Portable electric energy quality detection system and measurement method based on virtual instrument

Abstract

The invention relates to the field of current measurement, in particular to a portable electric energy quality detection system based on a virtual instrument and a measurement method. The signal conversion and conditioning unit is connected with a tested single-phase alternating current, converts high voltage and high current into low voltage signals, and carries out conditioning output through a sampling resistor. The digital-to-analog conversion unit receives the conditioned low-voltage signal, performs analog-to-digital conversion, and transmits a digital signal through a corresponding output interface; and the calculation system unit is connected with the digital-to-analog conversion unit to realize electric energy quality parameter calculation, data storage and alarm. According to the invention, the precision and real-time performance of electric energy quality monitoring are obviously improved, the portability is enhanced through modular design and low-power battery driving, and the manufacturing and maintenance cost is reduced; the functions of parameter analysis, threshold judgment and exception protection are realized, and the intelligent level and the data integrity are improved; the method is suitable for high-requirement scenes such as on-site detection, ensures safe and stable operation of a power grid and reduces economic loss.

Description

Technical Field

[0001] This invention relates to the field of current measurement, and in particular to a portable power quality detection system and measurement method based on a virtual instrument. Background Technology

[0002] Currently, power quality monitoring systems have expanded from single monitoring points to multi-point centralized monitoring, and even to comprehensive monitoring across power supply systems. However, existing power quality monitoring systems still have significant shortcomings.

[0003] Traditional manual detection methods are inefficient, inaccurate, lack real-time performance, and have poor repeatability, failing to meet the high-efficiency requirements of modern power grids. Professional monitoring equipment is bulky, heavy, expensive, has fixed functions, and is complex to operate; meter-based equipment also lacks the necessary accuracy to achieve efficient and precise measurements.

[0004] Furthermore, the existing monitoring system lacks a complete and unified communication standard, has poor real-time performance, poor data timeliness, and cannot promptly identify and improve potential power quality hazards. Data management and utilization are also insufficient, resulting in a single form of information dissemination.

[0005] Therefore, a portable power quality detection system is needed that supports low-power battery operation, can acquire, condition, and convert voltage and current signals of 220V single-phase AC power into analog-to-digital signals, and integrates these signals into a single housing to form a unified structure. Simultaneously, a threshold determination mechanism and data storage and alarm mechanism should be introduced, and a portable power quality detection system and measurement method based on virtual instruments should be adopted using Fast Fourier Transform to improve detection accuracy and efficiency to meet the needs of the current environment. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this section, the abstract and title of the invention. Such simplifications or omissions shall not be used to limit the scope of the present invention.

[0007] Given that the existing technologies mentioned above are characterized by low efficiency, poor accuracy, insufficient real-time performance, and poor repeatability of traditional manual detection methods, they cannot meet the high-efficiency requirements of modern power grids. Professional monitoring equipment is bulky, heavy, expensive, has fixed functions, and is complex to operate. Meter-based equipment also lacks the detection accuracy to achieve efficient and precise measurements.

[0008] Therefore, the technical problem to be solved by the present invention is to design a portable power quality detection system that supports low-power battery drive, can realize the acquisition, conditioning and analog-to-digital conversion of voltage and current signals of 220V single-phase AC power, and is integrated into a housing to form an integrated structure to meet the needs of the current environment.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a portable power quality detection system based on virtual instruments, comprising, The signal conversion and conditioning unit is connected to the single-phase AC power being measured, converts high voltage and high current into low voltage signals, and conditions the output through a sampling resistor. The digital-to-analog converter unit is connected to the output of the signal conversion and conditioning unit. It receives the conditioned low-voltage signal, performs analog-to-digital conversion, and transmits the digital signal through the corresponding output interface. The computing system unit, connected to the digital-to-analog converter unit, realizes the calculation, data storage and alarm of power quality parameters, and enables real-time monitoring and display of voltage deviation, frequency deviation and harmonic analysis.

[0010] As an improvement of the present invention, The signal conversion and conditioning unit includes a voltage transformer, a current transformer, and a sampling resistor; The primary side of the voltage transformer is connected to the live wire and neutral wire of a single-phase AC power supply, and the secondary side is connected to a sampling resistor. The output is a low voltage signal that is proportional to the input voltage. The primary side of the current transformer is connected to the live wire, and the secondary side is connected to the sampling resistor. The output is a low voltage signal that is proportional to the input current. The sampling resistor ensures the accuracy of signal conditioning, converting the transformer output into a voltage signal that can be connected to a digital-to-analog converter.

[0011] As an improvement of the present invention, The digital-to-analog converter unit performs analog-to-digital conversion on the conditioned voltage signal and supports differential input channels connected to sampling resistors for output. The digital-to-analog converter unit transmits data and supplies power to the computing system unit via a USB interface.

[0012] As an improvement of the present invention, The entire system is integrated into the housing, with the signal conversion and conditioning unit, digital-to-analog conversion unit, and computing system unit fixed by screws and connected by ribbon cables.

[0013] Given that the existing monitoring systems lack a complete and unified communication standard, have poor real-time performance, poor data timeliness, are unable to identify and improve potential power quality hazards in a timely manner, and have insufficient data management and utilization, resulting in a single form of information dissemination.

[0014] To solve the above-mentioned technical problems, the present invention provides the following technical solution: Signal acquisition and conversion: The voltage and current signals of the single-phase AC power being measured are conditioned and converted, and then converted from analog to digital to obtain digital signals; Power quality parameters are calculated by converting digital signals from the time domain to the frequency domain using virtual instrument software, extracting fundamental and harmonic components, calculating parameters, and achieving real-time monitoring. Threshold determination involves setting a threshold parameter and comparing the calculated parameters against the threshold. The data storage and alarm process involves selecting parameters for file storage and executing alarm operations based on the threshold determination results.

[0015] As an improvement of the present invention, In the signal acquisition and conversion process, The signal conversion and conditioning unit is connected to single-phase AC power, which is converted into a low-voltage signal through voltage transformers and current transformers, and then conditioned by sampling resistors before being output. The digital-to-analog converter receives the conditioning signal, performs analog-to-digital conversion through the differential input channel, and transmits the digital signal to the computing system unit via the USB interface.

[0016] As an improvement of the present invention, In the power quality parameter calculation process, Discrete time-domain signals are acquired and converted into frequency-domain signals using a fast Fourier transform algorithm to extract the fundamental frequency, amplitude, and harmonic components. The phase of voltage and current signals is obtained using a single-frequency measurement function, and the power factor is calculated. The effective values ​​of the signals are obtained using the periodic average value and the root mean square function, and the effective voltage value Urms, the effective current value Irms, the active power P, the reactive power Q, and the apparent power S are calculated. Calculate the voltage deviation and frequency deviation. The voltage deviation is (actual voltage - rated voltage) / rated voltage × 100%, and the frequency deviation is the actual frequency - rated frequency. The nth harmonic content rate is the percentage of the ratio of the effective value of the nth harmonic to the effective value of the fundamental frequency, and the total harmonic distortion rate is the percentage of the ratio of the root mean square of each harmonic to the effective value of the fundamental frequency. Use harmonic distortion analysis functions to quickly obtain the fundamental frequency, amplitude of each harmonic, and total harmonic distortion rate of a signal.

[0017] As an improvement of the present invention, In the threshold determination process, Alarm thresholds are set according to different types of parameters, and threshold comparisons are performed on the calculated parameters; If any parameter such as voltage deviation, frequency deviation, total harmonic distortion rate, odd harmonic content rate, or even harmonic content rate exceeds the alarm threshold, then there is a parameter abnormality. If the voltage deviation, frequency deviation, total harmonic distortion rate, odd harmonic content, and even harmonic content do not exceed the alarm threshold, then there are no abnormal parameters.

[0018] As an improvement of the present invention, In the data storage and alarm process, The effective value of current, current frequency deviation, effective value of voltage, voltage frequency deviation, voltage deviation, total harmonic distortion of current, and total harmonic distortion of voltage are selected as storage parameters and saved locally to provide experimental reproduction and long-term data management. The system monitors parameter status and uses threshold results to determine whether an alarm light is triggered if the parameter is abnormal; otherwise, it is not triggered.

[0019] The beneficial effects of this invention are: significantly improving the accuracy and real-time performance of power quality monitoring; enhancing portability through modular design and low-power battery drive, reducing manufacturing and maintenance costs; realizing parameter analysis, threshold determination, and anomaly protection functions, improving the level of intelligence and data integrity; suitable for high-requirement scenarios such as on-site testing, ensuring the safe and stable operation of the power grid, reducing economic losses, and providing clear data support and solutions for power users. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a connection architecture diagram of the portable power quality detection system based on virtual instruments in this invention.

[0021] Figure 2 This is a schematic diagram of the analog-to-digital conversion unit of the portable power quality detection system based on virtual instruments in this invention.

[0022] Figure 3 This is a hardware architecture connection diagram of the portable power quality detection system based on virtual instruments in this invention.

[0023] Figure 4 This is a flowchart of the detection calculation and judgment process of the measurement method in this invention. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] Example 1 Reference Figures 1-2 This embodiment provides a portable power quality detection system based on virtual instruments.

[0026] In this scheme, the hardware architecture of the detection system mainly includes a signal conversion and conditioning unit 1, a digital-to-analog conversion unit 2, and a computing system unit 3. The various units within the hardware architecture work collaboratively through specific electrical connections and signal interactions to achieve high-precision monitoring and data processing of power quality.

[0027] Signal conversion and conditioning unit 1, as the core of the device's signal acquisition, is responsible for receiving the single-phase AC power being measured and converting high voltage and high current into low voltage signals. In this scheme, signal conversion and conditioning unit 1 adopts the principle of electromagnetic induction, using a current transformer to achieve voltage and current isolation and proportional conversion, ensuring safe signal transmission. In the subsequent connection architecture, signal conversion and conditioning unit 1 is connected to a high-precision sampling resistor for conditioning output, filtering noise and adjusting signal amplitude to ensure the signal can adapt to the subsequent analog-to-digital conversion requirements.

[0028] The design of the signal conversion and conditioning unit 1 provides reliable signal acquisition support and enhances the system's stability and anti-interference capability through high-precision sampling resistors, making it suitable for real-time monitoring in complex power grid environments.

[0029] The digital-to-analog converter 2 receives the low-voltage signal output from the signal conversion and conditioning unit 1, converts it into a digital signal, and transmits it to the computing system unit 3. The digital-to-analog converter 2 typically supports differential input channels for high-resolution analog-to-digital conversion, ensuring low noise and high-fidelity characteristics of the signal.

[0030] The digital-to-analog converter 2 can achieve data transmission through the corresponding output interface, which can be either USB or serial bus in this solution. This ensures the stable operation of subsequent units under different working conditions and lays the foundation for power quality analysis.

[0031] The computing system unit 3 is the core processing unit of this system, capable of calculating, storing, and alarming power quality parameters. The computing system unit 3 processes digital signals based on software algorithms, including time-domain to frequency-domain conversion to extract fundamental and harmonic components, thereby calculating indicators such as voltage deviation, frequency deviation, harmonic content, and total harmonic distortion.

[0032] The computing system unit 3 also supports a threshold determination mechanism, which can issue an alarm when parameters exceed a preset range. Furthermore, it can store data to a file for subsequent analysis and sharing. The computing system unit 3 is externally connected to a human-computer interaction interface, enabling real-time monitoring and display.

[0033] Example 2 Reference Figures 1-3 This embodiment is based on the previous embodiment, and differs from the previous embodiment in that: The core component of the signal conversion and conditioning unit 1 is the voltage transformer 11. In this scheme, the voltage transformer 11 adopts an iron core structure. The primary winding is connected to the live wire and neutral wire of the single-phase AC power being measured, and the secondary winding is connected to the sampling resistor 13.

[0034] When alternating current is applied to the primary side of voltage transformer 11, the alternating current generates an alternating magnetic field in the iron core. According to Faraday's law of electromagnetic induction, an electromotive force is induced in the secondary winding, enabling the output of a low-voltage signal proportional to the input voltage. The turns ratio of voltage transformer 11 is typically 1:1 or adjusted according to actual needs to ensure that the secondary voltage remains within a safe range.

[0035] In the primary circuit, the primary voltage is 220V, 50Hz AC. After passing through a current transformer with a coil ratio of 1:1, the primary current is the same as the secondary current. The input voltage is calculated using the following formula, obtained by passing a high-precision sampling resistor with a specific resistance value on the secondary side: Where U is the voltage being measured, and α is the transformation ratio. Due to slight differences in the errors of sampling resistor 13 and voltage transformer, this scheme will use a high-precision relay protection tester for verification and calculation. in1 To regulate the transformed voltage, it is connected to digital-to-analog converter unit 2.

[0036] The current transformer 12 is wound around the live wire to pass the measured current. It generates magnetic flux in the magnetic ring or iron core through the principle of electromagnetic induction. The primary winding has few turns (usually one or a few turns), while the secondary winding has many turns. When a primary current flows through, a low-current signal proportional to the input current is induced on the secondary side of current transformer 12d1. This signal is also converted into voltage form by sampling resistor 13. The design of current transformer 12 takes into account electrical isolation, measurement and monitoring, and relay protection functions. The transformation ratio error is also corrected through verification to minimize the effects of sampling resistor error and the transformer's own nonlinearity. Current transformer 12 can handle non-sinusoidal currents generated by nonlinear loads and avoids signal distortion caused by magnetic saturation.

[0037] When a primary current flows through, the iron core generates an alternating magnetic flux, inducing a proportional current in the secondary winding. Then, similarly, the secondary winding passes through a high-precision sampling resistor of a specific resistance value, and the formula for calculating the input current is as follows: Where I is the voltage being measured, β is the turns ratio, and due to slight differences in the errors of sampling resistor 13 and current transformer, this solution can also be used with a high-precision relay protection tester for verification and calculation. in2To regulate the transformed voltage, it is connected to digital-to-analog converter unit 2.

[0038] The sampling resistor 13 is responsible for converting the current signal on the secondary side of the transformer into a voltage signal. The sampling resistor 13 is made of high-precision, low-temperature-coefficient material, and its resistance value is selected according to the actual system requirements to ensure the accuracy and stability of signal conditioning.

[0039] The sampling resistor 13 not only filters out high-frequency noise but also provides impedance matching, converting the transformer output into a voltage signal that can be directly connected to the digital-to-analog converter unit 2. The error of the sampling resistor 13 is compensated through calibration, further improving the fidelity of the overall signal link. The design of the sampling resistor 13 effectively solves the problems of low accuracy and weak anti-interference capability in traditional equipment, ensuring that the signal input to the digital-to-analog converter unit 2 is pure and reliable.

[0040] The analog-to-digital converter 2 is used to convert the conditioned analog signal into a digital signal. The analog-to-digital converter 2 includes a differential input channel and a USB interface. The differential input channel is connected to the output of the sampling resistor 13, senses the conditioned signal, and converts the conditioned signal into digital form.

[0041] Since the signal is typically a differential output, the signal generated by the differential input channel first undergoes noise reduction processing through an internal filtering circuit to filter out grid interference and high-frequency harmonics. The filtered signal then enters the conversion core within the digital-to-analog converter unit 2, where it is digitized via an ADC, supporting at least 16-bit resolution and an appropriate sampling rate.

[0042] The analog-to-digital converter 2 can be connected to the computing system unit 3 via a USB interface or serial bus to achieve data transmission and power supply, ensuring low-power operation and real-time data flow. This design significantly improves anti-interference capabilities and is particularly suitable for power quality monitoring in complex electromagnetic environments, overcoming the shortcomings of existing professional equipment in terms of fixed functions and complex operation.

[0043] The computing system unit 3 is the key component for parameter calculation. It receives the digital signals from the digital-to-analog converter unit 2 and ultimately calculates the power quality parameters using an algorithm. In this solution, the computing system unit 3 utilizes a portable computer platform, namely a tablet computer, to run the corresponding computing software.

[0044] The parameters calculated by the calculation system unit 3 are used to drive the dynamic storage and alarm functions, and also support threshold judgment. When the parameters exceed the corresponding standards, such as GB / T 12325-2008 voltage deviation, GB / T 15945-2008 frequency deviation, and GB / T14549-1993 harmonic limits, the calculation system unit 3 will use a red indicator light to alarm and save the data to an Excel file.

[0045] The computing system unit 3 adopts a low-voltage DC battery power supply design, which ensures portability while providing graphical operation through a touch screen, reducing the user threshold.

[0046] In this system architecture, the output port of the signal conversion and conditioning unit 1 is connected to the digital-to-analog converter unit 2, providing a stable analog signal for the entire system. The secondary sides of the voltage transformer 11 and current transformer 12 output low-voltage signals through the sampling resistor 13, which are then connected to the differential input channel of the digital-to-analog converter unit 2 via a ribbon cable, achieving electrical isolation and signal transmission. The USB interface of the digital-to-analog converter unit 2 transmits digital data and provides power to the computing system unit 3, ensuring seamless integration. The entire system is integrated into a housing; the signal conversion and conditioning unit 1, the digital-to-analog converter unit 2, and the computing system unit 3 are fixed with screws, forming an integrated portable structure that supports low-power battery operation, avoiding dependence on external power sources. This modular architecture enhances system stability and security, making it suitable for demanding scenarios such as new energy and industrial automation.

[0047] Example 3 Reference Figures 1-4 This embodiment is based on the previous embodiment, and differs from the previous embodiment in that: This acquisition method, through signal acquisition and conversion, power quality parameter calculation, threshold determination, and data storage and alarm, combined with power quality calculation mechanism and threshold determination mechanism, can achieve real-time monitoring, parameter analysis, and system protection of voltage deviation, frequency deviation, and harmonics.

[0048] The method is applicable to on-site testing scenarios of 220V single-phase AC power. It uses virtual instrument software to process digital signals, achieving efficient and intelligent power quality assessment, and avoiding the problems of low efficiency, poor accuracy and insufficient real-time performance in traditional methods.

[0049] First, in the signal acquisition and conversion process, signal conversion and conditioning unit 1 acquires the voltage and current signals of the single-phase AC power being measured, performs conditioning and conversion, and then inputs them into digital-to-analog conversion unit 2. Signal conversion and conditioning unit 1 is connected to the AC power being measured, and the high voltage is converted to a low voltage signal on the secondary side by connecting the primary side of voltage transformer 11 to the live wire and neutral wire; the high current is converted to a low current signal on the secondary side by connecting the primary side of current transformer 12 to the live wire. Subsequently, the output is conditioned by high-precision sampling resistor 13, which converts the secondary side signal of the transformer into a suitable voltage form while compensating for errors.

[0050] The analog-to-digital converter 2 receives the conditioned signal and performs analog-to-digital conversion primarily through the differential input channel, supporting noise suppression and signal isolation to ensure high-resolution digitization. After conversion, the signal can be transmitted to the computing system unit 3 via a USB interface to provide basic data for subsequent analysis.

[0051] This process utilizes the principles of electromagnetic induction and differential technology to significantly improve the accuracy and anti-interference capability of signal acquisition, ensuring the reliability and real-time performance of digital signals.

[0052] Subsequently, in the power quality parameter calculation process, some basic power quality parameters are obtained by calculating parameters such as voltage RMS (Urms), current RMS (Irms), active power (P), reactive power (Q), and apparent power (S).

[0053] The formula for calculating the effective voltage value Urms is: The formula for calculating the effective value of current Irms is: The formula for calculating active power P is: The formula for calculating reactive power Q is: The formula for calculating apparent power S is: The formula for calculating the power factor cosφ is: Acquiring discrete time domain signals At that time, by using Fast Fourier Transform to convert the signal into a frequency domain signal, this algorithm can efficiently decompose the discrete-time signal into frequency domain components and obtain the frequency, amplitude, and phase information of the signal. When subsequently calculating voltage and frequency deviations, the voltage deviation is (actual voltage - rated voltage) / rated voltage × 100%, and the frequency deviation is the actual frequency - rated frequency.

[0054] In practical power supply systems, factors such as long-distance power transmission, the connection of various loads, and system layout cause changes in output voltage, resulting in voltage deviations. In actual operation, excessive voltage deviations can affect the stability of the power grid system, cause equipment malfunctions or damage, and lead to serious economic losses. In this study, the measurement object is everyday 220V single-phase AC power. According to the national standard GB / T 12325-2008, its allowable voltage deviation range is between -10% and +7%.

[0055] Frequency deviation is the difference between the actual frequency and the rated frequency in the power supply system, and its calculation formula is as follows: ∆f=f-f0 In the formula, f is the actual power supply frequency, and f0 is the rated power supply frequency.

[0056] In practical power systems, an increase in electrical load can lead to an imbalance between power generation and load, causing changes in system frequency. Faults in the power generation system also alter the system frequency. The addition of a large number of nonlinear loads, with their irregular power transformations, causes frequent interference to the system frequency; if not adjusted in time, this can also result in frequency deviation.

[0057] For 220V single-phase AC power, the rated frequency is 50Hz, and the allowable frequency deviation is within ±0.2Hz. When the installed capacity of the power grid is small, this can be relaxed to within ±0.5Hz.

[0058] In power systems, harmonics are periodic sine waves with frequencies that are integer multiples of the fundamental frequency. For 220V single-phase AC power, if the fundamental frequency is 50Hz, then the second harmonic frequency is 100Hz, the third harmonic frequency is 150Hz, and so on.

[0059] The harmonic content rate is the percentage of the effective value of the voltage / current of the nth harmonic to the effective value of the fundamental voltage / current, calculated using the following formula: Voltage nth harmonic content: Current nth harmonic content: The total harmonic distortion (THD) is the percentage of the ratio of the root mean square value of each harmonic to the effective value of the fundamental frequency. The formula for the voltage THD is: Total harmonic distortion of current The calculation formula is: The total harmonic distortion rate of 220V AC power should be less than 5%, and the content of odd harmonics should not exceed 4%, and the content of even harmonics should not exceed 2%.

[0060] Subsequently, a threshold determination process is performed. Operators pre-set threshold parameters and compare the calculated parameters against these thresholds. Alarm thresholds are set according to different types of parameters, including voltage deviation thresholds of -10% to +7%, frequency deviation thresholds of ±0.5Hz, total harmonic distortion thresholds of 5%, odd harmonic content thresholds of 4%, and even harmonic content thresholds of 2%.

[0061] Next, threshold comparisons are performed on the calculated parameters. If any parameter—voltage deviation, frequency deviation, total harmonic distortion (THD), odd harmonic content, or even harmonic content—exceeds the alarm threshold, then a parameter anomaly exists. If none of these parameters exceed the alarm threshold, then no parameter anomaly exists. This process monitors the parameter status in real time through a step-by-step comparison mechanism, ensuring timely identification of anomalies, thereby supporting stable power grid operation and providing a basis for subsequent alarms.

[0062] Finally, in the data storage and alarm process, the system selects the effective value of current, current frequency deviation, effective value of voltage, voltage frequency deviation, voltage deviation, total harmonic distortion of current, and total harmonic distortion of voltage as storage parameters, thereby enabling data reproduction and long-term data management.

[0063] If the parameters are abnormal, a red alarm light will be triggered; otherwise, a green indicator light will illuminate instead. This testing process can improve the integrity of data and the reliability of the system, ensuring the safe operation of the system when parameters are abnormal and avoiding economic losses and equipment damage.

[0064] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A portable power quality detection system based on virtual instrument, characterized in that: Comprising, signal conversion and conditioning unit (1) access to the measured single-phase alternating current, high voltage and high current conversion to low voltage signal, and through the sampling resistance conditioning output; digital-to-analog conversion unit (2) connected to the output of the signal conversion and conditioning unit (1), receiving the conditioned low voltage signal, analog-to-digital conversion, and through the corresponding output interface transmission digital signal; computing system unit (3) connected to the digital-to-analog conversion unit (2), realizing power quality parameter calculation, data storage and alarm, realizing real-time monitoring and display of voltage deviation, frequency deviation and harmonic analysis.

2. The portable power quality detection system based on virtual instrument according to claim 1, characterized in that: the signal conversion and conditioning unit (1) comprises a voltage transformer (11), a current transformer (12) and a sampling resistor (13); the voltage transformer (11) is connected to the live wire and the neutral wire of the single-phase alternating current on the primary side, and the secondary side is connected to the sampling resistor (13) to output a low voltage signal proportional to the input voltage; the current transformer (12) is connected to the live wire on the primary side, and the secondary side is connected to the sampling resistor (13) to output a low voltage signal proportional to the input current; the sampling resistor (13) ensures the accuracy of signal conditioning and converts the transformer output into a voltage signal that can be connected to the digital-to-analog conversion unit (2).

3. The portable power quality detection system based on virtual instrument according to claim 2, characterized in that: the digital-to-analog conversion unit (2) realizes analog-to-digital conversion of the conditioned voltage signal, supports differential input channel connection to the output of the sampling resistor (13), the digital-to-analog conversion unit (2) transmits data and supplies power to the computing system unit (3) through the USB interface.

4. The portable power quality detection system based on virtual instrument according to any one of claims 1-3, characterized in that: the system is integrated in the shell, and the signal conversion and conditioning unit (1), the digital-to-analog conversion unit (2) and the computing system unit (3) are fixed by screws and connected by wire.

5. A method of measurement, characterized by: The portable power quality detection system based on virtual instrument of claim 4, and signal acquisition and conversion, the voltage and current signals of the measured single-phase alternating current are conditioned and converted, and then subjected to analog-to-digital conversion to obtain digital signals; power quality parameter calculation, based on virtual instrument software, time domain to frequency domain conversion is performed on the digital signals, the fundamental and harmonic components are extracted, the parameters are calculated, and real-time monitoring is realized; threshold determination, setting parameter threshold, threshold comparison of calculated parameters; data storage and alarm process, selecting parameters for file storage, and executing alarm operation according to threshold determination result.

6. The measurement method according to claim 5, characterized in that: in the signal acquisition and conversion process, based on the signal conversion and conditioning unit (1) accessing the single-phase alternating current, converting it into a low voltage signal through the voltage transformer (11) and the current transformer (12), and conditioning and outputting it through the sampling resistor (13); the digital-to-analog conversion unit (2) receives the conditioned signal, performs analog-to-digital conversion through the differential input channel, and transmits the digital signal to the computing system unit (3) through the USB interface.

7. The measurement method according to claim 6, characterized in that: in the power quality parameter calculation process, discrete time domain signals are collected, converted into frequency domain signals through fast Fourier transform algorithm, fundamental frequency, amplitude and harmonic components are extracted; single frequency measurement function is used to obtain the phase of voltage and current signals, to calculate power factor; period average and root mean square function are used to obtain the effective value of signals, to calculate voltage effective value Urms, current effective value Irms, active power P, reactive power Q and apparent power S; voltage deviation and frequency deviation are calculated, voltage deviation is (actual voltage - rated voltage) / rated voltage x 100%, frequency deviation is actual frequency - rated frequency; nth harmonic content rate is the percentage of nth harmonic effective value to fundamental effective value, total harmonic distortion rate is the percentage of root mean square of each harmonic to fundamental effective value; harmonic distortion analysis function is used to quickly obtain the fundamental frequency, harmonic amplitude and total harmonic distortion rate of signals.

8. The measurement method according to claim 7, characterized in that: in the threshold determination process, different types of parameters are respectively set with alarm thresholds, and threshold comparison is performed on the calculated parameters; if any of voltage deviation, frequency deviation, total harmonic distortion rate, odd harmonic content rate and even harmonic content rate exceeds the alarm threshold, there is parameter abnormality; if none of voltage deviation, frequency deviation, total harmonic distortion rate, odd harmonic content rate and even harmonic content rate exceeds the alarm threshold, there is no parameter abnormality.

9. The measurement method according to claim 8, characterized in that: in the data storage and alarm process, current effective value, current frequency deviation, voltage effective value, voltage frequency deviation, voltage deviation, current total harmonic distortion and voltage total harmonic distortion are selected as storage parameters, saved to local, and used for experimental reproduction and long-term data management; parameter state is monitored, and threshold determination result is combined, if there is parameter abnormality, the alarm light is triggered, otherwise it is not triggered.

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