FVOA type ADSS optical cable leakage current optical fiber measurement system and method based on voltage-controlled PWM

Abstract

The invention provides an FVOA type ADSS optical cable leakage current optical fiber measurement system and method based on voltage-controlled PWM. Relates to the technical field of current measurement, and realizes high-precision and quick-response measurement of direct current by combining optical characteristics of the FVOA and a voltage-controlled PWM (Pulse Width Modulation) technology. In the system, the FVOA utilizes a silicon substrate and a silicon nitride grating structure suspended on the silicon substrate to adjust the attenuation degree of light according to an applied driving voltage so as to generate a light PWM (Pulse Width Modulation) signal. The direct current Rogowski coil converts direct current to be measured into a voltage signal, and the voltage-controlled PWM module converts the voltage signal into a square wave signal with the duty ratio changing along with the voltage and drives the FVOA to generate a corresponding light PWM signal. And the photoelectric detector is responsible for converting the light PWM signal into an electric signal so as to carry out further signal processing. And the light energy supply module provides remote power supply for the voltage-controlled PWM module at the high-voltage end, so that stable operation of the system is ensured.

Description

Technical Field

[0001] This invention relates to the field of current measurement technology, specifically to an FVOA-type ADSS optical cable leakage current fiber optic measurement system and method based on voltage-controlled PWM. Background Technology

[0002] ADSS (Advanced Dielectric Self-Supported) optical cables are widely used in power communication systems due to their numerous advantages. However, ADSS cables face the problem of electro-corrosion during operation, which poses a serious threat to the normal operation of power communication networks and the safety and stability of power systems.

[0003] ADSS optical cables are laid near high-voltage power lines. The electric field in the space around the power lines will cause the optical cable to be at space potential position 1. In polluted and humid weather, a resistive layer forms on the surface of the optical cable. Under the influence of the space potential, a grounding leakage current will be generated between the surface of the optical cable and the tower or the grounding hardware of the optical cable. The current generates heat and forms a dry zone. When the induced voltage on the dry zone is high enough, a discharge will occur, forming an electric arc, i.e., a dry zone arc. Repeated arc discharges will cause dendritic carbonization channels to form on the surface of the optical cable sheath, resulting in electrical corrosion of the optical cable.

[0004] Currently, conventional methods for detecting electrical corrosion in ADSS optical cables mainly rely on manual inspection and sensor monitoring. However, these methods are susceptible to external environmental interference, resulting in high rates of missed and false detections. While image-based detection methods can mitigate interference to some extent, existing image-based methods lack targeted deep learning algorithms specific to the characteristics of ADSS optical cables, leading to insufficient inspection accuracy. Therefore, there is an urgent need for a system and method that better ensures the safe and stable operation of power communication systems and improves the accuracy and reliability of ADSS optical cable leakage current detection. Conducting research on passive leakage current detection of ADSS optical cables has significant technical background and practical importance. Summary of the Invention

[0005] Purpose of the invention: To address the problems mentioned in the background art, this invention discloses an FVOA-type ADSS optical cable leakage current fiber optic measurement system based on voltage-controlled PWM. By combining the optical characteristics of the FVOA module with voltage-controlled PWM technology, high-precision and fast-response measurement of DC current is achieved.

[0006] Technical solution:

[0007] This invention discloses an FVOA-type ADSS optical cable leakage current fiber measurement system based on voltage-controlled PWM, the system including an FVOA module, a voltage-controlled PWM module, a branching module and a signal processing module;

[0008] The FVOA module consists of a silicon substrate and a silicon nitride grating suspended on the silicon substrate, and is used to adjust the light attenuation based on the modulation signal output by the voltage-controlled PWM module as the external driving voltage.

[0009] The voltage-controlled PWM module is connected to the FVOA module and is used to convert the DC current to be measured into a voltage signal, and then into a square wave signal with a duty cycle that varies with the voltage as a modulation signal to drive the FVOA module to generate an optical PWM signal. The FVOA module then transmits the optical PWM signal to the signal processing module.

[0010] The splitting module includes a light source, a splitter, and an optical power supply module. It is used to split the light signal emitted by the light source into two paths, A and B, after entering the splitter. Path A is transmitted to the FVOA module through optical fiber, and path B is transmitted to the input end of the optical power supply module through optical fiber and transmitted from the output end of the optical power supply module to the voltage-controlled PWM module. The optical power supply module is used to supply bias power to the FVOA module and power the voltage-controlled PWM module.

[0011] The signal processing module includes a photodetector PD1, which is connected to the output of the FVOA module. The photodetector PD1 is used to convert the light source light signal and light PWM signal transmitted by the FVOA module into an electrical signal, calculate the duty cycle, and obtain the magnitude of the DC current to be measured.

[0012] Furthermore, the light power supply module includes a photodetector PD2, a step-up transformer, and a rectifier filter connected in sequence from the direction the light source enters through path B.

[0013] Furthermore, the input terminal of the voltage-controlled PWM module is connected to a Rogowski coil, and a sampling resistor is connected in series with the Rogowski coil to convert the DC current to be measured into a voltage signal, which is then applied to the voltage-controlled PWM module as a drive signal. When the DC current to be measured flows through the Rogowski coil, a millivolt-level voltage proportional to the DC current to be measured appears across the Rogowski coil. After passing through the voltage-controlled PWM module, this voltage outputs a square wave signal with a duty cycle that varies with the voltage. This square wave signal is used as the modulation signal of the FVOA module to drive the FVOA module to generate an optical PWM signal identical to the square wave signal. The optical PWM signal is then sent via optical fiber to the photodetector PD1 to be converted into an electrical signal. The duty cycle of the electrical signal is calculated, and the magnitude of the DC current to be measured is deduced from this calculation. The deduction formula is as follows:

[0014]

[0015] Where D is the duty cycle of the electrical signal, and V shunt To generate a voltage across the sampling resistor that is proportional to the current intensity, K is the proportionality coefficient.

[0016] Furthermore, the sampling resistor is a short conductor made of metal or alloy, with uniformly distributed small holes on its outer side.

[0017] Furthermore, the square wave signal output by the voltage-controlled PWM module has a frequency of 3kHz and a duty cycle of 45%.

[0018] Furthermore, the step-up transformer uses a GU36 can-type ferrite transformer, and the optical fiber uses a single-mode communication optical fiber.

[0019] Furthermore, this invention also discloses a method for measuring leakage current of FVOA-type ADSS optical cable based on voltage-controlled PWM, the method comprising the following steps:

[0020] S1, the light signal emitted by the light source is split into two paths, A and B, by the splitter:

[0021] Path A transmits data to the input of the FVOA module via optical fiber;

[0022] The B-channel input optical power module converts the light power into electrical energy, which is used to bias the FVOA module and power the voltage-controlled PWM module.

[0023] S2, the current to be measured is input to the voltage-controlled PWM module and converted into a voltage signal. The voltage-controlled PWM module generates a square wave modulation signal with a corresponding duty cycle according to the voltage value. This signal directly drives the FVOA module to generate an optical PWM signal.

[0024] S3, the FVOA module generates light source light signals and light PWM signals, which are then transmitted to the signal processing module;

[0025] S4, the optical signal transmitted by the FVOA module is converted into an electrical signal by the photodetector PD1. The signal processing module analyzes the duty cycle of the electrical signal, deduces the DC current to be measured, and displays the result.

[0026] Beneficial effects:

[0027] This invention splits the optical signal emitted by the light source into two paths using an optical splitter. One path is used to modulate the FVOA module, and the other path is designed with a voltage-controlled PWM circuit. While achieving the detection purpose, only the duty cycle of the signal needs to be detected, avoiding the influence of fiber optic losses and interface losses on the results, thereby effectively improving the accuracy and response speed of DC current measurement. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the system configuration of the present invention;

[0029] Figure 2 This is a schematic diagram of photoelectric conversion according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the photoelectric PWM signal of the present invention;

[0031] Figure 4 This is a schematic diagram illustrating the basic principle of the FVOA module of the present invention;

[0032] Figure 5 This is a schematic diagram illustrating the effect of the bias voltage on the change in optical power according to the present invention.

[0033] Figure 6 This is a schematic diagram of the sampling resistor of the present invention;

[0034] Figure 7 This is a schematic diagram of the optical power supply module of the present invention; Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] like Figure 1 As shown, this invention discloses an FVOA-type ADSS optical cable leakage current fiber optic measurement system based on voltage-controlled PWM. The system includes an FVOA module, a voltage-controlled PWM module, a splitter module, and a signal processing module.

[0037] The FVOA module consists of a silicon substrate and a silicon nitride grating suspended on the silicon substrate. It is used to adjust the light attenuation based on the modulation signal output from the voltage-controlled PWM module as an external driving voltage.

[0038] The voltage-controlled PWM module is connected to the FVOA module to convert the voltage signal into a square wave signal whose duty cycle varies with the voltage, and to drive the FVOA module to generate an optical PWM signal. The voltage-controlled PWM module then transmits the optical PWM signal to the signal processing module.

[0039] The splitting module includes a light source, a splitter, and a light power supply module, which is used to split the optical signal into two paths. The optical signal emitted by the light source enters the splitter and is split into two paths, A and B. Path A is transmitted to the FVOA module through an optical fiber, and path B is connected to the input end of the light power supply module through an optical fiber and connected to the voltage-controlled PWM module from the output end. The light power supply module is used to provide energy for the bias of the FVOA module and to power the voltage-controlled PWM circuit.

[0040] The signal processing module includes a photodetector PD1, which is connected to the output of the FVOA module. It is used to convert the light source light signal and light PWM signal generated by the FVOA module into electrical signals and display the results.

[0041] The optical power supply module, starting from the light source entering the B-path, sequentially includes and connects the following: photodetector PD2, step-up transformer, and rectifier filter. The step-up transformer uses a GU36 can-type ferrite transformer. The structure of the optical power supply module is as follows: Figure 7 As shown.

[0042] The output light from path B passes through the power fiber and enters the photodetector (PD2) for photoelectric conversion, specifically as follows: Figure 2 As shown, this embodiment uses an OPF472 series silicon-based photodiode as the photodetector PD2 to convert the AC optical signal into an AC electrical signal. After being stepped up by a transformer, the signal is rectified and filtered to output a DC electrical signal. This DC electrical signal powers the voltage-controlled PWM circuit and provides energy for the bias of the FVOA module. Another path outputs optical transmission into the FVOA module to generate an optical signal, which is then sent to the photodetector (PD1) to be converted into an electrical signal. Since the electrical signal generated from this optical signal is affected by the optical fiber, it can lead to errors in the judgment of experimental results. Therefore, it is necessary to consider another set of more stable photoelectric signals for observation and inference, which is the innovation of this invention.

[0043] The input terminal of the voltage-controlled PWM module is connected to a Rogowski coil. A sampling resistor is connected in series with the Rogowski coil to convert the DC current at the signal terminal under test into a voltage signal, which is then applied to the PWM module as a drive signal. When the DC current under test flows through the Rogowski coil, a millivolt-level voltage proportional to the current under test appears across the Rogowski coil. This voltage, after passing through the voltage-controlled PWM module, outputs a square wave signal with a duty cycle varying with the voltage. In this embodiment, the square wave signal output by the voltage-controlled PWM module has a frequency of 3kHz and a duty cycle of 45%. This square wave signal is used as the modulation signal to drive the FVOA module, generating an identical optical PWM signal. The optical PWM signal is then sent via optical fiber to the photodetector PD1, where it is converted into an electrical signal, such as... Figure 3 As shown, the magnitude of the current to be measured can be deduced by using a dedicated signal measurement circuit or by manually calculating the duty cycle of the PWM signal.

[0044] The structure and working principle of the FVOA module are as follows:

[0045] The voltage to be measured is connected to the driver terminal of the FVOA module via a Zener diode. The voltage applied to the FVOA module modulates the optical signal output from the light source. The magnitude of the voltage acting on the device can be indirectly obtained through the change in the optical signal. The main components inside the FVOA module are a silicon substrate and a silicon nitride grating suspended on the silicon substrate. When coherent light is incident on the FVOA module through an optical fiber, it is reflected at the surfaces of the silicon substrate and the silicon nitride grating. The two reflected beams interfere due to the optical path difference, which is related to the distance between the silicon substrate and the silicon nitride grating. When a voltage is applied to the FVOA module, the electrostatic force changes the distance between the silicon substrate and the silicon nitride grating, thereby changing the interference optical path difference and causing the interference phenomenon to change between constructive and destructive interference. Assuming the wavelength of the coherent light is λ, when the distance between the silicon substrate and the silicon nitride grating is... At times, such as Figure 4 (a) The incident light undergoes total internal reflection when the distance between the silicon substrate and the silicon nitride grating is... At times, such as Figure 4 (b) The incident light will diffract into higher-order diffraction modes. The relationship between the attenuation of light by the FVOA module and the driving voltage applied to it can be expressed as:

[0046] P O =P i ·K(V i )

[0047] In the formula, Vi is the driving voltage applied to the FVOA module, Pi and Po are the input and output optical power of the FVOA module, respectively, and K(Vi) is the attenuation function of the FVOA module. Because the FVOA module uses a symmetrical structure, its polarization dependent loss (PDL) is only 0.2 dB. Therefore, only single-mode optical fiber is needed, eliminating the need for polarization-maintaining fiber, which greatly reduces cost and increases stability. Furthermore, the FVOA module using this method has a short grating movement distance, resulting in fast response and large bandwidth.

[0048] The control principle of a voltage-controlled PWM (Pulse Width Modulation) module is as follows: The basic principle of PWM control is to use a pulse signal with a constant period but a variable duty cycle to simulate the change of a continuous signal; by adjusting the pulse width and frequency, the intensity, speed, or other parameters of the output signal can be controlled. In this embodiment, the voltage-controlled PWM circuit first generates a PWM signal proportional to the input signal, and its duty cycle is proportional to the input voltage. This PWM signal drives the FVOA module to generate an identical optical PWM signal. After the receiver receives the PWM signal, it demodulates its duty cycle and can then recover the original voltage signal.

[0049] Regarding bias (bias voltage), since the change in optical power directly affects the receiver's output voltage range, when the input signal amplitude is constant, a bias voltage with a larger change in optical power should be selected to ensure optimal performance of the FVOA module. Because the signal under test is a symmetrical sinusoidal signal with positive and negative half-cycles, if the FVOA module has no bias (i.e., the bias voltage is 0), the corresponding change in optical power during measurement is ΔP1; when a certain bias voltage is provided to the FVOA module, the change in optical power when measuring the same magnitude of sinusoidal signal is ΔP2. Figure 5 It can be seen that the value of ΔP2 is much larger than the value of ΔP1, which means that the voltage output range of the optical receiver can be wider when biased. Therefore, a certain bias voltage should be applied to the FVOA module.

[0050] Figure 6 The diagram shows a sampling resistor, also known as a current sensing resistor, current detection resistor, or current sensing resistor. It is typically connected in series in a circuit to convert current into a voltage signal for measurement. Generally, the resistance value of a sampling resistor is chosen to be below 1Ω, belonging to the milliohm range. However, some resistors require higher resistance values ​​to meet specific requirements, such as sampling voltage. This results in a larger base resistance, leading to greater errors. To reduce errors, high-precision resistors are needed. However, increased precision comes at the cost of higher cost. This sampling resistor is based on the principle that a voltage is generated across a resistor when a direct current flows through it, and is commonly used to measure direct current. Essentially, it is a short conductor, which can be made of metal or alloy, with evenly distributed small holes on the outside. The shielding gas ejected from the welding torch passes through a Rogowski coil and is ejected in a laminar flow pattern to improve the protection effect. It is mainly designed for measuring large direct currents, and its rated current corresponds to its rated output voltage, meaning that a large current is converted into a small voltage for measurement through a very small internal resistor. To more accurately detect the current signal at the high-voltage end, the sampling resistor used in this invention can operate under high current. Since an increase in the surface temperature of the resistor leads to a change in its internal resistance, thus affecting detection accuracy, the system has certain requirements regarding the temperature drift of the Rogowski coil. To minimize the impact of temperature on detection accuracy, a sampling resistor with low temperature drift, low power coefficient, and low thermal potential energy is selected.

[0051] For ease of understanding, the working principle of the voltage-controlled PWM module driving the FVOA module is as follows:

[0052] The system achieves high-precision, fast-response measurement of DC current through the collaborative operation of a voltage-controlled PWM (PWM) module and an FVOA (Fulfilled VOA) module. The system workflow includes DC current signal conversion, PWM modulation, FVOA response, and photoelectric conversion, ultimately completing the accurate measurement of the DC current under test. The specific process is as follows:

[0053] DC-DC signal conversion: In the DC current measurement circuit, the input of the voltage-controlled PWM module is connected in series with a Rogowski coil through a sampling resistor to the circuit under test for signal conditioning. According to Ohm's law, when the DC current I to be measured flows through the sampling resistor, a voltage Vshunt proportional to the current intensity is generated across the sampling resistor, and its mathematical expression is Vshunt. shunt =I*R shunt Where Rshunt is the resistance value of the sampling resistor. This voltage drop serves as the electrical signal to be measured.

[0054] Voltage-Controlled PWM (VDC) Module Signal Modulation: The VDC module receives a voltage signal Vshunt from a sampling resistor. The integrated voltage-to-duty-cycle conversion circuit converts the input voltage signal into a PWM square wave signal with an adjustable duty cycle, based on preset conversion characteristics. The conversion relationship can be expressed as D = f(Vshunt). shunt ), where D is the duty cycle of the output PWM signal. Under ideal linear operating conditions, the conversion relationship satisfies D = K * V. shunt The proportional coefficient K is determined by the hardware parameters and circuit design of the voltage-controlled PWM module. Through this conversion process, the continuously changing DC voltage signal is modulated into a discrete pulse signal, effectively improving the signal's anti-interference capability and transmission performance.

[0055] The FVOA module performs electro-optical conversion: the PWM square wave signal output from the voltage-controlled PWM module is applied to the FVOA module as a driving source. The electro-optical conversion unit inside the FVOA module is based on the semiconductor light-emitting principle, converting the input electrical signal into an optical signal. During the electro-optical conversion process, the duty cycle of the optical PWM signal is strictly kept consistent with the duty cycle of the input electrical signal, that is, the duty cycle of the output optical PWM signal is also D.

[0056] Optical Signal Transmission and Photoelectric Conversion: The PWM optical signal generated by the FVOA module is transmitted via optical fiber. Optical fiber, as the optical signal transmission medium, ensures the integrity and stability of the optical signal during transmission due to its low attenuation, high insulation, and strong resistance to electromagnetic interference. After the PWM optical signal is transmitted to the photodetector PD1, PD1 converts the optical signal into an electrical signal based on the photoelectric effect. During the photoelectric conversion process, the amplitude of the output electrical signal is linearly related to the intensity of the input optical signal. Since the duty cycle of the PWM optical signal is D, the converted electrical signal completely retains the duty cycle characteristics of the PWM signal.

[0057] Current parameter inversion calculation: The electrical signal output by photodetector PD1 is digitized, and the duty cycle D of the PWM signal is accurately calculated using a dedicated signal measurement circuit. Combining the voltage-duty cycle conversion relationship of the voltage-controlled PWM module and the voltage-current relationship of the sampling resistor, the calculation expression for the DC current to be measured can be derived through formula derivation:

[0058]

[0059] This calculation process enables the determination of the magnitude of the DC current to be measured from the final measured PWM signal duty cycle parameter, thus completing the entire DC current measurement process.

[0060] The overall execution flow of this system is as follows:

[0061] The light signal emitted by the S1 light source is split into two paths, A and B, by a splitter:

[0062] Path A transmits data to the input of the FVOA module via optical fiber;

[0063] The B-channel input optical power module converts the light into electrical energy, which powers the bias voltage of the FVOA and the voltage-controlled PWM module.

[0064] The S2 current under test is input to the voltage-controlled PWM module, which converts it into a voltage signal. The voltage-controlled PWM module generates a square wave modulation signal with a corresponding duty cycle based on the voltage value. This signal directly drives the FVOA module to generate an optical PWM signal.

[0065] The S3FVOA module generates light signals and optical PWM signals from the light source and transmits them to the signal processing module.

[0066] The optical signal transmitted by the S4FVOA module is converted into an electrical signal by the photodetector PD1. The signal processing module analyzes the duty cycle of the electrical signal, deduces the DC current to be measured, and displays the result.

[0067] The foregoing description of the embodiments enables those skilled in the art to make or use the present invention. Various modifications to the embodiments will be readily apparent to those skilled in the art. The general principles of the invention may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention should not be limited to the embodiments shown herein, but should cover the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fiber optic measurement system for leakage current of FVOA-type ADSS optical cable based on voltage-controlled PWM, characterized in that, The system includes an FVOA module, a voltage-controlled PWM module, a branching module, and a signal processing module; The FVOA module consists of a silicon substrate and a silicon nitride grating suspended on the silicon substrate, used to drive the voltage and adjust the light attenuation. The voltage-controlled PWM module is connected to the FVOA module and is used to convert the DC current to be measured into a voltage signal, and then into a square wave signal with a duty cycle that varies with the voltage as a modulation signal to drive the FVOA module to generate an optical PWM signal. The FVOA module then transmits the optical PWM signal to the signal processing module. The splitting module includes a light source, a splitter, and an optical power supply module. It is used to split the light signal emitted by the light source into two paths, A and B, after entering the splitter. Path A is transmitted to the FVOA module through optical fiber, and path B is transmitted to the input end of the optical power supply module through optical fiber and transmitted from the output end of the optical power supply module to the voltage-controlled PWM module. The optical power supply module is used to supply bias power to the FVOA module and power the voltage-controlled PWM module. The signal processing module includes a photodetector PD1, which is connected to the output of the FVOA module. The photodetector PD1 is used to convert the light source light signal and light PWM signal transmitted by the FVOA module into an electrical signal, calculate the duty cycle, and obtain the magnitude of the DC current to be measured.

2. The fiber optic measurement system for leakage current of FVOA-type ADSS optical cable based on voltage-controlled PWM according to claim 1, characterized in that, The light power supply module includes a photodetector PD2, a step-up transformer, and a rectifier filter connected in sequence from the direction where the light source enters B.

3. The fiber optic measurement system for leakage current of FVOA type ADSS optical cable based on voltage-controlled PWM according to claim 1, characterized in that, The input terminal of the voltage-controlled PWM module is connected to a Rogowski coil. A sampling resistor is connected in series with the Rogowski coil to convert the DC current to be measured into a voltage signal, which is then applied to the voltage-controlled PWM module as a drive signal. When the DC current to be measured flows through the Rogowski coil, a millivolt-level voltage proportional to the DC current to be measured appears across the Rogowski coil. After passing through the voltage-controlled PWM module, this voltage outputs a square wave signal with a duty cycle that varies with the voltage. This square wave signal is used as the modulation signal for the FVOA module to drive the FVOA module to generate an optical PWM signal identical to the square wave signal. The optical PWM signal is then sent via optical fiber to the photodetector PD1 to be converted into an electrical signal. The duty cycle of the electrical signal is calculated, and the magnitude of the DC current to be measured is deduced from this calculation. The deduction formula is as follows: Where D is the duty cycle of the electrical signal, V shunt To generate a voltage across the sampling resistor that is proportional to the current intensity, K is the proportionality coefficient.

4. The fiber optic measurement system for leakage current of FVOA type ADSS optical cable based on voltage-controlled PWM according to claim 3, characterized in that, The sampling resistor is a short conductor made of metal or alloy, with evenly distributed small holes on its outer side.

5. The fiber optic measurement system for leakage current of FVOA type ADSS optical cable based on voltage-controlled PWM according to claim 1, characterized in that, The square wave signal output by the voltage-controlled PWM module has a frequency of 3kHz and a duty cycle of 45%.

6. The fiber optic measurement system for leakage current of FVOA type ADSS optical cable based on voltage-controlled PWM according to claim 2, characterized in that, The step-up transformer uses a GU36 can-type ferrite transformer, and the optical fiber uses a single-mode communication optical fiber.

7. The method for measuring leakage current of FVOA type ADSS optical cable based on voltage-controlled PWM according to any one of claims 1-6, characterized in that, The method includes the following steps: S1, the light signal emitted by the light source is split into two paths, A and B, by the splitter: Path A transmits data to the input of the FVOA module via optical fiber; The B-channel input optical power module converts the light power into electrical energy, which is used to bias the FVOA module and power the voltage-controlled PWM module. S2, the current to be measured is input to the voltage-controlled PWM module and converted into a voltage signal. The voltage-controlled PWM module generates a square wave modulation signal with a corresponding duty cycle according to the voltage value. This signal directly drives the FVOA module to generate an optical PWM signal. S3, the FVOA module generates light source light signals and light PWM signals, which are then transmitted to the signal processing module; S4, the optical signal transmitted by the FVOA module is converted into an electrical signal by the photodetector PD1. The signal processing module analyzes the duty cycle of the electrical signal, deduces the DC current to be measured, and displays the result.

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