A system and method for real-time simulation of full-core neutron flux signals in a reactor

Abstract

The application discloses a system and method for simulating full reactor neutron flux signals in real time, which comprises a core detector simulation data pool, a calculation unit and n output control units; the core detector simulation data pool outputs simulation data and transmits the simulation data to the calculation unit; the calculation unit converts the simulation data output by the core detector simulation data pool into output data corresponding to each output channel and transmits the output data to the corresponding output control units for dynamic simulation output. The application can stably simulate the signal output of a reactor neutron detector, provides a stable, reliable and high-precision signal source for a core neutron flux measurement system, provides a stable and reliable signal source for equipment testing, debugging, inspection and other links, and greatly reduces the workload of each link.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor equipment inspection and verification technology, specifically to a system and method for real-time simulation of the neutron flux signal of the entire reactor. It can stably simulate the signal output of the reactor's self-powered neutron detector, solving problems such as the large workload and human error caused by too many measurement points in the precision debugging and measurement during the equipment development stage and the inspection and testing during the equipment manufacturing stage. It also provides a testing environment for equipment reliability verification and core algorithm verification. Background Technology

[0002] The reactor core neutron flux measurement system acquires core neutron flux data by collecting the current signal from the core neutron detector. This data can be used to calculate a series of important reactor safety parameters online, such as the three-dimensional power distribution of the reactor core, the linear power density (LPD) of fuel assemblies, and the deviated nucleus boiling ratio (DNBR). Neutron flux data measurement is crucial for reactor safe operation, fuel management, and physics experiments. Therefore, for the core neutron flux measurement system, signal acquisition from the core neutron detector is paramount, requiring extremely high accuracy and reliability.

[0003] Calculating the three-dimensional power distribution of the entire reactor requires setting up a large number of measurement points. Taking a pressurized water reactor nuclear power plant as an example, the reactor core has 44 × 7 neutron detector test points. The current signal of the sensor at each test point is extremely weak and easily affected by external interference. Due to the special nature of the neutron flux measurement system, the development and production of the entire system have been greatly challenged.

[0004] 1. Due to the large number of measurement points and the fact that each measurement point contains an extremely weak signal, the verification and testing of functional performance is quite complicated.

[0005] 2. Furthermore, due to the special nature of the reactor environment, it is difficult to build an actual environment, making it challenging to verify the stability, reliability, and adaptability of the equipment to the actual reactor.

[0006] 3. A series of physical, thermal, and hydraulic algorithms, such as total reactor power distribution, LPD, and DNBR, cannot be effectively verified;

[0007] 4. The real-time reactor data collected and stored cannot be reviewed in actual measurement equipment, thus providing a basis for further correction and improvement of the equipment's functions and algorithms. Summary of the Invention

[0008] To address the problems of existing neutron flux measurement systems, such as numerous measurement points, weak signals, and susceptibility to external interference, which lead to cumbersome and labor-intensive precision debugging and measurement during equipment development and inspection and testing during equipment manufacturing, as well as difficulties in verifying equipment reliability, this invention provides a system and method for real-time simulation of the entire reactor core neutron flux signal. This invention can stably simulate the signal output of reactor neutron detectors, providing a stable, reliable, and high-precision signal source for the core neutron flux measurement system. It provides a stable and reliable signal source for equipment testing, debugging, and inspection, greatly reducing the workload at each stage and simplifying testing procedures. Simultaneously, it can provide simulation of the entire reactor core neutron flux signal for the core neutron flux measurement system, providing a reliable environment for the stability, reliability, and core algorithm verification of the system.

[0009] This invention is achieved through the following technical solution:

[0010] A system for real-time simulation of the total neutron flux signal of a reactor reactor, comprising:

[0011] It includes a core detector analog data pool, computing units, and n output control units; n is a positive integer;

[0012] The core detector's analog data pool outputs analog data and transmits it to the computing unit.

[0013] The computing unit converts the analog data output from the core detector's analog data pool into the output data for each corresponding output channel and transmits it to the corresponding output control unit.

[0014] One of the output control units includes an FPGA controller, m-channel D / A modules and m-channel V / I modules; and the m-channel D / A modules and m-channel V / I modules are configured in a one-to-one correspondence; m is a positive integer greater than or equal to 3;

[0015] The FPGA controller independently controls the on / off state of each D / A module and sends the converted output data.

[0016] The D / A module outputs an analog voltage signal to the corresponding V / I module;

[0017] The V / I module converts an analog voltage signal into a current signal output by an analog detector.

[0018] In a preferred embodiment, the system of the present invention further includes an m-channel output module; and the m-channel output module and the m-channel V / I module are configured in a one-to-one correspondence.

[0019] The output module is used to filter and output the current signal output by its corresponding V / I module.

[0020] In a preferred embodiment, the system of the present invention further includes an A / D detection module;

[0021] The A / D detection module is used to detect the output signals of the m output modules respectively and feed them back to the FPGA controller for adjustment to ensure high-precision output of real-time analog data.

[0022] In a preferred embodiment, the core detector simulation data pool of the present invention includes actual dynamic data of the reactor neutron detector, calibration data of equipment inspection and testing, algorithm simulation data and other simulation data collected and stored.

[0023] In a preferred embodiment, the V / I module of the present invention includes a first operational amplifier U1, a second operational amplifier U2, a third operational amplifier U3, and a transistor Q1;

[0024] Specifically, the analog voltage signal Vi output by the D / A module is compared with the feedback voltage Vf output by the third operational amplifier U3, which is input to the first operational amplifier U1. An output voltage V1 is obtained at the output terminal of the first operational amplifier U1. The output voltage V1 controls the output voltage V2 of the second operational amplifier U2. The output voltage V2 is input to the base of the transistor Q1, thereby changing the output current I of the transistor Q1. The output current I of the transistor Q1 is related to the feedback voltage Vf, thus enabling the feedback voltage Vf to track the analog voltage signal Vi.

[0025] On the other hand, the present invention proposes a method for real-time simulation of the whole-reactor neutron flux signal, comprising:

[0026] A core detector analog data pool, a computing unit, and n output control units are provided; each output control unit includes an FPGA controller, m D / A modules, and m V / I modules; and the m D / A modules and m V / I modules are configured in a one-to-one correspondence, where m is a positive integer greater than or equal to 3 and n is a positive integer;

[0027] Simulated data is output through the simulated data pool of the core detector;

[0028] The computing unit converts the analog data output from the core detector's analog data pool into the output data for each corresponding output channel and transmits it to the corresponding output control unit.

[0029] The FPGA controller independently controls the on / off state of each D / A module and sends the converted output data.

[0030] The D / A module outputs an analog voltage signal to the corresponding V / I module.

[0031] The analog voltage signal is converted into a current signal output by the analog detector using the V / I module shown.

[0032] In a preferred embodiment, the method of the present invention further includes:

[0033] An m-channel output module is provided, and each of the m-channel output module and the m-channel V / I module are configured to correspond one-to-one. The current signal output by the corresponding V / I module is filtered and output through the output module.

[0034] In a preferred embodiment, the method of the present invention further includes:

[0035] An A / D detection module is provided to detect the output signals of the m output modules respectively and feed them back to the FPGA controller for adjustment to ensure high-precision output of real-time analog data.

[0036] In a preferred embodiment, the core detector simulation data pool of the present invention includes collected and stored actual dynamic data of the reactor neutron detector, calibration data of equipment inspection and testing, algorithm simulation data, and other simulation data.

[0037] In a preferred embodiment, the V / I module of the present invention includes a first operational amplifier U1, a second operational amplifier U2, a third operational amplifier U3, and a transistor Q1;

[0038] Specifically, the analog voltage signal Vi output by the D / A module is compared with the feedback voltage Vf output by the third operational amplifier U3, which is input to the first operational amplifier U1. An output voltage V1 is obtained at the output terminal of the first operational amplifier U1. The output voltage V1 controls the output voltage V2 of the second operational amplifier U2. The output voltage V2 is input to the base of the transistor Q1, thereby changing the output current I of the transistor Q1. The output current I of the transistor Q1 is related to the feedback voltage Vf, thus enabling the feedback voltage Vf to track the analog voltage signal Vi.

[0039] The present invention has the following advantages and beneficial effects:

[0040] This invention obtains calibration data from a real-time simulated detector data pool, enabling real-time and accurate simulation of reactor neutron detector signal output. This provides a stable, reliable, and high-precision signal source for the reactor core neutron flux measurement system, greatly facilitating the debugging, testing, experimentation, and inspection of equipment development and manufacturing. It significantly reduces the workload and complexity of testing, while also providing a reliable standard source for verifying the reliability and stability of the equipment.

[0041] This invention can simultaneously acquire actual core operation data from the core detector simulation data pool, simulate the current signals output by the reactor neutron detectors in real time, and simulate the core state under various operating conditions such as reactor start-up, criticality, power increase, power decrease, and emergency shutdown, providing an effective verification environment for core algorithms. Furthermore, it can dynamically restore all neutron detector signals collected and stored by the reactor core neutron flux measurement system for further precise data analysis and computation. Attached Figure Description

[0042] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0043] Figure 1 This is a system principle block diagram according to an embodiment of the present invention.

[0044] Figure 2 This is a block diagram illustrating the principle of the simulated data pool for the reactor core detector in an embodiment of the present invention.

[0045] Figure 3 This is a circuit diagram of the V / I module according to an embodiment of the present invention. Detailed Implementation

[0046] In the following, the terms “comprising” or “may include” as used in various embodiments of the invention indicate the presence of an inventive function, operation, or element, and do not limit the addition of one or more functions, operations, or elements. Furthermore, as used in various embodiments of the invention, the terms “comprising,” “having,” and their cognates are intended only to indicate a specific feature, number, step, operation, element, component, or combination of the foregoing, and should not be construed as primarily excluding the presence of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing, or adding one or more combinations of the foregoing.

[0047] In various embodiments of the invention, the expression "or" or "at least one of A and / or B" includes any combination or all combinations of the words listed simultaneously. For example, the expression "A or B" or "at least one of A and / or B" may include A, may include B, or may include both A and B.

[0048] The expressions used in the various embodiments of the present invention (such as "first," "second," etc.) may modify various constituent elements in the various embodiments, but do not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing one element from other elements. For example, a first user device and a second user device refer to different user devices, although both are user devices. For example, a first element may be referred to as a second element without departing from the scope of the various embodiments of the present invention, and similarly, a second element may also be referred to as a first element.

[0049] It should be noted that if a description is made of "connecting" one component to another, then the first component can be directly connected to the second component, and a third component can be "connected" between the first and second components. Conversely, when a component is "directly connected" to another component, it can be understood that there is no third component between the first and second components.

[0050] The terminology used in the various embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the various embodiments of the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the invention pertain. The terms (such as those defined in a generally used dictionary) are to be interpreted as having the same meaning as in the context of the relevant technical field and are not to be interpreted as having an idealized or overly formal meaning, unless clearly defined in the various embodiments of the invention.

[0051] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0052] Example

[0053] To address the challenges of high workload and tedious procedures in equipment development and manufacturing, such as debugging, testing, and experimentation, as well as the difficulty in verifying equipment reliability and stability, this embodiment provides a system for real-time simulation of the entire reactor neutron flux signal. The system in this embodiment mainly includes a core detector simulation data pool, a computing unit, and n output control units, as shown below. Figure 1-2 As shown in the diagram. Each output control unit includes an FPGA controller, an A / D detection module, m-channel D / A modules, m-channel V / I modules, m-channel filtering / output modules, etc., and its structure is as follows. Figure 1 As shown in the diagram. In this embodiment, n and m are determined by the number of detectors (i.e., the number of measurement points) and the number of FPGA I / Os, where n is a positive integer and m is a positive integer greater than or equal to 3. The core detector's analog data pool transmits analog data to the computing unit, which converts the analog data into output data for each corresponding output channel. The computing unit then transmits the converted output data and control commands to the FPGA controller in the output control unit. The FPGA controls the n-channel D / A module circuits to output different data precisely. The n-channel D / A module circuits are connected one-to-one with the n-channel V / I module circuits, and the n-channel V / I module circuits are connected one-to-one with the n-channel filter / output module circuits. The D / A module circuit outputs a voltage signal to its corresponding V / I module circuit for V / I conversion. After processing by the corresponding filter / output circuit, it outputs a current signal from a real analog detector. The A / D detection circuit is used to perform feedback detection on the output current signal and transmits the detection result to the FPGA controller for adjustment to ensure high-precision output of real-time analog data.

[0054] The core detector analog data pool is the source of data for the entire system. The computing unit integrates and controls the data to provide corresponding real-time analog data output to the output control unit. The core detector analog data pool outputs analog data to the computing unit, which converts the analog data into D / A output data and allocates it to the corresponding output channels. The computing unit then sends the D / A output data and switching commands of each channel to the FPGA controller of the output control unit via the data bus. The FPGA controller can perform individual on / off control and data transmission operations for each D / A module circuit in the backend. In this way, the FPGA controller can simultaneously and accurately control multiple D / A analog circuits to output different data precisely. The D / A analog circuit outputs a voltage signal to V / I, which is then converted into a current signal of a real analog detector.

[0055] To accurately and reliably simulate this signal, the system output signal may experience fluctuations or deviations due to different loads connected to it. To avoid this problem, a filter is added to the system output to minimize interference from the load. An A / D conversion circuit is also included to provide feedback adjustment of the output result, ensuring high-precision output of real-time simulation data. In this way, the entire system can completely and accurately simulate the self-sufficient neutron flux signal of a complete reactor in real time.

[0056] Furthermore, such as Figure 2As shown, the core detector simulation data pool primarily provides the computing unit with real-time, dynamic simulation data. The data pool's data sources mainly include four: actual dynamic data from the reactor neutron detectors collected and stored by the online core neutron flux measurement and processing system; calibration data from equipment testing; core physics algorithm simulation data (i.e., core data calculated by simulating core changes through algorithms); and other simulation data (i.e., manually input custom data) that can be used to debug the neutron flux signal acquisition equipment. Then, the data from the data sources is input to the computing unit for integration processing (converting the data in the data pool into data corresponding to each output channel and allocating it to the corresponding output channel). The computing unit integrates the data according to the distribution relationship of the multiple detectors, converts it into corresponding digital voltage signals, and transmits them to the output control unit. The output control unit then performs real-time dynamic simulation output based on timeliness requirements.

[0057] The primary function of an FPGA controller is to simultaneously and independently control multiple D / A module circuits using the FPGA's multiple I / O channels, achieving fully synchronous DA data output to ensure the timeliness of multi-channel data synchronization. A typical reactor has hundreds of neutron flux measurement points across the entire reactor. By deploying multiple output control units connected via a bus, hundreds of analog neutron flux signals can be simultaneously output to accommodate neutron flux signal simulations for reactors of different sizes. For example, if 200 neutron flux signals need to be simulated simultaneously, but an FPGA controller can only handle a maximum of 20 signals, then 10 FPGA controllers can be used to achieve the output of 200 signals, i.e., n = 10 and m = 20.

[0058] The D / A module circuit is mainly used to convert digital voltage signals into analog voltage signals with high precision. The D / A module circuit has high precision requirements and a high output rate in order to simulate neutron flux signals in real time.

[0059] The V / I module circuit is primarily a voltage signal to constant current signal output converter, designed to completely simulate the micro-current signal output of neutron flux. The V / I module circuit employs a low-noise operational amplifier (op-amp), where the offset current is a critical parameter; its maximum offset current must not exceed 1 PA, and its offset voltage also needs to be sufficiently low to ensure the accuracy requirements of the V / I conversion. The D / A module circuit outputs an analog voltage signal to the V / I module circuit, which, after V / I conversion, outputs a high-precision current signal.

[0060] The V / I module circuit is a voltage-to-current converter circuit composed of operational amplifiers, resistors, and transistors. It linearly converts DC voltage signals into current signals. The first operational amplifier U1A acts as a comparator, and the third operational amplifier U3A acts as a voltage follower, forming a negative feedback loop. The input voltage Vi is compared with the feedback voltage Vf, resulting in an output voltage V1 at the output of comparator U1A. V1 controls the output voltage V2 of the second operational amplifier U2A, thereby changing the output current I of transistor Q1. The output current I, in turn, affects the feedback voltage Vf, achieving the goal of tracking the input voltage Vi. Specifically... Figure 3 As shown, the V / I module includes a first operational amplifier U1, a second operational amplifier U2, a third operational amplifier U3, and a transistor Q1. The inverting input of the first operational amplifier U1 is connected to the output signal of the D / A module, the non-inverting input of the first operational amplifier U1 is connected to the output of the third operational amplifier U3, the output of the first operational amplifier U1 is connected to its inverting input via resistor R2, and the output of the first operational amplifier U1 is connected to the inverting input of the second operational amplifier U2 via resistor R5. The non-inverting input of the second operational amplifier U2 is grounded via resistor R6, the output of the second operational amplifier U2 is connected to the base of transistor Q1, the source of transistor Q1 is connected to the power supply VCC, the drain of transistor Q1 is connected to the inverting input of the third operational amplifier U3 via resistor RL, and the drain of transistor Q1 is grounded sequentially via resistors RL, R7, and RW.

[0061] The output current of transistor Q1 is the output signal of the V / I module.

[0062] The output current I can be calculated using the following formula:

[0063]

[0064] Because of the negative feedback effect, Vi = Vf, the output current I can be expressed as:

[0065]

[0066] In this way, the output current changes with the input voltage, thus achieving the conversion from voltage to current.

[0067] The signal output from the V / I module circuit is fed to the filter / output circuit. The filter / output circuit mainly filters the signal and filters and isolates crosstalk from the load device to ensure the stability of the analog signal output. At the same time, it can control the output or shutdown of the signal.

[0068] The A / D detection module can sample the output current of the filter / output circuit in real time to monitor the accuracy of the simulated neutron flux signal. If the V / I module circuit suffers from insufficient output accuracy due to overheating or other noise, the A / D detection module can provide feedback adjustment to ensure the accuracy of the output simulated neutron flux signal. In this embodiment, the A / D detection module includes n A / D converters, each corresponding to one of the n filter / output modules, and performs feedback detection on each of the n filter / output modules.

[0069] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for real-time simulation of the total neutron flux signal of a reactor reactor, characterized in that, It includes a core detector analog data pool, computing units, and n output control units; n is a positive integer; The core detector's analog data pool outputs analog data and transmits it to the computing unit. The computing unit converts the analog data output from the core detector's analog data pool into the output data for each corresponding output channel and transmits it to the corresponding output control unit. One of the output control units includes an FPGA controller, m-channel D / A modules and m-channel V / I modules; and the m-channel D / A modules and m-channel V / I modules are configured in a one-to-one correspondence; m is a positive integer greater than or equal to 3; The FPGA controller independently controls the on / off state of each D / A module and sends the converted output data. The D / A module outputs an analog voltage signal to the corresponding V / I module; The V / I module converts an analog voltage signal into a current signal output by an analog detector; The core detector simulation data pool includes the actual dynamic data of the reactor neutron detector, the calibration data of equipment inspection and testing, the algorithm simulation data, and other simulation data collected and stored. The system acquires calibration data from the core detector simulation data pool, simulates the reactor neutron detector signal output, provides a signal source for the core neutron flux measurement system, and provides a standard source for verifying the reliability and stability of the equipment. The system also acquires actual core operation data from the core detector simulation data pool, simulates the current signal output by the reactor neutron detector in real time, and simulates the core state under various operating conditions such as reactor start-up, criticality, power increase, power decrease, and emergency shutdown, providing an effective verification environment for core algorithms. The value of n is determined by the total number of neutron flux signals to be simulated and the number of signals that the FPGA controller can process.

2. The system for real-time simulation of the total neutron flux signal of a reactor reactor according to claim 1, characterized in that, It also includes m-channel output modules; and the m-channel output modules and m-channel V / I modules are configured in a one-to-one correspondence. The output module is used to filter and output the current signal output by its corresponding V / I module.

3. A system for real-time simulation of the total neutron flux signal of a reactor reactor according to claim 2, characterized in that, It also includes an A / D detection module; The A / D detection module is used to detect the output signals of the m output modules respectively and feed them back to the FPGA controller for adjustment to ensure high-precision output of real-time analog data.

4. A system for real-time simulation of the total neutron flux signal of a reactor reactor according to any one of claims 1-3, characterized in that, The V / I module includes a first operational amplifier U1, a second operational amplifier U2, a third operational amplifier U3, and a transistor Q1; Specifically, the analog voltage signal Vi output by the D / A module is compared with the feedback voltage Vf output by the third operational amplifier U3, which is input to the first operational amplifier U1. An output voltage V1 is obtained at the output terminal of the first operational amplifier U1. The output voltage V1 controls the output voltage V2 of the second operational amplifier U2. The output voltage V2 is input to the base of the transistor Q1, thereby changing the output current I of the transistor Q1. The output current I of the transistor Q1 is related to the feedback voltage Vf, thus enabling the feedback voltage Vf to track the analog voltage signal Vi.

5. A method for real-time simulation of the total neutron flux signal of a reactor reactor, characterized in that, include: It provides a core detector simulation data pool, a computing unit, and n output control units; One of the output control units includes an FPGA controller, an m-channel D / A module, and an m-channel V / I module; and the m-channel D / A module and the m-channel V / I module are configured in a one-to-one correspondence, where m is a positive integer greater than or equal to 3; and n is a positive integer. Simulated data is output through the simulated data pool of the core detector; The computing unit converts the analog data output from the core detector's analog data pool into the output data for each corresponding output channel and transmits it to the corresponding output control unit. The FPGA controller independently controls the on / off state of each D / A module and sends the converted output data. The D / A module outputs an analog voltage signal to the corresponding V / I module. The analog voltage signal is converted into a current signal output by the analog detector through the V / I module shown. The core detector simulation data pool includes the actual dynamic data of the reactor neutron detector, the calibration data of equipment inspection and testing, the algorithm simulation data, and other simulation data collected and stored. The method acquires calibration data from the core detector simulation data pool, simulates the reactor neutron detector signal output, provides a signal source for the core neutron flux measurement system, and provides a standard source for verifying the reliability and stability of the equipment. The method also acquires actual core operating data from the core detector simulation data pool, simulates the current signal output by the reactor neutron detector in real time, and simulates the core state under various operating conditions such as reactor startup, criticality, power increase, power decrease, and emergency shutdown, providing an effective verification environment for the core algorithm. The value of n is determined by the total number of neutron flux signals to be simulated and the number of signals that the FPGA controller can process.

6. A method for real-time simulation of the total neutron flux signal of a reactor according to claim 5, characterized in that, Also includes: An m-channel output module is provided, and each of the m-channel output module and the m-channel V / I module are configured to correspond one-to-one. The current signal output by the corresponding V / I module is filtered and output through the output module.

7. A method for real-time simulation of the total neutron flux signal of a reactor according to claim 6, characterized in that, Also includes: An A / D detection module is provided to detect the output signals of the m output modules respectively and feed them back to the FPGA controller for adjustment to ensure high-precision output of real-time analog data.

8. A method for real-time simulation of the total neutron flux signal of a reactor according to any one of claims 5-7, characterized in that, The V / I module includes a first operational amplifier U1, a second operational amplifier U2, a third operational amplifier U3, and a transistor Q1; Specifically, the analog voltage signal Vi output by the D / A module is compared with the feedback voltage Vf output by the third operational amplifier U3, which is input to the first operational amplifier U1. An output voltage V1 is obtained at the output terminal of the first operational amplifier U1. The output voltage V1 controls the output voltage V2 of the second operational amplifier U2. The output voltage V2 is input to the base of the transistor Q1, thereby changing the output current I of the transistor Q1. The output current I of the transistor Q1 is related to the feedback voltage Vf, thus enabling the feedback voltage Vf to track the analog voltage signal Vi.

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