Junghwan Chang

Effect of Stationary Pole Pieces with Bridges on Electromagnetic and Mechanical Performance of a Coaxial Magnetic Gear

In a coaxial magnetic gear, bridges connecting separate pole pieces are useful for fabrication and also improve mechanical reliability. However, they have a negative influence on electromagnetic performance parameters such as transmission torque and iron loss. This paper investigates the effect of stationary pole pieces connected by bridges on the electromechanical characteristics. The bridge type and thickness are the main parameters influencing the performance of a coaxial magnetic gear. The inner, center, and outer bridge types each show the best performance in terms of different characteristics. However, for any bridge type, an increase in the bridge thickness reduces the overall electromagnetic performance, except for the torque ripple, and improves the overall mechanical performance, including the deformation, von Mises stress, and natural frequency of the stationary part.

Back EMF Design of an AFPM Motor using PCB Winding by Quasi 3D Space Harmonic Analysis Method

This paper presents a method to design the waveform of a back electromotive force (back EMF) of an axial flux permanent magnet (AFPM) motor using printed circuit board (PCB) windings. When the magnetization distribution of permanent magnet (PM) is given, the magnetic field in the air gap region is calculated by the quasi three dimensional (3D) space harmonic analysis (SHA) method. Once the flux density distribution in the winding region is determined, the required shape of the back EMF can be obtained by adjusting the winding distribution. This can be done by modifying the distance between patterns of PCB to control the harmonics in the winding distribution. The proposed method is verified by finite element analysis (FEA) results and it shows the usefulness of the method in eliminating a specific harmonic component in the back EMF waveform of a motor.

Effects of Flux Modulation Poles on the Radial Magnetic Forces in Surface-Mounted Permanent Magnet Vernier Machines

This paper investigates the characteristics of the radial force density according to the shapes of the flux modulation poles (FMP) in a surface-mounted vernier machine (SPMVM). The air-gap flux density harmonics obtained from the finite-element analysis method are analyzed using the analytical equations derived from the magnetomotive force and the air-gap permeance distributions. Then, in order to find the radial force density harmonics that generate the exciting force on the stator, the spatial orders and the angular frequencies of the radial force density harmonics are calculated by using the Maxwell stress tensor method. The analysis results show that the permeance harmonics generate the radial force density harmonics, but the resulting harmonics of the radial force density are time-invariant in the spatial domain. Consequently, the variation of the FMP shape can improve the torque characteristics of the SPMVM without the increase of the exciting force on the stator core.

Performance Comparison of PM Synchronous and PM Vernier Machines Based on Equal Output Power per Unit Volume

This paper compares the performances of permanent-magnet synchronous (PMS) and permanent-magnet vernier (PMV) machines for low-speed and high-torque applications. For comparison with the PMS machines, we consider two types of the PMV machine. The first one has surface-mounted permanent magnets (PMs) on the rotor and the other has PMs inserted on both sides of the stator and rotor. The PMS and PMV machines are designed to meet the condition of equal output power per unit volume. We analyze the magnetic fields of the machines using a twodimensional finite element analysis (FEA). We then compare their performances in terms of the generated torque characteristics, power factor, loss, and efficiency.

Analytical Magnetic Field Calculation of Coaxial Magnetic Gear With Flux Concentrating Rotor

In this paper, the analytical model for coaxial magnetic gear (CMG) having a flux concentrating rotor is presented using 2-D space harmonic analysis (SHA). Comparing the conventional CMG with surface-mounted permanent magnet (SPM) on both rotors, the differences are described in terms of governing equations, magnetizations of PMs, general solutions, and boundary conditions. To apply the superposition principle, the analytical model is divided into two cases, such as model for SPM rotor and model for flux concentrating rotor with inset PM. Based on the proposed SHA, the radial and tangential components of flux densities at both air-gap regions are calculated, and the pull-out torques of both rotors are also determined by the Maxwell stress tensor. The results of SHA are in good agreement with the results obtained from finite-element analysis.

Investigation on back EMF charicteristics of a permanent-magnet vernier machine for brushless DC operation

The aim of this paper is to design the trapezoidal back electro-motive force (EMF) waveform of a permanent magnet vernier machine for brush less DC operation. The back EMF equation is derived by using the magneto-motive force (MMF) of the rotor PMs and the permeance function in the air gap region. In the derived equation, the harmonics of the back EMF are influenced by the number of the flux modulated poles (FMPs) and winding patterns. The effects of the variables on the back EMF are verified by the finite element analysis and the torque characteristics are compared according to the operation modes.

Effects of flux modulation poles on the radial magnetic forces in permanent magnet vernier machines

This paper studies the effects of the flux modulation poles (FMPs) on the radial magnetic forces in permanent magnet vernier (PMV) machines. The air-gap flux density distribution in the PMV machine is analyzed by using a combination of the finite element analysis and analytical methods. And then, the radial force density is calculated by Maxwells stress method. At no-load condition, the permeance harmonics by FMPs generate various air-gap flux density harnmonics by interacting with the magneto-motive force (MMF) harmonics of the magnet. As a result, the low order harmonics of the radial force density which may induce significant vibration is caused in the PMV machine. Furthermore, the characteristics of the radial force density under the load condition will be investigated.

Analysis and design of armature magnetic field distribution in permanent-magnet vernier machines

This paper presents an analytical method to determine the air-gap flux density caused by armature windings in a permanent magnet vernier (PMV) machine. In this method, the air-gap flux density is calculated by the magneto-motive force and the air-gap permeance function. The permeance function is defined by using the simple magnetic reluctance network. Based on the analysis method, the working harmonic of the air-gap flux density that generates the torque is analyzed according to the shapes of the stator. And then, its validity is confirmed by the results from a finite element analysis method.