Application analysis of frequency converter in automobile air-conditioning

1 Preface

The rapid development of the automobile market is bound to drive the development of related industries. As a necessary comfort function for automobiles, automobile air conditioners have also encountered unprecedented development opportunities. The car air conditioning system is a comfortable equipment for cooling, heating, ventilating and purifying the air in the cabin. It can provide passengers with a comfortable riding environment, reduce the fatigue strength of the driver, and improve driving safety. The air-conditioning device has become a sign to measure whether the car’s function is perfect.

2The working principle of car air conditioner

2.1 Car refrigeration system

Automotive air conditioning* The basic and complex is the on-board refrigeration system. The compressor power of modern on-board refrigeration systems is driven by an electric motor. The refrigeration system consists of a compressor, a condenser, a receiver dryer, an expansion valve, an evaporator, and a blower, as shown in Figure 1. The various components of the vehicle refrigeration system are connected by copper pipes (or aluminum pipes) and high-pressure rubber pipes to form a closed system. When the refrigeration system is working, the refrigerant circulates in this closed system in two forms of compression and expansion.

Figure 1 Schematic diagram of the refrigeration system

2.2 Refrigerant cycle refrigeration process

The refrigerant (refrigerant) cycle of the refrigeration system is divided into four basic processes:

(1) Compression process: The compressor sucks in the low-temperature and low-pressure refrigerant gas at the outlet of the evaporator, compresses it into high-temperature and high-pressure gas and removes it from the compressor.

(2) Heat dissipation process: The superheated refrigerant gas of high temperature and high pressure enters the condenser. Due to the decrease of pressure and temperature, the refrigerant gas condenses into liquid and discharges a large amount of heat.

(3) Throttle process: The refrigerant liquid with higher temperature and pressure becomes larger after passing through the expansion device, the pressure and temperature drop sharply, and it is discharged from the expansion device in the form of mist (fine droplets).

(4) Heat absorption process: The mist refrigerant liquid enters the evaporator, so the boiling point of the refrigerant is much lower than the temperature in the evaporator, so the refrigerant liquid evaporates into a gas. In the evaporation process, a large amount of surrounding heat is absorbed, and then the low-temperature and low-pressure refrigerant vapor enters the compressor.

The expansion and compression process of the refrigerant is repeated repeatedly to achieve the purpose of reducing the air temperature around the evaporator.

2 Delta E series inverter automotive air conditioning system solutions

With the continuous development of automobile air-conditioning technology, the technology of compressor evaporator is also constantly improving, and with the increasing demand for energy conservation and environmental protection, Delta Mechatronics relies on its technology in the field of motor drive in this environment** Advantages, provide its variable frequency drive solutions in the automotive air-conditioning industry. The Delta E-series intelligent inverters embedded with simple PLCs have good applicability for vehicle-mounted economical and economical drive control requirements.

2.1 Inverter refrigeration system

Inverter refrigeration system control is shown in Figure 2. The system uses Delta E series 15KW frequency converter to drive the compressor, and 7.5KW frequency converter to drive the evaporator. The common-line bus of the inverter battery detects the supply voltage value, which is calculated by the internal PLC program to determine which state the compressor and evaporator should work at this time to obtain the output frequency value of the inverter. At the same time, the external PLC detects the analog quantity returned by the temperature sensor and the temperature value set by the controller to calculate the frequency at which the inverter should work, and accelerate or decelerate the inverter to adjust the temperature change in the car to reach the temperature inside the car. The purpose of automatic adjustment.

Figure 2 System Control Diagram

2.2 Electric control system design

Since the automotive electrical is a DC power supply system, the inverter should be able to directly use DC power supply. Delta E series

The inverter can be used with DC bus collinear, so it can also be directly powered by DC. However, considering that it only uses DC power supply, it is recommended that customers connect the positive and negative terminals to the RT terminals of the E series inverter powerinput, so that it can be done To prevent foolishness, it can also prevent the inverter bus voltage from recharging.

In addition, if the inverter’s power supply is too high or too low, it will cause a fault alarm. The voltage of the car’s power system is generally low. Therefore, in order to make the system work normally, the low-voltage alarm of the special inverter designed for car air-conditioning is accurate. Bit

will be lower than the standard inverter. The electronic control system of automobile air conditioner is shown as in Fig. 3. The physical object of the automotive air-conditioning electronic control system project is shown in Figure 4.

Figure 3 Principles of the electronic control system of automobile air-conditioning

Figure 4 Actual car air conditioning system diagram

3 Output frequency flow chart

When the air conditioning system is working, first check the voltage of the voltage system to determine whether it is within the normal working range. After normal startup, the internal PLC of the inverter detects the DCBUS (DC bus) value, and then calculates the required value according to the set V/F curve. The output frequency is controlled according to the temperature value set by the air conditioner controller and then sent to the control PLC. The PLC then converts it into a 0~10V analog signal and sends it to the AVI of the inverter, which is the frequency command source of the inverter. The inverter compares the magnitude of the two frequency command values, and then outputs according to the smaller frequency command. The PLC control flow of inverter refrigeration is shown in Figure 5.

Figure 5 PLC control flow of inverter refrigeration

4 Conclusion

The internal PLC capacity of Delta E series inverters can reach 500 steps, so the sequence control or simple detection of small systems can fully meet the requirements, so the cost of external PLC is saved. At the same time, because the PLC is embedded in the inverter Inside, there is no compatibility and communication problems, so it is very convenient to use.

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