From fuel vehicles to electric vehicles, air conditioning compressors are also becoming "new energy"

Since 1939, when mechanical refrigeration and air conditioning were first installed on cars, the air conditioning system has also undergone significant changes, from air-conditioned fuel vehicles to electric vehicles.

The "new energy" of air-conditioning compressors

In traditional fuel vehicles, the air-conditioning compressors used for refrigeration are mainly driven by the engine through the belt drive, and can operate even when the engine is idling. Since electric vehicles do not have fuel engines, the air-conditioning compressors need to be driven by motors.

At the same time, due to the large heat dissipation requirements of electric vehicles, including batteries, motors, main drive inverters, BMS, etc., all need to be cooled, and the heat dissipation of these components requires the participation of air-conditioning compressors in this part of the heat dissipation in addition to traditional air cooling.

Previously, when an institution conducted extreme summer tests on electric vehicles, the cooling effect of the air conditioning in the cabin was not obvious. The main reason was that the pressure of the air-conditioning system increased in high temperature environments. In order for the system to operate normally, it is necessary to give priority to cooling the battery pack, motor, inverter, etc.

The air-conditioning compressor has limited power. Due to different priorities, the cooling effect of the air-conditioning in the cabin of electric vehicles is not obvious in extremely high temperature environments.

In addition to cooling, there are also differences in air conditioning heating. Because fuel vehicles have low energy conversion efficiency, generally speaking, nearly 50% of the energy is released in the form of heat. Therefore, in winter, this "waste heat" can be converted into heating for air conditioning and delivered to the cabin.

However, in electric vehicles, the energy conversion efficiency of the main drive motor and the inverter is as high as 90% or more, and the heat generation of the power battery is unstable under different working conditions, which also means that it is more difficult to recover the heat of these core components for air conditioning and heating

. Therefore, in the early electric vehicles, air conditioning and heating use PTC heating, which is equivalent to adding a heating element to heat the blown air on the basis of refrigeration and air conditioning. Although the structure is simple, this heating method has high energy consumption and will seriously affect the vehicle's cruising range.

Therefore, the heat pump air conditioning + PTC auxiliary system has basically been popularized in mid-to-high-end electric vehicles. Heat pump air conditioning switches between cooling and heating modes through heat exchanger systems such as reversing valves on the basis of traditional compressor refrigeration cycles. Some heat pump air conditioning systems also have waste heat recovery channels that can recover waste heat from batteries, motors, and inverters.

Existing heat pump air conditioners can be divided into three types. The first is the vapor compression heat pump system, which switches the cooling and heating modes through the reversing valve on the basis of the traditional vapor compression refrigeration cycle to realize the function of air conditioning heating in the car. However, when the outdoor ambient temperature is too low, this heat pump system is inefficient. In the case of more than ten degrees below zero in the winter in the north, it may be basically unable to heat.

In order to solve the heating condition of the ambient temperature being too low in winter, the jet air heat pump system has emerged. This is an efficient heat energy conversion technology that improves the performance of the system through the ejector (supercharger). In the jet air heat pump, part of the high-temperature and high-pressure gas of the exhaust is guided to the ejector. The ejector mixes this part of the exhaust with the low-temperature and low-pressure refrigerant coming out of the evaporator. The high energy of the exhaust causes the temperature and pressure of the mixed refrigerant to increase, but the overall pressure is still lower than the pressure at the compressor outlet. The mixed gas enters the condenser, releasing more heat and improving the heating efficiency of the system. At the same time, the low-pressure area caused by the high-speed airflow in the ejector can attract more refrigerant on the evaporator side to enter the condenser, increasing the circulation volume of the system.

Of course, the jet air heat pump system is obviously more complex and more expensive.

There is also a waste heat recovery heat pump system, which is based on the heat pump system mentioned above, and adds a waste heat recovery channel. It can convert the low-temperature heat of components such as batteries, motors, inverters, etc. into heat energy for heating the air conditioner in the car. It can be understood that this heat can be used to assist the heat pump to reduce the energy consumption of the system.

However, due to the increase in the number of pipelines for recovering waste heat, the complexity of the system is further increased, and the control strategy of the system is very demanding.

Electric vehicle compressors follow the development of high-voltage platforms

In electric vehicles, the compressor is not only used for air conditioning in the car cabin, but also related to the heat dissipation of the three-electric system of the whole vehicle. Therefore, the operating power is relatively large. For example, the power consumption of the compressor in spring and autumn is generally 300~1000W, and in summer and winter it is mostly 1000~2500W. Therefore, as an air-conditioning compressor related to the core component of the car drive, it is integrated into the high-voltage system of the whole vehicle and directly powered by the core battery pack.

For example, the platform voltage of electric vehicles was generally around 400V before, and the rated voltage of the air-conditioning compressor of electric vehicles was at the level of 400V accordingly. The Porsche Taycan, which was the first to use the 800V voltage platform, could only use a 400V air-conditioning compressor due to supply chain problems, and powered the compressor through an additional DC-DC step-down.

In electric vehicles, due to space limitations, air-conditioning compressors are generally an all-in-one system like the main drive system, mainly including motors, mechanical scroll structures, and power modules for control.

In the 400V era, air-conditioning compressors generally use IGBT-based IPM modules; but the platform voltage of electric vehicles is currently developing towards 800V and has been widely used. Therefore, air-conditioning compressors also need to use SiC power devices like the main drive.

In particular, air-conditioning compressors operate for a long time in light load scenarios, and the conduction loss of SiC MOSFET is lower than that of silicon IGBT, so the efficiency in low-load scenarios is significantly improved.

According to Zhizhan Technology's data, for the 800V voltage platform, because the 1200V IGBT device and the anti-parallel diode switching loss characteristics are poor, the advantages of the SiC MOSFET solution are more obvious. Under light load conditions, the overall loss is only 11% to 17% of the traditional IGBT IPM solution, while under heavy load conditions it becomes about 23% to 27%.

So we can see that in recent years, electric vehicle air-conditioning compressors have basically adopted SiC MOSFET devices in the process of developing towards 800V.

Summary:

In the process of electric vehicle development, due to different drive forms, there will be more opportunities in the electric vehicle industry chain compared to the fixed industrial structure of fuel vehicles. Including in air-conditioning compressors, we can see that traditional home appliance giants such as Midea and Hisense have accelerated the layout of products for electric vehicle applications in recent years, and have already achieved mass production on vehicles.