How to adjust the frequency converter

Variable Frequency Drive (VFD) is a kind of power electronic equipment used to control the speed and torque of AC motor. By adjusting the frequency and voltage of the output power supply, the precise control of the motor running state is realized. Inverter is widely used in industrial production, construction, HVAC and other fields, and its adjustment function can not only improve the operating efficiency of equipment, but also achieve the goal of energy saving and consumption reduction. This paper will introduce the adjustment method of frequency converter and its precautions in detail.

First, the basic adjustment principle of frequency converter

The core function of the inverter is to convert the input AC with fixed frequency and voltage into AC with adjustable frequency and voltage to meet the needs of the motor under different working conditions. Its adjustment is mainly based on the principle of "V/F control" or "vector control". V/F control means keeping the ratio of voltage to frequency constant; Vector control is more advanced, which can control the excitation current and torque current of the motor respectively to achieve higher dynamic response and control accuracy.

Second, the main way of frequency converter regulation

1. Panel adjustment
Most general frequency converters are equipped with operation panels, and users can set parameters such as operating frequency, acceleration and deceleration time, maximum frequency, etc. by pressing keys. This method is suitable for field debugging or small-scale adjustment.

2. External analog input adjustment
Inverter is usually equipped with analog input interface (such as 4~20mA or 0~10V), and the frequency is set by external PLC, potentiometer or other control equipment. This method is suitable for occasions that need remote or automatic control.

3. Communication control
Through RS485, Modbus, Profibus and other communication protocols, the upper computer (such as PLC and industrial computer) sets the parameters and adjusts the frequency of the inverter. This method is suitable for integrated and highly automated systems.

4. Multistage speed control
The frequency converter can switch the operating frequency through external terminals by setting multiple preset frequency points. Suitable for equipment requiring multi-speed control, such as conveyor belts and fans.

5. PID closed-loop control
In some applications that need constant voltage, constant temperature and constant current, the PID function of frequency converter can be used to realize automatic adjustment through sensor feedback signal. For example, in the constant pressure water supply system of water pump, the pressure sensor feeds back the signal to the frequency converter, and the frequency converter adjusts the motor speed accordingly, thus maintaining the pressure stability.

Third, the steps of frequency converter adjustment

1. Confirm the load characteristics: know the motor power, rated voltage, rated frequency and other parameters to ensure that the inverter matches the motor.
2. Set the basic parameters:
-Set motor parameters (rated power, current, speed, etc.)
-Set the highest frequency and basic frequency.
-Adjust the acceleration and deceleration time
3. Selection of control mode: Select the appropriate control mode according to the application requirements, such as V/F control, vector control or direct torque control.
4. Debugging and operation: load the test step by step to observe whether the operation is stable and whether there are abnormal conditions such as overload and overcurrent.
5. Parameter optimization: According to the actual operation effect, fine-tune the frequency response and PID parameters to achieve the best performance.

IV. Matters needing attention during adjustment

-Power off before adjustment to prevent equipment damage caused by misoperation;
-Pay attention to the mechanical matching between motor and load during adjustment to avoid mechanical damage caused by too fast or too slow speed;
-For the closed-loop control system, ensure the accuracy of sensor signals;
-Pay attention to the heat dissipation of the frequency converter during debugging to avoid faults caused by overheating;
-Regularly check the parameter setting and running state of the frequency converter to ensure long-term stability.

tag

With the continuous improvement of industrial automation level, frequency converter plays an increasingly prominent role in energy saving and control accuracy. Mastering the adjustment method of frequency converter is not only the basic skill of technicians, but also an important means to improve the operation efficiency of equipment and reduce energy consumption. Reasonable setting and adjustment of frequency converter can not only prolong the service life of equipment, but also bring remarkable economic benefits to enterprises.