This paper proposed an electromagnetic-thermal-fluidic coupling model for the accurate evaluation of electromagnetic and thermal performance of a permanent magnet synchronous machine. 2-D transient finite-element method is used to investigate electromagnetic loss including copper loss, iron loss, and magnet eddy loss. The calculated electromagnetic power loss is taken as the main source of the thermal-fluidic field and the materials property is in turn updated according to the temperature distribution. The simulation result of a rated 8 kW permanent magnetic machine is compared with the measured result, which validates the accuracy of the proposed model.

This work establishes an optimized third-harmonic shaping model in order to reach the goals of high power density and low torque ripple of the surface-mounted permanent magnet motor (SPMM) The establishment of the model takes the non-ideal factors into consideration, including PM relative permeability, stator slotting, pole leakage, pole edge effect and magnetic circuit saturation. The formula of third-harmonic shaping and the optimal third-harmonic injection factor am(m) are derived from the model. Then a finite-element(FE) model was established to compare the electromagnetic(EM) performance of different magnetic poles. It is found that the average torque of the modified third-harmonic motor is 3.5% higher than that of the simplified third-harmonic motor, and the torque ripple is 47% lower than that of the simplified third-harmonic motor. This proves the superiority of the modified model. And experiments demonstrate that the modified model is feasible and effective.

The circular winding brushless direct current (CWBLDC) motor is a special type of multiphase permanent magnet motors with non-sinusoidal EMFs and circularly connected phase windings. The motor does not rely on conventional PWM inverters and has high torque density and low torque ripple, making it a promising choice for high-power and high-performance applications, such as marine propulsions. This paper studies the radial electromagnetic force of CWBLDC motors. The effect of slot-pole combinations on harmonic contents of the radial force density is analytically derived. Moreover, two computationally efficient numerical methods to calculate the radial electromagnetic force density distribution are proposed based on the space-time symmetry of CWBLDC motors and superposition principle of the magnetic field respectively. In order to validate the analysis, vibration testing of a 10kW CWBLDC prototype is performed.

Circular winding brushless dc (CWBLdc) motor is a novel square-wave multiphase permanent magnet motor with high torque density and excellent vibration performance. It has good prospect in high power and performance applications. However, the control of CWBLdc motor depends on a precise rotor position. Consequently, its application is restricted in some situations where it is difficult to install position sensors. In view of the fact that the existing sensorless control methods are not suitable for the novel CWBLdc motor, a sensorless control algorithm based on the phase voltages and dc current detection is proposed to obtain a continuous and precise rotor position. The fundamental harmonic amplitude of the phase current is estimated based on the dc current, which eliminates the process of phase currents detection and reduces the complexity of the circuit. The error of the algorithm is derived in detail and its accuracy is analyzed theoretically in the paper. The experimental results show that the performance of the proposed sensorless control algorithm is equivalent to that of control with position sensor.

Parallel interleaved three-level inverters (PITIs) are much appreciated in flywheel energy storage systems (FESS), for their great reliability and efficiency. However, the subsequent circulating currents generated by the common-dc-link and asynchronous carriers can lead to excessive harmonic distortion and power losses. To solve this issue, a multiobjective optimization based pulse-width modulation (MOOPWM) scheme is proposed in this article. First, a multiconstraint vector preselection criterion is developed to reconcile the targets such as eliminating circulating currents, diminishing common-mode voltage (CMV) amplitude, and executing the nearest equilateral/isosceles vector synthesis. On this basis, the optimal vector set is determined. Then, a novel carrier-based implementation strategy is developed to synthesize the above optimal vectors set of MOOPWM. The implementation strategy incorporates smooth segmented compensation to the reference signal alongside a nonclamping phase carrier exchange algorithm, which conducts the modulation with lower computational cost. Compared with existing modulation schemes, a simultaneous reduction of circulating currents, CMV and switching loss can be achieved with the proposed MOOPWM. Finally, comparative simulations and experiments on a 300-kW PITI fed FESS motor are carried out to validate the effectiveness of the proposed scheme.

This article deals with the issue of manufacturing processes leading to rotor surface losses through analytical, finite element analysis (FEA) and experimental methods. Based on experiments, it is found that the rotor surface losses make the rotor temperature of radial magnetic bearings (MBs) higher than expected, and thermal ablation appeared on the rotor surface. First, we investigate the mechanism of rotor surface loss in radial MBs using an improved analytical method. The FEA is then used to validate the analytical results and explore the correlation between the degree of short-circuit faults on the rotor surface and the surface losses. This yields a more comprehensive understanding of the loss characteristics and provides ideas for improving manufacturing methods to reduce surface losses. Finally, a simple method of rotor outer circle machining, namely finish turning with fine feed, is proposed. Comparison prototypes were manufactured using the proposed method and the conventional method. The results demonstrate that the proposed method can effectively reduce the rotor surface losses of radial MBs.