Chao Bi

Modeling and numerical simulation of a brushless permanent-magnet DC motor in dynamic conditions by time-stepping technique

A method of modeling and numerical simulation of a brushless permanent-magnet dc motor using time-stepping finite-element technique is presented. In the proposed model, the electromagnetic field equations, the stator circuit equation, and the motion equation are solved simultaneously at each time step; thus, the eddy-current effect, the saturation effect, the rotor movement, and the nonsinusoidal quantities can all be taken into account directly in the system of equations. Dynamic conditions of the motor at starting, step voltage variation, and load torque changes are investigated using the proposed dynamic model.

Automatic learning control for unbalance compensation in active magnetic bearings

This paper proposes a new control scheme, automatic learning control, to eliminate unbalance effects, which adversely affect the operation of active magnetic bearings. This control method is based on time-domain iterative learning control and gain-scheduled control. The controller can utilize the optimal control currents for the unbalance compensations. In addition, the variable learning cycle and variable learning gain are employed in the learning process to achieve better performance against rotating speed fluctuations. The control algorithm does not require large memory size and intensive computation. We tested the control system in experiments, and the experimental results prove that the control method is effective over a wide range of operation speeds.

Unbalanced-magnetic-pull induced by the EM structure of PM spindle motor

The electromagnetic structure of the permanent-magnet spindle motor may induce intrinsic unbalanced-magnetic-pull (UMP). In the paper, this kind of UMP is analyzed with a method developed from the magnetic-circuit and magnetic field analysis. The principle of the method is introduced in the paper. The analysis shows that using the even slot can avoid the generation of the intrinsic UMP. Several spindle motors are used as example to explain the application, and the results prove the effectiveness of the proposed method.

A high bandwidth piezoelectric suspension for high track density magnetic data storage devices

Maintaining the trend towards higher track densities and data rates in magnetic recording devices requires track following servo systems of increasing bandwidth for reliable storage and retrieval of data. The increase in bandwidth is limited by the presence of mechanical resonance modes and other nonlinearities in the voice coil motor (VCM) actuators. One approach to overcoming the problem is by using a dual-stage servo mechanism. In such a mechanism, a VCM is used as a primary stage while a microactuator is used as a secondary stage. The paper proposes a planar piezoelectric actuator design and a piezoelectric suspension made of the planar piezoelectric actuator. The design has a high bandwidth, simple structure and low cost. A prototype of the piezoelectric suspension is designed, fabricated and tested. The experimental results demonstrate that the piezoelectric suspension can satisfy the requirements for the dual-stage servo system.

Reduction of acoustic noise in FDB spindle motors by using drive technology

In the operation of fluid-dynamic-bearing (FDB) motors, the acoustic noise caused by the electromagnetic forces takes a big ratio in the noise level. The authors analyze the relationship between the acoustic noise frequency, harmonic current, and harmonic field, and propose a drive mode for reducing the acoustic noise of the FDB motors. The drive mode can also reduce the copper loss in the motor operation.

Effect of drive modes on the acoustic noise of fluid dynamic bearing spindle motors

The torque ripple is one of the major sources of acoustic noise in the fluid dynamic bearing (FDB) spindle motors. This paper analyzes the relationship between the acoustic noise frequency, harmonic current and harmonic field, and compares the acoustic noise produced in FDB motors driven by different modes. Results show the effect of drive mode on acoustic noise is significant in the FDB spindle motors.

A Demodulation Technique for Spindle Rotor Position Detection With Resolver

This paper presents a demodulation technique for amplitude modulated signals from a resolver based on amplitude detection of a sinusoidal waveform by numerical integration. The proposed technique performs synchronous integration on output signals of the resolver. The integration period is determined from zero crossing detection of the same output signals. The actual envelopes of the signal waveforms are obtained by utilizing the phase relationship of the integrated waveforms with the delayed carrier signal. Due to integration, the noise and disturbance effects are averaged out and the achievable accuracy is improved without applying filters. The method is developed from exploration of detecting HDD spindle rotor position in high resolution. The effectiveness of the proposed technique is demonstrated with the simulations and compared to the other methods. Experimental results are also provided to support the proposed method.

Estimation of back-EMF of PM BLDC motors using derivative of FE solutions

Based on finite element analysis, an effective method is developed to estimate the back-emf produced in electric machines during operation. For a given rotor position, the method utilizes only one finite element solution in its computation, and no numerical derivative is required. The accuracy of the back-emf estimated can thus be improved, and the computing time can be reduced. Computational results obtained from the proposed method to calculate the back-emf of permanent magnet brushless DC motor is introduced in the paper.

Incline Unbalanced Magnetic Pull Induced by Misalignment Rotor in PMSM

This paper analyzes the incline unbalanced magnetic pull (IUMP) generated in the permanent magnetic synchronous motor (PMSM) with the rotor misalignment. The motor magnetic field in such a motor is asymmetric, and both the magnitude and the action point of UMP vary in motor operation. This paper presents an analytical model for analyzing the 3-D effects of the UMP induced by the misalignment rotor. The numerical simulation results prove the effectiveness of the proposed analytic model.

Influence of winding structure and the effect of MMF harmonics to the spindle motor performance for ultra-high TPI HDD

The technologies for maintaining high recording density to suppress mechanical vibration and media flutter for ultrahigh TPI hard disk drive (HDD) require advance spindle motor design and technology against the traditional norms. To realize multimagnetic poles with limited stator slots, spindle motors generally use concentrated windings which offer small end winding and simple structure suitable for mass production. There is a variety of ways to construct a motor with different winding structures based on different pole/slot combinations. Winding structures directly affect the producing of motor back-emf and torque which determine motor capacity, reliability and efficiency. In this work, detailed analysis is carried out to identify the optimal winding structures of the high speed spindle motor and analyze their effect on the motor performances by using magneto-motive force harmonics analysis and electromagnetic magnetic field analysis. Results are useful in preliminary and final optimal designs of the high speed spindle motors.The technologies for maintaining high recording densities to suppress mechanical vibration and media flutter require advance spindle motor design and technology. To realize multi-magnetic poles with limited stator slots, radial air gap field HDD spindle motor are normally used concentrated winding. Based on different pole/slots combinations, there would be a variety of winding configurations. In this work, detailed analysis is carried out to identify the optimal winding structures of the high speed spindle motor and analyze their effect to the motor performances by using MMF harmonics analysis and FEM. Results are useful in preliminary and final optimal designs of the high speed spindle motors.