Dynamic Analysis of Surface-Mounted Permanent Magnet Type Coaxial Magnetic Gear With Damper Bar Considering Magnetic Field Modulation Effect

Coaxial Magnetic Gear (CMG) has unstable dynamic characteristics by hunting or pull-out action of the output rotor when the load or speed are changed, unlike traditional mechanical gears. These dynamic characteristics need to be improved in order to secure the reliability of mechanical power transmission system by fast and accurate response. In this paper, the damper bar used in synchronous machines is considered as a method to improve the dynamic characteristics of CMG. The Surface-mounted Permanent Magnet (SPM) type CMG is selected as the analysis model. The space harmonics of the magnetic flux density of stationary and rotary members of CMG namely, modulating pieces, inner and outer rotor, are analyzed and characterized the influence of them on the improvement of dynamic characteristics as well as torque reduction. Also, the magnetic flux density characteristics and the damping effect are compared according to the position of the damper bars on two rotors and the modulating pieces. In conclusion, the considerations about the perspective for design and application are presented when using the damper bar for SPM type CMG.

*Published in the IEEE Magnetics Society Section within IEEE Access.

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Investigation and Analysis of Novel Skewing in a 140 kW Traction Motor of Railway Cars That Accommodate Limited Inverter Switching Frequency and Totally Enclosed Cooling System

This study facilitated the improvement of no-load back electromotive force (back-EMF) wave form, total harmonic distortion (THD) of back-EMF, and torque ripple using a novel skew angle formula, considering the specific order of a no-load THD. In real usage environments, it is taken into consideration for the fully enclosed cooling system and limited inverter switching frequency of urban railway car traction motors. Since the most railway car traction motors use high-withstand voltage rectangular wires in slot-open structure, a no-load back EMF waveform includes large space slot harmonics, which should be smaller as possible. For 6-step control, the no-load back EMF waveform is important because switching for motor control is performed once after the rotor position is determined. To improve the no-load back EMF waveform and THD, two-dimensional and three-dimensional finite element analysis (FEA) were performed using a novel skew angle formula considering specific harmonic order reduction, while the fundamental amplitude was minimally reduced. A prototype with the novel skew was fabricated and verified. In addition, it was designed by calculating a low current density for a fully enclosed cooling system. A temperature saturation experiment was also performed, and successfully verified. Therefore, we suggest that the no-load back EMF characteristics and torque ripple are improved by applying the novel skew angle instead of a traditional skew angle.

*Published in the IEEE Magnetics Society Section within IEEE Access.

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A Simple and Adjustable Technique for Effective Linearization of Power Amplifiers Using Harmonic Injection

A simple and effective method for linearization of power amplifiers (PAs) is proposed. The method is based on the second harmonic injection into the input of the PA. The second harmonic is generated in a feedback path by taking the low-power transistors of a pseudo-differential pair amplifier to their nonlinear regime. The amplitude and phase of the second harmonics are controlled by tunable matching networks of the pseudo-differential pair which include trimmer capacitors. Using a theoretical analysis, we show that the proposed method is capable of canceling the third-order intermodulation signal at the PA output. As a proof of concept, a 10-W PA in a frequency band of 1.4 – 1.6 GHz is designed and linearized. By fabricating both the reference and linearized PAs and performing measurements under several conditions, it is experimentally demonstrated that applying the proposed scheme, thanks to its adjustability, highly linearizes the PA in a wide bandwidth and a wide range of output power.

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