Method for testing alternating-current impedance value of internal resistance of battery

Abstract

A battery internal resistance alternating current impedance value testing method comprises the steps that (1) a battery to be tested, a switch K1, an auxiliary capacitor C, an auxiliary resistor R, an auxiliary resistor R0, a switch K2 and a sine excitation source are connected, and the initial states of the switch K1 and the switch K2 are in an off state; (2) the switch K1 is closed, and the auxiliary capacitor C starts to charge until charging is finished; (3) the switch K2 is closed, and the sine excitation source starts to excite the circuit network according to the set frequency; (4) synchronously monitoring and recording a section of voltage at the two ends of the R0 and a section of voltage between the two points of the T1T2; (5) calculating the total complex impedance of the impedance network containing the battery to be measured, the auxiliary capacitor C and the auxiliary resistor R between the two points T1T2 according to a formula; (6) calculating the alternating current impedance value of the internal impedance of the battery under the set frequency according to a formula; and (7) carrying out frequency sweeping test on the alternating-current impedance value of the internal resistance of the battery at more frequency points by using the same method to form an alternating-current impedance spectrum of the internal resistance of the battery.

Description

Technical Field

[0001] The present application relates to a method for testing the AC impedance value of a battery internal resistance.

[0002] A battery is a device that can convert chemical energy, solar energy or other energy into electrical energy.

[0003] Batteries have positive and negative poles. Battery voltage is essentially a DC voltage. Even if there is a slight fluctuation under certain special conditions, the fluctuation amplitude is very small. The performance parameters of batteries mainly include electromotive force, capacity, specific energy and internal resistance. The terminal voltage of a battery in an open circuit state is called the open circuit voltage. Generally, it can be approximated that the open circuit voltage of a battery is the electromotive force of the battery. The internal resistance of a battery refers to the resistance encountered by the current when passing through the battery. It is an important indicator that determines the performance of the battery and directly affects the operating voltage, operating current, output power, etc. of the battery. Testing its impedance value is of great significance to evaluating its performance.

[0004] The internal resistance (or internal impedance) of a battery can be equivalent to a large capacitor and a resistor in series, that is, it can be regarded as a complex impedance (or simply impedance), and its AC impedance value is different at different frequencies. The existing battery internal impedance test method is mainly carried out through an external resistor, and the measured internal impedance is equivalent to the value of the DC resistance and capacitance. Background Art

[0005] A battery can be equivalent to a series connection of an electromotive force E and an internal impedance Zx, such as Figure 2 As shown; the internal impedance Zx can be equivalent to a series connection of a large capacitor Cx and a pure resistor Rx.

[0006] One method of measuring the internal impedance of a battery is: (1) First measure the open circuit voltage of the battery, i.e. Figure 2 The voltage between points T3 and T4 in the figure is the open circuit voltage, which is considered to be the value of the electromotive force E. (2) Then, a resistor r is connected to the battery, such as Figure 3 As shown, the change of voltage Vr across the resistor r is measured and recorded from the moment the circuit is closed, and the Rx and Cx values ​​of the internal impedance are calculated based on this. The calculation principle is as follows:

[0007]

[0008] The equivalent capacitance Cx and equivalent resistance Rx calculated by formula (1) above do not have the problem of changing with frequency. Therefore, Zx obtained in this way can be called the DC internal impedance value of the battery, including the DC capacitance value of the equivalent capacitance Cx and the DC resistance value of the equivalent resistance Rx.

[0009] One method of measuring the AC impedance of a passive capacitive device is to apply an AC excitation to the impedance to be measured Zx. At the same time, an auxiliary resistor R0 is connected in series in the circuit, such as Figure 4 As shown, the voltage waveform v at both ends of Zx and R0 is recorded at the same time Zx and v R0 , based on which the AC impedance value of the impedance to be measured Zx at the frequency ω is calculated, the real part is the AC resistance value, and the imaginary part is the AC reactance value. The imaginary part of the impedance of a capacitive device is generally negative. The calculation principle is as follows:

[0010]

[0011] If the AC impedance value of the battery internal resistance is directly measured by the above passive capacitive device measurement method, that is, according to Figure 5 The circuit is equivalent to the following connection method: Figure 6 The superposition of the two circuits shown in the figure gives That is, the voltage across R0 has an additional transition process (superimposed component) caused by the electromotive force E compared to the impedance measurement of passive capacitive devices. Since Zx is regarded as the series connection of Rx and Cx, the superimposed component generated by the electromotive force E can be further described as:

[0012]

[0013] The appearance of the superposition component expressed in equation (3) will affect the phase quantity in equation (2) and The estimation of the corresponding sine wave amplitude and phase parameters will be incorrect, which will eventually lead to a large error in the estimation of the AC impedance value of the battery internal impedance Zx.

[0014] Figure 7 The battery is treated as a passive device. Figure 4 The AC impedance spectrum of a 3V button battery (CR1220) at 30 frequencies in the 0.1Hz-1000Hz frequency band was measured using the passive device AC impedance measurement method shown in the figure. The measurement was performed 6 times (data0 to data5). The measurement results show that the repeatability of the measurement results is poor. The absolute repeatability errors of the resistance spectrum and reactance spectrum are 1.5962e+03 and 4.2595e+02 ohms, respectively. The relative repeatability errors (relative mean) of the resistance spectrum and reactance spectrum are only 5.0367e-01 and 7.4691e-01, respectively.

[0015] In addition, in practice Figure 5 There is a basic problem in measuring the AC impedance value of the battery internal impedance: the battery electromotive force E has many specifications such as 1.5V, 3V, 5V, 12V, 24V, 36V, 48V, etc. When E is large, it is likely to cause the superposition component v R01(t) will exceed the input range of the detection system, resulting in failure of normal detection, such as Figure 8 As shown in the figure, when directly measuring the internal impedance of a 9V battery, R0 and the voltage across the battery are saturated or nearly saturated. Summary of the invention

[0016] Purpose of the Invention

[0017] A feasible test scheme for the AC impedance value of battery internal resistance is proposed.

[0018] Technical Solution

[0019] A method for testing the internal resistance of a battery, characterized in that it comprises the following steps: (1) Figure 1 As shown in the figure, the battery to be tested, switch K1, auxiliary capacitor C, auxiliary resistor R, auxiliary resistor R0, switch K2 and sinusoidal excitation source are connected, and the initial state of switches K1 and K2 is in the disconnected state; (2) switch K1 is closed, and the auxiliary capacitor C starts to charge until the charging is completed; (3) switch K2 is closed, and the sinusoidal excitation source starts to excite the circuit network at the set frequency ω; (4) the voltage across a section R0 is synchronously monitored and recorded. The voltage between points T1 and T2 is v T1-T2 (5) Calculate the total complex impedance of the impedance network between points T1 and T2, which includes the battery to be tested, the auxiliary capacitor C, and the auxiliary resistor R, according to the formula: (6) Calculate the battery internal resistance AC impedance value at the set frequency ω according to the formula in (7) The excitation frequency ω of the sinusoidal excitation source can be changed, and the AC impedance value of the battery internal resistance at the new frequency point can be calculated using the same method, or even the AC impedance value of the battery internal resistance at more frequency points can be calculated by sweeping the frequency to form the AC impedance spectrum of the battery internal resistance, including the resistance spectrum and the reactance spectrum.

[0020] It should be noted that any changes based on the above scheme, such as adding a switch or subtracting a switch, or changing the presentation form of the AC impedance value, which do not change the essential content of this scheme, are within the scope of protection of this application.

[0021] Beneficial effects.

[0022] It can be seen that in the present application scheme, the circuit network including the battery to be tested, the auxiliary capacitor C and the auxiliary resistor R, before being connected to the sinusoidal excitation loop, first completes the charging of the auxiliary capacitor C. After the charging is completed, the magnitude of E is fully distributed to the auxiliary capacitor C and the internal equivalent capacitor Cx, and the voltage across the auxiliary resistor R becomes 0. Therefore, the closing of K2 will no longer cause an impact on the sinusoidal excitation loop, and will no longer cause the monitoring and v T1-T2 Saturation occurs.

[0023] At the same time, the circuit network including the battery to be tested, the auxiliary capacitor C and the auxiliary resistor R is connected to the sinusoidal excitation circuit after charging is completed, which also avoids the superposition of the electromotive force E. The trend transition component on the voltage ensures that the monitored voltage has sufficient sinusoidal properties, thus ensuring the accuracy and repeatability of the sinusoidal parameters and the final impedance value estimation.

[0024] The AC impedance spectrum of the internal impedance of a 3V button battery (CR1220) was tested according to the present application scheme. The results of 5 measurements are as follows: Fig. 9 As shown, Figure 7 The monitoring results formed a sharp contrast. The measurement results showed good repeatability. The repeatability absolute errors of the AC resistance spectrum and reactance spectrum of the battery internal resistance were calculated to be 3.8586e+02 and 5.2416e+02 ohms, respectively, and the repeatability relative errors (relative mean) were 1.4663e-02 and 8.8376e-03, respectively. The repeatability relative error (relative mean) was significantly reduced compared to the AC impedance spectrum that directly tested the battery internal resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 , schematic diagram of the principle of the method of the present application.

[0026] Figure 2 , the equivalent circuit diagram of the battery

[0027] Figure 3 , Schematic diagram of the test principle of the DC impedance value of the battery internal resistance

[0028] Figure 4 , Schematic diagram of the AC impedance test principle of passive capacitive devices

[0029] Figure 5 , Connection diagram for directly measuring the battery internal resistance AC impedance using passive device testing method

[0030] Figure 6 , equivalent decomposition of the connection circuit for direct measurement of the battery internal resistance

[0031] Figure 7 , Schematic diagram of the repeatability of the results of directly measuring the AC impedance spectrum of the battery internal resistance

[0032] Figure 8 , Schematic diagram of the saturation phenomenon caused by directly measuring the AC impedance value of the battery internal resistance

[0033] Fig. 9 , schematic diagram of the repeatability of the results of the AC impedance spectrum of the battery internal resistance detected by the method of this application DETAILED DESCRIPTION

[0034] Example.

[0035] The first step is to press Figure 1 As shown, a battery to be tested (3V button battery CR1220), switch K1, auxiliary capacitor C, auxiliary resistor R, auxiliary resistor R0, switch K2 and sinusoidal excitation source are connected. The initial state of switches K1 and K2 is in the disconnected state. As for the value of the auxiliary capacitor C, there are also the values ​​of the auxiliary resistors R and R0. As long as they are not broken down and the rated working voltage meets the requirements, the specific value of the auxiliary capacitor C in the embodiment is 8uF, and the specific values ​​of the auxiliary resistors R and R0 are 10kΩ; the second step is to close the switch K1, and the auxiliary capacitor C starts to charge until the charging is completed (according to the size of R and C, the charging time can be roughly estimated). At the end of charging, the voltage across the auxiliary resistor R is approximately 0; the third step is to close the switch K2, and the sinusoidal excitation source starts to excite the circuit network at the set frequency ω; the fourth step is to synchronously monitor and record the voltage across a section of R0 The voltage between points T1 and T2 is v T1-T2 The record length is generally not less than the length of two cycles; the fifth step is to calculate the total complex impedance value of the impedance network between points T1 and T2, which includes the battery to be tested, the auxiliary capacitor C and the auxiliary resistor R. Step 6: Calculate the battery internal resistance AC impedance value at the set frequency ω according to the formula in In the seventh step, the excitation frequency ω of the sinusoidal excitation source can be changed, and the AC impedance value of the battery internal resistance at the new frequency point can be calculated by the same method, or even the AC impedance value of the battery internal resistance at more frequency points can be calculated by sweeping the frequency to form the AC impedance spectrum of the battery internal resistance, including the resistance spectrum and the reactance spectrum. Here, the excitation frequency ω of the sinusoidal excitation source is swept from 0.1Hz-1000Hz at logarithmic equal intervals for a total of 30 frequency points, and the corresponding AC impedance spectrum value of the battery internal resistance is tested and calculated, such as Fig. 9 shown.

Claims

1. A method for testing the AC impedance value of a battery internal resistance, characterized in that: The method comprises the following steps: (1) as shown in FIG1 , connecting a battery to be tested, a switch K1, an auxiliary capacitor C, an auxiliary resistor R, an auxiliary resistor R0, a switch K2 and a sinusoidal excitation source, wherein the switches K1 and K2 are initially in an off state; (2) Close switch K1, and the auxiliary capacitor C starts to charge until the charging is completed; (3) Close switch K2, and the sinusoidal excitation source starts to excite the circuit network at the set frequency ω; (4) Synchronously monitor and record the voltage across a section of R0 The voltage between points T1 and T2 is v T1-T2 (5) Calculate the total complex impedance of the impedance network between points T1 and T2, which includes the battery to be tested, the auxiliary capacitor C, and the auxiliary resistor R, according to the formula: (6) Calculate the battery internal resistance AC impedance value at the set frequency ω according to the formula in (7) The excitation frequency ω of the sinusoidal excitation source can be changed, and the AC impedance value of the battery internal resistance at the new frequency point can be calculated using the same method, or even the AC impedance value of the battery internal resistance at more frequency points can be calculated by sweeping the frequency to form the AC impedance spectrum of the battery internal resistance, including the resistance spectrum and the reactance spectrum.

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