This paper provide two methods to analyze the cogging torque of PM motor with radial magnetic field and parallel magnetic field, FEM method and Analytic method. The FEM model and Analytic model of PM motor with radial magnetic field and parallel magnetic field are founded. We analyze the model in both methods. From the result of analysis. The air-gap magnetic density of PM motor can be analyzed. We can find the cogging torque of radial magnetic field PM motor is much heavily than the cogging torque of parallel magnetic field PM motor. The result of Analytic method is close to the result of FEM method. The Analytic method is useful in analyze the cogging torque of PM motor.
Direct torque control (DTC) which replaces the conventional current loop with torque loop can directly control the electromagnetic torque in order to reduce the torque error within the hysteresis bandwidth, and it can attenuated commutation torque ripple and the torque ripple of brushless DC (BLDC) motor with un-ideal back electromotive force (EMF) waveforms. Further, the key issue of feedback torque calculation in torque loop is the estimation of back-EMF in sensorless DTC of BLDC motor. So a sliding mode observer (SMO) is employed to estimate the back-EMF in real time. The torque and rotor speed can be derived from the estimated back-EMF. Simulation results demonstrate the proposed method is valid and effective.
Due to electromagnetic coupling and structure restriction of the two rotors, the design of anti-rotary PMSM is very complex. Inner motor and outer motor are designed respectively and then integrated in aspect of electromagnetic coupling and size restriction in this paper. Main size and electromagnetic relationship are designed according to objectives, and key design equation and project procedure are presented as well. Parameters effect on motor performance such as efficiency and torque density are analyzed. The performance of the prototype, well matches the theory analysis, whose validity is verified by FEA results
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