In the face of the continuous heating up of the new energy market, customers have higher requirements for the mileage of electric vehicles and higher requirements for car charging rates. Based on the "New Standard European Cycle Standard" (NEDC), the cruising range of mainstream electric vehicles in China has reached about 600 kilometers, which is equivalent to the mileage of a tank of fuel for ordinary fuel vehicles. The next increase in charging rate will be a key pain point to solve the "mileage anxiety" of new energy electric vehicles.
Generally speaking, the charging rate depends on the charging power, and the charging power = charging voltage charging current. The large charging current means that the line loss increases, and the charging gun line needs to increase the water-cooled heat dissipation after the current exceeds 350A, which further increases the operation difficulty of the charging line and reduces the charging efficiency. Increasing the charging voltage can increase the charging rate of electric vehicles and reduce charging losses while keeping the charging current unchanged. In order to achieve the above needs, more and more OEMs are introducing high-voltage electrical systems of 800V or even higher.
Electrical architecture scheme for vehicles to achieve high-voltage fast charging
● 800V power battery and 800V high voltage system
At present, the charging level of the power battery system of the mainstream electric vehicle passenger market is 400V, and the charging pile and the high-voltage components of the vehicle are physically limited by the current, and the direct way to increase the charging power is to increase the voltage of the battery. Figure 1. Boost power batteries and high-voltage components to 800V systems.
( △ Picture 1 )
● 800V power battery and 400V high voltage system
Considering factors such as cost, using the existing component platform and charging infrastructure under the 400V voltage level, it is possible to consider adding a DCDC device between the vehicle charging interface and the power battery and the high-voltage component. Figure 2.
( △Picture 2 )
● 400V power battery and 400V high voltage system
Through the series parallel distribution of the battery, a configurable power battery system is designed to provide 800V charging voltage in series and 400V voltage drive in parallel. This solution requires a high degree of complexity in the design of the battery management system and requires additional control circuitry.
( △Picture 3 )
In charging mode, charging piles of different voltage levels are connected to the corresponding charging ports in the high-voltage system through charging guns. When the 800V DC charging pile (hereinafter referred to as the "high-voltage pile") is connected, it is directly connected to the battery management system (BMS) in the battery through the charging gun to achieve 800V charging, and the maximum instantaneous charging power exceeds 300kW. When the charging pile output is 400V DC, the charging gun is connected to the DC module interface, which charges the battery through the Boost circuit by boosting the 400V DC to 800VDC.
Taking Porsche as an example, Porsche Taycan earlier adopted 800V high-voltage system, in order to be compatible with 400V charging piles at the same time, Taycan in addition to the standard 800V DC charging system, but also added 400V to 800V Boost (boost) charging module. As an optional feature, the solution squeezes out the body space while increasing the development cost and hardware cost of the high-voltage system.
800V fast charging technology electrical system design impact
● Electric vehicle standards
At present, the charging standard of electric vehicles in mainland China is still using the 2015 "National Standard for Electric Vehicle Conductive Charging System", and the mainstream fast charging mode is mainly based on the 400V voltage platform. If you want to achieve a charging voltage of 800V or above and achieve high-power charging, it is necessary to revise and improve the relevant regulations and standards for electric vehicles.
●Power battery design
Higher battery packs, achieved by stringing and paralleling more monomer cells. Charging the battery at a high rate has a certain impact on battery life and thermal management. In order to realize the cooling requirements during high-current charging, it is necessary to expand the power of the on-board thermal management system or improve the cooling system design to ensure safety during charging.
●Electrical safety design
Higher battery voltages will have higher requirements for the level of electrical isolation of electrical components, and requirements such as clearance and creepage distance need to be considered when designing high-voltage safety systems.
●Charging cable connection design
Liquid-cooled charging cables are usually required to achieve fast charging, with charging power exceeding 200kW, but there is currently no established protocol on how to incorporate liquid-cooled cables into electrical codes. In addition, the liquid-cooled charging cable connection is too bulky and will bring trouble to the customer. For this issue, another option for a fast charging connection might be to use a robot or wireless charging.
●Charging facilities
In order to achieve the above high-voltage charging technology, it is also necessary to match the supporting charging infrastructure. In 2021, GAC Aean, which achieved the world record of the fastest charging speed of pure electric vehicles, is to use its dedicated A480 super charging pile, and porsche Taycan, which launched 800V DC charging pile charging as early as 2019, also needs to complete "charging for 4 minutes, endurance of 100 kilometers, and charging 80% in 15 minutes" on its special charging pile.
However, there are very few charging piles that can meet the conditions of super fast charging. Even Tesla, which laid out the earliest layout on this track, as of the end of August 2021, the number of super fast charging stations built nationwide was only 920, and the number of super fast charging piles was only more than 7100, which was far from meeting the demand.
Summary: In 2021, with the continuous improvement of the demand for new energy market, 800V high-voltage charging is of great significance to solve the "mileage anxiety" of new energy vehicle owners, and OEMs need to balance between the feasibility of technical solutions and commercial impact to achieve the wide promotion of high-voltage charging technology.
Senior engineers in luxury car companies switched from engine testing to battery testing.
At present, he focuses on the research of battery testing technology.
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