Frequency converter is a device to realize variable speed operation of motor. It is an AC power supply device that converts power frequency (50 Hz or 60 Hz) into various frequencies.
Frequency converter is an electric control equipment of AC motor, which uses frequency conversion technology and microelectronics technology to control AC motor by changing the frequency of motor power supply. It has many frequency setting modes, such as keyboard setting, contact signal setting, analog signal setting, pulse signal setting and communication mode setting. By using the on-off function of power semiconductor devices, power frequency power supply can be converted to another frequency. It can complete soft starting, energy saving, frequency conversion speed regulation, improve operation accuracy, change power factor, over-current/over-current of AC asynchronous motor. Voltage/overload protection and other functions, its role is mainly in the following aspects.
1. Adjustable Torque Limit [Converter Matching Equipment]
After adjusting the speed by frequency conversion, the corresponding torque limit can be set to protect the machinery from damage, so as to ensure the continuity of the process and the reliability of the product. Current frequency conversion technology makes not only the torque limit adjustable, but also the control accuracy of the torque can reach about 3%~5%. In the power frequency state, the motor can only be controlled by detecting the current value or thermal protection, but can not be operated by setting the precise torque value as in the frequency conversion control.
Controlled stopping mode is the same as controllable acceleration. In variable frequency speed regulation, stopping mode can be controlled, and different stopping modes can be selected (decelerated parking, free parking, decelerated parking 10 DC braking). Similarly, it can reduce the impact on mechanical components and motors, so that the whole system is more reliable and its life will increase accordingly.
3. Energy Conservation
The energy consumption of centrifugal fans or pumps can be greatly reduced by using frequency converters, which has been reflected in more than ten years’L-range experience. Since the final energy consumption is proportional to the speed of the motor, the return on investment is faster when frequency conversion is adopted.
4. Reversible Operation
In the control of frequency converter to achieve reversible operation control, no additional reversible control device is needed, only the phase sequence of output voltage is changed, which can reduce maintenance and save installation space.
5. Reduce components
At present, Vector-controlled frequency converter and synchronous motor can achieve high-efficiency torque output, Save gearbox and other mechanical transmission components, and eventually form a direct frequency conversion drive system. In this way, the cost and space can be reduced and the stability can be improved.
6. Lower power required for startup
The power of the motor is proportional to the product of current and voltage, so the power consumed by the motor starting directly through frequency I will be much higher than that required by frequency conversion. When the distribution system has reached the maximum limit, the surge generated by starting the motor directly will have a serious impact on other users on the same network, which will be warned by the grid operators, or even fined. It will not happened, If use frequency converter.
7. Control Acceleration
Frequency conversion speed regulation can start at zero speed and accelerate uniformly according to user’s needs, and its acceleration curve can also be selected (linear acceleration, S-shaped acceleration or automatic acceleration). Electric motors or connected mechanical parts will produce violent vibration when starting through I. frequency. This vibration will further aggravate the mechanical wear and loss, and reduce the life of mechanical components and motors.
8. Adjustable running speed
Frequency conversion speed regulation can optimize the operation process, and can change rapidly according to the process, but also through remote control of PLC or other controllers to achieve speed change.
9. Control Start Current of Motor
When the motor starts directly through I frequency, it will generate 7 to 8 times the rated current of the motor. This current value will greatly increase the electrical stress of the motor winding and generate heat, thus reducing the life of the motor. Frequency conversion speed regulation can be started at zero speed and zero voltage (also can be properly increased by torque). Once the relationship between frequency and voltage is established, the converter can drive the load according to V/F or vector control mode. Frequency conversion speed regulation can fully reduce the starting current and improve the bearing capacity of the winding. The most direct benefit of users is that the maintenance cost of the motor will be further reduced and the life of the motor will be increased accordingly.
10. Reducing Voltage Fluctuation of Power Line
When the motor starts at L-frequency, the voltage will fluctuate dramatically as the current increases sharply. The magnitude of the voltage drop will depend on the power of the starting motor and the capacity of the distribution network. Voltage drop will lead to fault tripping or L abnormality of voltage sensitive devices in the same power supply network, such as PC, sensors, proximity switches and contactors, will all wrong. After adopting frequency conversion speed regulation, these situations can be eliminated to the greatest extent because it can start gradually at zero frequency and zero voltage.
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