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The three-phase asynchronous motor speed formula is as follows:
v=60f/n
v motor speed
frequency
n Number of motor pole pairs
When there is no frequency converter, the speed of the motor can only be changed by changing the number of pole pairs of the motor, and the frequency is 50HZ;
The speed regulation through the frequency converter is to change the frequency of the motor operation, and the speed regulation can be realized without replacing the motor. Therefore, the principle of frequency converter speed regulation is the above formula

The frequency converter is a power control device that uses the on-off function of power semiconductor devices to convert the power frequency power supply to another frequency. The frequency converter we use now mainly adopts the AC-DC-AC method (VVVF frequency conversion or vector control frequency conversion). AC power to supply the motor. The circuit of the frequency converter is generally composed of four parts: rectification, intermediate DC link, inverter and control. The rectification part is a three-phase bridge uncontrolled rectifier, the inverter part is an IGBT three-phase bridge inverter, and the output is a PWM waveform, and the intermediate DC link is filtering, DC energy storage and buffering reactive power.

According to the working principle of the above-mentioned frequency converter, the frequency converter changes the speed by changing the frequency of the motor, so it is generally used together with the frequency conversion speed regulation motor. So what's the point of using a frequency converter to adjust the speed of the motor? What does the inverter do? The following Taizhou Hengfu Motor Factory will take you to analyze:

1. Frequency conversion energy saving
The energy saving of the frequency converter is mainly manifested in the application of fans and water pumps. In order to ensure the reliability of production, a certain amount of margin is left when all kinds of production machinery are designed to be equipped with power drives. When the motor cannot run at full load, in addition to meeting the power drive requirements, the excess torque increases the consumption of active power, resulting in a waste of electric energy. The traditional speed regulation method of fans, pumps and other equipment is to adjust the air supply volume and water supply volume by adjusting the inlet or outlet baffle and valve opening. middle. When using frequency conversion speed regulation, if the flow requirement is reduced, the requirement can be met by reducing the speed of the pump or fan.

2. Soft start energy saving
The hard start of the motor will cause a serious impact on the power grid, and it will also require too high a capacity of the power grid. The large current generated during start-up and the vibration will greatly damage the baffle and valve, and will damage the equipment, pipes, etc. The service life of the road is extremely unfavorable. After using the frequency conversion energy-saving device, the soft start function of the frequency converter will make the starting current start from zero, and the maximum value will not exceed the rated current, which reduces the impact on the power grid and the requirements for power supply capacity, and prolongs the use of equipment and valves. life. Save equipment maintenance costs.

3. Power factor compensation and energy saving
Reactive power not only increases line loss and heating of equipment, but more importantly, the reduction of power factor leads to the reduction of active power of the grid. Finally, due to the function of the filter capacitor inside the frequency converter, the reactive power loss is reduced and the active power of the grid is increased.

4.For synchronous speed regulation
When multiple motors form an electric shaft system, using a frequency converter to adjust the speed can make the system stable.
Using a frequency converter to adjust the speed of the motor has so many functions, so how to choose a suitable frequency converter to control the speed of the asynchronous AC motor? When selecting the frequency converter, the following points should be determined:
1) The purpose of using frequency conversion; constant voltage control or constant current control, etc.
2) The matching problem between the inverter and the load;
I. Voltage matching: The rated voltage of the inverter is consistent with the rated voltage of the load.
II. Current matching: For ordinary centrifugal pumps, the rated current of the frequency converter matches the rated current of the motor. For special loads such as deep water pumps, etc., it is necessary to refer to the motor performance parameters to determine the inverter current and overload capacity with the maximum current.
III. Torque matching; this situation may occur when there is a constant torque load or a reduction device.
3) The load type of the frequency converter; such as vane pump or positive displacement pump, etc., pay special attention to the performance curve of the load, which determines the method of application.
4) If the inverter needs to run with a long cable, measures should be taken to suppress the influence of the long cable on the ground coupling capacitance to avoid insufficient output of the inverter. An output reactor is installed at the output end.
5) When using a frequency converter to drive a high-speed motor, due to the small reactance of the high-speed motor, the increase in high-order harmonics will lead to an increase in the output current value. Therefore, the selection of the frequency converter used for high-speed motors has a slightly larger capacity than that of ordinary motors.
6) For some special applications, such as high temperature and high altitude, this will cause the derating of the inverter, and the capacity of the inverter should be enlarged by one gear