A current measurement circuit and current measurement method for lithium battery cell testing

Abstract

The present invention belongs to the field of lithium battery cell testing, and discloses a current measurement circuit and current measurement method for lithium battery cell testing, the current measurement circuit comprising: a resistance sampling circuit and a current sampling circuit, wherein the resistance sampling circuit is used to switch gears according to different current sizes, switch to the corresponding sampling resistor, and obtain a sampling signal I-Test; the current sampling circuit is used to obtain the sampling signal I-Test, use a two-stage amplifier buffer circuit to process the sampling signal I-Test, and output the processed sampling signal I-Test to an analog-to-digital converter, and obtain the measured current value through the analog-to-digital conversion processing of the analog-to-digital converter. The current measurement circuit designed by the present invention uses a relay to switch gears, realizes the rapid measurement of the measured current, improves the anti-interference and stability of the circuit, and solves the problem of low current accuracy when the internal insulation resistance of the lithium battery cell under test is large and the measured current is small.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery cell testing, and in particular to a current measurement circuit and a current measurement method for lithium battery cell testing. Background Art

[0002] The pulse test method is one of the commonly used measurement methods to identify short circuits or micro-short circuits between the positive and negative electrodes of lithium battery cells. The pulse test is divided into three stages: charging, voltage maintenance, and discharge. In both the charging and voltage maintenance stages, the current of the lithium battery cell under test needs to be monitored to better analyze the characteristics of the lithium battery cell under test. When the equivalent capacitance inside the lithium battery cell is small, the charging speed is fast, so a fast current measurement circuit is required; when the insulation resistance inside the lithium battery cell is large, the current in the voltage maintenance stage is small, so a high-precision current measurement circuit is required.

[0003] The current measurement circuit currently used in lithium battery cells has low accuracy and large errors when the current is below 1uA. The sampling circuit mostly uses an inverting amplifier cascade and an analog switch to control the amplification ratio. This method has a relatively slow test speed.

[0004] Therefore, how to provide a current measurement circuit and current measurement method for lithium battery cell testing is a problem that needs to be solved urgently. Summary of the invention

[0005] The embodiments of the present invention provide a current measurement circuit and a current measurement method for testing a lithium battery cell to solve the above technical problems existing in the prior art.

[0006] 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.

[0007] According to a first aspect of an embodiment of the present invention, a current measurement circuit for testing a lithium battery cell is provided.

[0008] In one embodiment, the current measurement circuit for lithium battery cell testing includes: a resistance sampling circuit and a current sampling circuit, wherein:

[0009] The resistor sampling circuit is used to switch to the corresponding sampling resistor according to different current sizes to obtain a sampling signal I-Test;

[0010] The current sampling circuit is used to obtain a sampling signal I-Test, process the sampling signal I-Test using a two-stage amplifier buffer circuit, and output the processed sampling signal I-Test to an analog-to-digital converter, and obtain a measured current value through analog-to-digital conversion processing by the analog-to-digital converter.

[0011] In one embodiment, the resistance sampling circuit includes a signal relay RY1, a signal relay RY2, a signal relay RY3, a signal relay RY4, a signal relay RY5, a transient voltage suppression diode Z1, a resistor R2, a resistor R3, a resistor R6, a resistor R7, a resistor R10, a resistor R11, a resistor R18, a resistor R19, a resistor R20, a resistor R21, a resistor R25, a diode D3, a diode D4, a diode D7, a diode D8 and a diode D10, wherein:

[0012] The anode of the diode D10 and one end of the signal relay RY5 are connected to the Switch1 signal, the anode of the diode D8 and one end of the signal relay RY4 are connected to the Switch1 signal, the anode of the diode D7 and one end of the signal relay RY3 are connected to the Switch1 signal, the anode of the diode D4 and one end of the signal relay RY2 are connected to the Switch1 signal, the anode of the diode D3 and one end of the signal relay RY1 are connected to the Switch1 signal, the cathode of the diode D3, the other end of the signal relay RY1, the cathode of the diode D4, the other end of the signal relay RY2, the cathode of the diode D7, the other end of the signal relay RY3, the cathode of the diode D8, the other end of the signal relay RY4, the cathode of the diode D10 and the other end of the signal relay RY5 are all kept connected and connected to the +5VA signal;

[0013] The resistor R2, the resistor R6, the resistor 10, the resistor R18, and the resistor R20 are connected in series to form a left resistor, and the resistor R3, the resistor R7, the resistor R11, the resistor R19, and the resistor R21 are connected in series to form a right resistor. The left resistor and the right resistor are paired in sequence to form a series voltage dividing point. The resistor R25 and the resistor R20 form a series voltage dividing point, and the divided voltage of the resistor R2 and the resistor R6 is connected to the coil of the signal relay RY1, the divided voltage of the resistor R6 and the resistor R10 is connected to the coil of the signal relay RY2, the divided voltage of the resistor R10 and the resistor R18 is connected to the coil of the signal relay RY3, the divided voltage of the resistor R18 and the resistor R20 is connected to the coil of the signal relay RY4, the divided voltage of the resistor R20 and the resistor R25 is connected to the coil of the signal relay RY5, and the other end of the resistor R25 is connected to one end of the bidirectional diode Z1 and outputs a sampling signal I-Test.

[0014] In one embodiment, the resistor R6, the resistor R7, the resistor R10, the resistor R11, the resistor R18, the resistor R19, the resistor R20, the resistor R21, and the resistor R25 form a resistor network to constitute a sampling resistor for each current level.

[0015] In one embodiment, the transient voltage suppression diode Z1 is used to protect the subsequent current sampling circuit, and the resistor R2 and the resistor R3 are used for current limiting protection.

[0016] In one embodiment, the diode D3 , the diode D4 , the diode D7 , the diode D8 , and the diode D10 are used to protect the signal relay and prevent reverse current.

[0017] In one embodiment, the current sampling circuit includes: a diode D1, a diode D2, a resistor R1, a resistor R4, a resistor R5, a capacitor C1, a capacitor C2, an operational amplifier IC1A, an operational amplifier IC1B and an analog-to-digital converter ADC, wherein:

[0018] One end of the resistor R5 is connected to the sampling signal I-Test, the other end of the resistor R5 is connected to the inverting input end of the operational amplifier IC1A, the output end of the operational amplifier IC1A is connected to one end of the resistor R4 and one end of the resistor R8, the other end of the resistor R8 is connected to the non-inverting input end of the operational amplifier IC1A, the other end of the resistor R4 is connected to one end of the capacitor C2 and the non-inverting input end of the operational amplifier IC1B, the output end and the inverting input end of the operational amplifier IC1B are both connected to one end of the resistor R1, and the other end of the resistor R1 is connected to one end of the capacitor C1, the cathode of the diode D1, the anode of the diode D2 and the analog-to-digital converter ADC.

[0019] In one embodiment, the operational amplifier IC1A and the operational amplifier IC1B both form a voltage follower to play a buffering role.

[0020] In one embodiment, the diode D1 and the diode D2 are both used for voltage clamping to protect the analog-to-digital converter ADC in the subsequent stage.

[0021] In one embodiment, the resistor R1 , the resistor R4 , and the resistor R5 are current limiting resistors, and the resistor R8 is a compensation resistor for compensating for input bias current and input offset current of the operational amplifier IC1A.

[0022] According to a second aspect of an embodiment of the present invention, a current measurement method for testing a lithium battery cell is provided.

[0023] In one embodiment, the current measurement method for lithium battery cell testing includes:

[0024] Based on the value of the current to be measured, the resistance sampling circuit is switched to the corresponding sampling resistor to obtain a sampling signal I-Test;

[0025] The sampling signal I-Test is input into the current sampling circuit, the sampling signal I-Test is processed by a two-stage amplifier buffer circuit, and the processed sampling signal I-Test is output to the analog-to-digital converter, and the measured current value is obtained through the analog-to-digital conversion processing of the analog-to-digital converter.

[0026] The technical solution provided by the embodiment of the present invention may include the following beneficial effects: the current measurement circuit designed by the present invention uses a relay to switch gears, thereby realizing rapid measurement of the measured current; a diode buffer is added to the sampling circuit, thereby improving the anti-interference and stability of the circuit; a compensation resistor is added, thereby solving the problem of large internal insulation resistance of the measured lithium battery cell and low current accuracy when the measured current is small, thereby improving the accuracy of the circuit in measuring current.

[0027] 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

[0028] 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.

[0029] Figure 1 is a circuit schematic diagram of a resistance sampling circuit in a current measurement circuit for testing a lithium battery cell according to an exemplary embodiment;

[0030] Figure 2 is a circuit schematic diagram of a current sampling circuit in a current measurement circuit for testing a lithium battery cell according to an exemplary embodiment;

[0031] Figure 3 The present invention is a flow chart showing a current measurement method for testing a lithium battery cell according to an exemplary embodiment. DETAILED DESCRIPTION

[0032] As used herein, the term "plurality" means two or more than two, unless otherwise specified.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0037] Figure 1-Figure 2 An embodiment of a current measurement circuit for testing a lithium battery cell of the present invention is shown.

[0038] In this optional embodiment, the current measurement circuit for testing the lithium battery cell includes: a resistor sampling circuit and a current sampling circuit, wherein the resistor sampling circuit is used to switch to the corresponding sampling resistor according to different current sizes to obtain a sampling signal I-Test; the current sampling circuit is used to obtain the sampling signal I-Test, use a two-stage amplifier buffer circuit to process the sampling signal I-Test, and output the processed sampling signal I-Test to an analog-to-digital converter, and obtain the measured current value through analog-to-digital conversion processing of the analog-to-digital converter.

[0039] In this optional embodiment, the resistance sampling circuit includes a signal relay RY1, a signal relay RY2, a signal relay RY3, a signal relay RY4, a signal relay RY5, a transient voltage suppression diode Z1, a resistor R2, a resistor R3, a resistor R6, a resistor R7, a resistor R10, a resistor R11, a resistor R18, a resistor R19, a resistor R20, a resistor R21, a resistor R25, a diode D3, a diode D4, a diode D7, a diode D8 and a diode D10, wherein the anode of the diode D10 and one end of the signal relay RY5 are connected to the Switch1 signal. , the anode of the diode D8 and one end of the signal relay RY4 are connected to the Switch1 signal, the anode of the diode D7 and one end of the signal relay RY3 are connected to the Switch1 signal, the anode of the diode D4 and one end of the signal relay RY2 are connected to the Switch1 signal, the anode of the diode D3 and one end of the signal relay RY1 are connected to the Switch1 signal, the cathode of the diode D3, the other end of the signal relay RY1, the cathode of the diode D4, the other end of the signal relay RY2, the cathode of the diode D7, the other end of the signal relay RY3, The cathode of the diode D8, the other end of the signal relay RY4, the cathode of the diode D10 and the other end of the signal relay RY5 are all kept connected and connected to the +5VA signal; the resistors R2, R6, R10, R18 and R20 are connected in series to form the left resistor, the resistors R3, R7, R11, R19 and R21 are connected in series to form the right resistor, the left resistors and the right resistors are paired in sequence to form a series voltage dividing point, the resistor R25 and the resistor R20 form a series voltage dividing point, and the resistor R2 is connected in series with the resistor R7. The divided voltage of the resistor R6 is connected to the coil of the signal relay RY1, the divided voltage of the resistor R6 and the resistor R10 is connected to the coil of the signal relay RY2, the divided voltage of the resistor R10 and the resistor R18 is connected to the coil of the signal relay RY3, the divided voltage of the resistor R18 and the resistor R20 is connected to the coil of the signal relay RY4, the divided voltage of the resistor R20 and the resistor R25 is connected to the coil of the signal relay RY5, and the other end of the resistor R25 is connected to one end of the bidirectional diode Z1 and outputs a sampling signal I-Test.

[0040] In this optional embodiment, the resistor R6, the resistor R7, the resistor R10, the resistor R11, the resistor R18, the resistor R19, the resistor R20, the resistor R21, and the resistor R25 form a resistor network to constitute a sampling resistor for each current level.

[0041] In this optional embodiment, the transient voltage suppression diode Z1 is used to protect the subsequent current sampling circuit, and the resistor R2 and the resistor R3 are used for current limiting protection.

[0042] In this optional embodiment, the diode D3, the diode D4, the diode D7, the diode D8 and the diode D10 are used to protect the signal relay and prevent reverse current.

[0043] In this optional embodiment, the current sampling circuit includes: a diode D1, a diode D2, a resistor R1, a resistor R4, a resistor R5, a capacitor C1, a capacitor C2, an operational amplifier IC1A, an operational amplifier IC1B and an analog-to-digital converter ADC, wherein one end of the resistor R5 is connected to the sampling signal I-Test, the other end of the resistor R5 is connected to the inverting input end of the operational amplifier IC1A, the output end of the operational amplifier IC1A is connected to one end of the resistor R4 and one end of the resistor R8, the other end of the resistor R8 is connected to the non-inverting input end of the operational amplifier IC1A, the other end of the resistor R4 is connected to one end of the capacitor C2 and the non-inverting input end of the operational amplifier IC1B, the output end and the inverting input end of the operational amplifier IC1B are both connected to one end of the resistor R1, and the other end of the resistor R1 is connected to one end of the capacitor C1, the cathode of the diode D1, the anode of the diode D2 and the analog-to-digital converter ADC.

[0044] In this optional embodiment, the operational amplifier IC1A and the operational amplifier IC1B both form a voltage follower to play a buffering role.

[0045] In this optional embodiment, the diode D1 and the diode D2 are both used for voltage clamping to protect the analog-to-digital converter ADC in the subsequent stage.

[0046] In this optional embodiment, the resistor R1 , the resistor R4 , and the resistor R5 are current limiting resistors, and the resistor R8 is a compensation resistor for compensating for input bias current and input offset current of the operational amplifier IC1A.

[0047] Figure 3 An embodiment of a current measurement method for testing a lithium battery cell of the present invention is shown.

[0048] In this optional embodiment, the current measurement method for lithium battery cell testing includes:

[0049] Step 101: based on the value of the current to be measured, the resistance sampling circuit is switched to the corresponding sampling resistor to obtain a sampling signal I-Test;

[0050] Step 103: input the sampling signal I-Test to the current sampling circuit, use a two-stage amplifier buffer circuit to process the sampling signal I-Test, and output the processed sampling signal I-Test to the analog-to-digital converter, and obtain the measured current value through the analog-to-digital conversion processing of the analog-to-digital converter.

[0051] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0052] The present invention provides a high-precision and fast current measurement circuit for lithium battery core measurement, which can measure the current flowing through the lithium battery core under test in real time during a pulse test, and can also accurately measure the internal equivalent insulation resistance of the lithium battery core under test as high as 100GΩ. The circuit has high measurement accuracy and fast response speed, and can be applied to the measurement of lithium battery cores with high internal insulation resistance.

[0053] The present invention provides the following technical solutions:

[0054] The current measurement circuit consists of a resistor sampling circuit and a current sampling circuit. The resistor sampling current collects the corresponding voltage signal through the sampling resistor, and the voltage signal is output to the current sampling circuit. After being processed by the current sampling circuit, it is output to the ADC, and the measured current value is obtained after ADC processing.

[0055] The specific resistance sampling circuit is as follows: Figure 1 As shown: This circuit is a resistor sampling circuit, which switches to the appropriate sampling resistor according to different current sizes to obtain the sampling signal I-Test.

[0056] 1. R6, R7, R10, R11, R18, R19, R20, R21 and R25 form the sampling resistor for each current level;

[0057] 2. RY1, RY2, RY3, RY4 and RY5 are 5 signal relays, which are turned on and off by the signals of Switch1, Switch2, Switch3, Switch4 and Switch5. When different current gears are selected, the corresponding relays are turned on;

[0058] 3. Z1 is a TVS tube (transient voltage suppression diode), which plays a role in protecting the subsequent current measurement circuit;

[0059] 4. The resistance of R2 and R3 is small, which plays the role of current limiting protection;

[0060] 5.D3, D4, D7, D8 and D10 are diodes that protect the relay and prevent reverse current.

[0061] The specific current sampling circuit is as follows: Figure 2As shown: This circuit is a current sampling circuit. After I-Test is processed by a two-stage amplifier buffer circuit, it is output to the ADC for processing.

[0062] 1. Operational amplifiers IC1A, IC1B and surrounding devices form a current measurement circuit. IC1A and IC1B both form voltage followers, which act as buffers and send the I-Test signal to the ADC for processing.

[0063] 2.D1 and D2 are two diodes that act as voltage clamps to protect the subsequent ADC;

[0064] 3. R1, R4 and R5 are current limiting resistors;

[0065] 4.C1 and C2 are filter capacitors;

[0066] 5. R8 is a resistor that acts as a compensation. When the output current is small, less than 100nA, the input bias current and input offset current of the in-phase and inverting terminals of the operational amplifier IC1A will absorb current from the resistor sampling circuit, causing the sampling voltage to decrease, resulting in a smaller measured current. After adding R8, although the sampling voltage at the front end is small, after adding the voltage drop across R8, the voltage at the output terminal of IC1A is equal to the theoretically calculated voltage, thereby achieving the purpose of compensating for the influence of the input bias current and input offset current of the operational amplifier. In this way, when the insulation resistance being measured is large and the current is small, a more accurate current value can still be measured.

[0067] 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 current measurement circuit for testing a lithium battery cell, characterized in that: The current measurement circuit includes: a resistance sampling circuit and a current sampling circuit, wherein: The resistor sampling circuit is used to switch to the corresponding sampling resistor according to different current sizes to obtain a sampling signal I-Test; The current sampling circuit is used to obtain a sampling signal I-Test, process the sampling signal I-Test using a two-stage amplifier buffer circuit, and output the processed sampling signal I-Test to an analog-to-digital converter, and obtain a measured current value through analog-to-digital conversion processing by the analog-to-digital converter.

2. The current measurement circuit for testing a lithium battery cell according to claim 1, characterized in that: The resistance sampling circuit includes a signal relay RY1, a signal relay RY2, a signal relay RY3, a signal relay RY4, a signal relay RY5, a transient voltage suppression diode Z1, a resistor R2, a resistor R3, a resistor R6, a resistor R7, a resistor R10, a resistor R11, a resistor R18, a resistor R19, a resistor R20, a resistor R21, a resistor R25, a diode D3, a diode D4, a diode D7, a diode D8 and a diode D10, wherein: The anode of the diode D10 and one end of the signal relay RY5 are connected to the Switch1 signal, the anode of the diode D8 and one end of the signal relay RY4 are connected to the Switch1 signal, the anode of the diode D7 and one end of the signal relay RY3 are connected to the Switch1 signal, the anode of the diode D4 and one end of the signal relay RY2 are connected to the Switch1 signal, the anode of the diode D3 and one end of the signal relay RY1 are connected to the Switch1 signal, the cathode of the diode D3, the other end of the signal relay RY1, the cathode of the diode D4, the other end of the signal relay RY2, the cathode of the diode D7, the other end of the signal relay RY3, the cathode of the diode D8, the other end of the signal relay RY4, the cathode of the diode D10 and the other end of the signal relay RY5 are all kept connected and connected to the +5VA signal; The resistor R2, the resistor R6, the resistor 10, the resistor R18, and the resistor R20 are connected in series to form a left resistor, and the resistor R3, the resistor R7, the resistor R11, the resistor R19, and the resistor R21 are connected in series to form a right resistor. The left resistor and the right resistor are paired in sequence to form a series voltage dividing point. The resistor R25 and the resistor R20 form a series voltage dividing point, and the divided voltage of the resistor R2 and the resistor R6 is connected to the coil of the signal relay RY1, the divided voltage of the resistor R6 and the resistor R10 is connected to the coil of the signal relay RY2, the divided voltage of the resistor R10 and the resistor R18 is connected to the coil of the signal relay RY3, the divided voltage of the resistor R18 and the resistor R20 is connected to the coil of the signal relay RY4, the divided voltage of the resistor R20 and the resistor R25 is connected to the coil of the signal relay RY5, and the other end of the resistor R25 is connected to one end of the bidirectional diode Z1 and outputs a sampling signal I-Test.

3. The current measurement circuit for testing a lithium battery cell according to claim 2, characterized in that: The resistor R6, the resistor R7, the resistor R10, the resistor R11, the resistor R18, the resistor R19, the resistor R20, the resistor R21, and the resistor R25 form a resistor network to constitute a sampling resistor for each current level.

4. The current measurement circuit for testing a lithium battery cell according to claim 2, characterized in that: The transient voltage suppression diode Z1 is used to protect the subsequent current sampling circuit, and the resistor R2 and the resistor R3 are used for current limiting protection.

5. The current measurement circuit for testing a lithium battery cell according to claim 2, characterized in that: The diode D3 , the diode D4 , the diode D7 , the diode D8 , and the diode D10 are used to protect the signal relay and prevent reverse current.

6. The current measurement circuit for testing a lithium battery cell according to claim 1, characterized in that: The current sampling circuit includes: a diode D1, a diode D2, a resistor R1, a resistor R4, a resistor R5, a capacitor C1, a capacitor C2, an operational amplifier IC1A, an operational amplifier IC1B and an analog-to-digital converter ADC, wherein: One end of the resistor R5 is connected to the sampling signal I-Test, the other end of the resistor R5 is connected to the inverting input end of the operational amplifier IC1A, the output end of the operational amplifier IC1A is connected to one end of the resistor R4 and one end of the resistor R8, the other end of the resistor R8 is connected to the non-inverting input end of the operational amplifier IC1A, the other end of the resistor R4 is connected to one end of the capacitor C2 and the non-inverting input end of the operational amplifier IC1B, the output end and the inverting input end of the operational amplifier IC1B are both connected to one end of the resistor R1, and the other end of the resistor R1 is connected to one end of the capacitor C1, the cathode of the diode D1, the anode of the diode D2 and the analog-to-digital converter ADC.

7. The current measurement circuit for testing a lithium battery cell according to claim 6, characterized in that: The operational amplifier IC1A and the operational amplifier IC1B both form a voltage follower to play a buffering role.

8. The current measurement circuit for testing a lithium battery cell according to claim 6, characterized in that: The diode D1 and the diode D2 are both used for voltage clamping to protect the analog-to-digital converter ADC in the subsequent stage.

9. The current measurement circuit for testing a lithium battery cell according to claim 6, characterized in that: The resistor R1 , the resistor R4 , and the resistor R5 are current limiting resistors, and the resistor R8 is a compensation resistor for compensating for input bias current and input offset current of the operational amplifier IC1A.

10. A current measurement method for testing a lithium battery cell, characterized in that: include: Based on the value of the current to be measured, the resistance sampling circuit is switched to the corresponding sampling resistor to obtain a sampling signal I-Test; The sampling signal I-Test is input into the current sampling circuit, the sampling signal I-Test is processed by a two-stage amplifier buffer circuit, and the processed sampling signal I-Test is output to the analog-to-digital converter, and the measured current value is obtained through the analog-to-digital conversion processing of the analog-to-digital converter.

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