Frequency characteristic compensation method of capacitor voltage transformer

Abstract

A frequency characteristic compensation method for a capacitor voltage transformer comprises the following steps: establishing a broadband equivalent model of the capacitor voltage transformer, deducing a transfer function, and analyzing error characteristics of the capacitor voltage transformer under different frequencies; selecting a plurality of test points according to different frequencies, injecting primary voltages U1 of different frequencies into the capacitive voltage transformer, and collecting a secondary voltage value U2; and an error compensation model is established, the secondary voltage U2 under different frequencies and the corresponding error value epsilon serve as input, the calibrated secondary voltage U2'serves as output, and error compensation of the capacitor voltage transformer is achieved through the error compensation model. The compensated secondary voltage U2'is compared with the initial secondary voltage U2, it is verified that the error compensation model shows a remarkable compensation effect under different frequencies, and the compensated voltage error is greatly reduced. The compensation method is simple and convenient to operate and low in cost; the error of the capacitor voltage transformer can be effectively compensated, so that the measurement precision is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage transformer error compensation, and particularly relates to a frequency characteristic compensation method for a capacitive voltage transformer. Background Art

[0002] As an important power equipment, a capacitive voltage transformer (CVT) is widely used in voltage measurement, relay protection, and electric energy metering in high-voltage and extra-high-voltage power systems. It is favored for its advantages such as low cost and good insulation performance. However, a capacitive voltage transformer (CVT) cannot correctly transmit harmonic voltages, and its error can be as high as 80% - 120%. This requires finding a method to compensate for the error of the capacitive voltage transformer (CVT) to improve its accuracy.

[0003] Currently, the error compensation of a capacitive voltage transformer (CVT) mainly relies on improving the structure of the transformer or using intelligent algorithms, and both methods have their own defects:

[0004] The structure improvement method will increase the volume and cost of the capacitive voltage transformer (CVT), and may also damage the original power frequency resonance structure, resulting in unbalanced frequency band response and affecting normal operation. For example, by connecting a capacitor C3 in series at the low-voltage end of the voltage divider of a conventional capacitive voltage transformer (CVT), the principle of capacitive voltage division is used to obtain the power grid harmonic measurement signal. However, this method will generate phase errors when measuring harmonic voltages, and has high requirements for the accuracy of the series capacitor, thus increasing the cost. In addition, when modifying the structure inside the capacitive voltage transformer (CVT), it is also necessary to redesign the electrical isolation of the device.

[0005] Intelligent algorithms have disadvantages such as strong dependence on training set data, overfitting risk, and high computational complexity. First, the performance of intelligent algorithms usually depends on a large amount of high-quality training data. Insufficient or low-quality data will directly affect the generalization ability of the model, resulting in inaccurate prediction results. Second, overfitting is a common problem in intelligent algorithms, especially when the training data is scarce or the model is too complex. The model may overfit the details and noise in the training data instead of learning more general rules, and thus perform poorly when facing new data. Therefore, the Dropout method proposed by some scholars specifically aims at the overfitting problem in deep neural networks, aiming to reduce overfitting by randomly discarding neurons and thus improving the generalization ability of the model. The overfitting problem is particularly prominent when the data volume is small and the model structure is complex.

[0006] The large-scale application of power electronics technology in fields such as high-voltage direct current transmission, flexible alternating current transmission, and new energy power generation has brought huge harmonic pollution problems to high-voltage power grids. Accurately monitoring the harmonic content in the power grid is the basis and key for harmonic governance. At present, the monitoring of voltage in high-voltage power grids is mainly achieved through the measurement of capacitive voltage transformers (CVTs). The measurement accuracy of capacitive voltage transformers (CVTs) for power frequency voltage can fully meet the requirements of the power grid, but there are large errors in their measurement of harmonics. Therefore, it is necessary to establish a broadband equivalent model of the capacitive voltage transformer and analyze the error characteristics at different frequencies. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a frequency characteristic compensation method for a capacitive voltage transformer, which does not require modifying the structure of the voltage transformer, is simple to operate and has low cost; it can effectively compensate the errors of the capacitive voltage transformer, thereby significantly improving its measurement accuracy.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A frequency characteristic compensation method for a capacitive voltage transformer includes the following steps:

[0010] Step 1: Establish a broadband equivalent model of the capacitive voltage transformer and deduce the transfer function, and analyze the error characteristics of the capacitive voltage transformer at different frequencies;

[0011] Step 2: Select several test points according to different frequencies, inject the primary voltage U1 of different frequencies into the capacitive voltage transformer, and collect the secondary voltage value U2;

[0012] Step 3: Establish an error compensation model, use the secondary voltage U2 at different frequencies and the corresponding error value ε as inputs, and the calibrated secondary voltage U2' as the output, and realize the error compensation of the capacitive voltage transformer through the error compensation model. It also includes Step 4: Compare the compensated secondary voltage U2' with the initial secondary voltage U2, and verify that the error compensation model shows significant compensation effects at different frequencies, and the voltage error after compensation is greatly reduced.

[0013] In the above Step 1, considering the distributed parameters, including: the stray capacitance of the compensating reactor, the stray capacitance of the primary and secondary sides of the intermediate transformer to the ground, and the stray capacitance between the primary and secondary windings of the intermediate transformer, etc., establish a broadband equivalent model, deduce the transfer function, and analyze the frequency characteristics of the capacitive voltage transformer in MATLAB.

[0014] The establishment of the broadband equivalent model is as Figure 1 shown, and the deduction of the transfer function includes the following steps:

[0015] 1) Convert the CVT broadband equivalent circuit parameters into impedance form:

[0016]

[0017] Z5(s) = R T1 + sL T1 (5);

[0018] Z6(s) = R' T2 + sL' T2 (6);

[0019] Z7(s) = R m / / sL m (7);

[0020]

[0021] In the above formula, C1 is the high-voltage capacitor, C2 is the low-voltage capacitor, L k , R k respectively represent the inductance and equivalent resistance of the compensation reactor, C k represents the equivalent stray capacitance of the compensation reactor, C p is the stray capacitance between the primary winding of the intermediate transformer and the ground; R T1 , L T1 respectively represent the primary-side DC resistance and inductance; R' T2 , L' T2 respectively represent the secondary-side DC resistance and inductance; R m , L m respectively represent the exciting resistance and inductance of the intermediate transformer; R' D , L' D respectively represent the resistance and inductance of the damping device; R' L and L' L respectively represent the load resistance and inductance; C s represents the stray capacitance between the secondary winding and the ground; C ps represents the stray capacitance between the primary and secondary windings; s represents the complex frequency domain variable; Z1(s) represents the impedance of the high-voltage capacitor; Z2(s) represents the impedance of the low-voltage capacitor; Z3(s) represents the impedance of the compensation reactor; Z4(s) represents the impedance of the stray capacitance between the primary side of the intermediate transformer and the ground; Z5(s) represents the impedance of the primary side of the intermediate transformer; Z6(s) represents the impedance of the secondary side of the intermediate transformer; Z7(s) represents the exciting impedance of the intermediate transformer; Z8(s) represents the sum of the impedance values of the damping device, the load, and the stray capacitance between the secondary side of the intermediate transformer and the ground; Z9(s) represents the impedance of the stray capacitance between the primary and secondary windings of the intermediate transformer;

[0022] 2) Through methods such as series-parallel combination and star-delta transformation, for Figure 1Simplify the broadband equivalent circuit of the capacitive voltage transformer and calculate the transfer function based on this.

[0023]

[0024] Analyze the error characteristics of the capacitive voltage transformer at different frequencies; specifically as follows:

[0025] According to Figure 1 The established broadband equivalent circuit of the capacitive voltage transformer, derive the transfer function to characterize the relationship between the output voltage and the input voltage of the CVT, and use MATLAB for frequency characteristic analysis.

[0026] In step 2, select multiple test points such as 100Hz, 500Hz, 1000Hz, 2000Hz, 2500Hz, 3000Hz, etc. to ensure coverage of the main working frequency band, collect error data at the test point frequencies; then, inject the voltage U1 at different frequencies into the capacitive voltage transformer through a high-precision voltage source, and collect the actual output secondary voltage U2. The specific results are shown in Table 1.

[0027] Table 1 Error data collection table of capacitive voltage transformer

[0028]

[0029] In step 3, the error compensation model is specifically as follows:

[0030]

[0031] In formula (11), U2 is the collected secondary voltage value, ε is the error value at different frequencies, and U2’ is the compensated secondary voltage.

[0032] For the frequency characteristic compensation method of a capacitive voltage transformer of the present invention, the technical effects are as follows:

[0033] 1) By establishing a broadband equivalent model and an error compensation model, the present invention realizes the error correction of the capacitive voltage transformer, without the need to upgrade the hardware or transform the structure of the existing equipment. Compared with the traditional method, it avoids high hardware cost investment and does not rely on complex intelligent algorithms, greatly reducing the implementation cost. This economical and efficient characteristic makes this method highly applicable and popularizable in various voltage measurement scenarios such as high-voltage power grids and harmonic measurements.

[0034] 2) By analyzing the real-time measured frequency and secondary voltage values, the method of the present invention can quickly adjust the compensation parameters and dynamically correct the output error of the capacitive voltage transformer. Whether under the condition of rapid change of power grid harmonic frequency or in the voltage measurement scenarios of different frequencies, this method can efficiently compensate the secondary voltage value and ensure the measurement accuracy and stability. This real-time compensation ability greatly improves the practicability and reliability of the capacitive voltage transformer (CVT) in a complex power grid environment.

[0035] 3) The present invention only relies on the collected error data and mathematical model, and can achieve error compensation through a simple calculation formula, avoiding the modification of the hardware structure of the capacitive voltage transformer. This not only protects the functional integrity of the original equipment, but also greatly reduces the technical complexity and workload in the engineering implementation process. With simple operation and remarkable effect, this method is especially suitable for rapid application in the engineering field. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described below in conjunction with the drawings and examples;

[0037] Figure 1 It is a schematic diagram of the broadband equivalent model of the capacitive voltage transformer.

[0038] Figure 2 It is a frequency characteristic curve. DETAILED DESCRIPTION OF THE INVENTION

[0039] A frequency characteristic compensation method for a capacitive voltage transformer. First, considering the influence of stray capacitance, a broadband equivalent model of the capacitive voltage transformer is established, the transfer function is derived, and the frequency characteristics of the capacitive voltage transformer (CVT) are analyzed. Secondly, the errors of the CVT at different frequencies are collected. Several representative test points are selected, and a high-precision voltage source is used to inject primary voltages of different frequencies into the CVT, and the output secondary voltage values are collected. Subsequently, the collected secondary voltages and the corresponding error values are used as inputs, and the compensated secondary voltage is used as the output, and the error compensation of the capacitive voltage transformer is realized through a mathematical model. Finally, by comparing the compensated secondary voltage with the original secondary voltage, it shows that the method of the present invention has a good error compensation effect and can effectively improve the measurement accuracy of the capacitive voltage transformer. The specific steps are as follows:

[0040] Step 1: Establish a broadband equivalent model of the capacitive voltage transformer:

[0041] Considering distributed parameters, such as the stray capacitance of the compensation reactor, the stray capacitance between the primary and secondary sides of the intermediate transformer to the ground, and the stray capacitance between the primary and secondary windings of the intermediate transformer, etc., a broadband equivalent model is established, the transfer function is derived, and the frequency characteristics of the capacitive voltage transformer are analyzed in MATLAB.

[0042] Table 2 Parameters of 110 kV Fast Saturation Type CVT

[0043]

[0044]

[0045] Table 2 shows the broadband equivalent circuit parameter values of the CVT, which are required for deriving the transfer function. Among them, it includes distributed parameters, and the distributed parameters are C k , C p , C ps , Cc, these four stray capacitance values.

[0046] Among them, deriving the transfer function includes the following steps:

[0047] 1) Convert the circuit parameters into impedance form:

[0048]

[0049] Z5(s) = R T1 + sL T1 (5);

[0050] Z6(s) = R' T2 + sL' T2 (6);

[0051] Z7(s) = R m / / sL m (7);

[0052]

[0053] In the formula, C1 is the high-voltage capacitor, C2 is the low-voltage capacitor, L k , R k respectively represent the inductance of the compensation reactor and the equivalent resistance, C k represents its equivalent stray capacitance, C p is the stray capacitance between the primary winding of the intermediate transformer and the ground, R T1 , L T1 represent the primary side DC resistance and inductance, R' T2 , L' T2 respectively represent the secondary side DC resistance and inductance, R m , L m respectively represent the exciting resistance and inductance of the intermediate transformer, R' D , L' D respectively represent the resistance and inductance of the damping device, R' L and L' L respectively represent the load resistance and inductance, C s represents the stray capacitance between the secondary winding and the ground; Cps represents the stray capacitance between the primary and secondary windings, and s represents the complex frequency domain variable.

[0054] 2) By simplifying and combining the equivalent circuit, calculate the transfer function:

[0055]

[0056] In Equation (10), Z1(s) is the high-voltage capacitor impedance, Z2(s) is the low-voltage capacitor impedance, Z3(s) is the compensation reactor impedance, Z4(s) is the stray capacitance impedance between the primary side of the intermediate transformer and the ground, Z5(s) is the primary side impedance of the intermediate transformer, Z6(s) is the secondary side impedance of the intermediate transformer, Z7(s) is the excitation impedance of the intermediate transformer, Z8(s) is the sum of the impedance values of the damping device, the load, and the stray capacitance between the secondary side of the intermediate transformer and the ground, and Z9(s) is the stray capacitance impedance between the primary and secondary windings of the intermediate transformer.

[0057] Step 2: Collect data:

[0058] Select multiple test points such as 100Hz, 500Hz, 1000Hz, 2000Hz, 2500Hz, 3000Hz, etc. to ensure coverage of the main working frequency band, and collect the error data ε at the test point frequencies; then, inject the voltage U1 at different frequencies into the capacitive voltage transformer through a high-precision voltage source, and collect the actual output secondary voltage U2

[0059] Step 3: Establish an error compensation model:

[0060] Take the secondary voltage U2 at different frequencies and the corresponding error values ε as inputs, and the calibrated secondary voltage U2’ as the output, and realize the error compensation of the capacitive voltage transformer through a mathematical model. The formula is:

[0061]

[0062] In Equation (11), U2 is the collected secondary voltage value, Kc is the voltage division ratio of the capacitive voltage divider, Z1(s) is the high-voltage capacitor impedance of C1, Z2(s) is the low-voltage capacitor impedance of C2, Z3(s) is the compensation reactor impedance, Z4(s) is the p stray capacitance impedance between the primary side of the intermediate transformer and the ground, Z5(s) is the primary side impedance of the intermediate transformer, Z6(s) is the secondary side impedance of the intermediate transformer, Z7(s) is the excitation impedance of the intermediate transformer, Z8(s) is the sum of the impedance values of the damping device, the load, and the stray capacitance between the secondary side of the intermediate transformer and the ground, Z9(s) is the stray capacitance impedance between the primary and secondary windings of the intermediate transformer, and U2’ is the compensated secondary voltage.

[0063] Step 4: Accuracy verification:

[0064] By comparing the corrected secondary voltage U2’ with the initial secondary voltage U2, it is verified that the compensation model shows significant compensation effects at different frequencies (such as 100Hz, 500Hz, 1000Hz, 2000Hz, etc.). The voltage measurement error after compensation is greatly reduced and meets the accuracy requirements at each test frequency point, as shown in Table 3.

[0065] Table 3 Correction Table of Capacitive Voltage Transformer Error Data

[0066]

[0067] Compared with the traditional compensation method, this method can improve the measurement accuracy without changing the hardware structure, has a lower implementation cost, and is easy to operate. It significantly enhances the applicability of CVT in the fields of power grid harmonic governance, relay protection, and power metering, providing important technical support for the accurate measurement and optimal operation of power systems.

Claims

1. A method for compensating the frequency characteristics of a capacitive voltage transformer, characterized in that The following steps are involved: Step 1: Establish a wide-band equivalent model of capacitor voltage transformer and derive the transfer function, and analyze the error characteristics of capacitor voltage transformer at different frequencies; Step 2: Select several test points according to different frequencies, inject the primary voltage U1 of different frequencies into the capacitive voltage mutual inductance, and collect the secondary voltage value U2; Step 3: Establish an error compensation model, take the secondary voltage U2 at different frequencies and the corresponding error value ε as input, and the calibrated secondary voltage U2' as output, and realize the error compensation of the capacitive voltage transformer through the error compensation model.

2. The method for compensating the frequency characteristics of a capacitive voltage transformer according to claim 1, characterized in that: The method further includes step 4: comparing the compensated secondary voltage U2' with the initial secondary voltage U2, and verifying that the voltage error after compensation by the error compensation model at different frequencies is significantly reduced.

3. The method for compensating the frequency characteristics of a capacitive voltage transformer according to claim 1, characterized in that: In the step 1, distributed parameters are considered, including: stray capacitance of the compensating reactor, stray capacitance of the primary and secondary sides of the intermediate transformer to ground, and stray capacitance between the primary and secondary windings of the intermediate transformer, etc., a broadband equivalent model is established, and a transfer function is derived, and the frequency characteristics of the capacitive voltage transformer are analyzed in MATLAB.

4. The method for compensating the frequency characteristics of a capacitive voltage transformer according to claim 3, characterized in that: Establishing a broadband equivalent model and deriving the transfer function includes the following steps: 1) Convert the CVT broadband equivalent circuit parameters into impedance form: Z5(s)=R T1 +sL T1 (5); Z6(s)=R' T2 +sL' T2 (6); Z7(s)=R m / / sL m (7); In the above formula, C1 is the high voltage capacitor, C2 is the low voltage capacitor, L k , R k Respectively represent the inductance and equivalent resistance of the compensation reactor, C k Indicates the equivalent stray of the compensation reactor, C p is the stray capacitance of the primary winding of the intermediate transformer to the ground; R T1 , L T1 Respectively represent the primary side DC resistance and inductance; R' T2 , L' T2 Respectively represent the secondary side DC resistance and inductance; R m , L m Respectively represent the magnetizing resistance and inductance of the intermediate transformer; R' D , L' D Respectively represent the resistance and inductance of the damping device; R' L and L' L Respectively represent load resistance and inductance; C s Represents the stray capacitance of the secondary winding to ground; C ps represents the stray capacitance between the primary and secondary windings; s represents a complex frequency domain variable; Z1(s) represents the high-voltage capacitor impedance; Z2(s) represents the low-voltage capacitor impedance; Z3(s) represents the compensating reactor impedance; Z4(s) represents the stray capacitance impedance of the primary side of the intermediate transformer to the ground; Z5(s) represents the primary impedance of the intermediate transformer; Z6(s) represents the secondary impedance of the intermediate transformer; Z7(s) represents the magnetizing impedance of the intermediate transformer; Z8(s) represents the sum of the impedance values ​​of the damping device, the load and the secondary stray capacitance of the intermediate transformer to the ground; Z9(s) represents the stray capacitance impedance between the primary and secondary windings of the intermediate transformer; 2) Simplify the broadband equivalent circuit of the capacitive voltage transformer and calculate the transfer function based on it; 5. The method for compensating the frequency characteristics of a capacitive voltage transformer according to claim 1, characterized in that: In step 2, multiple test points such as 100Hz, 500Hz, 1000Hz, 2000Hz, 2500Hz, and 3000Hz are selected to ensure that the main working frequency band is covered, and error data of the test point frequency is collected; then, the voltage U1 at different frequencies is injected into the capacitive voltage transformer through a voltage source, and the actual output secondary voltage U2 is collected.

6. The method for compensating the frequency characteristics of a capacitive voltage transformer according to claim 1, characterized in that: In step 3, the error compensation model is specifically as follows: In formula (11), U2 is the collected secondary voltage value, ε is the error value at different frequencies, and U2' is the compensated secondary voltage.

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