A high voltage protection circuit for high voltage lithium battery pack AC impedance test

Abstract

The present invention belongs to the field of lithium battery testing, and discloses a high-voltage protection circuit in the AC impedance test of a high-voltage lithium battery pack, the high-voltage protection circuit comprising: a single-chip microcomputer, a protection module, a DC voltage sampling circuit and an AC impedance test circuit; the single-chip microcomputer is connected to the protection module, one end of the protection module is connected to the high-voltage lithium battery pack and the DC voltage sampling circuit in turn, and the other end of the protection module is connected to the AC impedance test circuit. The present invention directly eliminates the impact of high voltage on the AC impedance test circuit device in principle, and the present invention enables the high-voltage lithium battery pack tester to measure lithium battery packs with higher voltages, has lower requirements on the DC blocking capacitor and its charging resistor, is convenient for selection and design, and saves design space.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery testing, and in particular to a high voltage protection circuit in an alternating current impedance test of a high voltage lithium battery pack. Background Art

[0002] During the AC impedance test of a high-voltage lithium battery pack, the excitation end of the tester needs to produce a constant AC signal, and then the sampling end of the tester collects the AC voltage formed on the battery pack by the excitation signal into the tester for processing and calculation, and finally obtains the AC impedance of the high-voltage lithium battery pack.

[0003] During the test, if Figure 1 As shown in the figure, since the tester measures AC impedance by processing small AC signals, capacitors are connected in series at both the excitation end and the sampling end to isolate the DC signal. However, before and after the tester tests the high-voltage lithium battery pack, the two DC-isolating capacitors will be quickly charged / discharged, causing the high voltage of the high-voltage lithium battery pack to impact the test circuit of the tester for a short time, causing damage to the tester.

[0004] Existing high voltage protection measures for battery internal resistance testers, such as Figure 2 As shown, the high voltage protection device is a high power resistor R1, a transient suppression diode D1 and a high discharge resistor R2. Thus, the main charging circuit of the DC blocking capacitor C1 is the path ac formed by the high power resistor R1 and the transient suppression diode D1; the main charging circuit of the DC blocking capacitor C1 is the path bca formed by the high discharge resistor R2, the transient suppression diode D1 and the high power resistor R1.

[0005] When the high-voltage lithium battery pack is just connected to the test circuit, the transient suppression diode D1 is turned on and the DC blocking capacitor C1 begins to charge. The voltage Uba across the DC blocking capacitor C1 increases rapidly from 0V to U1; the voltage Uac across the internal components of the test circuit drops rapidly from U1 to 0V. Then the transient suppression diode D1 is turned off, the charging of the DC blocking capacitor C1 is completed, and the high voltage of the high-voltage lithium battery pack is isolated by the DC blocking capacitor C1. During the charging process of the DC blocking capacitor C1, the internal components of the test circuit will be impacted by the high voltage of the high-voltage lithium battery pack only in the very short time at the beginning. The internal components of the test circuit can withstand the impact in a very short time, thus protecting the internal components of the test circuit during the charging process of the DC blocking capacitor C1.

[0006] When the test is completed, the high-voltage lithium battery pack is removed from the test end, and the DC-blocking capacitor C1 begins to discharge through the path bca. The voltage Uba across the DC-blocking capacitor C1 drops from U1 to 0V quickly; the voltage Uac across the internal components of the test circuit drops from It drops to 0V relatively quickly. Since the large discharge resistor R2>>high power resistor R1, the voltage Uac across the internal components of the test circuit is the initial voltage during the discharge of the DC blocking capacitor C1. Very low, thus protecting the internal components of the test circuit during the discharge process of the DC blocking capacitor C1.

[0007] The biggest drawback of the above existing method is that if the charging time of the DC blocking capacitor C1 is not short enough, it will still cause damage to the internal components of the test circuit. Figure 2 As shown, the charging time constant τ of the DC-isolating capacitor C1 can be roughly calculated as R1×C1 (C1 is the capacitance of the DC-isolating capacitor C1; R1 is the resistance of the main resistor R1 in the charging circuit of the DC-isolating capacitor CI). It is generally believed that after 3 to 5 time constants, the capacitor is considered to be fully charged. Therefore, when using the above method for high-voltage protection, to shorten the charging time of the DC-isolating capacitor C1, the values ​​of R1 and C1 must be reduced.

[0008] For resistor R1, when the voltage U1 of the high-voltage lithium battery pack being measured remains unchanged, the maximum instantaneous power on resistor R1 is To reduce R1, the maximum instantaneous power that the resistor can withstand must be increased. A resistor with a small resistance and high power will be very large and difficult to select. Even if multiple parallel and multiple series are used to increase the maximum instantaneous power that R1 can withstand, it will take up a lot of space, which is not conducive to the integrated design of the circuit.

[0009] For the DC blocking capacitor C1, due to the special location of the capacitor, it is connected in series in the main test circuit, and the AC impedance test of the high-voltage lithium battery pack requires the processing of the AC signal. If the value of the DC blocking capacitor C1 is reduced, the capacitor impedance (f is the test signal frequency, C is the capacitance of the capacitor) will inevitably increase, which will lead to a decrease in the driving ability of the test circuit excitation end (the loss of the DC blocking capacitor C1 increases).

[0010] Therefore, how to provide a high-voltage protection circuit in the AC impedance test of a high-voltage lithium battery pack is a problem that needs to be solved urgently. Summary of the invention

[0011] The embodiment of the present invention provides a high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack to solve the problem of limitations brought by the high power resistor R1 and the DC blocking capacitor C1 in the prior art to the AC impedance test of a high voltage lithium battery pack.

[0012] In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended to be a general review, nor is it intended to identify key / important components or to delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

[0013] According to an embodiment of the present invention, a high voltage protection circuit for an AC impedance test of a high voltage lithium battery pack is provided.

[0014] In one embodiment, a high voltage protection circuit in an AC impedance test of a high voltage lithium battery pack includes: a single chip microcomputer, a protection module, a DC voltage sampling circuit and an AC impedance test circuit;

[0015] The single chip microcomputer is connected to the protection module, one end of the protection module is connected to the high voltage lithium battery pack and the DC voltage sampling circuit in turn, and the other end of the protection module is connected to the AC impedance test circuit;

[0016] The single chip microcomputer is used to judge the test status of the high-voltage lithium battery pack according to the voltage value collected by the DC voltage sampling circuit; in the DC isolation capacitor charging stage of the high-voltage lithium battery pack test process, the delay operation is performed according to the preset time;

[0017] A protection module is used to protect the DC voltage sampling circuit and the AC impedance test circuit;

[0018] DC voltage sampling circuit, used to perform open circuit voltage test on high-voltage lithium battery pack;

[0019] The AC impedance test circuit is used to test the internal resistance of a high-voltage lithium battery pack and includes an AC excitation output part and an AC voltage sampling circuit.

[0020] In one embodiment, the protection module includes a relay RY1, a relay RY2, a resistor R3, a resistor R4, a diode D2 and a capacitor C4;

[0021] Among them, the first end of relay RY1 is connected to the AC impedance test circuit, the third end of relay RY1 is connected to the single-chip microcomputer, the second end of relay RY1 is connected to one end of resistor R3 and one end of capacitor C4 in sequence, the other end of resistor R3 is connected to one end of diode D2, the other end of diode D2 is connected to the AC impedance test circuit, one end of resistor R4, the negative electrode of the high-voltage lithium battery pack and the DC voltage sampling circuit in sequence, the other end of capacitor C4 is connected to the first end of relay RY2, the third end of relay RY2 is connected to the single-chip microcomputer, and the second end of relay RY2 is connected to the other end of resistor R4, the positive electrode of the high-voltage lithium battery pack and the DC voltage sampling circuit in sequence.

[0022] In one embodiment, the AC excitation output portion includes a sine signal generator, an operational amplifier U1B, an operational amplifier U1A, a resistor R5, a resistor R7, a resistor R6, a power amplifier, and a capacitor C5;

[0023] Among them, the sinusoidal signal generator is connected to the fifth end of the operational amplifier U1B, the sixth end of the operational amplifier U1B is connected to the seventh end of the operational amplifier U1B and one end of the resistor R5 in sequence, the other end of the resistor R5 is connected to the third end of the operational amplifier U1A, the second end of the operational amplifier U1A is connected to one end of the resistor R7 and the high-voltage lithium battery pack in sequence, the first end of the operational amplifier U1A is connected to one end of the resistor R6, the other end of the resistor R6 is connected to one end of the power amplifier, the other end of the power amplifier is connected to one end of the capacitor C5, and the other end of the capacitor C5 is connected to the high-voltage lithium battery pack.

[0024] In one embodiment, the AC voltage sampling circuit includes a resistor R9, a resistor R10, an operational amplifier U2, an operational amplifier U3, a capacitor C6, a resistor R8, a resistor R11, a resistor R12, an analog switch and an operation circuit;

[0025] Among them, one end of resistor R9 is connected to one end of resistor R10 and the second end of operational amplifier U2 in sequence, the other end of resistor R10 is connected to the sixth end of operational amplifier U2 and the first end of analog switch in sequence, the third end of operational amplifier U2 is connected to one end of resistor R8, the other end of resistor R8 is connected to one end of capacitor C6, the other end of capacitor C6 is connected to the high-voltage lithium battery pack and one end of resistor R11 in sequence, the other end of resistor R11 is connected to the third end of operational amplifier U3 and one end of resistor R12 in sequence, the other end of resistor R12 is connected to the high-voltage lithium battery pack and grounded, the second end of operational amplifier U3 is connected to the sixth end of operational amplifier U3 and the second end of analog switch in sequence, and the third end of analog switch is connected to the operation circuit.

[0026] In one embodiment, the operation circuit includes a resistor R13, a resistor R14, a resistor R15, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a resistor R20, an operational amplifier U4A, an operational amplifier U4B, an operational amplifier U5A, an operational amplifier U5B and an analog-to-digital conversion chip;

[0027] Among them, one end of resistor R13 is connected to one end of resistor R15, the other end of resistor R13 is connected to one end of resistor R14 and the first end of op amp U4A in sequence, the other end of resistor R15 is connected to one end of resistor R16 and the first end of op amp U4B in sequence, the other end of resistor R16 is connected to one end of resistor R17, the other end of resistor R17 is connected to one end of resistor R18 and the second end of op amp U4A in sequence, the third end of op amp U4A is connected to the first end of op amp U5A, the second end of op amp U5A is connected to the other end of resistor R18, the third end of op amp U5A and the first end of analog-to-digital conversion chip in sequence, the second end of op amp U4B is connected to one end of resistor R19 and one end of resistor R20 in sequence, the other end of resistor R19 is connected to the second end of analog-to-digital conversion chip, the third end of op amp U5B and the second end of op amp U5B in sequence, the first end of op amp U5B is connected to the third end of op amp U4B, and the third end of analog-to-digital conversion chip is connected to the single-chip microcomputer.

[0028] In one embodiment, the AC voltage sampling loop is the same as the DC voltage sampling loop and they share a sampling terminal of the tester.

[0029] In one embodiment, the AC excitation output part and the AC voltage sampling loop are connected to their respective corresponding protection modules.

[0030] In one embodiment, judging the test status of the high-voltage lithium battery pack according to the voltage value collected by the DC voltage sampling circuit includes:

[0031] When the collected voltage of the DC voltage sampling circuit is greater than the preset value, it is determined that the high-voltage lithium battery pack is connected to the test circuit, and the relay RY2 is in the energized state, the relay RY1 is in the disconnected state, and the capacitor C4 is charged.

[0032] In one embodiment, during the DC blocking capacitor charging phase of the high voltage lithium battery pack test process, performing a delay operation according to a preset time includes:

[0033] The charging time constant of capacitor C4 is calculated according to the circuit parameters, and after a number of charging time constants, the single chip microcomputer performs a delay operation according to a preset time; relays RY1 and RY2 are both in the energized state.

[0034] In one embodiment, after the high-voltage battery pack test is completed, the relay RY1 is in the disconnected state and the relay RY2 is in the closed state;

[0035] When the collected voltage of the DC voltage sampling circuit is lower than the preset value, the capacitor C4 is fully discharged, and the relay RY1 and the relay RY2 are both in the disconnected state.

[0036] The technical solution provided by the embodiment of the present invention may have the following beneficial effects:

[0037] The present invention directly eliminates the impact of high voltage on the AC impedance test circuit components in principle (the AC impedance test path will be connected only after the DC blocking capacitor is fully charged). Since the high-voltage lithium battery pack is very large, the assembly line rapid test mode is rarely used, that is, the test time requirement is not high. The present invention ensures the safety and reliability of the high-voltage lithium battery pack test by sacrificing relatively unimportant test time parameters. Compared with the prior art, the present invention enables the high-voltage lithium battery pack tester to measure lithium battery packs with higher voltages. The present invention has lower requirements for the DC blocking capacitor and its charging resistor, facilitates the selection design, and saves design space.

[0038] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0040] Figure 1 This is the schematic diagram of AC impedance test of high voltage lithium battery pack;

[0041] Figure 2 This is a schematic diagram of high voltage protection of an existing battery internal resistance meter;

[0042] Figure 3 This is the test schematic diagram of the simulation circuit of the high-voltage lithium battery pack tester;

[0043] Figure 4 is a circuit schematic diagram of a relay high voltage protection method according to an exemplary embodiment;

[0044] Figure 5 is a working timing diagram of relay RY1 / RY2 according to an exemplary embodiment;

[0045] Figure 6 is a schematic diagram of an AC excitation output principle of a lithium battery pack according to an exemplary embodiment;

[0046] Figure 7 is a schematic diagram of AC / DC voltage collection of a lithium battery pack according to an exemplary embodiment;

[0047] Figure 8 is a diagram of an operation circuit according to an exemplary embodiment. DETAILED DESCRIPTION

[0048] The following description and accompanying drawings fully illustrate the specific embodiments of this article so that those skilled in the art can practice them. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of the embodiments of this article includes the entire scope of the claims, as well as all available equivalents of the claims. Herein, the terms "first", "second", etc. are only used to distinguish one element from another, without requiring or implying any actual relationship or order between these elements. In fact, the first element can also be called the second element, and vice versa. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the structure, device or equipment including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also include elements inherent to such structure, device or equipment. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the structure, device or equipment including the elements. Each embodiment is described in a progressive manner herein, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other.

[0049] The terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. in this document indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing this document and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of this document, unless otherwise specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, it can also be the internal communication of two elements, it can be a direct connection, or it can be an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0050] As used herein, the term "plurality" means two or more than two, unless otherwise specified.

[0051] In this document, the character " / " indicates that the preceding and following objects are in an "or" relationship. For example, A / B means: A or B.

[0052] In this article, the term "and / or" is a description of the association relationship between objects, indicating that three relationships may exist. For example, A and / or B means: A or B, or, A and B.

[0053] It should be understood that, although the various steps in the flow chart are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear description in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the figure may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0054] Each module in the device or system of the present application can be implemented in whole or in part by software, hardware, or a combination thereof. The above modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to the above modules.

[0055] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0056] Figure 1 An embodiment of a high-voltage protection circuit in an AC impedance test of a high-voltage lithium battery pack of the present invention is shown.

[0057] In this optional embodiment, the high-voltage protection circuit in the AC impedance test of the high-voltage lithium battery pack includes: a single-chip microcomputer, a protection module, a DC voltage sampling loop and an AC impedance test circuit;

[0058] The single chip microcomputer is connected to the protection module, one end of the protection module is connected to the high voltage lithium battery pack and the DC voltage sampling circuit in turn, and the other end of the protection module is connected to the AC impedance test circuit;

[0059] The single chip microcomputer is used to judge the test status of the high-voltage lithium battery pack according to the voltage value collected by the DC voltage sampling circuit; in the DC isolation capacitor charging stage of the high-voltage lithium battery pack test process, the delay operation is performed according to the preset time;

[0060] A protection module is used to protect the DC voltage sampling circuit and the AC impedance test circuit;

[0061] DC voltage sampling circuit, used to perform open circuit voltage test on high-voltage lithium battery pack;

[0062] The AC impedance test circuit is used to test the internal resistance of a high-voltage lithium battery pack and includes an AC excitation output part and an AC voltage sampling circuit.

[0063] In this optional embodiment, the protection module includes a relay RY1, a relay RY2, a resistor R3, a resistor R4, a diode D2 and a capacitor C4; wherein, the first end of the relay RY1 is connected to the AC impedance test circuit, the third end of the relay RY1 is connected to the single-chip microcomputer, the second end of the relay RY1 is connected to one end of the resistor R3 and one end of the capacitor C4 in sequence, the other end of the resistor R3 is connected to one end of the diode D2, the other end of the diode D2 is connected to the AC impedance test circuit, one end of the resistor R4, the negative electrode of the high-voltage lithium battery pack and the DC voltage sampling circuit in sequence, the other end of the capacitor C4 is connected to the first end of the relay RY2, the third end of the relay RY2 is connected to the single-chip microcomputer, and the second end of the relay RY2 is connected to the other end of the resistor R4, the positive electrode of the high-voltage lithium battery pack and the DC voltage sampling circuit in sequence.

[0064] In this optional embodiment, the AC excitation output part includes a sinusoidal signal generator, an operational amplifier U1B, an operational amplifier U1A, a resistor R5, a resistor R7, a resistor R6, a power amplifier and a capacitor C5; wherein the sinusoidal signal generator is connected to the fifth end of the operational amplifier U1B, the sixth end of the operational amplifier U1B is connected to the seventh end of the operational amplifier U1B and one end of the resistor R5 in sequence, the other end of the resistor R5 is connected to the third end of the operational amplifier U1A, the second end of the operational amplifier U1A is connected to one end of the resistor R7 and a high-voltage lithium battery pack in sequence, the first end of the operational amplifier U1A is connected to one end of the resistor R6, the other end of the resistor R6 is connected to one end of the power amplifier, the other end of the power amplifier is connected to one end of the capacitor C5, and the other end of the capacitor C5 is connected to the high-voltage lithium battery pack.

[0065] In this optional embodiment, the AC voltage sampling loop includes a resistor R9, a resistor R10, an operational amplifier U2, an operational amplifier U3, a capacitor C6, a resistor R8, a resistor R11, a resistor R12, an analog switch and an operation circuit; wherein, one end of the resistor R9 is connected to one end of the resistor R10 and the second end of the operational amplifier U2 in sequence, the other end of the resistor R10 is connected to the sixth end of the operational amplifier U2 and the first end of the analog switch in sequence, the third end of the operational amplifier U2 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to the high-voltage lithium battery pack and one end of the resistor R11 in sequence, the other end of the resistor R11 is connected to the third end of the operational amplifier U3 and one end of the resistor R12 in sequence, the other end of the resistor R12 is connected to the high-voltage lithium battery pack and grounded, the second end of the operational amplifier U3 is connected to the sixth end of the operational amplifier U3 and the second end of the analog switch in sequence, and the third end of the analog switch is connected to the operation circuit.

[0066] In this optional embodiment, the operation circuit includes a resistor R13, a resistor R14, a resistor R15, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a resistor R20, an operational amplifier U4A, an operational amplifier U4B, an operational amplifier U5A, an operational amplifier U5B and an analog-to-digital conversion chip; wherein one end of the resistor R13 is connected to one end of the resistor R15, the other end of the resistor R13 is sequentially connected to one end of the resistor R14 and the first end of the operational amplifier U4A, the other end of the resistor R15 is sequentially connected to one end of the resistor R16 and the first end of the operational amplifier U4B, the other end of the resistor R16 is connected to one end of the resistor R17, and the The other end is connected to one end of resistor R18 and the second end of op amp U4A in sequence, the third end of op amp U4A is connected to the first end of op amp U5A, the second end of op amp U5A is connected to the other end of resistor R18, the third end of op amp U5A and the first end of the analog-to-digital conversion chip in sequence, the second end of op amp U4B is connected to one end of resistor R19 and one end of resistor R20 in sequence, the other end of resistor R19 is connected to the second end of the analog-to-digital conversion chip, the third end of op amp U5B and the second end of op amp U5B in sequence, the first end of op amp U5B is connected to the third end of op amp U4B, and the third end of the analog-to-digital conversion chip is connected to the microcontroller.

[0067] In this optional embodiment, the AC voltage sampling circuit is the same as the DC voltage sampling circuit and they share a sampling terminal of the tester.

[0068] In this optional embodiment, the AC excitation output part and the AC voltage sampling loop are connected to their respective corresponding protection modules.

[0069] In this optional embodiment, the test status of the high-voltage lithium battery pack is judged according to the voltage value collected by the DC voltage sampling circuit, including: when the collected voltage of the DC voltage sampling circuit is greater than the preset value, it is judged that the high-voltage lithium battery pack is connected to the test circuit, and the relay RY2 is in the energized state, the relay RY1 is in the disconnected state, and the capacitor C4 is charged.

[0070] In this optional embodiment, during the DC blocking capacitor charging stage of the high-voltage lithium battery pack test process, a delay operation is performed according to a preset time, including: calculating the charging time constant of capacitor C4 according to circuit parameters, and after a number of charging time constants, the microcontroller performs a delay operation according to the preset time; relay RY1 and relay RY2 are both in the energized state.

[0071] In this optional embodiment, after the high-voltage battery pack test is completed, relay RY1 is in the disconnected state and relay RY2 is in the attracted state; when the collection voltage of the DC voltage sampling circuit is lower than the preset value, capacitor C4 is discharged, and relay RY1 and relay RY2 are both in the disconnected state.

[0072] In order to facilitate understanding of the above technical solutions of the present invention, the above technical solutions of the present invention are further described below from the perspective of architecture and principle, as follows:

[0073] like Figure 3 As shown, the existing high-voltage lithium battery pack tester can perform two test items: battery pack AC internal resistance and battery pack open circuit voltage. The present invention utilizes the battery pack open circuit voltage test function to control the high-voltage relay to protect the battery pack AC internal resistance test circuit. Figure 5 As shown in the figure, the high-voltage lithium battery pack test process is divided into four stages, namely, the test preparation stage, the DC blocking capacitor charging stage, the AC impedance test stage and the DC blocking capacitor discharging stage. The AC impedance test process of the prior art overlaps with other stages, mainly because the battery pack AC internal resistance test circuit will be damaged during the DC blocking capacitor charging stage.

[0074] like Figure 4 As shown, in the test preparation stage of the present invention, when the single-chip microcomputer detects that the voltage collected by the DC voltage sampling loop is greater than a certain value (close to the voltage U2 of the high-voltage lithium battery pack), it will determine that the high-voltage battery pack is connected to the test circuit, RY2 is pulled in, RY1 remains disconnected, and the DC blocking capacitor C4 begins to be charged; the charging time constant τ=R3×C4 of the DC blocking capacitor C4 is calculated according to the circuit parameters, and it is generally believed that after 3 to 5 time constants, the capacitor is considered to be full, and the charging stage of the DC blocking capacitor ends. After the single-chip microcomputer delays for a corresponding time, RY1 is pulled in, and RY2 remains pulled in; the AC impedance test of the high-voltage battery pack is performed; after the test is completed, the high-voltage lithium battery pack is removed from the test circuit, and the voltage collected by the DC voltage sampling loop drops rapidly, and RY1 is first disconnected, and RY2 remains pulled in; when the voltage collected by the DC voltage sampling loop is lower than a certain value (close to 0V), the DC blocking capacitor C4 is considered to be fully discharged, RY2 is disconnected, RY1 remains disconnected, and the discharge stage of the DC blocking capacitor ends.

[0075] The high voltage lithium battery pack tester can perform two tests: battery pack AC internal resistance and battery pack open circuit voltage. The test schematic diagram is as follows: Figure 3 shown.

[0076] The battery pack AC internal resistance test item is implemented by the AC excitation output circuit and the AC voltage sampling circuit. The tester outputs a constant AC signal through the AC excitation output terminal, which is then collected through the AC voltage sampling terminal. Finally, the battery pack internal resistance is calculated by the program. There are DC blocking capacitors C2 and C3 in these two circuits.

[0077] The battery pack open circuit voltage test item is sampled and tested by the DC voltage sampling circuit of the tester. The DC voltage sampling circuit and the AC voltage sampling circuit share the sampling terminal of the tester (see Figure 6 and Figure 7 introduce).

[0078] like Figure 4 As shown, RY1 is high-voltage relay 1; RY2 is high-voltage relay 2; C4 is the DC blocking capacitor of the AC impedance test circuit; R3 is the main resistor of the capacitor C4 charge / discharge circuit; R4 is the main resistor of the capacitor C4 discharge circuit; D2 is a transient suppression diode, which only works during the charge / discharge process of capacitor C4; U2 is the voltage difference between the two ends of the high-voltage battery pack; the AC impedance test circuit includes two parts: AC excitation output and AC voltage sampling. For details of the components and circuits, see Figure 6 and Figure 7 .according to Figure 3 Test principle: the battery AC internal resistance tester has four test terminals, two of which are Figure 6 The middle one is connected to the AC excitation output terminal of the lithium battery pack, and the other two are Figure 7 Connect the voltage collection terminal of the lithium battery pack. Figure 6 and Figure 7 The circuit is not electrically connected, and the only electrical connection is made by testing the lithium battery pack together. Figure 4 The high-voltage relays RY1 and RY2, resistors R3 and R4, transient suppression diode D2, and DC blocking capacitor C4 can be replaced Figure 6 The DC blocking capacitor C5 in Figure 6 The power amplifier, resistor R6 and op amp U1A in the circuit form protection; similarly Figure 7 The DC blocking capacitor C6 in the circuit is also protected by a protection module consisting of another set of high-voltage relays RY1 and RY2, resistors R3 and R4, transient suppression diode D2 and DC blocking capacitor C4. Figure 6 The right side of the medium power amplifier is connected Figure 4 The left end of the high voltage relay RY1 in the Figure 6 The upper end of the middle resistor R7 is connected Figure 4 The lower end of the middle transient suppression diode D2; Figure 7 The left end of the middle resistor R8 is connected Figure 4 The left end of the high voltage relay RY1 in the Figure 7 Zero potential GND0 connection Figure 4 The lower end of the transient suppression diode D2. It should be noted that Figure 6 and Figure 7 The middle circuit does not share a set of protection modules composed of high-voltage relays RY1 and RY2, resistors R3 and R4, transient suppression diode D2 and DC blocking capacitor C4, but a total of two sets of the protection modules protect the AC excitation output circuit and the AC voltage sampling circuit respectively.

[0079] like Figure 5As shown, the high level represents the relay is energized, and the low level represents the relay is disconnected. 0~t1 stage, test preparation stage, at t1, the high voltage battery pack is connected to the test circuit, the DC voltage sampling circuit collects the high voltage, and the relay RY2 is energized; t1~t2 stage, the DC blocking capacitor C4 charging stage, the time is 3~5 times the time constant τ=R3×C4( Figure 4 : C4, the capacitance of the DC blocking capacitor C4; R3, the main resistance of the charging circuit of the DC blocking capacitor C4), the MCU program is delayed to time t2, and the relay RY1 is energized; t2~t3 stage, the AC impedance test stage, the sampling and calculation of the AC impedance is completed, the test is completed at time t3, the high-voltage lithium battery pack is removed, and the relay RY1 is disconnected; t3~t4 stage, the DC blocking capacitor C4 discharge stage, the discharge is completed at time t4, the DC voltage sampling circuit collects a low voltage (close to 0V), the relay RY2 is disconnected, and the state is restored to the state before the test.

[0080] Lithium battery pack AC impedance test principle:

[0081] like Figure 6 As shown in the figure, a 1KHZ sinusoidal voltage signal with a constant amplitude is emitted by a 1KHZ (the test signal frequency requirement in the lithium battery AC internal resistance test industry is 1KHZ) sinusoidal signal generator (conventional technology), which is followed by an op amp U1B (two op amps on the same chip as U1A, model OPA2227U) and a current limiting resistor R1 to an amplifier op amp U1A (two op amps on the same chip as U1B, model OPA2227U, the power supply voltage of this chip in this application scenario is ±15V); according to the op amp virtual short principle, the 2 The voltage of pin 1 is the same as that of pin 3, both of which are 1KHZ sinusoidal voltage signals with constant amplitude. According to the virtual disconnection principle of the operational amplifier, the current flowing to pin 2 of the amplifier U1A is 0, so the current of the resistance to be measured Rx (AC internal resistance of the lithium battery pack) and the grounding resistance R3 are equal. The power amplifier (conventional technology) improves the output capacity of the operational amplifier U1A. Since the AC voltage flowing to pin 2 of the amplifier U1A is constant, the effective value I of the AC current flowing through the resistance to be measured Rx (AC internal resistance of the lithium battery pack) and the grounding resistance R3 is constant. The effective value of the AC current is (U0 is the effective value of the constant AC voltage emitted by the 1KHZ sinusoidal signal generator).

[0082] like Figure 7 As shown, the constant current I output by the AC excitation output circuit of the lithium battery pack forms an AC voltage U on the lithium battery pack. This voltage flows into the operational amplifier U2 (model OPA1611A, the power supply voltage in this application scenario is ±5V) through the DC isolation capacitor C6 (isolating the open circuit voltage of the lithium battery pack itself) and the resistor R8. The operational amplifier U2 and the resistors R9 and R10 form a reverse amplification circuit with an amplification factor of Then it flows into the operation circuit through the analog switch. The operation circuit converts the analog signal into a digital signal and sends it to the microcontroller. The microcontroller calculates the AC internal resistance of the lithium battery according to the formula. (I is the constant current output by the AC excitation output circuit of the lithium battery pack, and U is the AC voltage formed on the lithium battery pack by this current).

[0083] like Figure 7 As shown, the open-circuit voltage Ux of the lithium battery pack is sampled by the resistor R11 and R12 voltage divider, and flows into the operational amplifier U3 (model LTC2057, the power supply voltage in this application scenario is ±5V), which acts as a follower, and then flows into the operation circuit through the analog switch. The operation circuit converts the analog signal into a digital signal and sends it to the microcontroller, which is converted into the open-circuit voltage of the lithium battery pack by geometric conversion.

[0084] Figure 8 for Figure 7 The operational circuit is expanded in detail. Among them, U4A and U4B are the same operational amplifier chip (OPA2188AID), and U5A and U5B are the same operational amplifier chip (OPA2340UA). According to the virtual short principle of the operational amplifier, it can be known that the currents on the in-phase and inverting ends of the operational amplifiers U4A, U4B, U5A and U5B can be approximately equivalent to 0, so it can be obtained that the currents flowing through R13 and R14 are equal, the currents flowing through R15 and R16 are equal, the currents flowing through R17 and R18 are equal, and the currents flowing through R19 and R20 are equal. According to the virtual short principle of the operational amplifier, it can be known that the potentials of the in-phase and inverting ends of the operational amplifier U4A are the same, the potentials of the in-phase and inverting ends of the operational amplifier 4B are the same, the potentials of the in-phase and inverting ends of the operational amplifier U5A are the same, and the potentials of the in-phase and inverting ends of the operational amplifier U5B are the same. According to the above two principles, the differential input positive voltage U0′ of the analog-to-digital conversion chip can be obtained. + =2+0.9U 0 ( Figure 7 The AC voltage acquisition signal or DC voltage acquisition signal collected by the circuit is switched through the analog switch and transmitted to Figure 8 The input terminal is used as the input voltage of the operation circuit, U 0 Represents the size of the input voltage), AD chip differential input negative voltage U0′ - =2-0.9U 0 ( Figure 7 The AC voltage acquisition signal or DC voltage acquisition signal collected by the circuit is switched through the analog switch and transmitted to Figure 8 The input terminal is used as the input voltage of the operation circuit, U 0 represents the magnitude of the input voltage), so the gain coefficient of the operational circuit is

[0085] The present invention comprises:

[0086] (1) When the single-chip microcomputer detects that the voltage collected by the DC voltage sampling circuit is greater than a certain value (close to the voltage U2 of the high-voltage lithium battery pack), it is determined that the high-voltage battery pack is connected to the test circuit, RY2 is attracted, RY1 remains disconnected, and the DC blocking capacitor C4 is charged.

[0087] (2) The charging time constant τ = R3 × C4 of the DC blocking capacitor C4 is calculated based on the circuit parameters. It is generally considered that after 3 to 5 time constants, the capacitor is considered to be fully charged. After the microcontroller delays for a corresponding period of time, RY1 is energized and RY2 remains energized.

[0088] (3) Perform an AC impedance test on the high-voltage battery pack. After the test is completed, remove the high-voltage lithium battery pack from the test circuit. The DC voltage sampling circuit collects a rapid drop in voltage. First, disconnect RY1 and keep RY2 closed.

[0089] (4) When the voltage collected by the DC voltage sampling circuit is lower than a certain value (close to 0V), the DC blocking capacitor C4 is considered to be fully discharged, RY2 is disconnected, RY1 remains disconnected, and the state before the test is restored.

[0090] The present invention is not limited to the structures which have been described above and shown in the drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack, characterized in that: The high voltage protection circuit comprises: a single chip microcomputer, a protection module, a DC voltage sampling circuit and an AC impedance testing circuit; The single chip microcomputer is connected to the protection module, one end of the protection module is connected to the high voltage lithium battery pack and the DC voltage sampling circuit in sequence, and the other end of the protection module is connected to the AC impedance test circuit; The single chip microcomputer is used to determine the test status of the high-voltage lithium battery pack according to the voltage value collected by the DC voltage sampling circuit; in the DC blocking capacitor charging stage of the high-voltage lithium battery pack test process, the delay operation is performed according to a preset time; The protection module is used to protect the DC voltage sampling circuit and the AC impedance testing circuit; The DC voltage sampling circuit is used to perform an open circuit voltage test on the high-voltage lithium battery pack; The AC impedance test circuit is used to perform internal resistance test on a high-voltage lithium battery pack, and includes an AC excitation output part and an AC voltage sampling circuit.

2. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 1, characterized in that: The protection module includes a relay RY1, a relay RY2, a resistor R3, a resistor R4, a diode D2 and a capacitor C4; Among them, the first end of the relay RY1 is connected to the AC impedance test circuit, the third end of the relay RY1 is connected to the single-chip microcomputer, the second end of the relay RY1 is connected to one end of the resistor R3 and one end of the capacitor C4 in sequence, the other end of the resistor R3 is connected to one end of the diode D2, the other end of the diode D2 is connected to the AC impedance test circuit, one end of the resistor R4, the negative electrode of the high-voltage lithium battery pack and the DC voltage sampling circuit in sequence, the other end of the capacitor C4 is connected to the first end of the relay RY2, the third end of the relay RY2 is connected to the single-chip microcomputer, and the second end of the relay RY2 is connected to the other end of the resistor R4, the positive electrode of the high-voltage lithium battery pack and the DC voltage sampling circuit in sequence.

3. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 1, characterized in that: The AC excitation output part includes a sine signal generator, an operational amplifier U1B, an operational amplifier U1A, a resistor R5, a resistor R7, a resistor R6, a power amplifier and a capacitor C5; Among them, the sinusoidal signal generator is connected to the fifth end of the operational amplifier U1B, the sixth end of the operational amplifier U1B is connected to the seventh end of the operational amplifier U1B and one end of the resistor R5 in sequence, the other end of the resistor R5 is connected to the third end of the operational amplifier U1A, the second end of the operational amplifier U1A is connected to one end of the resistor R7 and the high-voltage lithium battery pack in sequence, the first end of the operational amplifier U1A is connected to one end of the resistor R6, the other end of the resistor R6 is connected to one end of the power amplifier, the other end of the power amplifier is connected to one end of the capacitor C5, and the other end of the capacitor C5 is connected to the high-voltage lithium battery pack.

4. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 1, characterized in that: The AC voltage sampling circuit includes a resistor R9, a resistor R10, an operational amplifier U2, an operational amplifier U3, a capacitor C6, a resistor R8, a resistor R11, a resistor R12, an analog switch and an operation circuit; Among them, one end of the resistor R9 is connected to one end of the resistor R10 and the second end of the operational amplifier U2 in sequence, the other end of the resistor R10 is connected to the sixth end of the operational amplifier U2 and the first end of the analog switch in sequence, the third end of the operational amplifier U2 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to one end of the capacitor C6, the other end of the capacitor C6 is connected to the high-voltage lithium battery pack and one end of the resistor R11 in sequence, the other end of the resistor R11 is connected to the third end of the operational amplifier U3 and one end of the resistor R12 in sequence, the other end of the resistor R12 is connected to the high-voltage lithium battery pack and grounded, the second end of the operational amplifier U3 is connected to the sixth end of the operational amplifier U3 and the second end of the analog switch in sequence, and the third end of the analog switch is connected to the operation circuit.

5. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 4, characterized in that: The operation circuit includes a resistor R13, a resistor R14, a resistor R15, a resistor R16, a resistor R17, a resistor R18, a resistor R19, a resistor R20, an operational amplifier U4A, an operational amplifier U4B, an operational amplifier U5A, an operational amplifier U5B and an analog-to-digital conversion chip; Among them, one end of the resistor R13 is connected to one end of the resistor R15, the other end of the resistor R13 is connected to one end of the resistor R14 and the first end of the operational amplifier U4A in sequence, the other end of the resistor R15 is connected to one end of the resistor R16 and the first end of the operational amplifier U4B in sequence, the other end of the resistor R16 is connected to one end of the resistor R17, the other end of the resistor R17 is connected to one end of the resistor R18 and the second end of the operational amplifier U4A in sequence, the third end of the operational amplifier U4A is connected to the first end of the operational amplifier U5A The second end of the operational amplifier U5A is connected in sequence to the other end of the resistor R18, the third end of the operational amplifier U5A and the first end of the analog-to-digital conversion chip, the second end of the operational amplifier U4B is connected in sequence to one end of the resistor R19 and one end of the resistor R20, the other end of the resistor R19 is connected in sequence to the second end of the analog-to-digital conversion chip, the third end of the operational amplifier U5B and the second end of the operational amplifier U5B, the first end of the operational amplifier U5B is connected to the third end of the operational amplifier U4B, and the third end of the analog-to-digital conversion chip is connected to the single-chip microcomputer.

6. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 1, characterized in that: The AC voltage sampling circuit is the same as the DC voltage sampling circuit and shares a sampling terminal of the tester.

7. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 1, characterized in that: The AC excitation output part and the AC voltage sampling loop are connected to the corresponding protection modules.

8. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 2, characterized in that: The step of judging the test status of the high-voltage lithium battery pack according to the voltage value collected by the DC voltage sampling circuit includes: When the collected voltage of the DC voltage sampling circuit is greater than a preset value, it is determined that the high-voltage lithium battery pack is connected to the test circuit, and the relay RY2 is in the energized state, the relay RY1 is in the disconnected state, and the capacitor C4 is charged.

9. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 8, characterized in that: The delay operation according to a preset time during the DC blocking capacitor charging stage of the high-voltage lithium battery pack test process includes: The charging time constant of the capacitor C4 is calculated according to the circuit parameters, and after a number of charging time constants, the single chip microcomputer performs a delay operation according to a preset time; the relay RY1 and the relay RY2 are both in the energized state.

10. The high voltage protection circuit in the AC impedance test of a high voltage lithium battery pack according to claim 9, characterized in that: After the high-voltage battery pack test is completed, the relay RY1 is in the disconnected state, and the relay RY2 is in the closed state; When the collected voltage of the DC voltage sampling circuit is lower than a preset value, the capacitor C4 is completely discharged, and both the relay RY1 and the relay RY2 are in a disconnected state.

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