Since the inverter switching devices are high-power transistors, thyristors over current capacity than small, so choosing the right capacity is directly associated with their use safety.
And motor power and load match. The same capacity for the drive motor drive motor carried by the ability to vary the nature of the load, the same power of the motor, due to the different nature of the required load capacity of the drive is not the same. One square torque load (fan) than the capacity required to drive a low constant torque load. Usually the drive is directly suitable for driving the motor is given power rating or the apparent power, in the chemical industry for the fans, pumps such square torque load, according to motor power to select the appropriate drive. The following cases, the inverter must increase the capacity of:
① mechanical inertia starter motor a short time a large load;
② requires frequent increases the motor, deceleration;
③ In the hope that the acceleration and deceleration time, maximum current is greater than the drive motor overload capacity (when l min up to 1.5 times the rated current.) These cases can not simply drive by electric motor power to matching.
Light load with a small capacity motor is not free to drive. Big horse motor car, the power output of less than, matching the motor while allowing smaller than the nominal power inverter motor, but motors greater capacity of the smaller inductance, caused by the harmonic ripple current component will increase. So when the induction motor load less wish to use a smaller capacity drive on the one hand, taking into account the large capacity motor no-load current is high, once loaded, the total load current is over the rated current, the other On the one hand is the need to take note of the pulsating current situation will increase.
Inverter V / f graph correctly selected. For 50Hz, 380V AC induction motor, which in actual operation the motor should be the actual needs and the scope of work allowed to choose the appropriate graphics Vif. In the chemical industry, mainly used for inverter speed control of pumps, so choose Vif graphics should normally be met at the rated voltage 380V, the output frequency and maximum output frequency of this condition are 50Hz. I plant the pump motor speed inverter Vif selected graphic principles on the basis of the above election.
Torque boost curve choice. Torque boost can improve the motor output torque. Select the curve too small will lack the motor output torque to start the problems; election too large, the corresponding increase in loss of motor flux saturation, the motor temperature increase is not conducive to energy conservation. Increase in the choice of the torque curve should be selected according to the nature of the load.
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