AC internal resistance measuring circuit

Abstract

The invention provides an AC internal resistance measuring circuit, which belongs to the technical field of electrical variable measurement, and comprises a wave table generator used for outputting a digital signal S1 with set frequency and phase; one path of the output ends of the constant-current source module and the digital-to-analog conversion unit is connected with the non-inverting input end of the constant-current driving unit, and the output end of the constant-current driving unit is sequentially connected with a load and a sampling resistor in series and then is connected with the ground end of a constant-current source; the other path of the output end of the digital-to-analog conversion unit is connected with the current phase detection circuit, and the current phase detection circuit is used for detecting the phase of the analog signal S8; the voltage detection circuit is used for receiving a load voltage when a constant current flows through the load. According to the alternating current internal resistance measuring circuit, the noise of an alternating current internal resistance measuring system is reduced, the surge fluctuation of the input end of the measuring system is reduced, the output current error of a constant current source is reduced, the error of the measuring system is calibrated, and the accuracy and stability of a measuring result are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of measuring electric variables, and in particular relates to an AC internal resistance measuring circuit. Background Art

[0002] The internal resistance of a battery has a significant impact on its discharge performance and is a very important parameter for determining battery performance. During the operation, maintenance, and management of a battery pack, it is necessary to regularly measure the internal resistance of each battery in the pack to assess the current battery capacity and performance, and to predict the battery life based on the changing trend of the internal resistance value. Currently, one method for measuring the internal resistance of a battery is the AC injection method. This method does not require the battery to be discharged during the measurement process, and can safely monitor the internal resistance of the battery, so it does not affect the performance of the battery. However, existing measurement circuits have problems such as amplifying noise when amplifying the signal, and introducing new noise into the circuit itself. This results in low measurement accuracy, and fluctuations or significant jumps in the displayed value. Using software averaging can improve the fluctuation of the displayed value, but the effect is limited and the measurement speed is affected. Summary of the Invention

[0003] In order to solve the technical problems of low measurement accuracy and fluctuation or obvious jump of displayed values ​​in existing internal resistance measurement circuits, the present invention proposes an AC internal resistance measurement circuit that can solve the above problems.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions: An AC internal resistance measurement circuit, comprising: A wave table generator is used to output a digital signal of set frequency and phase, which is a digital reference signal S1; A constant current source module, comprising a digital-to-analog conversion unit and a constant current drive unit, wherein the constant current drive unit comprises a negative feedback circuit composed of a first operational amplifier, wherein a digital reference signal S1 is digital-to-analog converted by the digital-to-analog conversion unit to generate an analog signal S8, wherein one of the output ends of the digital-to-analog conversion unit is connected to the non-inverting input end of the constant current drive unit, and the output end of the constant current drive unit is sequentially connected in series with a load and a sampling resistor, and then connected to a constant current source ground end, and the voltage output end of the sampling resistor is connected to the reverse input end of the constant current drive unit; A current phase detection circuit, wherein another output end of the digital-to-analog conversion unit is connected to the current phase detection circuit, and the current phase detection circuit is used to detect the phase of the analog signal S8 as the phase φ2 when the constant current flows through the load; a voltage detection circuit, configured to receive a load voltage when a constant current flows through the load, and obtain an amplitude U and a phase φ1 of the load voltage; Calculate the AC internal resistance of the load based on φ1, φ2, and U.

[0005] Compared with the prior art, the advantages and positive effects of the present invention are as follows: an AC internal resistance measurement circuit of the present invention is implemented by a constant current drive unit using a negative feedback circuit composed of a first operational amplifier. A digital-to-analog conversion unit performs digital-to-analog conversion on a digital reference signal S1 to generate an analog signal S8. Analog signal S8 is connected to the non-inverting input terminal of the constant current drive unit. The current output by the constant current drive unit flows through the load and the sampling resistor. The sampling resistor outputs the voltage across the sampling resistor to the inverting input terminal of the constant current drive unit. Utilizing the principle of virtual short of the first operational amplifier, the amplitude and phase of the signal at its inverting input terminal and the non-inverting input terminal are the same, that is, the phase of the constant current source current flowing through the load is the same as the phase of analog signal S8. Therefore, the current phase detection circuit of the present embodiment detects the phase of analog signal S8 as the phase φ2 of the constant current flowing through the load, avoiding the problem of directly detecting the phase of the signal sampled by the sampling resistor, which would adversely affect the output current accuracy of the constant current source due to leakage current and temperature drift of the leakage current. In other words, the problem of new noise introduced by the sampling resistor is solved, and the measurement accuracy is high and stable.

[0006] Other features and advantages of the present invention will become more apparent after reading the detailed description of the embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a principle block diagram of an embodiment of an AC internal resistance measurement circuit proposed by the present invention; Figure 2 This is a principle block diagram of another embodiment of the AC internal resistance measurement circuit proposed by the present invention; Figure 3 It is a principle block diagram of a bandpass filtering unit in an embodiment of the AC internal resistance measurement circuit proposed by the present invention. DETAILED DESCRIPTION

[0008] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0009] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0010] It should be noted that, in the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0011] Example 1: This embodiment proposes an AC internal resistance measurement circuit, such as Figure 1 As shown, it includes a wavetable generator, a constant current source module, a current phase detection circuit, and a voltage detection circuit. The wavetable generator is used to output a digital signal of set frequency and phase, which is a digital reference signal S1. The constant current source module includes a digital-to-analog conversion unit and a constant current drive unit. The constant current drive unit includes a negative feedback circuit composed of a first operational amplifier. The digital reference signal S1 is converted from digital to analog by the digital-to-analog conversion unit to generate an analog signal S8. One of the output terminals of the digital-to-analog conversion unit is connected to the non-inverting input terminal of the constant current drive unit. The output terminal of the constant current drive unit is connected in series with the load and the sampling resistor in sequence, and then connected to the ground terminal of the constant current source. The voltage output terminal of the sampling resistor is connected to the inverting input terminal of the constant current drive unit.

[0012] The current phase detection circuit, another output end of the digital-to-analog conversion unit is connected to the current phase detection circuit, which is used to detect the phase of the analog signal S8 as the phase φ2 when the constant current flows through the load.

[0013] The voltage detection circuit is used to receive the load voltage when a constant current flows through the load, and obtain the amplitude U and phase φ1 of the load voltage.

[0014] Calculate the AC internal resistance of the load based on φ1, φ2, and U.

[0015] The present invention provides an AC internal resistance measurement circuit. A constant current drive unit is implemented using a negative feedback circuit comprised of a first operational amplifier. A digital-to-analog conversion unit performs digital-to-analog conversion on a digital reference signal S1 to generate an analog signal S8. Analog signal S8 is connected to the non-inverting input of the constant current drive unit. The current output by the constant current drive unit flows through a load and a sampling resistor, and the sampling resistor outputs the voltage across the resistor to the inverting input of the constant current drive unit. Utilizing the principle of a virtual short circuit in the first operational amplifier, the amplitude and phase of the signals at its inverting input and non-inverting input are identical, meaning that the phase of the constant current source current flowing through the load is identical to the phase of analog signal S8. Therefore, the current phase detection circuit of this embodiment detects the phase of analog signal S8 as the phase φ2 of the constant current flowing through the load, thereby avoiding the problem of directly detecting the phase of the signal sampled by the sampling resistor, which would adversely affect the accuracy of the constant current source output current due to leakage current and temperature drift of the components. This also addresses the issue of new noise introduced by the sampling resistor.

[0016] In some embodiments, such as Figure 2 As shown, the constant current source module further includes a power amplifier unit and an LC frequency selection network sequentially connected between the constant current driving unit and the load, and the gating frequency of the LC frequency selection network is consistent with the frequency of the digital reference signal S1.

[0017] In this embodiment, a battery is used as an example for description.

[0018] In some embodiments, the wavetable generator outputs a digital signal S1 with a frequency fa according to actual configuration, the digital-to-analog conversion unit is AC coupled output, the analog signal S8 is an AC signal without a DC component, and the frequency of the analog signal S8 is consistent with the digital reference signal S1, which is fa.

[0019] The constant current drive unit is a negative feedback circuit composed of an op amp, with a non-inverting input terminal and a reverse input terminal. The analog signal S8 is input to the non-inverting input terminal of the constant current drive unit. When the output current starts to be output, the output current will flow through the current sampling resistor and generate an AC voltage signal on the current sampling resistor. This AC voltage signal is also input as an input signal to the reverse input terminal of the constant current drive unit. The constant current drive unit outputs a drive signal, drives the power amplifier unit to output current, and gradually achieves constant current output.

[0020] The output current passes through the LC frequency selection network. Since the frequency fa of the output current matches the parameters of the LC frequency selection network, the LC frequency selection network has no obstruction effect on the output current. The LC frequency selection network presents a high impedance state to other frequency components.

[0021] In some embodiments, the constant current source module further includes a second surge absorption unit connected between the power amplification unit and the LC frequency selection network.

[0022] In some embodiments, the current phase detection circuit includes a zero-crossing comparator and a second digital phase detection unit. The zero-crossing comparator is used to receive the analog signal S8 output by the digital-to-analog conversion unit, perform zero-crossing detection on the analog signal S8, and output a zero-crossing measurement signal S6.

[0023] The second digital phase detection unit is connected to the zero-crossing comparator and is used to receive the zero-crossing measurement signal S6.

[0024] The wave table generator is further connected to a phase shifter, which is used to perform a 90° phase shift on the digital reference signal S1 to generate a phase-shifted signal.

[0025] The second digital phase detector receives the digital reference signal S1 and the phase-shifted signal simultaneously, and calculates the zero-crossing measurement signal S6 with the digital reference signal S1 and the phase-shifted signal to obtain the phase of the analog signal S8 as the phase φ2 when the constant current flows through the load.

[0026] An AC internal resistance measurement circuit also includes an isolator having multiple isolation channels, and a wave table generator is connected to a digital-to-analog conversion unit via one of the isolation channels of the isolator.

[0027] The zero-crossing comparator is connected to the second digital phase detector unit through one of the isolation channels of the isolator. The zero-crossing measurement signal S6 is isolated by the isolator and outputs a signal S2 with a frequency fa to the second digital phase detector unit.

[0028] In some embodiments, the frequency fa of analog signal S8 is typically 1 kHz. The zero-crossing comparator and isolator are both high-speed devices with speeds exceeding hundreds of megahertz, resulting in negligible delay. Therefore, the phases of signal S2, zero-crossing measurement signal S6, and analog signal S8 are all identical and equal to the phase of the current flowing through the battery under test. By performing digital phase detection on signal S2 using a digital reference signal S1 output by a wavetable generator at a frequency fa and its phase-shifted signal, the phase of signal S2 can be determined. The phase of signal S2 obtained here is relative to the phase of digital reference signal S1. Measuring this phase is equivalent to measuring the phase of the current flowing through the battery under test relative to digital reference signal S1. Because components all have leakage current and leakage current temperature drift, the traditional method of detecting current phase by directly connecting components in parallel with a sampling resistor can adversely affect the accuracy of the constant current source's output current. This effect is greater the closer the magnitude of the component's leakage current is to the magnitude of the constant current source's output current.

[0029] In some embodiments, multiple resistors are connected in parallel to form a sampling resistor array. An AC internal resistance measurement circuit also includes a third gating unit, which is connected to the sampling resistor array. The control end of the third gating unit is connected to the control unit. The third gating unit is controlled to select one of the resistors in the sampling resistor array as the sampling resistor corresponding to the constant current source.

[0030] The sampling resistor array has a built-in multiplexer and precision resistors of varying resistance values ​​and extremely low annual drift. The multiplexer has one output and multiple inputs. One end of each resistor is connected to the ground network on the constant current source side, and the other end is connected to one of the multiplexer's inputs. By controlling the third selection unit, a precision resistor is selected as the constant current source sampling resistor. Selecting sampling resistors of different resistance values ​​can achieve constant current outputs of varying current values.

[0031] In some embodiments, the voltage detection circuit includes a first-stage amplification unit for amplifying the load voltage. When a constant current source flows through the battery under test, a small AC voltage signal to be measured is generated across the battery's internal resistance, typically in the microvolt range. The AC voltage signal generated across the battery's internal resistance then passes through capacitor C1. After high-frequency interference is eliminated by a high-frequency filter, the small AC voltage signal reaches the input of the first-stage amplification unit for amplification. Typically, the input signal to be measured is in the microvolt range, so even if it is amplified to only the millivolt range, it must be amplified by at least 100 times. Traditional designs employ a bandpass filter for amplification. Because the bandpass filter circuit itself is noisy, amplifying the input signal by more than 100 times also amplifies the noise of the bandpass filter circuit itself by more than 100 times. The peak-to-peak value of the noise is 6.6 times the effective value, resulting in a high peak-to-peak dynamic noise in the output signal. In this case, the measurement results can be highly unstable. Although filtering in software can make the measurement results relatively stable to a certain extent, the effect is really limited. Moreover, adding additional software filtering to the system will seriously affect the test speed of the system.

[0032] In order to solve the above problem, the first-stage amplification unit in this embodiment includes a bandpass filtering unit group, a first noise reduction controller and an amplitude-frequency adjustment unit.

[0033] A bandpass filter unit group includes multiple bandpass filter units connected in parallel, namely An (n=1, 2...), the input end of each bandpass filter unit is respectively connected to the input end of the bandpass filter unit group, and the output end of each bandpass filter unit is respectively connected to the output end of the bandpass filter unit group, an input switch is provided between the input end of one or more bandpass filter units and the input end of the bandpass filter unit group, and an output switch is provided between the output end of the bandpass filter unit and the output end of the bandpass filter unit group, and the on-off states of the input switch and the output switch corresponding to the same bandpass filter unit are consistent.

[0034] The first noise reduction controller is used to control the on / off states of each input switch and output switch based on the noise reduction factor. The more bandpass filter units incorporated into the system, the higher the system's signal-to-noise ratio and the more stable the measurement results. Furthermore, increasing the number of bandpass filter units incorporated into the system does not increase testing time.

[0035] like Figure 3As shown, the bandpass filter unit includes multiple RC networks, a second operational amplifier, and an analog switch. The analog switch has multiple channels, and each RC network is connected to the inverting input of the second operational amplifier via one of the channels of the analog switch. The on / off state of each analog switch channel is controlled by a control unit. By controlling the analog switch channels to engage, the RC networks can be connected in parallel between the output and inverting input of the second operational amplifier.

[0036] In this embodiment, n identical bandpass filter units A1, A2...An are connected in parallel in a program-controlled manner, which can reduce the output noise to n times the output noise when a single bandpass filter is used for amplification. -0.5 The specific reduction in output noise is achieved by controlling the first noise reduction controller, which drives switches K1, K2, ..., Kn-1, and Kn, via signal CTRL2 to open or close them. This approach is similar to software filtering, but does not affect test speed. It can also significantly improve the signal-to-noise ratio of the measurement system, ensuring stable display of measurement results within the specified time.

[0037] The amplitude-frequency adjustment unit is connected to the control end of each band-pass filter unit respectively, and is used to select one of the RC networks in the band-pass filter unit according to the measuring range.

[0038] In some embodiments, the voltage detection circuit further includes a capacitor and a high-frequency filter connected to the front end of the first-stage amplification unit, and a DC isolation unit, an analog-to-digital conversion unit, and a first digital phase detection unit connected to the rear end of the first-stage amplification unit.

[0039] Generally, the test instrument divides the measurement range into different measurement ranges. Small impedance is measured using one range and large impedance is measured using another range. When measuring large impedance, the constant current source will generate a large-amplitude AC voltage signal on the large impedance and input it into the first-stage amplifier circuit through capacitor C1. After the large input signal is amplified by the first-stage amplifier unit, the output voltage amplitude will exceed the linear input range of the subsequent circuit. In this case, the measurement result will become very non-linear. The traditional approach is to place a voltage divider resistor at the output end of the first-stage amplifier circuit to reduce the amplified signal output by the first-stage amplifier unit, thereby achieving linear measurement results. However, due to the presence of thermal noise and excess noise in the voltage divider resistor, adding the voltage divider resistor may cause the measurement result to fluctuate. This embodiment uses a program-controlled method to adjust the amplitude-frequency characteristics of the conductive bandpass filter unit. For different measurement ranges, the program-controlled selection of different RC networks enables the first-stage amplifier unit to achieve different amplification factors for the input signal to be measured at different ranges. The above functions can be achieved by controlling the amplitude-frequency adjustment unit through the CTRL1 signal to select the multiple-choice RC network in the band-pass filter unit An (n=1, 2...).

[0040] In addition to amplifying useful signals and dynamic noise, the first-stage amplifier unit also amplifies the voltage generated by the offset voltage and offset current on the gain resistor. These DC influences affect the measurement resolution of the instrument. The present invention uses a DC isolation unit to eliminate these DC influences.

[0041] After DC isolation, filtering, amplification, and analog-to-digital conversion, the load voltage generates a digital voltage signal S9 to be measured. The first digital phase detection unit receives the digital voltage signal S9 to be measured, and also receives the digital reference signal S1 and the phase-shifted signal respectively. The digital voltage signal S9 to be measured is calculated with the digital reference signal S1 and the phase-shifted signal to obtain the amplitude U and phase φ1 of the load voltage.

[0042] The front end of the analog-to-digital conversion unit is connected to a second-stage amplifier unit, which includes a bandpass filter unit B1, responsible for further signal amplification. The bandwidth of bandpass filter unit B1 further reduces the impact of noise. The second-stage amplifier unit can also adopt an architecture similar to the first-stage amplifier unit, depending on the needs.

[0043] The analog-to-digital conversion unit converts the amplified analog voltage signal to be measured into a digital voltage signal S9 to be measured. Signal S9 is processed by the first digital phase detector unit to obtain the amplitude and phase of signal S9. The phase of signal S9 obtained here is relative to the phase φ1 of digital reference signal S1. Combined with the phase φ2 of signal S2 obtained by the second digital phase detector unit relative to digital reference signal S1, the difference between φ1 and φ2 is used to obtain the phase of signal S9 relative to signal S2. This is equivalent to calculating the phase difference between the AC voltage generated by the battery's internal resistance and the current flowing through the battery's internal resistance. Using the amplitude of signal S9 obtained from digital phase detector unit 1 and the phase difference between phases φ1 and φ2, the battery's internal resistance value, Ro = U*cos(φ1-φ2), can be calculated.

[0044] The present invention adopts an algorithm to perform phase detection on the signal to be measured. The modulation signal adopts the AC signal output by the wave table generator. The harmonic component is smaller than the harmonic component of the square wave modulation signal used in the analog phase detection. Therefore, the accuracy of the measurement result is improved by using the algorithm for detection and phase detection.

[0045] A first surge absorption unit is connected between capacitor C1 and the high-frequency filter. When the battery load is connected, the capacitor absorbs current, generating a surge signal at the negative plate of the capacitor. This is true for both capacitor C1 and the capacitor in the LC frequency selection network in this system. If the DC voltage amplitude of the battery is V1, a surge will be generated on the negative plate of the capacitor, which will quickly rise from 0V to near the amplitude of V1 and then slowly drop to 0V in a negative exponential trend. At the moment the battery load is connected, since the AC voltage generated on the internal resistance of the battery is superimposed on the surge, the measurement result during this period will first be large, then small, and then slowly stabilize. The user cannot obtain the correct result during this period. Taking capacitor C1 as an example, the first surge absorption unit in this embodiment can achieve rapid discharge of the surge signal at the negative plate of capacitor C1, so that the measurement result is stable. The first surge absorption unit is composed of an operational amplifier, a diode, and a TVS. When the surge voltage of the negative plate of capacitor C1 is higher than the sum of the turn-on voltage of the diode and the TVS, the TVS turns on, and the surge signal of the negative plate of capacitor C1 is discharged through the diode and the TVS. At this time, the surge signal of the negative plate of capacitor C1 will not rise to the level of V1. Due to the action of the operational amplifier, the maximum voltage amplitude of the negative plate of capacitor C1 is the sum of the maximum clamping voltage of the diode and the TVS. After the action of the first surge absorption unit, the surge of the negative plate of capacitor C1 is quickly eliminated. The measurement results of the instrument are stable. Since the surge signal contains high-frequency components, the LC frequency selection network in the present invention has a suppressive effect on the surge signal. Combined with the second surge absorption unit composed of a resistor and a TVS, it can achieve protection for the power amplifier unit. It will not affect the measurement results.

[0046] A clamping protection unit is connected between the DC isolation unit and the second-stage amplification unit. If a slightly larger fluctuation occurs at capacitor C1, it may cause abnormal operation of the subsequent circuit after being amplified by the first-stage amplification unit. Therefore, the present invention adds a clamping protection unit after the DC isolation unit. When the DC isolation unit outputs a higher dynamic voltage fluctuation, the clamping protection unit will take effect and clamp the high fluctuating voltage to a pre-designed voltage amplitude to protect the subsequent circuit.

[0047] In some embodiments, the clamping protection unit may be composed of a dual-limit comparator and a diode. The dual-limit comparator input serves as the clamping protection unit input. When the input voltage signal amplitude exceeds the dual-limit comparator threshold, the diode connected in parallel between the dual-limit comparator output and input will conduct, and the comparator will function as an operational amplifier with negative feedback. The input voltage signal amplitude will be clamped to the comparator threshold, achieving clamping protection. The protection measurement system operates normally.

[0048] After a period of use, the instrument's measurement results may drift significantly. This is the result of long-term accumulation due to component aging. This phenomenon renders the measurement results inaccurate. To address this issue, in some embodiments, an AC internal resistance measurement circuit further includes a sampling switch K7, a first calibration switch K8, a multiplexer, and a standard resistor array.

[0049] The sampling switch K7 is connected between the load voltage output terminal of the load battery and the capacitor C1. One end of the first calibration switch K8 is connected to the capacitor C1. The multiplexer includes a control terminal, an output terminal, and multiple input terminals. The standard resistor array includes a number of standard resistors connected in series. One end of the standard resistor array is connected to the ground terminal, and the other end is connected to the output terminal of the constant current source module through the second calibration switch K3. The connection point between each two adjacent standard resistors is correspondingly connected to one of the input terminals of the multiplexer. The output terminal of the multiplexer is connected to the first calibration switch K8. The control terminal of the fourth gating unit is connected to the control unit for receiving the control signal CTRL3 sent by the control unit. The output terminal of the fourth gating unit is connected to the control terminal of the multiplexer. A measuring switch K5 is connected between the load and the output terminal of the constant current source module.

[0050] A control end of the first gating unit is connected to the control unit for receiving a control signal CTRL4. One of the output ends of the first gating unit is connected to the control end of the sampling switch K7, and the other output end is connected to the control end of the first calibration switch K8. The sampling switch and the first calibration switch K8 are not turned on at the same time. A control end of the second gating unit is connected to the control unit for receiving a control signal CTRL5. One of the output ends of the second gating unit is connected to the control end of the second calibration switch K3, and the other output end of the second gating unit is connected to the measurement switch K5 via an inverter.

[0051] The standard resistor array is connected to the sampling resistor via the fourth switch K4 . The control end of the fourth switch K4 is connected to the second selection unit, and the received control signal is consistent with the control signal of the second calibration switch K3 .

[0052] When calibration is required, the control unit controls the second selection unit to drive the switch K3 and the switch K4 to be closed.

[0053] The constant current flows through both ends of the standard resistor array. Since the precision standard resistors of different resistance values ​​in the standard resistor array are in series, a different standard AC voltage signal will be generated on each precision resistor. The control unit controls the fourth selection unit to select the standard AC voltage signal or the measurement ground network signal on a link in the multiplexer. The control unit controls the first selection unit to drive the switch K8 to be attracted, so that the standard AC voltage signal or the measurement ground network signal can be transmitted to the capacitor C1 to calibrate the gain error or offset error of the measurement system. The control unit controls the third selection unit to select a certain precision resistor as the constant current source sampling resistor. Selecting sampling resistors of different resistance values ​​can achieve constant current outputs of different current values. During self-calibration, for constant current outputs of different current values, different precision standard resistors need to correspond to each other.

[0054] During normal use of the measuring instrument, if the system ambient temperature changes, the temperature sensor senses the change and notifies the control unit. In some embodiments, an AC internal resistance measurement circuit further includes a temperature sensor and a fan. The temperature sensor is configured to detect the ambient temperature surrounding the AC internal resistance measurement circuit and transmit the information to the control unit. The control unit controls the fan speed based on the ambient temperature to maintain a stable ambient temperature.

[0055] The control unit simultaneously controls the second gating unit to drive switches K3 and K4 to close, and controls the first gating unit to drive switch K8 to close, and performs system self-calibration to ensure the accuracy of the measurement results.

[0056] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. An AC internal resistance measurement circuit, characterized in that: include: A wave table generator is used to output a digital signal of set frequency and phase, which is a digital reference signal S1; A constant current source module, comprising a digital-to-analog conversion unit and a constant current drive unit, wherein the constant current drive unit comprises a negative feedback circuit composed of a first operational amplifier, wherein a digital reference signal S1 is digital-to-analog converted by the digital-to-analog conversion unit to generate an analog signal S8, wherein one of the output ends of the digital-to-analog conversion unit is connected to the non-inverting input end of the constant current drive unit, and the output end of the constant current drive unit is sequentially connected in series with a load and a sampling resistor, and then connected to a constant current source ground end, and the voltage output end of the sampling resistor is connected to the reverse input end of the constant current drive unit; A current phase detection circuit, wherein another output end of the digital-to-analog conversion unit is connected to the current phase detection circuit, and the current phase detection circuit is used to detect the phase of the analog signal S8 as the phase φ2 when the constant current flows through the load; a voltage detection circuit, configured to receive a load voltage when a constant current flows through the load, and obtain an amplitude U and a phase φ1 of the load voltage; Calculate the AC internal resistance of the load based on φ1, φ2, and U.

2. The AC internal resistance measurement circuit according to claim 1, characterized in that: The constant current source module further includes a power amplifying unit and an LC frequency selection network connected in sequence between the constant current driving unit and the load, and the gating frequency of the LC frequency selection network is consistent with the frequency of the digital reference signal S1.

3. The AC internal resistance measurement circuit according to claim 2, characterized in that: The constant current source module further includes a second surge absorption unit connected between the power amplification unit and the LC frequency selection network.

4. The AC internal resistance measurement circuit according to claim 1, characterized in that: The current phase detection circuit includes: a zero-crossing comparator, configured to receive the analog signal S8 output by the digital-to-analog conversion unit, perform zero-crossing detection on the analog signal S8 and output a zero-crossing measurement signal S6; a second digital phase detection unit, connected to the zero-crossing comparator and configured to receive the zero-crossing measurement signal S6; The wave table generator is further connected to a phase shifter, which is used to perform a 90° phase shift on the digital reference signal S1 to generate a phase-shifted signal; The second digital phase detector receives the digital reference signal S1 and the phase-shifted signal simultaneously, and calculates the zero-crossing measurement signal S6 with the digital reference signal S1 and the phase-shifted signal to obtain the phase of the analog signal S8 as the phase φ2 when the constant current flows through the load.

5. The AC internal resistance measurement circuit according to claim 1, characterized in that: A plurality of resistors are connected in parallel to form a sampling resistor array, and the AC internal resistance measurement circuit further includes: The third gating unit is connected to the sampling resistor array. The control end of the third gating unit is connected to the control unit. The third gating unit is controlled to select one resistor in the sampling resistor array as a sampling resistor.

6. The AC internal resistance measurement circuit according to claim 4, characterized in that: The voltage detection circuit includes a first-stage amplifying unit for amplifying the load voltage, wherein the first-stage amplifying unit includes: A bandpass filter unit group, comprising a plurality of bandpass filter units connected in parallel, wherein the input end of each bandpass filter unit is respectively connected to the input end of the bandpass filter unit group, and the output end of each bandpass filter unit is respectively connected to the output end of the bandpass filter unit group, an input switch is provided between the input end of one or more bandpass filter units and the input end of the bandpass filter unit group, and an output switch is provided between the output end of the bandpass filter unit and the output end of the bandpass filter unit group, and the input switch and output switch corresponding to the same bandpass filter unit have the same on-off state; a first noise reduction controller, configured to control the on / off states of the input switches and the output switches according to the noise reduction factor; The bandpass filter unit includes a plurality of RC networks, a second operational amplifier, and an analog switch, wherein the analog switch has multiple channels, and each of the RC networks is connected to the inverting input terminal of the second operational amplifier via one of the channels of the analog switch; The amplitude-frequency adjustment unit is connected to the control end of each band-pass filter unit and is used to select one of the RC networks in the band-pass filter unit according to the range.

7. The AC internal resistance measurement circuit according to claim 6, characterized in that: The voltage detection circuit further includes a capacitor and a high-frequency filter connected to the front end of the first-stage amplifying unit, and a DC isolation unit, an analog-to-digital conversion unit, and a first digital phase detection unit connected to the rear end of the first-stage amplifying unit; The load voltage is subjected to DC isolation, filtering, amplification, and analog-to-digital conversion to generate a digital voltage signal S9 to be measured. The first digital phase detection unit receives the digital voltage signal S9 to be measured, and also receives the digital reference signal S1 and the phase-shifted signal respectively. The digital voltage signal S9 to be measured is calculated with the digital reference signal S1 and the phase-shifted signal to obtain the amplitude U and phase φ1 of the load voltage.

8. The AC internal resistance measurement circuit according to claim 7, characterized in that: The AC internal resistance measurement circuit further includes: a sampling switch connected between a load voltage output terminal of the load and the capacitor; a first calibration switch, one end of which is connected to the capacitor; A multiplexer comprising a control terminal, an output terminal, and a plurality of input terminals; A standard resistor array, comprising a plurality of standard resistors connected in series, one end of the standard resistor array being connected to a ground terminal, and the other end being connected to the output terminal of the constant current source module via a second calibration switch, the connection point between each two adjacent standard resistors being connected to a corresponding input terminal of a multiplexer, and the output terminal of the multiplexer being connected to the first calibration switch; a fourth gating unit, wherein a control end of the fourth gating unit is connected to the control unit, and an output end of the fourth gating unit is connected to the control end of the multiplexer; A measurement switch is connected between the load and the output end of the constant current source module; a first gating unit, wherein a control end of the first gating unit is connected to the control unit, one output end of the first gating unit is connected to the control end of the sampling switch, and the other output end of the first gating unit is connected to the control end of the first calibration switch, and the sampling switch and the first calibration switch are not turned on at the same time; The control end of the second gating unit is connected to the control unit, one of its output ends is connected to the control end of the second calibration switch, and the other output end of the second gating unit is connected to the measurement switch through an inverter.

9. An AC internal resistance measurement circuit according to any one of claims 1 to 8, characterized in that: The AC internal resistance measurement circuit further includes: a temperature sensor for detecting the ambient temperature around an AC internal resistance measurement circuit and sending the temperature to a control unit; The fan control unit controls the fan speed according to the ambient temperature to maintain the stability of the ambient temperature.

10. An AC internal resistance measurement circuit according to any one of claims 1 to 8, characterized in that: The AC internal resistance measurement circuit further includes an isolator having multiple isolation channels, and the wavetable generator is connected to the digital-to-analog conversion unit via one of the isolation channels of the isolator.

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