Heating system for electric vehicle battery system

Winter is coming soon, and it is time for electric vehicles to face the challenge of low temperatures. The diesel heating system that WM Motor has developed in its electric vehicles is an interesting experiment, which is more for users in the north or even the northeast. The previous initial version of thermal management (PTC electric heating + diesel heating battery pack) mainly focused on batteries. After analysis, it is found that the heating of car owners takes up more energy in winter, and it is more in line with the needs of car owners in the north. The newly added diesel heating cabin function released in the past few days directly provides heat for the air conditioner, and mainly considers using fuel to heat the passengers. By exchanging this heat for electric heating, the problem of air conditioning eroding the battery life in winter is solved. When encountering traffic jams at low temperatures, the more passengers use hot air conditioning, the more obvious the corresponding reduction in energy consumption.

Note: It is troublesome to obtain diesel. Perhaps only users in the north are prepared to buy it. For customers in the south where it is only cold in winter, this thing is useless. No one thinks of preparing diesel to add to it.

According to the diagram, this system is compatible with a hydrothermal system. In battery heating, this auxiliary fuel can also be fully utilized. The design focuses on the low temperature section (-30 degrees ~ 0 degrees): There are not many strategies that can be used for batteries at this stage. The usual practice is to heat the coolant through PTC. If diesel heating is used, a good effect can be achieved in this most difficult section. Above 0 degrees, as the battery can be activated faster, the discharge or charging process can accelerate the temperature of the battery to reach the optimal working point. This aspect is the same.

In this section, several methods currently proposed include:

Self-heating: using built-in nickel sheets, which we have discussed before

Using electric drive system assistance: Denso tried to use the inverter oscillation method at the high voltage end, and the method used in Tesla later used the method of blocking the rotor to generate heat first, and then use the heated coolant to conduct it to the battery surface

This effect is directly related to the battery size, control strategy and low-temperature battery internal resistance + drive system parameters.

In the figure previously provided by Porsche, its 270kW fast charging power is directly related to the temperature of the battery cell. At low temperatures, the acceptable fast charging power drops a lot (going towards 100kW at 10°, and further down at low temperatures). Porsche did not say much about the heating method except PTC.

Summary: As the fast charging power of 60kW increases to 120kW and 150kW, the heating speed of fast charging in winter will be greatly reduced, and this issue will become a hot topic at this stage.