Min-Fu Hsieh

A Review of the Design Issues and Techniques for Radial-Flux Brushless Surface and Internal Rare-Earth Permanent-Magnet Motors

This paper reviews many design issues and analysis techniques for the brushless permanent-magnet machine. It reviews the basic requirements for the use of both ac and dc machines and issues concerning the selection of pole number, winding layout, rotor topology, drive strategy, field weakening, and cooling. These are key issues in the design of a motor. Leading-edge design techniques are illustrated. This paper is aimed as a tutor for motor designers who may be unfamiliar with this particular type of machine.

Alternative Rotor Designs for High Performance Brushless Permanent Magnet Machines for Hybrid Electric Vehicles

This paper investigates different rotor topologies based on the spoke design as an alternative to the internal permanent magnet design currently used in the Toyota Prius 2004 design. Reference is made to the 2010 model where the magnet material and maximum torque are reduced, but the speed is doubled. A rare-earth spoke design is shown to be a viable alternative. The paper then goes further and investigates a ferrite alternative. While the torque density is reduced, it illustrates that the spoke magnet arrangement may a viable solution and may open up ferrite magnet use. To offset the reduction in torque density then the speed may be increased; this is the solution Toyota used in the 2010 machine for rare-earth magnet material reduction.

A Generalized Magnetic Circuit Modeling Approach for Design of Surface Permanent-Magnet Machines

This paper proposes a generalized equivalent magnetic circuit model for the design of permanent-magnet (PM) electric machines. Conventional approaches have been applied to PM machine design but may be insufficiently accurate or generalized without taking pole-slot counts into consideration. This would result in reduction of dimensioning accuracy at the initial design stage. Also, magnetic saturation is often ignored or compensated by correction factors in simplified models since it is difficult to determine the flux in individual stator teeth. In this paper, the flux produced by stator winding currents and PMs can be calculated accurately and rapidly using the developed model, taking saturation into account. A new modeling technique for PM poles is proposed so that the magnetic circuit is applicable to any pole-slot combinations. This aids machine dimensioning without the need for computationally expensive finite-element analysis (FEA). A 540-kW PM machine is first designed using the proposed method and then verified with FEA. Another 350-W machine is subsequently designed, manufactured, and validated by both FEA and experiments. The comparisons demonstrate the effectiveness of the proposed model.

Unbalanced Magnet Pull in Large Brushless Rare-Earth Permanent Magnet Motors With Rotor Eccentricity

Permanent magnet motors are now the focus of application in larger drive and generator systems. They often utilize rare-earth magnets where attractive forces are large and unbalanced magnetic pull (UMP) will be generated even when unexcited. In this paper, a 4-pole machine design is utilized which has either surface magnets or consequent poles. Dynamic eccentricity up to 80% is put into the machine model and a variety of simulations carried out to investigate the UMP. It is found that with strong and thick magnets the machine is robust and the UMP is almost load independent. The consequent pole rotor arrangement produces much higher UMP when the dynamic eccentricity aligns with the steel poles. In the simulations, the different stress components are investigated to assess the validity of a commonly held approximation where the radial force is taken to be a function of the square of the radial air-gap flux.

Different Arrangements for Dual-Rotor Dual-Output Radial-Flux Motors

This paper describes different arrangements for a dual-rotor, radial-flux, and permanent-magnet brushless dc motor for application to variable-speed air conditioners. In conventional air conditioners, two motors of appropriate ratings are usually used to drive the condenser and evaporator separately. Alternatively, a motor with two output shafts may be employed, and this is studied here. The motor has inner and outer rotors with a stator in between which is toroidally wound or axially wound with inner and outer slotted stator surfaces. The power sharing on the two rotors is designed to meet the requirement of the condenser and evaporator. Finite element analysis (FEA) is employed to verify the designs. A prototype is made and tested to evaluate the performance. Alternative windings are investigated to assess the possibilities of decoupling the rotors so that they run independently. In the final section, a new and novel arrangement is proposed, where one three-phase winding set and one two-phase winding set (both toroidal) are wound on the same stator to control two rotors of different pole numbers. The two winding sets can be bifilar or share the same set of phase windings. This design simplifies the winding (because it is toroidal) and reduces the copper loss or amount of copper required. The design is tested using FEA solutions, and the initial results indicate that this machine could operate successfully.

An investigation on influence of magnet arc shaping upon back electromotive force waveforms for design of permanent-magnet brushless motors

This paper presents the technique to effectively obtain required back EMF waveforms, e.g., sinusoidal, for permanent-magnet (PM) brushless motors by magnet arc shaping rather than the common stator arc shaping method. Motor back EMF waveforms partly depend on the air-gap flux distribution produced by magnets. Therefore, in this paper, the relationship between the flux distribution of a magnet and its shape is derived using the Laplaces equation so that the magnet shape can be determined in accordance with the back EMF waveform required. Having determined the magnet shape, finite element analysis is employed to verify the effectiveness of the technique developed by comparing the back EMF waveforms of the unmodified arc-shape magnet, the shaped breadloaf and the idea sinusoids. The simulation results show that, by properly shaping the magnets, a back EMF waveform with close approximation to the ideal sinusoid can be obtained, differing from the quasi trapezoidal waveform generated by the original arc shape magnet. Moreover, the results also show that the cogging torque is significantly improved by the magnet shaping. The major advantage of using the developed method is that the required back EMF waveform can be easily obtained at the preliminary design stage so that the entire design efficiency can be improved.

Design of Large-Power Surface-Mounted Permanent-Magnet Motors Using Postassembly Magnetization

This paper reports the design process for the manufacture of higher-power rare-earth permanent-magnet (PM) motors using postassembly magnetization. Difficulties can be encountered in production using normal manufacturing processes due to the high intensity of rare-earth magnets that are premagnetized. Postassembly magnetization utilizes the stator windings of a PM motor to magnetize the magnets after assembly. With this method, some parameters, such as slot-fill factor, number of turns, wire diameter, etc., must be considered for the magnetization and motor operation. In this paper, a design process that incorporates the design considerations for postassembly magnetization (for complete magnetization) together with the design requirements is described for successful motor operation. A 6-kW surface-mounted PM (SPM) motor is designed using the proposed process as a demonstration, which is verified using finite-element analysis. Another 400-W SPM motor is also designed for experimental purpose. The experimental results validate the effectiveness of the proposed method.

Investigation on End Winding Inductance in Motor Stator Windings

This paper presents an analytical approach for the calculation of end winding inductance in motor windings. The method aims to provide a rapid and accurate solution for inclusion in motor and drive design, analysis and simulation programs. In this paper, Laplaces equation is first applied to derive the magnetic vector potential within the end winding region. The flux density is then obtained from the magnetic vector potential. Hence, the inductance can be determined by consideration of the flux linkage. This analytical method is experimentally verified using a specially constructed experimental rig. Comparison with other available methods is also made. It is found that the presented method has a better accuracy than the others based on the experimental results. The experiments also show that the end winding inductance can be increasingly significant as the stack length decreases

Development of a Wave Energy Converter Using a Two Chamber Oscillating Water Column

This paper presents the development and system analysis of segmented oscillating water columns (OWC) for wave energy conversion based on the wave conditions around Taiwan. The OWC chambers are designed for a target site and the power converted by each component (i.e., the chambers, turbine and generator) in the power chain is analyzed so that the overall power output and efficiency can be calculated. The characteristic match between the turbine and the generator is also discussed. The developed OWC is side-mounted and this allows the waves to penetrate and continue propagating after transferring power to the chambers. The OWC consists of two adjacent chambers which are aligned in the direction of the wave propagation. Each chamber has one Savonius turbine on top to convert the chamber power into mechanical shaft power. The two turbines are connected in-line and the individual chambers transfer power to the turbines with a phase difference, so that the power output can be smoothed. A brushless permanent-magnet generator is used to convert the turbine output power into electricity. Experiments are conducted on a scaled-down model in a wave tank to evaluate the performance and the results verify the design. It is also found that the successive chamber should have a different design to the first one as it suffers slight wave attenuation.

Post Assembly Magnetization Patterns in Rare-Earth Permanent-Magnet Motors

This paper illustrates a method for verifying the full magnetization of a rare-earth permanent-magnet motor when it is magnetized using a post-assembly method. The usual method of manufacturing a rare-earth magnet machine is to premagnetize before assembly, however, the assembly can be cumbersome. It is possible to magnetize after assembly. This is a critical procedure. If the magnetizing current is too low, then incomplete magnetization occurs. If it is too high, then the winding will overheat and be damaged. A simple method can be used to ascertain the correct magnetization current and this is put forward here. The method is verified experimentally