A method for testing AC internal resistance and power factor of lithium batteries based on FFT

Abstract

The present invention provides a method for testing the AC internal resistance and power factor of a lithium battery based on FFT in the field of lithium battery testing technology, including: step S10, sequentially adjusting the gear position of the reference resistor connected to the device interface module; step S20, the control module outputs a sinusoidal voltage signal to the sinusoidal current generation module, and samples the sinusoidal voltage signal and the sinusoidal current signal flowing through the reference resistor through the high-speed sampling module to calculate the reference resistance parameter; step S30, connecting the lithium battery to the device interface module; step S40, sampling the sinusoidal current signal flowing through the lithium battery through the high-speed sampling module, and then calculating the lithium battery parameters; step S50, the control module calculates the AC internal resistance, power factor and AC internal resistance component of the lithium battery based on the reference resistance parameter and the lithium battery parameter. The advantages of the present invention are: greatly reducing the testing cost of the AC internal resistance and power factor of the lithium battery, and greatly improving the testing accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery testing, and in particular to a method for testing the alternating current internal resistance and power factor of a lithium battery based on FFT. Background Art

[0002] With the rise and development of new energy, lithium batteries, as green high-energy chemical power sources, have been widely used in the new energy industry with the advantages of high energy, high power, and low cost. In order to ensure the safety of lithium batteries, a series of tests need to be carried out on lithium batteries before leaving the factory, and AC internal resistance and power factor are important indicators that need to be tested.

[0003] For the test of AC internal resistance, the hardware is traditionally used to switch to the internal reference resistor and the external device respectively, so as to generate the conversion level signal of the effective value of the signal when the sinusoidal current flows through, for sampling by the sampling module, and then convert the impedance value of the external device through proportional operation. However, the traditional method requires an additional effective value conversion module, and the effective value conversion module can only obtain the effective value of the sinusoidal current signal, and cannot obtain the spectrum and phase of each component. The need to provide an effective value conversion module leads to high test costs, and the test accuracy needs to be improved.

[0004] For power factor testing, the traditional method is to capture the edge generated when two signals cross zero to obtain their time difference, and then convert the corresponding phase angle. However, the traditional method requires an additional phase detection module, and the accuracy of the calculated phase angle is limited by the resolution of the timer. When the waveform is disturbed, the test result will jump. The need to provide a phase detection module leads to high test costs, and the test accuracy and stability need to be improved.

[0005] Traditionally, tests for AC internal resistance and power factor are performed by configuring reference resistors on the original circuit. A corresponding number of four-wire resistors need to be provided according to the hardware gear. If the output is increased, the production cost will increase significantly.

[0006] Therefore, how to provide a FFT-based lithium battery AC internal resistance and power factor testing method to reduce the testing cost of lithium battery AC internal resistance and power factor and improve the testing accuracy has become a technical problem that needs to be solved urgently. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for testing the AC internal resistance and power factor of a lithium battery based on FFT, thereby reducing the testing cost of the AC internal resistance and power factor of a lithium battery and improving the testing accuracy.

[0008] The present invention is implemented as follows: a method for testing the AC internal resistance and power factor of a lithium battery based on FFT, comprising the following steps:

[0009] Step S10: The host computer sets the control module to enter the debugging mode, and sequentially adjusts the level of the reference resistor of the access device interface module;

[0010] Step S20: the control module outputs a sinusoidal voltage signal to the sinusoidal current generating module, samples the sinusoidal voltage signal and the sinusoidal current signal flowing through the reference resistor through the high-speed sampling module, and then calculates the reference resistor parameters under each gear reference resistor through fast Fourier transform;

[0011] Step S30: The host computer sets the control module to enter the use mode and connects the lithium battery to the device interface module;

[0012] Step S40: the control module continues to output a sinusoidal voltage signal to the sinusoidal current generating module, samples the sinusoidal current signal flowing through the lithium battery through the high-speed sampling module, and then calculates the lithium battery parameters of the lithium battery through fast Fourier transform;

[0013] Step S50: The control module calculates the AC internal resistance, power factor and AC internal resistance component of the lithium battery based on the reference resistance parameters and the lithium battery parameters, and sends the calculation results to the host computer.

[0014] Furthermore, the step S20 specifically includes:

[0015] Step S21, the control module outputs a sinusoidal voltage signal to the sinusoidal current generating module;

[0016] Step S22: The sinusoidal current generating module generates a sinusoidal current signal based on the sinusoidal voltage signal and inputs a reference resistor;

[0017] Step S23: The signal amplification module amplifies and filters the sinusoidal current signal flowing through the reference resistor through the device interface module and then inputs it into the high-speed sampling module, and amplifies and filters the sinusoidal voltage signal received by the sinusoidal current generation module and then inputs it into the high-speed sampling module;

[0018] Step S24: The high-speed sampling module samples the sinusoidal current signal and the sinusoidal voltage signal and inputs the samples into the control module;

[0019] Step S25, the control module calculates the reference resistance parameters including the first AC signal amplitude, the first phase angle sine value, the first phase angle cosine value and the reference resistance value under each gear reference resistance through fast Fourier transform based on the received sinusoidal current signal and sinusoidal voltage signal, and stores the reference resistance parameters.

[0020] Furthermore, the step S22 is specifically as follows:

[0021] The sinusoidal current generating module generates a sinusoidal current signal after rectifying and filtering the input sinusoidal voltage signal, and inputs the sinusoidal current signal into a reference resistor through a device interface module.

[0022] Furthermore, the step S24 is specifically as follows:

[0023] The high-speed sampling module samples the sinusoidal current signal and the sinusoidal voltage signal at a preset sampling frequency and then inputs the samples into the control module; the sampling frequency is at least twice the frequency of the sinusoidal voltage signal.

[0024] Furthermore, the step S25 specifically includes:

[0025] Step S251: The control module calculates the real component Rex and the imaginary component Im x of the sinusoidal current signal under each gear reference resistance through fast Fourier transform, and calculates the real component Remcu and the imaginary component Im mcu of the sinusoidal voltage signal;

[0026] Step S252: Calculate AC signal amplitudes Ax and Amcu based on Rex, Im x, Remcu, and Im mcu, and use Ax as the first AC signal amplitude:

[0027]

[0028]

[0029] Step S253: Calculate the first phase angle sine value sin delta and the first phase angle cosine value cos delta based on Rex, Im x, Remcu, Im mcu, Ax and Amcu:

[0030] sin delta=sin x*cos mcu-cos x*sin mcu;

[0031] cos delta=cos x*cos mcu+sin x*sin mcu;

[0032] sin x = Re x / Ax;

[0033] sin mcu=Re mcu / Amcu;

[0034] cos x = Im x / Ax;

[0035] cos mcu=Im mcu / Amcu;

[0036] Step S254, recording the reference resistance value of each gear reference resistor, and storing the reference resistance parameters including the amplitude of the first AC signal, the sine value of the first phase angle, the cosine value of the first phase angle, and the reference resistance value.

[0037] Furthermore, the step S40 specifically includes:

[0038] Step S41, the control module continues to output a sinusoidal voltage signal to the sinusoidal current generating module;

[0039] Step S42: The sinusoidal current generating module generates a sinusoidal current signal based on the sinusoidal voltage signal and inputs the sinusoidal current signal into the lithium battery;

[0040] Step S43: The signal amplification module amplifies and filters the sinusoidal current signal flowing through the lithium battery through the device interface module, and then inputs the amplified current signal into the high-speed sampling module;

[0041] Step S44: The high-speed sampling module samples the sinusoidal current signal and inputs the sample into the control module;

[0042] Step S45: The control module calculates the lithium battery parameters of the sinusoidal current signal flowing through the lithium battery, including the second AC signal amplitude, the second phase angle sine value, and the second phase angle cosine value, through fast Fourier transform.

[0043] Furthermore, in step S50, the steps of calculating the AC internal resistance are as follows:

[0044] The control module obtains the first AC signal amplitude and the reference resistor value corresponding to the reference resistance level of the lithium battery, and calculates the AC internal resistance based on the first AC signal amplitude, the reference resistor value and the second AC signal amplitude:

[0045] AC internal resistance = second AC signal amplitude / first AC signal amplitude * reference resistance value;

[0046] The power factor calculation formula is as follows:

[0047] cosα=cos delta*cos L+sin delta*sin L;

[0048] Wherein, cosα represents the power factor; cos L represents the cosine value of the second phase angle; sin L represents the sine value of the second phase angle;

[0049] The calculation formula of the AC internal resistance component is as follows:

[0050] AC internal resistance component = AC internal resistance * cosα.

[0051] The advantages of the present invention are:

[0052] By replacing the traditional reference resistor configured in the original circuit with an external reference resistor, the hardware cost is greatly reduced and the flexibility of the test is improved. By sampling the sinusoidal voltage signal and the sinusoidal current signal at the same time and using the fast Fourier transform to calculate the AC internal resistance, power factor and AC internal resistance component of the lithium battery, there is no need to provide an additional effective value conversion module and phase detection module circuit as in the traditional way, which further reduces the hardware cost and facilitates subsequent maintenance. The error caused by the DC component and other frequency components in the sinusoidal current signal to the calculation result is eliminated by the fast Fourier transform, so that the calculation result of the AC internal resistance is more accurate, and the resolution and accuracy of the calculation result of the power factor are higher, thereby making the calculation result of the AC internal resistance component more stable, and ultimately achieving a greatly reduced test cost for the AC internal resistance and power factor of the lithium battery and greatly improving the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0054] Figure 1 The present invention is a flow chart of a method for testing the AC internal resistance and power factor of a lithium battery based on FFT.

[0055] Figure 2 It is a hardware architecture diagram of the present invention. DETAILED DESCRIPTION

[0056] The technical solution in the embodiment of the present application has the following overall idea: an external reference resistor is used instead of the traditional reference resistor configured in the original circuit, and the AC internal resistance, power factor and AC internal resistance component of the lithium battery are calculated using fast Fourier transform, thereby eliminating the traditional effective value conversion module and phase detection module to reduce the testing cost of the AC internal resistance and power factor of the lithium battery; the error caused by the DC component and other frequency components in the sinusoidal current signal to the calculation result is eliminated by fast Fourier transform to improve the test accuracy.

[0057] Please refer to Figure 1 to Figure 2 As shown, the test system of the present invention includes a host computer, a control module, a sinusoidal current generation module, a device interface module, a signal amplification module, a high-speed sampling module, a reference resistor and a lithium battery;

[0058] The input end of the control module is connected to the host computer and the high-speed sampling module, and the output end is connected to the sinusoidal current generating module and the reference resistor; the device interface module is respectively connected to the sinusoidal current generating module, the signal amplifying module, the reference resistor and the lithium battery; the output end of the signal amplifying module is connected to the high-speed sampling module.

[0059] The host computer is used to control the operation of the test system; the control module is used to output a sinusoidal voltage signal of a fixed frequency to the sinusoidal current generation module, obtain sampling data from the high-speed sampling module, and perform fast Fourier transform on the sampling data to calculate the AC internal resistance, power factor and AC internal resistance component of the lithium battery; the sinusoidal current generation module is used to convert the sinusoidal voltage signal into a sinusoidal current signal, and output it to a reference resistor and a lithium battery; the device interface module is used to connect a reference resistor or a lithium battery; the signal amplification module is used to filter and amplify the signal; the high-speed sampling module is used to sample the signal output by the signal amplification module; the reference resistor is used to provide a reference for related calculations, and is a four-wire reference resistor; the lithium battery is a lithium battery whose AC internal resistance, power factor and AC internal resistance component are to be tested.

[0060] A preferred embodiment of a method for testing AC internal resistance and power factor of a lithium battery based on FFT of the present invention comprises the following steps:

[0061] Step S10: The host computer sets the control module to enter the debugging mode, and sequentially adjusts the level of the reference resistor of the access device interface module;

[0062] Step S20: the control module outputs a sinusoidal voltage signal to the sinusoidal current generating module, samples the sinusoidal voltage signal and the sinusoidal current signal flowing through the reference resistor through the high-speed sampling module, and then calculates the reference resistor parameters under each gear reference resistor through the fast Fourier transform (FFT); that is, calibrates and records the relevant data of the reference resistor;

[0063] Step S30: The host computer sets the control module to enter the use mode and connects the lithium battery to the device interface module; that is, the reference resistor connected to the circuit is switched to the lithium battery;

[0064] Step S40: the control module continues to output a sinusoidal voltage signal to the sinusoidal current generating module through the internal DAC unit, samples the sinusoidal current signal flowing through the lithium battery through the high-speed sampling module, and then calculates the lithium battery parameters of the lithium battery through fast Fourier transform;

[0065] Step S50: The control module calculates the AC internal resistance, power factor and AC internal resistance component of the lithium battery based on the reference resistance parameters and the lithium battery parameters, and sends the calculation results to the host computer.

[0066] The step S20 specifically includes:

[0067] Step S21, the control module outputs a sinusoidal voltage signal to the sinusoidal current generating module;

[0068] Step S22: The sinusoidal current generating module generates a sinusoidal current signal based on the sinusoidal voltage signal and inputs a reference resistor;

[0069] Step S23: The signal amplification module amplifies and filters the sinusoidal current signal flowing through the reference resistor through the device interface module and then inputs it into the high-speed sampling module, and amplifies and filters the sinusoidal voltage signal received by the sinusoidal current generation module and then inputs it into the high-speed sampling module;

[0070] Step S24: The high-speed sampling module samples the sinusoidal current signal and the sinusoidal voltage signal in real time and inputs the samples into the control module through the communication interface;

[0071] Step S25, the control module calculates the reference resistance parameters including the first AC signal amplitude, the first phase angle sine value, the first phase angle cosine value and the reference resistance value under each gear reference resistance through fast Fourier transform based on the received sinusoidal current signal and sinusoidal voltage signal, and stores the reference resistance parameters.

[0072] The step S22 is specifically as follows:

[0073] The sinusoidal current generating module generates a sinusoidal current signal after rectifying and filtering the input sinusoidal voltage signal, and inputs the sinusoidal current signal into a reference resistor through a device interface module.

[0074] The step S24 is specifically as follows:

[0075] The high-speed sampling module samples the sinusoidal current signal and the sinusoidal voltage signal at a preset sampling frequency and then inputs the samples into the control module; the sampling frequency is at least twice the frequency of the sinusoidal voltage signal.

[0076] The step S25 specifically includes:

[0077] Step S251: The control module calculates the real component Rex and the imaginary component Im x of the sinusoidal current signal under each gear reference resistance through fast Fourier transform, and calculates the real component Remcu and the imaginary component Im mcu of the sinusoidal voltage signal;

[0078] Step S252: Calculate AC signal amplitudes Ax and Amcu based on Rex, Im x, Remcu, and Im mcu, and use Ax as the first AC signal amplitude:

[0079]

[0080]

[0081] Step S253: Calculate the first phase angle sine value sin delta and the first phase angle cosine value cos delta based on Rex, Im x, Remcu, Immcu, Ax and Amcu:

[0082] sin delta=sin x*cos mcu-cos x*sin mcu;

[0083] cos delta=cos x*cos mcu+sin x*sin mcu;

[0084] sin x = Re x / Ax;

[0085] sin mcu=Re mcu / Amcu;

[0086] cos x = Im x / Ax;

[0087] cos mcu=Im mcu / Amcu;

[0088] Step S254, record the reference resistance value of each gear reference resistance, and store the reference resistance parameters including the first AC signal amplitude, the first phase angle sine value, the first phase angle cosine value and the reference resistance value in the EEPROM. That is, each of the reference resistance values ​​corresponds to a first AC signal amplitude, a first phase angle sine value and a first phase angle cosine value.

[0089] The step S40 specifically includes:

[0090] Step S41, the control module continues to output a sinusoidal voltage signal to the sinusoidal current generating module;

[0091] Step S42: The sinusoidal current generating module generates a sinusoidal current signal based on the sinusoidal voltage signal and inputs the sinusoidal current signal into the lithium battery;

[0092] Step S43: The signal amplification module amplifies and filters the sinusoidal current signal flowing through the lithium battery through the device interface module, and then inputs the amplified current signal into the high-speed sampling module;

[0093] Step S44: The high-speed sampling module samples the sinusoidal current signal and inputs the sample into the control module;

[0094] Step S45, the control module calculates the lithium battery parameters of the sinusoidal current signal flowing through the lithium battery, including the second AC signal amplitude, the second phase angle sine value and the second phase angle cosine value, through fast Fourier transform. The calculation formulas for the second AC signal amplitude, the second phase angle sine value and the second phase angle cosine value are the same as the calculation formulas for the first AC signal amplitude, the first phase angle sine value and the first phase angle cosine value, respectively.

[0095] In step S50, the steps of calculating the AC internal resistance are as follows:

[0096] The control module obtains the first AC signal amplitude and the reference resistor value corresponding to the reference resistance level of the lithium battery from the EEPROM, and calculates the AC internal resistance based on the first AC signal amplitude, the reference resistor value and the second AC signal amplitude:

[0097] AC internal resistance = second AC signal amplitude / first AC signal amplitude * reference resistance value;

[0098] The power factor calculation formula is as follows:

[0099] cosα=cos delta*cos L+sin delta*sin L;

[0100] Wherein, cosα represents the power factor; cos L represents the cosine value of the second phase angle; sin L represents the sine value of the second phase angle;

[0101] Because the sinusoidal voltage signal formed on the reference resistor and the sinusoidal current signal flowing through the reference resistor are in phase, it can be approximately considered that the phase angle α between the signal of the lithium battery and the signal of the reference resistor of this gear is approximately equal to the impedance angle of the lithium battery;

[0102] The calculation formula of the AC internal resistance component is as follows:

[0103] AC internal resistance component = AC internal resistance * cosα.

[0104] In summary, the advantages of the present invention are:

[0105] By replacing the traditional reference resistor configured in the original circuit with an external reference resistor, the hardware cost is greatly reduced and the flexibility of the test is improved. By sampling the sinusoidal voltage signal and the sinusoidal current signal at the same time and using the fast Fourier transform to calculate the AC internal resistance, power factor and AC internal resistance component of the lithium battery, there is no need to provide an additional effective value conversion module and phase detection module circuit as in the traditional way, which further reduces the hardware cost and facilitates subsequent maintenance. The error caused by the DC component and other frequency components in the sinusoidal current signal to the calculation result is eliminated by the fast Fourier transform, so that the calculation result of the AC internal resistance is more accurate, and the resolution and accuracy of the calculation result of the power factor are higher, thereby making the calculation result of the AC internal resistance component more stable, and ultimately achieving a greatly reduced test cost for the AC internal resistance and power factor of the lithium battery and greatly improving the test accuracy.

[0106] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for testing AC internal resistance and power factor of lithium batteries based on FFT, characterized in that: The steps include: Step S10: The host computer sets the control module to enter the debugging mode, and sequentially adjusts the level of the reference resistor of the access device interface module; Step S20: the control module outputs a sinusoidal voltage signal to the sinusoidal current generating module, samples the sinusoidal voltage signal and the sinusoidal current signal flowing through the reference resistor through the high-speed sampling module, and then calculates the reference resistor parameters under each gear reference resistor through fast Fourier transform; Step S30: The host computer sets the control module to enter the use mode and connects the lithium battery to the device interface module; Step S40: the control module continues to output a sinusoidal voltage signal to the sinusoidal current generating module, samples the sinusoidal current signal flowing through the lithium battery through the high-speed sampling module, and then calculates the lithium battery parameters of the lithium battery through fast Fourier transform; Step S50, the control module calculates the AC internal resistance, power factor and AC internal resistance component of the lithium battery based on the reference resistance parameter and the lithium battery parameter, and sends the calculation result to the host computer; The step S20 specifically includes: Step S21, the control module outputs a sinusoidal voltage signal to the sinusoidal current generating module; Step S22: the sinusoidal current generating module generates a sinusoidal current signal after rectifying and filtering the input sinusoidal voltage signal, and inputs the sinusoidal current signal into a reference resistor through a device interface module; Step S23: The signal amplification module amplifies and filters the sinusoidal current signal flowing through the reference resistor through the device interface module and then inputs it into the high-speed sampling module, and amplifies and filters the sinusoidal voltage signal received by the sinusoidal current generation module and then inputs it into the high-speed sampling module; Step S24: the high-speed sampling module samples the sinusoidal current signal and the sinusoidal voltage signal at a preset sampling frequency and inputs the samples into the control module; the sampling frequency is at least twice the frequency of the sinusoidal voltage signal; Step S25, the control module calculates reference resistance parameters including the first AC signal amplitude, the first phase angle sine value, the first phase angle cosine value and the reference resistance value under each gear reference resistance by fast Fourier transform based on the received sinusoidal current signal and the sinusoidal voltage signal, and stores the reference resistance parameters; The step S25 specifically includes: Step S251: The control module calculates the real component Rex and the imaginary component Imx of the sinusoidal current signal under each gear reference resistance through fast Fourier transform, and calculates the real component Remcu and the imaginary component Immcu of the sinusoidal voltage signal; Step S252: Calculate AC signal amplitudes Ax and Amcu based on Rex, Imx, Remcu, and Immcu, and use Ax as the first AC signal amplitude: Step S253: Calculate the first phase angle sine value sindelta and the first phase angle cosine value cosdelta based on Rex, Imx, Remcu, Immcu, Ax and Amcu: sindelta=sinx*cosmcu-cosx*sinmcu; cosdelta=cosx*cosmcu+sinx*sinmcu; sinx=Rex / Ax; sinmcu=Remcu / Amcu; cosx = Imx / Ax; cosmcu=Immcu / Amcu; Step S254, recording the reference resistance value of each gear reference resistor, and storing the reference resistance parameters including the amplitude of the first AC signal, the sine value of the first phase angle, the cosine value of the first phase angle, and the reference resistance value.

2. The method for testing AC internal resistance and power factor of a lithium battery based on FFT as claimed in claim 1, characterized in that: The step S40 specifically includes: Step S41, the control module continues to output a sinusoidal voltage signal to the sinusoidal current generating module; Step S42: The sinusoidal current generating module generates a sinusoidal current signal based on the sinusoidal voltage signal and inputs the sinusoidal current signal into the lithium battery; Step S43: The signal amplification module amplifies and filters the sinusoidal current signal flowing through the lithium battery through the device interface module, and then inputs the amplified current signal into the high-speed sampling module; Step S44: The high-speed sampling module samples the sinusoidal current signal and inputs the sample into the control module; Step S45: The control module calculates the lithium battery parameters of the sinusoidal current signal flowing through the lithium battery, including the second AC signal amplitude, the second phase angle sine value, and the second phase angle cosine value, through fast Fourier transform.

3. A method for testing AC internal resistance and power factor of a lithium battery based on FFT as claimed in claim 2, characterized in that: In step S50, the steps of calculating the AC internal resistance are as follows: The control module obtains the first AC signal amplitude and the reference resistor value corresponding to the reference resistance level of the lithium battery, and calculates the AC internal resistance based on the first AC signal amplitude, the reference resistor value and the second AC signal amplitude: AC internal resistance = second AC signal amplitude / first AC signal amplitude * reference resistance value; The power factor calculation formula is as follows: cosα=cosdelta*cosL+sindelta*sinL; Wherein, cosα represents the power factor; cosL represents the cosine value of the second phase angle; sinL represents the sine value of the second phase angle; The calculation formula of the AC internal resistance component is as follows: AC internal resistance component = AC internal resistance * cosα.

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