Method for improving PT residual voltage frequency measurement accuracy based on rotation vector characteristics

Abstract

The invention provides a method for improving PT residual voltage frequency measurement accuracy based on rotation vector characteristics, and relates to the technical field of generator set rotation speed measurement. The method comprises the following steps: acquiring a three-phase voltage alternating current signal through a generator end PT; processing the three-phase voltage signal to obtain projections of a voltage rotation vector on alpha and beta static coordinate axes; frequency characteristics are extracted based on projection and voltage amplitude and can be realized through direct calculation or a phase locking link; performing low-pass filtering on the frequency characteristic direct current quantity; a generator speed is calculated based on the filtered frequency and provided to a governor. According to the method, the limitation that a traditional PT residual voltage method only depends on zero crossing point information is broken through, frequency characteristics are extracted through a complete voltage sequence, alternating current signal filtering distortion is avoided through direct current filtering, high measurement precision and high anti-interference capacity can still be kept under the low-speed working condition, the problems that an existing speed measurement method is insufficient in precision and weak in anti-interference capacity are effectively solved, and the method is suitable for popularization and application. And reliable guarantee is provided for safe and stable operation of a unit.

Description

Technical Field

[0001] This invention relates to the field of generator set speed measurement technology, and in particular to a method for improving the accuracy of PT residual voltage frequency measurement based on rotating vector characteristics. Background Technology

[0002] In the control systems of generator sets, especially hydroelectric generator sets, real-time and accurate measurement of rotor speed is a core element in ensuring the safe and stable operation of the unit. Rotor speed, as a key mechanical quantity characterizing the unit's operating state, directly serves as the core feedback input signal for the speed governor. The speed control system adjusts the guide vane opening based on the speed deviation to control the water intake, thereby achieving frequency stability and power regulation. Accurate speed measurement is crucial for smooth unit startup, grid synchronization, power regulation, and safe shutdown, and is fundamental to maintaining grid frequency stability and preventing equipment damage.

[0003] Existing generator speed measurement methods are mainly divided into two categories: direct measurement and indirect measurement. Direct measurement uses the gear disc speed measurement method, which directly measures the speed change by installing a ring gear disc and sensor at the end of the generator shaft. However, its measurement accuracy is heavily dependent on the mechanical installation process and the machining accuracy of the gear disc. The swaying, vibration, and slight non-uniformity of the tooth pitch during generator operation can introduce low-frequency interference, causing fluctuations in the speed measurement signal and affecting the stability of the control system. Indirect measurement uses the PT residual voltage method, which indirectly calculates the speed by measuring the residual voltage signal of the generator terminal voltage transformer (PT). Although this method is not affected by mechanical factors, when the generator is running at low speed, the terminal voltage amplitude is low and the waveform distortion is severe. It is difficult to obtain the true frequency information based solely on the AC voltage zero-crossing point information, resulting in a sharp drop in speed measurement accuracy. This puts critical control systems such as the governor at risk of "no reliable data available" under extreme operating conditions, restricting further improvement in the control performance and safety level of the generator. Summary of the Invention

[0004] This invention aims to solve the technical problems of insufficient speed measurement accuracy in existing speed measurement methods, such as the susceptibility of the gear disc speed measurement method to mechanical interference and the difficulty in accurately extracting frequency information under low-speed conditions in the PT residual pressure method. The invention provides a method to improve the accuracy of PT residual pressure frequency measurement based on rotational vector characteristics.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for improving the accuracy of PT residual voltage frequency measurement based on rotation vector features includes the following steps: Step S1: Obtain the three-phase AC voltage signal through the generator terminal voltage transformer PT; Step S2: Process the three-phase AC voltage signal to obtain a voltage rotation vector, and extract the frequency feature information of the voltage based on the voltage rotation vector; Step S3: Process the frequency characteristic information through a low-pass filter to obtain voltage frequency information with high-frequency interference filtered out; Step S4: Based on the voltage frequency information after filtering out high-frequency interference, calculate the generator speed and provide it to the speed governor.

[0006] Furthermore, in step S2, the processing method for the three-phase voltage AC signal is as follows: ; in, , , It is a three-phase voltage AC signal. , This is the projection of the voltage rotation vector onto the stationary coordinate axes α and β.

[0007] Furthermore, in step S2, the method for extracting the voltage amplitude feature V is as follows: ; in, , This is the projection of the voltage rotation vector onto the stationary coordinate axes α and β.

[0008] Furthermore, in step S2, the voltage frequency characteristic ω is extracted by directly calculating it through the projection of the voltage onto the α and β axes and the voltage amplitude. The calculation formula is as follows: or ; in, , Let ω be the projection of the voltage onto the α and β axes, and ω be the frequency of the voltage.

[0009] Furthermore, in step S2, the voltage frequency feature ω is extracted by obtaining it through a phase-locked loop via the projection of the voltage onto the α and β axes and the voltage amplitude.

[0010] Furthermore, in the phase-locked loop (PLL), the formula for calculating the projection of the voltage onto the d and q coordinate axes of the PLL is as follows: ; in, , The voltage is projected onto the d and q axes of the phase-locked loop. The phase is the phase of the phase-locked coordinate system.

[0011] Furthermore, in a phase-locked loop, the formula for calculating the voltage frequency ω is: ; ; in, , The voltage is projected onto the d and q axes of the phase-locked loop. For the phase of the phase-locked coordinate system, , These are the proportional and integral coefficients for phase-locked control.

[0012] Furthermore, in step S3, the filtering method for the voltage frequency characteristics is as follows: ; in, The frequency after filtering. This is the transfer function of the low-pass filter.

[0013] Furthermore, in step S3, the filter's transfer function... for: or ; in, This represents the passband gain of the low-pass filter. This is the cutoff angular frequency of the first-order filter. The natural angular frequency of the second-order filter. is the damping coefficient of the second-order filter.

[0014] Furthermore, in step S4, the formula for calculating the generator speed n is: ; Wherein, ω is the voltage frequency after filtering out high-frequency interference, and p is the number of pole pairs of the generator; the method is applicable to hydro generators, steam turbine generators, and other equipment that requires measuring the speed or frequency of rotating parts.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention synthesizes a voltage rotating vector based on a complete three-phase AC voltage sequence and extracts frequency features. Compared to the traditional PT residual voltage method, which only relies on zero-crossing information, it includes more effective information such as voltage change trends, amplitude, and phase. Even under conditions of low-speed unit operation and severe voltage waveform distortion, it can still accurately capture true frequency information, significantly improving the speed measurement accuracy under low-speed conditions. Figure 3 As shown, within the range of 50% to 90% of the rated speed, the measurement results of this invention closely match the actual speed, while the traditional zero-crossing method shows a significant deviation in the range of 50% to 80%.

[0016] 2. This invention adopts a processing method of "extracting frequency DC first and then filtering". Compared with the method of directly filtering the three-phase AC signal, it avoids the phase shift and amplitude distortion caused by filtering, greatly reduces the measurement deviation introduced by the filtering link, and makes the frequency and speed calculation results closer to the true value and stronger anti-interference ability.

[0017] 3. This invention provides two frequency extraction methods and two filtering schemes, which can be flexibly selected according to different unit types, operating conditions and accuracy requirements. It has a wide range of applications and can be applied to various equipment that need to measure the speed or frequency of rotating parts, such as hydro generators and steam generators. It has strong practicality and promotion value.

[0018] 4. This invention does not require additional complex hardware equipment. It can improve measurement accuracy simply by optimizing the signal processing algorithm. The modification cost is low and it is easy to integrate into existing generator set control systems. It is of great significance for improving the control performance and operational safety of the generator set. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the principle of extracting voltage frequency information based on rotating vector features in this invention; Figure 3 This is a comparison chart of the rotational speed measurement results of the method of the present invention and the traditional zero-crossing method.

[0020] in, V Let be the voltage rotating vector, a, b, and c be the three-phase coordinate axes, α and β be the stationary coordinate axes, and d and q be the phase-locked rotating coordinate axes. V The magnitude of the voltage rotation vector. ω The frequency of the voltage rotation vector, Let be the phase of the voltage rotation vector, where For the initial phase, For phase-locked phase, , , Let be the projection of the voltage rotation vector onto the three-phase coordinate axes a, b, and c. , This represents the projection of the voltage rotation vector onto the stationary coordinate axes α and β. , This is the projection of the voltage rotation vector onto the d and q coordinate axes of the phase-locked loop. Detailed Implementation

[0021] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] This invention provides a method for improving the accuracy of PT residual voltage frequency measurement based on rotating vector features, such as... Figure 1 As shown, the core idea is to collect three-phase AC voltage signals through voltage transformers, synthesize them into a voltage rotating vector, fully utilize the complete voltage sequence information to extract frequency features, and then filter the frequency DC data to accurately calculate the generator speed. The specific technical solution is as follows: 1. Acquiring three-phase AC voltage signals: The three-phase AC voltage signals are acquired through the generator terminal voltage transformer (PT). , , This embodiment uses a JDZ-10 voltage transformer with a measurement accuracy class of 0.2, which can accurately capture the three-phase AC voltage signals under different operating conditions of the unit, providing a reliable data source for subsequent signal processing.

[0023] 2. Synthesizing the Voltage Rotation Vector: The acquired three-phase AC voltage signals are processed by coordinate transformation to obtain the projection of the voltage rotation vector onto the α and β stationary coordinate axes. , The transformation formula is as follows: ; like Figure 2 As shown, a, b, and c are the three-phase coordinate axes, α and β are the stationary coordinate axes, and the voltage rotation vector is... V The projection onto the three-phase coordinate axes represents the acquired three-phase AC voltage. , , By using the above coordinate transformation, the projection of the voltage rotation vector on the α and β axes can be derived in reverse, realizing the conversion of the three-phase AC signal to a two-dimensional stationary coordinate system signal, laying the foundation for frequency feature extraction.

[0024] 3. Extracting voltage frequency features: First, extract the voltage amplitude characteristics. V The calculation formula is: ; in V The magnitude of the voltage rotation vector reflects the strength of the voltage signal.

[0025] Voltage frequency characteristics ω Extraction can be performed in two ways: Method 1: Direct calculation method, calculated using the voltage projections on the α and β axes and the voltage amplitude. The formula is: or ; This method directly uses the rate of change and amplitude information of the voltage signal to derive the frequency, resulting in high computational efficiency.

[0026] Method 2: Phase-locked loop method, such as Figure 2 As shown, d and q are phase-locked rotating coordinate axes. First, the projection signals of the α and β axes are converted to the d and q axes. The conversion formula is as follows: ; The frequency is then calculated using a phase-locked loop (PLL) control algorithm, as shown in the formula: ; ; in, , The voltage is projected onto the d and q axes of the phase-locked loop. For the phase of the phase-locked coordinate system, , These are the proportional and integral coefficients for phase-locked control.

[0027] In this embodiment, the phase-locked control proportional coefficient =60, integral coefficient =1400, through proportional-integral adjustment, the phase-locked coordinate system tracks the phase change of the voltage rotation vector, thereby accurately obtaining the voltage frequency. ω This method has stronger anti-interference capabilities and is suitable for low-speed operating conditions with severe voltage waveform distortion.

[0028] 4. Low-pass filtering: This process applies to the extracted voltage frequency characteristics. ω This stream undergoes low-pass filtering to remove high-frequency interference. This invention can use a first-order or second-order low-pass filter: The transfer function of a first-order low-pass filter is: ; The transfer function of a second-order low-pass filter is: ; in, This represents the passband gain of the low-pass filter. This is the cutoff angular frequency of the first-order filter. The natural angular frequency of the second-order filter. is the damping coefficient of the second-order filter.

[0029] Filtering can effectively remove high-frequency noise from the frequency signal, preventing interference signals from affecting the accuracy of speed calculation.

[0030] 5. Calculate generator speed: based on the filtered voltage frequency. ω Through the formula: ; Where ω is the voltage frequency after filtering out high-frequency interference, and p is the number of pole pairs of the generator. The calculated speed signal is transmitted to control components such as the speed governor to provide reliable feedback for unit regulation.

[0031] The workflow of this invention is as follows: Figure 1 As shown, accurate speed measurement is achieved through a complete process of "signal acquisition - vector synthesis - frequency extraction - filtering - speed calculation". Its core principle is that the frequency of the voltage rotating vector has a fixed correspondence with the generator rotor speed. By synthesizing the rotating vector from a complete three-phase voltage sequence, the amplitude, phase, and trend information of the voltage signal can be fully utilized, overcoming the limitation of the traditional PT residual voltage method which only relies on zero-crossing information. Simultaneously, filtering the frequency DC signal avoids phase shift and amplitude distortion caused by directly filtering the AC signal, ensuring the accuracy of the measurement results.

[0032] This embodiment is applied to a hydroelectric generator set with 40 pole pairs and a rated speed of 75 r / min. A JDZ-10 type voltage transformer is selected to collect the three-phase AC voltage signal. , , The sampling frequency is 1kHz.

[0033] The signal processing procedure is as follows: 1. The three-phase AC voltage signal during unit operation is collected by voltage transformer. At a speed of 37.5 r / min (50% of rated speed), the collected voltage signal has low amplitude and severe waveform distortion.

[0034] 2. According to the formula The coordinate transformation of the three-phase voltage signal yields the projection signals of the α and β axes. , .

[0035] 3. According to the formula Calculate voltage amplitude V Frequency extraction is performed using a phase-locked loop (PLL) method: [Settings are missing from the original text] =60、 =1400, passed Convert to d-axis and q-axis, then via and Calculated voltage frequency ω =156 rad / s.

[0036] 4. A second-order low-pass filter is used for filtering. The filter parameters are set as follows: passband gain of 1, natural angular frequency of 1250 rad / s. =0.7, the filtered frequency ω=153rad / s.

[0037] 5. According to the formula Calculate the rotational speed and substitute the data to get The deviation from the actual rotational speed is less than 0.5%, and the measurement accuracy is significantly better than the traditional zero-crossing method.

[0038] When the unit speed increased to 67.5 r / min (90% of the rated speed), the speed calculated using the same method was 66.3 r / min, and the deviation was still less than 0.5%, which verified the measurement stability and accuracy of the present invention in a wide speed range.

[0039] Combination Figure 3 The comparison chart shows that the measurement results of this embodiment are consistent with the curve of the "Method of the Invention" in the figure, closely matching the actual speed within the range of 50% to 90% of the rated speed. In contrast, the traditional zero-crossing method has a measurement deviation of more than 3% at 37.5 r / min (50% of the rated speed), which is significantly higher than that of the present invention. This embodiment fully verifies the measurement stability and accuracy of the present invention over a wide speed range, especially its outstanding advantages under low-speed conditions, and fully meets the requirements of generator set speed control for speed measurement accuracy.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the accuracy of PT residual voltage frequency measurement based on rotation vector features, characterized in that, The method comprises the following steps: Step S1: obtaining three-phase voltage alternating current signals through a generator terminal voltage transformer PT; Step S2: processing the three-phase voltage alternating current signals to obtain a voltage rotating vector, and extracting frequency characteristic information of the voltage based on the voltage rotating vector; Step S3: processing the frequency characteristic information through a low-pass filter link to obtain voltage frequency information filtered from high-frequency interference; Step S4: calculating a generator rotating speed based on the voltage frequency information filtered from high-frequency interference, and providing the generator rotating speed for a speed regulator.

2. The method for improving PT residual voltage frequency measurement accuracy based on rotation vector characteristics according to claim 1, characterized in that, In step S2, the processing mode of the three-phase voltage alternating current signals is as follows: ； wherein , , is a three-phase voltage alternating signal, , is the projection of the voltage rotating vector on the α, β stationary axes.

3. The method of claim 1, wherein the PT residual voltage frequency measurement accuracy is improved based on the rotation vector feature. In step S2, the mode of extracting the voltage amplitude characteristic V is as follows: ； wherein , is the projection of the voltage rotating vector on the α, β stationary axes.

4. The method of claim 3, wherein the PT residual voltage frequency measurement accuracy is improved based on the rotation vector feature. In S2, the voltage frequency characteristic ω The extraction method is: through the projection of voltage on the α, β axis and the direct calculation of voltage amplitude, the calculation formula is: or ; wherein, , is the projection of the voltage on the α, β axis, ω is the frequency of the voltage.

5. The method of claim 3, wherein the PT residual voltage frequency measurement accuracy is improved based on the rotation vector feature. In step S2, the voltage frequency characteristic ω is extracted by means of the projection of the voltage on the α, β axes and the voltage amplitude via a phase-locked loop.

6. The method of claim 5, wherein the PT residual voltage frequency measurement accuracy is improved based on the rotation vector feature. In the phase-locked loop, the projection calculation formula of the voltage on the phase-locked d, q coordinate axes is as follows: ； wherein , is the projection of the voltage on the locked phase d, q axes, is the phase of the locked phase coordinate system.

7. The method of claim 6, wherein the PT residual voltage frequency measurement accuracy is improved based on the rotation vector feature. In the phase-locked loop, the calculation formula of the voltage frequency ω is: ； ； wherein , is the projection of the voltage on the locked phase d, q axes, is the phase of the locked phase coordinate system, , are the proportional and integral coefficients of the locked phase control.

8. The method of claim 1, wherein the PT residual voltage frequency measurement accuracy is improved based on the rotation vector feature. In step S3, the filtering mode of the voltage frequency characteristic is as follows: ； wherein is the filtered frequency, is the transfer function of the low-pass filter.

9. The method of claim 1, wherein the PT residual voltage frequency measurement accuracy is improved based on the rotation vector feature. In step S3, the transfer function of the filter is: or ; wherein is the passband gain of the low-pass filter, is the corner angular frequency of the first order filter, is the natural angular frequency of the second order filter, is the damping coefficient of the second order filter.

10. The method of claim 1, wherein the method is based on a rotation vector feature to improve the accuracy of PT residual voltage frequency measurement. In step S4, the engine rotation speed n The calculation formula is: ； wherein, ω is the voltage frequency after filtering out high frequency interference, p is the number of pole pairs of the generator; the method is applicable to hydroelectric generators, steam turbine generators and other devices that need to measure the rotational speed or frequency of the rotating part.

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