Internal resistance measuring circuit for backup power supply of power distribution automation terminal

Abstract

The utility model discloses an internal resistance measuring circuit for a backup power supply of a distribution automation terminal. The internal resistance measuring circuit comprises an MCU, a V / I conversion circuit and an amplification sampling part. The output port of the DAC module of the MCU is connected with the input end of the V / I conversion circuit; the positive and negative electrodes of the output end of the V / I conversion circuit are correspondingly connected with the positive and negative electrodes of the backup power supply. The positive and negative electrodes of the input end of the amplification sampling part are correspondingly connected with the positive and negative electrodes of the backup power supply, and the output end is connected with the input end of the ADC module of the MCU. The internal resistance of the battery is estimated by measuring the impedance characteristic of the battery under an alternating current signal, a high-power resistor is not needed, the size can be effectively controlled, a back-up power supply cannot be damaged by a small current signal, and a measurement result with higher precision can be conveniently obtained after signal amplification.

Description

A circuit for measuring the internal resistance of backup power supply in a power distribution automation terminal Technical Field

[0001] This utility model belongs to the field of power distribution, specifically relating to a backup power supply internal resistance measurement circuit. Background Technology

[0002] Backup power supplies for distribution automation terminals are crucial components for ensuring the reliable operation of power systems, providing emergency power support to terminal equipment and communication modules during grid faults or power outages. Battery internal resistance, a core parameter reflecting the health of the backup power supply, directly affects its discharge capacity and lifespan. Specifically, internal resistance refers to the resistance encountered when current flows through the battery's interior; increased internal resistance leads to decreased utilization of active materials, reduced charge and discharge efficiency, and consequently, accelerated battery aging. Therefore, accurate measurement of internal resistance is of great significance for assessing battery performance, predicting remaining lifespan, and preventing sudden failures.

[0003] Currently, internal resistance measurement typically employs a high-current discharge method, which involves controlling a high-power resistor via a MOSFET to discharge the battery with a high current for a short period (usually between 1 and 10 seconds) (Figure 8 shows the discharge quantity control using an NMOS, and Figure 9 shows the discharge quantity control using a PMOS). The voltage and current values ​​across the resistor are then collected, and the internal resistance value is calculated based on Ohm's law.

[0004] However, this method has the following drawbacks: First, high-power resistors are bulky, which is not conducive to equipment miniaturization. Second, high-current discharge can cause battery polarization, damaging the backup power supply and shortening its lifespan. Therefore, the measurement must be completed in a very short time, resulting in low measurement accuracy. Summary of the Invention

[0005] This utility model proposes a circuit for measuring the internal resistance of a backup power supply in a power distribution automation terminal. Its purpose is to solve the problems of large size, easy damage to the backup power supply, and low measurement accuracy of high-power resistor discharge schemes.

[0006] The technical solution of this utility model is as follows:

[0007] A circuit for measuring the internal resistance of a backup power supply in a power distribution automation terminal includes an MCU, a V / I conversion circuit, and an amplification and sampling section.

[0008] The output port MCU_DAC_OUT of the MCU's DAC module is connected to the input terminal of the V / I conversion circuit, and is used to output an AC sine wave to the V / I conversion circuit.

[0009] The positive and negative terminals of the output of the V / I conversion circuit are connected to the positive and negative terminals of the backup power supply, respectively, to convert the AC sine wave into a constant current source and apply it to the backup power supply.

[0010] The positive and negative terminals of the input end of the amplification and sampling section are connected to the positive and negative terminals of the backup power supply, respectively, and the output end is connected to the input end of the ADC module of the MCU. It is used to amplify the small signal collected from the backup power supply and then input the amplified voltage signal into the MCU.

[0011] As a further improvement to the backup power supply internal resistance measurement circuit of the power distribution automation terminal, the V / I conversion circuit includes operational amplifier D3A and operational amplifier D3B.

[0012] The MCU_DAC_OUT is connected to the non-inverting input of operational amplifier D3A via capacitor C12. The 5V power supply is grounded through resistors R6 and R11 connected in series. The connection point between resistors R6 and R11 is connected to the non-inverting input of operational amplifier D3A. The inverting input of operational amplifier D3A is connected to its output. The output of operational amplifier D3A is connected to the non-inverting input of operational amplifier D3B via resistor R8. The non-inverting input of operational amplifier D3B is connected to one end of transient voltage suppressor V5 via resistor R12. The other end of transient voltage suppressor V5... Grounded; the inverting input of operational amplifier D3B is grounded through a series resistor R3 and capacitor C8, and is also connected to one end of resistor R7 through resistor R4; the output of operational amplifier D3B is directly connected to one end of resistor R7, or connected to one end of resistor R7 through a class AB amplifier; the other end of resistor R7 is connected to one end of transient voltage suppressor V5, and also to one end of capacitor C9; the other end of capacitor C9 serves as the positive terminal of the V / I converter output and is connected to the positive terminal of the backup power supply, and the other end of transient voltage suppressor V5 serves as the negative terminal of the V / I converter output and is connected to the negative terminal of the backup power supply.

[0013] As a further improvement to the internal resistance measurement circuit of the backup power supply of the power distribution automation terminal, the AB class amplifier includes diode V10, diode V12, NPN transistor V8 and PNP transistor V13.

[0014] The output terminal of operational amplifier D3B is connected to the negative terminal of diode V10 and the positive terminal of diode V12. A 5V power supply is connected to the positive terminal of diode V10 through resistor R1. The positive terminal of diode V10 is also connected to the base of NPN transistor V8. The 5V power supply is also connected to the collector of NPN transistor V8. The negative terminal of diode V12 is grounded through resistor R2 and is also connected to the base of PNP transistor V13. The collector of PNP transistor V13 is grounded. The emitters of NPN transistor V8 and PNP transistor V13 are connected and connected to one end of resistor R7.

[0015] As a further improvement to the backup power supply internal resistance measurement circuit of the power distribution automation terminal, the amplification sampling section includes a small signal amplification circuit, a voltage signal amplification circuit, and an MCU acquisition input circuit.

[0016] The input terminal of the micro-signal amplifier circuit is connected to the backup power supply, and the output terminal is connected to the input terminal of the MCU's ADC module through a parallel first branch and a second branch. The first branch only contains the MCU's acquisition input circuit, and the second branch contains a series voltage signal amplifier circuit and the MCU's acquisition input circuit. There are more than one second branch, and the amplification factor of the voltage signal amplifier circuit in different second branches is different.

[0017] As a further improvement to the internal resistance measurement circuit of the backup power supply of the power distribution automation terminal, the small signal amplification circuit includes amplifier D4, capacitors C10, C11, C14, and C16, resistors R5, R10, and R13, diodes V1, V2, V6, and V7.

[0018] The positive and negative input terminals of the small signal amplifier circuit, which are used to connect the positive and negative terminals of the backup power supply, are connected to one end of capacitor C11 and one end of capacitor C14, respectively.

[0019] The other end of capacitor C11 is grounded through resistor R5, and is also connected to the positive terminal of diode V1, the negative terminal of diode V2, and the IN+ pin of amplifier D4 respectively. The negative terminal of diode V1 is connected to a 3.3V power supply, and the positive terminal of diode V2 is connected to a -3.3V power supply.

[0020] The other end of capacitor C14 is grounded through resistor R13, and is also connected to the positive terminal of diode V6, the negative terminal of diode V7, and the IN- pin of amplifier D4. The negative terminal of diode V6 is connected to the 3.3V power supply, and the positive terminal of diode V7 is connected to the -3.3V power supply.

[0021] The resistor R10 is connected between the two RG pins of amplifier D4; the -VS pin of amplifier D4 is connected to the -3.3V power supply and is also grounded through capacitor C10; the +VS pin of amplifier D4 is connected to the 3.3V power supply and is also grounded through capacitor C16; the OUT pin of amplifier D4 is connected to the output terminal OUT1 of the small signal amplifier circuit; and the REF pin of amplifier D4 is grounded.

[0022] As a further improvement to the internal resistance measurement circuit of the backup power supply of the power distribution automation terminal, the MCU acquisition input circuit in the first branch includes capacitor C13, resistor R9, diode V3 and diode V4.

[0023] The output terminal OUT1 of the micro-signal amplifier circuit is connected to one end of capacitor C13, and the other end of capacitor C13 is connected to the output terminal MCU-ADC1 of the first branch. The output terminal MCU-ADC1 is used to connect to the ADC module of the MCU. The other end of capacitor C13 is also connected to a 1.65V power supply, the positive terminal of diode V3, and the negative terminal of diode V4 through resistor R9. The negative terminal of diode V3 is connected to a 3.3V power supply, and the positive terminal of diode V4 is grounded.

[0024] As a further improvement to the internal resistance measurement circuit of the backup power supply of the power distribution automation terminal: the voltage signal amplification circuit in the second branch includes operational amplifier D5, resistor R14, resistor R16 and resistor R17; the output terminal OUT1 of the micro-signal amplification circuit is connected to the non-inverting input terminal of operational amplifier D5 through resistor R17, the inverting input terminal of operational amplifier D5 is grounded through resistor R16 and also connected to the output terminal of operational amplifier D5 through resistor R14, and the output terminal of operational amplifier D5 is connected to the output terminal OUT2 of the voltage signal amplification circuit;

[0025] The MCU input circuit in the second branch includes capacitor C18, resistor R15, diode V8, and diode V9. The output terminal OUT2 of the voltage signal amplification circuit is connected to one end of capacitor C18, and the other end of capacitor C18 is connected to the output terminal MCU-ADC2 of the second branch. The output terminal MCU-ADC2 is used to connect to the ADC module of the MCU. The other end of capacitor C18 is also connected to a 1.65V power supply, the anode of diode V8, and the cathode of diode V9 through resistor R15. The cathode of diode V8 is connected to a 3.3V power supply, and the anode of diode V9 is grounded.

[0026] As a further improvement to the internal resistance measurement circuit of the backup power supply of the power distribution automation terminal, the internal resistance measurement circuit also includes a power supply circuit for outputting 3.3V power, -3.3V power and 1.65V power.

[0027] The input 5V power supply is connected to one end of capacitor C1 and also to the Vin pin of the low dropout linear regulator D1; the Vout pin of the low dropout linear regulator D1 is used to output 3.3V power supply and is connected to one end of capacitor C2; the other end of capacitor C1, the other end of capacitor C2, and the GND pin of the low dropout linear regulator D1 are all grounded.

[0028] A 3.3V power supply is connected to the IN pin of the switching DC-DC converter D2 and one end of capacitor C5. The OUT pin of the switching DC-DC converter D2 is used to output a -3.3V power supply and is connected to one end of capacitor C6. The other ends of capacitor C5, capacitor C6, and the GND pin of the switching DC-DC converter D2 are all grounded. A capacitor C3 is connected between the Cfly- and Cfly+ pins of the switching DC-DC converter D2.

[0029] The 3.3V power supply is grounded through resistors R1 and R2 connected in series with equal resistance. The connection point between resistors R1 and R2 is used to output a 1.65V power supply. Resistor R1 is connected in parallel with capacitor C4, and resistor R2 is connected in parallel with capacitor C7.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] This invention applies a small current (e.g., 20mA) at a fixed frequency (e.g., 1kHz) to a backup power supply via a V / I conversion circuit to obtain a small signal. This signal is then amplified to obtain a voltage value, and the battery's internal resistance is calculated based on Ohm's law. Essentially, this method estimates the battery's internal resistance by measuring its impedance characteristics under AC signals. It eliminates the need for high-power resistors, effectively controlling the size of the battery, and the small current signal does not damage the backup power supply. Furthermore, the amplified signal facilitates more accurate measurement results. This method can be completed quickly (approximately 100ms) and is applicable to all types and capacities of batteries. Attached Figure Description

[0032] Figure 1 is a diagram of the overall structure of this utility model;

[0033] Figure 2 shows the circuit diagram of the V / I conversion circuit and the backup power supply section;

[0034] Figure 3 shows the circuit diagram of the backup power supply and small signal amplification circuit.

[0035] Figure 4 shows the circuit diagram of the voltage signal amplification circuit and the MCU input acquisition circuit;

[0036] Figure 5 is a circuit diagram of the power supply circuit of this utility model;

[0037] Figure 6 shows a V / I converter circuit with a Class AB amplifier;

[0038] Figure 7 is a circuit diagram of the instrumentation amplifier replacement circuit;

[0039] Figure 8 is a schematic diagram of the prior art using NMOS for discharge quantity control;

[0040] Figure 9 is a schematic diagram of the existing technology for discharge quantity control using PMOS. Detailed Implementation

[0041] The technical solution of this utility model will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0042] As shown in Figure 1, a power distribution automation terminal backup power supply internal resistance measurement circuit includes an MCU, a V / I conversion circuit, and an amplification and sampling section.

[0043] The output port MCU_DAC_OUT of the MCU's DAC module is connected to the input of the V / I conversion circuit to output a 1kHz AC sine wave. The positive and negative terminals of the V / I conversion circuit's output are connected to the positive and negative terminals of the backup power supply, respectively, to convert the AC sine wave into a constant current source and apply it to the backup power supply. The positive and negative terminals of the amplification and sampling section are connected to the positive and negative terminals of the backup power supply, respectively, and its output is connected to the input of the MCU's ADC module. This amplifies the small signal acquired from the backup power supply and then inputs the amplified voltage signal into the MCU.

[0044] The MCU should be selected with DAC and ADC functions. In this embodiment, the domestically produced HC32F448 from Xiaohua Semiconductor Co., Ltd. is used.

[0045] Specifically:

[0046] As shown in Figure 2, the V / I conversion circuit includes operational amplifiers D3A and D3B. The MCU_DAC_OUT is connected to the non-inverting input of operational amplifier D3A via capacitor C12. The 5V power supply is grounded through resistors R6 and R11 connected in series, with the connection point between R6 and R11 connected to the non-inverting input of operational amplifier D3A. The inverting input of operational amplifier D3A is connected to its output, and the output of operational amplifier D3A is connected to the non-inverting input of operational amplifier D3B via resistor R8. The non-inverting input of operational amplifier D3B is connected to one end of transient voltage suppressor V5 via resistor R12, with the other end of transient voltage suppressor V5 grounded. The inverting input of operational amplifier D3B is grounded through resistor R3 and capacitor C8 connected in series, and is also connected to one end of resistor R7 via resistor R4. The output of operational amplifier D3B is directly connected to one end of resistor R7, or connected to one end of resistor R7 via a Class AB amplifier. The other end of resistor R7 is connected to one end of transient voltage suppressor V5 and also to one end of capacitor C9. The other end of capacitor C9 serves as the positive terminal of the V / I converter output and is connected to the positive terminal of the backup power supply. The other end of transient voltage suppressor V5 serves as the negative terminal of the V / I converter output and is connected to the negative terminal of the backup power supply.

[0047] Furthermore, since the output current of conventional operational amplifiers is typically between a few milliamps and tens of milliamps, excessively small current signals require a subsequent amplifier stage with a higher amplification factor, which can lead to noise amplification. Therefore, as shown in Figure 6, an AB-class amplifier can be added to appropriately increase the current applied to the backup power supply, thereby obtaining a larger voltage. This allows for a smaller amplification factor in the subsequent stage, reducing the noise introduced by the subsequent amplification and improving measurement accuracy.

[0048] Specifically, the Class AB amplifier includes diodes V10 and V12, an NPN transistor V8, and a PNP transistor V13. The output of operational amplifier D3B is connected to both the cathode of diode V10 and the anode of diode V12. A 5V power supply is connected to the anode of diode V10 through resistor R1. The anode of diode V10 is also connected to the base of NPN transistor V8. The 5V power supply is also connected to the collector of NPN transistor V8. The cathode of diode V12 is grounded through resistor R2 and is also connected to the base of PNP transistor V13. The collector of PNP transistor V13 is grounded. The emitters of NPN transistor V8 and PNP transistor V13 are connected and then connected to one end of resistor R7.

[0049] The amplification and sampling section specifically includes a small signal amplification circuit, a voltage signal amplification circuit, and an MCU acquisition input circuit. The input terminal of the small signal amplification circuit is connected to a backup power supply, and its output terminal is connected to the input terminal of the MCU's ADC module through a parallel first branch and a second branch. The first branch only contains the MCU acquisition input circuit, while the second branch contains a voltage signal amplification circuit and the MCU acquisition input circuit connected in series.

[0050] Specifically, as shown in Figure 3, the small signal amplifier circuit includes amplifier D4, capacitors C10, C11, C14, and C16, resistors R5, R10, and R13, and diodes V1, V2, V6, and V7. The positive and negative input terminals of the small signal amplifier circuit, used to connect to the positive and negative terminals of the backup power supply, are connected to one end of capacitor C11 and one end of capacitor C14, respectively. The other end of capacitor C11 is grounded through resistor R5 and is also connected to the anode of diode V1, the cathode of diode V2, and the IN+ pin of amplifier D4. The cathode of diode V1 is connected to a 3.3V power supply, and the anode of diode V2 is connected to a -3.3V power supply. The other end of capacitor C14 is grounded through resistor R13, and is also connected to the anode of diode V6, the cathode of diode V7, and the IN- pin of amplifier D4. The cathode of diode V6 is connected to a 3.3V power supply, and the anode of diode V7 is connected to a -3.3V power supply. Resistor R10 is connected between the two RG pins of amplifier D4. The -VS pin of amplifier D4 is connected to a -3.3V power supply and grounded through capacitor C10. The +VS pin of amplifier D4 is connected to a 3.3V power supply and grounded through capacitor C16. The OUT pin of amplifier D4 is connected to the output terminal OUT1 of the small signal amplifier circuit, and the REF pin of amplifier D4 is grounded.

[0051] The amplifier D4 is preferably an instrumentation amplifier chip (model TPA1286 from Suzhou Sipu Microelectronics Technology Co., Ltd.). To reduce costs, three operational amplifiers can also be used to form an instrumentation amplifier (structure shown in Figure 7).

[0052] As shown in Figure 4, the MCU input circuit in the first branch includes capacitor C13, resistor R9, diode V3, and diode V4. The output terminal OUT1 of the small signal amplifier circuit is connected to one end of capacitor C13, and the other end of capacitor C13 is connected to the output terminal MCU-ADC1 of the first branch. Output terminal MCU-ADC1 is used to connect to the MCU's ADC module. The other end of capacitor C13 is also connected to a 1.65V power supply, the anode of diode V3, and the cathode of diode V4 through resistor R9. The cathode of diode V3 is connected to a 3.3V power supply, and the anode of diode V4 is grounded.

[0053] The voltage signal amplification circuit in the second branch includes operational amplifier D5, resistors R14, R16, and R17. The output terminal OUT1 of the small signal amplification circuit is connected to the non-inverting input terminal of operational amplifier D5 through resistor R17. The inverting input terminal of operational amplifier D5 is grounded through resistor R16 and also connected to the output terminal of operational amplifier D5 through resistor R14. The output terminal of operational amplifier D5 is connected to the output terminal OUT2 of the voltage signal amplification circuit.

[0054] The MCU input circuit in the second branch includes capacitor C18, resistor R15, diode V8, and diode V9. The output terminal OUT2 of the voltage signal amplifier circuit is connected to one end of capacitor C18, and the other end of capacitor C18 is connected to the output terminal MCU-ADC2 of the second branch. Output terminal MCU-ADC2 is used to connect to the MCU's ADC module. The other end of capacitor C18 is also connected to a 1.65V power supply, the anode of diode V8, and the cathode of diode V9 via resistor R15. The cathode of diode V8 is connected to a 3.3V power supply, and the anode of diode V9 is grounded.

[0055] In this embodiment, the operational amplifier D5 uses the domestically produced TPA1881 from Suzhou Sipu Microelectronics Technology Co., Ltd.

[0056] The first branch does not have amplification capability, while the second branch has the ability to further amplify the signal, thus enabling multi-range selection. Furthermore, the second branch can be a single branch or multiple branches with the same structure but different voltage signal amplification circuit parameters (different amplification factors), thereby achieving more ranges and connecting to ADCs with different internal resistances in the MCU, such as 0~100mΩ as one range, 100mΩ~1Ω as one range, 1Ω~10Ω as one range, etc.

[0057] The internal resistance measurement circuit also includes a power supply circuit for outputting 3.3V, -3.3V and 1.65V power supplies.

[0058] As shown in Figure 5, the input 5V power supply is connected to one end of capacitor C1, and also to the Vin pin of the low-dropout linear regulator D1. The Vout pin of the low-dropout linear regulator D1 is used to output a 3.3V power supply and is connected to one end of capacitor C2. The other ends of capacitor C1, capacitor C2, and the GND pin of the low-dropout linear regulator D1 are all grounded.

[0059] A 3.3V power supply is connected to the IN pin of the switching DC-DC converter D2 and one end of capacitor C5. The OUT pin of the switching DC-DC converter D2 outputs a -3.3V power supply and is connected to one end of capacitor C6. The other ends of capacitors C5 and C6, as well as the GND pin of the switching DC-DC converter D2, are grounded. A capacitor C3 is connected between the Cfly- and Cfly+ pins of the switching DC-DC converter D2.

[0060] The 3.3V power supply is grounded through resistors R1 and R2 connected in series. The connection point between resistors R1 and R2 is used to output a 1.65V power supply. Resistor R1 is connected in parallel with capacitor C4, and resistor R2 is connected in parallel with capacitor C7. To obtain a stable DC bias of 1.65V, the resistance values ​​of R1 and R2 must be equal, and ideally, they should be selected from the same manufacturer and batch.

[0061] In this embodiment, the low-dropout linear regulator D1 can use a common LDO chip, such as the SGM2034 chip from domestic SGMicroelectronics (Beijing) Co., Ltd. The switching DC-DC converter D2 uses the SGM3206 chip from domestic SGMicroelectronics (Beijing) Co., Ltd. The operational amplifier D3 uses the LMV358B from domestic Suzhou Sipu Microelectronics Technology Co., Ltd.

[0062] It is important to note that the selection of DC blocking capacitors C9 and C11 is crucial. High-voltage capacitors should be chosen based on the backup power supply voltage to isolate DC voltage. If measuring the AC impedance of the FTU's backup power supply, since its voltage is around 24V, 50V or 100V capacitors can be selected.

[0063] The operation process of the internal resistance measurement circuit is as follows:

[0064] 1. Power supply circuit: First, the 5V voltage is converted into 3.3V voltage through the low dropout linear regulator D1. The 3.3V voltage is then converted into -3.3V voltage through the switching DC power converter D2. The 3.3V voltage is then divided by two equal resistors to generate 1.65V voltage.

[0065] 2. V / I Conversion Circuit: The MCU is equipped with a DAC (Digital-to-Analog Converter) function, which outputs a 1kHz AC sine wave (MCU-DAC-OUT). This sine wave passes through the DC blocking capacitor C12, then through the D3A op-amp voltage follower, which has high input impedance and low output impedance, and then through D3B to form a constant current source. The output current is I = Vin / R7*(R4 / R3). The constant current source is applied to the backup power supply through the DC blocking capacitor C9. Because the backup power supply has internal AC resistance, and the internal resistance of the backup power supply is very small, usually tens of milliohms, a small voltage signal will be generated.

[0066] 3. Small Signal Amplification Circuit: This circuit amplifies small signals before sending them to the MCU for ADC (Analog-to-Digital Converter) acquisition. The small signal passes through DC blocking capacitors C11 and C14 before being amplified by instrumentation amplifier D4. The instrumentation amplifier efficiently amplifies weak signals, improving measurement accuracy.

[0067] 4. Voltage Signal Amplification Circuit / MCU Input Circuit: The signal amplified by the micro-signal amplification circuit is directly input to the MCU through the MCU input circuit. Alternatively, it can be amplified again by the voltage signal amplification circuit before being input to the MCU. Since the output signal is both positive and negative voltage, and the MCU is typically powered by 3.3V and GND, the MCU input circuit needs to convert the negative voltage to a positive voltage before inputting it to the MCU. The MCU input circuit uses a 1.65V DC voltage to boost the output signal, meaning there is a 1.65V DC bias in the AC signal input to the MCU. The MCU will automatically compensate for this DC bias during calculations.

[0068] 5. Internal resistance calculation: The MCU calculates the internal resistance of the backup power supply based on the magnitude of the constant current source current corresponding to the transmitted AC sine wave and the acquired voltage signal using Ohm's law.

[0069] It should be noted that, as will be apparent to those skilled in the art, this utility model is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this utility model. The scope of this utility model is defined by the claims rather than the foregoing description.

Claims

1. A circuit for measuring the internal resistance of a backup power supply in a power distribution automation terminal, characterized in that: The system includes an MCU, a V / I conversion circuit, and an amplification and sampling section. The output port MCU_DAC_OUT of the MCU's DAC module is connected to the input of the V / I conversion circuit to output an AC sine wave. The positive and negative terminals of the V / I conversion circuit's output are connected to the positive and negative terminals of a backup power supply, respectively, to convert the AC sine wave into a constant current source and apply it to the backup power supply. The positive and negative terminals of the amplification and sampling section are connected to the positive and negative terminals of the backup power supply, respectively, and its output is connected to the input of the MCU's ADC module. This amplifies the small signal acquired from the backup power supply and then inputs the amplified voltage signal into the MCU.

2. The power distribution automation terminal backup power supply internal resistance measurement circuit as described in claim 1, characterized in that: The V / I conversion circuit includes operational amplifiers D3A and D3B. The MCU_DAC_OUT is connected to the non-inverting input of operational amplifier D3A via capacitor C12. The 5V power supply is grounded through resistors R6 and R11 connected in series, with the connection point between R6 and R11 connected to the non-inverting input of operational amplifier D3A. The inverting input of operational amplifier D3A is connected to its output, and the output of operational amplifier D3A is connected to the non-inverting input of operational amplifier D3B via resistor R8. The non-inverting input of operational amplifier D3B is connected to one end of transient voltage suppressor V5 via resistor R12. The other end of transient voltage suppressor V5 is grounded; the inverting input of operational amplifier D3B is grounded through resistor R3 and capacitor C8 connected in series, and is also connected to one end of resistor R7 through resistor R4; the output of operational amplifier D3B is directly connected to one end of resistor R7, or connected to one end of resistor R7 through a class AB amplifier; the other end of resistor R7 is connected to one end of transient voltage suppressor V5, and also to one end of capacitor C9; the other end of capacitor C9 serves as the positive terminal of the V / I converter output and is connected to the positive terminal of the backup power supply, and the other end of transient voltage suppressor V5 serves as the negative terminal of the V / I converter output and is connected to the negative terminal of the backup power supply.

3. The power distribution automation terminal backup power supply internal resistance measurement circuit as described in claim 2, characterized in that: The Class AB amplifier includes diodes V10 and V12, an NPN transistor V8, and a PNP transistor V13. The output of operational amplifier D3B is connected to the cathode of diode V10 and the anode of diode V12. A 5V power supply is connected to the anode of diode V10 through resistor R1. The anode of diode V10 is also connected to the base of NPN transistor V8. The 5V power supply is also connected to the collector of NPN transistor V8. The cathode of diode V12 is grounded through resistor R2 and is also connected to the base of PNP transistor V13. The collector of PNP transistor V13 is grounded. The emitters of NPN transistor V8 and PNP transistor V13 are connected and connected to one end of resistor R7.

4. The power distribution automation terminal backup power supply internal resistance measurement circuit as described in claim 1, characterized in that: The amplification and sampling section includes a small signal amplification circuit, a voltage signal amplification circuit, and an MCU acquisition input circuit; the input terminal of the small signal amplification circuit is connected to the backup power supply, and the output terminal is connected to the input terminal of the MCU's ADC module through a parallel first branch and a second branch. The first branch contains only the MCU acquisition input circuit, while the second branch contains a voltage signal amplification circuit and the MCU acquisition input circuit connected in series. There are more than one second branch, and the amplification factor of the voltage signal amplification circuit in different second branches is different.

5. The power distribution automation terminal backup power supply internal resistance measurement circuit as described in claim 4, characterized in that: The small signal amplifier circuit includes amplifier D4, capacitors C10, C11, C14, and C16, resistors R5, R10, and R13, and diodes V1, V2, V6, and V7. The positive and negative input terminals of the small signal amplifier circuit, used to connect to the positive and negative terminals of the backup power supply, are connected to one end of capacitor C11 and one end of capacitor C14, respectively. The other end of capacitor C11 is grounded through resistor R5 and is also connected to the anode of diode V1, the cathode of diode V2, and the IN+ pin of amplifier D4. The cathode of diode V1 is connected to a 3.3V power supply, and the anode of diode V2 is connected to a -3.3V power supply. The other end of capacitor C14 is grounded through resistor R13, and is also connected to the anode of diode V6, the cathode of diode V7, and the IN- pin of amplifier D4. The cathode of diode V6 is connected to a 3.3V power supply, and the anode of diode V7 is connected to a -3.3V power supply. Resistor R10 is connected between the two RG pins of amplifier D4. The -VS pin of amplifier D4 is connected to a -3.3V power supply and is also grounded through capacitor C10. The +VS pin of amplifier D4 is connected to a 3.3V power supply and is also grounded through capacitor C16. The OUT pin of amplifier D4 is connected to the output terminal OUT1 of the small signal amplifier circuit, and the REF pin of amplifier D4 is grounded.

6. The power distribution automation terminal backup power supply internal resistance measurement circuit as described in claim 4, characterized in that: The MCU input circuit in the first branch includes capacitor C13, resistor R9, diode V3, and diode V4. The output terminal OUT1 of the micro-signal amplifier circuit is connected to one end of capacitor C13, and the other end of capacitor C13 is connected to the output terminal MCU-ADC1 of the first branch. The output terminal MCU-ADC1 is used to connect to the ADC module of the MCU. The other end of capacitor C13 is also connected to a 1.65V power supply, the anode of diode V3, and the cathode of diode V4 through resistor R9. The cathode of diode V3 is connected to a 3.3V power supply, and the anode of diode V4 is grounded.

7. The power distribution automation terminal backup power supply internal resistance measurement circuit as described in claim 4, characterized in that: The voltage signal amplification circuit in the second branch includes operational amplifier D5, resistors R14, R16, and R17. The output terminal OUT1 of the small signal amplification circuit is connected to the non-inverting input terminal of operational amplifier D5 through resistor R17. The inverting input terminal of operational amplifier D5 is grounded through resistor R16 and also connected to the output terminal of operational amplifier D5 through resistor R14. The output terminal of operational amplifier D5 is connected to the output terminal OUT2 of the voltage signal amplification circuit. The MCU acquisition input circuit in the second branch includes capacitor C18 and resistors... R15, diode V8, and diode V9; the output terminal OUT2 of the voltage signal amplifier circuit is connected to one end of capacitor C18, and the other end of capacitor C18 is connected to the output terminal MCU-ADC2 of the second branch; the output terminal MCU-ADC2 is used to connect to the ADC module of the MCU; the other end of capacitor C18 is also connected to a 1.65V power supply, the anode of diode V8, and the cathode of diode V9 through resistor R15; the cathode of diode V8 is connected to a 3.3V power supply, and the anode of diode V9 is grounded.

8. The power distribution automation terminal backup power supply internal resistance measurement circuit as described in any one of claims 1 to 7, characterized in that: The internal resistance measurement circuit also includes a power supply circuit for outputting 3.3V, -3.3V, and 1.65V power supplies. The input 5V power supply is connected to one end of capacitor C1 and also to the Vin pin of the low-dropout linear regulator D1. The Vout pin of the low-dropout linear regulator D1 is used to output the 3.3V power supply and is connected to one end of capacitor C2. The other ends of capacitor C1, capacitor C2, and the GND pin of the low-dropout linear regulator D1 are all grounded. The 3.3V power supply is connected to the IN pin of the switching DC-DC power converter D2 and one end of capacitor C5. The OUT pin of the switching DC-DC converter D2 is used to output a -3.3V power supply and is connected to one end of capacitor C6; the other ends of capacitor C5, capacitor C6, and the GND pin of the switching DC-DC converter D2 are all grounded; capacitor C3 is connected between the Cfly- and Cfly+ pins of the switching DC-DC converter D2; the 3.3V power supply is grounded through resistors R1 and R2 connected in series with equal resistance; the connection point between resistors R1 and R2 is used to output a 1.65V power supply; capacitor C4 is connected in parallel with resistor R1, and capacitor C7 is connected in parallel with resistor R2.

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