A controllable current charging system and method for lithium battery measurement

Abstract

The present invention belongs to the field of lithium battery cell testing and discloses a controllable current charging system and method for lithium battery measurement. The system includes a bus power supply for providing a bus supply voltage; a test module for transforming a pulse width modulated signal via a transformer and converting it into a DC voltage for testing a product under test; a sampling module for acquiring output voltage sampling signals and output current sampling signals and transmitting them to a control module; and a control module for regulating the test module and the sampling module, respectively. The present invention achieves output current control by switching different current-limiting resistors on the primary side of the transformer and switching coils with different numbers of turns on the secondary side of the transformer. The system also collects output voltage and current at the initial stage of the test, calculates the expected test time in real time, and performs gear control to increase charging speed.

Description

Technical Field

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

[0002] With the rapid development of lithium battery cell materials and related processes, the cell capacity of lithium batteries is increasing, reaching up to several hundred uF. Current lithium battery cell testers primarily charge the cell to a set voltage and then detect voltage drops and insulation resistance values ​​at both ends of the cell. If there is a voltage drop or the insulation resistance value is below the specified value, it is determined that there is a short circuit or micro-short circuit problem within the cell.

[0003] The measurement method of the above-mentioned lithium battery cell tester has a good measurement effect for low- and medium-capacity battery cells. However, for large-capacity battery cells of several hundred uF, the charging speed is too slow and the charging time is too long, making it impossible to complete the test of the tested battery cells in a short time. This not only seriously affects the testing efficiency of the lithium battery cells on the production line, but also the charging current cannot be controlled, and thus it is impossible to set a reasonable charging current for the tested battery cells with different capacitance values.

[0004] Therefore, how to provide a controllable current charging system and method for lithium battery measurement is an urgent problem to be solved. Summary of the Invention

[0005] The embodiments of the present invention provide a controllable current charging system and method for lithium battery measurement to solve the problem in the prior art that the charging speed is too slow, the charging time is too long, and the battery cell under test cannot be tested in a short time.

[0006] To provide a basic understanding of some aspects of the disclosed embodiments, the following is a brief summary. This summary is not intended to be an extensive review, identify key or critical elements, or delineate the scope of these embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the detailed description that follows.

[0007] According to a first aspect of an embodiment of the present invention, a controllable current charging system for lithium battery measurement is provided.

[0008] In one embodiment, a controllable current charging system for lithium battery measurement includes a bus power supply, a test module, a sampling module, and a control module:

[0009] Bus power supply, used to provide bus power supply voltage;

[0010] A test module is used to transform the pulse width modulation signal into a DC voltage through a transformer to test the product under test;

[0011] The sampling module is used to obtain the output voltage sampling signal and the output current sampling signal and transmit them to the control module;

[0012] The control module is used to regulate the test module and the sampling module respectively.

[0013] In one embodiment, the test module includes a half-bridge topology circuit, a current limiting circuit, a voltage transformation control circuit, and an output circuit:

[0014] The half-bridge topology circuit is used to transform the received pulse width modulation signal through the transformer and output the voltage to test the product under test;

[0015] A current limiting circuit is used to limit the primary current of the transformer;

[0016] A voltage transformation control circuit, used for switching the output voltage;

[0017] The output circuit is used to rectify the AC voltage output by the transformer into a DC voltage.

[0018] In one embodiment, limiting the primary current of the transformer includes:

[0019] The relay switch in the current limiting circuit is turned on and off so that any current limiting resistor in the current limiting circuit is connected to the half-bridge topology circuit.

[0020] In one embodiment, switching the output voltage includes:

[0021] The relay switch in the transformer control circuit is turned on and off so that one of the secondary coils of the transformer in the transformer control circuit is connected to the output circuit, while the other secondary coils of the transformer are disconnected.

[0022] In one embodiment, a plurality of diodes in the output circuit form a rectifier full bridge, and rectify the AC voltage output by the transformer into a DC voltage.

[0023] In one embodiment, the sampling module includes a signal output circuit, a voltage sampling circuit, and a current sampling circuit;

[0024] A signal output circuit is used to obtain an output voltage sampling signal and an output current sampling signal;

[0025] A voltage sampling circuit is used to transmit the output voltage sampling signal to the control module;

[0026] The current sampling circuit is used to transmit the output current sampling signal to the control module.

[0027] In one embodiment, obtaining the output voltage sampling signal and the output current sampling signal includes:

[0028] Performing a voltage dividing operation on the voltage sampling resistor in the signal output circuit to obtain an output voltage sampling signal;

[0029] Connect the current sampling resistor in the signal output circuit in series to the loop of the product under test to obtain the output current sampling signal.

[0030] In one embodiment, transmitting the output voltage sampling signal to the control module includes:

[0031] Perform low-pass filtering on the voltage sampling circuit to filter out interference signals in the output voltage sampling signal;

[0032] The output voltage sampling signal after filtering out the interference signal is buffered and transmitted to the control module after the buffering process is completed.

[0033] In one embodiment, transmitting the output current sampling signal to the control module includes:

[0034] Perform low-pass filtering on the current sampling circuit to filter out interference signals in the output current sampling signal;

[0035] The output current sampling signal after filtering out the interference signal is buffered and transmitted to the control module after the buffering process is completed.

[0036] According to a second aspect of an embodiment of the present invention, a controllable current charging method for lithium battery measurement is provided.

[0037] In one embodiment, a controllable current charging method for lithium battery measurement includes:

[0038] Before testing, the charging voltage and charging time are set based on the test requirements, and the control module is used to switch to the secondary coil with the maximum current limiting resistance and the maximum number of turns;

[0039] Start the test and calculate the expected charging time based on the boost voltage under several PWM pulse cycles obtained by the voltage sampling circuit and the current sampling circuit;

[0040] If the expected charging time is less than the charging time, the secondary coil with the maximum current limiting resistance and the maximum number of turns is maintained for testing. If the expected charging time is greater than the charging time, the secondary coil is switched through the control module to reduce the turns ratio;

[0041] After switching the secondary coil, if the expected charging time is still greater than the charging time, the control module switches the current limiting resistor to reduce the resistance of the current limiting resistor and increase the primary current and secondary current of the transformer. Otherwise, the current secondary coil and current limiting resistor are maintained for testing.

[0042] The technical solution provided by the embodiment of the present invention may have the following beneficial effects:

[0043] 1. The present invention controls the output current by switching different current-limiting resistors on the primary side of the transformer and coils with different numbers of turns on the secondary side of the transformer. The output voltage and current are collected at the initial stage of the test, and the expected test time is calculated in real time to perform gear control, thereby improving the charging speed.

[0044] 2. The present invention can realize rapid testing of large-capacity battery cells, thereby improving the testing speed of the battery production line. At the same time, it can automatically detect battery cells with different capacitance values ​​and adaptively switch to the maximum charging current for charging, thereby ensuring the controllability of the test and improving the reliability of the test.

[0045] 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

[0046] 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.

[0047] Figure 1 This is one of the principle diagrams of a controllable current charging system for lithium battery measurement according to an exemplary embodiment;

[0048] Figure 2 This is a second schematic diagram of a controllable current charging system for lithium battery measurement according to an exemplary embodiment;

[0049] Figure 3 is a circuit diagram of a controllable current charging system for lithium battery measurement according to an exemplary embodiment;

[0050] Figure 4 This is a flow chart showing a controllable current charging method for lithium battery measurement according to an exemplary embodiment;

[0051] Figure 5 is a charging test curve diagram of a controllable current charging method applied to lithium battery measurement according to an exemplary embodiment;

[0052] Figure 6 is a circuit diagram showing a current sampling circuit in a controllable current charging system for lithium battery measurement according to an exemplary embodiment;

[0053] Figure 7 The present invention is a circuit diagram showing a voltage sampling circuit in a controllable current charging system for lithium battery measurement according to an exemplary embodiment.

[0054] Reference numerals:

[0055] 1. Bus power supply; 2. Test module; 201. Half-bridge topology circuit; 202. Current limiting circuit; 203. Voltage transformation control circuit; 204. Output circuit; 3. Sampling module; 301. Signal output circuit; 302. Voltage sampling circuit; 303. Current sampling circuit; 4. Control module; 5. Product under test. DETAILED DESCRIPTION

[0056] It should be understood that, although the various steps in the flowchart are shown in sequence as indicated by the arrows, these steps are not necessarily performed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps may be performed 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 performed at the same time, but may be performed at different times. The execution order of these sub-steps or stages is not necessarily to be performed in sequence, but may be performed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0057] 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 the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software so that the processor can call and execute the operations corresponding to the above modules.

[0058] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0059] Figure 1 An embodiment of a controllable current charging system for lithium battery measurement according to the present invention is shown.

[0060] In this optional embodiment, a controllable current charging system for lithium battery measurement includes a bus power supply 1, a test module 2, a sampling module 3, and a control module 4:

[0061] Bus power supply 1, used for providing bus power supply voltage;

[0062] The test module 2 is used to transform the pulse width modulation signal into a DC voltage through a transformer to test the product under test 5;

[0063] The sampling module 3 is used to obtain the output voltage sampling signal and the output current sampling signal and transmit them to the control module 4;

[0064] The control module 4 is used to regulate the test module 2 and the sampling module 3 respectively;

[0065] The bus power supply module 1 is electrically connected to the test module 2 , the test module 2 is electrically connected to the sampling module 3 , and the sampling module 3 is electrically connected to the control module 4 .

[0066] In this optional embodiment, the test module 2 includes a half-bridge topology circuit 201, a current limiting circuit 202, a voltage transformation control circuit 203, and an output circuit 204:

[0067] The half-bridge topology circuit 201 is used to transform the received pulse width modulation signal through a transformer and output a voltage to test the product under test 5;

[0068] a current limiting circuit 202 for limiting the primary current of the transformer;

[0069] The voltage conversion control circuit 203 is used to switch the output voltage;

[0070] The output circuit 204 is used to rectify the AC voltage output by the transformer into a DC voltage.

[0071] The half-bridge topology circuit 201 is electrically connected to the current limiting circuit 202 , the current limiting circuit 202 is electrically connected to the voltage conversion control circuit 203 , and the voltage conversion control circuit 203 is electrically connected to the output circuit 204 .

[0072] In this optional embodiment, the bus power supply 1 provides a bus supply voltage for the half-bridge topology circuit 201, and the control module 4 outputs a pulse width modulation signal to drive the half-bridge topology circuit 201;

[0073] The half-bridge topology circuit 201 starts to operate after receiving the pulse width modulation signal sent by the control module 4 , and then tests the product under test 5 by outputting the voltage after voltage transformation through the voltage transformation control circuit 203 .

[0074] It should be noted that the half-bridge topology circuit 201 includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a field effect transistor Q1, a field effect transistor Q2, a capacitor C1 and a capacitor C2;

[0075] One end of resistor R1 is connected to the PWMA signal, the other end of resistor R1 is connected to the gate of field-effect transistor Q1, the drain of field-effect transistor Q1 is connected to one end of resistor R3 and one end of capacitor C1, and is connected to +V, the other end of resistor R3 is connected to the other end of capacitor C1, one end of resistor R4, one end of capacitor C2, and current limiting circuit 202, the other end of resistor R4 is connected to the other end of capacitor C2 and the source of field-effect transistor Q2, and is connected to -V, the drain of field-effect transistor Q2 is connected to the source of field-effect transistor Q1 and voltage transformation control circuit 203, the gate of field-effect transistor Q3 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the PWMB signal.

[0076] In this optional embodiment, limiting the primary current of the transformer includes: performing on-off operations on a relay switch in the current limiting circuit 202 so that any current limiting resistor in the current limiting circuit 202 is connected to the half-bridge topology circuit 201 .

[0077] It should be noted that the control module 4 controls the on and off of the relay switches S1, S2, S3 and S4 in the current limiting circuit 202 so that any resistor among the resistor R7 (current limiting resistor), R8, R9 and R10 is connected to the half-bridge topology circuit 201.

[0078] It should be noted that the current limiting circuit 202 includes R7, resistor R8, resistor R9, resistor R10, relay switch S1, relay switch S2, relay switch S3 and relay switch S4;

[0079] One end of the resistor R7 is respectively connected to the resistor R3, one end of the resistor R8, one end of the resistor R9 and one end of the resistor R10, the other end of the resistor R7 is connected to one end of the relay switch S1, the other end of the resistor R8 is connected to one end of the relay switch S2, the other end of the resistor R9 is connected to one end of the relay switch S3, the other end of the resistor R10 is connected to one end of the relay switch S4, and the other end of the relay switch S1 is respectively connected to the other end of the relay switch S2, the other end of the relay switch S3, the other end of the relay switch S4 and the transformer control circuit 203.

[0080] In this optional embodiment, switching the output voltage includes: turning on and off the relay switch in the transformer control circuit 203 so that one of the secondary coils of the transformer in the transformer control circuit 203 is connected to the output circuit 204, while the remaining secondary coils of the transformer are in a disconnected state.

[0081] It should be noted that the transformer control circuit 203 is composed of a transformer T1, a relay switch S5, a relay switch S6, a relay switch S7 and a relay switch S8, and the transformer T1 includes a primary coil and several secondary coils with different numbers of turns; the control module 4 controls the on and off of the relay switches S5, S6, S7 and S8 so that one of the secondary coils is connected to the output circuit 204 and the other secondary coils are in a disconnected state.

[0082] It should be noted that the voltage transformation control circuit 203 includes a transformer T1, a relay switch S5, a relay switch S6, a relay switch S7 and a relay switch S8;

[0083] A first pin of the transformer T1 is connected to the field effect transistor Q1, a second pin of the transformer T1 is connected to the relay switch S1, a third pin of the transformer T1 is connected to one end of the relay switch S5, a fifth pin of the transformer T1 is connected to one end of the relay switch S6, a seventh pin of the transformer T1 is connected to one end of the relay switch S7, a ninth pin of the transformer T1 is connected to one end of the relay switch S8, and a fourth pin of the transformer T1 is respectively connected to the sixth pin, the eighth pin, and the tenth pin, and to the output circuit 204.

[0084] In this optional embodiment, the diode D1 , the diode D2 , the diode D3 and the diode D4 in the output circuit 204 form a rectifier full bridge for rectifying the AC voltage output by the transformer into a DC voltage.

[0085] In this optional embodiment, the sampling module 3 includes a signal output circuit 301 , a voltage sampling circuit 302 , and a current sampling circuit 303 ;

[0086] The signal output circuit 301 is used to obtain an output voltage sampling signal and an output current sampling signal;

[0087] The voltage sampling circuit 302 is used to transmit the output voltage sampling signal to the control module 4;

[0088] The current sampling circuit 303 is used to transmit the output current sampling signal to the control module 4 .

[0089] The signal output circuit 301 is electrically connected to the voltage sampling circuit 302 , and the voltage sampling circuit 302 is electrically connected to the current sampling circuit 303 .

[0090] In this optional embodiment, the capacitor C5 and the resistor R20 of the product under test 5 are connected in parallel to form a cell under test, and the output voltage charging the cell under test is equivalent to charging the capacitor C5.

[0091] In this optional embodiment, obtaining the output voltage sampling signal and the output current sampling signal includes:

[0092] Performing a voltage dividing operation on the voltage sampling resistor in the signal output circuit 301 to obtain an output voltage sampling signal;

[0093] The current sampling resistor in the signal output circuit 301 is connected in series to the loop of the device under test 5 to obtain an output current sampling signal.

[0094] It should be noted that the resistor R18 in the signal output circuit 301 obtains the output voltage sampling signal U-back by dividing the voltage with the resistor R17, and the R19 in the signal output circuit 301 is connected in series to the loop of the battery cell under test to obtain the output current sampling signal I-back.

[0095] In this optional embodiment, transmitting the output voltage sampling signal to the control module 4 includes:

[0096] Performing low-pass filtering on the voltage sampling circuit 302 to remove interference signals in the output voltage sampling signal;

[0097] The output voltage sampling signal after filtering out the interference signal is buffered and transmitted to the control module 4 after the buffering process is completed.

[0098] It should be noted that the resistor R16 and capacitor C4 in the voltage sampling circuit 302 form a low-pass filter to filter out the interference signal in the front-end sampling U-back, and the operational amplifier U2A, resistor R12, resistor R14 and resistor R6 form a buffer to transmit U-back to the control module 4.

[0099] In this optional embodiment, transmitting the output current sampling signal to the control module 4 includes:

[0100] Performing low-pass filtering on the current sampling circuit 303 to filter out interference signals in the output current sampling signal;

[0101] The output current sampling signal after filtering out the interference signal is buffered and transmitted to the control module 4 after the buffering process is completed.

[0102] It should be noted that the resistor R15 and capacitor C3 in the current sampling circuit 303 form a low-pass filter to filter out interference signals in the front-end sampling I-back, and the operational amplifier U1A, resistor R13, resistor R11 and resistor R5 form a buffer to transmit the I-back to the control module 4;

[0103] It should be noted that if Figure 7 As shown, the voltage sampling circuit 302 includes a resistor R6, a resistor R12, a resistor R14, a resistor R16, a capacitor C4 and an operational amplifier U2A;

[0104] A first pin of the operational amplifier U2A is respectively connected to one end of the resistor R6 and one end of the resistor R12, the other end of the resistor R6 is connected to U_BACK, the other end of the resistor R12 is respectively connected to the fifth pin of the operational amplifier U2A and one end of the resistor R14, the other end of the resistor R14 is grounded, the fourth pin of the operational amplifier U1A is respectively connected to one end of the resistor R16 and one end of the capacitor C4, the other end of R16 is connected to U_back, the other end of the capacitor C4 is grounded, the second pin of the operational amplifier U2A is connected to +5V, and the third pin of the operational amplifier U2A is connected to -5V.

[0105] It should be noted that if Figure 6As shown, the current sampling circuit 303 includes a resistor R5, a resistor R11, a resistor R13, a resistor R15, a capacitor C3 and an operational amplifier U1A;

[0106] A first pin of the operational amplifier U1A is connected to one end of a resistor R5 and one end of a resistor R11, respectively. The other end of the resistor R5 is connected to I_BACK. The other end of the resistor R11 is connected to the fifth pin of the operational amplifier U1A and one end of a resistor R13, respectively. The other end of the resistor R13 is grounded. A fourth pin of the operational amplifier U1A is connected to one end of a resistor R15 and one end of a capacitor C3, respectively. The other end of R15 is connected to I_back. The other end of the capacitor C3 is grounded. A second pin of the operational amplifier U1A is connected to +5V. A third pin of the operational amplifier U1A is connected to -5V.

[0107] It should be noted that the bus power supply 1 provides a bus power supply voltage for the half-bridge topology circuit 201 .

[0108] The half-bridge topology circuit 201 receives the PWM signal sent by the control module 4 and starts to operate, and then outputs the voltage after the transformer is transformed to test the product 5;

[0109] The current limiting circuit 202 is composed of multiple power resistors and corresponding multiple relays, and is used to limit the current in the primary of the transformer;

[0110] Transformer T1 consists of a primary and multiple secondaries, each of which has a different number of turns.

[0111] The output circuit 204 is composed of a rectifier full bridge.

[0112] The signal output circuit 301 in the sampling module 3 is composed of a voltage sampling resistor and a current sampling resistor. The sampled voltage is transmitted to the control module 4 after passing through the current sampling circuit 303 and the voltage sampling circuit 302 respectively.

[0113] The control module 4 controls the half-bridge topology circuit 201 , the current limiting circuit 202 , and the secondary coil of the transformer T1 .

[0114] The product under test 5 can be equivalent to a capacitor C5 and a resistor R20 connected in parallel.

[0115] like Figure 2-Figure 3 As shown, the control module 4 controls the output PWMA and PWMB signals to drive the half-bridge topology circuit 201;

[0116] The current limiting circuit 202 is composed of multiple resistors with different resistance values ​​and multiple relay switches. The control module 4 controls the on and off of the relay switches S1, S2, S3, and S4, so that one of the resistors R7, R8, R9, and R10 is connected to the half-bridge topology circuit 201.

[0117] The transformer T1 in the voltage transformation control circuit 203 has one primary coil and multiple secondary coils with different numbers of turns. The control module 4 controls the on and off of relay switches S5, S6, S7, and S8, so that one of the secondary coils is connected to the output circuit 204 at the rear end, and the other secondary coils are disconnected.

[0118] The output circuit 204 is a rectifier bridge composed of four diodes D1 , D2 , D3 and D4 , and is used to rectify the AC voltage output by the transformer into a DC voltage.

[0119] Resistors R17 (voltage sampling resistor) and R18 in signal output circuit 301 are connected in parallel between outputs OUTA+ and GNDA. Resistor R18 divides the voltage with resistor R17 to obtain the output voltage sampling signal U-back. Resistor R19 (current sampling resistor) is connected in series in the loop of the battery cell under test to obtain the output current sampling signal I-back.

[0120] The capacitor C5 and the resistor R20 in the tested product 5 are connected in parallel, which can be equivalent to the tested battery cell. The system output voltage charges the tested battery cell, which is equivalent to charging the capacitor C5.

[0121] The resistor R15 and capacitor C3 in the current sampling circuit 303 form a low-pass filter to filter out the interference signal in the front-end sampling I-back. The operational amplifier U1A, resistor R13, resistor R11, and resistor R5 form a buffer. Finally, the current sampling signal I-back enters the control module 4 of the system.

[0122] The resistor R16 and capacitor C4 in the voltage sampling circuit 302 form a low-pass filter to filter out the interference signal in the front-end sampling U-back. The operational amplifier U2A, resistor R12, resistor R14, and resistor R6 form a buffer. Finally, the voltage sampling signal U-back enters the control module 4 of the system.

[0123] Figure 4 An embodiment of a controllable current charging method for lithium battery measurement according to the present invention is shown.

[0124] In this optional embodiment, a controllable current charging method for lithium battery measurement includes:

[0125] Before the test, the charging voltage and charging time are set based on the test requirements, and the control module 4 is switched to the secondary coil with the maximum current limiting resistance and the maximum number of turns;

[0126] Start the test and calculate the expected charging time based on the boost voltage under several PWM pulse cycles acquired by the voltage sampling circuit 302 and the current sampling circuit 303;

[0127] If the expected charging time is less than the charging time, the secondary coil with the maximum current limiting resistance and the maximum number of turns is maintained for testing. If the expected charging time is greater than the charging time, the secondary coil is switched by the control module 4 to reduce the turns ratio;

[0128] After switching the secondary coil, if the expected charging time is still greater than the charging time, the control module 4 switches the current limiting resistor to reduce the resistance of the current limiting resistor and increases the primary current and secondary current of the transformer. Otherwise, the current secondary coil and current limiting resistor are maintained for testing.

[0129] The controllable current charging method for lithium battery measurement in the present invention will be further described below with reference to specific embodiments.

[0130] The voltage across the equivalent capacitance of the cell being tested is Uc.

[0131] The maximum output voltage of the transformer is , Ub is the bus voltage of the system, Np is the number of turns of the primary winding of the transformer, and Ns is the number of turns of the secondary winding of the transformer.

[0132] The maximum output current of the transformer primary is Ip, and the maximum output current of the secondary is Is.

[0133] The instantaneous charging current across the equivalent capacitance of the cell under test , Ro is the equivalent loop resistance of the circuit composed of the equivalent capacitance of the transformer secondary and the measured cell.

[0134] The charging current across the equivalent capacitor of the cell under test is Ic.

[0135] The charging voltage across the equivalent capacitance of the cell under test , C is the equivalent capacitance of the tested cell.

[0136] like Figure 5 As shown in the figure, before time t1, Im>Is, that is, the maximum output current of the transformer at this time cannot reach the instantaneous current of the equivalent capacitance of the measured battery cell. Then, from the start of charging to time t1, charging will be carried out with the maximum output current of the transformer, that is, Ic=Is. At this time, the output current Ic remains unchanged, and the output voltage Uc increases linearly.

[0137] At the moment t1-t2, Im>Is, the charging current of the equivalent capacitance of the tested cell is , the output voltage rise rate slows down.

[0138] After time t2, Uc=Us. At this time, the charging current of the equivalent capacitance of the measured cell drops to the minimum, and the output voltage remains unchanged.

[0139] As can be seen from the above, in order to charge the measured battery cell at a constant current, the magnitude of the output voltage Uc should be controlled to ensure that Im > Is, so that the output will always charge with the maximum output current Is of the secondary of the transformer.

[0140] The relationship between the output current Is of the secondary of the transformer and the output current Ip of the primary of the transformer is: .

[0141] Since the control unit of the system controls the on / off of the relay switches S5, S6, S7 and S8, one of the secondary coils is connected to the output circuit at the rear end, and different secondary turns Ns1, Ns2, Ns3 and Ns4 will be obtained.

[0142] The maximum output current of the primary of the transformer: , Ub is the bus supply voltage of the half-bridge inverter circuit, and Rt is the value of the current-limiting resistor at the primary of the transformer.

[0143] Since the control module 4 of the system controls the on / off of the relay switches S1, S2, S3 and S4, one of the resistors R7 (as the current-limiting resistor), R8, R9 and Rl0 is connected to the half-bridge inverter circuit, and different current-limiting resistors Rt1, Rt2, Rt3 and Rt4 will be obtained.

[0144] The number of current-limiting resistors and the number of secondary coils of the transformer can be increased according to the actual situation.

[0145] By controlling the relay of the current-limiting resistor and the relay of the secondary of the transformer through the control unit of the system, the magnitude of the output current Is of the secondary of the transformer can be controlled, that is, the magnitude of the charging current of the measured battery cell.

[0146] Among them, as Figure 4 shown, the test methods for battery cells with different capacitance values are as follows:

[0147] Before the test, the customer sets the charging voltage Vp and the charging time Tp according to the requirements, and the system automatically switches to the maximum current-limiting resistor Rt-max and the secondary coil Ns-max with the maximum number of turns;

[0148] Start the test. By collecting the boost Vd under several PWM pulse periods td through the voltage and current sampling circuit, the expected charging time can be calculated ;

[0149] If tp < Tp, the test can be carried out while maintaining Rt-max and Ns-max; if tp > Tp, the control unit of the system controls the switching of the secondary coil to reduce the turn ratio, but it is necessary to ensure that ;

[0150] If tp > Tp still, the system control unit controls the switching of the current-limiting resistor Rt to reduce the resistance value of the current-limiting resistor, and increase the primary current Ip and the secondary current Is of the transformer; if it is calculated that tp < Tp, the existing secondary coil and the current-limiting resistor Rt can be maintained for testing.

[0151] The present invention is not limited to the structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A controllable current charging system for lithium battery measurement, characterized in that: The system includes bus power supply, test module, sampling module and control module: The bus power supply is used to provide a bus power supply voltage; The test module is used to transform the pulse width modulation signal into a DC voltage through a transformer to test the product under test; The sampling module is used to obtain the output voltage sampling signal and the output current sampling signal, and transmit them to the control module; The control module is used to regulate the test module and the sampling module respectively; The test module includes a half-bridge topology circuit, a current limiting circuit, a voltage transformation control circuit and an output circuit: The half-bridge topology circuit is used to transform the received pulse width modulation signal through a transformer and output voltage to test the product under test; The current limiting circuit is used to limit the primary current of the transformer; The voltage transformation control circuit is used to switch the output voltage; The output circuit is used to rectify the AC voltage output by the transformer into a DC voltage; The current limiting circuit includes resistors R7, R8, R9, R10 and their corresponding relay switches S1, S2, S3 and S4; The control module controls the on and off of relay switch S1, relay switch S2, relay switch S3 and relay switch S4 in the current limiting circuit so that any resistor among resistor R7, resistor R8, resistor R9 and resistor R10 is connected to the half-bridge topology circuit; The voltage transformation control circuit is composed of a transformer T1, relay switches S5, S6, S7, and S8. The transformer T1 includes a primary coil and several secondary coils with different numbers of turns. The control module controls the on and off of the relay switches S5, S6, S7, and S8 so that one of the secondary coils is connected to the output circuit and the other secondary coils are disconnected. Among them, the controllable current charging system used for lithium battery measurement is used for charging test, which specifically includes: Set the charging voltage and charging time based on the test requirements, and switch to the secondary coil with the maximum current limiting resistance and the maximum number of turns through the control module; Based on the boost voltage under several PWM pulse cycles acquired by the sampling circuit, the expected charging time is calculated; if the expected charging time is less than the charging time, the secondary coil with the maximum current limiting resistance and the maximum number of turns is maintained for testing; if the expected charging time is greater than the charging time, the secondary coil is switched through the control module; After switching the secondary coil, if the expected charging time is still greater than the charging time, the control module switches the current limiting resistor; otherwise, the current secondary coil and current limiting resistor are maintained for testing.

2. A controllable current charging system for lithium battery measurement according to claim 1, characterized in that: A plurality of diodes in the output circuit form a rectifier full bridge, and rectify the AC voltage output by the transformer into a DC voltage.

3. The controllable current charging system for lithium battery measurement according to claim 2, characterized in that: The sampling module includes a signal output circuit, a voltage sampling circuit and a current sampling circuit; The signal output circuit is used to obtain the output voltage sampling signal and the output current sampling signal; The voltage sampling circuit is used to transmit the output voltage sampling signal to the control module; The current sampling circuit is used to transmit the output current sampling signal to the control module.

4. The controllable current charging system for lithium battery measurement according to claim 3, characterized in that: The obtaining of the output voltage sampling signal and the output current sampling signal comprises: Performing a voltage dividing operation on the voltage sampling resistor in the signal output circuit to obtain an output voltage sampling signal; Connect the current sampling resistor in the signal output circuit in series to the loop of the product under test to obtain the output current sampling signal.

5. The controllable current charging system for lithium battery measurement according to claim 4, characterized in that: The step of transmitting the output voltage sampling signal to the control module comprises: Perform low-pass filtering on the voltage sampling circuit to filter out interference signals in the output voltage sampling signal; The output voltage sampling signal after filtering out the interference signal is buffered and transmitted to the control module after the buffering process is completed.

6. The controllable current charging system for lithium battery measurement according to claim 5, characterized in that: The step of transmitting the output current sampling signal to the control module comprises: Perform low-pass filtering on the current sampling circuit to filter out interference signals in the output current sampling signal; The output current sampling signal after filtering out the interference signal is buffered and transmitted to the control module after the buffering process is completed.

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