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Some skills of frequency converter application

2020-12-18

Brake unit supplier reminds you: with the rapid development of power electronic technology, computer technology and automatic control technology, electric drive technology is facing a new revolution. In the field of electric drive, the frequency control system has become the mainstream because of its high efficiency and good performance. Benefiting from the promotion of energy saving and emission reduction, green environmental protection and other strategies, as an important equipment of frequency conversion and speed regulation, the inverter industry has become one of the industries with great market potential in the next few years, followed by the research and development and application of frequency converter functions. Let's talk about some application skills of frequency converter.


1. Shielding wire shall be selected for signal line and control line, which is beneficial to prevent interference. When the line is long, such as the distance of 100m, the conductor section should be enlarged. The signal line and control line should not be placed in the same cable trench or bridge with the power line to avoid mutual interference. It is better to place the signal line and control line through the pipe, which is more appropriate.


2. The current signal is the main transmission signal, because the current signal is not easy to decay and is not easy to be interfered. In practical application, the output signal of sensor is voltage signal, which can be transformed into current signal by converter.


3. Frequency converter closed-loop control is generally positive, that is, the input signal is large, the output is also large. But there is also a reaction, that is, a large input signal and a small output.


4. In the closed-loop control can choose the pressure signal, do not choose the flow signal. This is because of the low price of pressure signal sensor, easy installation, small workload and convenient debugging. However, if the process has the requirement of flow proportioning and requires accuracy, the flow controller must be selected, and the appropriate flowmeter should be selected according to the actual pressure, flow rate, temperature, medium, speed, etc.


5. The built-in PLC and PID functions of the inverter are suitable for the system with small signal variation and relatively stable. However, due to the built-in PLC and PID functions only adjust the time constant, it is difficult to get a more satisfactory transition process requirements, and debugging is more time-consuming.


6. Signal converter is often used in the peripheral circuit of frequency converter, which is composed of Hall element and electronic circuit. According to the signal transformation and processing methods, it can be divided into voltage to current, Er to voltage, DC to AC, AC to DC, voltage to frequency, Er to frequency, one in and many out, multiple in and one out, signal superposition, signal shunt, etc.


7. The frequency converter is often equipped with peripheral circuit when it is applied


(1) The logic function circuit is composed of self-made relay and other control elements;


(2) Buy ready-made unit external circuit;


(3) Simple programmable controller is selected;


(4) When using different functions of frequency converter, function card can be selected;


(5) Small and medium-sized programmable controllers are selected.


8. Reducing the base frequency is the most effective way to improve the starting torque. The principle analysis is as follows.


As the starting torque is greatly increased, some difficult to start equipment, such as extruder, cleaning machine, dryer, mixer, coating machine, mixer, large fan, water pump, roots blower, etc., can start smoothly. This is more effective than the usual starting frequency. By using this method and combining with the measures of changing heavy load to light load, the current protection can be increased to the maximum value, and almost all equipment can be started. Therefore, it is the most effective and convenient way to increase the starting torque by reducing the base frequency.


(1) In the application of this condition, it is not necessary to reduce the base frequency to 30Hz. Step down can be adopted every 5Hz. The frequency of descending is as long as the system can be started.


(2) The lower limit of base frequency should not be lower than 30Hz. From the torque point of view, the lower the lower limit, the greater the torque. However, it should also be considered that IGBT will be damaged when the voltage rises too fast and the dynamic Du / DT is too large. The result of practical use is that when the frequency of 50 Hz drops to 30 Hz, it can be safely used to improve the torque.


(3) Some people worry, for example, the voltage has reached 380V when the base frequency is 30Hz. Then when the normal operation may need to reach 50 Hz, whether the output voltage jumps to 380V, so that the motor can not stand, the answer is that this phenomenon will not happen.


(4) Some people worry that if the substrate is lowered to 30Hz, the voltage will reach 380V. If the output frequency can reach the rated frequency of 50 Hz, the answer is: of course, the output frequency can reach 50 Hz.


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