Halbach array-based permanent magnet (PM) brushless machines exhibit attractive features when compared with conventional PM brushless machines with normal segmented magnets, including the flux-concentration effect, essentially sinusoidal air-gap flux density due to PMs, and negligible cogging torque. However, as for a motor/generator used in flywheel, an external rotor composed of Halbach array and rotor back-iron is necessary to increase the inertia of flywheel system, which is different from the conventional external-rotor machines. In this paper, a Halbach array PM motor is studied compared with the radial magnet array. The relationship between the air-gap field distribution and the magnet array is discussed. Finally, the eddy current loss in PMs of the external-rotor ironless brushless dc motor is analyzed between the Halbach PM motor and the conventional PM motor.

In field-oriented vector control of permanent magnet synchronous machine (PMSM) drives, the dead time will cause the 5th and 7th current harmonics in the stationary reference frame. They are mapped to the negative and positive 6th harmonic current in the synchronous reference frame (SynRF), resulting in torque ripple and deterioration of control performance. To solve this problem, a new dead-time compensation method is proposed in this article. First, a multiple complex coefficient filter is modified with a low-pass filter being paralleled to extract positive and negative sequence components of 6th harmonic from dq -axes currents. Then, based on the extracted harmonics, a voltage feedback path with variable gains is designed in SynRF to eliminate the dead-time effect. Finally, the proposed method is implemented in a prototyped PMSM drive to verify its effectiveness. Both the simulations and experiments indicate that the proposed method can significantly weaken the dead-time effect with no additional hardware. Besides, it is also proved robust to the variable machine parameters.

Rotor eccentricity commonly exists in permanent magnet synchronous machines (PMSMs) due to improper assembly, excessive vibration, and continuous operation. Consequently, the unbalanced magnetic pull, introduced by rotor eccentricity, may lead to unfavorable noise, vibration, and even bear damage, which makes the detection of eccentricity meaningful. Although motor current signal analysis is the most popular method to diagnose eccentricity based on the amplitudes of sideband component, it is a big challenge to classify different types of eccentricities and quantify the eccentric ratio due to the spatiotemporal coupling effect. In this article, by installing a set of Hall sensors at stator slots of PMSMs to measure the magnetic flux density in time domain, the static eccentricity and dynamic eccentricity can be easily separated. This article provides a novel complex-analytical model to reveal the single side band modulation effect in air-gap filed due to dynamic eccentricity. Moreover, a diagnosis algorithm based on frequency-adaptive notch filter is designed to identify the eccentricity type and the corresponding degree. The effectiveness of the novel diagnosis method is validated by both simulations and experiments.

The purpose of this paper is to analyze ac copper losses of the ironless brushless dc machine (BLDCM) used in the flywheel energy storage system. The influence factors of the ac copper losses, such as the winding diameter, phase current, and machine speed, are analyzed. The research results show that the winding wire diameter has a huge effect on the ac losses in ironless BLDCM, and the shunt wound structure with multiple wires method can reduce winding ac losses effectively. However, due to induced voltage and impedance unbalance, additional circulating current losses are induced. For circulating current losses calculation, a winding circulating current equivalent calculation model is built. The circulating current losses are calculated by a simplified three-dimensional finite element method and the winding wires arrangement methods to reduce circulating current losses are explored. Three winding wires arrangements are compared and discussed. The results show that the ironless BLDCM using multiwires with suitable arrangements can reduce the copper losses.

The yokeless and segmented armature axial flux machine is considered an excellent topology for electric vehicles application. However, its performance is severely limited by the stator cooling system. The heat pipe, as the small size, lightweight, but highly efficient passive phase-change cooling element, has been attracting more and more attention in the thermal management methods of electric motors. Therefore, the relationship between the thermal performance of the heat pipe with temperature is measured in detail through an experimental test platform in this paper. Further, a novel stator cooling structure that combines the heat pipe with the housing water-cooling method is introduced to improve the temperature distribution of the stator. Computational fluid dynamics (CFD) simulation verifies that the proposed cooling structure can accelerate the release of heat from the stator and reduce the temperature of the stator significantly.

In sensorless control of high-speed permanent magnet synchronous machines (PMSMs), online inductance identification techniques can be employed to improve the position estimation precision. The high-order inductance identification model which is affected by the flux error, the dead-time effect equivalent voltage and initial rotor position error adopted in conventional methods often face challenges including robustness and accuracy. To address this issue, this article uses a first-order discrete-time model in the estimated γδ -frame to identify the winding inductance with disturbance injection. The first-order model allows the identification to be independent of flux error, initial rotor position error, and inverter nonlinearity, thus the robustness is improved. The proposed method takes the computational delay and discrete-time nature of pulsewidth modulation into account to avoid the model error brought by low ratio of carrier-to-fundamental-frequency. Additionally, the results are estimated by least square method to solve fluctuation problem caused by measurement noise and the possible surge phenomenon. Experiments are carried out on a high-speed surface-mounted PMSM for vacuum cleaner to verify the proposed method.