A direct torque control (DTC) strategy of five-phase permanent magnet synchronous motor (PMSM) is proposed in this study. The proposed DTC scheme uses five-phase inverter to output basic voltage vector or discrete synthesised voltage vectors in one control period to realise the direct control of torque and flux on the fundamental and third harmonic planes simultaneously, and then realise the third harmonic current injection to enhance the load capacity. In order to realise the third harmonic current injection with maximum torque outputting and minimum peak of stator current, the maximum torque per ampere (MTPA) scheme is proposed in which the minimum copper loss and the same phase relation between fundamental and third harmonic currents are taken as the constraint conditions, and the amplitude of the fundamental and third harmonic fluxes and the optimal torque distribution ratio are derived in MTPA. A TMS320F2812-based digital controller is adopted as a core to construct the DTC experimental platform of the five-phase PMSM with 800 W rated power. The results of experiment and simulation show that the proposed DTC strategy can improve the maximum load torque of the motor, reduce the flux density of the stator and improve the core utilisation rate of the stator.
A doubly-salient relative permeance method is presented herein to predict the magnetic field of bearingless fluxswitching permanent-magnet machines (BFSPMMs). Firstly, the subdomain model method is used to compute the magnetic field of slotless BFSPMMs. Then, the slotting effect of the stator and rotor is obtained by the doubly-salient relative permeance method. By combining the two above, the air-gap magnetic field of slotted BFSPMMs can be obtained. The doubly-salient relative permeance method is based on the theory of the subdomain model method. The whole doubly-salient structure is divided into several subdomains, and the Laplace equations for subdomains are established. Then, according to the boundary conditions between subdomains and the core, and the continuity conditions between adjacent subdomains, the equations are solved to calculate the slotting effect. Based on the proposed analytical model, the flux density and electromagnetic performances including back-electromotive force (EMF), torque, and suspension force are predicted and compared with the finite element method results. Furthermore, the back-EMF of the prototype motor is measured and the suspension experiments are carried out based on the analytical method. The comparison results and experiment results verify the validity of the analytical method.
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