Sampling method of direct-current voltage component

Abstract

The invention discloses a direct current voltage component sampling method, which comprises the following steps of: respectively sampling voltage between a first input end and a signal ground end and voltage between a second input end and the signal ground end, respectively averaging sampling results, and then carrying out differential operation to obtain a direct current voltage component. The sampling method of the direct-current voltage component can adapt to different reference grounds, can improve the control precision while the sampling range is not limited, and is low in cost.

Description

[0001] This application is a divisional application of the invention patent application with the application date of February 27, 2025, application number 2025102203511, and invention name “A sampling circuit and sampling method for DC voltage components”. Technical Field

[0002] The present invention relates to the technical field of DC voltage component sampling, and in particular to a DC voltage component sampling method. Background Art

[0003] DCV is the DC voltage component extracted from the 230V AC output voltage at the load end. Energy storage inverters require this DC voltage component (DCV) to be below 0.1V. However, in actual operation, DCV often exceeds 0.1V. This phenomenon stems from both software control and sampling accuracy. Since DCV sampling accuracy has a significant impact on control, insufficient sampling accuracy can prevent the software from controlling DCV within 0.1V.

[0004] 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 sending them to the control chip for calculation and adjustment through isolation. Figure 1 If the control chip's power reference point isn't the N line, it needs to be isolated via an isolation op amp. This approach isn't adaptable to systems with different reference grounds and is expensive. Because isolation op amps are typically fixed-gain devices, attenuation-gain op amps affect control accuracy, while amplification-gain op amps affect sampling range. Due to these limitations, current technology has poor DCV sampling accuracy and cannot meet the stringent DCV requirements of energy storage inverters.

[0005] Right now Figure 1 The existing DCV sampling implementation shown requires two types of power supplies: an N-referenced power supply for the input side of the non-isolated and isolated op amps, and a GND-referenced power supply for the control chip. This complex power supply architecture and component types also limit sampling accuracy and range.

[0006] Specifically, the attenuation gain op amp has insufficient accuracy: the output range is less than the input range. For example, the TI / AMC1350 op amp has an input range of ±5V, an output range of ±2V, and a gain of 0.4V / V. Therefore, an actual DCV of 0.1V corresponds to an AD sampling value change of 0.04V, and an actual DCV of 0.11V corresponds to an AD sampling value change of 0.044V. Consequently, a DCV of 10mV corresponds to a sampling value change of 4mV. This means that the recognition accuracy of the op amp or control chip after the isolation op amp output must be controlled within 4mV. This accuracy is prone to recognition errors, affecting DCV control.

[0007] Insufficient op amp gain range: Output range > input range. For example, the TI / AMC1200 op amp has an input range of ±0.25V, an output range of ±2V, and a gain of 8V / V. Therefore, a 10mV DCV change corresponds to an 80mV change in the AD sample value. Considering the chip's AD input range of 0-3V, this translates to: To ensure 80mV recognition accuracy, the maximum DCV sample value is 0.375V. 0.375V > 0.25V, exceeding the input range of the isolation op amp and causing device failure. Ensuring a ±250mV isolation op amp input results in wasted AD values in the 0-1V and 2-3V ranges.

[0008] 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.

[0009] Existing patents such as CN202222755708.0-Energy Storage Inverter DC Voltage Isolation Sampling Circuit use the same method as Figure 1 The existing solutions shown are basically identical.

[0010] Another example is CN201420298403.4 - AC / DC voltage isolation differential sampling circuit, which adopts the following method: op amp + filter + isolation op amp + op amp + clamp, Figure 1 The principle of the existing solution shown is the same, except that several stages of operational amplifiers and a voltage clamping protection control chip are added.

[0011] The two closest existing patents mentioned above are Figure 1 The scheme shown in the figure has the same principle, but its disadvantages are: 1. You can only choose between sampling range and sampling accuracy, and it is impossible to ensure sufficiently high sampling accuracy without sacrificing sampling range; 2. Isolation is required, which increases circuit 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 circuit sampling range and gain are limited by the isolation device.

[0012] 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 this application. In the absence of clear evidence showing that the above content has been disclosed before the filing date of this application, the above background technology should not be used to evaluate the novelty and creativity of this application. Summary of the Invention

[0013] 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 method, which can simultaneously improve the DCV sampling accuracy and sampling range.

[0014] In order to achieve the above object, the present invention adopts the following technical solutions:

[0015] A DC voltage component sampling circuit includes 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. 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 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. 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.

[0016] The first differential sampling unit includes a first sampling module, which 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 by the first sampling module;

[0017] The second differential sampling unit includes a second sampling module, which includes a second operational amplifier. The second input terminal N is connected to a non-inverting input terminal of the second operational amplifier, and the inverting input terminal of the second operational amplifier is connected to a signal ground terminal. The voltage between the second input terminal N and the signal ground terminal is obtained by the second sampling module.

[0018] Preferably, the signal ground 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 a subtraction operation, LN(AVG) is obtained, which is the DC voltage component DCV.

[0019] Preferably, the control unit includes a control chip.

[0020] 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.

[0021] According to some preferred implementations of the present invention, the first differential sampling unit includes a first filtering module connected between the output terminal of the first operational amplifier and the first operational amplifier unit. The first filtering module filters a sampling result of the voltage between the first input terminal L and the signal ground terminal.

[0022] According to some preferred embodiments 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.

[0023] 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.

[0024] According to some preferred embodiments of the present invention, the second differential sampling unit includes a second filtering module connected between the output terminal of the second operational amplifier and the first operational amplifier unit. The second filtering module filters the sampling result of the voltage between the second input terminal N and the signal ground terminal.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] According to some preferred implementation aspects of the present invention, 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.

[0029] 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.

[0030] 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.

[0031] 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 meet the requirements of a large sampling range or high control precision. 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 precision.

[0032] The present invention also provides a method for sampling a DC voltage component according to the sampling circuit described above, comprising the following steps:

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Due to the adoption of the above technical solution, compared with the prior art, the benefits of the present invention are: the DC voltage component sampling method of the present invention can adapt to different reference grounds, can improve control accuracy while the sampling range is not limited, and is low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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.

[0038] Figure 1 This is a sampling circuit diagram of a DC voltage component in the prior art;

[0039] Figure 2 1 is a sampling circuit diagram of a DC voltage component in a preferred embodiment 1 of the present invention;

[0040] Figure 3 This is a sampling circuit diagram of the DC voltage component in the preferred embodiment 2 of the present invention. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the technical solutions of the present invention, 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 should fall within the scope of protection of the present invention.

[0042] Example 1

[0043] 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 terminal 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 terminal. Preferably, the control unit includes a control chip, and the signal ground terminal is the system ground (control chip reference ground) GND, which is the reference potential point in the circuit system.

[0044] The first differential sampling unit is used to sample the voltage between the first input terminal L and the signal ground terminal, and the second differential sampling unit is used to sample the voltage between the second input terminal N and the signal ground terminal. The first operational amplifier unit is used to perform a differential operation on the sampling results of the first and second differential sampling units. By sampling the voltage between L and GND and the voltage between N and GND, the sampled values are averaged through RC filtering and then subtracted to obtain LN(AVG), which is the DC voltage component DCV.

[0045] 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 by the first sampling module, and the sampling result of the voltage between the first input terminal (L) and the signal ground terminal is filtered by the first filtering module.

[0046] 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.

[0047] Similar in structure to 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, with a second input terminal N connected to the non-inverting input terminal of the second operational amplifier OPA2, and an inverting input terminal of the second operational amplifier OPA2 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.

[0048] 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.

[0049] Preferably, a first resistor R1 is connected to both the non-inverting input and the inverting input of the first operational amplifier OPA1. One first resistor R1 is connected between the first input terminal L and the non-inverting input of the first operational amplifier OPA1, and the other first resistor R1 is connected between the signal ground and the inverting input of the first operational amplifier OPA1. A third resistor R3 is connected to both the non-inverting input and the inverting input of the second operational amplifier OPA2. One third resistor R3 is connected between the second input terminal N and the non-inverting input of the second operational amplifier OPA2, and the other third resistor R3 is connected between the signal ground and the inverting input of the second operational amplifier OPA2.

[0050] The first operational amplifier unit includes a third operational amplifier OPA3 and a fifth resistor R5 disposed at the non-inverting input and inverting input 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 non-inverting input of the third operational amplifier OPA3, and the second differential sampling unit is connected to the inverting input of the third operational amplifier OPA3, for transmitting the sampling results to the third operational amplifier OPA3.

[0051] Example 2

[0052] 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 in parallel with the first operational amplifier unit, and the output end of the second operational amplifier unit is connected to the control unit.

[0053] The second operational amplifier unit includes a fourth operational amplifier OPA4 and a sixth resistor R6 provided at the non-inverting input and the inverting input of the fourth operational amplifier OPA4. One end of the sixth resistor R6 at the non-inverting input 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 at the inverting input 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 of the fourth operational amplifier OPA4, and the second differential sampling unit is connected to the inverting input of the fourth operational amplifier OPA4.

[0054] 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 meet the requirements of a large sampling range or high control precision. 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 precision.

[0055] Example 3

[0056] The present invention also provides a method for sampling a DC voltage component, comprising the following steps:

[0057] 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.

[0058] 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 used as the reference point, DCV can be expressed as LN(AVG).

[0059] 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.

[0060] According to the above expression, the voltage between L and GND and the voltage between N and GND are sampled, 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.

[0061] According to the above principle, the DC voltage component sampling method in this embodiment specifically includes the following steps:

[0062] (1) Sampling

[0063] Based on the sampling circuit in Example 1 or Example 2, differential sampling is performed on the voltages between L, N, and GND, using the control chip reference ground GND as a reference. A first sampling module is used to sample and output the voltage between the first input terminal L and the signal ground terminal GND, and a second sampling module is used to sample and output the voltage between the second input terminal N and the signal ground terminal GND.

[0064] During the sampling process, the sampling ratio can be adjusted freely according to the demand, but the gains of the L and N channels (the first sampling module and the second sampling module) must be kept consistent.

[0065] (2) Filtering

[0066] 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.

[0067] The filtering parameters of the two paths (the first filtering module and the second filtering module) are consistent.

[0068] (3) Taking the average value

[0069] 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 L-GND voltage average value AVG1 and the N-GND voltage average value AVG2.

[0070] (4) Differential operation

[0071] The average voltage value AVG1 of L-GND and the average voltage value AVG2 of N-GND are subjected to a differential operation, that is, subtraction, to obtain the average voltage value of LN, that is, the DC voltage component DCV.

[0072] In the entire sampling process as described 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 op amp and an AD sampling port can be added to achieve this, i.e., the sampling circuit in Example 2, as shown in FIG. Figure 3The large sampling range port is used for control and adjustment when DCV is greater than 0.1V, and the high-precision port is used for control and adjustment when DCV is less than 0.1V.

[0073] 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 current energy storage inverter DC V cannot meet the specification of less than 0.1V. It can adapt to different reference grounds, improve control accuracy while the sampling range is not limited, and ensure low cost. Compared with the existing technology, 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.

[0074] The above-described embodiments, prepared by the methods of the present invention, are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A method for sampling a DC voltage component, 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 sampling results are averaged and then subjected to differential operation to obtain the DC voltage component.

2. The sampling method according to claim 1, characterized in that The signal ground terminal is the system ground GND, which is the reference potential point in the sampling circuit.

3. The sampling method according to claim 1, characterized in that The first input end is the L end of the power supply, and the second input end is the N end of the power supply.

4. The sampling method according to claim 1, characterized in that The sampling is performed by using a first differential sampling unit to sample the voltage between the first input terminal and the signal ground terminal, and using a second differential sampling unit to sample the voltage between the second input terminal and the signal ground terminal; The differential operation is to use the first operational amplifier unit to perform a differential operation on the sampling results of the first differential sampling unit and the second differential sampling unit.

5. The sampling method according to claim 4, characterized in that: During the sampling process, the gains of the first differential sampling unit and the second differential sampling unit remain consistent.

6. The sampling method according to claim 4, characterized in that The sampling results are filtered and then averaged, and the filtering parameters of the first differential sampling unit and the second differential sampling unit are consistent.

7. The sampling method according to claim 4, characterized in that: 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.

8. The sampling method according to claim 4, 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 method according to claim 4, characterized in that: The first differential sampling unit includes a first sampling module, which includes a first operational amplifier. The first input terminal is connected to a non-inverting input terminal of the first operational amplifier, and an inverting input terminal of the first operational amplifier is connected to a signal ground terminal.

10. The sampling method according to claim 4, characterized in that: 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.

11. The sampling method according to claim 9, 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; the first resistor on the non-inverting input terminal is connected between the first input terminal and the first operational amplifier, and the first resistor on the inverting input terminal is connected between the signal ground terminal and the first operational amplifier.

12. The sampling method according to claim 11, characterized in that: The first differential sampling unit includes a first filtering module for filtering a sampling result of the voltage between the first input terminal and the signal ground terminal; the first filtering module is connected between the output terminal of the first operational amplifier and the first operational amplifier unit.

13. The sampling method according to claim 12, 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, one end of the first capacitor is connected to the second resistor, and the other end is connected to the signal ground, and the first capacitor is located between the second resistor and the first operational amplifier unit.

14. The sampling method according to claim 10, characterized in that: A third resistor is connected to the non-inverting input and / or the inverting input of the second operational amplifier; the third resistor on the non-inverting input is connected between the second input and the second operational amplifier, and the third resistor on the inverting input is connected between the signal ground and the second operational amplifier.

15. The sampling method according to claim 10, characterized in that: The second differential sampling unit includes a second filtering module for filtering a sampling result of the voltage between the second input terminal and the signal ground terminal; the second filtering module is connected between the output terminal of the second operational amplifier and the first operational amplifier unit.

16. The sampling method according to claim 15, 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. One end of the second capacitor is connected to the fourth resistor, and the other end is connected to the signal ground.

17. The sampling method according to claim 4, characterized in that: The sampling circuit includes a second operational amplifier unit, which 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; the first operational amplifier unit or the second operational amplifier unit corresponds to the requirements of a large sampling range or high control precision, respectively, the large sampling range port is used for control and regulation when the DCV is greater than 0.1V, and the high-precision port is used for control and regulation when the DCV is less than 0.1V.

18. The sampling method according to claim 17, 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.

19. The sampling method according to any one of claims 1 to 18, characterized in that: The specific steps include: (1) Sampling A first sampling module is used to sample and output the voltage between the first input terminal L and the signal ground terminal GND, and a second sampling module is used to sample and output the voltage between the second input terminal N and the signal ground terminal GND; during the sampling process, the gains of the first sampling module and the second sampling module are kept consistent; (2) Filtering 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; the filtering parameters of the first filtering module and the second filtering module are consistent; (3) Taking the average value averaging the voltage sampled values between the first input terminal L and the signal ground terminal GND after filtering and the voltage sampled values between the second input terminal N and the signal ground terminal GND after filtering to obtain an L-GND voltage average value AVG1 and an N-GND voltage average value AVG2; (4) Differential operation Performing a differential operation, i.e., subtraction, on the average voltage AVG1 of L-GND and the average voltage AVG2 of N-GND yields the average voltage of LN, which is the DC voltage component DCV.

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