Franco Leonardi

Consequent-pole permanent-magnet machine with extended field-weakening capability

In this paper a description and operating principles of a consequent-pole permanent-magnet machine are presented. In addition, a sizing analysis, finite-element analysis, and experimental results for a prototype machine are addressed. Due to its particular configuration, this machine allows for a wide range of control of the air-gap flux with minimum field ampere-turn requirements and without brushes or slip rings. Two components of the field flux are produced. One, which is almost constant, is produced by the permanent magnet located on the rotor surface. The other, which is variable, is produced by a field winding positioned circumferentially in the center of the stator. These two flux components converge in the air gap. The excitation level of the machine is manipulated by controlling the DC field current. Three-dimensional finite-element analysis and experimental results demonstrate that it is possible to vary the flux over a wide range to keep the terminal voltage constant as the speed increases. A 3 kW 1000-3000 r/min eight-pole and 32 VAC generator using this configuration is tested to verify the flux control capability of this structure.

A comparison of power density for axial flux machines based on general purpose sizing equations

Based on the concept of the converter fed machine (CFM), an optimal machine design can be considered as the best match of the machine topology, the power electronic converter and the performance specification. To compare power production potential of axial flux machines with various topologies, different waveforms of back EMF and current, general purpose sizing and power density equations for such machines are needed. In this paper, a general approach is presented to develop and to interpret these equations. Sample applications of the sizing and power density equations are the axial flux toroidal permanent magnet utilized to compare the axial flux toroidal permanent magnet (AFTPM) machine and the axial flux two-stator permanent magnet (AF2SPM) machine.

Starter-alternator for hybrid electric vehicle: comparison of induction and variable reluctance machines and drives

This paper presents the experimental results of using induction and variable reluctance machines as the starter-alternator in a hybrid electric vehicle. The frame sizes of these machines are dictated by transient engine cranking loads. Therefore, in their design, the machines are assumed to be in deep magnetic saturation and the resultant thermally constrained electric loadings are predicted from the calculated electromagnetic air gap surface traction. This design approach results in machine performance predictions in close agreement with prototype measured results for the induction machine. Similar conditions hold for the variable reluctance machine. Experimental results show that both machines require substantial inverter kVA rating to meet magnetizing and overdrive requirements. The series configured induction motor developed 300 Nm of torque at 250 RPM with 115 A/sub RMS/ phase current from the inverter drive whereas in its parallel connection it required nearly 240 A/sub RMS/. The same held for the variable reluctance machine.

Design considerations and test results for a doubly salient PM motor with flux control

A prototype of a new permanent magnet machine is presented in this paper, and its experimental tests fully documented. The motor incorporates the benefits of PM machines, namely the high power density and efficiency, overcoming some of its major disadvantages, such as high cost and limited speed range. Low cost is achieved due to the utilization of simple ceramic PM (ferrite) magnets but the unique flux concentrating magnetic structure allows for the maintenance of a high air gap flux density and consequently high power density. All the active material (coils and magnets) are placed in the stator, so that the rotor structure is very simple like that of the switched reluctance machine (SRM). An extended speed range is obtained thanks to a field coil that can be used to weaken the PM field at high speed or to boost the field at low speed.

Consequent pole permanent magnet machine with field weakening capability

The electromagnetic design procedure and laboratory test results are presented in this paper for a consequent pole permanent machine (CPPM) with field weakening capability. Due to its particular configuration, the CPPM allows one to easily control the air-gap flux in a wide range so that the speed range of the machine is increased. Two components of the flux: one-almost constant-coming from the permanent magnet located in the rotor surface of the machine, and the other-variable-coming from a field winding located in the middle of the stator, converge in the air-gap, characterizing the level of excitation of the machine. Preliminary 3D finite element analysis results establish that with 10% of the phase MMF, it is possible to vary the flux in a wide range. A 3 kW, 1000 to 3000 RPM velocity range, 8 pole and 32 AC volt generator using this configuration is tested to verify the flux control capability of this structure.

Integrated starter generator based HEVs: a comparison between low and high voltage systems

The purpose of this project has been to investigate the feasibility of 42 V mild hybrid electric versions of relatively large vehicles, like SUVs and light trucks. More specifically, this report focuses on the consequences on the integrated starter generator (ISG) performance brought by a reduction in voltage from the high (300 V) level of conventional hybrid electric vehicles to the new proposed standard (42 V). The discussion on ISG performance is substantiated by experimental tests conducted on two ISG prototypes, wired for 42 V operation, and the comparison with data from a 300 V version of the same machine. Inverter, battery and wiring limitations are discussed to give the specific motor performance broader significance. Safety considerations that play a significant role in the voltage selection decision-making process are not addressed in this paper. These 42 V inverters and motors are laboratory prototypes, not targeted to any specific vehicle.

A design procedure for a PM machine with extended field weakening capability

A design procedure for the consequent pole permanent magnet (CPPM) machine is presented. Due to its double excitation nature (PM and field winding) and inherent three-dimensional flux distribution, an appropriate set of equations must be derived to model its magnetic structure. For practical operating conditions, radial, axial and tangential flux components are present. Therefore a convenient representation of the magnetic sources and their magnetic paths are necessary. For this purpose, a simplified reluctance-based equivalent circuit for 2-poles is developed to capture the main features of the machine. Approximated expressions for the airgap flux and the airgap flux density are derived. In these expressions the constant contribution of the PM and the variable flux provided by the field winding are taken into account. In addition, a formulation to calculate AC and DC slot geometry, copper and iron losses estimation and output power are developed. Finally, an optimization procedure is outlined based on maximum material utilization under current and magnetic loading constraints.

Soft-switched PWM converter with inductive DC filter

This paper presents a soft-switched AC/DC power converter structure, useful for current-fed inverters and forced commutated PWM rectifiers with an inductive load. Typical applications are high-power AC motor drives, magnet power supplies and active power filters with inductive energy storage. As compared to hard switched converters, the proposed solution calls for some increase of the circuit complexity, but provides improved input and output performances due to the higher switching frequency. Further improvements are ensured by proper control of the commutation process. Actual power converter capabilities are demonstrated by experimental results.<<ETX>>

Nonlinear model and momentary performance capability of a cage rotor induction machine used as an automotive combined starter-alternator

This paper presents the calculated and the measured performance capability of a cage rotor induction machine used as a direct connected, crankshaft speed, combined starter-alternator for an automotive diesel engine in an experimental hybrid electric vehicle. The calculated results are based on a nonlinear equivalent circuit model of the machine which considers saturation in the stator and rotor magnetizing flux paths. The development details of this model are given as well as several sets of calculation results for the induction machine previously described. Finally, measured maximum performance results for the test machine are presented and compared with model based calculated results for the same operating conditions of speed, terminal voltage and current.

Advancements in Tools and Methods for the Design of Permanent Magnet Integrated Starter Alternators

This paper describe the simulation tools utilized to design a permanent magnet starter alternator. From the more common steady state finite element analysis to short circuit simulations, to the integration of time domain (transient) FEA into complete electromechanical system simulation, a whole array of simulations based on Ansoft software is presented. Experimental results collected on a Ford prototype are presented and compared with the simulation results. The outcome is a user assessment of the state of the art integrated software solution for the design and simulation of electrical machines