Study and analysis of some interesting BMS-related patents in recent years

It’s the start of the school year recently and my kid is in kindergarten. When I’m distracted from work during the day, I’m always worried about how he’s doing at school. Then when I get home at night, we dislike each other. My life is quite fulfilling.

I have been very busy recently. I am continuing to debug to improve the accuracy of current sampling. I have also been doing patent analysis for a few days. I have discovered some new and interesting things from it. I would like to share them with you today.

1. Patent on network transformer disconnection detection

As we all know, the device used for communication between AFEs is called a network transformer. Its failure mode is mainly wire breakage, which may be caused by a variety of reasons, such as the winding method, tension control, or stress pulling in the case of thermal shock during the transformer production process. The impact of its failure is relatively serious, causing the vehicle to be unable to operate normally.

In CATL's patent "CN115825794 Battery Cell Sampling Circuit, Circuit Fault Warning Method and Battery Management System", a disconnection detection method for a daisy chain network transformer is mentioned. The specific scheme is as shown in the figure below: by detecting the coil resistance of the transformer to determine whether it is at risk of disconnection; the specific method is relatively simple, similar to the NTC detection circuit, by pulling up the power supply and dividing the resistance, allowing the AFE to collect the divided voltage value, and then calculate the coil resistance, and then make some diagnostic strategies.

2. Patent on Negative Relay Adhesion Detection

Previously, we have summarized some patent solutions for negative relay adhesion detection. This time, let’s look at a few different ones. SAIC-GM-Wuling’s patent "CN107942243A Relay Adhesion Detection Circuit and Detection Method" introduces a method of using insulation resistance to detect relay adhesion failure. The solution is as shown in the figure below: Briefly speaking, a resistor bridge with a fixed resistance is arranged at the rear end of the relay, and then it is artificially connected in parallel to the position of the insulation resistor. When a relay is adhered, this resistor bridge will affect the insulation detection result at the battery end.

Deep Blue Automobile's patent "CN116540087 A relay detection circuit and method" introduces such a method. The specific scheme is as shown in the figure below: Briefly speaking, a string of resistors is connected to the positive and negative poles of the battery and the rear end of the relay at the same time, so that the main positive and main negative relays will participate in the voltage division after closing, which will affect the voltage at the observation point. Fundamentally speaking, it is an active injection method; Regarding the active injection method for negative pole relay adhesion diagnosis, I will summarize it in a separate chapter later, because I found that some things in it are worth discussing .

In Suzhou Times' patent "CN117590217A Main Negative Relay Adhesion Detection System and Detection Method for Electric Vehicles", this negative relay adhesion detection scheme is achieved by controlling the timing of the relay, as shown in the following figure: Briefly speaking, it is to close the pre-charge relay, and then collect the voltage value across the X capacitor, and use this voltage value to determine whether the negative relay is adhered. This similar scheme has actually always existed. The main negative can be diagnosed, but fast charging negative is more difficult.

3. Patents on insulation detection

In the patent "CN117250529A Power battery insulation detection device, system, method and battery pack", the block diagram of the scheme is as follows: In short, this resistance bridge uses one switch to satisfy the switching of two states. When S1 in the figure is disconnected, resistors R1 and R2 serve as the upper bridge arm, and R4 and R4 serve as the lower bridge arm; when S1 is closed, resistor R1 is connected to the positive and negative terminals of the battery, and the negative bridge arm becomes the parallel value of R2 and R3+R4, and the positive bridge arm is suspended.

This architecture is also similarly applied in the manual of the BJB chip. The main advantage of this solution is that it can save switches.

Of course, there are some variations. For example, in the patent "CN112285500A An insulation detection circuit and its control method", the switch is arranged at both ends of R2, as shown in the figure below.

4. Low-cost high-voltage sampling solution

In CATL's patent "CN107526041A Battery Detection Circuit and Battery Management System", there is an ultimate cost-reduction solution. The solution block diagram is as follows: high-voltage sampling, insulation detection, and adhesion detection are all integrated together, and the reference plane is placed on the low-voltage ground. The advantages of this solution have been introduced in a previous article " Analysis of the High-voltage Sampling Scheme Using Low-voltage Ground as the Reference Plane on BMS " . If you are interested, you can take a look.

Summarize:

I found that even if you don’t have enough talent, you can still win by relying on numbers; all of the above is for reference only.