From Xiaomi SU7, we can see the application trend of OBC and the selection of main control chip

A week after the launch of Xiaomi Auto SU7, my good friend finally received the Huawei S7 that he had ordered in November last year. I asked him how much power the OBC of his S7 had, but he didn’t know. He said he didn’t have a charger installed at home .

"Look, this car has a range of about 800 kilometers, and can run for two weeks on a full charge. There are fast chargers near my home and at work, and it only takes about 30 minutes to charge.

Why would I spend thousands of dollars to install charging stations ?

Thinking about problems based on scenarios is a common way to observe industry trends (as well as technology and policies). Thinking back to the topic of the past two years, "Will OBC disappear?", some companies were happy while others were sad...

Xiaomi SU7's luxurious OBC configuration

400V and 800V OBC power supply topology

OBC control strategy and main control chip selection

1. Xiaomi SU7's luxurious OBC configuration

The waiter looked at the official website introduction and configuration of Huawei Zhijie S7 and Zhiyi's new car, but there was no information about OBC. Only Xiaomi's official website and Lei Jun's press conference had a very detailed introduction to OBC.

Different models of Xiaomi SU7 have 2 OBC configurations, namely 400V and 800V high-voltage platforms, and the 800V high-voltage platform is an ASIL-D certified product .

Regarding the 400V and 800V issues, there is a detailed introduction in previous articles. If you are interested, please visit:

Why is it high voltage, why 800V?

The following figure shows ST's classification of new energy vehicle charging. Level 1 and Level 2 are basically covered by OBC, and Level 3 is covered by supercharging. It can be seen that Xiaomi Motors still spent a lot of thought on the selection and configuration of OBC, and made OBC a publicity highlight (the high-end version is equipped with 800V)

Xiaomi's OBC supplier is Fute Technology. According to the cost of SU7 bikes on the Internet , the price of a 6.6KW OBC is 3577 RMB. According to the information in Fute Technology's prospectus, the average price is about 2258 RMB.

An 11KW ASIL-D OBC would probably cost around 5,000 RMB?

2. 400V and 800V OBC topologies

The current mainstream OBC products include two-in-one and three-in-one products. The two-in-one mainly combines the charger and DCDC, while the three-in-one adds a power distribution unit.

The mainstream power of 400V OBC is 6.6KW, which is generally a PFC + LLC + PSFB (low-voltage DCDC) topology;

For example, the reference design PMP22650 promoted by TI has the following topology, which uses a two-phase totem pole PFC+CLLLC+ synchronous rectification to achieve a peak efficiency of 96.5%; (it can achieve bidirectional flow and V2G/V2L functions)

For 800V, different manufacturers recommend different solutions.

ST DCDC recommends a variety of options

One is the cascaded DAHB topology, which can be configured to be 400V or 800V, corresponding to the use of 650V GaN tubes.

One is LLC/ZVS based on 1200V SiC

If a two-way solution is required to implement V2L or V2G, DAB is recommended.

The solution recommended by Infineon Technologies ' GaN Systems is a bit special. It has 3 levels of FC PFC + 3 levels of FC DAB (FC, Flying Capacitor), achieving 11KW of power. The peak efficiencies of PFC and DAB are 99% and 98.5% respectively. According to their publicity, it is far ahead.

3. OBC control strategy and main control chip selection

As mentioned earlier, the two-in-one OBC has multiple stages, the front-stage PFC and high-voltage DCDC, and the low-voltage DCDC, and correspondingly have different control strategies:

The three chips control PFC, HV DCDC, HV/LV DCDC respectively

One chip controls PFC+HV DCDC, and one chip controls HV/LV DCDC

One chip controls the entire link

The three different topologies have different considerations for the circuit design of isolation control and isolation sampling . Interested friends can calculate the cost of different solutions separately;

For the above-mentioned three topology controls completed by one chip, there is a solution based on TI AM263X in the industry that can achieve control + management (such as functional safety, communication protocol );

Based on the AM263X solution, this chip uses the ARM Cortex-R5 real-time CPU and is equipped with C2000 real-time control peripherals, thus achieving a combination of real-time computing power and general computing power;

Interestingly, this chip is supposed to be designed for electric drives and does not have an FPU...