2013年5月28日星期二

Elevator inverter works


When the elevator parts - elevator inverter to greater than 50Hz frequency, the motor output torque will be reduced.
       The motors are generally designed and manufactured according to 50Hz voltage, the rated torque in this voltage range is given. Therefore, under the nominal frequency governor called constant torque speed. (T = Te, P <= Pe)
       Frequency converter output frequency is 50Hz, the torque generated by the motor and the frequency is inversely proportional to to decrease the linear relationship.
       When the motor speed greater than 50Hz frequency, the motor load size must be given consideration to prevent the motor output torque is insufficient.
       For example, the motor torque generated at about 100Hz to 50Hz, the generated torque is reduced to 1/2.
       Therefore, above the rated frequency governor called the constant power speed. (P = Ue * Ie)
   
(Six) than 50Hz elevator inverter applications
       As you know, for a particular motor, the rated voltage and rated current is constant.
       Such as the elevator inverter and motor ratings are: 15kW/380V/30A, motors can operate at 50Hz or more
       When the speed is 50Hz, the elevator inverter output voltage is 380V, current is 30A. Then if increasing the output frequency to 60Hz, maximum elevator inverter output voltage and current can only to 380V/30A. Obviously the output power constant. So we called constant power speed.
       Then the torque situation do?
       Since P = wT (w: angular, T: torque) because P constant, w increased, so torque is reduced accordingly.
       We can also find another point of view:
       The stator voltage U = E + I * R (I is the current, R is the electrical resistance, E is the EMF)
       As can be seen, U, I is constant, E is constant.
       And E = k * f * X, (k: constant, f: frequency, X: flux), when f the 50 -> 60Hz, X is reduced accordingly
       The motor is, T = K * I * X, (K: constant, I: current, X: flux), so the torque T will follow the flux X decreases.
       At the same time, less than 50Hz, since the I * R is small, so the U / f = E / f constant, the magnetic flux (X) is constant and the current is proportional to the torque T, which is why usually the drive to describe its flow capacity overload (torque) capabilities. known as constant torque speed (rated current is constant -> Maximum torque constant)
       Conclusion: When the elevator inverter output frequencies from 50Hz above increases, the output torque of the motor is reduced.

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