Research On Control Strategy Of In-wheel Disc Coreless Permanent Magnet Synchronous Motor For Electric Vehicles

The disc coreless permanent magnet synchronous motor(DCPMSM) has several advantages, such as strong overload capacity, zero cogging torque, sinusoidal distribution of flux density and back EMF and linear parameters. It is particularly suitable for the workplace where are special requirements of the motor volume, low-speed performance, fast response and strong overload ability. The motors tend to have low inductance because of the coreless structure. There is a stringent current ripple in the motor winding that produces unacceptable torque ripple if driven from conventional drivers with a PWM control method based on voltage source inverter(VSI).The purpose of this project is to research a drive system for the DCPMSM, and it will give full play to the advantages of its structure and dynamic performance. The analysis of the mechanism of current fluctuations was made based on the characteristics of the DCPMSM. The following several control strategies for the DCPMSM were analyzed and researched:1. The control method of the series inductance in the stator winding circuit. Three inductances were added in the stator winding circuit to increase the value of the stator inductance, and a rotor flux oriented control algorithm was adopted in the DCPMSM driver. The torque ripple with different values of the series inductor was discussed, as well as the operating characteristics at different speed was discussed.2. The control method based on the current chopper converter. The six-step conduction method was used in the system, each phase conducted 120°(electrical angle). The reference current vector was adjusted by the proposed current control algorithm according to the rotor angle. To control the motor electromagnetic torque, the amplitude of output current and duty cycle of the switching device of the current source chopper is calculated by a feedback loop of instantaneous torque control.3. The control method based on the three-level inverter. In order to improve the switching frequency of the inverter, and reduce the torque ripple caused by small inductance, the MOSFET was used as the main power switching devices. A three-level neutral point clamped(NPC) inverter was proposed to drive the DCPMSM, the working principle of the system is introduced detailedly. The rotor flux oriented control algorithm was employed in the system, which can dramatically reduce the current ripple caused by small inductance.4. But for the coreless structure, the DCPMSM tend to have small effect of the armature reaction because of the long effective air gap. As a result, the speed range was limited because of the weak capability of flux-weakening. To solve this problem, an optimal control strategy was proposed, which can adjust the inverter DC-link voltage by using the Buck-Boost converter. The speed range of the motor can be widened by increasing the dc-link voltage.