Wubin Kong

Air-Gap and Yoke Flux Density Optimization for Multiphase Induction Motor Based on Novel Harmonic Current Injection Method

This paper investigates a novel harmonic current injection method to optimize air-gap and yoke flux density distribution for multiphase motor simultaneously. The effect of harmonic currents on air-gap flux density and yoke flux density is analyzed as a whole, while the traditional method focuses on air-gap flux density optimization only. The proposed method fully makes use of multiple control freedoms and the optimal coefficients for corresponding harmonic current are derived. The theoretical analysis and experimental results indicate that novel harmonic current injection method is suitable for heavy load condition. Maintaining the same stator current density, a nine-phase induction motor improves torque density up to 8.47% with the proposed method. A three-phase induction motor is designed to verify the effectiveness of multiphase motor with concentrated full-pitched winding. Furthermore, the torque density and efficiency for two motors are compared under various load condition. Finally, a multiphase variable speed drive system is constructed and the proposed method is validated by experiments.

A Stator-PM Consequent-Pole Vernier Machine with Hybrid Excitation and DC-Biased Sinusoidal Current

This paper proposes a novel hybrid excitation vernier permanent magnet machine (HE-VPM). The characteristics of the proposed machine are: 1) The PMs are embedded in the stator teeth, which is helpful for heat dissipation; 2) the rotor is salient structure without PMs and windings, which ensures the reliability of high speed running; 3) The non-overlapping concentrated winding shortens the end-winding, and improves the torque density, 4) Only half of the stator teeth possess PMs, and the total amount of PMs are decreased; 5) The DC current are injected to the armature coils, therefore, the exciting field can be adjusted flexibly. In this paper, the electromagnetic performance, including back-EMF, torque, etc. are analyzed with finite element analysis (FEA). The results show that the proposed machine exhibits flexible field adjustment capability, which may be suitable for applications requiring wide speed range operation. Besides, it is found that, compared with fed with the existing pure sinusoidal phase current, higher torque can be obtained with DC-biased phase current under constant stator copper loss.

Air-gap and yoke flux density optimization for multiphase induction motor based on novel harmonic current injection method

This paper investigates a novel harmonic current injection method to optimize air-gap and yoke flux density distribution for multiphase motor simultaneously. The effect of harmonic currents on air-gap flux density and yoke flux density is analyzed as a whole. The proposed method fully makes use of multiple control freedoms, and the optimal coefficients for corresponding harmonic current are derived. Maintaining the same stator current density, a nine-phase induction motor improves torque density about 6.6% with the proposed method. A three-phase induction motor is designed to verify the effectiveness of multiphase motor with concentrated full-pitched winding. Furthermore, the torque density and efficiency for two motors are compared under various load condition. Finally, a multiphase variable speed drive system is constructed and the proposed method is validated by experiments.

Investigation of Spatial Harmonic Magnetic Field Coupling Effect on Torque Ripple for Multiphase Induction Motor Under Open Fault Condition

This paper investigates spatial harmonic magnetic field coupling effect on torque ripple for multiphase induction motor under open fault condition. The coupling results in severe torque ripple generated by ellipse asynchronous magnetomotive force, and the current space vectors are utilized for coupling phenomenon analysis in the multiple planes. The optimal current space vector is proposed to achieve the minimum torque ripple, and the traditional method is used for comparison. Both fundamental and harmonic current space vectors are derived, when single-phase and two-phase open fault conditions are analyzed, respectively. Furthermore, the proportional integral resonant controller is used to realize zero-error tracking, and proper values of parameters in the transfer function are derived. Finally, a five-phase variable speed drive system is constructed and the proposed method is validated by experiments.

A Novel Dual-Stator Vernier Permanent Magnet Machine

In many direct-drive applications such as servo system, wind power generation, etc., it is desirable to use motors having a high torque density at a low rotation speed without reduction gears for the improvement of noises, reliability and maintenance.

Harmonic current suppression control strategy for hybrid excited vernier PM machines

Recently, a novel hybrid excited vernier permanent magnet machine (HE-VPM) is proposed. The proposed machine is with stator located PMs, and concentrated armature windings. The current waveforms of the armature windings are sinusoidal with DC bias, as the injected DC biased current can weaken or enhance the exciting fields at high/low speed. Due to the characteristics of double salient structure, a massive amount of back-EMF harmonics in phase windings will appear when the machine is operating, and the DC flow path will lead to current waveform distortion in phase windings, result in torque ripple and influence the efficiency of the motor. By analyzing the mathematical equations in dq0-axis, a harmonic current suppression control strategy for HE-VPMs is proposed. The control strategy produces the corresponding voltage compensation in dq-axis, counteract with the back-EMF harmonics to achieve the purpose of eliminating the circulating harmonic current. Finally, the experimental results verified that the proposed control strategy can suppress the harmonic current in phase windings effectively.

Genetic-algorithm-based analytical method of SMPM motors

In this paper, an exact analytical method is developed to computer the air-gap magnetic field of surface-mounted permanent-magnet (SMPM) motors for valuating slotting effects accurately. In order to improve the flux density and reduce cogging torque, the genetic algorithm toolbox of Matlab is used to optimize the motor, in which the actual depth of slot, slot opening, the length of gap and pole-arc to pole-pitch ratio are taken into account in the computation. Magnetic field distributions, induced back electromotive force (EMF) and optimized cogging torque computed from the proposed analytical method are compared with those issued from two-dimensional finite-element method (FEM), the comparison results are consistent and shows the correctness and effectiveness of the proposed analytical method.

Drive for DC-biased sinusoidal current vernier reluctance motors with reduced power electronics devices

DC-excited vernier reluctance motors are usually fitted into two sets of stator windings: DC current winding for generating magnetic field and armature winding for producing rotating magnetic flux. However, two separated sets of stator windings require larger motor size and complex winding structure. Two sets of power electronics converters are required to drive both the excited and rotational windings. This paper investigates DC-biased sinusoidal current vernier reluctance motors with single stator winding compared with traditional structure. Furthermore, the structure of power electronics inverter for supplying the stator currents with DC-biased component is proposed, due to unipolar direction of current flow. The proposed inverter can reduce the quantity of power electronics devices by 50%. Also, the half-bridge structure of the proposed drive can avoid DC-bus shoot-through failure physically. A prototype of the DC-biased sinusoidal current vernier reluctance motor has been developed together with the proposed drive and controller. Finally, the experimental results verify that the proposed inverter configuration can be effectively applied in DC-Biased sinusoidal current vernier reluctance motor drives.

Improved Torque Capacity for Flux Modulated Machines by Injecting DC Currents into the Armature Windings

Flux modulated machine (FMM) comprises three parts: a conventional stator with armature winding, a rotor with permanent magnet, and iron flux modulation pole. Thanks to the inherent magnetic gearing effect, FMMs have been gaining more attention for their features of high torque density. So far, the windings of existing FMMs are fed with pure sinusoidal current. In this paper, to further improve the torque density using the magnetic gear principle, dc-biased sinusoidal current is innovatively injected into the armature coils which are arranged in a specific way, and the electromagnetic performance is analyzed by the finite element analysis. The results show that the electromagnetic torque contains not only the preexisting PM torque, but also the additional torque produced by the dc current interacted with the ac armature current. What is more, it is found that with the proposed dc-biased current, the torque density is improved under the constant copper loss compared with the existing pure sinusoidal current. Besides, the flux adjustment ability is greatly enhanced since the exciting field can be easily adjusted by the injected dc current.

A stator-PM consequent-pole vernier machine with hybrid excitation and DC-biased sinusoidal current

This paper proposes a novel hybrid excitation vernier permanent magnet machine (HE-VPM). The characteristics of the proposed machine are: 1) the PMs are embedded in the stator teeth, which is helpful for the heat dissipation; 2) the rotor is salient structure without PMs and windings, which ensures the reliability of high-speed operation; 3) the nonoverlapping concentrated winding shortens the end-connection, and improves the torque density, 4) only half of the stator teeth possess PMs, and the total amount of PMs are decreased; and 5) the dc current are injected to the armature coils, therefore, the exciting field can be adjusted flexibly. In this paper, the electromagnetic performance, including back electromotive force, torque, etc. are analyzed with finite element analysis. The results show that the proposed machine exhibits flexible field adjustment capability, which may be suitable for applications requiring wide speed range operation. Besides, it is found that, compared with the existing pure sinusoidal phase current, higher torque density can be obtained with dc-biased phase current under constant stator copper loss.