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10 Functions of Variable Frequency Drive

Adjustable torque limit
Through variable frequency drive speed control, corresponding torque limit can be set to protect the machinery from damage, so as to ensure the continuity of process and the reliability of products. The current frequency conversion technology not only makes the torque limit adjustable, but also controls the torque accuracy to be about 3%~5%. In power frequency state, the motor can only be controlled by detecting the current value or thermal protection, but can not be operated by setting a precise torque value as in the VFD control.

Controllable stopping mode
Just the same as the controllable acceleration, the stopping mode can also be controlled in variable frequency drive speed regulation, and different stopping modes can be selected (deceleration stop, free stop, deceleration stop+ DC braking). Meanwhile, it can reduce the impact on mechanical components and motors, thus making the whole system more reliable and the extending the service life accordingly.

Energy consumption of the centrifugal blower or water pump can be greatly reduced after using the VFD. As the final energy consumption is proportional to the motor speed, the return on investment will be obtained faster with VFD.

Reversible operation control
In the control of VFD there is no need for additional reversible control device to realize the reversible operation control, but only to change the phase sequence of output voltage, thus reducing the maintenance costs and saving installation space.

Reduce mechanical transmission components
At present, vector controlled VFD and synchronous motor can achieve efficient torque output, so mechanical transmission components such as gear box can be saved, and a direct VFD (variable frequency drive) system is formed, thus reducing the cost and space, improving the stability.

Lower power required for start-up

Motor power is proportional to the product of current and voltage, so the motor started directly by a power frequency consumes more power than that started by variable frequency. In some cases, the power distribution system has reached the maximum limit, and the surge generated from motor start-up under a direct power frequency will have a serious impact on other users on the same network. If a variable frequency drive is used for motor start-up, such a problem would not occur.

Controllable acceleration function

The variable frequency drive can start at zero speed and accelerate uniformly according to user’s needs, its acceleration curve can also be selected (linear acceleration, S-shaped acceleration or automatic acceleration). However, serious vibration will be generated on the motor or connected mechanical parts (such as shaft or gear) when starting under power frequency, such a vibration will further aggravate mechanical wear and loss, reduce the service life of mechanical components and motors. Moreover, variable frequency start-up can also be used on similar filling lines to prevent bottles from overturning or damage.

Adjustable running speed

VFD control can optimize the process and adjust rapidly according to the process, it can also change speed by remote control PLC or other controllers.

Control the motor’s starting current

When the motor is directly started under a power frequency, it will produce a current that is 7~8 times of its rated current. This current will greatly increase the electrical stress of motor winding and generate heat, thus reducing the service life of the motor. However, the VFD control can be started at zero speed and zero voltage (torque boost can also be added properly). Once the relationship between frequency conversion and voltage is established, the variable frequency drive can drive the load according to V/F or vector control mode. Application of VFD can fully reduce the starting current and improve the bearing capacity of winding, the most direct benefit for user is that maintenance cost of the motor will be further reduced and service life will be increased accordingly.

Reduce voltage fluctuation of power line

When the motor starts at power frequency, the voltage will fluctuate greatly while the current increases sharply, the magnitude of voltage drop will depend on the power starting the motor and the capacity of power distribution network. Voltage drop will lead to fault tripping or abnormal operation of voltage sensitive equipment in the same power supply network, such as PC, sensors, proximity switch and contactor. After using the frequency control, as the motor can start gradually at zero frequency and zero voltage, voltage drop will be eliminated to a maximum extent.

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