Power battery sampling circuit and full-isolation sampling method

Abstract

The invention provides a power battery sampling circuit and a full-isolation sampling method, and the method comprises the steps: firstly, a single-chip microcomputer unit outputs an isolation gating signal through an IO gating circuit, and then controls a multipath gating switch circuit to gate the positive and negative electrodes of a core; the voltage signals are isolated and amplified through the first-stage operational amplifier circuit, the second-stage differential isolation operational amplifier circuit and the third-stage differential-to-single-ended operational amplifier circuit, then the voltage signals are collected by the single-chip microcomputer, and when all the cell voltages are collected, data are stored through the storage circuit, and information is reported through the isolation digital communication circuit. According to the method, polling gating of a plurality of cells is realized by using a multi-path analog multiplexing switch, so that the complexity and the size of a rear-end operational amplifier circuit are reduced, and the voltage of the cells is isolated by using an isolation operational amplifier to improve the anti-interference capability; the method not only realizes full-isolation sampling, but also can effectively collect the voltage of all the cells when a certain cell breaks down or back voltage occurs due to too slow activation.

Description

Technical Field

[0001] This invention relates to the field of power batteries, and more specifically to a power battery sampling circuit and sampling method. Background Technology

[0002] Battery cell voltage acquisition is currently the basis for monitoring the health status of power batteries. The conventional method is to use integrated analog front-end (AFE) chips. These chips can acquire voltage data from up to 18 cells and integrate a communication interface. With a sampling period of ≤100 milliseconds, they significantly reduce the design complexity and cost of battery management systems, making them a common solution in the new energy vehicle industry. While integrated AFE chips offer many advantages, they also have limitations, such as slow sampling and communication cycles, the inability to use other AFE channels when a cell fails, and interference due to the inability to isolate sampling.

[0003] For high-speed aerial unmanned aerial vehicles and underwater unmanned submersibles, lithium batteries and primary batteries are mostly used for power supply. These fields require unmanned vehicles to have high maneuverability, so the discharge rate of the power battery is required to be very high. In addition, a high battery sampling rate and anti-interference capability are required during the discharge process of the power battery to ensure that the unmanned system can quickly and accurately monitor the health status of the power battery. Therefore, conventional AFE chips are not universal.

[0004] In the development of a certain power battery, in response to the requirements of rapid sampling, isolated sampling, high reliability, and reverse voltage problems caused by slow activation of some cells during the primary battery activation process, this invention provides a new sampling circuit and a fully isolated sampling method. Summary of the Invention

[0005] The purpose of this invention is to provide a battery pack isolation sampling method. First, a microcontroller is used to control a multiplexer to sequentially select each cell. Then, a multi-stage operational amplifier circuit is used to isolate and amplify the selected cell voltage signal. Finally, the microcontroller samples the isolated voltage signal, thereby achieving rapid isolation sampling of multiple cells in the battery pack.

[0006] This invention is achieved through the following technical solution:

[0007] This solution provides a power battery sampling circuit including: a multi-channel selection switch circuit, a first-stage operational amplifier circuit, a second-stage differential isolation operational amplifier circuit, a third-stage differential-to-single-ended operational amplifier circuit, a microcontroller unit, a secondary power supply circuit, an I / O selection circuit, a storage circuit, and an isolated digital communication circuit.

[0008] Preferably, the multi-channel selection switch is a 16-channel analog multiplexer, and one 16-channel analog multiplexer can select the positive and negative terminals of 8 battery cells.

[0009] Preferably, the first-stage operational amplifier circuit consists of a voltage reference circuit, a differential amplifier circuit, and a voltage boosting circuit. The voltage boosting circuit is used to boost the negative voltage caused by a cell being open or poorly connected to a positive voltage. The voltage reference circuit provides a voltage reference for the voltage boosting circuit, and the differential amplifier circuit is used to reduce the voltage difference between the positive and negative terminals of the cell to the measurement range of the second-stage differential isolation operational amplifier circuit.

[0010] Preferably, the operational amplifier of the two-stage isolation differential operational amplifier circuit is a differential isolation operational amplifier, whose input and output power supplies are isolated from each other, and whose input and output power supplies are provided by the secondary power supply circuit.

[0011] Preferably, the three-stage differential-to-single-ended operational discharge circuit consists of an operational amplifier and a voltage clamping circuit. The operational amplifier is used to convert the front-end differential voltage signal into a single-ended voltage signal within a certain voltage amplitude range, and the voltage clamping circuit clamps the voltage amplitude to protect the ADC pins of the microcontroller.

[0012] Preferably, the secondary power supply circuit is used to provide the required power to the multi-channel selection switch circuit, the first-stage operational amplifier circuit, the second-stage differential isolation operational amplifier circuit, the third-stage differential-to-single-ended operational amplifier circuit, the microcontroller unit, the I / O selection circuit, the storage circuit, and the isolated digital communication circuit.

[0013] Preferably, the IO gating circuit uses a multi-channel digital isolator to isolate the IO control signal, and its input and output power supplies are isolated from each other and are provided by a secondary power supply circuit.

[0014] Preferably, when the battery sampling circuit needs to collect more cell voltages, it only needs to expand the number of channels of the multi-channel gating switch circuit, the first-stage operational amplifier circuit, the second-stage differential isolation operational amplifier circuit, the third-stage differential-to-single-ended operational amplifier circuit, and the IO gating circuit, without expanding the number of channels of the microcontroller unit, the storage circuit, and the isolated digital communication circuit.

[0015] The present invention provides a fully isolated sampling method, comprising the following steps:

[0016] First, the microcontroller program is initialized, and the first cell selection signal is output through the IO selection circuit.

[0017] Furthermore, the cell selection signal controls the multiplexer to select the positive and negative terminals of the first cell in the battery pack;

[0018] Furthermore, a single-stage operational amplifier circuit is used to boost and scale down the selected cell voltage signal;

[0019] Furthermore, a two-stage differential isolation operational amplifier circuit is used to isolate and amplify the reduced voltage signal;

[0020] Furthermore, a three-stage differential-to-single-ended operational amplifier circuit is used to convert the isolated and amplified differential signal into a single-ended voltage signal;

[0021] Furthermore, the single-ended voltage signal is acquired using the ADC sampling channel of the microcontroller at a fixed period.

[0022] Furthermore, the microcontroller program performs digital filtering on the sampled cell voltage;

[0023] Furthermore, the microcontroller makes the following judgment: when the current sampling circuit has finished collecting the voltage of the last cell, the microcontroller is responsible for judging and sorting the voltage signals of multiple cells, and storing the maximum and minimum voltage values ​​obtained through the sorting circuit and transmitting them to the host computer system through the isolated digital communication interface. Then, the microcontroller initializes the strobe IO signal to the strobe signal of the first cell and then proceeds to the next step; if the current sampling is not of the last cell voltage, then proceed to the next step.

[0024] Furthermore, the microcontroller outputs the next set of strobe IO signals according to a fixed cycle, and isolates the IO signals through a digital isolation circuit. The isolated IO signals control the multiplexer to select a new channel, that is, repeat steps

[0017] to

[0023] .

[0025] In step

[0022] , the digital filtering requires storing six sampling data of the same cell during the initial filtering. In subsequent filtering, it is only necessary to update the sampling data for each time. The filtering method is as follows: first, the largest and smallest sampling values ​​are removed, and then the average value of the remaining four data is calculated.

[0026] By adopting the above technical solutions, this invention provides a power battery sampling circuit and a fully isolated sampling method. This method uses a multiplexed analog switch to poll and select multiple battery cells, thereby reducing the complexity and size of the back-end operational amplifier circuit. It also uses an isolation operational amplifier to isolate the cell voltage to improve anti-interference capability. In the microcontroller, a high sampling rate can be flexibly set to improve the sampling speed. This method not only achieves fully isolated sampling, but also can effectively collect the voltage of all battery cells when a certain battery cell is faulty or activates too slowly and reverse voltage occurs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the multi-channel selection switch circuit of the present invention;

[0029] Figure 3 This is a schematic diagram of the real-time multi-channel selection switch circuit of the present invention;

[0030] Figure 4 This is a schematic diagram of the real-time multi-stage operational amplifier circuit of the present invention;

[0031] Figure 5 This is a schematic diagram of the real-time IO gating circuit of the present invention;

[0032] Figure 6 This is a schematic diagram of the real-time isolated digital communication circuit of the present invention;

[0033] Figure 7 This is a flowchart illustrating a real-time example of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0035] Combination Figure 1 As shown, the power battery sampling circuit provided by this invention includes nine parts: S01 multiplexer switch circuit, S02 first-stage operational amplifier circuit, S03 second-stage differential isolation operational amplifier circuit, S04 third-stage differential-to-single-ended operational amplifier circuit, S05 microcontroller unit, S06 secondary power supply circuit, S07 I / O gating circuit, S08 storage circuit, and S09 isolated digital communication circuit. S06 provides the necessary power for S01-S05 and S07-S09 respectively.

[0036] Figure 2 This is a schematic diagram of the multiplexing switch circuit in this embodiment. In this embodiment, two multiplexers, S011 and S012, are used. Each multiplexer has 16 input channels and two output channels A / B. That is, each multiplexer can poll and connect the positive and negative terminals of 8 battery cells. Since the maximum voltage of the battery cells does not exceed 4.5V, S011 and S012 in this embodiment are powered by two isolated 36V power supplies. The 36V power supply is provided by the S06 secondary power supply circuit.

[0037] Figure 3 This is a schematic diagram of the multi-stage operational amplifier in this embodiment, namely, S02 is a first-stage operational amplifier circuit, S03 is a second-stage differential isolation operational amplifier circuit, and S04 is a third-stage differential-to-single-ended operational amplifier circuit. There are a total of 2 channels in this embodiment. Figure 3 The multi-stage operational amplifier circuit shown has two channels. Figure 3 The circuits shown are respectively with Figure 2The multiplexer shown is connected; S02 consists of two operational amplifiers and a voltage reference, where S021 and the voltage reference form a voltage boosting circuit, and the operational amplifier shown in S022 is a differential operational amplifier. S022 is used to... Figure 2 The 0-4.5V cell voltage signal output from the multiplexer is reduced to the acceptable voltage range of the S03 differential isolation operational amplifier. Figure 3 Positive and negative terminals of S022 Figure 2 The multiplexer switch shown has two output channels A / B, where A is connected to the positive terminal of S022 and B is connected to the negative terminal of S022. S03 requires two power supplies, where VDD1 / GND1 is a 5V power supply and VDD2 / GND2 is a 3.3V power supply. VDD1 / GND1 and VDD2 / GND2 are isolated from each other. S04 uses a single operational amplifier to convert the differential voltage signal output by S03 into an amplified single-ended voltage signal. The power supply of S04 is the same as that of VDD2 / GND2.

[0038] Figure 4 This is a schematic diagram of the secondary power supply circuit in this embodiment. In this embodiment, a total of 2 36V isolation power supplies, namely 36V_1 and 36V_2, 3 5V power supplies, 2 voltage rise references, and 2 3.3V power supplies are used. Among them, 5V_1 and 5V_2 are generated by the corresponding 36V power supplies, and the two voltage rise references are generated by 5V_1 and 5V_2 respectively. Figure 4 The 5V power supply is generated from the total 27V power supply through an isolated power supply module. This 5V power supply is then regulated to produce 3.3VD and 3.3VA power. The 36V_1 and 36V_2 isolated power supplies are... Figure 2 The power supply is provided by a two-way analog multiplexer switch, with 5V_1 and 5V_2 for each of the two channels. Figure 3 The S03 differential isolation op-amp is supplied with VDD1 / GND1 power, and the 3.3VA power supply is provided by two channels. Figure 3 The S03 differential isolation operational amplifier provides power to VDD2 / GND2 and to S04; in addition, the 3.3VD and 3.3VA power supplies also power the microcontroller unit, storage circuit and communication circuit.

[0039] Figure 5 This is the schematic diagram of the IO gating circuit in this embodiment. Two channels are used in this embodiment. Figure 5 The circuit shown in this embodiment uses a digital isolation chip as the isolation device for the IO strobe signal. This device supports isolation of 3 outputs and 1 input signal, with the 5V power supply side connected to... Figure 2 The selection logic pins of the multiplexer are connected to the I / O pins of the microcontroller on the 3.3VD side. In this embodiment, one I / O selection circuit corresponds to one multiplexer.

[0040] Figure 6 This is a schematic diagram of the communication circuit in this embodiment. Only one channel is used in this embodiment. Figure 6 The circuit shown in this embodiment uses an RS485 bus for communication. Figure 6 The U6 chip is an RS485 communication interface chip. This chip uses a 3.3V power supply and has its own isolated power supply. Figure 6 The L2 common-mode inductor, CR3A, CR3B, CR1, and CR2 are anti-interference and anti-static surge devices.

[0041] Figure 7 The sampling method flowchart provided in this embodiment is completed by the following steps:

[0042] 1. First, the microcontroller unit initializes the flag N=1. This flag represents Figure 2 The channel markers or cell numbers connected by the multi-channel analog multiplexer shown are as follows: Since this embodiment uses two multi-channel analog multiplexers, N represents the cell number selected by S011, and N+8 represents the cell number selected by S012.

[0043] 2. After the microcontroller is initialized, it passes through two channels. Figure 5 The IO strobe signal outputs a strobe signal, which is used to connect cell N connected to S011 and cell N+8 connected to S012.

[0044] 3. The voltages of the selected cell N and cell 8+N are boosted, reduced, isolated, and differential-to-single-ended processed by two multi-stage operational amplifier circuits, namely S02, S03, and S04.

[0045] 4. Use the two ADC pins of the microcontroller to simultaneously acquire the single-ended voltage signal processed in step 3. During the initial acquisition, the data of the two ADC channels needs to be acquired and stored 6 times. In subsequent acquisitions, the data can be updated sequentially. Then, the maximum and minimum values ​​of each channel are removed according to the sorting method, and the average value of the remaining 4 data is the corresponding cell voltage.

[0046] 5. Determine if the flag N is 8. If N! = 8, increment N by 1, re-output the new IO strobe signal, and execute steps 2 to 5; if N = 8, execute step 6.

[0047] 6. If N==8, it means that data has been collected from all 16 battery cells. At this point, all cells can be sorted to find the maximum and minimum values ​​to determine the battery health status. The data can then be reported to the host computer via RS485 and stored. Then, proceed with step 1.

[0048] Steps 4 through 6 are all executed within the same ADC fixed interrupt timer. By following the above steps, the voltage acquisition of 16 battery cells can be completed periodically.

[0049] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A power battery sampling circuit, characterized in that, include: The circuit includes a multi-channel selection switch circuit, a first-stage operational amplifier circuit, a second-stage differential isolation operational amplifier circuit, a third-stage differential-to-single-ended operational amplifier circuit, a microcontroller unit, a secondary power supply circuit, an I / O selection circuit, a storage circuit, and an isolated digital communication circuit.

2. The power battery sampling circuit according to claim 1, characterized in that, The aforementioned multi-channel selection switch uses a 16-channel analog multiplexer, which can select the positive and negative terminals of 8 battery cells.

3. The power battery sampling circuit according to claim 1, characterized in that, The first-stage operational amplifier circuit consists of a voltage reference, a differential amplifier circuit, and a voltage boosting circuit. The voltage boosting circuit is used to boost the negative voltage caused by a cell being open-circuited or poorly connected to a positive voltage. The voltage reference provides a voltage reference for the voltage boosting circuit. The differential amplifier circuit is used to reduce the voltage difference between the positive and negative terminals of the cell to the measurement range of the second-stage differential isolation operational amplifier circuit.

4. The power battery sampling circuit according to claim 1, characterized in that, The operational amplifier in the aforementioned two-stage isolation differential operational amplifier circuit is a differential isolation operational amplifier. The power supplies at the input and output terminals of this differential isolation operational amplifier are isolated from each other, and the power supplies at the input and output terminals are provided by the aforementioned secondary power supply circuit.

5. A power battery sampling circuit according to claim 1, characterized in that, The aforementioned three-stage differential-to-single-ended operational amplifier circuit consists of an operational amplifier and a voltage clamping circuit. The operational amplifier is used to convert the front-end differential voltage signal into a single-ended voltage signal within a certain voltage amplitude range, and the voltage clamping circuit clamps the voltage amplitude to protect the ADC pins of the microcontroller.

6. A power battery sampling circuit according to claim 1, characterized in that, The secondary power supply circuit is used to provide the power required by the multi-channel selection switch circuit, the first-stage operational amplifier circuit, the second-stage differential isolation operational amplifier circuit, the third-stage differential-to-single-ended operational amplifier circuit, the microcontroller unit, the IO selection circuit, the storage circuit, and the isolated digital communication circuit.

7. A power battery sampling circuit according to claim 1, characterized in that, The IO gating circuit uses a multi-channel digital isolator to isolate the IO control signal. Its input and output power supplies are isolated from each other and are provided by a secondary power supply circuit.

8. A power battery sampling circuit according to claim 1, characterized in that, To collect more cell voltages, the battery sampling circuit only needs to expand the number of channels in the multi-channel gating switch circuit, the first-stage operational amplifier circuit, the second-stage differential isolation operational amplifier circuit, the third-stage differential-to-single-ended operational amplifier circuit, and the IO gating circuit, without needing to expand the number of channels in the microcontroller unit, the storage circuit, and the isolated digital communication circuit.

9. A fully isolated sampling method for a power battery sampling circuit according to claim 1, characterized in that, The method includes the following steps: S1. The microcontroller program initializes N=1, where N is the selection channel number and cell number of the multiplexer, and outputs the selection signal of the Nth cell through the IO selection circuit; S2, the gating signal controls the multiplexing switch to select the positive and negative terminals of the Nth cell in the battery pack; S3. Use a single-stage operational amplifier circuit to boost and scale down the selected cell voltage signal; S4. Use a two-stage differential isolation operational amplifier circuit to isolate and amplify the reduced voltage signal; S5. Use a three-stage differential-to-single-ended operational amplifier circuit to convert the isolated and amplified differential signal into a single-ended signal. S6. The single-ended voltage signal is acquired using the ADC sampling channel of the microcontroller at a fixed cycle. S7. The microcontroller program performs digital filtering on the sampled cell voltage; S8. When the current sampling circuit has finished collecting the voltage of the 8th cell, i.e., N = 8, the microcontroller is responsible for sorting the voltage signals of the multiple cells, identifying the battery status based on the maximum and minimum voltage values, storing the data through the storage circuit, and transmitting it to the host computer system through the isolated digital communication interface. Then, N = 1 and the strobe IO signal is initialized as the strobe signal for the first cell. If N ! = 8, then N is incremented and step S9 is executed. S9. The microcontroller outputs the next set of strobe IO signals according to a fixed cycle, and isolates the IO signals through a digital isolation circuit. The isolated IO signals control the multiplexer in S2 to select a new channel, that is, repeat steps S2 to S8.

10. The fully isolated sampling method according to claim 9, characterized in that, In step S7, the digital filtering requires storing six sampling data points of the same battery cell during the first filtering. Subsequent filtering only requires updating the sampling data for each time. The filtering method is to remove the largest and smallest sampling values ​​and then calculate the average of the remaining four data points.

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