Peter Thelin

Determination of d and q reactances of permanent-magnet synchronous motors without measurements of the rotor position

The interest in permanent-magnet synchronous motors (PMSMs) is increasing in a wide area of applications. Since most PMSMs will operate without a shaft sensor in the future, valuable information for experimental determination of machine parameters will be lost. In this paper, therefore, a method is presented where the induced EMF and the d-axis reactance are determined in a no-load test and the q-axis reactance is determined in a load test. The load angle /spl delta/ is determined from the load test by means of a new analytical method. In this way, no separate measurement of the load angle is required. The method is especially suitable for line-start PMSMs which normally operate with negative d-axis current and, therefore, are not saturated in the d-axis flux paths. Moreover, the method is very simple to carry out for any laboratory technician, since the only tests that have to be made are standard tests which are made on standard induction motors on a regular basis.

Research on the Cooling System of a 4QT Prototype Machine Used for HEV

A four-quadrant transducer (4QT) is a hybrid electric vehicle (HEV) power train concept. It can enable the internal combustion engine (ICE) to operate at optimum efficiency during all driving conditions with both torque and speed control. The thermal property is a vital problem due to its special configuration. Aiming to find the hot spot and investigate the cooling system of the 4QT, the thermal field is calculated with finite-element method (FEM). The simulation is validated by the comparisons with the experiment. The influences of the forced-air cooling, water cooling, and the distribution of the cooling channels on the cooling performance are discussed, respectively. The stator air ducts are removed, and 12 water channels evenly distributed in the housing are employed. The design principle of the cooling system is presented. The speed impacts of air flow and water flow are discussed and provide a parameter reference for choosing the forced-air cooling fan and water pump properly.

Use of transverse-flux machines in a free-piston generator

This paper investigates the use of transverse-flux machines (TFMs) in a free-piston generator, an integration of a combustion engine and a linear electrical machine. For hybrid vehicles (the intended application), this integrated device has benefits in efficiency, emissions, reliability, etc. Conventional TFMs are dimensioned and their shortcomings illustrated. Several surface-mounted TFM designs are suggested. These designs, initially believed to be promising, are later discovered to be poor during the three-dimensional finite-element method (3-D FEM) analysis. These designs suffered from a large axial pole-to-pole armature-flux leakage in the stator. This problem is solved in the proposed buried-magnets TFM variants, for which patents have been filed as well. A 5-kW proof-of-concept prototype of one such design is dimensioned that allowed the near fulfilment of 3-D FEM verifiable system demands. One phase of this dimensioned three-phase prototype is built. Measurements on this prototype showed that the use of short pole lengths in the machine had led to manufacturing defects. Nevertheless, the electromagnetic viability of the design could still be approximately verified.

Research on a Tubular Longitudinal Flux PM Linear Generator Used for Free-Piston Energy Converter

The free-piston energy converter (FPEC) is used for a series hybrid electric vehicle scheme, which may have the advantages of high efficiency, compact structure, and reliable operation. The linear generator is an important part in the FPEC, and a tubular longitudinal flux permanent-magnet (PM) linear generator scheme is investigated in this paper. The electromagnetic and thermal properties of the generator are analyzed with commercial software Flux 2D. The generator is optimized from the aspects of material selection and structure optimization. Rare-earth PM material VACODYM 655HR is selected for the permanent magnets, and low-performance low-loss material M235-35A is chosen for the stator lamination. The pole number and machine size are optimized, and the optimum scheme with efficiency of 0.935 and specific power of 1.49 kW/kg is obtained, which meets the requirements of FPEC application

Research on the Parameters and Performances of a 4QT Prototype Machine Used for HEV

A four-quadrant transducer (4QT) is a hybrid electric vehicle (HEV) power train concept. In this paper, a 4QT prototype machine, which is integrated radially by two permanent-magnet synchronous machines [one stator machine (SM) and one double-rotor machine (DRM)], is investigated. The inductances of both the SM and the DRM are calculated with a phasor-diagram based 2-D finite-element method (FEM), which can include the effects of eddy current and saturation. The calculated results show that the effect of eddy current can be neglected for both the SM and DRM inductances, and the cross-magnetization influence on the SM inductances can be ignored but is remarkable on the DRM inductances. The magnetic coupling between the SM and the DRM is calculated with 2-D FEM, and it is found that little magnetic coupling exists, so the SM and the DRM can be controlled independently, which is a very good feature for HEV applications. With the effect of skewed slots considered, the torque and no-load line-to-line back electromotive force (BEMF) curves of the SM and the DRM are calculated with multislice 2-D time-stepping FEM. The average torques of the SM and the DRM both meet the requirements, and the torque ripples are quite low. The calculated and tested no-load line-to-line BEMF curves of the SM and the DRM are both in good agreements. Both the BEMF curves of the SM and the DRM are somewhat similar to sinusoidal ones, which proves a good design of the magnetic structure

Comparison between different ways to calculate the induced no-load voltage of PM synchronous motors using finite element methods

In this paper two different ways of calculating the induced no-load voltage of permanent magnet synchronous motors (PMSM), by the use of a finite element method (FEM) program, have been compared. Neither of the two calculation methods require a FEM software package that can perform time-stepping. The number of required static FEM-calculations is limited to just a few, or even to one. The calculations are performed on five motor geometries. The results are compared to values obtained from time-stepping FEM-calculations, and to the measured induced no-load voltages of the five manufactured prototype motors. It can be seen that the least time-consuming method is accurate enough in most of these cases. The exceptions, in this study, are when there are relatively large airgaps and/or when the stator teeth are saturated.

Investigation of the winding current distribution in a 4-quadrant-transducer prototype machine

The 4-quadrant energy transducer (4QT) is a solution to realize both the torque and speed control of the internal combustion engine (ICE) for hybrid electric vehicles. Since the base frequency of the prototype 4QT is much higher than the industrial one, the effect of eddy current on winding current distribution is considered in this paper. A two-dimensional (2-D) eddy-current FEM model is established and used for analysis. Current density and strand current distribution are given. It is pointed out that owing to the effect of eddy current, the conductor currents are unevenly distributed within the strands of the same turn. According to the 2-D FEM analysis, when the uneven current distribution is considered, the average rms turn current is increased by 1.05 times for the stator and 1.65 times for the inner rotor, and the copper loss is increased by 1.1 times for the stator and 3.16 times for the inner rotor. Since the inner rotor slots are much deeper than the stator slots, the inner rotor current distribution is more uneven than the stator. It means that for high-frequency deep-slot machine the eddy current effect should be considered seriously. Because of the increased current and copper loss, more ventilation will be needed for the 4QT, especially for the inner rotor. The average torques of stator machine and double rotor machine meet the requirements, and the torque ripples are small owing to the skewed slots.

Two-dimensional finite element method simulation of a four-quadrant transducer prototype machine considering skewed slots

A four-quadrant transducer (4QT) electric machine is an integrated electric machine used for hybrid electric vehicles. In this article a 4QT prototype machine that is radially integrated by two permanent-magnet synchronous machines is analyzed. Skewed slots are adopted for the two machines, and the multislice two-dimensional time-stepping finite element method is used to calculate the performance. The dividing method of the 4QT, the choice of calculated cutplanes and the determination of the number of slices are discussed. The no-load and load performance of the 4QT are calculated. The 4QT prototype machine was tested. The tested no-load line-to-line back electromotive force curves are in good agreement with the calculated ones, which verifies the feasibility of the proposed method.

Development and efficiency measurements of a compact 15 kW 1500 r/min integral permanent magnet synchronous motor

This paper presents the development of a 15 kW, 1500 r/min integral motor, with the same outer dimensions as an equivalent standard induction motor, but with the possibility of operating with speed control and at a higher efficiency. To make a compact integral motor, a permanent magnet rotor is used, the coils of the line-filter and the coil of the DC-link have been integrated with the stator core, only a small DC-link capacitor is employed, and the motor is controlled without a shaft sensor. Temperature and efficiency measurements on the manufactured prototype machine are performed and the results are very promising.