The rapid development of the automotive market is bound to drive the development of related industries. As a must-have comfort feature, automotive air conditioners have also encountered unprecedented opportunities for development. The automotive air conditioning system is a comfort device for cooling, heating, ventilating, and purifying air in the cabin. It can provide a comfortable ride environment for the occupants, reduce the fatigue of the driver and improve traffic safety. Air-conditioning devices have become a measure of the perfection of car functions.
2 Automotive air conditioning works
2.1 Vehicle refrigeration system
The most basic and complex automotive air conditioning is the on-board refrigeration system. The compressor power of modern automotive refrigeration systems is driven by a motor. The refrigeration system consists of a compressor, a condenser, a liquid storage dryer, an expansion valve, an evaporator, and a blower, as shown in FIG. Between the components of the vehicle refrigeration system, copper tubes (or aluminum tubes) and high-pressure rubber tubes are used to connect a closed system. When the refrigeration system is operating, the refrigerant circulates in the closed system in two states of compression and expansion.
Figure 1 Schematic diagram of the refrigeration system
2.2 Refrigerant circulation cooling process
The refrigerant (refrigerant) cycle of a refrigeration system is divided into four basic processes:
(1) Compression: The compressor sucks the low-temperature and low-pressure refrigerant gas at the outlet of the evaporator and compresses it into high-temperature and high-pressure gas to eliminate the compressor.
(2) Heat Dissipation Process: The high-temperature and high-pressure superheated refrigerant gas enters the condenser. Because of the decrease in pressure and temperature, the refrigerant gas condenses into a liquid and discharges a large amount of heat.
(3) The throttling process: the refrigerant liquid with a higher temperature and pressure will increase in volume after passing through the expansion device, and the pressure and temperature will drop rapidly, and the expansion device will be ejected in a mist (fine droplets).
(4) Endothermic process: The mist-like refrigerant liquid enters into the evaporator, so the boiling point of the refrigerant is much lower than the temperature inside the evaporator, so the refrigerant liquid evaporates into gas. Abundantly absorbs the surrounding heat during evaporation, and then the low-temperature, low-pressure refrigerant vapor enters the compressor again.
As the expansion and compression process of the refrigerant continues over and over again, the purpose of lowering the air temperature around the evaporator can be achieved.
2 Delta E Series Inverter Automotive Air Conditioning System Solution
The continuous development of automotive air-conditioning technology, compressor evaporation machine technology is also continuous improvement, and with the increasingly high voice of energy saving and environmental protection, Delta Electronics in this environment, with its technical leadership in the field of motor drive Provides its variable frequency drive solutions in the automotive air conditioning industry. Delta E series intelligent inverters embedded in simple PLCs have good applicability to vehicle-mounted, compact and economical drive control requirements.
2.1 Frequency Conversion Refrigeration System
The frequency conversion refrigeration system control is shown as in Fig. 2. The system uses Delta E series 15KW inverter to drive the compressor and 7.5KW inverter to drive the evaporator. Inverter battery common bus detection of the supply voltage value, by the internal PLC program operation, determines that the compressor and the evaporator should work in that state, to get the inverter output frequency value. At the same time, the external PLC detects the returned analog value through the temperature sensor and the temperature value set by the controller to calculate the frequency that the frequency converter should work in, so that the frequency converter can accelerate or decelerate to adjust the temperature change inside the vehicle to reach the internal temperature. The purpose of automatic adjustment.
Figure 2 System Control Chart
2.2 Electronic Control System Design
Since the car's electrical power belongs to the DC power supply system, the frequency converter should be able to use DC power directly. Delta E Series
The frequency converter can be used in parallel with the DC bus, so it can also be directly powered by DC, but considering that it is just a simple use of DC power supply, it is recommended that customers connect positive and negative to the RT terminal of the E series inverter powerinput. To prevent foolproof, it can also prevent the inverter bus voltage recharging.
In addition, if the power supply of the inverter is too high or too low, it will cause a fault alarm, and the voltage of the power supply system of the automobile is generally low. Therefore, in order to enable the system to work normally, the low voltage alarm for the special inverter designed for the automobile air conditioning is accurate. Bit
It will be lower than the standard inverter. Automotive air-conditioning electronic control system shown in Figure 3. Automobile air conditioning electronic control system engineering physical as shown in Figure 4.
Fig. 3 Principles of automotive air-conditioning electronic control system
Figure 4 The actual system diagram of a car air conditioner
3 output frequency flow chart
When the air conditioning system is working, it is necessary to detect the voltage of the voltage system first to determine whether the DCBUS (DC bus) value detected by the internal PLC of the inverter is normally started within the normal operation range, and then calculate according to the set V/F curve. The output frequency is controlled and converted to the control PLC according to the temperature value set by the air-conditioning controller. The PLC then converts it to an analog signal of 0~10V and sends it to the AVI of the inverter, which is the frequency command source of the inverter. The comparator compares the magnitudes of the two frequency command values â€‹â€‹and then outputs them according to the smaller frequency instructions. Frequency conversion refrigeration PLC control process shown in Figure 5.
Figure 5 inverter cooling PLC control process
Delta E series inverter internal PLC capacity can be up to 500steps, so for the small system of sequential control or simple detection, can fully meet the requirements, so the cost of the plug-in PLC is omitted, at the same time, because the PLC is embedded in the inverter Inside, there are no problems such as compatibility and communication, so it is very convenient to use.
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