A method for measuring internal resistance of high-voltage battery packs using multi-frequency mixed injection

Abstract

The present invention discloses a method for measuring the internal resistance of a high-voltage battery pack by multi-frequency mixed injection, comprising the following steps: S1, outputting a superimposed mixed voltage signal, and outputting square wave signals with the same frequency and phase as the single sine wave before synthesis one by one. A mixed current signal is generated through a voltage-current conversion circuit; S2, a mixed excitation signal source performs high-voltage coupling processing and injects it into the high-voltage battery pack; S3, an amplifier circuit is used to amplify the weak signal, a synchronous detector extracts the small signal in the noise floor, and the square wave signal controls two analog switches. After passing through a low-pass filter, the output voltage is in a positive proportional function relationship with the pure internal resistance of the battery. S4, an ADC is used to collect the output DC signal, and the acquisition controller is synchronized with the FPGA in the mixed excitation signal source, and the calculated battery internal resistance is sent to the host computer. This method measures the battery internal resistance with high accuracy, high efficiency, safety and reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of battery internal resistance measurement, and specifically refers to a method for measuring the internal resistance of a high-voltage battery pack with multi-frequency hybrid injection. Background Art

[0002] As a representative of clean energy vehicles, electric vehicles carry the common expectations of humanity for environmental protection and sustainable development. The high-voltage battery pack is one of the key components of electric vehicles, and its performance is directly related to the driving range, charging speed, and safety of electric vehicles. In a high-voltage battery pack, the accurate detection of micro internal resistance is an important part of ensuring battery performance and vehicle safety. In industrial applications, the precise measurement of battery internal resistance is carried out by dedicated equipment.

[0003] At present, there are mainly two methods for measuring battery internal resistance in the industry: 1. DC discharge internal resistance measurement method. This measurement method has a high accuracy, and the measurement accuracy error can be controlled within 0.1%. However, the disadvantage is that it can only measure large-capacity batteries or storage batteries, and cannot measure small-capacity batteries. And it has a certain damage to the internal electrodes of the battery. 2. AC injection internal resistance measurement method. This measurement method is applicable to the internal resistance measurement of almost all batteries, and will not cause any damage to the battery. However, the disadvantage is that the accuracy is limited and it is easily affected by interference.

[0004] Due to the characteristics of high voltage, low internal resistance, and large energy of the high-voltage battery pack, it is very difficult to measure its internal resistance. High-precision measurement, safety during the test process, and non-damage to the battery cannot be simultaneously satisfied in the existing high-voltage battery test schemes. And measuring the internal resistance is of great significance for judging the deterioration of the battery. In terms of battery internal resistance measurement, most of the existing devices are of low voltage, and the injected signals are mostly 1KHz signals. For the internal resistance of a high-voltage battery, its internal resistance is composed of ohmic resistance, diffusion polarization resistance, charge transfer resistance, contact resistance, etc. Therefore, there are different impedances for different frequencies. If the internal resistance at multiple frequencies can be measured, it is of great significance for subsequent use of tools such as machine learning to judge the deterioration of the battery. A method for measuring the internal resistance of a high-voltage battery pack with multi-frequency, high-precision, miniaturization, and static safety is an urgent problem to be solved in the current battery industry. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention proposes a method for measuring the internal resistance of a high-voltage battery pack with multi-frequency hybrid injection, which has high test accuracy, high measurement efficiency, and is safe and reliable.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows:

[0007] A method for measuring the internal resistance of a high-voltage battery pack with multi-frequency hybrid injection, comprising the following steps:

[0008] Step 1: Use scientific computing software (such as MATLAB) to generate sampled signal data of the required frequency and store it in the ROM of the FPGA. Use the direct digital synthesis (DDS) method to obtain a mixed voltage signal, and at the same time generate a switchable square wave signal that is of the same frequency and in-phase as the sine wave before mixing. Take the mixed voltage signal as the input and output a mixed current signal through a voltage-current conversion circuit;

[0009] Step 2: Preset a mixed excitation signal source, perform high-voltage coupling processing on the mixed excitation signal source, and inject it into the high-voltage battery pack;

[0010] Step 3: When a weak voltage generated by the current flowing through the battery is obtained through a weak signal processing circuit as a weak voltage signal, and amplify the weak voltage signal through an operational amplifier;

[0011] Step 4: Use a synchronous detector composed of analog switches to extract the small signal submerged in the noise floor from the amplified signal. Control the two analog switches with the square wave signal generated in Step 1. Since the sine wave and the square wave at the same frequency have the same phase, when the amplified sine wave at the same frequency is positive, it is equivalent to the analog switches outputting signals with gains of +1 and 0 respectively; when the amplified sine wave at the same frequency is negative, it is equivalent to the analog switches outputting signals with gains of 0 and +1 respectively. Take the difference between the output signals of the two analog switches through a low-noise instrumentation amplifier. The above process is equivalent to multiplying the amplified signal by the reference square wave mathematically. The output RC filter will filter out signals of any other frequencies, so the output DC voltage U 4 and the output voltage has a proportional function relationship with the pure internal resistance of the battery;

[0012] Step 5: Collect the DC voltage U 4 through a signal acquisition circuit, and use an analog-to-digital conversion circuit to transmit the pre-conditioned DC voltage U 4 to the acquisition controller. The acquisition controller is synchronized with the FPGA in the mixed excitation signal source, determines the frequency of the square wave, calculates the magnitude of the internal resistance of the battery according to the frequency of the square wave, and sends the calculated internal resistance of the battery to the host computer.

[0013] Preferably, the generated frequency is f 1 f 2 ......f 2n of the sampled signal superimposed on the sine wave.

[0014] Preferably, the method for generating the mixed voltage signal in Step 1 is: use a finite state machine to control the ROM to output parallel digital signals for the generated frequency, connect to the DAC to output the superimposed mixed voltage signal, and the expression is as follows:

[0015] U1 = A 0 sinωt + A 0 sin2ωt + … + A 0 sinαnωt (n ∈ R).

[0016] Preferably, in step 3, a passive filter network is added between the operational amplifier and the weak signal processor to suppress noise.

[0017] Preferably, in step 3, the method for the signal of the operational amplifier is:

[0018]

[0019] The present invention has the following characteristics and beneficial effects:

[0020] The mixed excitation signal is safely injected into the high-voltage battery pack, and then the AC voltage on the high-voltage battery pack is synchronously detected and sampled and calculated. Finally, the battery internal resistance is calculated. This method has a relatively simple circuit structure, a safe measurement process, and high measurement accuracy. By switching the square wave, the internal resistance values at multiple frequency points can be obtained, improving the measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 It is a step flow chart of a method for measuring the internal resistance of a high-voltage battery pack with multi-frequency mixed injection according to an embodiment of the present invention;

[0023] Figure 2 It is a system block diagram of a method for measuring the internal resistance of a high-voltage battery pack with multi-frequency mixed injection according to an embodiment of the present invention;

[0024] Figure 3 It is a circuit schematic diagram of S3 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0026] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following will further describe the present invention in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] In contrast, the present invention covers any alternatives, modifications, equivalent methods, and solutions that are defined by the claims and fall within the spirit and scope of the present invention. Further, in order to enable the public to better understand the present invention, some specific details are described in detail in the following detailed description of the present invention. Those skilled in the art can fully understand the present invention without the description of these details.

[0028] First of all, it should be understood that the method for measuring the internal resistance of a high-voltage battery pack with multi-frequency hybrid injection described in the present invention is used to measure a high-voltage battery pack in this embodiment. By using this method, the internal resistance of the high-voltage battery pack at several frequencies can be obtained, and the measurement process is safe, the measurement time is short, and the accuracy is guaranteed.

[0029] See Figure 1 and Figure 2 , which is an embodiment of the present invention, a step flowchart of a method for measuring the internal resistance of a high-voltage battery pack with multi-frequency hybrid injection, including the following steps:

[0030] S1. Use software to generate a sampled signal superimposed by sine waves with required frequencies of f 1 , f 2 , f 3 , and store it in the ROM of the FPGA. Use frequency synthesis technology to control the ROM to output parallel digital signals through a finite state machine, and connect them to the DAC to output the superimposed mixed voltage signal.

[0031] In this embodiment, the input signal is: U 1 =A 0 sinωt, U 2 =A 0 sin2ωt, U 3 =A 0 sin4ωt.

[0032] Then the output voltage can be expressed as:

[0033] U in =A 0 sinωt + A 0 sin2ωt + A 0 sin4ωt

[0034] Output square wave signals with the same frequency and phase as the single sine wave before synthesis one by one. The mixed signal is connected to the voltage-current conversion circuit to generate a mixed current signal, which can be expressed as:

[0035] I 1 =A 0 sinωt + A 0 sin2ωt + A 0sin4ωt connects the mixed current signal to the high-voltage coupling circuit;

[0036] S2. The mixed excitation signal source performs high-voltage coupling processing using a 2.2 uF CBB capacitor and injects it into the high-voltage battery pack;

[0037] S3. The weak signal processing circuit processes the battery voltage signal. The weak voltage generated when current flows through the battery can be expressed as:

[0038]

[0039] An operational amplifier is used to amplify the weak AC voltage signal generated across the battery. At the same time, a passive filter network is added in the middle of the amplifier to suppress some noise. Assume the amplification factor of the operational amplifier is A 1 , and the amplified voltage can be described as:

[0040]

[0041] Specifically, as Figure 3 shown, a synchronous detector composed of analog switches is used to extract the small signal submerged in the noise floor from the amplified signal. The square wave signal generated in step 1 controls the two analog switches. Since the sine wave and the square wave of the same frequency have the same phase, when the amplified signal of the same frequency is positive, it is equivalent to the analog switches respectively outputting signals with gains of +1 and 0; when the amplified signal of the same frequency is negative, it is equivalent to the analog switches respectively outputting signals with gains of 0 and +1; it is equivalent to multiplying the signal by the square wave. When measuring the internal resistance with a frequency of 2πω, a square wave signal of the same frequency is input, and the analog switches output U o1

[0042]

[0043] The difference between the two signals is taken by a low-noise instrumentation amplifier. The output RC filter will filter out any signals of other frequencies, so the output voltage is a DC signal U o2 , and the output voltage has a proportional function relationship with the pure internal resistance of the battery. After passing through the low-pass filter, the output DC component is equivalent to the integral value of U o1 over one cycle

[0044]

[0045] S4. The signal acquisition circuit collects and processes the final data, and uses an analog-to-digital conversion circuit to convert the DC voltage U conditioned by the previous stage 4Transmitted to the acquisition controller, the acquisition controller synchronizes with the FPGA in the hybrid excitation signal source, determines the frequency of the square wave, calculates the magnitude of the battery internal resistance according to the frequency of the square wave, and sends the calculated battery internal resistance to the host computer.

[0046] At a frequency of 2πω, the impedance is |Z 1 |, pure internal resistance

[0047] That is:

[0048] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for measuring the internal resistance of a high-voltage battery pack by multi-frequency mixed injection, characterized in that: The steps include: Step 1: Use scientific computing software to generate sampling signal data of the required frequency and store it in the ROM of the FPGA. Use the direct frequency synthesis method to obtain a mixed voltage signal, and at the same time generate a switchable square wave signal with the same frequency and phase as the pre-mixed sinusoidal signal. Use the mixed voltage signal as input to output a mixed current signal through a voltage-current conversion circuit. Step 2: preset a hybrid excitation signal source, perform high-voltage coupling processing on the hybrid excitation signal source, and inject it into the high-voltage battery pack; Step 3: The current flows through the battery to generate a weak voltage signal, the weak voltage signal is obtained through a weak signal processing circuit, and the weak voltage signal is amplified by an operational amplifier; Step 4: Use a synchronous detector composed of analog switches to extract small signals submerged in the noise floor from the amplified signal. The square wave signal generated in step 1 controls two analog switches. When the amplified sine wave of the same frequency is positive, it is equivalent to the analog switch outputting signals with gains of +1 and 0 respectively; when the amplified sine wave of the same frequency is negative, it is equivalent to the analog switch outputting signals with gains of 0 and +1 respectively. The output signals of the two analog switches are subtracted through a low-noise instrument amplifier. The output RC filter will filter out any other frequency signals, so the DC voltage U4 is output. Step 5. The DC voltage U4 is collected through a signal acquisition circuit, and the DC voltage U4 conditioned by the previous stage is transmitted to the acquisition controller using an analog-to-digital conversion circuit. The acquisition controller is synchronized with the FPGA in the mixed excitation signal source to determine the frequency of the square wave, and the battery internal resistance is calculated according to the frequency of the square wave, and the calculated battery internal resistance is sent to the host computer.

2. The method for measuring internal resistance of a high-voltage battery pack by multi-frequency mixed injection according to claim 1 is characterized in that: The frequencies generated are f1, f2...f 2n The sampled signal is superimposed with a sine wave.

3. The method for measuring internal resistance of a high-voltage battery pack by multi-frequency mixed injection according to claim 1, characterized in that: The method for generating the mixed voltage signal in step 1 is: the generated frequency is controlled by the finite state machine to output the parallel digital signal of the ROM, and connected to the DAC to output the superimposed mixed voltage signal, and the expression is as follows: U1=A0sinωt+A0sin2ωt+…+A0sin2nωt(n∈R).

4. The method for measuring internal resistance of a high-voltage battery pack by multi-frequency mixed injection according to claim 3 is characterized in that: In step 3, a passive filtering network is added between the operational amplifier and the weak signal processor to suppress noise.

5. The method for measuring internal resistance of a high-voltage battery pack by multi-frequency mixed injection according to claim 4 is characterized in that: In step 3, the method of amplifying the signal by the operational amplifier is:

Images