An Adaptive Forced Discharge Control System for Lithium Batteries

Abstract

The present invention discloses an adaptive forced discharge control system for lithium batteries, which includes a control unit, a fully controlled test unit matrix, a controllable DC power supply, multiple electronic loads, and a human-machine interaction unit. This system can flexibly adapt to requirements such as the number of battery cells, parameter indicators, and connection methods of the lithium battery samples to be tested, automatically discharge the lithium batteries to the state specified by the standard, and precisely adjust the magnitude and form of the current flowing through the lithium batteries, so as to accurately control the state and depth of over-discharge of the lithium battery samples. Therefore, the present invention fills the gap in the efficient and automated test system in this test field, can improve the efficiency of relevant test projects, and save test costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery testing, and particularly relates to an adaptive forced discharge control system for lithium batteries. Background Art

[0002] Lithium batteries are a type of battery with lithium metal or lithium alloy as the positive / negative electrode material and a non-aqueous electrolyte solution, mainly including lithium metal batteries and lithium-ion batteries. Among them, lithium-ion batteries, as the current mainstream secondary batteries, have the advantages of high energy density, long cycle life, good discharge performance, and low environmental pollution, and are widely used in various consumer electronic products, power tools, light electric vehicles and other fields. As a basic performance energy support component, lithium batteries will continue to play a key role in the energy storage system supporting new energy power generation and the trend of electrification of transportation represented by electric vehicles, and have broad development prospects.

[0003] In recent years, the production and application of lithium batteries have been continuously promoted. According to the prediction of relevant institutions, the total global shipment of lithium-ion batteries in 2021 was 562.4 GWh, a significant year-on-year increase of 91.0%; the shipment of lithium-ion batteries in China accounted for 59.4% of the global total, and the industry entered a period of rapid development. While the usage and production of lithium batteries are advancing at a high speed, the safety issues of lithium batteries have come into the public's view, and the frequent spontaneous combustion problems of electric vehicles and electric bicycles have attracted extensive attention from all sectors of society. For this reason, domestic and foreign standardization institutions have formulated safety requirement standards for various lithium batteries, such as GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles", GB 31241-2014 "Safety Requirements for Lithium-Ion Batteries and Battery Packs for Portable Electronic Products", UL1642 in the United States, and UN38.3 in the United Nations Manual of Tests and Criteria for the Transport of Dangerous Goods. Since lithium batteries are usually used in series and parallel combinations of multiple single cells to form modules in actual applications, the differences between single cells may cause unbalanced charging and discharging in actual applications, and may even lead to thermal runaway in severe cases. Therefore, in the above standards, forced discharge tests for single lithium battery cells in different states are specified.

[0004] However, there are still many problems in the current forced discharge test of lithium batteries, and the main reasons are as follows:

[0005] First, different standards have different requirements for forced discharge tests. For example, the GB 31241-2014 standard requires that for the discharged samples, they should be charged reversely at a current of 1C for 90 minutes; in the UN38.3 clause of the United Nations Manual of Tests and Criteria for the Transport of Dangerous Goods, it is required to connect a 12V DC power supply in series with the discharged samples and discharge at the nominal maximum discharge current for a certain period of time; while in some enterprise standard tests, forced discharge is carried out on series samples in different states of charge.

[0006] Second, the parameters of different types of battery cells are different. Currently, the mainstream lithium batteries mainly include lithium cobalt oxide batteries, nickel cobalt manganese (ternary) lithium batteries, lithium iron phosphate batteries, etc.; in terms of working voltage, the working voltages of the first two types of lithium batteries are generally 2.7V - 4.2V, and the working voltage of the latter is 2.5V - 3.7V. The voltage of the battery pack after series connection is an integer multiple of the single-cell voltage; in terms of current, different lithium batteries vary greatly according to their types and capacities.

[0007] Third, the series-parallel structure relationships to be simulated are different for different products. Since the single-cell capacity of lithium battery cells is small and the voltage is not high, in actual applications, a large number of battery cells are connected in series and parallel to form a battery pack for use. The series-parallel structures inside the lithium battery packs in different application scenarios vary greatly. For example, the lithium batteries in consumer electronics products are usually single-cell battery packs; in electric vehicles, a high voltage of the battery pack is required, so generally the number of series connections is large and the structure is complex; while in energy storage batteries, generally a large capacity and strong discharge ability of the battery pack are required, and generally the number of parallel connections is large inside the battery pack.

[0008] In summary, the combination of the differences in the safety standard requirements of lithium batteries and the differences in the parameter structures of different lithium battery products poses a severe challenge to the forced discharge test of lithium batteries. Currently, regarding the over-discharge protection of lithium battery products, there are already many mature research results. For example, the Chinese patent with the publication number CN102299365A proposes a lithium-ion battery and battery pack for preventing over-discharge, and the Chinese patent with the publication number CN109450017A proposes a protection circuit for preventing overcharge and over-discharge of lithium-ion secondary batteries. However, there is still no method and system specifically for the forced discharge test of lithium batteries, with strong adaptability and high working efficiency on the market. This absence restricts the working efficiency of the forced discharge and over-discharge tests of lithium batteries, and further affects the evaluation and research work on the safety issues of lithium batteries. Summary of the Invention

[0009] In view of the above, the present invention provides an adaptive lithium battery forced discharge control system, which can flexibly adapt to the requirements of the number of battery cells, parameter indicators, connection methods, etc. of the lithium battery sample to be tested for various forced discharge difference requirements specified by different standards, automatically discharge the lithium battery to the state specified by the standard, and precisely adjust the magnitude and form of the current flowing through the lithium battery, so as to accurately control the state and depth of over-discharge of the lithium battery sample, and thus improve the efficiency of relevant tests.

[0010] An adaptive lithium battery forced discharge control system includes: a control unit, a full-controlled test unit matrix, a controllable DC power supply, a multi-channel electronic load, and a human-machine interaction unit, where:

[0011] The control unit obtains the operating configuration parameters and operation instructions input by the user through the human-machine interaction unit, uses the built-in forced discharge control algorithm to control the operation process of the fully controlled test unit matrix, the controllable DC power supply, and the multi-channel electronic load, and collects their working state variables, and then transmits the test state information of the system to the outside through the human-machine interaction unit;

[0012] Each column of the fully controlled test unit matrix is composed of multiple fully controlled test units connected in series. After being connected in series, one end is connected to the controllable DC power supply, and the other end is used as the output end to connect to the corresponding electronic load. The output ends between adjacent two columns are connected through a parallel switch; each fully controlled test unit is connected to the corresponding lithium battery sample, and the entire matrix realizes different discharge paths according to the control signal provided by the control unit;

[0013] The controllable DC power supply adjusts its own working mode according to the instruction provided by the control unit, converts the alternating current into direct current, so as to provide a stable DC voltage or DC current for the lithium battery sample;

[0014] The multi-channel electronic load adjusts its own working mode according to the instruction provided by the control unit, and converts the direct current output by connecting the power supply in series with the lithium battery sample into alternating current and feeds it back to the power grid;

[0015] The human-machine interaction unit serves as an interaction interface between the user and the system, is used to receive the test state information transmitted by the control unit, display the operating state of the system, and at the same time receive the operating configuration parameters and operation instructions set by the user for the system.

[0016] Further, the control unit is composed of a processor, a communication module, a sampling module, and a driving module. The processor has a built-in forced discharge control algorithm and is connected to the communication module, the sampling module, and the driving module; the communication module is connected to the human-machine interaction unit, and is used to obtain the configuration information and operation instructions input by the user and transmit the state information of the system to the outside; the sampling module is connected to the fully controlled test unit, and is used to collect the electrical parameters of the lithium battery sample; the driving module is connected to the fully controlled test unit, and it drives the on-off states of the switches in the fully controlled test unit according to the control signal provided by the processor.

[0017] Further, the fully controlled test unit includes a voltage and current sampling circuit, a bypass switch, a circuit breaker switch, and a clamping tool for fixing the lithium battery sample. The voltage and current sampling circuit is used to collect the voltage and current signals of the lithium battery sample. One end of the circuit breaker switch is connected to the positive electrode of the lithium battery sample, and the other end of the circuit breaker switch is connected to one end of the bypass switch and serves as one end of the fully controlled test unit. The other end of the bypass switch is connected to the negative electrode of the lithium battery sample and serves as the other end of the fully controlled test unit. The bypass switch and the circuit breaker switch adjust their on-off states according to the control signal provided by the control unit.

[0018] Further, the clamping tool is adaptively installed and fixed to lithium battery samples of different shapes such as cylindrical and prismatic.

[0019] Further, the open circuit switch is composed of a switching tube, and both the bypass switch and the parallel switch are formed by connecting two switching tubes back to back to form a bidirectional switch. Therefore, the entire fully controlled test unit matrix includes (3m×n + 2(m - 1)) switching tubes, which can reorganize the topology of the lithium battery sample array with a quantity of m×n, flexibly control the discharge circuit, and thus adapt to different test requirements.

[0020] Further, the controllable DC power supply can be realized by the topology of a power electronic converter, specifically adopting a two-stage structure of a front-stage AC-DC rectifier and a rear-stage DC-DC converter, having two working modes of constant voltage control and constant current control; it can convert the AC mains into the electrical energy form and amplitude required by the lithium battery sample, and has the characteristics of adjustable current and comprehensive protection functions.

[0021] Further, the multi-channel electronic load can be realized by multi-channel independent two-stage converters, having working modes such as constant resistance and constant power to control the corresponding resistance value, power value or other electrical quantities. The front stage adopts a full-bridge converter topology for voltage regulation and simultaneously realizes high-frequency isolation. The rear stage adopts a full-bridge inverter topology to realize the function of energy feedback to the power grid.

[0022] Further, the human-machine interaction unit can be developed by an embedded solution or use an X86 computer as the upper computer, and a two-way communication connection is established between the human-machine interaction unit and the control unit by a communication module.

[0023] Based on the above technical solutions, the present invention has the following beneficial technical effects:

[0024] 1. The adaptive lithium battery forced discharge control system of the present invention can adapt to different test requirements brought by different standards and different sample parameters, flexibly change the connection topology of the test samples, accurately control the discharge path and the discharge depth of the samples, greatly improve the efficiency of the lithium battery forced discharge test, and save the test cost.

[0025] 2. The adaptive lithium battery forced discharge control system of the present invention integrates multi-channel multi-functional electronic loads, can automatically complete the preparation of the sample test state before the test, further improve the test efficiency, and optimize the human resource cost.

[0026] 3. The adaptive lithium battery forced discharge control system of the present invention can conveniently connect various electrical parameter and gas parameter sensors to realize the integration of multiple detection functions. Description of the Drawings

[0027] Figure 1 This is the structural block diagram of the adaptive forced discharge control system for lithium batteries of the present invention.

[0028] Figure 2 This is the schematic structural diagram of the control unit in the system of the present invention.

[0029] Figure 3 This is the schematic flow diagram of the forced discharge control algorithm for the built-in lithium battery in the system of the present invention.

[0030] Figure 4 This is the schematic structural diagram of the fully controlled test unit matrix in the system of the present invention.

[0031] Figure 5 (a) is the schematic diagram of the actual working discharge path of the fully controlled test unit matrix under the GB 31241 standard.

[0032] Figure 5 (b) is the schematic diagram of the actual working discharge path of the fully controlled test unit matrix under the UN38.3 standard. Detailed implementation manners

[0033] In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners. [[ID=2,8]]

[0034] As Figure 1 shown, the adaptive forced discharge control system for lithium batteries of the present invention includes a control unit, a fully controlled test unit matrix, a controllable DC power supply, a multi-channel electronic load, and a human-computer interaction unit, where:

[0035] The control unit is composed of a processor, a communication module, a sampling module, and a driving module. The control unit obtains the configuration information and operation instructions input by the user through the communication module. The control unit has a built-in forced discharge control algorithm. The control unit controls the operation of the test unit matrix, the controllable DC power supply, and the multi-channel DC load according to the forced discharge control algorithm, collects the working state variables of each unit, and transmits the state information to the human-computer interaction unit.

[0036] In this embodiment, the specific implementation of the control unit is as Figure 2 shown. It is controlled by a processor with a built-in forced discharge control algorithm, and exchanges data and transmits instructions with the human-computer interaction unit, the controllable DC power supply, and the multi-channel electronic load through the communication module; collects the electrical parameters of the test sample and controls the discharge path of the test unit matrix through the sampling module and the driving module respectively. The selection of the processor includes but is not limited to MCU, DSP, FPGA, X86, etc. The flow of the built-in forced discharge control algorithm is as Figure 3As shown in the figure, specifically: after the test is started, each part of the forced discharge control system completes the initialization after power-on. The fully controlled test unit matrix scans the open-circuit voltage of each test node to determine the presence or absence of the test battery cells and generates a test topology to be confirmed. Subsequently, the test standard is selected through the human-machine interface and the test parameters are input, thereby determining the output electrical energy form and parameters of the controllable DC power supply, setting the working modes and specific values of each electronic load; after the test topology is confirmed by clicking on the human-machine interface, the control unit controls the states of the switches of the test unit matrix and pre-treats the sample for discharge according to the standard requirements. After the pre-treatment is completed and the sample state meets the standard requirements, the working conditions of the controllable DC power supply and the multi-channel electronic load are set, and the forced discharge test is started. After the test is completed, various data during the test process are summarized to generate a test report.

[0037] The fully controlled test unit matrix is composed of multiple fully controlled test units connected in series and parallel. Each test unit includes a clamping tool for connecting a lithium battery sample, and corresponding bypass switches and disconnect switches. The clamping tool can be adapted to and install lithium batteries with different shapes such as cylindrical and prismatic; the bypass switches and disconnect switches adjust their respective on-states according to the instructions of the control unit. Multiple test units are first connected in series and then form a matrix through parallel switches. The matrix realizes different discharge paths with the change of each switch state.

[0038] In this embodiment, the specific implementation of the fully controlled test unit matrix is as Figure 4 shown. The matrix includes m×n fully controlled units. Each fully controlled unit includes a clamping tool for connecting a lithium battery sample, a disconnect switch tube, two bypass switch tubes, and corresponding voltage sampling and current sampling circuits. The m columns of series-connected fully controlled units can be paralleled through m - 1 parallel switches. The fully controlled test unit matrix receives the switch control signal sent by the control unit and sends the electrical parameter acquisition signal to the control unit.

[0039] In actual work, taking the requirements of the two standards of GB 31241 and UN38.3 as an example, the working mode of the fully controlled test unit matrix is described in detail. In the GB31241 standard, it is required to charge in the reverse direction with a current of 1C for 90 minutes. Figure 5 (a) demonstrates the discharge path of a string of the fully controlled test unit matrix under this test condition. Only the disconnect switch of the unit installing the test sample in this string is in the on-state, and the bypass switch is in the off-state; the disconnect switches of the remaining units are in the off-state, and the bypass switches are in the on-state. The parallel switches between the strings can be off or on; according to the sample parameters (cut-off voltage 3.0V, capacity 2000mAh, 1C current is 2A), the DC power supply charges the sample in the reverse direction with a constant current of 2A and stops after working for 90 minutes.

[0040] In the UN38.3 standard, it is required to connect a 12V DC power supply in series with a sample in a fully discharged state and discharge it at the nominal maximum discharge current for a certain period of time. Figure 5 As shown in (b), for a string of the fully controlled test unit matrix under this test condition, only the circuit breaker switch of the unit where the test sample is installed is in the on state, and the bypass switch is in the off state; the circuit breaker switches of the remaining units are in the off state, and the bypass switches are in the on state, and the parallel switches between the strings are in the off state, which means that each string discharges to an independent load; the DC power supply is set to the constant voltage mode, with an output of DC 12V. According to the sample parameters (cut-off voltage 3.0V, capacity 2000mAh, maximum discharge current 3C, i.e., 6000mA), it can be calculated that the electronic load is set to the constant resistance mode, with a resistance value of 2.5 ohms, and the test time is 20 minutes.

[0041] The controllable DC power supply can adjust its working mode according to the instructions of the control unit, such as the constant voltage mode, constant current mode, etc., and control the output voltage or current. In this embodiment, the controllable DC power supply is implemented by using a common power electronic converter topology. It converts alternating current into direct current output, adopts a two-stage structure of a front-stage AC-DC rectifier and a rear-stage DC-DC converter, and has two working modes of constant voltage control and constant current control.

[0042] The multi-channel electronic load can adjust its working mode according to the instructions of the control unit, such as the constant resistance mode, constant power mode, etc., and control the corresponding resistance value, power value or other control quantities. In this embodiment, the multi-channel electronic load is implemented by using a common power electronic converter topology. It converts the direct current output by connecting the power supply in series with the battery sample under test into alternating current and feeds it back to the power grid. Specifically, it adopts a multi-channel independent two-stage converter design. The front stage uses a full-bridge converter topology for voltage regulation and simultaneously realizes high-frequency isolation; the rear-stage converter uses a full-bridge inverter topology to perform the function of energy feedback to the power grid.

[0043] The human-machine interaction unit serves as an interaction interface for users to operate and control the entire test system. It can receive the status information transmitted from the control unit, display the operating status of the system, or be used to set the system operating parameters, etc. The human-machine interaction unit can be developed using an embedded solution or an X86 computer as the upper computer. The communication module of the human-machine interaction unit and the control unit establishes two-way communication. It can send user operation instructions to the control unit and also receive the status information sent by the control unit, and can display the user operation feedback and system status information through an external screen.

[0044] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art based on the disclosure of the present invention should fall within the protection scope of the present invention.

Claims

1. An adaptive forced discharge control system for lithium batteries, characterized in that It includes a control unit, a fully-controlled test unit matrix, a controllable DC power supply, multiple electronic loads, and a human-machine interaction unit, where: The control unit obtains the operation configuration parameters and operation instructions input by the user through the human-machine interaction unit, controls the working processes of the fully-controlled test unit matrix, the controllable DC power supply, and the multiple electronic loads by using the built-in forced discharge control algorithm, and collects their working state variables, and then externally transmits the test state information of the system through the human-machine interaction unit; Each column of the fully-controlled test unit matrix consists of multiple fully-controlled test units connected in series. After being connected in series, one end is connected to the controllable DC power supply, and the other end is used as the output end to connect to the corresponding electronic load. The output ends between adjacent two columns are connected through a parallel switch; each fully-controlled test unit is connected to the corresponding lithium battery sample. The fully-controlled test unit includes a voltage and current sampling circuit, a bypass switch, a break switch, and a clamping tool for fixing the lithium battery sample. Among them, the voltage and current sampling circuit is used to collect the voltage and current signals of the lithium battery sample. One end of the break switch is connected to the positive electrode of the lithium battery sample, and the other end of the break switch is connected to one end of the bypass switch and serves as one end of the fully-controlled test unit. The other end of the bypass switch is connected to the negative electrode of the lithium battery sample and serves as the other end of the fully-controlled test unit. The bypass switch and the break switch adjust their on-off states according to the control signals provided by the control unit; the entire matrix realizes different discharge paths according to the changes of each switch state; The controllable DC power supply adjusts its own working mode according to the instructions provided by the control unit, converts alternating current into direct current, so as to provide a stable DC voltage or DC current for the lithium battery sample; The multiple electronic loads adjust their own working modes according to the instructions provided by the control unit, and convert the direct current output by connecting the power supply in series with the lithium battery sample into alternating current and feedback it to the power grid; The human-machine interaction unit serves as an interaction interface between the user and the system, is used to receive the test state information transmitted by the control unit, display the operation state of the system, and at the same time receive the operation configuration parameters and operation instructions set by the user for the system.

2. The adaptive forced discharge control system for lithium batteries according to claim 1, wherein: The control unit is composed of a processor, a communication module, a sampling module, and a driving module. The processor has a built-in forced discharge control algorithm and is connected to the communication module, the sampling module, and the driving module; the communication module is connected to the human-machine interaction unit, and is used to obtain the configuration information and operation instructions input by the user and externally transmit the state information of the system; the sampling module is connected to the fully-controlled test unit, and is used to collect the electrical parameters of the lithium battery sample; the driving module is connected to the fully-controlled test unit, and it drives the on-off states of the switches in the fully-controlled test unit according to the control signals provided by the processor.

3. The adaptive forced discharge control system for lithium batteries according to claim 1, characterized in that: The clamping tool is adaptively installed and fixed for cylindrical or prismatic lithium battery samples.

4. The adaptive forced discharge control system for lithium batteries according to claim 1, wherein: The break switch consists of a switch tube. The bypass switch and the parallel switch both adopt two switch tubes connected back to back to form a bidirectional switch. The entire fully-controlled test unit matrix includes (3m×n + 2(m - 1)) switch tubes, reorganizes the topology of the lithium battery sample array with the quantity of m×n, and flexibly controls the discharge circuit, so as to adapt to different test requirements.

5. The adaptive forced discharge control system for lithium batteries according to claim 1, wherein: The controllable DC power supply is implemented by a power electronic converter topology, adopting a two-stage structure of a front-stage AC-DC rectifier and a rear-stage DC-DC converter, and having two operating modes: constant voltage control and constant current control.

6. The adaptive forced discharge control system for lithium batteries according to claim 1, wherein: The multi-channel electronic load is implemented by multi-channel independent two-stage converters, having a constant resistance or constant power operating mode to control the corresponding resistance value or power value. The front stage adopts a full-bridge converter topology for voltage regulation and simultaneously realizes high-frequency isolation. The rear stage adopts a full-bridge inverter topology to realize the function of energy feedback to the power grid.

7. The adaptive forced discharge control system for lithium batteries according to claim 1, characterized in that: The human-machine interaction unit is developed using an embedded solution or uses an X86 computer as the host computer. A two-way communication connection is established between the human-machine interaction unit and the control unit by a communication module.

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