Pump storage unit protection method based on frequency-independent phasor calculation

Abstract

A frequency-independent phasor calculation method suitable for pumped storage unit protection, the electrical quantity of the pumped storage unit is sampled to form electrical quantity sampling values; the response signal corresponding to the time domain signal of the electrical quantity sampling values is obtained by using Hilbert transform, the data window length in the Hilbert transform is determined by using the lower limit of the frequency range to be protected during the starting of the pumped storage unit, and the amplitude and phase of the electrical quantity are determined by using the time domain signal and the response signal; the over-current protection phasor and the negative sequence protection phasor are calculated by using the electrical quantity. The method provided by the application only needs to select a fixed data window according to the lower limit of the frequency, greatly improves the response speed, has higher calculation accuracy without frequency measurement, and has stronger noise and higher harmonic resistance.

Description

Technical Field

[0001] This invention belongs to the field of power system automation technology, specifically, it relates to a protection method for pumped storage units based on frequency-independent phasor calculation. Background Technology

[0002] With the deepening construction of new energy power systems, the installed capacity of new energy sources such as wind power and photovoltaics in the power system is increasing day by day. However, their intermittency and volatility have adverse effects on the operation of the power system. In order to overcome the problems of intermittency and volatility of new energy, the National Energy Administration is accelerating the development and construction of pumped storage projects, and has confirmed that during the "14th Five-Year Plan" period, the approved installed capacity will reach 270 million kilowatts, with a total investment of 1.6 trillion yuan. Developing pumped storage is of great significance for promoting the large-scale and high-proportion development of new energy, improving the safe and stable operation of the power system, and expanding effective investment.

[0003] Pumped storage units can function as both generators and motors. Their operating status is arranged according to the needs of power grid dispatch. During the switching between generator and motor modes, their operating conditions are not a stable 50Hz power frequency, but rather must be able to adapt to a large frequency fluctuation range from starting from a standstill to the power frequency and braking from the power frequency to a standstill.

[0004] In existing technologies, pumped storage units, due to their large operating frequency variation range, traditional relay protection methods first measure the signal frequency and then perform Fourier transform calculations based on a selected complete cycle to obtain the frequency. Accurate signal frequency measurement requires a long cycle, and frequency measurement itself contains errors. Once the frequency changes, it will lead to significant errors in the phasor calculations of the Fourier algorithm. The greater the frequency difference, the greater the phasor calculation error. In some cases, when the signal amplitude is low or contains high-order harmonic interference, frequency measurement may fail, making phasor calculation impossible. The proposed "A Phasor Calculation Method for Power Systems with Frequency Deviation" (CN103884910B) can only calculate signals fluctuating around a certain frequency. For example, for a 50Hz power frequency signal, this method can only calculate the phasor of signals around 48Hz-52Hz; signals with a larger range cannot be calculated. The "Synchronous Phasor Measurement Method for Power Signals Based on Multi-Frequency Phasor Model" (CN107589299B) is only applicable to phasor calculations near a fixed frequency. Frequency estimation based on FFT Fourier transform requires multiple iterations and repeated verifications, resulting in a huge computational workload and making real-time phasor calculation impossible. The "Synchronous Phasor Measurement Method and System with Hamming Window" (CN108614155B) only applies to cases with small frequency shifts, as its mathematical quantitative relationship between the error caused by frequency shift and the degree of frequency shift only applies to cases with small frequency shifts. For a power frequency of 50Hz, this method can only calculate phasors for signals around 48Hz-52Hz; it cannot calculate signals with a larger frequency range. Therefore, there is an urgent need to research phasor calculation methods that can automatically adapt to a wider range of frequency variations.

[0005] According to its mathematical definition, the traditional Hilbert transform requires a relatively long data window for signal processing, which contradicts the speed requirements of power system relay protection. Therefore, it is necessary to balance speed and accuracy and select a data window of appropriate width for the Hilbert transform calculation. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a protection method for pumped storage units based on frequency-independent phasor calculation. This method is suitable for pumped storage units operating under frequency variations of tens of hertz and does not require prior frequency measurement. By performing a Hilbert transform on the original signal with a fixed data window, the real and imaginary parts of the signal are obtained, and then the amplitude and phase of the phasor are derived.

[0007] The present invention adopts the following technical solution.

[0008] This invention proposes a protection method for pumped storage units based on frequency-independent phasor calculation, comprising:

[0009] Step 1: Sample the electrical quantities of the pumped storage unit to generate electrical quantity sample values. ,in Sampling time The electrical quantity sampling values, , This represents the total number of sampling times.

[0010] Step 2: Obtain the time-domain signal of the electrical quantity sample values ​​using Hilbert transform. Corresponding response signal The data window length in the Hilbert transform is determined by using the lower limit of the frequency range to be protected during the startup of the pumped storage unit, satisfying the following relationship:

[0011]

[0012] In the formula, For the length of the data window, This is the lower limit of the frequency range to be protected during the startup of a pumped storage unit.

[0013] Step 3, using time-domain signals and response signal Determine the amplitude and phase of the electrical quantity;

[0014] Step 4: Calculate the overcurrent protection phasor and the negative sequence protection phasor using electrical quantities.

[0015] Preferably, in step 1, the electrical quantities include voltage and current.

[0016] Preferably, in step 2, the response signal The following relationship must be satisfied:

[0017]

[0018] In the formula, For window functions, This is a convolution operation.

[0019] Window function The following relationship must be satisfied:

[0020]

[0021] After the time-domain signal undergoes the Hilbert transform, the amplitude of each frequency component in the frequency domain remains unchanged, but the phase will shift by 90°.

[0022] Preferably, in step 2, the frequency range to be protected during the startup of the pumped storage unit is 10Hz to 65Hz.

[0023] The data window length is twice the cycle corresponding to the lower limit of the frequency range to be protected during the startup of the pumped storage unit, which is 10Hz.

[0024] Preferably, in step 3, the time-domain signal As the real part of an electrical quantity, the response signal As the imaginary part of an electrical quantity, the magnitude of the electrical quantity at time t satisfies the following relationship:

[0025]

[0026] In the formula, This refers to the amplitude of the electrical quantity.

[0027] The phase of the electrical quantities at time t satisfies the following relationship:

[0028]

[0029] In the formula, The phase of an electrical quantity.

[0030] Preferably, in step 4, the calculation of the overcurrent protection phasor includes:

[0031] Step 4.1.1: Perform steps 1 to 3 to obtain the phasors of the three-phase currents, which satisfy the following relationship:

[0032]

[0033]

[0034]

[0035] In the formula,

[0036] , , These are the phasors of the three-phase currents.

[0037] , , These are the time-domain signals of the three-phase current sample values,

[0038] , , These are the response signals of the three-phase current sample values ​​obtained after Hilbert transformation;

[0039] Step 4.1.2, Overcurrent Protection Phasor The following relationship must be satisfied:

[0040]

[0041] In the formula, When the current exceeds the overcurrent protection setting, the overcurrent protection will activate.

[0042] Preferably, in step 4, the calculation of the negative sequence protected phasor includes:

[0043] Step 4.2.1: Perform steps 1 to 3 to obtain the phasors of the three-phase currents, which satisfy the following relationship:

[0044]

[0045]

[0046]

[0047] In the formula,

[0048] , , These are the phasors of the three-phase currents.

[0049] , , These are the time-domain signals of the three-phase current sample values,

[0050] , , These are the response signals of the three-phase current sample values ​​obtained after Hilbert transformation;

[0051] Step 4.2.2, Negative-sequence protected phasor The following relationship must be satisfied:

[0052]

[0053] In the formula, When the value exceeds the negative sequence protection setting, the negative sequence protection will activate.

[0054] The beneficial effect of this invention is that, compared with the prior art, the method proposed in this invention avoids the traditional phasor calculation method that requires measuring the frequency before performing phasor calculations. The advantages include:

[0055] 1. Traditional methods require frequency measurement first, which necessitates a long data window. The higher the frequency calculation accuracy, the longer the data window needs to be, resulting in a longer response time for calculating phasors. However, the method proposed in this invention only requires selecting a fixed data window based on the lower limit of the frequency, which greatly improves the response speed.

[0056] 2. Traditional methods use the number of zero-crossings to estimate frequency in the frequency measurement stage, which is easily affected by noise and high-order harmonic interference, resulting in poor frequency measurement accuracy. However, the present invention does not require frequency measurement, so the calculation accuracy is higher and the ability to withstand noise and high-order harmonics is stronger. Attached Figure Description

[0057] Figure 1 This is a flowchart of a pumped storage unit protection method based on frequency-independent phasor calculation proposed in this invention;

[0058] Figure 2 This is a waveform diagram of the original signal undergoing Hilbert transform to obtain the imaginary part signal in an embodiment of the present invention, where the solid line represents the original signal and the dashed line represents the imaginary part signal;

[0059] Figure 3 This is a waveform diagram illustrating the acquisition of amplitude and phase using the original signal and the imaginary part signal in an embodiment of the present invention, where the solid line represents the phase and the dashed line represents the amplitude. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0061] This invention proposes a protection method for pumped storage units based on frequency-independent phasor calculations, such as... Figure 1 ,include:

[0062] Step 1: Sample the electrical quantities of the pumped storage unit to generate electrical quantity sample values. ,in Sampling time The electrical quantity sampling values, , This represents the total number of sampling times.

[0063] Electrical quantities include, but are not limited to, voltage and current. In this embodiment, the voltage and current of the pumped storage unit are sampled to form sampled values ​​of voltage and current signals. .

[0064] Step 2: Obtain the time-domain signal of the electrical quantity sample values ​​using Hilbert transform. Corresponding response signal Since real-world signals have finite widths and relay protection has time limitations, the data window length for Hilbert transform of electrical signals should be adapted to the relay protection function. The data window length in Hilbert transform satisfies the following relationship:

[0065]

[0066] In the formula, For the length of the data window, This is the lower limit of the frequency range to be protected during the startup of a pumped storage unit.

[0067] Traditional methods require frequency measurement first, which necessitates a long data window. The higher the frequency calculation accuracy, the longer the data window needs to be, resulting in a longer response time for calculating phasors. In contrast, the method proposed in this invention only requires selecting a fixed data window based on the lower limit of the frequency, which greatly improves the response speed.

[0068] Based on the mathematical principles of the Hilbert transform, time-domain signals are transformed... With window function Perform convolution operations to obtain the response signal. It satisfies the following relationship:

[0069]

[0070] In the formula, For window functions, This is a convolution operation.

[0071] Window function The following relationship must be satisfied:

[0072]

[0073] After the time-domain signal undergoes the Hilbert transform, the amplitude of each frequency component in the frequency domain remains unchanged, but the phase will shift by 90°.

[0074] The frequency range to be protected during the startup of pumped storage units is 10Hz to 65Hz.

[0075] The data window length is twice the cycle corresponding to the lower limit of the frequency range to be protected during the startup of the pumped storage unit, which is 10Hz.

[0076] Step 3, using time-domain signals and response signal Determine the amplitude and phase of the electrical quantity.

[0077] Specifically, in step 3, the time-domain signal As the real part of an electrical quantity, the response signal As the imaginary part of an electrical quantity, the magnitude of the electrical quantity at time t satisfies the following relationship:

[0078]

[0079] In the formula, This refers to the amplitude of the electrical quantity.

[0080] The phase of the electrical quantities at time t satisfies the following relationship:

[0081]

[0082] In the formula, The phase of an electrical quantity.

[0083] Step 4: Calculate the overcurrent protection phasor and the negative sequence protection phasor using electrical quantities.

[0084] Specifically, in step 4, the calculation of the overcurrent protection phasors includes:

[0085] Step 4.1.1: Perform steps 1 to 3 to obtain the phasors of the three-phase currents, which satisfy the following relationship:

[0086]

[0087]

[0088]

[0089] In the formula,

[0090] , , These are the phasors of the three-phase currents.

[0091] , , These are the time-domain signals of the three-phase current sample values,

[0092] , , These are the response signals of the three-phase current sample values ​​obtained after Hilbert transformation;

[0093] Step 4.1.2, Overcurrent Protection Phasor The following relationship must be satisfied:

[0094]

[0095] In the formula, The overcurrent protection action is triggered when the current exceeds the overcurrent protection setting.

[0096] Specifically, in step 4, the calculation of the negative sequence protected phasor includes:

[0097] Step 4.2.1: Perform steps 1 to 3 to obtain the phasors of the three-phase currents, which satisfy the following relationship:

[0098]

[0099]

[0100]

[0101] In the formula,

[0102] , , These are the phasors of the three-phase currents.

[0103] , , These are the time-domain signals of the three-phase current sample values,

[0104] , , These are the response signals of the three-phase current sample values ​​obtained after Hilbert transformation;

[0105] Step 4.2.2, Negative-sequence protected phasor The following relationship must be satisfied:

[0106]

[0107] In the formula, When the value exceeds the negative sequence protection setting, the negative sequence protection will activate.

[0108] Traditional methods use the number of zero-crossings to estimate frequency during frequency measurement, which is easily affected by noise and high-order harmonic interference, resulting in poor frequency measurement accuracy. However, this invention does not require frequency measurement, so the calculation accuracy is higher and the ability to withstand noise and high-order harmonics is stronger.

[0109] In order to adapt to the phasor calculation and relay protection methods of electrical equipment operating at different frequencies, the following uses the application of relay protection in the static frequency converter (SFC) process of a pumped storage unit as an example to illustrate the method of the present invention.

[0110] Measuring the three-phase current of a pumped storage unit using a current transformer , , It is also connected to a microcomputer protection device for digital sampling.

[0111] Considering the frequency range to be protected during the startup of the pumped storage unit is 10Hz to 65Hz, a Hilbert transform is performed using a data window of 2 × 0.1 seconds = 0.2 seconds, corresponding to the lower frequency limit of 10Hz, which is twice the period.

[0112]

[0113] For current , , The sampled value sequences were subjected to Hilbert transforms to obtain the imaginary part of the three-phase current within a 0.1-second data window. , , Thus, the phasors of the three-phase currents are obtained:

[0114]

[0115]

[0116]

[0117] For overcurrent protection ,satisfy The overcurrent protection action is triggered when the current exceeds the overcurrent protection setting.

[0118] For negative order protection, utilize , , The three-phase phasors yield negative sequence current:

[0119]

[0120] The method used in this invention can adapt well to the frequency changes of pumped storage units. Even during the gradual frequency change process, it can correctly calculate the electrical phasors. The signal in the figure below shows the process of the frequency gradually decreasing.

[0121] The method proposed in this invention can be used to calculate the imaginary part of the original signal, such as... Figure 2 As shown, the phasor amplitude and phase at each sampling time are then obtained, as follows: Figure 3 As shown.

[0122] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0123] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0124] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0125] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0126] Various aspects of this disclosure are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It should 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-readable program instructions.

[0127] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0128] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0129] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0130] 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 claims of the present invention.

Claims

1. A protection method for pumped storage units based on frequency-independent phasor calculation, characterized in that, The method includes: Step 1: Sample the electrical quantities of the pumped storage unit to generate electrical quantity sample values. ,in Sampling time The electrical quantity sampling values, , This represents the total number of sampling times. Step 2: Obtain the time-domain signal of the electrical quantity sample values ​​using Hilbert transform. Corresponding response signal The data window length in the Hilbert transform is determined by using the lower limit of the frequency range to be protected during the startup of the pumped storage unit, satisfying the following relationship: In the formula, For the length of the data window, This is the lower limit of the frequency range to be protected during the startup of a pumped storage unit. Step 3, using time-domain signals and response signal Determine the amplitude and phase of the electrical quantity; Step 4: Calculate the overcurrent protection phase quantity and the negative sequence protection phase quantity using electrical quantities; In step 4, the calculation of the overcurrent protection phasors includes: Step 4.1.1: Perform steps 1 to 3 to obtain the phasors of the three-phase currents, which satisfy the following relationship: In the formula, , , These are the phasors of the three-phase currents. , , These are the time-domain signals of the three-phase current sample values, , , These are the response signals of the three-phase current sample values ​​obtained after Hilbert transformation; Step 4.1.2, Overcurrent Protection Phasor The following relationship must be satisfied: In the formula, When the current exceeds the overcurrent protection setting, the overcurrent protection will activate. In step 4, the calculation of the negative sequence protected phasor includes: Step 4.2.1: Perform steps 1 to 3 to obtain the phasors of the three-phase currents, which satisfy the following relationship: In the formula, , , These are the phasors of the three-phase currents. , , These are the time-domain signals of the three-phase current sample values, , , These are the response signals of the three-phase current sample values ​​obtained after Hilbert transformation; Step 4.2.2, Negative-sequence protected phasor The following relationship must be satisfied: In the formula, When the value exceeds the negative sequence protection setting, the negative sequence protection will activate.

2. The pumped storage unit protection method based on frequency-independent phasor calculation according to claim 1, characterized in that, In step 1, the electrical quantities include: voltage and current.

3. The pumped storage unit protection method based on frequency-independent phasor calculation according to claim 1, characterized in that, In step 2, the response signal The following relationship must be satisfied: In the formula, For window functions, This is a convolution operation.

4. The pumped storage unit protection method based on frequency-independent phasor calculation according to claim 2, characterized in that, Window function The following relationship must be satisfied: After the time-domain signal undergoes the Hilbert transform, the amplitude of each frequency component in the frequency domain remains unchanged, but the phase will shift by 90°.

5. The pumped storage unit protection method based on frequency-independent phasor calculation according to claim 3, characterized in that, In step 2, the frequency range to be protected during the startup of the pumped storage unit is 10Hz to 65Hz.

6. The pumped storage unit protection method based on frequency-independent phasor calculation according to claim 4, characterized in that, The data window length is twice the cycle corresponding to the lower limit of the frequency range to be protected during the startup of the pumped storage unit, which is 10Hz.

7. The pumped storage unit protection method based on frequency-independent phasor calculation according to claim 1, characterized in that, In step 3, the time-domain signal As the real part of an electrical quantity, the response signal As the imaginary part of an electrical quantity, the magnitude of the electrical quantity at time t satisfies the following relationship: In the formula, This refers to the amplitude of the electrical quantity.

8. The pumped storage unit protection method based on frequency-independent phasor calculation according to claim 7, characterized in that, The phase of the electrical quantities at time t satisfies the following relationship: In the formula, The phase of an electrical quantity.

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