Design And Starting Performance Analysis Of Wound-Rotor Line-Start Permanent Magnet Synchronous Motor

Nowadays, reducer-asynchronous motor system is widely used in the drive of cranes. The characteristic of cranes is frequently starting under the heavy load, while mostly running under the light load; the rate of average load is low. The asynchronous motor's efficiency reduces along with load rate decrease. The crane's total efficiency is low. Permanent Magnet Synchronous Motor (PMSM) has the character of high power factor and efficiency, and both of them are irrelevant to load rate. But Squirrel cage Line-start Permanent Magnet (Squirrel cage LS-PMSM) can't be connected to rotor external resistance, so difficult to apply to crane. In addition, with the starting system of switching gradually the rotor external resistance, the motor will produce an impact torque, which should be avoided for security. So PWM chopper regulation of fixed value resistance in WR LS-PMSM has theoretical significance and practical engineering value.In this paper, a 7.5kW, 6 poles Wound-rotor Line-start Permanent Magnet Synchronous Motor (WR LS-PMSM) was designed to drive the crane to solve the problem of low efficiency and power factor, and the design method was analyzed. This paper built a mathematical model for the starting process, analyzed the magnetic field and checked the permanent magnet's temperature in the starting process by using Finite Element Method (FEM) simulation, discussed the influence of rotor's initial position and inertia. In starting process, alternating-current (AC) is produced in the rotor winding and then it was transformed to direct-current (DC) by the three phase all controlled rectifier circuit. In DC circuit, a definite value resistance was connected in series and an electronic power switch was connected in parallel in each side of it. By controlling the on-off of the switch, chopper regulation of fixed value resistance was equal to stepless regulation of externally connecting resistors. In this way, the impact torque in starting process could be greatly reduced. Due to the expression of asynchronous starting torque and rotor's resistance, the relation of rotor's resistance in AC circuit and speed was established. By the transforming in rectifying circuit, the expression of fixed value resistance in DC circuit an AC resistance was further established. So the maximum fixed value resistance was determined.Comparative analysis shows that connecting rotor external resistance in rotor-side contributed to reduce starting current and improve starting torque, which has a better starting performance than Squirrel cage LS-PMSM. WR LS-PMSM as the crane's driving not only improves the efficiency, but also has a stable start. Furthermore, due to the congenital advantage of PMSM, WR LS-PMSM has more superiority to be the drive system of the crane.