Design And Starting Process Research Of Wound-rotor Permanent Magnet Synchronous Motor

Nowadays, asynchronous motor is the main drive of crane, which has many characters.For example, the crane starts very frequently with heavy load usually, but works with alight load. It means the average load of crane is very low. it causes the efficiency ofasynchronous motor is very low, too. The permanent magnet synchronous motor (PMSM)has a character that the efficiency and power factor is still high in a heavy load. Theline-start PMSM cannot connect a resistance to rotor. so, it do not have a very high startingtorque. The wound-rotor PMSM uses PWM chopper to control the resistance whichconnects to rotor. With this method, the wound-rotor PMSM can start stepless. It has manysignatures both in theoretical and practical.A WPMSM model was designed and simulated in the paper. The rotor of wound rotorasynchronous motor is used in this model to save the cost, in addition, it’s easy to compare.The permanent magnet was putted in the inner of rotor and uses the formed coil aswindings to increase the starting torque. The rotor resistance of WPMSM can be changedcontinuously. Concerned this characteristic, the mathematical model was set and thecalculation method of outer resistance was deduced. With this model, the simulation wasfinished and compared with Squirrel cage PMSM, the result show that the WPMSM canreduce starting current and increase starting torque. The starting performance could beimproved by changing rotor resistance continuously.Starting control method is researched and speed detection circuit without sensor isdesigned in this paper. A constant resistance was series connected to rotor winding and apower electronic switch was parallel connected to this resistance. By controlling its on-off,the resistance can be changing stepless so that the impact torque is reduced greatly.