Subsynchronous traceability method based on improved multiple synchronous compression transformation

Abstract

The invention discloses a subsynchronous traceability method for a power system, and the method comprises the steps: firstly expanding a phase angle of a voltage signal, eliminating error data in the signal, and interpolating missing data; secondly, retaining subsynchronous frequency band components in the signal based on improved multiple synchronous compression transformation; 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 security and stability, and in particular to a power system subsynchronous source tracing method. Background Art

[0002] Subsynchronous oscillations (SSOs) in traditional power systems are primarily caused by negative damping of heavy lines, high-top multi-excitation systems, induction generator effects, shaft torsional vibration, and transient torque amplification. With the integration of high proportions of renewable energy and power electronics in modern power systems, low-inertia, stochastically processed renewable energy units interact with power generation equipment, transmission networks, and power loads, leading to a variety of new subsynchronous oscillation problems. These oscillations typically occur in the frequency range of 5-45Hz / 5-55Hz at a fundamental frequency of 50Hz / 60Hz. Their generation mechanism is complex, their impact is widespread, and they threaten the safe and stable operation of the power system. Therefore, analyzing and identifying SSO sources in the network is crucial for developing timely and effective mitigation strategies.

[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. As wide-area measurement systems mature, synchronized phasor data acquired from these systems can be used to identify SSO sources in a timely manner. Current data-based methods include modal estimation machine learning methods and subsynchronous / supersynchronous power. However, the research on these methods is not yet complete. For example, the applicability of SSO under different mechanisms has not been studied. Compared with many other methods, the dissipated energy flow (DEF) method shows excellent performance and physical interpretation, which provides a powerful tool for analyzing SSO and locating oscillation sources. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for tracing the source of subsynchronous oscillations in a power system. The method has simple calculation and high accuracy, can accurately identify the oscillation source when forced oscillations occur 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 subsynchronous tracing method for dissipative energy flow based on improved multiple synchronous compression transformation, the method comprising:

[0008] Step 1: Expand the phase angle of the voltage signal, eliminate erroneous data in the signal, and interpolate missing data;

[0009] Step 2: Preserve the subsynchronous frequency band components in the signal based on the improved multi-synchronous compression 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 A comparison of the energy concentration of the iterative process of the general multiple synchronous compression transformation and the improved multiple synchronous compression transformation in the embodiment of the present invention;

[0016] Figure 3 A comparison of the advantages of the general multiple synchronous compression transformation and the improved multiple synchronous compression transformation in various aspects of the embodiment of the present invention is provided;

[0017] Figure 4This is the final result presentation of the dissipative energy flow tracing based on the improved multiple synchronous compression transformation 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: Expand the phase angle of the voltage signal, eliminate erroneous data in the signal, and interpolate missing data;

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

[0022] Use the power quality online monitoring device to obtain the actual grid operation voltage data, or use PSCAD simulation software to obtain the voltage data of the power system under a certain operating condition, and then organize it and import it into MATLAB.

[0023] When using measured data such as PMU data, if the voltage phase angle data is not manipulated to extract the dynamic component, the phase angle will jump from -180° to +180° or +180° to -180°. Therefore, the unwarp function in MATLAB is used to derotate the voltage phase angle.

[0024] The missing data or abnormal data values ​​that may appear in the PMU data are processed by setting NaN values.

[0025] Step 2: Preserve the subsynchronous frequency band components in the signal based on the improved multi-synchronous compression 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.

[0026] In step 2, the specific process is:

[0027] Synchro-squeezed transform (SST) uses a frequency redistribution operator to group all coefficients with the same instantaneous frequency, expressed as

[0028]

[0029] Where: η is the frequency factor after compression; δ is the Dirac function.

[0030] The increase of non-stationarity of strong time-varying signals makes the SST instantaneous frequency estimation The actual instantaneous frequency The error between them will become larger, and eventually it will be impossible to lock the subsynchronous oscillation frequency. Therefore, the Multiple Synchronous Squeezing Transform (MSST) is proposed. We perform several SST operations on Ts(τ,η) for iteration. The energy of the TF result is gradually concentrated, which can be infinitely close to the actual instantaneous frequency.

[0031] IMSST algorithm First perform two rounding operations to get

[0032]

[0033] like Figure 2 、 Figure 3 , which is a comparison of the energy concentration and advantages and disadvantages of the iterative process of the general multi-synchronous compression transform and the improved multi-synchronous compression transform.

[0034] Step 3: For the preprocessed and filtered signals, calculate the instantaneous energy dissipation of each branch or each bus;

[0035] In step 3, the specific process is:

[0036] The reconstructed data obtained in step 2 based on the improved multiple synchronous compression transformation is analyzed by the following method:

[0037] In subsynchronous oscillation analysis, the focus is on energy consumption or generation, and the transient energy term of the branch needs to be removed from the energy flow. The article expresses each variable as the change relative to the steady-state value, and the expression for energy is:

[0038] W ij =∫(P ij,s +ΔP ij )d(θ i，s +Δθ i )+

[0039] ∫(Q ij，s +ΔQ ij )d(lnU| i，s +ΔlnU i )

[0040] =∫(P ij，s dΔθ i +Q ij，s d(ΔlnU i ))+

[0041] ∫(ΔPij dΔθ i +AQ ij d(ΔlnU i ))

[0042] Where: s represents the steady-state value of the corresponding variable.

[0043] remember:

[0044]

[0045] 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.

[0046]

[0047] 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.

[0048] Step 4: Compare the instantaneous energy dissipation of the branch and bus to determine the oscillation source.

[0049] In step 4, the specific process is:

[0050] 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.

[0051] 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.

[0052] 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 subsynchronous tracing of power systems, characterized in that: The method comprises: Step 1: Expand the phase angle of the voltage signal, eliminate erroneous data in the signal, and interpolate missing data; Step 2: Preserve the subsynchronous frequency band components in the signal based on the improved multi-synchronous compression 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 process of expanding the phase angle of the voltage signal, eliminating erroneous data in the signal, and interpolating missing data is specifically as follows: Use the power quality online monitoring device to obtain the actual grid operation voltage data, or use PSCAD simulation software to obtain the voltage data of the power system under a certain operating condition, and then organize it and import it into MATLAB. When using measured data such as PMU data, if the voltage phase angle data is not manipulated to extract the dynamic component, the phase angle will jump from -180° to +180° or +180° to -180°. Therefore, the unwarp function in MATLAB is used to derotate the voltage phase angle.

3. The power system subsynchronous tracing method according to claim 1, characterized in that: In step 2, the process of retaining the sub-synchronous frequency band components in the signal based on the improved multiple synchronous compression transformation is specifically as follows: IMSST algorithm We have optimized it. First calculate Then perform the SST operation. Therefore, although multiple SST operations are executed, the actual computational burden level is equivalent to that of a single SST operation. Compared with the MSST algorithm, the IMSST algorithm can effectively solve the time-frequency energy ambiguity problem caused by non-reassigned points.

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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