| Fraction-Slot Concentrated-Winding(FSCW) Permanent Magnet(PM) synchronous machines have been gaining interest over the last few years. This is mainly due to the several advantages, such as high efficiency, short end turns, low cogging torque and flux-weakening capability. The main research this paper is focused on the FSCW PM torque motor used for airborne radar servo system. In order to meet the application background of the machine, two requirements are presented: First, due to the limit of installation space and weight for airborne equipment, the motor must have high torque density. Second, in order to ensure the precise tracking of targets in any conditions, it’s necessary to restrain motor’s torque ripple. In this paper, according to the structural characteristics and the application requirements of FSCW PM machines, the following aspects had been studied.Compared with the Integer-Slot Distributed-Winding motor, the biggest differences of FSCW machine is the existence of fractional harmonic in the winding magnetic field, which lead to a very complex distribution and changing of the winding magnetic field. In this paper, the expression for the spatial distribution of the winding magnetic field has been derived by an analytical method. The winding magnetic field harmonic spectrum of FSCW machine has been calculated, and the impact of the main magnetic field, odd and fractional harmonic magnetic field on electromagnetic torque of the motor has been studied. The harmonic spectrum and inductance component of different slot-and-pole combination has been calculated by this method, which obtains the regularity of winding inductance in different winding form, and the flux-weakening properties of different slot-and-pole combination have been compared.The torque ripple caused by the motor itself will have a negative impact on the servo system, so the torque ripple must be restrained. Through analytical model, the production mechanism of two kinds of torque ripple has been analyzed, and the influence of winding type, number of poles and slots, pole arc coefficient on the torque ripple has been studied, finite element method has been used to confirm the correction of the results.Due to the limit of torque, weight, efficiency, temperature and the complex relationship between motor’s parameters, the motor’s parameter design is a really hard problem. Base on the magnetic circuit characteristics of FSCW machine, an analytic model has been established. The effect of number of poles, ratio of length to diameter, magnetic flux density coefficient and split ratio on the output torque, weight and loss performance of the motor has been studied, and the selection principle and selection range of motor’s parameters has been summarized.In order to prove the corrections and effectiveness of the proposed theoretical analysis and design methods above, a 45-slot/38-pole PM torque motor with FSCW is designed and manufactured. The rated speed of the prototype is 50 rpm, the output torque can be up to 40N·m, and the electromagnetic part is about 8.8 kg. The prototype test is completed by a dynamometer platform and a servo motor controller. The results show all the indexes of the prototype has reached the design requirement. |
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