Since the ALFA S model equipped with Huawei’s full-stack high-voltage solution was released by BeiQi JiHu at the Shanghai Auto Show, more than ten automakers have launched or are launching fast-charging vehicles, and the 800V high-voltage architecture has become the core theme of multiple industry forums in 2021.
On December 21st, at the 2021 Huawei Intelligent Automotive Solution Eco-Forum, Huawei invited industry partners to discuss how to collaboratively promote the industrialization process of high-voltage fast-charging, once again attracting widespread attention to the high-voltage platform in the industry.
As the marginal effect of the increase in electric vehicle range begins to diminish, the difference in experience brought about by going from 600 to 800 kilometers is not significant compared to previous ranges of 300 to 400 and 500 kilometers, and the requirements for size and weight need to match larger vehicles, which is no longer a simple proportional relationship.
Fast charging has become the inevitable direction for the next step in the development of power batteries, and domestic and foreign automakers have begun to meet consumers’ need for rapid charging by the concept of charging for 5 minutes and adding 200 kilometers of electricity.
Improving charging speed has two paths:
• Improving charging power for electric vehicles includes several core elements from an overall architecture perspective, and there are only two paths we can take:
○ Increasing current:
If we choose to increase current while keeping other components unchanged, the main limitation is the heat loss generated by high current, which will lead to significant differences in the overall design. High current in the circuit generates high heat loss because the resistance of all components (connectors, cables, battery connections, busbars, etc.) inevitably produces heat. For the overheating of batteries during charging, these heat losses need to be considered in the design of conductive elements and in determining the dimensions to avoid problems such as overload, overheating, or controlled reduction of charging current.
○ Increasing voltage:
As the increase in current has limits, and the limit is generally defined as 500A, which can achieve a power of about 200kW (Tesla has tried 600A or more above 400V), switching the 400V system to 800V becomes a choice. This is a systematic improvement for all electrical components. The core switching devices and other parts have also changed.
●High-voltage Fast Charging Architecture
For current vehicle upgrades, it is important to improve the fast charging experience while keeping the original system unchanged. There will be significant changes from 400V to 800V, so upgrading power around 400V in the short term is a choice. When the current is larger, the required cable cross-sectional area increases to transmit the same level of power without overheating.
Currently, the main high-power design targets 200kW, which is a current of about 500A sustained for about 5 minutes. To match this current, the current-carrying capacity of the vehicle charging socket, HV cable from charging socket to battery pack, fast charging contacts and the master positive/negative contacts, the main fuse, module terminal blocks, and cell internal wiring terminal blocks need to be increased.
However, in the long term, to achieve 5-10min fast charging and create a charging experience similar to refueling, it is necessary to have a charging power of more than 400kW. Therefore, the entire vehicle voltage platform must evolve towards 800V and above. Moreover, under the high-voltage architecture, the battery system has less heat dissipation, lower thermal management difficulty, smaller cable diameter, and lower cost at the same charging power.
In this field, in addition to the car manufacturers, Huawei is particularly proactive and has developed an 800V system in the form of a full-stack high-voltage platform solution. This includes OBC vehicle charging, battery management, powertrain, under-carriage high-voltage modules, and a solution that can fully charge from 30% to 80% in under 15 minutes, with a 7.5-minute solution to be launched within the next two years, and a 5-minute solution to be achieved by 2025.
In terms of battery safety, an AI BMS cloud-based battery safety solution has been developed combining big data, electrochemical mechanism models, and AI models. Based on AI algorithm training, the algorithm has been continuously improved through the coupling of digital twins, achieving faster, more accurate and precise prediction of battery thermal runaway to ensure battery safety.
Currently, there is a severe shortage of high-voltage DC stations capable of matching 800V and above fast charging models. In the initial stages of promoting high-voltage architecture, it may be necessary to equip the vehicle with a boost function to solve the boost issue from 400V to 800V.
The challenges and opportunities brought by the 800V system are diverse. Overall, there are several opportunities:
○ From the voltage topology perspective, it is possible to achieve gradient configuration with the same battery cells, i.e., differentiated configuration of high voltage for high-end and low voltage for low-end.
○ From the current direction, from the starting point of 350A, 500A or even up to 600A in the future, fast charging can also be supported, constantly improving power.
○ With the introduction of SiC, the efficiency of the overall power electronics can be improved and the volume can be reduced.
In the overall industry, the most crucial piece is the investment in charging infrastructure. Currently, major car companies such as Volkswagen, Tesla, and General Motors are building their own fast-charging networks. Facilities have already begun to consider establishing charging facilities that meet future 800V requirements. Huawei has designed the charging module, which is compatible with 200V-1000V, based on the efficient two-way 500V series output.
However, the 800V high-voltage platform also brings many challenges to electric drive, such as insulation, bearing corrosion, and EMC issues. Huawei has made many attempts in this aspect and has systematically solved these problems through core patented innovative technologies, such as high-voltage connectors, patented bearing flow-blocking and corrosion prevention structures, and EMC suppression software and hardware. Taking bearing corrosion prevention in the 800V system as an example, it has always been an unsolved problem in the industry. Currently, the motor bearings under 400V do not always have corrosion problems, but the probability of motor bearing corrosion in the 800V system will increase significantly.First of all, we need to pay attention to the shaft voltage generated by common mode current in the electric drive system. In electric vehicles, the shaft voltage of the driving motor is mainly “capacitive voltage”. Its source is the common mode voltage generated by PWM control, which is divided by parasitic capacitance layer by layer, and finally distributed to both ends of the bearing according to a certain proportion. The mechanism of high-frequency induction shaft voltage includes the asymmetry of parasitic capacitance between stator winding and machine casing, the change of leakage current between winding and machine casing in common mode circuit, and the equivalent change of common mode current and corresponding induced magnetic flux on the motor shaft.
Through innovative “Franklin” drainage technology, the current of the voltage of nearly 60V~80V on the bearing can be drained out, which can better solve the impact on the pressure resistance performance of the lubricating film between the bearings, thus greatly reducing the risk of bearing failure.
Summary: Leading car companies have begun to increase their investment in 800V high voltage. Although there are still some challenges in high voltage architecture, overall, 800V high voltage architecture will become the mainstream platform for the next generation of electric vehicles. 2022 will be the first year of China’s 800V system.
This article is a translation by ChatGPT of a Chinese report from 42HOW. If you have any questions about it, please email bd@42how.com.