A DC voltage component sampling circuit and sampling method

Abstract

The present invention discloses a sampling circuit and a sampling method for a DC voltage component, wherein the sampling circuit comprises a first operational amplifier unit, a first differential sampling unit connected between a first input terminal and the first operational amplifier unit, and a second differential sampling unit connected between a second input terminal and the first operational amplifier unit, wherein the output terminal of the first operational amplifier unit is connected to a control unit, wherein the first differential sampling unit, the second differential sampling unit, the first operational amplifier unit and the control unit are all connected to a signal ground terminal, wherein the first differential sampling unit is used to sample the voltage between the first input terminal and the signal ground terminal, wherein the second differential sampling unit is used to sample the voltage between the second input terminal and the signal ground terminal, and wherein the first operational amplifier unit is used to perform differential operations on the sampling results of the first differential sampling unit and the second differential sampling unit. The sampling circuit of the present invention can improve the control accuracy while the sampling range is not limited.

Description

Technical Field

[0001] The present invention relates to the technical field of DC voltage component sampling, and in particular to a DC voltage component sampling circuit and a method for sampling a DC voltage component by using the sampling circuit. Background Art

[0002] DCV is the DC voltage component extracted from the 230V AC output voltage at the load end. The energy storage inverter requires the DC voltage component (DCV) to be below 0.1V. However, in actual use, the DCV is often greater than 0.1V. This phenomenon is caused by software control and sampling accuracy. Since the sampling accuracy of DCV has a huge impact on control, insufficient sampling accuracy will cause the software to be unable to control DCV within 0.1V.

[0003] The current sampling method for DC voltage components (DCV) is mostly based on the N line as a reference, sampling the DC voltage components between L and N, and then providing them to the control chip for calculation and adjustment through isolation, such as Figure 1 If the power reference point of the control chip is not the N line, it needs to be isolated through an isolation amplifier, which cannot adapt to systems with different reference grounds and has a high cost. Since isolation amplifiers are basically fixed-gain devices, attenuation gain amplifiers affect control accuracy, and amplification gain amplifiers affect sampling range. Due to their limitations, the current technology has poor DCV sampling accuracy and cannot meet the strict requirements for DCV in energy storage inverters.

[0004] Right now Figure 1 The existing DCV sampling implementation scheme shown in the figure requires two types of power supplies, namely: the power supply with N as the reference is used to power the non-isolated op amp and the isolated op amp input side, and the power supply with GND as the reference is used to power the control chip. The power supply architecture and device types are relatively complex, and the sampling accuracy and range are also limited.

[0005] Specifically, the attenuation gain amplifier has insufficient precision: output range < input range. Taking the TI / AMC1350 op amp as an example, the input range is ±5V, the output range is ±2V, and the gain is 0.4V / V. Then, 0.1V actual DCV corresponds to 0.04V AD sampling value change, 0.11V actual DCV corresponds to 0.044V AD sampling value change, and 10mV DCV corresponds to 4mV sampling value change, that is, the recognition accuracy of the op amp or control chip after the isolation op amp output needs to be controlled within 4mV. This accuracy is prone to recognition errors, affecting DCV control.

[0006] The amplification gain op amp range is insufficient: the output range > input range. Taking the op amp TI / AMC1200 as an example, the input range is ±0.25V, the output range is ±2V, and the gain is 8V / V. Then, a 10mV DCV change corresponds to an 80mV AD sampling value change. Considering that the chip AD input range is 0~3V, it can be inferred that: under the premise of ensuring 80mV recognition accuracy, the DCV sampling maximum value is 0.375V, 0.375V>0.25V, which exceeds the input range of the isolation op amp and will cause the device to fail; ensuring ±250mV isolation op amp input will result in waste of AD values ​​in the range of 0~1V and 2~3V.

[0007] Therefore, to improve sampling accuracy, it is necessary to reduce the sampling range. However, the sampling range has relevant design specifications and cannot be reduced indefinitely. How to improve sampling accuracy while ensuring the sampling range is a problem that needs to be solved at present.

[0008] Existing patents such as CN202222755708.0-Energy storage inverter DC voltage isolation sampling circuit, the method used is similar to Figure 1 The existing solutions shown are basically completely consistent.

[0009] Another example is CN201420298403.4-AC / DC voltage isolation differential sampling circuit, which adopts the method of: op amp + filter + isolation op amp + op amp + clamp, and Figure 1 The principle of the existing solution shown is the same, except that a few more stages of operational amplifiers and a voltage clamping protection control chip are added.

[0010] The two closest existing patents mentioned above are Figure 1 The scheme shown has the same principle, but its disadvantages are: 1. You can only choose one between the sampling range and the sampling accuracy, and it is impossible to ensure that the sampling accuracy is high enough without sacrificing the sampling range; 2. Isolation is required, which increases the line cost, requires an additional isolated power supply, and complicates the power supply system; 3. Currently, most isolated op amps on the market are fixed gain devices, and the line sampling range and gain are limited by the isolation devices.

[0011] The disclosure of the above background technology content is only used to assist in understanding the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of the present application. In the absence of clear evidence that the above content has been disclosed before the filing date of the present application, the above background technology should not be used to evaluate the novelty and creativity of the present application. Summary of the invention

[0012] In view of this, in order to overcome the defects of the prior art, an object of the present invention is to provide an improved DC voltage component sampling circuit, which can improve the sampling accuracy and sampling range of DCV at the same time.

[0013] In order to achieve the above object, the present invention adopts the following technical solutions:

[0014] A sampling circuit for a DC voltage component comprises a first operational amplifier unit, a first differential sampling unit connected between a first input terminal L and the first operational amplifier unit, and a second differential sampling unit connected between a second input terminal N and the first operational amplifier unit, wherein the output terminal of the first operational amplifier unit is connected to a control unit, the first differential sampling unit, the second differential sampling unit, the first operational amplifier unit and the control unit are all connected to a signal ground terminal, the first differential sampling unit is used to sample a voltage between the first input terminal L and the signal ground terminal, the second differential sampling unit is used to sample a voltage between the second input terminal N and the signal ground terminal, and the first operational amplifier unit is used to perform a differential operation on the sampling results of the first differential sampling unit and the second differential sampling unit; the first input terminal is the L terminal of a power supply, and the second input terminal is the N terminal of the power supply;

[0015] The first differential sampling unit includes a first sampling module, the first sampling module includes a first operational amplifier, the first input terminal L is connected to the non-inverting input terminal of the first operational amplifier, and the inverting input terminal of the first operational amplifier is connected to the signal ground terminal. The voltage between the first input terminal L and the signal ground terminal is obtained through the first sampling module;

[0016] The second differential sampling unit includes a second sampling module, the second sampling module includes a second operational amplifier, the second input terminal N is connected to the non-inverting input terminal of the second operational amplifier, and the inverting input terminal of the second operational amplifier is connected to the signal ground terminal. The voltage between the second input terminal N and the signal ground terminal is obtained through the second sampling module.

[0017] Preferably, the signal ground terminal is the system ground (reference ground) GND, which is the reference potential point in the circuit system. By sampling the voltage between L and GND and the voltage between N and GND, averaging the sampled values ​​and performing subtraction operations, LN (AVG) is obtained, which is the DC voltage component DCV.

[0018] Preferably, the control unit includes a control chip.

[0019] According to some preferred implementation aspects of the present invention, a first resistor is connected to the non-inverting input terminal and / or the inverting input terminal of the first operational amplifier.

[0020] According to some preferred implementation aspects of the present invention, the first differential sampling unit includes a first filtering module, which is connected between the output terminal of the first operational amplifier and the first operational amplifier unit. The sampling result of the voltage between the first input terminal L and the signal ground terminal is filtered by the first filtering module.

[0021] According to some preferred implementation aspects of the present invention, the first filtering module includes a second resistor and a first capacitor, the second resistor is connected to the output end of the first operational amplifier, the first capacitor is connected to the signal ground end, and the first capacitor is located between the second resistor and the first operational amplifier unit.

[0022] According to some preferred implementation aspects of the present invention, a third resistor is connected to the non-inverting input terminal and / or the inverting input terminal of the second operational amplifier.

[0023] According to some preferred implementation aspects of the present invention, the second differential sampling unit includes a second filtering module, which is connected between the output terminal of the second operational amplifier and the first operational amplifier unit. The sampling result of the voltage between the second input terminal N and the signal ground terminal is filtered by the second filtering module.

[0024] According to some preferred implementation aspects of the present invention, the second filtering module includes a fourth resistor and a second capacitor, the fourth resistor is connected to the output end of the second operational amplifier, and the second capacitor is connected to the signal ground end.

[0025] According to some preferred implementation aspects of the present invention, the first operational amplification unit includes a third operational amplifier, the first differential sampling unit is connected to the non-inverting input terminal of the third operational amplifier, and the second differential sampling unit is connected to the inverting input terminal of the third operational amplifier.

[0026] According to some preferred implementation aspects of the present invention, the first operational amplification unit includes a fifth resistor arranged on the non-inverting input terminal and / or the inverting input terminal of the third operational amplifier.

[0027] According to some preferred implementation aspects of the present invention, the sampling circuit includes a second operational amplifier unit, the second operational amplifier unit is arranged in parallel with the first operational amplifier unit, and the output end of the second operational amplifier unit is connected to the control unit.

[0028] According to some preferred implementation aspects of the present invention, the second operational amplification unit includes a fourth operational amplifier, the first differential sampling unit is connected to the non-inverting input terminal of the fourth operational amplifier, and the second differential sampling unit is connected to the inverting input terminal of the fourth operational amplifier.

[0029] According to some preferred implementation aspects of the present invention, the second operational amplification unit includes a sixth resistor arranged on the non-inverting input terminal and / or the inverting input terminal of the fourth operational amplifier.

[0030] By setting the first operational amplifier unit and the second operational amplifier unit in parallel, and by setting the fifth resistor and the sixth resistor, the first operational amplifier unit or the second operational amplifier unit can respectively correspond to the requirements of a large sampling range or high control accuracy. The large sampling range port is used for control and adjustment when the DCV is greater than 0.1V, and the high-precision port is used for control and adjustment when the DCV is less than 0.1V, so as to better take into account the large sampling range and high control accuracy.

[0031] The present invention also provides a method for sampling a DC voltage component according to the sampling circuit as described above, comprising the following steps:

[0032] The voltage between the first input terminal L and the signal ground terminal GND and the voltage between the second input terminal N and the signal ground terminal GND are sampled respectively, and the sampling results are averaged and then differentially calculated to obtain a DC voltage component.

[0033] According to some preferred implementation aspects of the present invention, the first differential sampling unit is used to sample the voltage between the first input terminal L and the signal ground terminal GND, and the second differential sampling unit is used to sample the voltage between the second input terminal N and the signal ground terminal GND; during the sampling process, the gains of the first differential sampling unit and the second differential sampling unit remain consistent.

[0034] According to some preferred implementation aspects of the present invention, the sampling results are averaged after filtering, and filtering parameters of the first differential sampling unit and the second differential sampling unit are consistent.

[0035] Due to the adoption of the above technical solution, compared with the prior art, the advantages of the present invention are: the sampling circuit of the DC voltage component of the present invention can adapt to different reference grounds, can improve the control accuracy while the sampling range is not limited, and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 A sampling circuit diagram of a DC voltage component in the prior art;

[0038] Figure 2 The sampling circuit diagram of the DC voltage component in the preferred embodiment 1 of the present invention;

[0039] Figure 3 This is a sampling circuit diagram of the DC voltage component in the preferred embodiment 2 of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the 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 creative work should fall within the scope of protection of the present invention. Example 1

[0041] like Figure 2 As shown, the sampling circuit of the DC voltage component of this embodiment includes a control unit, a first operational amplifier unit, a first differential sampling unit connected between the first input terminal L and the first operational amplifier unit, and a second differential sampling unit connected between the second input terminal N and the first operational amplifier unit. The output end of the first operational amplifier unit is connected to the control unit, and the first differential sampling unit, the second differential sampling unit, the first operational amplifier unit and the control unit are all connected to the signal ground end. Preferably, the control unit includes a control chip, and the signal ground end is the system ground (control chip reference ground) GND, which is a reference potential point in the circuit system.

[0042] The first differential sampling unit is used to sample the voltage between the first input terminal L and the signal ground terminal, the second differential sampling unit is used to sample the voltage between the second input terminal N and the signal ground terminal, and the first operational amplifier unit is used to perform differential operations on the sampling results of the first differential sampling unit and the second differential sampling unit. By sampling the voltage between L and GND and the voltage between N and GND, the sampled values ​​are filtered through RC to obtain the average value and then subtracted to obtain LN (AVG), which is the DC voltage component DCV.

[0043] The first differential sampling unit includes a first sampling module and a first filtering module. The first sampling module includes a first operational amplifier OPA1. The first input terminal L is connected to the non-inverting input terminal of the first operational amplifier OPA1, and the inverting input terminal of the first operational amplifier OPA1 is connected to the signal ground terminal. The first filtering module is connected between the output terminal of the first operational amplifier OPA1 and the first operational amplifier unit. The voltage between the first input terminal L and the signal ground terminal is obtained through the first sampling module, and the sampling result of the voltage between the first input terminal L and the signal ground terminal is filtered through the first filtering module.

[0044] The first filtering module includes a second resistor R2 and a first capacitor C1. The second resistor R2 is connected to the output end of the first operational amplifier OPA1. One end of the first capacitor C1 is connected to the second resistor R2, and the other end is connected to the signal ground. The first capacitor C1 is located between the second resistor R2 and the first operational amplifier unit.

[0045] Similar to the structure of the first differential sampling unit, the second differential sampling unit includes a second sampling module and a second filtering module. The second sampling module includes a second operational amplifier OPA2, the second input terminal N is connected to the in-phase input terminal of the second operational amplifier OPA2, and the inverting input terminal of the second operational amplifier OPA2 is connected to the signal ground terminal. The second filtering module is connected between the output terminal of the second operational amplifier OPA2 and the first operational amplifier unit. The voltage between the second input terminal N and the signal ground terminal is obtained by the second sampling module, and the sampling result of the voltage between the second input terminal N and the signal ground terminal is filtered by the second filtering module.

[0046] The second filtering module includes a fourth resistor R4 and a second capacitor C2. The fourth resistor R4 is connected to the output end of the second operational amplifier OPA2. One end of the second capacitor C2 is connected to the fourth resistor R4, and the other end is connected to the signal ground. The second capacitor C2 is located between the fourth resistor R4 and the first operational amplifier unit.

[0047] Preferably, the first operational amplifier OPA1 has a first resistor R1 connected to both the non-inverting input terminal and the inverting input terminal, one first resistor R1 is connected between the first input terminal L and the non-inverting input terminal of the first operational amplifier OPA1, and the other first resistor R1 is connected between the signal ground terminal and the inverting input terminal of the first operational amplifier OPA1. The second operational amplifier OPA2 has a third resistor R3 connected to both the non-inverting input terminal and the inverting input terminal, one third resistor R3 is connected between the second input terminal N and the non-inverting input terminal of the second operational amplifier OPA2, and the other third resistor R3 is connected between the signal ground terminal and the inverting input terminal of the second operational amplifier OPA2.

[0048] The first operational amplifier unit includes a third operational amplifier OPA3 and a fifth resistor R5 arranged on the in-phase input terminal and the inverting input terminal of the third operational amplifier OPA3, one fifth resistor R5 is located between the first capacitor C1 and the third operational amplifier OPA3, and the other fifth resistor R5 is located between the second capacitor C2 and the third operational amplifier OPA3, that is, the first capacitor C1 is located between the second resistor R2 and the fifth resistor R5, and the second capacitor C2 is located between the fourth resistor R4 and the fifth resistor R5. The first differential sampling unit is connected to the in-phase input terminal of the third operational amplifier OPA3, and the second differential sampling unit is connected to the inverting input terminal of the third operational amplifier OPA3, for transmitting the sampling result to the third operational amplifier OPA3. Example 2

[0049] like Figure 3 As shown, the DC voltage component sampling circuit of this embodiment is based on the sampling circuit of Example 1, and a second operational amplifier unit is added to be arranged in parallel with the first operational amplifier unit, and the output end of the second operational amplifier unit is connected to the control unit.

[0050] The second operational amplifier unit includes a fourth operational amplifier OPA4 and a sixth resistor R6 arranged on the non-inverting input terminal and the inverting input terminal of the fourth operational amplifier OPA4, one end of the sixth resistor R6 on the non-inverting input terminal of the fourth operational amplifier OPA4 is connected between the first capacitor C1 and the fifth resistor R5; one end of the sixth resistor R6 on the inverting input terminal of the fourth operational amplifier OPA4 is connected between the second capacitor C2 and the fifth resistor R5. The first differential sampling unit is connected to the non-inverting input terminal of the fourth operational amplifier OPA4, and the second differential sampling unit is connected to the inverting input terminal of the fourth operational amplifier OPA4.

[0051] By setting the first operational amplifier unit and the second operational amplifier unit in parallel, and by setting the fifth resistor R5 and the sixth resistor R6, the first operational amplifier unit or the second operational amplifier unit can respectively correspond to the requirements of a large sampling range or high control accuracy. The large sampling range port is used for control adjustment when the DCV is greater than 0.1V, and the high-precision port is used for control adjustment when the DCV is less than 0.1V, so as to better take into account the large sampling range and high control accuracy. Example 3

[0052] The present invention also provides a DC voltage component sampling method, comprising the following steps:

[0053] The voltage between the first input terminal L and the signal ground terminal GND and the voltage between the second input terminal N and the signal ground terminal GND are sampled respectively, and the sampling results are averaged and then differentially calculated to obtain a DC voltage component.

[0054] The principle is as follows: Since the AC voltage output at the load end of the energy storage inverter is 230V 50Hz AC, the average value of the AC voltage is 0, and the average value of the DC voltage between the input terminals L and N is the DCV voltage value. When N is taken as the reference point, DCV can be expressed as LN (AVG).

[0055] According to the formula AC-(BC)=AB, the DCV sampling method with GND as the reference is obtained, that is: L-GND-(N-GND)=LN, and the DCV is sampled by changing the reference point.

[0056] According to the above expression, the voltage between L and GND and the voltage between N and GND are sampled, and the sampling structure is filtered through RC to obtain the average value and then subtracted to obtain LN (AVG), which is the DC voltage component DCV.

[0057] According to the above principle, the DC voltage component sampling method in this embodiment specifically includes the following steps:

[0058] (1) Sampling

[0059] Based on the sampling circuit in Example 1 or Example 2, the voltage between L, N and GND is differentially sampled with the reference ground GND of the control chip as a reference. The first sampling module is used to sample and output the voltage between the first input terminal L and the signal ground terminal GND, and the second sampling module is used to sample and output the voltage between the second input terminal N and the signal ground terminal GND.

[0060] During the sampling process, the sampling ratio can freely adjust the gain according to the demand, but the gains of L and N (the first sampling module and the second sampling module) must be kept consistent.

[0061] (2) Filtering

[0062] The sampling result of the voltage between the first input terminal L and the signal ground terminal is filtered by the first filtering module, and the sampling result of the voltage between the second input terminal N and the signal ground terminal is filtered by the second filtering module.

[0063] The filtering parameters of the two paths (the first filtering module and the second filtering module) are consistent.

[0064] (3) Taking the average value

[0065] The voltage sampling values ​​between the first input terminal L and the signal ground terminal GND after filtering and the voltage sampling values ​​between the second input terminal N and the signal ground terminal GND after filtering are averaged to obtain the voltage average value AVG1 of L-GND and the voltage average value AVG2 of N-GND.

[0066] (4) Difference operation

[0067] The average voltage value AVG1 of L-GND and the average voltage value AVG2 of N-GND are differentially calculated, that is, subtracted, to obtain the average voltage value of LN, that is, the DC voltage component DCV.

[0068] In the whole sampling process as above, the op amp gain and sampling range are adjustable, and the sampling accuracy is only related to the sampling range and is not limited by the device. If a large sampling range and high control accuracy are required, an operational amplifier and an AD sampling port can be added to achieve this, that is, the sampling circuit in Example 2, such as Figure 3The large sampling range port is used for control and regulation when DCV is greater than 0.1V, and the high-precision port is used for control and regulation when DCV is less than 0.1V.

[0069] The main reason why the specification of less than 0.1V cannot be met at present is that the circuit of the existing technical solution is limited by the device, resulting in insufficient sampling accuracy. The sampling circuit and sampling method of the DC voltage component (DCV) of the present invention can simultaneously improve the sampling accuracy of DCV and increase the sampling range of DCV, and can solve the problem that the DCV of the current energy storage inverter cannot meet the specification of less than 0.1V. It can not only adapt to different reference grounds, but also improve the control accuracy while the sampling range is not limited, and ensure low cost. Compared with the prior art, the sampling circuit and sampling method of the present invention have a sampling range that is not limited by devices and sampling accuracy, and can be freely adjusted according to actual needs; the sampling accuracy is not limited by devices and sampling range, and can be freely adjusted according to actual needs; no isolation is required, the power supply system is simple; and the cost is low.

[0070] The above embodiments prepared by the method of the present invention are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A sampling circuit for a DC voltage component, characterized in that: The invention comprises a first operational amplifier unit, a first differential sampling unit connected between a first input terminal and the first operational amplifier unit, and a second differential sampling unit connected between a second input terminal and the first operational amplifier unit, wherein the output terminal of the first operational amplifier unit is connected to a control unit, the first differential sampling unit, the second differential sampling unit, the first operational amplifier unit and the control unit are all connected to a signal ground terminal, the first differential sampling unit is used to sample a voltage between the first input terminal and the signal ground terminal, the second differential sampling unit is used to sample a voltage between the second input terminal and the signal ground terminal, and the first operational amplifier unit is used to perform differential operation on the sampling results of the first differential sampling unit and the second differential sampling unit; the first input terminal is an L terminal of a power supply, and the second input terminal is an N terminal of a power supply; The first differential sampling unit includes a first sampling module, the first sampling module includes a first operational amplifier, the first input terminal is connected to the non-inverting input terminal of the first operational amplifier, and the inverting input terminal of the first operational amplifier is connected to the signal ground terminal; the second differential sampling unit includes a second sampling module, the second sampling module includes a second operational amplifier, the second input terminal is connected to the non-inverting input terminal of the second operational amplifier, and the inverting input terminal of the second operational amplifier is connected to the signal ground terminal.

2. The sampling circuit according to claim 1, characterized in that: A first resistor is connected to the non-inverting input terminal and / or the inverting input terminal of the first operational amplifier.

3. The sampling circuit according to claim 1, characterized in that: The first differential sampling unit includes a first filtering module, and the first filtering module is connected between the output end of the first operational amplifier and the first operational amplification unit.

4. The sampling circuit according to claim 3, characterized in that: The first filtering module includes a second resistor and a first capacitor, the second resistor is connected to the output end of the first operational amplifier, the first capacitor is connected to the signal ground end, and the first capacitor is located between the second resistor and the first operational amplifier unit.

5. The sampling circuit according to claim 1, characterized in that: A third resistor is connected to the non-inverting input terminal and / or the inverting input terminal of the second operational amplifier.

6. The sampling circuit according to claim 1, characterized in that: The second differential sampling unit includes a second filtering module, and the second filtering module is connected between the output end of the second operational amplifier and the first operational amplification unit.

7. The sampling circuit according to claim 6, characterized in that: The second filtering module includes a fourth resistor and a second capacitor. The fourth resistor is connected to the output end of the second operational amplifier, and the second capacitor is connected to the signal ground end.

8. The sampling circuit according to claim 1, characterized in that: The first operational amplification unit includes a third operational amplifier, the first differential sampling unit is connected to a non-inverting input terminal of the third operational amplifier, and the second differential sampling unit is connected to an inverting input terminal of the third operational amplifier.

9. The sampling circuit according to claim 8, characterized in that: The first operational amplification unit includes a fifth resistor arranged on the non-inverting input terminal and / or the inverting input terminal of the third operational amplifier.

10. The sampling circuit according to claim 1, characterized in that: The sampling circuit includes a second operational amplifier unit, which is arranged in parallel with the first operational amplifier unit, and an output end of the second operational amplifier unit is connected to the control unit.

11. The sampling circuit according to claim 10, characterized in that: The second operational amplification unit includes a fourth operational amplifier, the first differential sampling unit is connected to a non-inverting input terminal of the fourth operational amplifier, and the second differential sampling unit is connected to an inverting input terminal of the fourth operational amplifier.

12. The sampling circuit according to claim 11, characterized in that: The second operational amplification unit includes a sixth resistor arranged on the non-inverting input terminal and / or the inverting input terminal of the fourth operational amplifier.

13. A method for sampling a DC voltage component using a sampling circuit according to any one of claims 1 to 12, characterized in that: The steps include: The voltage between the first input terminal and the signal ground terminal and the voltage between the second input terminal and the signal ground terminal are sampled respectively, and the average values ​​of the sampling results are taken and then a differential operation is performed to obtain a DC voltage component; The first differential sampling unit is used to sample the voltage between the first input terminal and the signal ground terminal, and the second differential sampling unit is used to sample the voltage between the second input terminal and the signal ground terminal; during the sampling process, the gains of the first differential sampling unit and the second differential sampling unit remain consistent.

14. The sampling method according to claim 13, characterized in that: The sampling results are averaged after filtering, and the filtering parameters of the first differential sampling unit and the second differential sampling unit are consistent.

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