An ultra-low frequency sinusoidal high voltage generator for power frequency high voltage modulation and demodulation

Abstract

This invention relates to an ultra-low frequency sinusoidal high-voltage generator for power frequency high-voltage modulation and demodulation, belonging to the field of high-voltage electrical equipment insulation performance testing technology. Addressing the problems of complex circuit structures and low voltage conversion efficiency in existing ultra-low frequency high-voltage power supplies, this invention incorporates boost, modulation, demodulation, feedback control, measurement, and filtering units. It utilizes a bridge-type silicon stack and a high-voltage power electronic switch to form an AC controllable switch for direct modulation of the power frequency high voltage. Dual voltage comparators, combined with XOR gate logic, control the switch's on / off state. A resistor-capacitor integration circuit completes demodulation and provides a time constant constraint formula to optimize the output waveform. The overall structure is simple, with high energy utilization, and can be widely applied to on-site insulation testing scenarios for XLPE power cables, including withstand voltage, dielectric loss, and water tree defects.

Description

Technical Field

[0001] This invention relates to the field of insulation performance testing of high-voltage insulating materials and high-voltage electrical equipment, and specifically to an ultra-low frequency sinusoidal high-voltage generator for power frequency high-voltage modulation and demodulation. Background Technology

[0002] Frequency-domain dielectric spectroscopy is one of the most widely accepted and used methods for diagnosing insulation condition. It characterizes the insulation state by measuring the wide-frequency characteristics of dielectric constant and dielectric loss. The low frequencies of frequency-domain dielectric spectra reach below 10⁻³ Hz, and the measurement voltage is typically below 1 kV. When measuring frequency-domain dielectric spectra with different electric field strengths, higher voltage levels are required to meet the testing requirements.

[0003] XLPE cables are widely used in power systems. Due to their long laying distances and large insulation equivalent capacitance, field testing at power frequency voltage is difficult, limited by power supply and equipment capacity. Ultra-low frequency (ULF) testing, on the other hand, requires very small power supply and equipment capacities, making it convenient for field use. It can perform withstand voltage tests and dielectric loss measurements, and its water tree defect detection is highly equivalent to power frequency testing, making it a primary test for power cable field testing. Given the massive amount of power cable laid in China, there is a high demand for a large quantity of ULF sinusoidal high-voltage power supplies to meet field testing needs.

[0004] High-voltage power at power frequency and high frequency is easily obtained by stepping up the voltage using a test transformer. However, due to the extremely low operating frequency, ultra-low frequency high voltage cannot be obtained using this method. Currently, commercially available ultra-low frequency sinusoidal low-voltage power supplies are achieved through linear power amplification. However, this method is very difficult to implement due to the limitations of the operating voltage of the linear amplification components. Commercially available ultra-low frequency sinusoidal high-voltage power supplies are achieved through modulation and demodulation. The common approach involves modulating a low-voltage, high-frequency power supply, stepping it up, rectifying it into a DC high voltage with variable amplitude and polarity, and finally using nonlinear resistors and capacitors for demodulation to obtain the ultra-low frequency sinusoidal voltage. The problems with ultra-low frequency sinusoidal high-voltage power supplies are complex circuit principles and relatively low voltage efficiency.

[0005] With the development of power electronics technology, high-voltage amplitude power electronic switches have been gradually put into use, including fully controlled power electronic switches with rated voltages exceeding 40kV. The emergence of high-voltage power electronic switches has made it possible to generate ultra-low frequency sinusoidal high voltage through modulation and demodulation under high voltage. This invention utilizes high-voltage power electronic switches to provide a new method for generating ultra-low frequency sinusoidal high voltage and a method for obtaining key electrical parameters.

[0006] Frequency-domain dielectric spectroscopy is one of the most widely accepted and used methods for diagnosing insulation condition. It characterizes the insulation state by measuring the wide-frequency characteristics of dielectric constant and dielectric loss. The low frequencies of frequency-domain dielectric spectra reach below 10⁻³ Hz, and the measurement voltage is typically below 1 kV. When measuring frequency-domain dielectric spectra with different electric field strengths, higher voltage levels are required to meet the testing requirements.

[0007] XLPE cables are widely used in power systems. Due to their long laying distances and large insulation equivalent capacitance, field testing at power frequency voltage is difficult, limited by power supply and equipment capacity. Ultra-low frequency (ULF) testing, on the other hand, requires very small power supply and equipment capacities, making it convenient for field use. It can perform withstand voltage tests and dielectric loss measurements, and its water tree defect detection is highly equivalent to power frequency testing, making it a primary test for power cable field testing. Given the massive amount of power cable laid in China, there is a high demand for a large quantity of ULF sinusoidal high-voltage power supplies to meet field testing needs.

[0008] High-voltage power at power frequency and high frequency is easily obtained by stepping up the voltage using a test transformer. However, due to the extremely low operating frequency, ultra-low frequency high voltage cannot be obtained using this method. Currently, commercially available ultra-low frequency sinusoidal low-voltage power supplies are achieved through linear power amplification. However, this method is very difficult to implement due to the limitations of the operating voltage of the linear amplification components. Commercially available ultra-low frequency sinusoidal high-voltage power supplies are achieved through modulation and demodulation. The common approach involves modulating a low-voltage, high-frequency power supply, stepping it up, rectifying it into a DC high voltage with variable amplitude and polarity, and finally using nonlinear resistors and capacitors for demodulation to obtain the ultra-low frequency sinusoidal voltage. The problems with ultra-low frequency sinusoidal high-voltage power supplies are complex circuit principles and relatively low voltage efficiency.

[0009] With the development of power electronics technology, high-voltage amplitude power electronic switches have been gradually put into use, including fully controlled power electronic switches with rated voltages exceeding 40kV. The emergence of high-voltage power electronic switches has made it possible to generate ultra-low frequency sinusoidal high voltage through modulation and demodulation under high voltage. This invention utilizes high-voltage power electronic switches to provide a new method for generating ultra-low frequency sinusoidal high voltage and a method for obtaining key electrical parameters. Summary of the Invention

[0010] To address the technical challenges of complex circuit structures and low voltage efficiency in existing ultra-low frequency sinusoidal high-voltage power supplies, this invention provides an ultra-low frequency sinusoidal high-voltage generator with power frequency high-voltage modulation and demodulation, comprising: a boost unit, a modulation unit, a demodulation unit, a feedback control unit, a measurement unit, and a filtering unit.

[0011] The boost unit uses a test transformer T1, whose input is connected to a power frequency power supply. The secondary high-voltage side is connected in series with the demodulation resistor R1 from the modulation unit and the demodulation unit, and then connected to the demodulation capacitor C.P One end of the demodulation capacitor C P The other end is connected to the test sample C X The high-voltage end;

[0012] The measurement unit includes a capacitive voltage divider and a resistive voltage divider; the capacitive voltage divider consists of a high-voltage arm capacitor C. H and low-voltage arm capacitor C L The capacitor C is connected in series and in parallel to the secondary side of the test transformer T1. L The voltage divider outputs a power frequency voltage signal at both ends; the resistor divider consists of a high-voltage arm resistor R. H and low voltage arm resistor R L It is connected in series and in parallel to the demodulation capacitor C. P At both ends, the low-voltage arm resistor R L The outputs ultra-low frequency voltage signals at both ends;

[0013] The filtering unit consists of a filtering resistor R2, which is connected in series with the demodulation capacitor C. P With the test sample C X between;

[0014] The modulation unit is composed of a bridge rectifier circuit consisting of high-voltage silicon stacks D1, D2, D3 and D4 connected in series with a fully controlled power electronic high-voltage switch K1. The fully controlled power electronic high-voltage switch K1 is controlled by the feedback control unit.

[0015] The input terminal of the feedback control unit receives the power frequency voltage signal and the ultra-low frequency voltage signal respectively, and its output terminal is connected to the control electrode of the fully controlled power electronic high-voltage switch K1. It is used to compare the ultra-low frequency voltage signal with the ultra-low frequency standard sine wave signal and the power frequency voltage signal respectively, and control the fully controlled power electronic high-voltage switch K1 to switch on and off based on the comparison result, thereby controlling the demodulation capacitor C. P An ultra-low frequency sinusoidal high voltage is generated and applied to the test sample C. X .

[0016] Furthermore, the feedback control unit includes: a first voltage comparator A1, a second voltage comparator A2, and an XOR gate U1;

[0017] The first voltage comparator A1 has an ultra-low frequency standard sine wave signal connected to its non-inverting input and an ultra-low frequency voltage signal connected to its inverting input; the second voltage comparator A2 has an industrial frequency voltage signal connected to its non-inverting input and an ultra-low frequency voltage signal connected to its inverting input.

[0018] The two input terminals of the XOR gate U1 are respectively connected to the output terminals of the first voltage comparator A1 and the second voltage comparator A2, and its output terminal is connected to the control terminal of the fully controlled power electronic high-voltage switch K1. When the output logic levels of the first voltage comparator A1 and the second voltage comparator A2 are the same, the XOR gate U1 outputs a high level to drive the fully controlled power electronic high-voltage switch K1 to conduct.

[0019] Furthermore, the demodulation resistor R1 and the demodulation capacitor C P The time constant satisfies the following constraint:

[0020]

[0021] Where k is the ratio of the power frequency high voltage amplitude to the target ultra-low frequency high voltage amplitude, and k>1; ω1 represents the initial phase of the power frequency voltage at the start of charging, and ω2 represents the angular frequency of the ultra-low frequency high voltage.

[0022] The beneficial effects of this invention are as follows: This solution directly relies on the power frequency high voltage for modulation and demodulation, resulting in a simple overall circuit architecture that facilitates engineering implementation; the use of a resistor-capacitor structure for demodulation processing leads to higher voltage conversion efficiency; the use of a high-voltage power electronic switch for power frequency high voltage modulation eliminates the need for multi-stage boost rectifier relay structures, reducing the number of supporting components; the addition of a filter structure effectively suppresses high-frequency components in the output voltage, resulting in superior output waveform quality; the entire system is adaptable to on-site cable insulation testing scenarios, offering ease of use and excellent overall operational stability. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the principle circuit of an ultra-low frequency sinusoidal high voltage generator for power frequency high voltage modulation and demodulation.

[0024] Figure 2 This is a schematic diagram comparing the waveforms of power frequency high voltage and ultra-low frequency high voltage.

[0025] Figure 3 The graph shows the relationship between the demodulation resistor-capacitor time constant and the initial phase and the power frequency voltage multiple. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, process equipment or devices not specifically specified are all conventional equipment or devices in the art. Unless specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0027] Example 1, combined with Figure 1 This embodiment describes an ultra-low frequency sinusoidal high voltage generator with power frequency high voltage modulation and demodulation, comprising: a boost unit, a modulation unit, a demodulation unit, a feedback control unit, a measurement unit, and a filtering unit;

[0028] The boost unit uses a test transformer T1, whose input is connected to a power frequency power supply. The secondary high-voltage side is connected in series with the demodulation resistor R1 from the modulation unit and the demodulation unit, and then connected to the demodulation capacitor C. P One end of the demodulation capacitor C P The other end is connected to the test sample C X The high-voltage end;

[0029] The measurement unit includes a capacitive voltage divider and a resistive voltage divider; the capacitive voltage divider consists of a high-voltage arm capacitor C. H and low-voltage arm capacitor C L The capacitor C is connected in series and in parallel to the secondary side of the test transformer T1. L The voltage divider outputs a power frequency voltage signal at both ends; the resistor divider consists of a high-voltage arm resistor R. H and low voltage arm resistor R L It is connected in series and in parallel to the demodulation capacitor C. P At both ends, the low-voltage arm resistor R L The outputs ultra-low frequency voltage signals at both ends;

[0030] The filtering unit consists of a filtering resistor R2, which is connected in series with the demodulation capacitor C. P With the test sample C X between;

[0031] The modulation unit is composed of a bridge rectifier circuit consisting of high-voltage silicon stacks D1, D2, D3 and D4 connected in series with a fully controlled power electronic high-voltage switch K1. The fully controlled power electronic high-voltage switch K1 is controlled by the feedback control unit.

[0032] The input terminal of the feedback control unit receives the power frequency voltage signal and the ultra-low frequency voltage signal respectively, and its output terminal is connected to the control electrode of the fully controlled power electronic high-voltage switch K1. It is used to compare the ultra-low frequency voltage signal with the ultra-low frequency standard sine wave signal and the power frequency voltage signal respectively, and control the fully controlled power electronic high-voltage switch K1 to switch on and off based on the comparison result, thereby controlling the demodulation capacitor C. P An ultra-low frequency sinusoidal high voltage is generated and applied to the test sample C. X .

[0033] Specifically, Figure 1This is a schematic diagram of the generator's circuit principle, fully illustrating the electrical topology and signal connections of each unit, including boost, modulation, demodulation, measurement, filtering, and feedback control. In this embodiment, the high-voltage silicon stack uses a bridge connection, with a fully controllable power electronic high-voltage switch connected to the DC side. Together, they form an AC controllable switch, serving as the generator's modulation component, its on / off state controlled by the modulation signal. The demodulation resistor and demodulation capacitor are connected in series to form an integrating circuit, used to demodulate the modulated power frequency high voltage. The filtering resistor and the test sample capacitor together form a first-order filtering circuit, which further eliminates high-frequency components in the output voltage, improving waveform quality. The entire circuit is grounded at the low-voltage end of the test sample. During operation, the test transformer outputs a power frequency high voltage, which is chopper-modulated by the AC controllable switch and then sent to the demodulation unit. Through RC integral demodulation, an ultra-low frequency sinusoidal high voltage is obtained, which is then optimized by the filtering unit before being output to the test sample.

[0034] Furthermore, the feedback control unit includes: a first voltage comparator A1, a second voltage comparator A2, and an XOR gate U1;

[0035] The first voltage comparator A1 has an ultra-low frequency standard sine wave signal connected to its non-inverting input and an ultra-low frequency voltage signal connected to its inverting input; the second voltage comparator A2 has an industrial frequency voltage signal connected to its non-inverting input and an ultra-low frequency voltage signal connected to its inverting input.

[0036] The two input terminals of the XOR gate U1 are respectively connected to the output terminals of the first voltage comparator A1 and the second voltage comparator A2, and its output terminal is connected to the control terminal of the fully controlled power electronic high-voltage switch K1. When the output logic levels of the first voltage comparator A1 and the second voltage comparator A2 are the same, the XOR gate U1 outputs a high level to drive the fully controlled power electronic high-voltage switch K1 to conduct.

[0037] Specifically, the first voltage comparator compares the ultra-low frequency standard sine wave signal with the ultra-low frequency voltage sampling signal. When the ultra-low frequency standard signal is greater than the ultra-low frequency voltage signal, it outputs a logic high level; otherwise, it outputs a logic low level. The second voltage comparator compares the power frequency voltage signal with the ultra-low frequency voltage signal. When the power frequency voltage signal is greater than the ultra-low frequency voltage signal, it outputs a logic high level; otherwise, it outputs a logic low level. When both comparator outputs are high, the high-voltage switch is on. The mains frequency high voltage is greater than the ultra-low frequency high voltage. The mains frequency high voltage charges the demodulation capacitor positively through the high-voltage switch and demodulation resistor, causing the voltage to rise continuously until the ultra-low frequency standard signal is less than or equal to the ultra-low frequency voltage signal. At this point, the first voltage comparator output goes low, the XOR gate output goes low, the high-voltage switch turns off, and the forward charging ends. When both comparator outputs are low, the high-voltage switch is also on. The mains frequency high voltage is lower than the ultra-low frequency high voltage. The mains frequency high voltage charges the demodulation capacitor negatively through the high-voltage switch and demodulation resistor, causing the voltage to fall continuously until the ultra-low frequency standard signal is greater than or equal to the ultra-low frequency voltage signal. At this point, the first voltage comparator output goes high, the XOR gate output goes low, the high-voltage switch turns off, and the reverse charging ends. By periodically switching the high-voltage switch on and off, the mains frequency voltage is modulated. Combined with RC filtering, a stable ultra-low frequency sinusoidal high voltage can be obtained on the demodulation capacitor.

[0038] Furthermore, the demodulation resistor R1 and the demodulation capacitor C P The time constant satisfies the following constraint:

[0039]

[0040] Where k is the ratio of the power frequency high voltage amplitude to the target ultra-low frequency high voltage amplitude, and k>1; ω1 represents the initial phase of the power frequency voltage at the start of charging, and ω2 represents the angular frequency of the ultra-low frequency high voltage.

[0041] Specifically, Figure 2 This diagram illustrates the waveform comparison between power frequency high voltage and ultra-low frequency high voltage, visually demonstrating the amplitude and frequency correspondence between the two, providing a waveform basis for demodulation parameter derivation. To obtain a good ultra-low frequency output waveform, the values ​​of the demodulation resistor and demodulation capacitor must be appropriately matched: when the demodulation circuit time constant is too small, the charging and discharging speed is fast, and the charging and discharging current within a single power frequency cycle is large; when the demodulation circuit time constant is too large, the charging and discharging speed is slow, and effective charging and discharging cannot be completed within a single power frequency cycle, resulting in ultra-low frequency high voltage waveform distortion and decreased voltage efficiency. The optimal parameter determination condition is: within a single power frequency cycle, under the action of effective charging time and corresponding power frequency voltage, the voltage change caused by the charging and discharging of the demodulation capacitor is exactly equal to the change in ultra-low frequency voltage within that power frequency cycle.

[0042] Assume the amplitude of the ultra-low frequency high voltage is the same as u. m The amplitude of the power frequency high voltage is kUm The voltage conversion efficiency is (1 / k)×100%. The frequency of the power frequency high voltage is 50Hz, and the frequency of the ultra-low frequency high voltage is 0.1Hz. Mathematical analysis is performed taking the example of the power frequency high voltage being greater than the ultra-low frequency high voltage, the high voltage switch being turned on, and the demodulation capacitor being forward charged. Let the instantaneous power frequency high voltage be u1, the instantaneous ultra-low frequency high voltage be u2, and the angular frequency of the power frequency high voltage be... At the initial moment of conduction, the initial phase of the power frequency is φ. At the initial charging moment (0), the initial voltage at the power frequency is u. 10 The initial voltage of the ultra-low frequency is u 20 To ensure the quality of the ultra-low frequency voltage on the capacitor under test, let C... P >>C x Ignoring the effect of the test sample's capacitance on charging, the voltage relationship of the charging circuit is as follows:

[0043] (1)

[0044] The voltage equation across the capacitor is:

[0045] (2)

[0046] The solution to the equation is:

[0047]

[0048] (3)

[0049] in:

[0050]

[0051] Only a tiny voltage change occurs across the demodulation capacitor in each power frequency cycle, satisfying the requirement... Condition, at this time:

[0052]

[0053] The solution to the equation can be simplified to:

[0054] (4)

[0055] The ultra-low frequency voltage only underwent a slight change, and the power frequency phase can be considered to be... The current charging ends at -2φ, with the highest voltage u obtained on the demodulation capacitor. 2m for:

[0056] (5)

[0057] Let the angular frequency of the ultra-low frequency voltage be... In one power frequency cycle, the phase change of the ultra-low frequency standard voltage is:

[0058] (6)

[0059] Let the initial phase of the ultra-low frequency voltage be... Its initial voltage is:

[0060] (7)

[0061] After one power frequency charging cycle is completed, the ultra-low frequency voltage is:

[0062] (8)

[0063] The generator can operate normally when the demodulation capacitor charging voltage is greater than or equal to the ultra-low frequency voltage within the power frequency cycle.

[0064]

[0065] (9)

[0066] Expanding the exponential function using Taylor and ignoring higher-order terms, we get:

[0067] (10)

[0068] Further organized as follows:

[0069]

[0070] Therefore, the time constant formed by the product of the demodulation resistor and the demodulation capacitor is determined by the power frequency voltage multiple k, the initial phase φ, and the angular frequency of the ultra-low frequency voltage. 2. Determine.

[0071] Figure 3 The relationship curve between the demodulation resistor-capacitor time constant and the initial phase and the power frequency voltage multiple clearly reflects the optimal parameter value rule: at any power frequency voltage multiple, as the initial phase increases, the product of the demodulation resistor and demodulation capacitor first decreases and then increases, with the minimum value being the optimal parameter; as the power frequency voltage multiple increases, the minimum value of the time constant gradually increases. In this embodiment, equality is taken as the optimal design condition. When the ultra-low frequency voltage frequency is 0.1Hz, the power frequency voltage frequency is 50Hz, and k=1.2, the corresponding voltage conversion rate is 83%, and the optimal time constant can be calculated.

[0072] (s)

[0073] When the demodulation capacitor is 1μF, the demodulation resistor is 168kΩ.

Claims

1. A low-frequency sinusoidal high-voltage generator for power frequency high-voltage modulation and demodulation, characterized in that, include: Boost unit, modulation unit, demodulation unit, feedback control unit, measurement unit, and filtering unit; The boost unit uses a test transformer T1, whose input is connected to a power frequency power supply. The secondary high-voltage side is connected in series with the demodulation resistor R1 from the modulation unit and the demodulation unit, and then connected to the demodulation capacitor C. P One end of the demodulation capacitor C P The other end is connected to the test sample C X The high-voltage end; The measurement unit includes a capacitive voltage divider and a resistive voltage divider; the capacitive voltage divider consists of a high-voltage arm capacitor C. H and low-voltage arm capacitor C L The capacitor C is connected in series and in parallel to the secondary side of the test transformer T1. L The voltage divider outputs a power frequency voltage signal at both ends; the resistor divider consists of a high-voltage arm resistor R. H and low voltage arm resistor R L It is connected in series and in parallel to the demodulation capacitor C. P At both ends, the low-voltage arm resistor R L The outputs ultra-low frequency voltage signals at both ends; The filtering unit consists of a filtering resistor R2, which is connected in series with the demodulation capacitor C. P With the test sample C X between; The modulation unit is composed of a bridge rectifier circuit consisting of high-voltage silicon stacks D1, D2, D3 and D4 connected in series with a fully controlled power electronic high-voltage switch K1. The fully controlled power electronic high-voltage switch K1 is controlled by the feedback control unit. The input terminal of the feedback control unit receives the power frequency voltage signal and the ultra-low frequency voltage signal respectively, and its output terminal is connected to the control electrode of the fully controlled power electronic high-voltage switch K1. It is used to compare the ultra-low frequency voltage signal with the ultra-low frequency standard sine wave signal and the power frequency voltage signal respectively, and control the fully controlled power electronic high-voltage switch K1 to switch on and off based on the comparison result, thereby controlling the demodulation capacitor C. P An ultra-low frequency sinusoidal high voltage is generated and applied to the test sample C. X .

2. The ultra-low frequency sinusoidal high voltage generator for power frequency high voltage modulation and demodulation according to claim 1, characterized in that, The feedback control unit includes: a first voltage comparator A1, a second voltage comparator A2, and an XOR gate U1; The first voltage comparator A1 has an ultra-low frequency standard sine wave signal connected to its non-inverting input and an ultra-low frequency voltage signal connected to its inverting input; the second voltage comparator A2 has an industrial frequency voltage signal connected to its non-inverting input and an ultra-low frequency voltage signal connected to its inverting input. The two input terminals of the XOR gate U1 are respectively connected to the output terminals of the first voltage comparator A1 and the second voltage comparator A2, and its output terminal is connected to the control terminal of the fully controlled power electronic high-voltage switch K1. When the output logic levels of the first voltage comparator A1 and the second voltage comparator A2 are the same, the XOR gate U1 outputs a high level to drive the fully controlled power electronic high-voltage switch K1 to conduct.

3. The ultra-low frequency sinusoidal high voltage generator for power frequency high voltage modulation and demodulation according to claim 1, characterized in that, The demodulation resistor R1 and the demodulation capacitor C P The time constant satisfies the following constraint: Where k is the ratio of the power frequency high voltage amplitude to the target ultra-low frequency high voltage amplitude, and k>1; ω1 represents the initial phase of the power frequency voltage at the start of charging, and ω2 represents the angular frequency of the ultra-low frequency high voltage.

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