Freezers are used for freezing and refrigerating foods. Therefore, in the food industry, the use of refrigerators is very popular, and more and more inverters are used in the control of refrigerators.
one. The purpose of inverter use:
Variable frequency control (variable compressor capacity control) of the compressor in the chiller allows the chiller to always operate at high efficiency close to the design conditions for changes in the refrigeration load. This is the main purpose of applying frequency converters to refrigeration compressors. The main advantages of inverter-controlled refrigerators are as follows
1) Energy saving Changes the compressor speed in response to changes in the cooling load so that it always runs at the optimum point. This reduces the power required.
2) Constant temperature The use of continuous capacity control results in a very small change in the temperature of the cold holdings. In addition, even with an increase in the temporary cooling load, it is possible to rely on the speed of the gallon to reduce the temperature change of the cold storage.
3) Improvement of refrigerating capacity The capacity of compressors directly connected with hermetic motor in the 50hz region is only 80% of that in the 60hz region. Inverter control, however, can be independent of the power supply frequency and always maintains certain capabilities.
two. Equipment composition
Figure 1 shows an example of a frequency converter controlling the No. 1 chiller in the Yellow River Brewery. In this example, the frequency converter selects 00KW frequency converter that Emerson model is TD2000-4T2000G, the refrigerator is produced for Dalian freezer factory, the electrical machinery power is 190KW. PID regulation is completed by the built-in PID regulator that comes with the inverter. In the method of controlling the rotation speed of the chiller according to the change of load, our purpose is to control the temperature of the suction inlet of the chiller. Due to the difficulty in sampling the temperature of the chiller, the temperature and pressure of the suction inlet have a certain corresponding relationship, and on the spot The pressure transmitter installed on the pipeline is more tolerable. Therefore, in this system, we use a pressure sensor to detect the suction pressure of the compressor. As long as the inverter controls the pressure to remain constant, the suction inlet temperature remains constant. At the same time taking into account the safety requirements of the refrigerator when working, we have the original temperature protection, oil pressure protection of the refrigerator through the relay access to the inverter, to ensure that there is a temperature protection or oil pressure protection action, the inverter can automatically Shut down to prevent damage to machinery and equipment. In addition, the chiller was originally controlled by the two places. After adopting the frequency conversion, we still maintain the original two-land control. In this way, it is easier for operators to operate.
three. Operating mode
Refrigerator is basically a constant torque characteristic, so just make the inverter output voltage proportional to the frequency on the line. However, the scope of use of the refrigerator combined with the actual machine is wide, and is generally not completely consistent with the design conditions of the motor. The voltage also needs to be changed in the operating conditions, and eventually it is still necessary to determine the best /F mode by experiment. In addition, in order to improve the efficiency at the time of acceleration, inverter-specific motors can be used instead. However, as a backup for inverter faults, it is difficult for frequency-converter-dedicated motors to directly operate with the power frequency power supply. In addition, the cost of switching to a variable-frequency motor will increase significantly. Therefore, we still use the original motor and mechanical equipment, but we will change the original auto-buck start to a pressure closed-loop system controlled by the inverter.
In the closed loop system configuration, Emerson inverter can define two typical input and output characteristics, namely positive action and negative action. These two characteristics can be flexibly used in the control system with different feedback characteristics. In this system, reactive characteristics are used, and the polarity of the feedback gain is negative. That is, when the inlet pressure increases, the output frequency of the inverter also increases. When the inlet pressure decreases, the output frequency also decreases.
In order to prevent the inverter output frequency from being low, the cooling of the refrigerator is poor and the overall efficiency is reduced. The minimum operating frequency is set to 30Hz on the inverter.
four. energy saving effect
The compressor load is basically a constant torque load. For a constant torque load, the general expression of the output power P of the motor is
PâˆT*N
In the expression, T: load torque N: motor speed
This means that, even with a constant torque load, using a frequency converter or the like will reduce the speed of the motor and the output power of the motor will decrease. Inverter input power
The PIN can be expressed by the following formula:
PIN=P/(ηINV*η m)
In the expression, PIN: inverter input power ηINV: inverter efficiency η m : motor efficiency
From the above equation, it is assumed that the total efficiency (ηINV*ηm) is constant for the motor rotation speed. Obviously, the decrease of the motor speed will cause the output power P of the motor to decrease, and the input power PIN of the inverter that is proportional to it will also decrease, that is, the power consumption will be reduced. However, as shown in FIG. 2 , in order to decrease the output frequency of the inverter in order to reduce the motor rotation speed, the total efficiency also decreases. However, because the frequency reduction is greater than the total efficiency reduction, there is still significant energy savings compared to the original control method. In addition, the electromagnetic speed control motor, squirrel cage motor stator voltage control, etc., in the former speed control motor, when the speed is reduced, the total efficiency will be greatly reduced, and therefore basically do not get the effect of energy saving at low speed. Therefore, the use of frequency converters to replace these previous speed control methods, can fully save energy.
In addition to the power conversion loss, the inverter method has about 5% of loss. This loss is basically independent of the power of the inverter. Therefore, the larger the motor power, the smaller the proportion of this loss, and the more significant the energy saving effect. At the same time, the inverter mode has the advantages of being resistant to short-term peak load in summer (depending on speed increase) and fine temperature control.
Fives. Precautions
The following describes the main issues that should be addressed when using inverters to control the freezer.
1) When the reciprocating compressor is decelerating below the rated speed, the oil film thickness of the piston ring or the like decreases, which may cause abnormal wear of cylinders and other components. In particular, for centrifugal oil supply and spatter injection, the deceleration will cause extreme reduction in oil supply, and lubrication should be paid more attention.
2) In the case of 5-10 HP class semi-hermetic compressors, the minimum frequency is limited to about 30 Hz due to the lubrication problems mentioned above, as well as motor efficiency at low loads, winding temperature increase, and the vibration frequency of the anti-vibration device.
3) In the case of reciprocating type, the actual upper limit of the maximum frequency is 100% of the rated frequency in consideration of problems such as vibration, noise, and valve durability.
4) When using the Freon series of refrigeration blitz freezers in capacity control operation, they will face evaporator oil return problems. Generally, in the capacity control operation, it is necessary to return to oil regularly.
ZGAR Accessories
ZGAR electronic cigarette uses high-tech R&D, food grade disposable pod device and high-quality raw material. All package designs are Original IP. Our designer team is from Hong Kong. We have very high requirements for product quality, flavors taste and packaging design. The E-liquid is imported, materials are food grade, and assembly plant is medical-grade dust-free workshops.
Our products include disposable e-cigarettes, rechargeable e-cigarettes, rechargreable disposable vape pen, and various of flavors of cigarette cartridges. From 600puffs to 5000puffs, ZGAR bar Disposable offer high-tech R&D, E-cigarette improves battery capacity, We offer various of flavors and support customization. And printing designs can be customized. We have our own professional team and competitive quotations for any OEM or ODM works.
We supply OEM rechargeable disposable vape pen,OEM disposable electronic cigarette,ODM disposable vape pen,ODM disposable electronic cigarette,OEM/ODM vape pen e-cigarette,OEM/ODM atomizer device.
ZGAR Accessories Disposable Pod Vape,ZGAR Accessories Disposable Vape Pen,ZGAR Accessories,ZGAR Accessories Electronic Cigarette,ZGAR Accessories OEM vape pen,ZGAR Accessories OEM electronic cigarette.
Zgar International (M) SDN BHD , https://www.szvape-pods.com