（1）D-Direct On Line: Advantages: less starting equipment, simple starting mode, low cost,  Disadvantages: the starting current is large, affecting the service life of the motor and unfavora to the stable operation of the power grid . （2）YD-Star-Delta: Advantages: small starting current and small starting torque， Disadvantages: can only be used for delta connected motors. （3）VFD: Advantages: small starting current, wide application range and simple operation， Disadvantages: high cost, complex internal structure.