Ten functions of the VFD
First, adjustable torque limit
After the frequency conversion speed regulation, the corresponding torque limit can be set to protect the machine from damage, thus ensuring the continuity of the process and the reliability of the product. The current frequency conversion technology makes not only the torque limit adjustable, but even the torque control accuracy can reach 3% to 5%. In the power frequency state, the motor can only be controlled by detecting the current value or thermal protection, and it is not possible to set an accurate torque value to operate as in the variable frequency control.
Second, controlled stop mode
Like controllable acceleration, in variable frequency speed regulation, the stop mode can be controlled, and different stop modes can be selected (deceleration stop, free stop, deceleration stop + DC brake), which can also reduce mechanical parts and The impact of the motor makes the entire system more reliable and the life expectancy increases accordingly.
Third, energy saving
Centrifugal fans or pumps use inverters to significantly reduce energy consumption, which has been reflected in more than a decade of engineering experience. Since the final energy consumption is proportional to the speed of the motor, the return on investment is faster with the use of frequency conversion.
Fourth, reversible operation control
In the inverter control, to achieve reversible operation control without additional reversible control device, only need to change the phase sequence of the output voltage, which can reduce maintenance costs and save installation space.
Fifth, reduce mechanical transmission components
Since the current vector control inverter plus the synchronous motor can achieve efficient torque output, the mechanical transmission components such as the gear box can be saved, and finally constitute a direct variable frequency transmission system. This reduces costs and space and improves stability.
Sixth, the power required at startup is lower
The motor power is proportional to the product of the current and the voltage, so the power consumed by the motor directly started by the power frequency will be much higher than the power required for the inverter start. In some working conditions, its power distribution system has reached the maximum limit, and the surge generated by its direct power frequency starter motor will have a serious impact on other users on the same network, and will be warned by the grid operator, even fine. . If the inverter is used to start and stop the motor, no similar problems will occur.
Seven, controllable acceleration function
The variable frequency speed control can be started at zero speed and uniformly accelerated according to the user’s needs, and its acceleration curve can also be selected (linear acceleration, S-shaped acceleration or automatic acceleration). When the power frequency is started, the motor or the connected mechanical part shaft or gear will produce severe vibration. This vibration will further exacerbate mechanical wear and tear and reduce the life of mechanical components and motors. In addition, variable frequency start-up can also be applied to similar filling lines to prevent the bottle from falling over or being damaged.
Eight, adjustable operating speed
The use of variable frequency speed control can optimize the process, and can be quickly changed according to the process, and can also achieve speed changes through remote control PLC or other controllers.
Nine, control the starting current of the motor
When the motor is started directly at the power frequency, it will produce 7 to 8 times the rated motor current. This current value will greatly increase the electrical stress of the motor windings and generate heat, thereby reducing the life of the motor. The frequency conversion speed regulation can be started at zero speed zero voltage (it can also be appropriately increased torque boost). Once the relationship between frequency and voltage is established, the inverter can drive the load to work according to V/F or vector control. The use of variable frequency speed regulation can fully reduce the starting current and improve the winding endurance. The most direct benefit of the user is that the maintenance cost of the motor will be further reduced and the life of the motor will increase accordingly.
Ten, reduce power line voltage fluctuations
When the motor power frequency starts, the current will increase sharply, and the voltage will fluctuate greatly. The magnitude of the voltage drop will depend on the power of the starting motor and the capacity of the distribution network. A voltage drop will cause voltage-sensitive devices in the same power supply network to trip or operate abnormally, such as PCs, sensors, proximity switches, and contactors. After the frequency conversion speed regulation is adopted, since the voltage can be gradually started at the zero frequency zero voltage, the voltage drop can be eliminated to the greatest extent.