The name of the 800V high-voltage system comes from the electrical perspective of the vehicle. The voltage range of the current mainstream new energy vehicle high-voltage electrical system is generally 230V-450V, taking the middle value of 400V, which is generally called a 400V system; with the application of fast charging, the voltage range of the vehicle high-voltage electrical system reaches 550-930V, taking the middle value The value is 800V, which can be generally called an 800V system.
A better understanding of 800V cost reduction is that under the same power condition, the current can be reduced (P=VxI, V is doubled, the theoretical I can be half), the current is reduced, and the cost of the power distribution system and high-voltage wiring harness system can be reduced;
However, 800V is not an independent device, but
it
involves major three electricity, small three electricity, power distribution, thermal management, etc.
The following is the comparison and cost reduction of 800V and 400V from the system level summarized by United Automotive Electronics
Vehicle system architecture under 800V system
As a top Tier1, United Electronics, in the article "
Driving Forces and System Architecture Analysis of 800V High Voltage Systems
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What Are the Architecture Selection and Product Challenges?" 》Compares different 800V system architectures and their advantages and disadvantages
The 800V high-voltage system supported by silicon carbide technology has many advantages. Judging from the trend, the 800V high-voltage system will become the mainstream solution for high-power charging technology (>200kW) in the future.
However, the development of technology does not happen overnight. Due to the inertia of the industrial chain, supporting facilities such as 800V charging piles and 800V vehicle-mounted high-voltage components are not yet complete in the short term, which is not enough to support the rapid promotion of the ultimate 800V high-voltage system. Two points need to be considered at the moment: Compatibility 400V charging pile and 800V charging pile applications; compatible with some 400V vehicle component applications. This derives five different automotive system architecture design solutions for 800V high-voltage systems, as shown in the following table:
The first solution
: all vehicle components are 800V, and the electric drive boost is compatible with the 400V DC pile solution. Its typical features are: DC fast charging, AC slow charging, electric drive, power battery, and high-voltage components are all 800V; boosted by the electric drive system, it is compatible with 400V DC charging piles.
Figure 2 The first 800V high voltage system architecture diagram
The second solution
: all vehicle components are 800V, and a new DCDC compatible 400V DC pile solution is added. Its typical features are: DC fast charging, AC slow charging, electric drive, power battery, and high-voltage components are all 800V; through the addition of 400V-800V DCDC boost, it is compatible with 400V DC charging piles.
Figure 3 The second type of 800V high-voltage system architecture diagram
The third solution
: all vehicle components are 800V, the power battery can flexibly output 400V and 800V, and is compatible with the 400V DC pile solution. Its typical features are: DC fast charging, AC slow charging, electric drive, power battery, and high-voltage components are all 800V; two 400V power batteries are connected in series and parallel, and can flexibly output 400V and 800V through relay switching, and are compatible with 400V DC charging piles.
Figure 4 Architecture diagram of the third 800V high-voltage system
The fourth solution
: only the DC fast charging related components are 800V, the other components are maintained at 400V, and DCDC components are added for the voltage converter solution. Its typical features are: only DC fast charging and power batteries are 800V; AC slow charging, electric drive, and high-voltage components are all 400V; a new 400V-800V DCDC is added to realize voltage conversion between 400V components and 800V power batteries, and is compatible with 400V DC charging pile.
Figure 5 The fourth 800V high-voltage system architecture diagram
The fifth solution
: only the DC fast charging related components are 800V, the rest of the components are maintained at 400V, and the power battery flexibly outputs 400V and 800V solutions. Its typical features are: only DC fast charging is 800V; AC slow charging, electric drive, and load are all 400V; two 400V power batteries are connected in series and parallel, and can flexibly output 400V and 800V through relay switching, and are compatible with 400V and 800V DC charging piles.
Figure 6 The fifth 800V high-voltage system architecture diagram
Figure 1 Comprehensive comparison diagram of common 800V high-voltage system architectures
Design Challenges of 800V System Architecture
The direct impact of upgrading the vehicle's 400V system to an 800V high-voltage system is the reliability design issues of voltage resistance and insulation caused by the increase in electrical voltage. This is a common issue for all three electrical components; potential impacts include increased charging power and driving power. The improvement and the ultimate development of silicon carbide technology have brought many challenges to the design of Sanden products:
Common voltage withstand insulation design challenges for three electrical components:
In terms of conventional design, the first is that the electrical gaps and creepage distances related to the main power circuit of electrical components need to be redesigned; the second is that the signal isolation circuits of high and low voltage components also need to be redesigned to deal with the problem of withstand voltage insulation; the third is to use higher withstand voltage of insulating materials. In terms of special design, such as motor components involving electrical, magnetic, thermal, mechanical and other factors, there may be partial discharge problems.
Battery pack technical challenges:
After the charging power is increased, the battery charging rate will be increased from 1C to >=3C. Under high charging rates, on the one hand, it will cause the loss of active materials, affecting the battery capacity and life; on the other hand, once the lithium dendrites pierce the separator, it will cause an internal short circuit in the battery, causing safety risks such as fire.
Motor technology challenges:
After the DC bus voltage increases, the insulation distance of the motor increases significantly, and additional insulation design needs to be considered. At the same time, high voltage will cause "corona" phenomenon. How to ensure full-life electrical fatigue is a dual test of cost and technology. In addition, due to the increase in voltage, the power and torque ratio of the original 400V motor has been changed, and the electromagnetic solution needs to be redesigned for 800V, which will inevitably lead to an increase in production line investment. Added to this is the challenge of increased risk of failure due to shaft currents. In summary, under the 800V architecture, how to meet customers' torque, power and efficiency requirements at a lower cost requires a certain technical threshold, which is a huge challenge.
Motor controller technical challenges:
First of all, the design of 800V motor controller must consider product reliability under high power density, high heat resistance, and high-frequency switching applications. Secondly, with the increase of 800V voltage and silicon carbide inverter frequency, the internal du/dt of the inverter has increased significantly, which brings huge challenges to the EMC design of the inverter.
Other component technical challenges:
800V OBC, 800V DCDC, 800V battery high-voltage relays/fuses/connectors, charging piles, etc. all need to be upgraded, which poses great challenges to automotive R&D designers.
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