| As the problem of worldwide energy crisis and environmental deterioration becoming more and more serious, electric vehicles(EVs) have been the development direction of automobile industry.What's more, as the core component of energy conversion, the motor drive system used in EV is of important significance. Among all kinds of motors, permanent-magnet synchronous motors(PMSMs),which have high efficiency and large torque-to-weight ratio, are widely used in electric vehicles(EVs),particularly in midsize and compact EVs. In this paper, the aim is to improve the flux-weakening ability of the motor in drive system used in EV and the control performance. From two aspects of the motor design and drive control, an outer-rotor permanent magnet in-wheel motor with wide constant power operating range and a novel method to improve system performance are proposed. This paper mainly includes the following contents:Firstly, to solve the problem of weak capacity of flux-weakening in PM in-wheel motor, a synchronous motor with two-part rotor is described whose rotor comprises a surface-magnet part and a reluctance part mounted adjacent to each other on the circumference of a circle. This structure expands the flux-weakening capability by increasing armature reaction. On the selection of pole-slot match, the consistency and compensation between the two sets of the coils belonging to one phase of the 9/5-pole motor is proposed by comparing with 9/4-pole. Thus, the nature of the sinusoidal waveform of the PM flux-linkage and inductances of the motor is discovered and explained theoretically, which is verified by the finite element analysis. The influence of motor structural parameters as thickness of PM and pole arc coefficient to cogging torque is emphasized by comparing with normal PM in-wheel. Besides, the change rule and corresponding solution methods are introduced. The arc iron core pole is introduced to further optimize the cogging torque.Secondly,the mathematic model of the PM in-wheel motor and the nonlinear change of motor parameters by finite element software are analysed, and the method of motor parameters testing is introduced. According to the mathematic model, a non-linear model of PM in-wheel motor is established using Matlab Simulink, and based on a complete control system, the new motor designed is up to more than 2.5 times of base speed.Thirdly, to satisfy the non-linear change in IPMSM, MTPA control strategies is adopted to improve the accuracy and robustness of the control system. To improve the dynamic response and the reliability of the system, the control strategies of voltage feedback with current feed-forward is proposed. Also, the matlab simulation model is established to validate feasibility of proposed controlmethod in this paper.Finally, the corresponding software programming is accomplished based on DSP2812, the experimental platform with 5Kw tested motor and 11 Kw accompanies motor are built. The motor test such as nonlinear d-q axis inductance, load with rating torque 25 N.m at the based speed, dash an increase and a decrease in the load, flux-weakening operation at 4000 rpm are given. The tested motor is up to 2 times of base speed. The experimental results show that the control strategies proposed is effective and reliable, and it can meet the basic needs of the electric vehicle applications. |
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