Ju Lee

Proposal of Improved Winding Method for VR Resolver

The variable reluctance (VR) resolver is generally used instead of an optical encoder as a position sensor on motors for hybrid electric vehicles or electric vehicles owing to its reliability, low cost, and ease of installation. The commonly used conventional winding method for the VR resolver has disadvantages, such as complicated winding and unsuitability for mass production. This paper proposes an improved winding method that leads to simpler winding and better suitability for mass production than the conventional method. In this paper, through the design and finite element analysis for two types of output winding methods, the advantages and disadvantages of each method are presented, and the validity of the proposed winding method is verified. In addition, experiments with the VR resolver using the proposed winding method have been performed to verify its performance.

Inductance Calculation of Flux Concentrating Permanent Magnet Motor through Nonlinear Magnetic Equivalent Circuit

In order to design a permanent magnet synchronous motor (PMSM), the inductance must be computed. In this paper, the flux concentrating PMSM (FCPMSM) is introduced. Calculating the inductance is difficult because of the complex structure of the rotor. Because the rib and the bridge consist of an iron core, they have nonlinear characteristics. In order to obtain the effective value of the inductance, nonlinear characteristics must be considered in a magnetic equivalent circuit (MEC). In this paper, to calculate the inductance of an FCPMSM, the relative permeance of the rotor was analyzed. Then, the dq-axis MEC, including the nonlinear magnetic reluctance, was created using the flux line. Finally, we verified the validity of the proposed inductance calculation method by comparing the results between the finite-element method and the proposed method.

An Analytic Analysis of the Multi-Degree-of-Freedom Actuator

This paper discusses the analysis and simulation method and the test method for a two-degree-of-freedom (2-DOF) actuator torque. The previous studies on the analysis of 2-DOF motors tilting torque were carried out only by finite element method (FEM), not by analytic method. This paper describes the operating principles of and the processes of inducing a tilting torque and a holding torque both of which exist only in special purpose electric machines. This allowed us to establish a design process. By overcoming the limits of the 3-D FEM, this paper introduced the 2-D model analysis by considering a real coil shape. Finally, this paper manufactured and tested the 2-DOF actuator to verify the introduced analytic analysis method.

Self-Excited Induction Generator as an Auxiliary Brake for Heavy Vehicles and Its Analog Controller

A self-excited induction generator (SEIG) can be a candidate for isolated applications because it does not require any external exciting power but can independently generate electricity. It is also a good candidate for auxiliary brakes in heavy vehicles for several reasons. First, the power efficiency in a brake system is not important as compared with motors or generators. Second, an SEIG can be controlled by a simple electrical circuit. Third, it can be used for regenerative braking. Finally, it is very robust. In this paper, an auxiliary brake for heavy vehicles is proposed by adapting an SEIG and its analog control circuit. The brake structure is the same as that in conventional eddy current brakes but operates as an SEIG. The suggested control circuit does not adopt an electric controller unit but only consists of simple electric devices. A miniature model was designed and manufactured, and the experimental results using the prototype verify that the proposed brake system, including the controller, is very useful.

Study on the Optimal Rotor Retaining Sleeve Structure for the Reduction of Eddy-Current Loss in High-Speed SPMSM

In the case of designing high-speed surface-mounted permanent magnet synchronous motor (SPMSM), the rotor retaining sleeve is inserted into the rotor to prevent the permanent magnets damage. It is quite an efficient way to consider manufacturability, but the sleeve becomes the major source of ohm loss in high-speed operation. In this paper, the high-speed motor for a turbo blower at the rating of 100 kW, 20000 r/min was introduced. To improve its efficiency, the retaining sleeves optimal design was needed. For this, parametric analysis on the shape of the retaining sleeve was carried out in a different type of motor. Within a range that meets the mechanical safety, sleeve designs have been changed. The effect of changing design variables of the sleeve was studied. This paper presents the optimized sleeves advantages in electrical efficiency from the results of the electromagnetic finite element analysis software. Finally, it suggests the optimal sleeve design to reduce eddy-current loss, which is related to motor shape.

Magnetic force characteristics according to the variation of asymmetric overhang ratio in brushless direct current motor

As usual, brushless dc motor (BLDCM) has the overhang structure of which permanent magnet (PM) length is longer than the stator’s stack length. Specially, in case of asymmetric overhang, we have to pay attention to the choice of suitable overhang ratio of the lower to the upper overhang length because of the effect of the ratio on the magnetic forces. In this article, the magnetic force characteristics of BLDCM with the asymmetric overhang and the cap of the rotor are analyzed. A three-dimensional equivalent magnetic circuit network (EMCN) method is used for the efficient analysis of the magnetic field. The magnetic forces and torque are calculated by Maxwell’s stress tensor. The variation of magnetic force characteristics is also analyzed according to the overhang ratio. From the results, when the overhang ratio is 0.38, the axial magnetic force characteristic could be improved remarkably. The validity of the analysis results is also clarified by comparison between calculated results and measured ones.

Multi-rate optimal controller design for electromagnetic suspension systems via linear matrix inequality optimization

This paper develops a discrete optimal control based on the multi-rate observer method for electromagnetic suspension systems in order to levitate the vehicle, maintaining the desired gap. The proposed multi-rate compensator consists of two parts which are the discrete Kalman filter and the optimal control law. The Kalman filter estimates all states with fast sampling rate time, using a slowly measured output from the gap sensor. The optimal control law is determined by linear matrix inequality optimization for the discrete time multiple input system obtained by the lifting operator. The proposed multi-rate controller has the advantages to guarantee the stability of the slow-rate optimal control and maintain the performance of fast-rate control. The simulation and experiment show the effectiveness of the proposed control method.

A Novel Methodology for the Demagnetization Analysis of Surface Permanent Magnet Synchronous Motors

A surface permanent magnet synchronous motor (SPMSM) using ferrite magnet represents small air gaps and high stack lengths relatively. Thus, it has small edge effects on the performance of the motor, and a 2-D finite-element analysis (FEA) method is largely used to design it. In the case of the demagnetization analysis in the SPMSM, however, it is difficult to neglect fringing effects in air gaps, because the permeability of the permanent magnet is the same as air and the direction of the armature reaction is opposite to the magnetization direction. Therefore, the accuracy of the 2-D FEA is significantly degraded. In this paper, the edge effect of SPMSM on the demagnetization analysis is analyzed. For achieving it, the opposing magnetic field that contributes to the demagnetization is analyzed by two different elements, such as permanent magnet and armature reaction. In addition, a simplification model of the yz plane that can consider the edge effect is proposed to increase the accuracy of the conventional 2-D FEA, which is analyzed on the xy plane, and correction factors are also induced. Finally, its validity is verified by applying the proposed method to the conventional motors.

Current Control Method of WRSM in High-speed Operation Range

This Paper analyzes the characteristics of the WRSM in high-speed operation range. To verify the control characteristics of various WRSM models, the relative position of the central point of current limit circle and voltage limit ellipse is defined as M value and 3 models according to M max value are designed through inductance change. Through the designed models, the current control method of 3-variables control for maximum power especially in high-speed operation range is presented.

Analysis of Motor Performance According to the Inductance Design of IPMSM

There is a relationship between motor performance and the d-q axis inductance of an interior permanent magnet synchronous motor (IPMSM). Three design approaches for d-q axis inductance were adopted to design the inductance of an IPMSM. Because a change in the pole-arc to pole-pitch ratio changed the d-q axis path, the motor characteristics were first analyzed according to the pole-arc to pole-pitch ratio. Next, the motor characteristics were analyzed according to the various combinations of air gap flux density and stack length. Finally, the models of 10 pole-12 slot and 10 pole-45 slot were analyzed. When the speed-torque characteristics of the inductance design models were satisfied, the d-q axis inductance and the motor performance were analyzed for each of the three methods. One model that satisfied the desired characteristics was manufactured for the experiments, and then the accuracy of the simulation and the claim of this paper were verified through the experiments.