Intelligent compensation type capacitor voltage transformer

Abstract

The invention discloses an intelligent compensation type capacitive voltage transformer which comprises a low-frequency compensation branch circuit which adopts a series resonance isolation and parallel capacitive compensation structure, a first series resonance inductor L1 and a first series resonance capacitor C1 are connected in series and then are connected with a parallel compensation capacitor Ccomp in parallel, and the series resonance of the L1 to the C1 at a power frequency is realized to realize the transparency of a power frequency signal; capacitive compensation is provided in a low-frequency band through the Ccomp; the power frequency unvarnished transmission branch adopts a parallel resonance selection + series fine adjustment structure, a second parallel resonance inductor L2 and a second parallel resonance capacitor C2 are connected in parallel and then are connected in series with a fine adjustment resistor Rfine, parallel resonance is carried out near the power frequency through the L2-C2 for fine adjustment, and resistive compensation is provided at the power frequency band through the Rfine; and the high-frequency compensation branch circuit adopts a parallel resonance isolation + series inductive compensation structure, a series compensation inductor Lcomp is connected in series with a branch circuit formed by connecting a third parallel resonance inductor L3 and a third parallel resonance capacitor C3 in parallel, parallel resonance is realized at a low-frequency position through the L3-C3 to realize isolation, and inductive compensation is provided at a high-frequency band through the Lcomp.

Description

Technical Field

[0001] This invention relates to the field of power system measurement technology, and more specifically, to an intelligent compensated capacitive voltage transformer. Background Technology

[0002] Capacitive voltage transformers (CVTs) are widely used voltage measurement devices in high-voltage transmission systems, mainly composed of voltage-dividing capacitors, electromagnetic units, and dampers. CVTs have advantages such as simple structure, low cost, and convenient maintenance, and are widely used in power systems with voltage levels of 110kV and above.

[0003] Traditional CVT structure, such as Figure 1 As shown, however, existing CVTs have the following technical problems:

[0004] 1. Severe limitations in frequency response

[0005] Traditional CVTs are mainly designed for power frequency (50Hz), and their frequency response characteristics have significant defects under non-power frequency conditions: (1) Low frequency band (0.01Hz~1Hz): the amplitude attenuation is severe, the error can reach 2-3%, and the phase lag is obvious; (2) High frequency band (1kHz~10kHz): the phase lag is aggravated, the amplitude response is not flat, and the error reaches 1-2%; (3) Transition frequency band: the frequency response is discontinuous, and there are resonance points and anti-resonance points.

[0006] 2. Insufficient multi-band signal processing capabilities

[0007] Modern power systems contain a large number of non-power frequency components: (1) broadband signals generated by new energy grid connection; (2) harmonic components introduced by power electronic equipment; (3) high-frequency components in transient processes; and (4) low-frequency components such as subsynchronous oscillations. Traditional CVTs cannot accurately measure these multi-band composite signals.

[0008] 3. Technical limitations of existing compensation methods

[0009] Current methods for improving CVT accuracy mainly include: (1) Single-point correction method: compensation can only be performed at a specific frequency point and cannot cover a wide frequency range; (2) Software compensation method: requires complex digital signal processing, is costly, and has poor real-time performance; (3) Active compensation method: relies on active devices, has low reliability, and is not suitable for high-voltage and harsh environments. However, none of these methods can solve the compensation problem of CVT in multiple frequency bands at the same time.

[0010] With the advancement of smart grid construction and the large-scale grid connection of new energy sources, the demand for wide-band precision measurement in power systems is becoming increasingly urgent, and existing CVT technology can no longer meet the requirements. Therefore, there is an urgent need for a device that can improve the measurement accuracy of CVT across the entire frequency band. Summary of the Invention

[0011] This invention proposes an intelligent compensated capacitive voltage transformer to solve the problem of how to achieve high-precision measurement of CVT across the entire frequency range.

[0012] To address the aforementioned problems, according to one aspect of the present invention, an intelligent compensated capacitive voltage transformer is provided. The device comprises: a three-branch parallel network connected to the output terminal of the original CVT secondary winding and the input terminal of the original CVT secondary load, respectively. The three-branch parallel network includes: a low-frequency compensation branch, a power frequency transparent transmission branch, and a high-frequency compensation branch connected in parallel. The power transmission of the three branches is superimposed at a common node to achieve full-frequency band compensation.

[0013] The low-frequency compensation branch adopts a series resonant isolation + parallel capacitive compensation structure, including: a first series resonant inductor L1 and a first series resonant capacitor C1 connected in series, and then connected in parallel with a compensation capacitor C. comp The parallel connection achieves transparency to the power frequency signal through series resonance of L1-C1 at the power frequency, and the parallel compensation capacitor C comp Provides capacitive compensation in the low-frequency band;

[0014] The power frequency transmission branch adopts a parallel resonant selection + series fine adjustment structure, including: a second parallel resonant inductor L2 and a second parallel resonant capacitor C2 connected in parallel and then connected in series with a fine adjustment resistor R. fine The series connection allows for fine adjustment via parallel resonance of L2-C2 near the power frequency, while the series fine adjustment resistor R... fine Provides resistive compensation in the power frequency band;

[0015] The high-frequency compensation branch adopts a parallel resonant isolation + series inductive compensation structure, including: a series compensation inductor L comp The branch connected in parallel with the third parallel resonant inductor L3 and the third parallel resonant capacitor C3 is connected in series. Isolation is achieved through the parallel resonance of L3-C3 at low frequencies, and the series compensation inductor L... comp Provides inductive compensation in the high-frequency band.

[0016] Preferably, the operating frequency range of the low-frequency compensation branch is 0.01Hz to 1Hz, and the series resonant frequency is set to 50Hz to meet the resonance condition. The parallel compensation capacitor provides 5% gain compensation; where ω is the angular frequency of the system signal.

[0017] Preferably, the operating frequency range of the power frequency transmission branch is 45Hz to 65Hz, and the parallel resonant frequency is set to 50Hz to meet the resonance condition. The adjustment range of the fine-tuning resistor is ±2%; where ω is the angular frequency of the system signal.

[0018] Preferably, the high-frequency compensation branch operates in the range of 1kHz to 10kHz, the parallel resonant isolation frequency is set to 500Hz to 1.6kHz, and the series compensation inductor provides a 5° phase lead compensation, satisfying the phase compensation formula. Among them, R load ω is the load resistance; ω is the angular frequency of the system signal.

[0019] Preferably, the overall transfer function of the device is:

[0020] H system (ω)=H divider (ω)·H electromagnetic (ω)·H damper (ω)·H compensation (ω),

[0021] Among them, H divider (ω) is the transfer function of the voltage divider capacitor; H electromagnetic (ω) is the electromagnetic unit transfer function; H damper (ω) is the damper transfer function; H compensation (ω) is the transfer function of the compensation network.

[0022] Preferably, the device optimizes parameters based on an objective function to achieve adaptation to different voltage levels;

[0023] The objective function includes:

[0024] The optimization constraints are:

[0025]

[0026] Where p = [L1, C1, C comp ,L2,C2,R fine ,L comp [L3,C3] T w is a parameter vector. i H is the frequency point weighting factor; ideal (ω i )=1.0+0j is the ideal flat response.

[0027] This invention provides an intelligent compensated capacitive voltage transformer, comprising: a low-frequency compensation branch, adopting a series resonant isolation + parallel capacitive compensation structure, including: a first series resonant inductor L1 and a first series resonant capacitor C1 connected in series, and then connected in parallel with a compensation capacitor C comp The parallel connection achieves transparency to the power frequency signal through series resonance of L1-C1 at the power frequency, and the parallel compensation capacitor C compCapacitive compensation is provided in the low-frequency band; the power frequency pass-through branch adopts a parallel resonant selection + series fine adjustment structure, including: the second parallel resonant inductor L2 and the second parallel resonant capacitor C2 are connected in parallel and then connected in series with the fine adjustment resistor R. fine The series connection allows for fine adjustment via parallel resonance of L2-C2 near the power frequency, while the series fine adjustment resistor R... fine Resistive compensation is provided in the power frequency band; the high-frequency compensation branch adopts a parallel resonant isolation + series inductive compensation structure, including: series compensation inductor L comp The branch connected in parallel with the third parallel resonant inductor L3 and the third parallel resonant capacitor C3 is connected in series. Isolation is achieved through the parallel resonance of L3-C3 at low frequencies, and the series compensation inductor L... comp Inductive compensation is provided in the high-frequency band. This invention employs a multi-branch frequency-selective compensation network, allowing different compensation branches to exhibit different impedance characteristics in different frequency bands, thereby achieving frequency-selective compensation. This enables simultaneous compensation of the CVT across the entire frequency band, including low frequency, power frequency, and high frequency, maintaining a high accuracy level within the range of 0.01Hz to 10kHz. Attached Figure Description

[0028] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0029] Figure 1 This is a schematic diagram of a traditional CVT structure;

[0030] Figure 2 This is a schematic diagram of the structure of an intelligent compensated capacitive voltage transformer 100 according to an embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram of a three-branch parallel compensation network according to an embodiment of the present invention;

[0032] Figure 4 This is a diagram illustrating the overall structure of a multi-branch frequency selective compensation network according to an embodiment of the present invention.

[0033] Figure 5 The circuit structure diagram of the low-frequency compensation branch according to an embodiment of the present invention is shown below.

[0034] Figure 6 This is a circuit structure diagram of the power frequency transparent transmission branch according to an embodiment of the present invention;

[0035] Figure 7 This is a circuit structure diagram of the high-frequency compensation branch according to an embodiment of the present invention;

[0036] Figure 8 This is an example diagram of a low-frequency compensation branch according to an embodiment of the present invention;

[0037] Figure 9 This is an example diagram of a power frequency transparent transmission branch according to an embodiment of the present invention;

[0038] Figure 10 This is an example diagram of a high-frequency compensation branch according to an embodiment of the present invention;

[0039] Figure 11 This is a comparison diagram of the three-branch frequency response characteristics according to an embodiment of the present invention;

[0040] Figure 12 This is a comparison diagram of the CVT frequency characteristics before and after compensation according to an embodiment of the present invention. Detailed Implementation

[0041] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0042] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0043] To achieve simultaneous compensation of CVTs across the entire frequency range—low frequency, power frequency, and high frequency—and maintain high accuracy within the 0.01Hz–10kHz range, thus addressing the shortcomings of traditional CVTs in wideband measurement performance, this invention provides a method for wideband retrofitting of CVT voltage transformers used in high-voltage transmission. This method employs a multi-branch frequency-selective compensation network, allowing different compensation branches to exhibit different impedance characteristics in different frequency bands, thereby achieving frequency-selective compensation.

[0044] Figure 2 This is a schematic diagram of the structure of an intelligent compensated capacitive voltage transformer 100 according to an embodiment of the present invention. Figure 2As shown, the intelligent compensated capacitive voltage transformer provided in this embodiment of the invention employs a multi-branch frequency selective compensation network, allowing different compensation branches to exhibit different impedance characteristics in different frequency bands, thereby achieving frequency selective compensation. This enables simultaneous compensation of the CVT across the entire frequency band, including low frequency, power frequency, and high frequency, maintaining a high accuracy level within the range of 0.01Hz to 10kHz. The intelligent compensated capacitive voltage transformer 200 provided in this embodiment of the invention includes: a three-branch parallel network connected to the output terminal of the original CVT secondary winding and the input terminal of the original CVT secondary load, respectively. The three-branch parallel network includes: a low-frequency compensation branch 201, a power frequency transparent transmission branch 202, and a high-frequency compensation branch 203 connected in parallel. The power transmission of the three branches is superimposed at a common node to achieve full-band compensation.

[0045] Preferably, the low-frequency compensation branch 201 adopts a series resonant isolation + parallel capacitive compensation structure, including: a first series resonant inductor L1 and a first series resonant capacitor C1 connected in series, and then connected in parallel with a compensation capacitor C. comp The parallel connection achieves transparency to the power frequency signal through series resonance of L1-C1 at the power frequency, and the parallel compensation capacitor C comp Provides capacitive compensation in the low-frequency band.

[0046] Preferably, the operating frequency range of the low-frequency compensation branch is 0.01Hz to 1Hz, and the series resonant frequency is set to 50Hz to meet the resonance condition. The parallel compensation capacitor provides 5% gain compensation; where ω is the angular frequency of the system signal.

[0047] Preferably, the power frequency transparent transmission branch 202 adopts a parallel resonant selection + series fine adjustment structure, including: a second parallel resonant inductor L2 and a second parallel resonant capacitor C2 connected in parallel and then connected in series with a fine adjustment resistor R. fine The series connection allows for fine adjustment via parallel resonance of L2-C2 near the power frequency, while the series fine adjustment resistor R... fine Provides resistive compensation in the power frequency band.

[0048] Preferably, the operating frequency range of the power frequency transmission branch is 45Hz to 65Hz, and the parallel resonant frequency is set to 50Hz to meet the resonance condition. The adjustment range of the fine-tuning resistor is ±2%; where ω is the angular frequency of the system signal.

[0049] Preferably, the high-frequency compensation branch 203 adopts a parallel resonant isolation + series inductive compensation structure, including: a series compensation inductor L compThe branch connected in parallel with the third parallel resonant inductor L3 and the third parallel resonant capacitor C3 is connected in series. Isolation is achieved through the parallel resonance of L3-C3 at low frequencies, and the series compensation inductor L... comp Provides inductive compensation in the high-frequency band.

[0050] Preferably, the high-frequency compensation branch operates in the range of 1kHz to 10kHz, the parallel resonant isolation frequency is set to 500Hz to 1.6kHz, and the series compensation inductor provides a 5° phase lead compensation, satisfying the phase compensation formula. Among them, R load ω is the load resistance; ω is the angular frequency of the system signal.

[0051] Preferably, the operating frequency range of the power frequency transmission branch is 45Hz to 65Hz, and the parallel resonant frequency is set to 50Hz to meet the resonance condition. The adjustment range of the fine-tuning resistor is ±2%; where ω is the angular frequency of the system signal.

[0052] In this invention, the first step is to analyze the frequency characteristics of the CVT and determine the compensation requirements.

[0053] 1. CVT Frequency Response Modeling: Conduct full-frequency band testing on the CVT to be modified and establish its frequency response mathematical model:

[0054]

[0055] Where, K0: DC gain coefficient; ω1, ω2: characteristic angular frequencies; ζ1, ζ2: damping coefficients; typical parameters: ω1 = 2 + 0.1 rad / s, ω2 = 2π × 50 rad / s

[0056] 2. Frequency Band Compensation Demand Analysis

[0057] Based on the CVT frequency characteristics, determine the compensation requirements for each frequency band:

[0058] frequency band Frequency range Main problems Compensation demand Compensation methods low frequency band 0.01Hz~1Hz Amplitude attenuation 2-3% Gain compensation +5% Capacitive compensation power frequency band 45Hz~65Hz Slight deviation ±0.3% Fine adjustment ±0.1% resistive fine-tuning High frequency band 1kHz~10kHz Phase lag 15°–45° Phase lead +5° to 8° Emotional compensation

[0059] In this invention, the multi-branch network architecture is as follows: Figure 4 As shown. The principle of frequency selectivity design is: each branch uses a different LC resonant network to achieve frequency selectivity.

[0060] Z branch (ω)=Z target (ω)·S(ω)+Z isolation (ω)·[1-S(ω)],

[0061] Where S(ω) is the frequency selection function, S(ω)→1 in the target frequency band and S(ω)→0 in the non-target frequency band; Z target(ω) represents the compensation impedance for the target frequency band; Z isolation (ω) represents the isolation high impedance for non-target frequency bands.

[0062] like Figure 5 As shown, in this invention, the low-frequency compensation branch adopts a series resonant isolation + parallel capacitive compensation structure. L1-C1 form a series resonant isolation network, which can resonate and short-circuit at the power frequency. C_comp is a parallel compensation capacitor used to provide low-frequency capacitive compensation.

[0063] The calculation of series resonance parameters includes:

[0064] Design goal: Minimize impedance at power frequency (50Hz) series resonance.

[0065] Resonance condition:

[0066] Resonant frequency:

[0067] If C1 = 0.47 μF (standard value), then:

[0068] Impedance at resonance: Z res =R series Parasitic resistance ≈10Ω.

[0069] The calculation of parallel compensation capacitors includes:

[0070] Design goal: To provide 5% gain compensation at 0.1Hz.

[0071] CVT attenuation at 0.1Hz: G cvt (0.1Hz) = 0.97 (-3% attenuation)

[0072] Target gain: G target =1.05 (+5% compensation)

[0073] Compensation required:

[0074] Capacitive compensation principle: At low frequencies, L1 has low impedance, and the circuit is equivalent to C. comp Parallel to load

[0075] Calculate C comp :

[0076] Let Z load =10kΩ, find G comp =1.082, solving for C gives: comp =1.6μF

[0077] The impedance characteristics of the low-frequency branch in different frequency bands are as follows:

[0078]

[0079] in,

[0080] The impedance at the key frequency point is:

[0081] f = 0.1 Hz: |Z| ≈ 995 Ω, ∠φ ≈ -90° (capacitive)

[0082] f = 50Hz: |Z| ≈ 10Ω, ∠φ ≈ 0° (resonance)

[0083] f = 2kHz: |Z| ≈ 27kΩ, ∠φ ≈ +90° (high inductive resistance).

[0084] like Figure 6 As shown, in this invention, the power frequency transparent transmission branch adopts a parallel resonant selection + series fine adjustment structure. L2∥C2 forms a parallel resonant network, which can present a specific impedance at the power frequency. R_fine is a fine adjustment resistor used to provide resistive compensation and fine adjustment.

[0085] The calculation of parallel resonance parameters includes:

[0086] Design goal: Parallel resonance at power frequency (50Hz), exhibiting high impedance.

[0087] Parallel resonance condition:

[0088] Resonant frequency:

[0089] If C2 = 0.1 μF, then:

[0090] Parallel resonant impedance:

[0091] If Q = 10 (quality factor), then: Z parallel =318kΩ power frequency impedance.

[0092] The calculation of fine-tuning resistors includes:

[0093] Design goals: accuracy ±0.1% in the power frequency band, fine-tuning range ±2%.

[0094] Reference resistance value: R fine =5kΩ Fine-tuning range: 4.9kΩ~5.1kΩ (±2%)

[0095] Impact on accuracy:

[0096] Actual accuracy control: via R fineFine-tuning allows for precise control of the power frequency gain to within ±0.1%. The frequency selectivity characteristics of the power frequency branch are as follows:

[0097] Z main (ω)=Z parallel (ω)+R fine ,

[0098] The parallel LC impedance is:

[0099] The impedance at the key frequency point is:

[0100] f = 1Hz: |Z| ≈ 5.6kΩ, minimal external influence at power frequency;

[0101] f=50Hz:|Z|≈323kΩ, parallel resonant high impedance;

[0102] f = 1kHz: |Z| ≈ 6.4kΩ, with minimal external influence at power frequency.

[0103] As shown in Figure 6, in this invention, the high-frequency compensation branch adopts a parallel resonant isolation + series inductive compensation structure. L3∥C3 is a parallel resonant isolation network that can provide high impedance isolation at low frequencies. L_comp is a series compensation inductor used to provide inductive compensation at high frequencies.

[0104] The calculation of parallel resonant isolation parameters includes:

[0105] Design goal: To achieve parallel resonance at the separation frequency (500Hz) and isolate low frequencies.

[0106] Resonant frequency:

[0107] Choosing L3 = 10mH, then:

[0108] Isolation effect: When f < 500Hz, the parallel network exhibits high impedance, L comp When isolated, the impedance of the parallel network decreases when f > 500Hz, L comp It's starting to work.

[0109] The calculation of series compensation inductance includes:

[0110] Design goal: To provide 5° phase lead compensation at 2kHz.

[0111] CVT phase lag at 2kHz: φ cvt = -35° Target phase lead: φ target = +5° Required compensation phase: φ comp =φ target -φ cvt =+40°

[0112] The principle of emotional compensation:

[0113] φ = 40°, R load =10kΩ, f=2kHz:

[0114] Solving for:

[0115] Considering the impact of parallel isolation networks, the actual choice is: L comp The compensation mechanism for the 160mH (optimized and adjusted) high-frequency branch is as follows:

[0116] Z high (ω)=Z comp (ω)+Z parallel (ω),

[0117] Among them, Z comp (ω)=jωL comp ,

[0118] The compensation effect analysis is as follows:

[0119] f = 50Hz: High impedance of the isolation network, L comp The isolation has no impact on the power frequency.

[0120] f = 1.6kHz: Isolation network resonance, minimum impedance, L comp Give full play to its role;

[0121] f = 5kHz: L comp Provides strong inductive compensation and improves high-frequency phase.

[0122] In this invention, the currents of the three branches at the common output node are superimposed to obtain:

[0123] I total =I low +I main +I high ,

[0124] The currents in each branch are as follows:

[0125] The low-frequency compensation current is: Low-frequency compensation current,

[0126] The power frequency regulating current is:

[0127] The high-frequency compensation current is:

[0128] The output voltage is: V out =I total ×Zload ,

[0129] The compensation effect is as follows:

[0130] The operating status of each branch in different frequency bands is as follows:

[0131]

[0132]

[0133] Preferably, the overall transfer function of the device is:

[0134] H system (ω)=H divider (ω)·H electromagnetic (ω)·H damper (ω)·H compensation (ω),

[0135] Among them, H divider (ω) is the transfer function of the voltage divider capacitor; H electromagnetic (ω) is the electromagnetic unit transfer function; H damper (ω) is the damper transfer function; H compensation (ω) is the transfer function of the compensation network.

[0136] Preferably, the device optimizes parameters based on an objective function to achieve adaptation to different voltage levels;

[0137] The objective function includes:

[0138] The optimization constraints are:

[0139]

[0140] Where p = [L1, C1, C comp ,L2,C2,R fine ,L comp [L3,C3] T w is a parameter vector. i H is the frequency point weighting factor; ideal (ω i )=1.0+0j is the ideal flat response.

[0141] In this invention, the overall compensation characteristics of the multi-branch network are as follows:

[0142]

[0143] The compensation transfer function is:

[0144] The compensation effect is as follows:

[0145] • 0.01Hz~1Hz: Amplitude compensation +5%, phase improvement capacitance;

[0146] • 45Hz~65Hz: Precision control ±0.1%, maintaining good power frequency characteristics;

[0147] • 1kHz~10kHz: Phase lead +5°, improving high-frequency response.

[0148] In this invention, parameter optimization based on the objective function includes:

[0149]

[0150] Where p = [L1, C1, C comp ,L2,C2,R fine ,L comp [L3,C3] T w is a parameter vector. i H is the frequency point weighting factor; ideal (ω i The response is ideally flat, where ) = 1.0 + 0j.

[0151] Optimize constraints:

[0152] In this invention, the influence of ambient temperature on device parameters is considered:

[0153] L(T) = L0[1+α] L (T-T0)],C(T)=C0[1+α C (T-T0)],

[0154] Where, α L =100×10 -6 / ℃: Temperature coefficient of inductance; α C =-200×10 -6 / ℃: Temperature coefficient of capacitor; T0=25℃;

[0155] Reference temperature, temperature-corrected resonant frequency:

[0156]

[0157] In this invention, the complete specifications of the device parameters are as follows:

[0158]

[0159] The technical solution of this invention has the following beneficial effects:

[0160] 1. High-precision measurement across the entire frequency band; specifically, within the full frequency range of 0.01Hz to 10kHz, the amplitude error is controlled within ±0.15%; the phase error is controlled within ±3′, achieving the accuracy requirement of 0.15 grade; significantly better than the 0.5 grade accuracy of traditional CVT;

[0161] 2. Frequency selective compensation; different branches automatically exhibit high impedance outside the target frequency band to avoid mutual interference; accurate compensation is provided within the target frequency band, with a highly targeted compensation effect; multi-band signals can be optimized simultaneously;

[0162] 3. Passive high-reliability design; it adopts a pure passive LC network, eliminating the risk of active component failure; suitable for long-term operation in harsh outdoor high-voltage environments; requires very little maintenance and has extremely high reliability;

[0163] 4. Significant cost-effectiveness; the retrofit cost is approximately 6,000 yuan, only 20% of the cost of building a new wide-band CVT; the retrofit can be completed without power outages; and the cost can be further reduced after mass application.

[0164] 5. Highly practical for engineering applications; the modification scheme does not affect the basic structure of the original CVT; it is applicable to various voltage levels such as 110kV, 220kV, and 500kV; it has a high degree of standardization, making it easy to promote and apply.

[0165] In this invention, the overall transfer function of the CVT system is:

[0166] H system (ω)=H divider (ω)·H electromagnetic (ω)·H damper (ω)·H compensation (ω)

[0167] Among them, H divider (ω) is the transfer function of the voltage divider capacitor; H electromagnetic (ω) is the electromagnetic unit transfer function; H damper (ω) is the damper transfer function; H compensation (ω) is the transfer function of the compensation network.

[0168] The parameters of the compensation network considering the damper impedance are corrected as follows:

[0169] The corrected impedance of the compensation network is:

[0170]

[0171] Among them, K correction The correction coefficients were determined through system simulation.

[0172] The system stability criterion of this invention is based on the Nyquist stability criterion, including: H open (ω)=H forward (ω)·H feedback (ω), the stability condition is: |H open (jω)|<1,

[0173] The following specific examples illustrate the embodiments of the present invention.

[0174] Example 1: 110kV CVT Retrofit

[0175] 1. Current Situation Analysis

[0176] A certain 110kV substation has a CVT model of TYD110 / √3-0.01H, a rated transformation ratio of 110000 / 100V, and an accuracy class of 0.5. Frequency characteristic testing revealed that:

[0177] Low frequency range (0.1Hz): Amplitude error +2.1%, Phase error -45′

[0178] Power frequency range (50Hz): Amplitude error +0.3%, Phase error -8′

[0179] High frequency range (2kHz): Amplitude error -1.8%, Phase error -35′

[0180] 2. Multi-branch compensation network design

[0181] Based on the frequency characteristic defects of CVT, a three-branch compensation network is designed:

[0182] Low-frequency compensation branch design:

[0183] Design goal: To compensate for low-frequency attenuation and provide capacitive compensation.

[0184] Series resonance parameters (short circuit at power frequency): f resonance =50Hz C1=0.47μF

[0185]

[0186] Parallel compensation capacitor (low-frequency compensation): Target: Provide 5% gain compensation at 0.1Hz. target =0.1Hz G target =1.05C comp =1.6μF

[0187] Power frequency transparent transmission branch design:

[0188] Design goal: To finely adjust the power frequency band and maintain good performance.

[0189] Parallel resonant parameters (power frequency selection): f main =50Hz C2=0.1μF

[0190] Fine adjustment resistor: R fine =5000Ω, adjustable by ±2%

[0191] High-frequency compensation branch design:

[0192] Design goal: High-frequency phase compensation to improve high-frequency response.

[0193] Isolated parallel resonance (low-frequency isolation): f separation =500Hz L3=10×10 -3 H

[0194]

[0195] Series compensated inductor (high frequency compensation): Target: Provide a 5° phase lead f at 2kHz target =2000Hzφ lead =5°L comp =160×10 -3 H

[0196] 3. Actual circuit implementation

[0197] Low-frequency compensation branch circuit, such as Figure 8 As shown, the working mechanism is as follows:

[0198] f < 1Hz: L1 impedance is small, signal mainly passes through C comp To obtain capacitive compensation;

[0199] f=50Hz: L1-C1 series resonance, impedance≈0, the branch is equivalent to a short circuit;

[0200] f > 1kHz: L1 impedance is high, the entire branch is high impedance, which does not affect the high frequency.

[0201] Power frequency transparent branch circuit such as Figure 9 As shown, the working mechanism is as follows:

[0202] f≈50Hz: L2-C2 parallel resonance, presenting moderate impedance, allowing for fine adjustment;

[0203] f≠50Hz: Parallel network detuning, impedance change, has little impact on non-power frequency frequencies;

[0204] R fine Provides resistive fine-tuning with a power frequency accuracy of ±0.1%.

[0205] High-frequency compensation branch circuit, such as Figure 10 As shown, the working mechanism is as follows:

[0206] f < 500Hz: L3-C3 parallel resonance, exhibiting high impedance, L comp Quarantined;

[0207] f≈1.6kHz: L3-C3 resonant point, impedance is maximum, L comp Give full play to its role;

[0208] f > 1 kHz: L comp It provides inductive compensation to improve high-frequency phase characteristics.

[0209] like Figure 11 The figure shows a comparison of the frequency response characteristics of the three branches. The horizontal axis represents the frequency range of 0.01Hz to 10kHz (logarithmic scale); the vertical axis represents the impedance magnitude |Z| (Ω); and the curves represent the impedance frequency characteristics of the three branches. The characteristics of each branch are shown below:

[0210] 1. Low-frequency compensation branch (blue curve): Low frequency band: low impedance, effective operation; 50Hz: series resonance, minimum impedance; High frequency band: high impedance, automatic isolation.

[0211] 2. Power frequency transparent transmission branch (red curve): Power frequency band: moderate impedance, fine adjustment; Non-power frequency: less impact.

[0212] 3. High-frequency compensation branch (green curve): Low frequency band: parallel resonance, extremely high impedance isolation; High frequency band: low impedance, effective compensation.

[0213] The core design verification includes: frequency selectivity: each branch operates with low impedance only in the target frequency band; automatic isolation: it automatically presents high impedance in non-operating frequency bands to avoid interference; and coordinated compensation: the three branches independently play a compensation role in their respective frequency bands.

[0214] like Figure 11 As shown, the core mechanism for automatic frequency selection in a multi-branch network is intuitively demonstrated, verifying the design concept of "frequency division compensation and non-interference".

[0215] In this invention, the comparison of CVT frequency characteristics before and after compensation is as follows: Figure 12 As shown in the figure, the horizontal axis represents the frequency range of 0.01Hz to 10kHz (logarithmic scale); the vertical axis represents the amplitude error (%) and phase error (minutes); and the curves compare the amplitude and phase characteristics before and after the modification.

[0216] The problems before the upgrade included: low frequency band: severe amplitude attenuation (+2.8%), significant phase lag (-52′); high frequency band: aggravated amplitude attenuation (-2.3%), severe phase lag (-42′); overall accuracy: only 0.5 level, frequency range limited to power frequency.

[0217] After the upgrade: Amplitude error across the entire frequency band is controlled within ±0.15%; Phase error across the entire frequency band is controlled within ±3′; Accuracy level is improved from 0.5 to 0.15; Frequency coverage is expanded from a single power frequency to the entire frequency band from 0.01Hz to 10kHz.

[0218] Depend on Figure 12 As can be seen, the multi-branch frequency selective compensation network achieves: amplitude error improvement rate of over 85%; phase error improvement rate of over 90%; and frequency response flattening with near-ideal characteristics across the entire frequency band. This comparison chart visually demonstrates the significant technical advantages and engineering application value of the retrofit scheme.

[0219] The integrated connection method of the present invention is as follows: original CVT output → three-branch parallel network → compensation output → measuring device. The specific connection includes: the input terminal is connected to the CVT secondary winding output, the output terminal is connected to the original CVT secondary load, the three branches are connected in parallel at the common node, and necessary protection and monitoring circuits are added at the same time.

[0220] The debugging steps include:

[0221] 1. Static parameter testing: Verify the parameters of each component using an LCR table;

[0222] 2. Independent branch testing: Test the frequency characteristics of each branch separately;

[0223] 3. System Joint Testing: Test the overall characteristics after the three branches are connected in parallel;

[0224] 4. Dynamic verification test: Verify the compensation effect using multi-frequency signals.

[0225] After the modification was completed, a comprehensive test was conducted, and the results are as follows:

[0226] Frequency point Before the modification, the amplitude error Amplitude error after modification Phase error before modification Phase error after modification 0.01Hz +2.8％ +0.12％ -52′ -2.1′ 0.1Hz +2.1％ +0.14％ -45′ -1.8′ 1Hz +0.8％ +0.11％ -15′ -1.2′ 50Hz +0.3％ +0.09％ -8′ -0.8′ 100Hz +0.5％ +0.10％ -12′ -1.0′ 1kHz -1.2％ +0.13％ -28′ +2.1′ 2kHz -1.8％ +0.14％ -35′ +2.8′ 5kHz -2.3％ +0.15％ -42′ +2.9′

[0227] The statistics on improvement effects include:

[0228] Amplitude error improvement rate:

[0229] Phase error improvement rate:

[0230] The statistical results are as follows: amplitude error across the entire frequency band: within ±0.15% (improvement of more than 85%); phase error across the entire frequency band: within ±3′ (improvement of more than 90%); accuracy level: improved from 0.5 level to 0.15 level; frequency range: expanded from 50Hz to 0.01Hz to 10kHz.

[0231] Example 2: 220kV CVT Retrofit

[0232] 1. Differences in technical requirements

[0233] The 220kV CVT upgrade needs to consider higher voltage level requirements: insulation strength: the compensation network needs 40.5kV insulation capacity; electromagnetic compatibility: more stringent EMC requirements; environmental adaptability: harsher outdoor environmental conditions.

[0234] 2. Parameter adjustment and optimization

[0235] For 220kV applications, the compensation network parameters are optimized:

[0236] Parameter optimization of 220kV CVT compensation network:

[0237] Low-frequency branch: Increase device capacity

[0238] L 1,220kV =2.5H (reinforced core), C 1,220kV =0.47μF (improved withstand voltage rating), C comp,220kV =1.8μF (optimized compensation amount);

[0239] Power frequency branch: Improve insulation level

[0240] L 2,220kV =120×10 -3 H (optimize Q value), C 2,220kV =0.08μF (adjusting the resonant frequency), R fine,220kV =6000Ω; (Enhanced power capability);

[0241] High-frequency branch: Enhances high-frequency characteristics

[0242] L comp,220kV =180×10 -3 H (enhanced compensation capacity), L 3,220kV =12×10 -3 H (optimize isolation properties), C 3,220kV =90×10 -9 F (Adjust the separation frequency);

[0243] 3. Enhanced insulation design

[0244] Component selection: Select inductors and capacitors with higher insulation levels; Insulation distance: Increase the insulation distance between components to meet the 40.5kV requirement; Housing design: Use SF6 gas insulation or high-quality epoxy resin encapsulation.

[0245] 4. Application Effects

[0246] After 6 months of on-site operation verification, the accuracy was maintained at ±0.15% across the entire frequency band; the reliability was excellent, with no faults and the equipment was in good condition; and the environmental adaptability withstood the test of severe weather conditions such as high temperature, low temperature, and thunderstorms.

[0247] The present invention has been described with reference to a few embodiments. However, it will be apparent to those skilled in the art that other embodiments besides those disclosed above fall equivalently within the scope of the present invention.

[0248] Generally, all terms used in this invention are interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed unless explicitly stated otherwise.

[0249] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0250] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0251] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0252] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0253] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A smart compensated capacitive voltage transformer, characterized in that, The device includes a three-branch parallel network connected to the output terminal of the original CVT secondary winding and the input terminal of the original CVT secondary load, respectively. The three-branch parallel network includes a low-frequency compensation branch, a power frequency transparent transmission branch, and a high-frequency compensation branch connected in parallel. The power transmission of the three branches is superimposed at a common node to achieve full-frequency band compensation. The low-frequency compensation branch adopts a series resonant isolation + parallel capacitive compensation structure, including: a first series resonant inductor L1 and a first series resonant capacitor C1 connected in series, and then connected in parallel with a compensation capacitor C. comp The parallel connection achieves transparency to the power frequency signal through series resonance of L1-C1 at the power frequency, and the parallel compensation capacitor C comp Provides capacitive compensation in the low-frequency band; The power frequency transmission branch adopts a parallel resonant selection + series fine adjustment structure, including: a second parallel resonant inductor L2 and a second parallel resonant capacitor C2 connected in parallel and then connected in series with a fine adjustment resistor R. fine The series connection allows for fine adjustment via parallel resonance of L2-C2 near the power frequency, while the series fine adjustment resistor R... fine Provides resistive compensation in the power frequency band; The high-frequency compensation branch adopts a parallel resonant isolation + series inductive compensation structure, including: a series compensation inductor L comp The branch connected in parallel with the third parallel resonant inductor L3 and the third parallel resonant capacitor C3 is connected in series. Isolation is achieved through the parallel resonance of L3-C3 at low frequencies, and the series compensation inductor L... comp Provides inductive compensation in the high-frequency band.

2. The voltage transformer according to claim 1, characterized in that, The operating frequency range of the low-frequency compensation branch is 0.01Hz to 1Hz, and the series resonant frequency is set to 50Hz to meet the resonance condition. The parallel compensation capacitor provides 5% gain compensation; where ω is the angular frequency of the system signal.

3. The voltage transformer according to claim 1, characterized in that, The operating frequency range of the power frequency transparent transmission branch is 45Hz to 65Hz, and the parallel resonant frequency is set to 50Hz to meet the resonance condition. The adjustment range of the fine-tuning resistor is ±2%; where ω is the angular frequency of the system signal.

4. The voltage transformer according to claim 1, characterized in that, The high-frequency compensation branch operates in the range of 1kHz to 10kHz, the parallel resonant isolation frequency is set to 500Hz to 1.6kHz, and the series compensation inductor provides a 5° phase lead compensation, satisfying the phase compensation formula. Among them, R load ω represents the load resistance; ω represents the angular frequency of the system signal.

5. The voltage transformer according to claim 1, characterized in that, The overall transfer function of the device is: H system (ω)=H divider (ω)·H electromagnetic (ω)·H damper (ω)·H compensation (oh), Among them, H divider (ω) is the transfer function of the voltage divider capacitor; H electromagnetic (ω) is the electromagnetic unit transfer function; H damper (ω) is the damper transfer function; H compensation (ω) is the transfer function of the compensation network.

6. The voltage transformer according to claim 1, characterized in that, The device optimizes parameters based on an objective function to achieve adaptation to different voltage levels; The objective function includes: The optimization constraints are: Where p = [L1, C1, C comp ,L2,C2,R fine ,L comp [L3,C3] T For the parameter vector; w i H is the frequency point weighting factor; ideal (ω i )=1.0+0j is the ideal flat response.

Images