A variable frequency series resonance withstand voltage detection device and detection method

Abstract

The present invention provides a variable frequency series resonant withstand voltage detection device and detection method, the detection device includes an integrated control box, an excitation transformer, a reactor group, a voltage divider and a compensation capacitor group, the output end of the integrated control box is electrically connected to the low voltage side of the excitation transformer, the high voltage side of the excitation transformer is electrically connected to the reactor group, the voltage divider and the compensation capacitor group in sequence, the compensation capacitor group is electrically connected to the device to be detected, the integrated control box is directly electrically connected to the voltage divider, the integrated control box is electrically connected to the low voltage side of the excitation transformer through a shunt resistor, the integrated control box is used to collect the sampled voltage at the voltage divider and the sampled current on the low voltage side of the excitation transformer, the integrated control box is also used to combine the sampled voltage and the sampled current to predict the resonant frequency interval where the resonance point is located, and the integrated control box is also used to output variable frequency alternating current to the low voltage side of the excitation transformer according to the resonant frequency interval. The present invention has the effect of improving the accuracy of the withstand voltage test results.

Description

Technical Field

[0001] The invention belongs to the technical field of resonant withstand voltage detection, and in particular relates to a variable frequency series resonant withstand voltage detection device and a detection method. Background Art

[0002] As the scale of power systems continues to expand and become more complex, the requirements for the safety and reliability of high-voltage equipment are becoming increasingly higher. These high-voltage equipment include but are not limited to transmission lines, transformers, switchgear, power cables, etc. During the production, installation, operation and maintenance of these equipment, strict voltage withstand tests are required to ensure that they can operate safely and reliably under high-voltage environments.

[0003] In the traditional test method, three-phase traditional phase-controlled and diode uncontrolled rectification is generally used, and the inverter part adopts SPWM modulation mode. In addition, the input power factor on the grid side is low, the current harmonic content on the AC input side is high, and the AC side grid voltage waveform will be distorted, causing the grid to generate a large amount of harmonics and reactive power, polluting the grid. The DC voltage obtained by rectification has large fluctuations and unstable voltage, resulting in poor smoothness of the AC output voltage waveform generated by the inverter circuit, affecting the effect of the series resonance test. On the other hand, operators often need to find the resonance point of the system through repeated tests and manual adjustments. This process is not only time-consuming and labor-intensive, but also easily affected by human factors, resulting in low accuracy and repeatability of the test results. Summary of the invention

[0004] The present invention provides a variable frequency series resonant withstand voltage detection device and a detection method to solve the problem of low accuracy and repeatability of withstand voltage test results.

[0005] In the first aspect, the present invention provides a variable frequency series resonant withstand voltage detection device, the detection device includes an integrated control box, an excitation transformer, a reactor group, a voltage divider and a compensation capacitor group, the input end of the integrated control box is connected to the input voltage, the output end of the integrated control box is electrically connected to the low voltage side of the excitation transformer, the high voltage side of the excitation transformer is electrically connected to the reactor group, the voltage divider and the compensation capacitor group in sequence, the compensation capacitor group is electrically connected to a device to be detected, the integrated control box is directly electrically connected to the voltage divider, the integrated control box is electrically connected to the low voltage side of the excitation transformer through a shunt resistor, the integrated control box is used to collect the sampled voltage at the voltage divider and the sampled current on the low voltage side of the excitation transformer, the integrated control box is also used to combine the sampled voltage and the sampled current to predict the resonant frequency range where the resonance point is located, and the integrated control box is also used to output variable frequency alternating current to the low voltage side of the excitation transformer according to the resonant frequency range.

[0006] Optionally, the integrated control box includes a box body, a variable frequency power supply control module, a resonant frequency sweep prediction module and a current and voltage sampling module, wherein the variable frequency power supply control module, the resonant frequency sweep prediction module and the current and voltage sampling module are all integrated in the box body; the input end of the variable frequency power supply control module is connected to the input voltage, the output end of the variable frequency power supply control module is electrically connected to the low voltage side of the excitation transformer, the variable frequency power supply control module is electrically connected to the resonant frequency sweep prediction module and supplies power to the resonant frequency sweep prediction module; the current and voltage sampling module is directly electrically connected to the voltage divider, and the current and voltage sampling module is connected to the voltage divider through the voltage divider. The shunt resistor is electrically connected to the low-voltage side of the excitation transformer. The current and voltage sampling module is used to collect the sampled voltage at the voltage divider and the sampled current on the low-voltage side of the excitation transformer, and is used to transmit the sampled voltage and the sampled current to the resonant frequency sweep prediction module after filtering. The resonant frequency sweep prediction module is used to predict the resonant frequency range where the resonant point is located in combination with the sampled voltage and the sampled current after filtering, and output the resonant frequency range to the variable frequency power supply control module, so that the variable frequency power supply control module outputs variable frequency alternating current to the low-voltage side of the excitation transformer according to the resonant frequency range.

[0007] Optionally, the variable frequency power supply control module is directly electrically connected to the voltage divider, and is also used to directly collect a sampled voltage at the voltage divider, and output variable frequency AC power to the low voltage side of the excitation transformer according to the sampled voltage.

[0008] Optionally, the integrated control box also includes a compensation capacitor control module, which is integrated in the box body, the compensation capacitor control module is electrically connected to the compensation capacitor group, the variable frequency power supply control module is electrically connected to the compensation capacitor control module and supplies power to the compensation capacitor control module, the compensation capacitor control module is electrically connected to the current and voltage sampling module and the resonant frequency sweep prediction module, respectively, the current and voltage sampling module is also used to transmit the sampled voltage and the sampled current to the compensation capacitor control module after filtering, the resonant frequency sweep prediction module is also used to output the resonant frequency range to the compensation capacitor control module, the compensation capacitor control module is used to generate a compensation capacitor control signal in combination with the sampled voltage, the sampled current after filtering, and the resonant frequency range, and transmit the compensation capacitor control signal to the compensation capacitor group to adjust the switching of each capacitor in the compensation capacitor group.

[0009] Optionally, the resonant frequency sweep prediction module includes a signal generating unit, a voltage following unit, a signal isolating unit, a resonance point prediction control unit and a phase detection unit, wherein the signal generating unit, the voltage following unit, the signal isolating unit, the resonance point prediction control unit and the phase detection unit are all electrically connected to the variable frequency power supply control module, and the variable frequency power supply control module is used to supply power to the signal generating unit, the voltage following unit, the resonance point prediction control unit and the phase detection unit; the signal generating unit is electrically connected to the resonance point prediction control unit, the voltage following unit and the phase detection unit, respectively, the signal generating unit is used to generate a frequency sweep auxiliary signal according to the frequency control instruction output by the resonance point prediction control unit, and output the frequency sweep auxiliary signal to the voltage following unit, and the signal generating unit is also used to output the auxiliary signal information of the frequency sweep auxiliary signal to the phase detection unit;

[0010] The voltage following unit is electrically connected to the signal isolation unit, and the voltage following unit and the signal isolation unit are used to isolate and amplify the sweep frequency auxiliary signal and then output it to the signal output main circuit of the variable frequency power supply control module; the phase detection unit is also electrically connected to the resonance point prediction control unit and the current and voltage sampling module, and the phase detection unit is used to receive the auxiliary signal information output by the signal generation unit and the sampling current and the sampling voltage output by the current and voltage sampling module, and calculate the sweep frequency detection result of the sweep frequency auxiliary signal in the main circuit of the detection device in combination with the auxiliary signal information, the sampling current and the sampling voltage, and the phase detection unit is also used to output the sweep frequency detection result to the resonance point prediction control unit; the resonance point prediction control unit is used to generate the frequency control instruction according to the sweep frequency detection result, and is also used to predict the resonance frequency interval where the resonance point is located according to the sweep frequency detection result, and output the resonance frequency interval to the variable frequency power supply control module, so that the variable frequency power supply control module outputs variable frequency alternating current to the low voltage side of the excitation transformer according to the resonance frequency interval, and the resonance point prediction control unit is also used to output the resonance frequency interval to the compensation capacitor control module.

[0011] Optionally, the current and voltage sampling module includes a current sampling unit, a voltage sampling unit, a first filtering unit and a second filtering unit, the first filtering unit and the second filtering unit respectively use different types of filters, the current sampling module is electrically connected to the low-voltage side of the excitation transformer through the shunt resistor, and the current sampling module is used to collect the sampled current from the low-voltage side of the excitation transformer; the current sampling module is electrically connected to the first filtering unit and the second filtering unit respectively, and the current sampling module is used to output the sampled current to the first filtering unit and the second filtering unit; the first filtering unit is electrically connected to the compensation capacitor control module, and the first The filtering unit is used to perform a first filtering process on the sampling current, and output the sampling current after the first filtering process to the compensation capacitor control module. The second filtering unit is electrically connected to the resonant frequency sweep prediction module. The second filtering unit is used to perform a second filtering process on the sampling current, and output the sampling current after the second filtering process to the resonant frequency sweep prediction module; the voltage sampling unit is electrically connected to the voltage divider, the resonant frequency sweep prediction module and the compensation capacitor control module, respectively, and the voltage sampling unit is used to collect a sampling voltage from the voltage divider, and output the sampling voltage to the resonant frequency sweep prediction module and the compensation capacitor control module, respectively.

[0012] Optionally, the voltage sampling unit includes a buffer amplifier, an overvoltage protection circuit, a voltage attenuation circuit and a first isolation amplifier. The low-voltage end of the voltage divider is electrically connected to the overvoltage protection circuit, the buffer amplifier, the voltage attenuation circuit and the first isolation amplifier in sequence. The first isolation amplifier is electrically connected to the resonant frequency sweep prediction module and the compensation capacitor control module, respectively.

[0013] Optionally, the current sampling unit includes a differential amplifier and a second isolation amplifier, the input end of the differential amplifier is connected to the two ends of the shunt resistor, the output end of the differential amplifier is electrically connected to the second isolation amplifier, and the second isolation amplifier is electrically connected to the first filtering unit and the second filtering unit respectively.

[0014] In a second aspect, the present invention further provides a variable frequency series resonant withstand voltage detection method, which is applied to the variable frequency series resonant withstand voltage detection device described in the first aspect, wherein the variable frequency series resonant withstand voltage detection device comprises an integrated control box, an excitation transformer, a reactor group, a voltage divider and a compensation capacitor group, wherein the input end of the integrated control box is connected to the input voltage, the output end of the integrated control box is electrically connected to the low voltage side of the excitation transformer, the high voltage side of the excitation transformer is electrically connected to the reactor group, the voltage divider and the compensation capacitor group in sequence, the compensation capacitor group is electrically connected to the device to be detected, the integrated control box is directly electrically connected to the voltage divider, and the integrated control box is electrically connected to the low voltage side of the excitation transformer through a shunt resistor;

[0015] The integrated control box comprises a box body, a variable frequency power supply control module, a resonant frequency sweep prediction module and a current and voltage sampling module, wherein the variable frequency power supply control module, the resonant frequency sweep prediction module and the current and voltage sampling module are all integrated in the box body; the input end of the variable frequency power supply control module is connected to the input voltage, the output end of the variable frequency power supply control module is electrically connected to the low voltage side of the excitation transformer, the variable frequency power supply control module is electrically connected to the resonant frequency sweep prediction module and supplies power to the resonant frequency sweep prediction module; the current and voltage sampling module is directly electrically connected to the voltage divider, and the current and voltage sampling module is electrically connected to the low voltage side of the excitation transformer through the shunt resistor;

[0016] The method comprises the following steps:

[0017] The device to be detected is electrically connected to the compensation capacitor group, so that the variable frequency series resonant withstand voltage detection device and the device to be detected form a detection main circuit;

[0018] Acquiring preset detection parameters and device parameters of the device to be detected;

[0019] Determining an initial frequency of the resonant frequency sweep prediction module in combination with the detection parameter and the device parameter;

[0020] Based on the initial frequency, the resonance frequency sweep prediction module is controlled to generate a frequency sweep auxiliary signal, and the frequency sweep auxiliary signal is input to the variable frequency power supply control module;

[0021] The variable frequency power supply control module is used to fuse the auxiliary frequency sweep signal and the preset base signal into a loop frequency sweep signal, and the loop frequency sweep signal is output to the detection main loop;

[0022] The current and voltage sampling module is used to collect the sampled voltage at the voltage divider, and the sampled current at the low-voltage side of the excitation transformer is collected through the shunt resistor, and the sampled voltage and the sampled current are filtered;

[0023] The filtered sampled voltage and the sampled current are transmitted to the resonance frequency sweep prediction module, and the resonance frequency sweep prediction module is used to predict the resonance frequency interval where the resonance point in the detection main loop is located;

[0024] Based on the resonant frequency range and utilizing the variable frequency power supply control module, variable frequency alternating current is output to the low voltage side of the excitation transformer.

[0025] Optionally, the integrated control box further includes a compensation capacitor control module, the compensation capacitor control module is integrated in the box, the compensation capacitor control module is electrically connected to the compensation capacitor bank, the variable frequency power supply control module is electrically connected to the compensation capacitor control module and supplies power to the compensation capacitor control module, and the compensation capacitor control module is electrically connected to the current and voltage sampling module and the resonant frequency sweep prediction module respectively;

[0026] The method further comprises the steps of:

[0027] estimating a loop quality factor of the detection main loop according to the resonant frequency interval;

[0028] The compensation capacitance increment of the detection main loop is calculated by combining the loop quality factor and the resonant frequency range;

[0029] According to the capacity errors and parallel effects of all the capacitors in the compensation capacitor group, an optimization constraint condition is established, with minimizing the compensation capacitance increment as the optimization goal, and based on the optimization constraint condition and using an optimization algorithm, an optimal switching scheme of the capacitors in the compensation capacitor group is calculated;

[0030] A compensation capacitor control signal is generated based on the optimal switching scheme, and the switching of each capacitor in the compensation capacitor group is adjusted by the compensation capacitor control signal.

[0031] The beneficial effects of the present invention are:

[0032] The device of the present invention can automatically collect and analyze voltage and current data, quickly predict the resonant frequency range, and thus achieve precise frequency control, which greatly reduces the need for manual operation, reduces the risk of operating errors, and improves the repeatability and consistency of the test. Since the device can find the resonance point more accurately, the required input power is greatly reduced, which not only improves the energy utilization efficiency, but also enhances the safety of the test process, especially when dealing with large-capacity test products, this advantage is more obvious. Through real-time data analysis and automatic adjustment, the present invention can quickly adapt to changes in test product characteristics, thereby improving the flexibility and adaptability of the test. This is particularly beneficial for handling high-voltage equipment of different types and capacities, and can maintain high efficiency and accuracy in different test scenarios. The present invention integrates multiple functional modules through an integrated control box, realizes the compactness and integration of the equipment, is conducive to reducing equipment costs, and improving system reliability and maintenance convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a circuit diagram of a variable frequency series resonant withstand voltage detection device in one embodiment of the present application.

[0034] Figure 2 This is a circuit diagram of an integrated control box in one embodiment of the present application.

[0035] Figure 3 FIG. 1 is a circuit diagram of a resonant frequency sweep prediction module in one embodiment of the present application.

[0036] Figure 4 This is a circuit diagram of a current and voltage sampling module in one embodiment of the present application.

[0037] Figure 5 It is a flow chart of a variable frequency series resonant withstand voltage detection method in one embodiment of the present application.

[0038] Description of reference numerals:

[0039] 1. Integrated control box; 2. Excitation transformer; 3. Reactor group; 4. Voltage divider; 5. Compensation capacitor group; 6. Device to be detected; 11. Variable frequency power supply control module; 12. Resonance sweep prediction module; 13. Current and voltage sampling module; 14. Compensation capacitor control module; 131. Current sampling unit; 132. Voltage sampling unit; 133. First filtering unit; 134. Second filtering unit; 121. Signal generating unit; 122. Voltage following unit; 123. Signal isolation unit; 124. Phase detection unit; 125. Resonance point prediction control unit. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0041] Reference Figure 1 The present application discloses a variable frequency series resonant withstand voltage detection device. In one embodiment, the variable frequency series resonant withstand voltage detection device is composed of an integrated control box, an excitation transformer, a reactor group, a voltage divider and a compensation capacitor group. These components together form a highly integrated high-voltage test system. The integrated control box serves as the core control unit of the entire system, and its input end is connected to an external power supply, usually a three-phase 380V AC power supply. The input voltage is converted into an AC power with adjustable frequency and amplitude inside the control box and output to the low-voltage side of the excitation transformer. The excitation transformer adopts a specially designed high-frequency transformer with wide-band characteristics and can operate in a frequency range of 20-300Hz. Its low-voltage winding adopts multi-layer winding to reduce leakage inductance and improve transmission efficiency; the high-voltage winding adopts segmented winding to reduce interlayer capacitance and improve withstand voltage capability. The core material of the transformer can be selected from silicon steel sheets or amorphous alloys to adapt to high-frequency working conditions.

[0042] In this embodiment, if Figure 1 As shown, the high-voltage side of the excitation transformer is electrically connected to the reactor group, the voltage divider and the compensation capacitor group in sequence to form a series resonant circuit. The reactor group is composed of multiple adjustable inductors connected in series and parallel. Each inductor adopts a hollow or iron core structure, and the coil is wound with silver-plated or tin-plated flat copper wire to reduce the skin effect at high frequencies. The voltage divider adopts a structure combining a capacitive voltage divider and a resistive voltage divider. The capacitive voltage divider uses a high-voltage ceramic capacitor, and the resistive voltage divider uses a special non-inductive wire-wound resistor to ensure good voltage division characteristics within a wide frequency band. The voltage division ratio can reach 1000:1 or higher, and the output signal is transmitted to the integrated control box via a shielded cable. The compensation capacitor group is composed of multiple high-voltage oil-immersed or SF6 gas-insulated capacitors in parallel.

[0043] In one embodiment, the integrated control box contains a complex circuit system, which is mainly composed of a power module, a frequency conversion control module, a data acquisition module and a central processing unit. The power module is responsible for providing a stable DC power supply for the entire control system, including multiple outputs, and adopts switching power supply technology, such as LLC resonant converter, to improve efficiency and reduce size. The frequency conversion control module is the core of the system, and adopts an architecture that combines a digital signal processor DSP and a field programmable gate array. The DSP is responsible for complex mathematical operations and control algorithm implementation, while the FPGA is used for high-speed data processing and PWM signal generation. The frequency conversion control module achieves precise adjustment of the output voltage frequency and amplitude by controlling the IGBT power module (such as FF300R12ME4). The data acquisition module is responsible for collecting the voltage and current signals of the system.

[0044] The working process of the whole system is as follows: First, the integrated control box outputs the initial frequency AC to the excitation transformer through the frequency conversion control module. After the excitation transformer boosts the low-voltage AC, it is transmitted to the device under test through the series resonant circuit formed by the reactor group, the voltage divider and the compensation capacitor group. At the same time, the voltage divider collects the high-voltage side voltage signal and transmits it to the integrated control box; the low-voltage side current is sampled by the shunt resistor and transmitted to the control box. The data acquisition module performs high-speed sampling and digital processing on these signals. The central processing unit uses the collected data to analyze the phase relationship, amplitude change and other characteristics of the voltage and current through complex digital signal processing algorithms to quickly estimate the possible resonant frequency range. Based on this prediction result, the frequency conversion control module adjusts the output frequency and gradually approaches the real resonance point. In the process of approaching the resonance point, the system will continuously fine-tune the frequency and voltage amplitude to ensure that the test voltage rises steadily and avoid overvoltage.

[0045] Through the above technical solutions, the time to find the resonance point is greatly shortened and the test efficiency is improved. Secondly, due to the ability to accurately locate the resonant frequency, the input power required when the system is running in a resonant state is greatly reduced, and energy consumption can usually be saved by 30% to 50%. This not only reduces the cost of testing, but also improves the safety of testing, especially when dealing with large-capacity test products, reducing the risk of equipment overheating and insulation breakdown. On the other hand, real-time voltage and current sampling and analysis enable the system to quickly respond to changes in test product characteristics and adapt to the testing needs of high-voltage equipment of different types and capacities. For example, for various types of high-voltage equipment with different capacities, the system can find the optimal operating point in a short time. In addition, the application of intelligent prediction algorithms reduces the need for manual operation, reduces the risk of operating errors, and improves the repeatability and consistency of testing.

[0046] In one embodiment, referring to Figure 2The integrated control box includes a box body, a variable frequency power supply control module, a resonant frequency sweep prediction module and a current and voltage sampling module, and the variable frequency power supply control module, the resonant frequency sweep prediction module and the current and voltage sampling module are all integrated in the box body; the input end of the variable frequency power supply control module is connected to the input voltage, the output end of the variable frequency power supply control module is electrically connected to the low voltage side of the excitation transformer, the variable frequency power supply control module is electrically connected to the resonant frequency sweep prediction module and supplies power to the resonant frequency sweep prediction module; the current and voltage sampling module is directly electrically connected to the voltage divider, the current and voltage sampling module is electrically connected to the low voltage side of the excitation transformer through a shunt resistor, the current and voltage sampling module is used to collect the sampling voltage at the voltage divider and the sampling current on the low voltage side of the excitation transformer, and is used to transmit the sampling voltage and the sampling current to the resonant frequency sweep prediction module after filtering; the resonant frequency sweep prediction module is used to predict the resonant frequency interval where the resonant point is located by combining the sampling voltage and the sampling current after filtering, and output the resonant frequency interval to the variable frequency power supply control module, so that the variable frequency power supply control module outputs variable frequency alternating current to the low voltage side of the excitation transformer according to the resonant frequency interval.

[0047] In this embodiment, the integrated control box integrates a variable frequency power supply control module, a resonant frequency sweep prediction module and a current and voltage sampling module. These three modules work together to achieve efficient and accurate resonance point detection and control. The box is made of high-strength aluminum alloy material with good electromagnetic shielding performance. It is equipped with multi-layer partitions inside to effectively separate the functional modules and reduce mutual interference. The outside of the box is equipped with an LCD display, control buttons and indicator lights to facilitate operators to monitor the operating status of the system in real time. The input end of the variable frequency power supply control module is connected to a three-phase 380V AC power supply. The module first suppresses grid interference and harmonics through an EMI filter (such as the FN2090 series), and then converts AC power into DC through a three-phase rectifier bridge. The rectified DC power passes through an LC filter circuit composed of a large-capacity electrolytic capacitor and an inductor to smooth the DC voltage fluctuation. The filtered DC power is converted into adjustable frequency AC power through an IGBT inverter module. The control signal of the IGBT is generated by a high-performance DSP, and the space vector pulse width modulation (SVPWM) technology is used to achieve precise control of the output voltage frequency and amplitude. The output end eliminates high-frequency switching ripple through an LC filter (using Sendust core inductor and polypropylene film capacitor), and finally outputs clean sinusoidal AC to the low-voltage side of the excitation transformer.

[0048] In one embodiment, Figure 2As shown, the integrated control box also includes a compensation capacitor control module, which is integrated in the box body. The compensation capacitor control module is electrically connected to the compensation capacitor group. The variable frequency power supply control module is electrically connected to the compensation capacitor control module and supplies power to the compensation capacitor control module. The compensation capacitor control module is electrically connected to the current and voltage sampling module and the resonant frequency sweep prediction module respectively. The current and voltage sampling module is also used to transmit the sampled voltage and the sampled current to the compensation capacitor control module after filtering. The resonant frequency sweep prediction module is also used to output the resonant frequency range to the compensation capacitor control module. The compensation capacitor control module is used to generate a compensation capacitor control signal in combination with the sampled voltage, the sampled current after filtering, and the resonant frequency range, and transmit the compensation capacitor control signal to the compensation capacitor group to adjust the switching of each capacitor in the compensation capacitor group.

[0049] In this embodiment, the compensation capacitor control module integrated in the integrated control box is a key component, which works closely with the variable frequency power supply control module, the current and voltage sampling module, the resonant frequency sweep prediction module and the compensation capacitor group to realize the intelligent and efficient operation of the series resonant withstand voltage detection device. The core of the compensation capacitor control module is a high-performance microcontroller, such as the STM32F407 series, which can quickly process complex control algorithms and data analysis tasks. The compensation capacitor control module obtains power supply from the variable frequency power supply control module through an isolated DC-DC converter. The raw data collected by the current and voltage sampling module is transmitted to the compensation capacitor control module after digital filtering. The filtering algorithm uses a finite impulse response (FIR) filter, such as a low-pass filter designed using a Kaiser window function, which can effectively remove high-frequency noise and retain the useful components of the signal. After receiving these data, the compensation capacitor control module first performs data fusion and analysis. It uses the Kalman filter algorithm to further eliminate noise and estimate the state of the voltage and current data to improve the measurement accuracy. Then, based on the current voltage, current value and predicted resonant frequency range, a complex optimization algorithm is run to determine the best capacitor switching scheme. The optimization algorithm uses the adaptive particle swarm optimization (APSO) method, combined with fuzzy logic control, which can quickly search for the optimal solution while having good convergence and robustness. The objective function of the algorithm includes multiple weight factors, such as the proximity of the resonant frequency, the system power factor, the resonant current amplitude, etc., taking into account the various performance indicators of the system.

[0050] Based on the optimization results, the compensation capacitor control module generates a compensation capacitor control signal and transmits it to the compensation capacitor group. The compensation capacitor group is composed of multiple groups of high-voltage capacitors of different capacities connected in parallel, and each group of capacitors is controlled by a separate switch. The capacitor uses a thin-film high-voltage capacitor. The compensation capacitor control module achieves flexible switching of the capacitor by accurately controlling the opening and closing of these switch elements. The switching strategy adopts a progressive method to avoid voltage mutations caused by the sudden input of large-capacity capacitors. In addition, the compensation capacitor control module also implements multiple protection functions. It continuously monitors the voltage, current and temperature of each group of capacitors. Once an abnormality is detected, such as overvoltage, overcurrent or overheating, the protection mechanism is immediately triggered to disconnect the corresponding capacitor. The module also implements a soft start function, which gradually increases the compensation capacity when the system starts, avoiding the large current shock at the startup moment.

[0051] In one embodiment, Figure 2 As shown, the variable frequency power supply control module is directly electrically connected to the voltage divider. The variable frequency power supply control module is also used to directly collect the sampled voltage at the voltage divider and output variable frequency AC power to the low voltage side of the excitation transformer according to the sampled voltage.

[0052] In this embodiment, the variable frequency power supply control module directly collects the voltage signal from the voltage divider through its built-in high-speed analog-to-digital converter (ADC). Based on the collected voltage information, the DSP runs a complex control algorithm to adjust the output variable frequency AC power. The control algorithm usually includes PID (proportional-integral-differential) control, fuzzy logic control, and adaptive control. These algorithms adjust the output frequency and amplitude in real time according to the difference between the current voltage and the target voltage. In some special cases (such as abnormal failure of the resonant sweep prediction module or the current and voltage sampling module), the variable frequency power supply control module can also skip the resonance point prediction stage, directly collect the voltage of the voltage divider, and adjust the output frequency and amplitude in real time.

[0053] In one embodiment, referring to Figure 3The resonance frequency sweep prediction module is the core component in the series resonance withstand voltage detection device, which is composed of a signal generating unit, a voltage following unit, a signal isolating unit, a resonance point prediction control unit and a phase detection unit. These units work together to achieve accurate resonance frequency prediction and control. The signal generating unit, the voltage following unit, the signal isolating unit, the resonance point prediction control unit and the phase detection unit are all electrically connected to the variable frequency power supply control module, and the variable frequency power supply control module is used to supply power to the signal generating unit, the voltage following unit, the resonance point prediction control unit and the phase detection unit; the signal generating unit is electrically connected to the resonance point prediction control unit, the voltage following unit and the phase detection unit respectively, and the signal generating unit is used to generate a frequency sweep auxiliary signal according to the frequency control instruction output by the resonance point prediction control unit, and output the frequency sweep auxiliary signal to the voltage following unit, and the signal generating unit is also used to output the auxiliary signal information of the frequency sweep auxiliary signal to the phase detection unit.

[0054] The voltage following unit is electrically connected to the signal isolation unit, and the voltage following unit and the signal isolation unit are used to isolate and amplify the sweep frequency auxiliary signal and then output it to the signal output main circuit of the variable frequency power supply control module; the phase detection unit is also electrically connected to the resonance point prediction control unit and the current and voltage sampling module, the phase detection unit is used to receive the auxiliary signal information output by the signal generation unit and the sampling current and sampling voltage output by the current and voltage sampling module, and calculate the sweep frequency detection result of the sweep frequency auxiliary signal in the main circuit of the detection device in combination with the auxiliary signal information, the sampling current and the sampling voltage, and the phase detection unit is also used to output the sweep frequency detection result to the resonance point prediction control unit; the resonance point prediction control unit is used to generate a frequency control instruction according to the sweep frequency detection result, and is also used to predict the resonance frequency interval where the resonance point is located according to the sweep frequency detection result, and output the resonance frequency interval to the variable frequency power supply control module, so that the variable frequency power supply control module outputs variable frequency alternating current to the low voltage side of the excitation transformer according to the resonance frequency interval, and the resonance point prediction control unit is also used to output the resonance frequency interval to the compensation capacitor control module.

[0055] In this embodiment, the signal generation unit can be a high-performance direct digital synthesis (DDS) chip, such as AD9910. This DDS chip has a sampling rate of up to 1GSPS and a 14-bit resolution, and can generate an accurate sine wave sweep signal. The signal generation unit is connected to the resonance point prediction control unit via an SPI interface and receives frequency control instructions. Based on these instructions, the DDS chip generates a sweep auxiliary signal, the frequency range of which is usually set between 10Hz and 1MHz, covering the possible resonant frequencies of most series resonant circuits. The generated sweep auxiliary signal is first output to the voltage follower unit. The voltage follower unit uses a high-speed operational amplifier. The main function of this unit is to provide low output impedance to ensure that the signal will not be affected by the load effect in subsequent processing.

[0056] The output of the voltage follower unit is connected to the signal isolation unit. The signal isolation unit uses a high-speed digital isolator, such as Si8660, which provides a data rate of up to 150Mbps and a propagation delay as low as 2ns. This isolation not only protects the low-voltage side circuit from high-voltage interference, but also eliminates the ground loop and improves the integrity of the signal. The isolated sweep frequency auxiliary signal is input to the signal output main circuit of the variable frequency power supply control module. Here, the sweep frequency auxiliary signal is superimposed with the main control signal to jointly determine the AC characteristics output to the low-voltage side of the excitation transformer. This design allows the frequency characteristics of the output signal to be finely adjusted without affecting the main control, providing a basis for the precise positioning of the resonance point. At the same time, the signal generation unit outputs detailed information of the sweep frequency auxiliary signal (such as instantaneous frequency, amplitude and phase) to the phase detection unit. The phase detection unit also receives sampled data from the current and voltage sampling module. A high-speed digital-to-analog converter (ADC) such as ADS131E08 is used here, which has a 24-bit resolution and a sampling rate of up to 64kSPS, and can accurately capture the details of the current and voltage waveforms.

[0057] The core of the phase detection unit is a field programmable gate array (FPGA). The FPGA implements complex digital signal processing algorithms, including fast Fourier transform (FFT) and phase comparison. It first performs FFT analysis on the sampled data to extract the amplitude and phase information of the fundamental component. Then, this information is compared with the parameters of the sweep frequency auxiliary signal to calculate the phase difference between the voltage and current, as well as the amplitude and phase angle of the impedance. These calculation results constitute the sweep frequency detection results, which reflect the response characteristics of the circuit under test at different frequencies. The sweep frequency detection results are transmitted to the resonance point prediction control unit. This unit uses a high-performance microprocessor, such as the STM32H743 series, which runs at a frequency of up to 480MHz and has powerful floating-point computing capabilities. The resonance point prediction control unit first analyzes the impedance-frequency curve in the sweep frequency detection results, finds the minimum impedance amplitude point and the point where the phase jumps from inductive to capacitive, and generates multiple possible resonant frequency candidate values. These candidate values ​​are evaluated and sorted to finally determine the most likely resonant frequency range.

[0058] The resonance point prediction control unit outputs the predicted resonance frequency range to the variable frequency power supply control module and the compensation capacitor control module. The variable frequency power supply control module uses this information to adjust the frequency of the AC power output to the low-voltage side of the excitation transformer to make it closer to the actual resonance frequency, thereby improving the test efficiency and accuracy. The compensation capacitor control module optimizes the switching strategy of the compensation capacitor according to the resonance frequency range, and further refines the positioning of the resonance point. At the same time, the resonance point prediction control unit generates a new frequency control instruction based on the prediction results and feeds it back to the signal generation unit. This forms a closed-loop control system that continuously optimizes the frequency sweep strategy to make the frequency sweep process more efficient and accurate. For example, after the resonant frequency range is preliminarily determined, the frequency sweep range can be narrowed and the scanning density within the range can be increased to obtain more detailed resonance characteristic information.

[0059] In one embodiment, referring to Figure 4 The current and voltage sampling module includes a current sampling unit, a voltage sampling unit, a first filter unit and a second filter unit. The first filter unit and the second filter unit respectively use different types of filters. The current sampling module is electrically connected to the low-voltage side of the excitation transformer through a shunt resistor. The shunt resistor usually uses a high-precision, low-temperature drift alloy resistor. The current sampling module is used to collect the sampling current from the low-voltage side of the excitation transformer; the current sampling module is electrically connected to the first filter unit and the second filter unit respectively, and the current sampling module is used to output the sampling current to the first filter unit and the second filter unit; the first filter unit is electrically connected to the compensation capacitor control module, the first filter unit is used to perform a first filtering process on the sampling current, and output the sampling current after the first filtering process to the compensation capacitor control module, the second filter unit is electrically connected to the resonant frequency sweep prediction module, the second filter unit is used to perform a second filtering process on the sampling current, and output the sampling current after the second filtering process to the resonant frequency sweep prediction module; the voltage sampling unit is electrically connected to the voltage divider, the resonant frequency sweep prediction module and the compensation capacitor control module respectively, the voltage sampling unit is used to collect the sampling voltage from the voltage divider, and output the sampling voltage to the resonant frequency sweep prediction module and the compensation capacitor control module respectively.

[0060] The core of the current sampling unit is a combination of a differential amplifier and an isolation amplifier. The differential amplifier uses an instrumentation amplifier with a high common-mode rejection ratio (CMRR), which can accurately amplify the tiny voltage difference across the shunt resistor while effectively suppressing common-mode interference. The output of the differential amplifier is connected to the isolation amplifier, which provides a common-mode rejection ratio of up to 120 dB and a common-mode transient suppression capability of 15 kV / μs, effectively isolating the high-voltage side and the low-voltage side, protecting the subsequent circuit. The voltage sampling unit is directly connected to the low-voltage end of the voltage divider, and uses multi-stage protection and signal conditioning circuits. The first is the overvoltage protection circuit, which uses fast-response transient suppression diodes and gas discharge tubes to prevent transient high voltage from causing damage to subsequent circuits. Next is the buffer amplifier, which uses a high-input impedance operational amplifier, and the minimum input current can reduce the load effect on the voltage divider. The voltage attenuation circuit uses a precision resistor network to adjust the signal to a range suitable for subsequent processing. Finally, the isolation amplifier provides electrical isolation to ensure that the high-voltage signal does not directly affect the low-voltage side control circuit.

[0061] The first filter unit and the second filter unit use different types of filters to meet the different requirements of the compensation capacitor control module and the resonant frequency sweep prediction module. The first filter unit is mainly used for compensation capacitor control, so a low-pass filter such as LTC1563-2 can be used, which has a linear phase response characteristic and can retain the time domain characteristics of the signal to the maximum extent, which is conducive to rapid response to compensation requirements. The second filter unit uses an elliptical filter such as LTC1563-3 for resonant frequency sweep prediction. It has a large attenuation in the stop band, can effectively suppress high-frequency noise and harmonics, and provide a purer fundamental signal for resonance analysis. The advantage of this dual filter design is that it can meet the needs of time domain and frequency domain analysis at the same time. The compensation capacitor control requires a fast response to current changes, so the low-pass filter used in the first filter unit can effectively remove high-frequency noise while maintaining signal integrity. The resonant frequency sweep prediction pays more attention to the frequency characteristics of the signal, and the elliptical filter of the second filter unit can provide a steeper roll-off characteristic to ensure the accuracy of spectrum analysis. The filtered signal is digitized by a high-speed data acquisition system. A high-performance analog-to-digital converter (ADC) can be used here, and the digitized data is transmitted to the subsequent processing module.

[0062] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0063] The present application also discloses a variable frequency series resonant withstand voltage detection method, which is applied to the variable frequency series resonant withstand voltage detection device described in any of the above-mentioned embodiments. The variable frequency series resonant withstand voltage detection device includes an integrated control box, an excitation transformer, a reactor group, a voltage divider and a compensation capacitor group. The input end of the integrated control box is connected to the input voltage, the output end of the integrated control box is electrically connected to the low voltage side of the excitation transformer, the high voltage side of the excitation transformer is electrically connected to the reactor group, the voltage divider and the compensation capacitor group in sequence, the compensation capacitor group is electrically connected to the device to be detected, the integrated control box is directly electrically connected to the voltage divider, and the integrated control box is electrically connected to the low voltage side of the excitation transformer through a shunt resistor.

[0064] The integrated control box includes a box body, a variable frequency power supply control module, a resonant frequency sweep prediction module and a current and voltage sampling module, and the variable frequency power supply control module, the resonant frequency sweep prediction module and the current and voltage sampling module are all integrated in the box body; the input end of the variable frequency power supply control module is connected to the input voltage, the output end of the variable frequency power supply control module is electrically connected to the low voltage side of the excitation transformer, the variable frequency power supply control module is electrically connected to the resonant frequency sweep prediction module and supplies power to the resonant frequency sweep prediction module; the current and voltage sampling module is directly electrically connected to the voltage divider, and the current and voltage sampling module is electrically connected to the low voltage side of the excitation transformer through a shunt resistor.

[0065] Reference Figure 5 , Figure 5 FIG. 1 is a flow chart of a method for detecting a voltage withstanding voltage of a variable frequency series resonant circuit in an embodiment. It should be understood that although Figure 5 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 5At least part of the steps in the above method may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps. Figure 5 As shown, a variable frequency series resonant withstand voltage detection method disclosed in the present invention specifically includes the following steps:

[0066] S101. The device to be detected is electrically connected to the compensation capacitor group, so that the variable frequency series resonant withstand voltage detection device and the device to be detected form a detection main circuit.

[0067] S102. Obtain preset detection parameters and device parameters of the device to be detected.

[0068] S103. Determine the initial frequency of the resonance frequency sweep prediction module in combination with the detection parameters and the device parameters.

[0069] S104. Based on the initial frequency, the resonance frequency sweep prediction module is controlled to generate a frequency sweep auxiliary signal, and the frequency sweep auxiliary signal is input to the variable frequency power supply control module.

[0070] S105. Utilize the variable frequency power supply control module to fuse the sweep frequency auxiliary signal and the preset base signal into a loop sweep frequency signal, and output the loop sweep frequency signal to the detection main loop.

[0071] S106. Use the current and voltage sampling module to collect the sampled voltage at the voltage divider, and collect the sampled current at the low-voltage side of the excitation transformer through the shunt resistor, and perform filtering on the sampled voltage and sampled current.

[0072] S107. The filtered sampled voltage and sampled current are transmitted to the resonance frequency sweep prediction module, and the resonance frequency sweep prediction module is used to predict the resonance frequency range where the resonance point in the main circuit is located.

[0073] S108. Based on the resonant frequency range and using the variable frequency power supply control module, output variable frequency AC power to the low voltage side of the excitation transformer.

[0074] In this embodiment, the connection terminals of the device to be tested are first checked to ensure that they are clean and intact. Then, the device to be tested is connected to the compensation capacitor bank using a high-voltage wire of appropriate specifications. In order to minimize parasitic inductance and capacitance, the connecting wires should be as short and straight as possible to avoid unnecessary bending. At the same time, the spacing between the wires needs to be considered. Generally, a spacing of at least 1 cm per 10kV voltage should be maintained to prevent corona discharge. After the connection is completed, a high-precision megohmmeter is used to test the insulation resistance of the entire circuit to ensure good insulation. At the same time, a partial discharge detector can be used to check whether there is partial discharge. These precautions can greatly reduce the risk of insulation breakdown during the test and ensure the safety of personnel and equipment.

[0075] The preset detection parameters usually include but are not limited to the following aspects:

[0076] Target withstand voltage value: This is determined based on the rated voltage of the device to be tested and the relevant standards (such as IEC 60060 or IEEE Std 4). For example, for a transformer with a rated voltage of 220 kV, its power frequency withstand voltage value may be set at 460 kV (2.1 times the phase voltage).

[0077] Voltage rise rate: usually in kV / s, needs to be set according to the characteristics of the device to be tested and the relevant standards. For example, for a large transformer, it may be set to 1-2kV / s.

[0078] Withstand voltage time: the duration at the target voltage, usually 1 minute or 5 minutes, depending on the requirements of relevant standards.

[0079] Frequency scanning range: usually set between 20Hz and 300Hz. The specific range needs to be determined based on the characteristics of the device to be tested and the estimated value of the system resonant frequency.

[0080] Sweep step size: can be set to a fixed value (such as 1Hz) or an adaptive value (using a smaller step size near the estimated resonance point).

[0081] The device parameters of the device to be tested include:

[0082] Rated voltage: The designed operating voltage of the equipment.

[0083] Capacitance value: can be measured at low voltage using a capacitance tester. For complex devices, it may be necessary to measure at different frequencies to obtain a more accurate value.

[0084] Induction voltage coefficient: It indicates the ratio of the induced voltage to the applied voltage of the equipment at rated frequency.

[0085] Dissipation factor (tanδ): reflects the insulation loss of the equipment and can be measured by a dielectric loss tester.

[0086] The geometric dimensions and structural characteristics of the device: This information helps to estimate the distributed capacitance and inductance of the device.

[0087] Combining the detection parameters and device parameters to determine the initial frequency of the resonant frequency sweep prediction module requires comprehensive consideration of multiple factors and the use of advanced algorithms. The purpose of this step is to provide a reasonable starting point for the frequency sweep process to speed up the location of the resonance point and improve the efficiency of the entire test. Specifically, it is necessary to establish an equivalent circuit model of the system. For a typical series resonant circuit, the resonant frequency can be expressed by the following formula:

[0088]

[0089] Where L is the equivalent inductance of the system and C is the equivalent capacitance of the system. The equivalent capacitance C includes the capacitance of the device under test. and compensation capacitor A series combination of:

[0090]

[0091] The equivalent inductance L mainly comes from the excitation transformer, but the stray inductance of the connecting wires also needs to be considered. It can be estimated by the following formula:

[0092]

[0093] Where V is the rated voltage of the transformer, is the rated frequency (usually 50Hz or 60Hz), and S is the rated capacity of the transformer.

[0094] The resonant frequency sweep prediction module needs to generate a high-quality frequency sweep auxiliary signal based on the initial frequency. This signal is usually a sine wave whose frequency changes linearly with time, which can be described by the following mathematical expression:

[0095]

[0096] Where A is the signal amplitude, is the initial frequency, k is the sweep frequency (in Hz / s), and φ is the initial phase.

[0097] To generate such a signal, direct digital synthesis (DDS) technology can be used. DDS technology digitally generates a sine wave with adjustable frequency and phase, and has the characteristics of high precision, fast switching and low phase noise.

[0098] The specific steps of signal generation are as follows:

[0099] 1. Initialize the DDS chip and set the clock frequency and initial phase.

[0100] 2. Calculate the frequency tuning word (FTW): ,in is the system clock frequency.

[0101] 3. Calculate the phase increment: .

[0102] 4. Update FTW every clock cycle: .

[0103] In order to improve the accuracy and efficiency of the frequency sweep, an adaptive frequency sweep algorithm can be used. For example, a larger frequency step size is used in areas far away from the estimated resonance point, and the step size is automatically reduced when approaching the resonance point. This can be achieved by monitoring the voltage response of the system:

[0104]

[0105] in, is the maximum step length, is the derivative of voltage with respect to frequency, and k is an adjustable parameter.

[0106] In the variable frequency power supply control module, the sweep frequency auxiliary signal will be fused with the base signal (usually a sine wave with an operating frequency of 50Hz or 60Hz). This process can be achieved through digital signal processing technology, such as using weighted average or more complex signal synthesis algorithms. The fused signal will be used to control the power conversion circuit (such as IGBT inverter) to produce the final high voltage output. Specifically, the commonly used fusion method is weighted superposition, which can be expressed as:

[0107]

[0108] in, is the fused output signal, is the sweep frequency auxiliary signal, is the basis signal, and α is the weight coefficient (0≤α≤1).

[0109] The weight coefficient α can be adjusted dynamically according to the test requirements. For example, a smaller α value can be set at the beginning of the frequency sweep, and as it approaches the resonance point, the α value can be gradually increased to enhance the frequency sweep effect. The following formula can be used to dynamically adjust α:

[0110]

[0111] After the signals are fused, they need to be converted into power control signals through digital pulse width modulation (PWM) technology. This is usually achieved using a high-performance digital signal processor (DSP) or field programmable gate array (FPGA).

[0112] The generation process of PWM signal is as follows:

[0113] 1. Normalize the fused signal so that its amplitude is between -1 and 1.

[0114] 2. Compare the normalized signal with a high-frequency triangle wave carrier.

[0115] 3. When the signal value is greater than the carrier, the PWM output is high level; otherwise it is low level.

[0116] Through this precise signal fusion and output control strategy, a high-quality loop sweep signal can be generated to accurately control the voltage and frequency of the main detection loop. This can not only accurately locate the resonance point of the system, but also maintain a stable voltage output during the withstand voltage test, avoiding overvoltage or undervoltage caused by frequency mutation, thereby protecting the device under test.

[0117] Next, the current and voltage sampling module is used to collect the sampled voltage at the voltage divider, and the sampled current on the low-voltage side of the excitation transformer is collected through the shunt resistor. The sampled voltage and sampled current are filtered and transmitted to the resonant frequency sweep prediction module, which predicts the resonant frequency range where the resonant point in the main circuit is located. Specifically, the resonant frequency sweep prediction module calculates the spectrum of the signal, and by analyzing the amplitude and phase characteristics of the spectrum, the frequency response characteristics of the system can be preliminarily determined, and then the resonant point is predicted through the following steps:

[0118] To find the peak point on the impedance-frequency curve, the condition of the second-order derivative being zero can be used to locate the peak;

[0119] Find the frequency point where the voltage and current phase difference is zero. The zero phase point can be accurately located by interpolation method;

[0120] Calculate the quality factor Q at different frequency points, and the point with the largest Q value is the resonance point;

[0121] Fit the impedance-frequency curve using a polynomial or rational function, and then analyze the characteristics of the fitted curve; for example, you can use a high-order polynomial to fit:

[0122]

[0123] Then solve dZ / df=0 to find the resonance point;

[0124] The resonant frequency range can be determined by performing a detailed scan near the resonance point.

[0125] Next, based on the predicted resonant frequency range, the variable frequency power supply control module is used to perform precise frequency sweeping within the range, and finally the resonant frequency of the detection main circuit is determined. Specifically, the variable frequency power supply control module needs to formulate an accurate frequency sweeping strategy based on the predicted resonant frequency range. A commonly used method is to use an adaptive step frequency sweeping algorithm, and its basic idea is as follows:

[0126] 1. Initialization: Set the initial frequency f0 as the lower limit of the prediction interval, the end frequency f1 as the upper limit of the prediction interval, and the initial frequency step Δf.

[0127] 2. Sweep frequency loop:

[0128] a. Set the current frequency fc=f0

[0129] b. Output test signal at fc and measure system response (voltage, current, impedance, etc.)

[0130] c. Calculate the quality factor Q of the current point:

[0131] d. If the Q value exceeds the preset threshold, enter the fine scanning mode

[0132] e. Otherwise, fc+=Δf, if fc>f1, end the frequency sweep

[0133] f. Repeat steps be

[0134] 3. Fine scanning mode:

[0135] a. Reduce the frequency step: Δfk=Δf / 10

[0136] b. Perform detailed scanning within the range of [fc-Δf, fc+Δf]

[0137] c. Find the point with the largest Q value, which is the resonant frequency.

[0138] In one embodiment, the integrated control box further includes a compensation capacitor control module, the compensation capacitor control module is integrated in the box, the compensation capacitor control module is electrically connected to the compensation capacitor bank, the variable frequency power supply control module is electrically connected to the compensation capacitor control module and supplies power to the compensation capacitor control module, and the compensation capacitor control module is electrically connected to the current and voltage sampling module and the resonant frequency sweep prediction module, respectively. The variable frequency series resonant withstand voltage detection method also includes the following steps:

[0139] Estimate the loop quality factor of the detection main loop according to the resonant frequency range;

[0140] The compensation capacitance increment of the detection main circuit is calculated by combining the circuit quality factor and the resonant frequency range;

[0141] According to the capacity error and parallel effect of all capacitors in the compensation capacitor group, the optimization constraint conditions are established, and the optimization goal is to minimize the compensation capacitance increment. Based on the optimization constraint conditions and using the optimization algorithm, the optimal switching scheme of the capacitors in the compensation capacitor group is calculated;

[0142] A compensation capacitor control signal is generated based on the optimal switching scheme, and the switching of each capacitor in the compensation capacitor group is adjusted through the compensation capacitor control signal.

[0143] In this embodiment, estimating the loop quality factor of the detection main loop based on the resonant frequency range is a key step. The loop quality factor Q is an important parameter for measuring the performance of the resonant circuit, reflecting the selectivity and energy storage capacity of the circuit. In the case of , the Q value can be estimated using the half-power bandwidth method. First, determine the resonant frequency , usually taken as the midpoint of the interval: Then, calculate the half-power bandwidth The Q value can be obtained by the formula For example, if the resonant frequency range is [95Hz,105Hz], then =100Hz, Δf=10Hz, and Q=100 / 10=10 is estimated. In addition, by measuring the voltage and current at the resonance point, a more accurate calculation can be performed using the formula Q=(1 / R)*sqrt(L / C), where R, L, and C are equivalent resistance, inductance, and capacitance, respectively. The purpose of estimating the Q value is to provide a basis for the subsequent calculation of the compensation capacitor, and it can also evaluate the performance of the main circuit. A higher Q value indicates that the circuit loss is small and the resonance effect is good.

[0144] Combining the circuit quality factor and the resonant frequency range to calculate the compensation capacitance increment of the detection main circuit is a key step in determining the required additional capacitance. First, use the resonant frequency And the estimated quality factor Q, the equivalent inductance L and equivalent resistance R of the main circuit can be calculated. The equivalent inductance L can be calculated by the formula Where C is the known capacitance value. The equivalent resistance R can be obtained by Calculate. In order to adjust the resonant frequency to the target frequency , it is necessary to increase the compensation capacitance ΔC. The calculation formula for the increase in compensation capacitance is: . For example, if the current resonant frequency is 100Hz, the target frequency is 50Hz, and the current capacitance is 10μF, then ΔC = 10μF*((100 / 50)²-1) = 30μF. The purpose of calculating the compensation capacitance increment is to accurately adjust the resonant frequency to match the grid operating frequency, thereby achieving the best resonance effect and test effect. The accuracy of this step directly affects the subsequent capacitor switching scheme and the performance of the entire test system.

[0145] According to the capacity error and parallel effect of all capacitors in the compensation capacitor group, the optimization constraint conditions are constructed to minimize the compensation capacitance increment. Specifically, the actual capacity of each capacitor is first considered. With nominal capacity There is an error between: ,in is the error percentage. The parallel effect is reflected in the total capacitance being the sum of the capacities of all the capacitors put in. The optimization constraint can be expressed as: , where δ is the total allowable error. The optimization objective function can be defined as: . To solve this problem, integer programming or genetic algorithms can be used. Taking genetic algorithms as an example, each chromosome represents a switching scheme, and the fitness function is the inverse of the objective function. Through selection, crossover and mutation operations, the switching scheme is optimized generation by generation. The algorithm outputs the optimal switching scheme, indicating the switching state of each capacitor. This optimization method can find the switching combination closest to the ideal compensation value while considering practical limitations, thereby improving the accuracy and efficiency of the system.

[0146] Based on the optimal switching scheme, the compensation capacitor control signal is generated, and the switching of each capacitor in the compensation capacitor group is adjusted by the compensation capacitor control signal. Specifically, the optimal switching scheme output by the optimization algorithm is converted into a binary control sequence, and each bit corresponds to the switching state of a capacitor (0 means disconnection, 1 means input). Then, these control signals are sent to the control unit of the capacitor bank through a digital output module (such as a digital output card of a PLC or a dedicated I / O module). The control unit usually contains a relay drive circuit for controlling a high-power relay or thyristor switch. In order to avoid transient shocks during the switching process, synchronous switching technology can be used, that is, switching operations are performed near the voltage zero point. At the same time, an appropriate time delay (usually several power supply cycles) is set to ensure system stability. During the switching process, system parameters (such as voltage, current, power factor, etc.) are monitored in real time to verify the switching effect and make necessary fine-tuning. This precise control method can achieve smooth adjustment of the compensation capacitor, minimize interference to the system, and improve the stability and reliability of the resonance effect, thereby creating the best conditions for subsequent withstand voltage testing.

[0147] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0148] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A variable frequency series resonant withstand voltage detection device, characterized in that: The detection device includes an integrated control box, an excitation transformer, a reactor group, a voltage divider and a compensation capacitor group. The input end of the integrated control box is connected to the input voltage, the output end of the integrated control box is electrically connected to the low-voltage side of the excitation transformer, the high-voltage side of the excitation transformer is electrically connected to the reactor group, the voltage divider and the compensation capacitor group in sequence, the compensation capacitor group is electrically connected to the device to be detected, the integrated control box is directly electrically connected to the voltage divider, the integrated control box is electrically connected to the low-voltage side of the excitation transformer through a shunt resistor, the integrated control box is used to collect the sampled voltage at the voltage divider and the sampled current on the low-voltage side of the excitation transformer, the integrated control box is also used to predict the resonant frequency interval where the resonance point is located in combination with the sampled voltage and the sampled current, and the integrated control box is also used to output variable-frequency alternating current to the low-voltage side of the excitation transformer according to the resonant frequency interval; The integrated control box includes a box body, a variable frequency power supply control module, a resonant frequency sweep prediction module and a current and voltage sampling module, wherein the variable frequency power supply control module, the resonant frequency sweep prediction module and the current and voltage sampling module are all integrated in the box body; the input end of the variable frequency power supply control module is connected to the input voltage, the output end of the variable frequency power supply control module is electrically connected to the low voltage side of the excitation transformer, the variable frequency power supply control module is electrically connected to the resonant frequency sweep prediction module and supplies power to the resonant frequency sweep prediction module; the current and voltage sampling module is directly electrically connected to the voltage divider, the current and voltage sampling module is electrically connected to the low voltage side of the excitation transformer through the shunt resistor, the current and voltage sampling module is used to collect the sampled voltage at the voltage divider and the sampled current on the low voltage side of the excitation transformer, and is used to transmit the sampled voltage and the sampled current to the resonant frequency sweep prediction module after filtering; The resonance frequency sweep prediction module is used to predict the resonance frequency interval where the resonance point is located by combining the sampled voltage and the sampled current after filtering, and output the resonance frequency interval to the variable frequency power supply control module, so that the variable frequency power supply control module outputs variable frequency alternating current to the low voltage side of the excitation transformer according to the resonance frequency interval; The integrated control box also includes a compensation capacitor control module, which is integrated in the box body, the compensation capacitor control module is electrically connected to the compensation capacitor group, the variable frequency power supply control module is electrically connected to the compensation capacitor control module and supplies power to the compensation capacitor control module, the compensation capacitor control module is electrically connected to the current and voltage sampling module and the resonant frequency sweep prediction module respectively, the current and voltage sampling module is also used to transmit the sampled voltage and the sampled current to the compensation capacitor control module after filtering, the resonant frequency sweep prediction module is also used to output the resonant frequency interval to the compensation capacitor control module, the compensation capacitor control module is used to generate a compensation capacitor control signal in combination with the sampled voltage, the sampled current after filtering, and the resonant frequency interval, and transmit the compensation capacitor control signal to the compensation capacitor group to adjust the switching of each capacitor in the compensation capacitor group; The resonance frequency sweep prediction module includes a signal generating unit, a voltage following unit, a signal isolating unit, a resonance point prediction control unit and a phase detection unit, wherein the signal generating unit, the voltage following unit, the signal isolating unit, the resonance point prediction control unit and the phase detection unit are all electrically connected to the variable frequency power supply control module, and the variable frequency power supply control module is used to supply power to the signal generating unit, the voltage following unit, the resonance point prediction control unit and the phase detection unit; the signal generating unit is electrically connected to the resonance point prediction control unit, the voltage following unit and the phase detection unit respectively, the signal generating unit is used to generate a frequency sweep auxiliary signal according to the frequency control instruction output by the resonance point prediction control unit, and output the frequency sweep auxiliary signal to the voltage following unit, and the signal generating unit is also used to output the auxiliary signal information of the frequency sweep auxiliary signal to the phase detection unit; The voltage following unit is electrically connected to the signal isolation unit, and the voltage following unit and the signal isolation unit are used to isolate and amplify the sweep frequency auxiliary signal and then output it to the signal output main circuit of the variable frequency power supply control module; the phase detection unit is also electrically connected to the resonance point prediction control unit and the current and voltage sampling module, and the phase detection unit is used to receive the auxiliary signal information output by the signal generation unit and the sampling current and the sampling voltage output by the current and voltage sampling module, and calculate the sweep frequency detection result of the sweep frequency auxiliary signal in the main circuit of the detection device in combination with the auxiliary signal information, the sampling current and the sampling voltage, and the phase detection unit is also used to output the sweep frequency detection result to the resonance point prediction control unit; the resonance point prediction control unit is used to generate the frequency control instruction according to the sweep frequency detection result, and is also used to predict the resonance frequency interval where the resonance point is located according to the sweep frequency detection result, and output the resonance frequency interval to the variable frequency power supply control module, so that the variable frequency power supply control module outputs variable frequency alternating current to the low voltage side of the excitation transformer according to the resonance frequency interval, and the resonance point prediction control unit is also used to output the resonance frequency interval to the compensation capacitor control module.

2. The variable frequency series resonant withstand voltage detection device according to claim 1, characterized in that: The variable frequency power supply control module is directly electrically connected to the voltage divider, and is also used to directly collect the sampled voltage at the voltage divider, and output variable frequency alternating current to the low voltage side of the excitation transformer according to the sampled voltage.

3. The variable frequency series resonant withstand voltage detection device according to claim 1, characterized in that: The current and voltage sampling module includes a current sampling unit, a voltage sampling unit, a first filtering unit and a second filtering unit. The first filtering unit and the second filtering unit respectively use different types of filters. The current sampling module is electrically connected to the low-voltage side of the excitation transformer through the shunt resistor. The current sampling module is used to collect the sampled current from the low-voltage side of the excitation transformer; the current sampling module is electrically connected to the first filtering unit and the second filtering unit respectively, and the current sampling module is used to output the sampled current to the first filtering unit and the second filtering unit; the first filtering unit is electrically connected to the compensation capacitor control module, and the first filtering The unit is used to perform a first filtering process on the sampling current, and output the sampling current after the first filtering process to the compensation capacitor control module, the second filtering unit is electrically connected to the resonant frequency sweep prediction module, the second filtering unit is used to perform a second filtering process on the sampling current, and output the sampling current after the second filtering process to the resonant frequency sweep prediction module; the voltage sampling unit is electrically connected to the voltage divider, the resonant frequency sweep prediction module and the compensation capacitor control module respectively, the voltage sampling unit is used to collect a sampling voltage from the voltage divider, and output the sampling voltage to the resonant frequency sweep prediction module and the compensation capacitor control module respectively.

4. The variable frequency series resonant withstand voltage detection device according to claim 3, characterized in that: The voltage sampling unit includes a buffer amplifier, an overvoltage protection circuit, a voltage attenuation circuit and a first isolation amplifier. The low-voltage end of the voltage divider is electrically connected to the overvoltage protection circuit, the buffer amplifier, the voltage attenuation circuit and the first isolation amplifier in sequence. The first isolation amplifier is electrically connected to the resonant frequency sweep prediction module and the compensation capacitor control module, respectively.

5. The variable frequency series resonant withstand voltage detection device according to claim 3, characterized in that: The current sampling unit includes a differential amplifier and a second isolation amplifier, the input end of the differential amplifier is connected to the two ends of the shunt resistor, the output end of the differential amplifier is electrically connected to the second isolation amplifier, and the second isolation amplifier is electrically connected to the first filtering unit and the second filtering unit respectively.

6. A variable frequency series resonant withstand voltage detection method, applied to the variable frequency series resonant withstand voltage detection device according to any one of claims 1 to 5, characterized in that: The variable frequency series resonant withstand voltage detection device comprises an integrated control box, an excitation transformer, a reactor group, a voltage divider and a compensation capacitor group, the input end of the integrated control box is connected to the input voltage, the output end of the integrated control box is electrically connected to the low voltage side of the excitation transformer, the high voltage side of the excitation transformer is electrically connected to the reactor group, the voltage divider and the compensation capacitor group in sequence, the compensation capacitor group is electrically connected to the device to be detected, the integrated control box is directly electrically connected to the voltage divider, and the integrated control box is electrically connected to the low voltage side of the excitation transformer through a shunt resistor; The integrated control box comprises a box body, a variable frequency power supply control module, a resonant frequency sweep prediction module and a current and voltage sampling module, wherein the variable frequency power supply control module, the resonant frequency sweep prediction module and the current and voltage sampling module are all integrated in the box body; the input end of the variable frequency power supply control module is connected to the input voltage, the output end of the variable frequency power supply control module is electrically connected to the low voltage side of the excitation transformer, the variable frequency power supply control module is electrically connected to the resonant frequency sweep prediction module and supplies power to the resonant frequency sweep prediction module; the current and voltage sampling module is directly electrically connected to the voltage divider, and the current and voltage sampling module is electrically connected to the low voltage side of the excitation transformer through the shunt resistor; The integrated control box also includes a compensation capacitor control module, which is integrated in the box, the compensation capacitor control module is electrically connected to the compensation capacitor bank, the variable frequency power supply control module is electrically connected to the compensation capacitor control module and supplies power to the compensation capacitor control module, and the compensation capacitor control module is electrically connected to the current and voltage sampling module and the resonant frequency sweep prediction module respectively; The method comprises the following steps: The device to be detected is electrically connected to the compensation capacitor group, so that the variable frequency series resonant withstand voltage detection device and the device to be detected form a detection main circuit; Acquiring preset detection parameters and device parameters of the device to be detected; Determining an initial frequency of the resonant frequency sweep prediction module in combination with the detection parameter and the device parameter; Based on the initial frequency, the resonance frequency sweep prediction module is controlled to generate a frequency sweep auxiliary signal, and the frequency sweep auxiliary signal is input to the variable frequency power supply control module; The variable frequency power supply control module is used to fuse the auxiliary frequency sweep signal and the preset base signal into a loop frequency sweep signal, and the loop frequency sweep signal is output to the detection main loop; The current and voltage sampling module is used to collect the sampled voltage at the voltage divider, and the sampled current at the low-voltage side of the excitation transformer is collected through the shunt resistor, and the sampled voltage and the sampled current are filtered; The filtered sampled voltage and the sampled current are transmitted to the resonance frequency sweep prediction module, and the resonance frequency sweep prediction module is used to predict the resonance frequency interval where the resonance point in the detection main loop is located; Based on the resonant frequency range and using the variable frequency power supply control module, outputting variable frequency alternating current to the low voltage side of the excitation transformer; The method further comprises the steps of: estimating a loop quality factor of the detection main loop according to the resonant frequency interval; The compensation capacitance increment of the detection main loop is calculated by combining the loop quality factor and the resonant frequency range; According to the capacity errors and parallel effects of all the capacitors in the compensation capacitor group, an optimization constraint condition is established, with minimizing the compensation capacitance increment as the optimization goal, and based on the optimization constraint condition and using an optimization algorithm, an optimal switching scheme of the capacitors in the compensation capacitor group is calculated; A compensation capacitor control signal is generated based on the optimal switching scheme, and the switching of each capacitor in the compensation capacitor group is adjusted by the compensation capacitor control signal.

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