Energy flow dissipation method based on synchronous compression generalized S transformation

Abstract

The invention discloses a method for tracing a dissipated energy flow of a power system. The method comprises the following steps: firstly, setting a sensitive subsynchronous oscillation online detection link with relatively low calculation complexity, and positioning subsynchronous oscillation in time at the initial stage of oscillation; secondly, retaining a subsynchronous frequency band component in the signal based on synchronous compression generalized S-transform; taking a 60 Hz system as an example, the subsynchronous oscillation (SSO) frequency is between 5 Hz and 55 Hz. Therefore, the band-pass filter in the frequency range can be used for variables such as voltage and active / reactive power; then, for the preprocessed and filtered signals, calculating instantaneous energy dissipation of each branch or each bus; and finally, comparing the instantaneous energy dissipation of the branches and the bus, and judging the oscillation source. The method is simple in calculation, can accurately calculate the frequency, the amplitude and the phase angle of each harmonic wave of the power system, and has a very high practical value.

Description

Technical Field

[0001] The present invention relates to the field of power system safety and stability, and in particular to a method for tracing the source of dissipated energy flow in a power system. Background Art

[0002] With the increasing penetration of renewable energy, the interaction between a large number of wind turbines connected to the grid via converters and the power grid has increased the risk of subsynchronous oscillations (SSOs). In recent years, SSO incidents have become frequent in power systems, posing a serious threat to the safe and stable operation of the power system. These oscillations typically occur in the 5-45Hz / 5-55Hz range, with a fundamental frequency of 50Hz / 60Hz. Their generation mechanism is complex, their impact is widespread, and they pose a threat to the safe and stable operation of the power system. Therefore, analyzing and identifying SSO sources within the network is crucial for developing timely and effective mitigation strategies. Rapidly and accurately locating the source of SSOs provides a reference for effective suppression measures in the early stages of oscillations, which is crucial for preventing further incidents and ensuring the safe and stable operation of the power system.

[0003] SSO source identification can be achieved in two ways, one is a model-based method and the other is a data-based method. Model-based methods usually use small signal analysis of state-space equations to calculate the participation factors of each component of the power system to obtain the probability of participating in subsynchronous oscillations (SSO). Another model-based method is the impedance analysis method. This method establishes an equivalent impedance network of the power system and then analyzes the stability of the system based on the stability criterion. However, these methods require internal data, detailed control parameters and wind farm structure, which are difficult to obtain because manufacturers usually keep the parameters confidential. In addition, the accuracy of these methods in identifying the source is greatly affected by the generator output and the power system topology. And the computational burden is also heavy, which makes them only suitable for offline analysis. Therefore, these model-based methods are unreliable in identifying SSO sources.

[0004] Another attractive approach is data-based source identification. With the gradual maturity of wide-area measurement systems, synchronized phasor data obtained from these systems can be used to promptly identify SSO sources. Some scholars have proposed combining transient energy flow with the electromagnetic transient model of a doubly-fed wind turbine to derive transient energy flow location criteria suitable for grid-connected doubly-fed wind turbines. Transient energy flow location methods are widely used in actual power grids due to their high positioning accuracy and clear physical meaning. The key to using transient energy flow to locate subsynchronous oscillation sources lies in accurately separating the subsynchronous oscillation components implicit in the measurement information. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for tracing the source of dissipated energy flow in a power system. The method has simple calculation and high accuracy, can accurately identify the oscillation source when forced oscillation occurs in the power system, and has strong practical value.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for tracing the source of dissipated energy flow based on synchrocompressed generalized S transform, the method comprising:

[0008] Step 1: Setting up a sensitive and computationally low-complexity subsynchronous oscillation online detection process to timely locate the subsynchronous oscillation in its early stages;

[0009] Step 2: Preserve the subsynchronous frequency band components in the signal based on the synchro-compressed generalized S-transform. Taking a 60Hz system as an example, the subsynchronous oscillation (SSO) frequency ranges from 5Hz to 55Hz. Therefore, a bandpass filter in this frequency range can be used for variables such as voltage and active / reactive power.

[0010] Step 3: For the preprocessed and filtered signals, calculate the instantaneous energy dissipation of each branch or each bus;

[0011] Step 4: Compare the instantaneous energy dissipation of the branch and bus to determine the oscillation source.

[0012] It can be seen from the technical solution provided by the present invention that the above method is simple to calculate, can accurately identify the oscillation source when forced oscillation occurs in the power system, and has great practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 A flowchart provided for an embodiment of the present invention;

[0015] Figure 2 Schematic diagram of continuous monitoring used in an embodiment of the present invention to complete the subsynchronous oscillation online detection link;

[0016] Figure 3 This is an SSGST time-frequency diagram of the self-synthesized analog signal by directly filtering out the power frequency signal component in the time-frequency domain according to an embodiment of the present invention;

[0017] Figure 4This is the final result presentation of the dissipative energy flow tracing based on the synchronous compression generalized S transform in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. Figure 1 The following is a confirmed architecture provided by an embodiment of the present invention, wherein the method includes:

[0020] Step 1: Setting up a sensitive and computationally low-complexity subsynchronous oscillation online detection process to timely locate the subsynchronous oscillation in its early stages;

[0021] In step 1, the specific process is:

[0022] Oscillation identification generally suffers from the problem of high computational complexity. To further reduce the computational burden of the system, the present invention provides an oscillation detection link to detect oscillations in real time. Therefore, the computational complexity of the detection link is the primary consideration during design. The energy ratio function can determine the signal change by calculating the ratio of the effective values ​​of the first and second halves of the signal within a fixed time window. This time window is then moved point by point to continuously describe the signal's mutation status, resulting in high computational efficiency. The calculation formula for the energy ratio PER is:

[0023]

[0024] Where: T is the total length of the time window, and T0 is the starting point of the time window.

[0025] The method proposed in this invention can realize online continuous monitoring of subsynchronous / supersynchronous oscillations through a sliding time window. The specific monitoring diagram is as follows: Figure 2 shown.

[0026] Step 2: Preserve the subsynchronous frequency band components in the signal based on the synchro-compressed generalized S-transform. Taking a 60Hz system as an example, the subsynchronous oscillation (SSO) frequency ranges from 5Hz to 55Hz. Therefore, a bandpass filter in this frequency range can be used for variables such as voltage and active / reactive power.

[0027] In step 2, the specific process is:

[0028] The generalized S transform (GST) is based on the ST by introducing a generalized parameter λ into the Gaussian window to change the window shape, allowing for flexible adjustment to meet the resolution requirements of practical problems. Taking the power system voltage signal xu(t) as an example, its generalized S transform can be expressed as:

[0029]

[0030] Where: f and t are frequency variables and time variables; τ is the time shift coefficient; j is the imaginary unit; λ is the scale factor of the window function transformation; is x u (t) is the time-frequency coefficient after GST transformation.

[0031] The Synchro-Squeezed Generalized S-Transform (SSGST) is based on the GST and compresses the energy in a certain range near the center frequency of each frequency band to the center frequency to suppress the low time-frequency resolution caused by energy diffusion and improve the decomposition of sub- / super-synchronous oscillation components. The SSGST of a signal can be expressed as:

[0032]

[0033] Where: η is the frequency factor after compression; δ is the Dirichlet function.

[0034] When oscillation is detected, the oscillation parameter identification procedure is executed and Xu is decomposed using SSGST. The obtained SSGST coefficient matrix is:

[0035]

[0036] Where: T u (τ n ,η q ) is the SSGST coefficient of u at the nth time coefficient and the qth frequency coefficient. In the SSGST coefficient matrix T u (τ,η), the power frequency signal component is directly filtered out in the time-frequency domain, and the SSGST time-frequency diagram of the self-synthesized analog signal is as follows: Figure 3 shown.

[0037] In order to accurately extract the SSGST time-frequency coefficients that characterize the sub / supersynchronous oscillation modes, a ridge extraction method is introduced to accurately track the instantaneous frequency trajectory of each oscillation mode and accurately extract the sub / supersynchronous oscillation components.

[0038] Step 3: For the preprocessed and filtered signals, calculate the instantaneous energy dissipation of each branch or each bus;

[0039] In step 3, the specific process is:

[0040] The reconstructed data obtained in step 2 after the synchronous compression generalized S transform is analyzed. The specific method is as follows:

[0041] In subsynchronous oscillation analysis, the focus is on energy consumption or generation, and the transient energy terms of the branches need to be removed from the energy flow. The article expresses each variable as a change relative to the steady-state value:

[0042]

[0043] When the forced power oscillation resonant steady-state system oscillates with constant amplitude, it is a component of constant amplitude oscillation, which contains a continuously changing component. The change in oscillation energy is dominated by dissipated energy, which is the quantity that needs to be focused on in the analysis.

[0044]

[0045] Here we use the engineering practical dissipated energy flow calculation method, which ignores the changes in reactive power transmitted in the network and node voltage. The calculation results are as follows Figure 4 shown.

[0046] Step 4: Compare the instantaneous energy dissipation of the branch and bus to determine the oscillation source.

[0047] In step 4, the specific process is:

[0048] According to the dissipated energy flow result obtained in step 3, the instantaneous energy dissipation of the branch and bus is compared. If the result is positive and the trend is rising, it is judged as an oscillation source. Otherwise, it is not considered to be an oscillation source.

[0049] It should be noted that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0050] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for tracing the source of dissipated energy flow in a power system, characterized in that: The method comprises: Step 1: Setting up a sensitive and computationally low-complexity subsynchronous oscillation online detection process to timely locate the subsynchronous oscillation in its early stages; Step 2: Preserve the subsynchronous frequency band components in the signal based on the synchro-compressed generalized S-transform. Taking a 60Hz system as an example, the subsynchronous oscillation (SSO) frequency ranges from 5Hz to 55Hz. Therefore, a bandpass filter in this frequency range can be used for variables such as voltage and active / reactive power. Step 3: For the preprocessed and filtered signals, calculate the instantaneous energy dissipation of each branch or each bus; Step 4: Compare the instantaneous energy dissipation of the branch and bus to determine the oscillation source. It can be seen from the technical solution provided by the present invention that the above method is simple to calculate, can accurately identify the oscillation source when forced oscillation occurs in the power system, and has great practical value.

2. The power system subsynchronous tracing method according to claim 1, characterized in that: In step 1, the subsynchronous oscillation online detection link with sensitive settings and low computational complexity timely locates the subsynchronous oscillation process in the early stage of oscillation as follows: In monitoring abnormal oscillations in the power system, an energy ratio function is set to determine the signal change by calculating the ratio of the effective values ​​of the first and second halves of the signal within a fixed time window, and this time window is moved point by point to continuously describe the sudden change of the signal.

3. The power system subsynchronous tracing method according to claim 1, characterized in that: In step 2, the process of retaining the subsynchronous frequency band components in the signal based on the synchronous compression generalized S transform is specifically as follows: The Synchro-Squeezed Generalized S-Transform (SSGST) is used. Based on the GST, it compresses the energy in a certain range near the center frequency of each frequency band to the center frequency to suppress the low time-frequency resolution caused by energy diffusion and improve the decomposition effect of sub- / super-synchronous oscillation components. The SSGST of the signal can be expressed as:

4. The power system subsynchronous tracing method according to claim 1, characterized in that: In step 3, for the pre-processed and filtered signal, the instantaneous energy dissipation of each branch or each bus is calculated as follows: The practical engineering dissipation energy flow calculation method is adopted, that is, the conservative term in the energy function is ignored, and the reactive power change in the network transmission is considered small, so it is ignored. The default node voltage is a constant value when calculating the source. At this time, the dissipation energy flow is 5. The power system subsynchronous tracing method according to claim 1, characterized in that: In step 4, the process of comparing the instantaneous energy dissipation of the branch and bus and determining the oscillation source is specifically as follows: According to the dissipated energy flow result obtained in step 3, the instantaneous energy dissipation of the branch and bus is compared. If the result is positive and the trend is rising, it is judged as an oscillation source. Otherwise, it is not considered to be an oscillation source.

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