Misunderstanding of air compressor frequency conversion and energy saving

In recent years, the frequency conversion energy-saving transformation of air compressors has received unprecedented attention in the industry, and major manufacturing companies have invested manpower and material resources in an attempt to seize market opportunities. This is a good thing and is worth vigorously advocating.

However, I personally think that during this process, many practitioners lack a systematic understanding of the frequency conversion of air compressors, and there are some misunderstandings, mainly as follows:

Misunderstanding 1: After the air compressor is converted to save energy, it is not correct to say that the air compressor does not have an empty state.

Correct: The variable frequency air compressor also has an empty state.

Use the frequency converter to adjust the motor speed to achieve the effect of energy saving. As the output frequency of the inverter decreases, the gas production of the air compressor compression mechanism decreases, so that the air compressor can be operated in a loaded state as much as possible, and the utilization rate of the air compressor can be improved. When the gas terminal stops using gas, or the gas reaches the pressure requirement, the air compressor will enter the empty state.

In order to save costs, most of the air compressors we remodel use the original three-phase asynchronous motor instead of replacing it with a variable frequency motor. Then the ordinary three-phase asynchronous motor, after the transformation, in order to ensure its own heat dissipation and ensure the motor torque. The loading and running frequency cannot be lower than 20Hz. The unloading frequency cannot be lower than 15Hz, otherwise, the motor may be overheated and damaged. On the other hand, the motor speed of the air compressor is too low, which affects the oil pressure system. If the internal pressure is too low, it is easy to make the air compressor head high temperature, and at the same time increase the possibility of oil leakage. This type of motor is also not suitable for overfrequency operation, the maximum frequency is 50Hz. That is to say, after the frequency conversion transformation of the air compressor, the dynamic frequency conversion range of the motor is between 20Hz and 50Hz when loaded. In addition, after we transform the air compressor with frequency conversion, the air compressor will set three pressure control points: loading point, constant pressure point, and unloading point. At the loading point, the motor runs at full frequency of 50Hz. When the pressure is close to the constant pressure set point, the frequency converter will run at reduced frequency. If it is stable, then the inverter will experience unstable frequency changes. At the same time, when the frequency converter is running at the lowest frequency of 20Hz, the gas production can still make the pressure reach the unloading pressure value, then the air compressor will enter the unloading state. The air compressor is empty, the pressure drops to the loading point pressure, the air compressor enters the loading state again, and the above process is repeated. This is why the air compressor will enter the empty state. It is wrong to say that there is no empty car after the air compressor is transformed into a frequency conversion energy-saving machine.

Misunderstanding 2: It is wrong to say that frequency conversion air compressors must save energy.

Correct: the air compressor frequency conversion energy-saving transformation, the current energy-saving state does not mean that it will always save energy, and the current energy-saving state is not ideal does not mean that it will never save energy.

After the air compressor frequency conversion energy-saving transformation, the frequency converter controls the frequency around the pressure. When the production air consumption is greater than the air compressor output, the pressure is relatively low at this time, so the frequency converter always runs at full frequency 50Hz, that is to say, the air compressor There is no room for energy saving in the machine. In this case, energy saving control seems to have no effect. But from another point of view, even if the air compressor does not need frequency conversion control, it is already in the state of the highest energy efficiency. In this process, the frequency converter only plays the role of soft start and energy saving of the motor and the energy saving effect of improving the power factor of the motor, and the energy saving during the pumping process is not obvious. up. At this time, if the pressure cannot meet the air demand of the factory, then the factory needs to add another air compressor.

If the factory purchases an air compressor and the total air output of the air compressor is in excess, then the air compressor that has been converted to frequency conversion control can also play the role of energy-saving regulation. In this process, the ordinary air compressor purchased later is used as the main air supply, and the frequency conversion air compressor is the auxiliary role to adjust the constant air supply.

Conversely, if the current frequency conversion energy saving of the air compressor is in the above-mentioned unsatisfactory state of energy saving. And if the production capacity of the factory is reduced, or the gas consumption is reduced, then the inverter air compressor will also achieve energy saving. The principle is contrary to the above situation, so we will not analyze it. In this situation, the production capacity of the factory generally decreases, or the production of the factory is divided into day and night shifts. The output is reduced and the gas consumption is reduced. The production volume of the day shift is large, and the production volume of the evening shift is reduced. Or the power consumption is staggered, the production of the day shift is reduced, and the production capacity is transferred to the evening shift, so that the price of electricity at night will be lower. Therefore, we say that after the frequency conversion energy-saving transformation of air compressors, the energy-saving effect depends on the working conditions. It is also not possible to blindly pursue energy saving and energy efficiency. The stability of the machine is the prerequisite for modification and parameter setting.

Sollant Focus on Energy Saving