Peter Omand Rasmussen

Development of a high-performance magnetic gear

This paper presents calculation and measurement results of a high-performance permanent-magnetic gear. The analyzed permanent-magnetic gear has a gear ratio of 5.5 and is able to deliver 27 N/spl middot/m. The analysis has shown that special attention needs to be paid to the system where the gear is to be installed because of a low natural torsion spring constant. The analyzed gear was also constructed in practice in order to validate the analysis and predict the efficiency. The measured torque from the magnetic gear was only 16 N/spl middot/m reduced by the large end-effects. A systematic analysis of the loss components in the magnetic gear is also performed in order to figure out why the efficiency for the actual construction was only 81%. A large magnetic loss component originated in the bearings, where an unplanned extra bearing was necessary due to mechanical problems. Without the losses of magnetic origin in the bearings and less end-effects caused by relatively short stack, an impressive efficiency estimated at 96% can be obtained. Comparison with classical mechanical gears has shown that the magnetic gear has a better efficiency and a comparable torque per volume density. Finally, it is concluded that the results in this paper may help to initiate a shift from mechanical gears to magnetic gears.

Influence of Battery/Ultracapacitor Energy-Storage Sizing on Battery Lifetime in a Fuel Cell Hybrid Electric Vehicle

Combining high-energy-density batteries and high-power-density ultracapacitors in fuel cell hybrid electric vehicles (FCHEVs) results in a high-performance, highly efficient, low-size, and light system. Often, the battery is rated with respect to its energy requirement to reduce its volume and mass. This does not prevent deep discharges of the battery, which are critical to the lifetime of the battery. In this paper, the ratings of the battery and ultracapacitors are investigated. Comparisons of the system volume, the system mass, and the lifetime of the battery due to the rating of the energy storage devices are presented. It is concluded that not only should the energy storage devices of a FCHEV be sized by their power and energy requirements, but the battery lifetime should also be considered. Two energy-management strategies, which sufficiently divide the load power between the fuel cell stack, the battery, and the ultracapacitors, are proposed. A charging strategy, which charges the energy-storage devices due to the conditions of the FCHEV, is also proposed. The analysis provides recommendations on the design of the battery and the ultracapacitor energy-storage systems for FCHEVs.

Improved digital current control methods in switched reluctance motor drives

This paper proposes a method to avoid current feedback filters in fast digital-based current loops in switched reluctance drives. Symmetrical pulsewidth modulation (PWM) and synchronized sampling of the phase current allow a noise-free current sampling with no antialiasing filter. This paper also proposes more efficient methods to chop the two transistors in the asymmetric inverter used with switched reluctance drives. A fast field-programmable gate array (FPGA)-based test system is used for validation of the new methods. Test results show a significant improvement in dynamic and steady-state current loop control compared with traditional methods. The new chopping method is found to reduce the switching losses and increase the drive efficiency.

Development of a high performance magnetic gear

This paper presents calculation and measurement results of a high-performance permanent-magnetic gear. The analyzed permanent-magnetic gear has a gear ratio of 5.5 and is able to deliver 27 N/spl middot/m. The analysis has shown that special attention needs to be paid to the system where the gear is to be installed because of a low natural torsion spring constant. The analyzed gear was also constructed in practice in order to validate the analysis and predict the efficiency. The measured torque from the magnetic gear was only 16 N/spl middot/m reduced by the large end-effects. A systematic analysis of the loss components in the magnetic gear is also performed in order to figure out why the efficiency for the actual construction was only 81%. A large magnetic loss component originated in the bearings, where an unplanned extra bearing was necessary due to mechanical problems. Without the losses of magnetic origin in the bearings and less end-effects caused by relatively short stack, an impressive efficiency estimated at 96% can be obtained. Comparison with classical mechanical gears has shown that the magnetic gear has a better efficiency and a comparable torque per volume density. Finally, it is concluded that the results in this paper may help to initiate a shift from mechanical gears to magnetic gears.This paper presents calculation and measurement results of a high performance permanent magnetic gear. The analysed permanent magnetic gear has a gear ratio of 5.5 and is able to deliver 27 Nm. The analysis has shown that special attention needs to be paid to the system where the gear is to be installed because of a low natural torsion spring constant. The analysed gear was also constructed in practice in order to validate the analysis and predict the efficiency. The measured torque from the magnetic gear was only 16 Nm reduced by the large end-effects. A systematic analysis of the loss components in the magnetic gear is also performed in order to figure out why the efficiency for the actual construction was only 81%. A large magnetic loss component originated in the bearings, where an unplanned extra bearing was necessary due to mechanical problems. Without the losses of magnetic origin in the bearings and less end-effects caused by relatively short stack, an impressive efficiency estimated at 96% can be obtained. Comparison with classical mechanical gears have shown that the magnetic gear has a better efficiency and a comparable torque per volume density. Finally it is concluded that the result in this paper may help to initiate a shift from mechanical gears to magnetic gears.

Motor integrated permanent magnet gear with a wide torque-speed range

This paper present a new motor integrated permanent magnet gear with a wide torque-speed range. In the paper a 35 kW permanent magnet motor with a base speed of 4000 rpm and a top speed of 14000 rpm is integrated into a permanent magnetic gear with a gearing ratio of 8.67. The design process of the combined unit is described together with a description of the construction of the part for a test model. The unit is unique in the sense that it has superior traction characteristics and a torque density of 130 Nm/l which is more 1.5 times of other reported motor integrated permanent magnet gears. The unit may be useful as a direct drive wheel motor for EVs and no liquid cooling system is required.

Two dimensional model of a permanent magnet spur gear

This paper extends an analysis method developed for a radial magnetized spur gear. The extension describes how a parallel magnetized spur gear can be modeled analytically. The analytical method for a parallel magnetized gear is verified with the finite element method, which showed good agreements. The results with the parallel magnetized are also compared with results from the previous developed analytical method for radial magnetized gear, and the parallel magnetized version turned out to give a better performance. A test model was also built to verify the theoretical calculations.

Design Considerations of Permanent Magnet Transverse Flux Machines

Permanent magnet transverse flux machine (PMTFM) is well known for its high torque density and is interested in various direct-drive applications. Due to its complicated 3-D flux components, design and design optimization of a PMTFM is more difficult and time consuming than for radial flux electrical machines. This paper addresses two important design considerations for PMTFM - the influence of permanent magnet leakage flux, which plays an important role in the determination of machine output torque, and the leakage inductance. A new simple method to provide a quick estimation of the armature leakage inductance is proposed, avoiding use of complicated 3-D equivalent reluctance network model to estimate the circumferential armature leakage flux component, and the pole face fringing flux component. Analysis results are supported by 2-D, and 3-D finite element (FE) analysis results, and measurement results on a prototype surface-mounted PMTFM.

Experimental evaluation of a motor integrated permanent magnet gear

This paper presents test results of a new motor integrated permanent magnet gear and clarifies a path for future optimizations. The prototype, which fabrication also is described, is initially targeting electrical traction for vehicles. Basic measured parameters in form of back-emf, stall torque and inductances are all in line with finite element calculations. However very high rotational losses are present in the prototype and these losses are higher than the calculations. Some of the losses are present due to poor aspects in the fabrication of the prototype, while others are identified to be caused by a non optimal diameter/length aspect ratio. The torque density is superior, the copper losses is only a fraction of the copper losses in other traction motors. With the proposed aspects to reduce the rotational losses is it believed that the unit has a great potential.

New advanced control methods for doubly salient permanent magnet motor

High performance and high efficiency in adjustable speed drives are needed and new motor constructions are investigated and analyzed world wide. This paper deals with advanced control of a doubly salient permanent magnet (DSPM) motor. The construction of the DSPM motor is shown and a dynamical model of the motor is used for simulations. As supply to the DSPM motor, a power converter with a split capacitor is used to reduce the number of devices, and a basic control method for this converter is explained. This control method will cause an unequal voltage distribution across the capacitors because the motor is asymmetrical and a decrease in efficiency and a poorer dynamic performance are the results. To minimize the problems with the unequal load of the capacitors in the converter, a new charge control strategy is developed. The efficiency of the motor can also be improved by using a power minimizing scheme based on changing the turn-on and turn-off angles of the current. The two different strategies are implemented in an adjustable-speed drive, and it is concluded that both control strategies improve the performance of the drive.

Investigation of battery/ultracapacitor energy storage rating for a Fuel Cell Hybrid Electric Vehicle

Combining high energy density batteries and high power density ultracapacitors in fuel cell hybrid electric vehicles (FCHEV) results in a high efficient, high performance, low size, and light system. Often the batteries are rated with respect to their energy requirement in order to reduce their volume and mass. This does not prevent deep discharges of the batteries, which is critical to their lifetime. In this paper, the ratings of the batteries and ultracapacitors in a FCHEV are investigated. Comparison of system volume, mass, efficiency, and battery lifetime due to the rating of the energy storage devices are presented. It is concluded, that by sufficient rating of the battery or ultracapacitors, an appropriate balance between system volume, mass, efficiency, and battery lifetime is achievable.