Principle and method of DC fast charging of electric vehicles

Description: Nowadays, for electric vehicles, increasing the range and making long-range electric vehicles is the main development path. When the cost of batteries decreases and the combined range reaches 500-600 kilometers, the main contradiction of electric vehicles will change from range anxiety to charging anxiety. Improving the charging power of electric vehicles mainly includes several core elements. The following are the main practices for analyzing the reasons:

1: Increase the current: If we keep other components unchanged and choose the path of increasing the current, the main limitation is the heat loss caused by the large current, which will lead to a significant difference in the overall design. High currents in the circuit will generate high heat losses because the resistance of all components (connectors, cables, electrical connections to the battery, busbars, etc.) will inevitably heat up. If the battery overheats during charging, these heat losses need to be considered when designing and sizing the conductive components to avoid problems such as overload, overheating, or controlled derating of the charging current.

Second: Increase voltage: Since the increase in current mentioned above is limited, the current limit is generally defined as 500A, and the power that can be achieved is about 200kW (Tesla designed more than 600A at 400V as an attempt), and increasing the voltage to switch the 400V system to 800V becomes an option. This is a systematic improvement of all electrical components. The core switchgear and other parts have changed. At the current cost, these modules developed according to the 800V specification are relatively expensive. Taking the main inverter as an example, the cost of the core SiC module is about 4 times that of the original IGBT module.

Let's take a closer look at some of the issues that need to be considered in the path that can be reached in both ways. Since several methods have the same requirements for the battery cell, we list the battery cell issues at the end and focus on the cable connection and thermal management inside.

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