Selection of the motor matched by the inverter:

(1) The data of the original stage motor is: R, = 60 kW, and = 1800 r/min.

(2) Determination of the capacity of the asynchronous motor. Since the high-speed section of the load has constant power characteristics, and the motor has constant power characteristics above the rated frequency, in order to fully utilize the potential of the motor, the operating frequency of the motor should be appropriately increased above the rated frequency, so that the effective torque is as shown in the figure. Curve 2 in 8.18 is shown. In the figure, curve 1 is the mechanical property of the load. As can be seen from the figure, the required motor capacity is proportional to the area OLKK', which is very close to the actual power required by the load. After the main motion of the above-mentioned A series gantry bed machine is controlled by frequency conversion, the capacity of the motor can be reduced to 3/4 of the original DC motor, that is, 45 kW is enough. Considering that the asynchronous motor is above the rated frequency, its effective torque still has the characteristics of constant power, but its overload capacity is reduced at high frequency. To leave room for selection, the 55kW motor is selected, and its maximum working frequency is set to 75Hz. .