The frequency converter controls the speed and power of the asynchronous motor mainly by adjusting the power frequency and voltage of the motor. Here is a detailed explanation of the process:
1.control the speed
Frequency conversion speed regulation principle:
The speed of an asynchronous motor is proportional to its power supply frequency. Therefore, by changing the frequency of the power supply, the speed of the asynchronous motor can be accurately controlled.
The inverter converts the input fixed frequency alternating current into adjustable lower frequency alternating current, so as to adjust the speed of the asynchronous motor.
Control mode:
VF control (voltage and frequency ratio constant control) : synchronously adjust the voltage and frequency of the motor power supply to maintain the stability of the motor flux. It is suitable for a wide range of speed regulation and ensures that the efficiency and power factor of the motor are not affected during the speed regulation process.
Slip frequency control: The speed detector such as a tachometer generator is installed on the motor rotor to monitor the speed of the motor in real time. On this basis, the output frequency of the inverter is set as the sum of motor speed and slip frequency to achieve more accurate speed control.
Vector control: An advanced asynchronous motor control method, according to the dynamic mathematical model of the motor, the torque current and the excitation current are carefully controlled, and the control performance is similar to that of DC motor.
Direct speed control (DSC) : Through real-time detection of the output voltage and current of the inverter, and through coordinate transformation processing, the magnetic flux and instantaneous speed of the motor are calculated to achieve direct control of the speed. This control mode has faster response speed, smaller torque ripple and higher accuracy.
2.control power
The relationship between power and speed and torque:
The power of asynchronous motor is closely related to its speed and torque. At a certain speed, the power is proportional to the torque.
By adjusting the output frequency and voltage of the inverter, the torque of the asynchronous motor can be changed, so as to control the power.
Energy saving control:
The frequency converter can adjust the speed and power of the motor according to the actual demand of the load, so as to avoid the excessive consumption of electric energy in the unnecessary high-speed running state of the motor.
In applications with large load changes, such as fans and pumps, the inverter can achieve accurate speed regulation and energy saving control, significantly improving production efficiency and reducing energy consumption.
Overload protection:
The inverter has overload protection function, when the motor load is too large, it can automatically reduce the output frequency and voltage to protect the motor from damage.
This also helps prevent excessive power problems due to overload.
3.Precautions in practical application
Select the right inverter model: Select the right inverter model according to the rated power, rated speed and load characteristics of the asynchronous motor.
Correct setting of frequency converter parameters: According to the actual application requirements, the correct setting of the frequency converter parameters, such as frequency range, acceleration time, deceleration time, etc.
Regular maintenance and inspection: Regular maintenance and inspection of the inverter to ensure its normal operation and extend the service life.
To sum up, the frequency converter realizes the precise control of speed and power by adjusting the power frequency and voltage of the asynchronous motor. In practical applications, it is necessary to select the appropriate inverter type and set the correct parameters according to the characteristics and load requirements of the asynchronous motor.