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Application Analysis of Frequency Converter in Refrigerator
The refrigerator is basically a constant torque characteristic, so as long as the inverter output voltage is proportional to the frequency. However, the refrigerator is widely used in combination with the actual machine, and generally it is not completely consistent with the design conditions of the motor. The voltage also needs to be changed over the operating conditions, and ultimately the optimal V/F mode still needs to be determined experimentally. In addition, in order to improve the efficiency during acceleration, it is possible to use a special motor for inverter, but as a backup when the inverter fails, it is difficult to directly use the power frequency power supply for the special motor for frequency conversion. Moreover, the cost of switching to a variable frequency motor will increase significantly, so we still use the original motor and mechanical equipment, but change the original auto-coupling step-down start to the inverter control system.
In order to prevent the poor heat dissipation of the refrigerator and the reduction of the overall efficiency when the output frequency of the inverter is low, the minimum operating frequency is set to 30Hz on the inverter.
energy saving effect:
1. When the motor is started with a frequency converter, the starting current is greatly reduced.
2. The use of inverter to control the motor can improve the power factor.
3. The frequency converter can be used to properly increase the frequency, which can save the number of starting motors.
To sum up, according to past experience, the power saving rate should reach about 5%.
Precautions:
The following describes the main problems that should be paid attention to when using the inverter to control the refrigerator.
1) When the reciprocating compressor decelerates below the rated speed, the thickness of the oil film of the piston ring, etc. decreases, which may cause abnormal wear of the cylinder and other components. Especially for centrifugal oil supply and splash oil supply, deceleration will cause an extreme reduction in oil supply, and more attention should be paid to lubrication.
2) In the case of 5-10HP semi-hermetic compressors, the minimum frequency is limited to about 30HZ due to the above-mentioned lubrication problems, motor efficiency at low load, winding temperature rise, resonance frequency of anti-vibration devices, etc.
3) The refrigeration unit using Freon series refrigeration blitz will face the problem of oil return of the evaporator when the capacity is controlled. Generally, in the capacity control operation, it is necessary to perform the oil return operation periodically.