. Using a frequency analysis technique SFRA (Sweep Frequency Response Analysis), it's possible to have a "signature" in frequency of the electric motor. The reference standard IEC 60076-18 (still in the process of study and development), which regulates the diagnosis through SFRA technique for power transformers, does not contain any guidelines on the interpretation of the results. Almost all of the existing researches are addressed on oil insulated transformers. The research aims to investigate the measurement methodologies for the characterization of the stators and for the faults detection caused by the manufacturing process.

In this paper there will be presented basically two main subjects: the development procedure of a particular fault-adaptive multiphase sensorless strategy, based on Neural techniques, and the design issues involved by the fault-detection and isolation stages included in the proposed sensorless method. The proposed strategy is particularly suitable to be applied for the implementation of a cheap additional redundancy feature in order to augment the still existing fault-tolerant capabilities of some multiphase drives employed in safety-critical applications. In particular this unusual sensorless strategy is based on a back-EMF observer plus a proper set of coordinate transformations and possesses reconfiguration capabilities with respect to the occurrence of some certain classes of phase faults, gained through the use of a specific fault-adaptation mechanism. At first, the developmental steps of the fault-adaptive strategy will be described in detail after a preliminary motor modeling section, while, in a second step, the design issues linked with the fault-detection and remedial stages will be deeper investigated. Detailed simulation results will be shown at the end to validate the fault-adaptive properties of the proposed multiphase sensorless strategy.

This paper presents the design and application of hybrid power train for city bus with zero greenhouse emissions and high work efficiency. The vehicle system configuration is based on two separately electric driven wheels powered by an hybrid unit composed by a hydrogen fuel cell and flywheel energy storage system. Numerical models were built to simulate the powertrain components and to downsize the fuel cell power satisfying the transient loads by the flywheel energy storage device. A simulation of the city bus (15 passengers of carrying capacity) was run over the European urban standard drive cycle in order to size the powertrain components. Finally the hydrogen production by water electrolysis was considered and consumption and CO2 emission per bus were estimated.

In this paper a measurement system for the characterization of electrical generators for the energy recovery from EMAs installed on airplanes is presented. The measurement system uses both mechanical transducers (position/speed/ - force) for the measure of mechanical power and electrical transducers (current - voltage) for the measure of electrical power. A test bench has been developed for the characterization and for the efficiency evaluation of the system for different values of speed, screw pitch and current supplied by the generator.

The performance and the reliability of the power transformers are critical parameters for the electric power production, transmission and utilization. In the last years diagnostic techniques have been widely utilized to improve the safety and to reduce the maintenance costs of power transformers. The Bticino group had recently acquired the plant in Castellalto, Italy, from the Zucchini EMM, that is devoted to the design and the production of cast-resin MV/LV power transformers; a research project concerning the application of the SFRA (Sweep Frequency Response Analysis) to Bticino transformers has been started as a cooperation with the Department of Electrical and Information Engineering of the University of L'Aquila, with the main aim of creating a database for the fault analysis. This paper presents the developed measurement system and the first experimental results that have been obtained by applying the SFRA to transformers of different rated power.

In the paper stator faults are analyzed by means of a procedure ba­ sed on the space-vector theory. The used approach, due to Stepina, allows to consider separately each conductor of every single slot and therefore to take easily into account the winding dissymmetry. The interactions among the different harmonic fields are studied by starting from the topological structure of windings and the harmonic ana­ lysis of the currents and of torque is carried out. The method is' tested to numerical computations of steady-state cur­ rents for an induction machine with different positions of stator short­ circuits. Finally the procedure is validated by using an experimental squirrel cage machine, having stator windings constructed so as to realize diffe­ rent short-circuits.

Today the application of PEM (Polymer Electrolyte Membrane) fuel cell stack in the automotive field is a topic on central interest. Unfortunately, a PEM fuel cell stack cannot directly supply variable speed drives because of their non-linear behaviour in dynamic conditions. This paper is mostly concerned with the sizing of the supply system, PEM fuel cell-supercapacitor-battery pack, of an electric vehicle, based on the urban/suburban drive cycle NEDC (New European Driving Cycle). The average required power is used to design the fuel cell stack by imposing a preset operating point; the battery capacity is chosen in order to satisfy the constrain on the minimum value of the state of charge during the cycle; finally, the supercapacitor is determined by imposing the current sharing between battery and supercapacitor in transient condition.

The electrical voltage fluctuations and their negative effects on industrial and domestic apparatuses represent one of the most interesting topics of research in the field of Power Quality. Early studies investigated the behavior of different types of lamps in presence of voltage amplitude modulations and the design of light flicker meters. In realistic conditions, the observed voltage fluctuations have usually more complex shapes, that are quite different from the rectangular or sinusoidal amplitude modulations defined in the IEC standard. In this paper we are mostly concerned with the development of an innovative testing system for the performance evaluation of electrical machines under realistic voltage fluctuations, whose parameters are suggested by international organizations. The desired amplitude fluctuations are obtained by introducing time variable current absorption in an ad hoc power electronic apparatus which is parallel connected to the electrical loads, as it frequently occurs in the real working conditions. A PC, hosting a DAQ board and an IEEE 488 board, performs the data acquisition of electrical and mechanical quantities and controls the firing unit. The proposed system can be adopted for testing electrical motors and transformers, as well as adjustable speed drives, by reproducing a wide set of voltage fluctuation shapes for long duration testing. The proposed technique can be also adopted for the generation of transitory voltage imbalances.

Today the application of PEM (Polymer Electrolyte Membrane) fuel cell stack in the automotive field is a topic on central interest. Unfortunately, a PEM fuel cell stacks cannot directly supply variable speed drives because of their non-linear behaviour in dynamic conditions. This paper is mostly concerned with the performance evaluation of the PEM fuel cell – supercapacitor system during repetitions of current step variations; in those cases, the supercapacitors cannot be completely recharged before supplying the load in the next dynamic, and the fuel cell stack can be overloaded. We propose the introduction of lithium battery packs and of a DC/DC converter. The obtained results shows that with the proposed configuration, the size of supercapacitors can be significantly reduced, reducing the stress on the battery pack without losses of performance. That will be useful in the design of the control strategy of variable speed drives supplied by the proposed system.

Today the application of PEM (Polymer Electrolyte Membrane) fuel cell stack in the automotive field is a topic on central interest. Unfortunately, a PEM fuel cell stack cannot directly supply variable speed drives because of their non-linear behaviour in dynamic conditions. This paper is mostly concerned with the performance evaluation of the PEM fuel cell - supercapacitor system during repetitions of current step variations; in those cases, the supercapacitors cannot be completely recharged before supplying the load in the next dynamic, and the fuel cell stack can be overloaded. We propose the introduction of lithium battery packs and of a DC/DC converter. The obtained results show that with the proposed configuration. That will be useful in the design of the control strategy of variable speed drives supplied by the proposed system.

The measurement of both electric power and energy, especially in non sinusoidal conditions, is today a still open research problem in the metrology community. Harmonic distortion, noise, transients, over-voltages and voltage dips have increased the difficulty in achieving accurate measurements. Besides, many of non-active power component definitions that have been proposed cannot be implemented in the traditional electro-mechanical or solid-state meters. This paper goes on to investigate about the possibility to process the instantaneous power signal when harmonics are likely to occur. The intent is not to resolve theoretical controversies, but instead to investigate about the possibility to easily process the instantaneous power signal in order to reduce the meter cost. Specifically, in the paper the measurement of a power parameter A*, which is sensible to the harmonic interferences with the fundamental component of the instantaneous power, is proposed. This parameter can be adopted for the development of a simplified single-phase electric energy meter able to operate in non sinusoidal conditions and to supply distortion information. Additionally, some simulation results are proposed, to confirm the applicability of the proposed measurement technique.

Speaking of linear machines, the waveform of the electromagnetic quantities is not sinusoidal, i.e. currents are not sinusoidal in time and magnetic field distributions are not sinusoidal in space, because of the asymmetry of both iron magnetic structure and windings. The performance of linear machines can be studied by means of one-dimensional or two- dimensional mathematical models. In both cases reliable results can be achieved only if the actual shape, or the harmonic content, of the electromagnetic quantities are considered and the models are able to handle space and time harmonics and their interaction. That increases the complexity of the linear machine model that must be used to obtain reliable results. Such models are very good tools for design purpose but can not be used in some applications, e.g. real time machine control, that require very short computation times. So a compromise between complexity and accuracy of the model must be achieved. That can be done by reducing the number of considered space harmonics and/or taking into account only the main space harmonics in order to simplify the model without significantly reducing the accuracy on the machine performance.

The adoption of fuel cells for industrial applications, transportations and home power generation has widely increased during recent years. The performance evaluation of a fuel cell system requires both static and dynamic model, especially for the automotive applications which involve step variations of electric load. Besides, current step variations abruptly change the fuel cell voltage causing a non-linear behavior (under-voltages). In this case, a parallel supercapacitor becomes an important element to provide energy during transients. Fuel cell dynamic models presented in literature adopt chemical-physic-electrical parameters that are not usually provided by factories. In this paper, we deal with the implementation of dynamic fuel cell model during step current transients from the electrical point of view [1]. The FC model is used to compute the minimum capacitance of the supercapacitor needed to obtain gradual variations of fuel cell terminal voltage from initial steady state to final steady state values.

The adoption of fuel cells for industrial applications, transportations and home power generation has widely increased during recent years. The performance evaluation of a fuel cell system requires both static and dynamic model, especially for the automotive applications which involve step variations of electric load. Besides, current step variations abruptly change the fuel cell voltage causing a non-linear behavior. In this case, a parallel supercapacitor becomes an important element to provide energy during transients. Fuel cell dynamic models presented in literature adopt chemical-physic-electrical parameters that are not usually provided by factories. In this paper, we concern the implementation of dynamic fuel cell model during step current transients from the electrical point of view. The model is used to evaluate the transient performance of the whole system, i.e. fuel cell and supercapacitor, by means of simulation software SIMULINK. Simulation results show gradual variations of fuel cell terminal voltage from initial steady state to final steady state values when a supercapacitor is parallel connected.

The paper deals with a voltage feeding algorithm for a linear induction drive that takes into account the end-effect and the actual distribution of the windings. It realises a decoupled control of the thrust and of the magnetising condition of the machine. In order to take into account the end effect, different space harmonics of the flux density distribution must be considered. For this reason a suitable state observer has been adopted. The considered observer is arranged as a diagonal system of linear differential equations, therefore it gives a fast evaluation of the estimated quantities. The reference currents computed according to the field oriented strategy, are used by the feeding algorithm in order to evaluate, at each sampling interval, the reference vector of the supply voltage. This vector is adequately modulated by means of the vector PWM.

The voltage fluctuations of the electrical power supply can generate many undesirable effects on both industrial and domestic apparatuses. The aim of this paper is the evaluation of the effects of the low-frequency voltage amplitude modulation on induction motors. An experimental analysis has been applied to a three phase, 7.5 kW induction motor with the adoption of an ad hoc system for the EMC low-frequency immunity testing. The experimental results show that a few percent amplitude modulations can involve a critical behavior in terms of torque. As for the light flicker effect measurement, a statistical approach can be adopted for the evaluation of the torque fluctuation.

A modified one-dimensional mathematical model based on the space-vectors theory is used to analyse the performance of permanent magnet linear synchronous motors with starting and dumping sheet. The end-effects are taken into account by assuming that the length of the iron core is infinite and the length of the armature winding is finite. The resulting differential equation set allows both steady state and transient operations to be analysed. The model is used to analyse the transient performance (starting and load step) of two low power motors

In this paper, a new control technique for low-harmonic content and unity-power factor active rectifiers is proposed. The common voltage-based control is replaced by the novel capacitor energy-based control, requiring only three sensors and the new modulation technique (PMM). Simulation and experimental results show the effectiveness of the proposed system and in particular its very low harmonic pollution of the main currents.

In this paper a new control technique for active rectifiers is proposed. The traditional voltage-based control is replaced by a novel capacitor-energy-based control. A new modulation technique (PMM) is developed. Two different implementations are presented: the former uses two current sensors and one voltage sensor, the latter only a dc-bus voltage sensor. The proposed method has been successfully tested by means of simulations and experiments demonstrating, in both configurations, its ability to guarantee output voltage regulation, unity power factor and low harmonic content.

A mathematical model based on space-vector theory is used to analyze inverter-fed induction motors faults. Inverter supply faults like an open phase fault, the failure of a transistor to switch on, the delay in a branch command, or the stand of the branch command are analyzed. These events introduce an asymmetry in the supply voltages, in the current values, and in the spatial field distribution. A detailed investigation of typical inverter supply failures is presented and discussed in order to identify remedial strategies. >

In this paper a new low cost induction motor drive for high performance applications is proposed. The system employs only one microcontroller and achieves both torque and speed regulation. The control system is based on the passivity theory and computes the reference torque, rotor angle and speed according to a reference speed signal, without any information about rotor quantities and load torque. In order to demonstrate the effectiveness of the proposed system, experimental results and discussion are presented.

The detection of anomalous operating conditions of electrical machines at an early stage allows maintenance to be scheduled in order to increase the machine operating life and to reduce the repair cost. The synthesis of the fault conditions is a hard task, therefore the problem is generally examined by means of analysis procedures. To this purpose the analysis of anomalous operations of asynchronous and synchronous machines has been developed by many authors in order to study-the tolerance of the drive to the faults and to find the correlation between faults and anomalous variables. This correlation constitutes the basis of a diagnostic system to detect faults. The presence of an electrical asymmetry in the stator windings of the synchronous and asynchronous machines gives rise to space and time deformations in the air-gap induction and time harmonic components in the stator and rotor currents. The current harmonic content is different for the two machines also because of the different physical structure (the healthy rotor is symmetric in the asynchronous machine and asymmetric in the synchronous one), but the interactions between different space and time harmonics are similar in both cases. In this paper a mathematical model based on the space-vectors theory is used to study AC machines with stator faults. Such an approach allows an easy handling of the mutual interactions between the different harmonic fields. Finally, numerical computations of the harmonic currents and of the performances of two faulted synchronous and asynchronous machines are compared. >

A novel adaptive current pulsewidth modulated technique (PWM) is proposed and analyzed in this paper. With this technique both the hysteresis bandwidth is adapted and the near optimal inverter gating signals are determined according to fuzzy logic rules. The main features of this controller are: reduced frequency fluctuations and nearly optimum switching pattern choice. In this paper both principles of operation and some simulations results are presented and discussed.

Torque ripple in inverter fed induction motors is a critical problem if high switching frequency cannot be achieved because of the drive power rating or when switching losses must be kept low. In that case, the torque ripple minimisation should be one of the goals of the control strategies. The paper presents a PWM technique that can be used to minimise the steady state torque ripple of variable speed induction motor drives when high dynamic is not required, i.e. scalar control. The torque ripple is expressed as function of the DC bus voltage and of the notches introduced in the output voltage waveform of a VSI and it is minimised by finding out the optimum dc voltage value and modulation pattern. The control of the DC voltage does not increase the cost of the whole drive when a PWM AC/DC converter is already used to reduce the current harmonics and to improve the power factor. The proposed PWM strategy is compared with the space vector modulation and experimental results are reported and examined.

A new linear induction drive is presented and analysed. The drive is used as traction unit as well as battery charger on-board of electrical vehicles intended for specific service typologies. The presence of a wound secondary and of a long stator gives the linear induction motor drive the potentiality to be adopted as traction motor and battery recharger on board. This opportunity can be exploited by means of a suitable power converter on-board that allows the regulation of both speed and battery current. The analysis of such converter in different operating conditions linked with the wound secondary of the linear motor is presented and some particular cases are discussed.

This paper deals with the passivity-based control of induction motors. This nonlinear control method is considered here mainly from the experimental point of view. Two different configurations have been considered: a current-regulated pulsewidth modulation inverter with hysteresis controllers and a space-vector-modulated voltage-source inverter. Experimental results show that both schemes give precise, fast, and robust torque and speed tracking in the full speed range. The first configuration is more attractive due to its better transient response and reduced complexity.

This paper deals with a comparison among some current controlled PWM techniques for induction motor drives working under different load conditions and sampling frequencies. Nonoptimal, optimal, pre-optimized and, more in detail, three fuzzy logic-based controllers are considered. The analysis is carried out by means of simulations done by using Simulink/sup (R)/. A novel useful switching frequency tool is also presented and discussed.

In this paper the on-line identification of the electrical parameters of induction motors is investigated. After a description of the main problems and of the adopted method, some experimental results are presented and discussed.

A high efficiency neural implementation of a current control scheme for a three-phase VSI-PWM inverter is analysed. The new structure offers the advantage of a control which is independent of the load type and is only based upon an equivalent circuit of the real load consisting for each phase of a resistor, an inductor and a voltage source (R, L, e). The scheme is based on a predictive current neural controller using a state-space observer. The observer is able to reconstruct the non-inductive voltage of the load (Ri+e) on the basis of the currents and voltages across the load, while a PWM control signal generator produces the switching pattern for the transistors in the inverter. The inductance L is identified online by a neuronal inductance estimator which ensures optimal current control across the load.

The energy-based approach, also known as "passivity based", is becoming a popular nonlinear control method allowing precise and stable control of the induction motor and more in general of AC motors. Its main features are: simple formulation; the actual possibility of the use of inexpensive microprocessors for its implementation; its global stability in the whole operating range including zero speed region; satisfactory tracking capabilities of position, speed, torque and flux; and high robustness in case of parameter variations. This paper, after a short theoretical background presents and discusses several experimental results.

The general mathematical model of asynchronous machines is represented by means of a non linear either 5-th or 6-th order system of differential equations, according to the shaft elasticity is either taken into account or not. These models are sometimes linearized to study particular phaenomena, as for example forced oscillations due to alternative compressors or pumps. The paper investigates on the validity limits of the linearized model and the study tries to predict when their results can be of practical interest for engineering purposes. Therefore, a comparative analysis was made for different motor parameters and for different alternative load torque with reference to the general mathematical model and to the linearized one. On the basis of the 6-th order model, the Authors report the main results obtained into the field and show the validity limits of the linearized mathematical model.

In this paper an IM drive with a passivity-based, torque speed control and a fuzzy CC-PWM is proposed. The torque-speed nonlinear controller offers good transient and steady state performance over an extended operating range. The fuzzy logic based current-controlled pulsewidth modulator improves drive performance because of the reduced harmonic content, the nearly constant switching frequency and the optimum switching sequences; furthermore its behavior can be easily modified in order to include fault tolerance capability.

The problem of reducing electromagnetic interferences (EMI) in industrial and commercial systems is today an issue of international interest, especially in the European Free Trade Area. Electromagnetic compatibility (EMC) tests are time intensive and require the use of expensive test facilities and measurement equipment. The availability of low-cost in-house testing will allow the designer to analyse EMI problems during the prototype implementation, reducing the time to market. In this paper a low-cost EMC precompliance test station is proposed. It is based on a general purpose VXI digital instrument. It allows the precertification testing of conducted emissions in the frequency ranges DC-9 kHz and 9 kHz-30 MHz to be performed without using an expensive EMI receiver. The data processing is carried out in order to satisfy the CISPR 16 measurement procedures. The comparison between the proposed system and a standard EMI receiver has been performed and the characterization results are given.

This paper proposes a sensorless technique capable to reconstruct the input currents of a three-phase active rectifier using only a DC-link voltage sensor and a PLL circuit in the line side. It has been developed in order to design a low cost three-phase active rectifier and it is based on the novel PMM (power matching modulation) technique and on the control of the capacitor energy. The proposed system guarantees close-to-unity power factor, excellent output voltage regulation, limited current harmonic content, high efficiency and low cost.

This paper deals with the problem of tile characterization of linear induction motors (LIMs) and specifically with the on-line measurement of some quantities, such as thrust, current density in the sheet and air-gap flux. In this paper we propose a solution based on the indirect estimation of these quantities, starting from the measurement of the supply voltages. The proposed measurement system can be also advantageously adopted to solve the problem of the dynamical response of the transducers, such as those adopted for the measurement of the strain. >

Gijón (Spain)