Energy storage method and system for damping low frequency oscillation based on damping controller and resonance controller

Abstract

The application provides a method and system for suppressing low-frequency oscillation based on a damping controller and a resonance controller, comprising: monitoring low-frequency power oscillation based on a WAMS system; extracting a dominant mode of the oscillation based on an EMD algorithm; performing envelope fitting analysis on the extracted oscillation waveform, and dividing the low-frequency oscillation into three categories, namely, negative damping oscillation, forced oscillation and generalized forced oscillation; if it is negative damping oscillation, switching the energy storage to an additional damping control mode; if it is forced oscillation, switching the energy storage to a power oscillation resonance control mode, judging the propagation direction of the oscillation relative to the energy storage, and modifying the input signal of the resonance controller accordingly; if it is generalized forced oscillation, first modifying the input signal of the resonance controller according to the propagation direction of the oscillation, and then iteratively updating the resonance coefficient to make the oscillation amplitude less than a threshold. The application can realize the monitoring, identification and suppression of multiple types of low-frequency oscillation, suppress the propagation of low-frequency oscillation generated by a disturbance source to other areas, and reduce the number of energy storage devices installed.

Description

Technical Field

[0001] This invention relates to the field of smart grid technology, and in particular to the identification and suppression technology of low-frequency oscillations in power grids. Specifically, it relates to a method and system for suppressing low-frequency oscillations in energy storage based on a damping controller and a resonant controller. Background Technology

[0002] Under the national grid interconnection strategy, high-gain excitation regulators are being used to improve generator voltage accuracy and system transient stability during the interconnection process between different regions. This has led to increasingly prominent dynamic stability issues, with low-frequency oscillations frequently occurring. Although power system static stabilizers (PSS) are commonly installed to suppress low-frequency oscillations, their effectiveness in suppressing oscillation propagation between regions is not ideal. Furthermore, unlike negatively damped low-frequency oscillation modes, forced oscillation modes are difficult to completely suppress by simply increasing the power system damping.

[0003] Currently, the common approach to dealing with forced oscillations is to cut off the source of the disturbance. However, the technology for quickly locating the disturbance source is not yet mature, and cutting off the generator may also lead to problems with the safety and stability of the power system. Summary of the Invention

[0004] Given that existing low-frequency oscillation suppression methods are difficult to suppress for various types of low-frequency oscillations separately, and that forced oscillation and generalized forced oscillation suppression are not effective, the purpose of this invention is to provide an energy storage method for suppressing low-frequency oscillations based on a damping controller and a resonant controller, which can automatically identify the type of low-frequency oscillation and take corresponding suppression measures.

[0005] According to a first aspect of the present invention, a method for suppressing low-frequency oscillations through energy storage based on a damping controller and a resonant controller is proposed, comprising:

[0006] Step 1: Based on the WAMS system, monitor and record the low-frequency power oscillations in the system.

[0007] Step 2: Extract the dominant oscillation mode based on the EMD algorithm;

[0008] Step 3: Perform envelope fitting analysis on the extracted oscillation waveforms to identify and classify low-frequency oscillations into three categories: negative damped oscillations, forced oscillations, and generalized forced oscillations.

[0009] Step 4: Based on the identification type of low-frequency oscillations, apply different oscillation suppression measures:

[0010] If it is a negative damped oscillation, then switch the energy storage to the additional damping control mode;

[0011] If it is forced oscillation, then switch the energy storage to power oscillation resonance control mode, determine the propagation direction of the oscillation relative to the energy storage, and modify the input signal of the resonance controller accordingly.

[0012] If it is a generalized forced oscillation, the input signal of the resonant controller is first modified according to the direction of oscillation propagation, and then the resonant coefficient is iteratively updated to make the oscillation amplitude less than the threshold.

[0013] As can be seen from the above technical solutions of the present invention, the significant advantages of the present invention are:

[0014] 1. Different control methods can be selected to suppress different types of low-frequency oscillations, which improves the shortcomings of existing damping controllers that cannot completely suppress forced oscillations and generalized forced oscillations. It realizes fully automatic monitoring and suppression of negative damped low-frequency oscillations, forced oscillations, and generalized forced oscillations.

[0015] 2. Depending on the location of the disturbance source, the system can monitor the propagation direction of forced oscillation and generalized forced oscillation at the node where the energy storage is located, and automatically modify the control direction according to the propagation direction, thereby effectively suppressing the propagation of oscillation to other areas of the power system. Attached Figure Description

[0016] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings.

[0017] Figure 1 This is a flowchart illustrating a method for suppressing low-frequency oscillations based on a damping controller and a resonant controller according to certain embodiments of the present invention.

[0018] Figure 2 This is a diagram showing the effect of the present invention on suppressing negatively damped low-frequency oscillations.

[0019] Figure 3 This is a diagram illustrating the effect of the present invention in suppressing periodic forced oscillations.

[0020] Figure 4 This is a diagram illustrating the suppression effect of the present invention on generalized forced oscillations under random perturbations. Detailed Implementation

[0021] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0022] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, which illustrate numerous illustrative embodiments. The embodiments of this disclosure are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed herein are not limited to any particular implementation. Furthermore, some aspects of the invention disclosed may be used alone or in any suitable combination with other aspects of the invention disclosed.

[0023] Combination Figure 1 The flowchart shown illustrates an exemplary embodiment of the present invention, a method for suppressing low-frequency oscillations through energy storage based on a damping controller and a resonant controller, comprising the following processes:

[0024] Step 1: Based on the WAMS system, monitor and record the low-frequency power oscillations in the system.

[0025] Step 2: Extract the dominant oscillation mode based on the EMD algorithm;

[0026] Step 3: Perform envelope fitting analysis on the extracted oscillation waveforms to identify and classify low-frequency oscillations into three categories: negative damped oscillations, forced oscillations, and generalized forced oscillations.

[0027] Step 4: Based on the identification type of low-frequency oscillations, apply different oscillation suppression measures:

[0028] If it is a negative damped oscillation, then switch the energy storage to the additional damping control mode;

[0029] If it is forced oscillation, then switch the energy storage to power oscillation resonance control mode, determine the propagation direction of the oscillation relative to the energy storage, and modify the input signal of the resonance controller accordingly.

[0030] If it is a generalized forced oscillation, the input signal of the resonant controller is first modified according to the direction of oscillation propagation, and then the resonant coefficient is iteratively updated to make the oscillation amplitude less than the threshold.

[0031] As a dynamic measurement system for the power grid, the WAMS system uses distributed phasor measurement units (PMUs) as the front-end acquisition units. These PMUs collect current and voltage data of each phase of each power grid line at high frequency. Through calculation, information such as power, phase, and power angle at the monitoring location can be obtained and transmitted to the master station in real time. This enables the monitoring center system to obtain real-time monitoring of the power grid's operating status. The data is stored in the monitoring and dispatch center and can be displayed on the monitoring screen. Power grid dispatchers can monitor the power grid's operating dynamics in real time and intervene accordingly.

[0032] In an embodiment of the present invention, the low-frequency power oscillation data of the power grid is obtained from the WAMS system interface and recorded for subsequent analysis and identification.

[0033] In an embodiment of the present invention, based on the EMD (Empirical Mode Decomposition) algorithm, signal analysis is performed on the power low-frequency oscillation data to identify the main oscillation modes in the oscillation.

[0034] As an alternative example, low-frequency oscillation data contains different oscillation variations across different frequency bands. Analysis using the EMD algorithm identifies patterns of steady-state oscillation variations, determines their Intrinsic Motion Flow (IMF), and reflects the dominant mode of oscillation variation.

[0035] As an optional embodiment, in step 3 above, the following condition is used as the criterion for determining the type of low-frequency oscillation:

[0036]

[0037]

[0038]

[0039] In the formula, formula (1) represents the envelope of negative damped oscillation; formulas (2) and (3) represent the envelopes of resonance and beat frequency oscillation, which together constitute the envelope of forced oscillation.

[0040] Where ξ represents the system damping ratio; δ represents the generator angle of attack.

[0041] Where A0, B, and B1 all represent constants related to the initial state.

[0042] for Where D represents the generator damping coefficient, T J ω represents the generator's inertial time constant, and ω0 represents the system's reference angular frequency.

[0043] Combination Figure 1 As shown in the process, we fit the envelope of the oscillation waveform as the dominant mode extracted based on the EMD algorithm with the above criteria A1, A2, and A3 respectively. The one with a fitting error less than the preset threshold represents the type of oscillation, that is, negative damped oscillation or forced oscillation; if the fitting error is greater than the preset threshold, it is a generalized forced oscillation.

[0044] As an optional implementation, in step 4 above, the determination of the forced oscillation and the propagation direction of the generalized forced oscillation is achieved by calculating whether the value of the energy flow direction factor is within a threshold, the expression of which is:

[0045]

[0046] In the formula, △P mij , △ωmi These represent the branch power and frequency variation amplitude, respectively; represents the initial phase of the branch power and frequency, respectively; b represents the energy flow direction factor.

[0047] When the energy flow direction factor is less than 0, it indicates that potential energy flows out of the node; when the energy flow direction factor is greater than 0, it indicates that potential energy flows into the node.

[0048] In this step, based on the identified type of low-frequency oscillation, different oscillation suppression measures are applied:

[0049] (1) If it is a negative damped oscillation, switch the energy storage to the additional damping control mode;

[0050] (2) If it is forced oscillation, switch the energy storage to power oscillation resonance control mode, determine the direction of oscillation relative to energy storage and modify the input signal of the resonance controller accordingly.

[0051] (3) If it is a generalized forced oscillation, first modify the input signal of the resonance controller according to the direction of oscillation propagation, and then iteratively update the resonance coefficient to make the oscillation amplitude less than the threshold.

[0052] As an optional example, in step 4 above, the additional damping control mode is set to be implemented through power oscillation damping (POD), and its control process includes the following steps:

[0053] 1) The difference between the power transmitted by the power grid lines (oscillation frequency) and the power before oscillation is calculated and then amplified to obtain the power oscillation component; the power transmitted by the power grid lines can be calculated using the existing Prony analysis algorithm to obtain the oscillation frequency;

[0054] 2) The obtained power oscillation component is filtered out by a low-pass filter to remove the stable component and retain the oscillation component;

[0055] 3) Perform phase compensation on the filtered oscillation components, with the phase of each compensation element being less than 60 degrees.

[0056] Therefore, the filtered oscillation component is phase-compensated according to the principle that the phase of a single compensation element is less than 60 degrees, so as to obtain the active power reference value for energy storage control, thereby completing the control of energy storage output.

[0057] As an optional embodiment, if forced oscillation is used, the energy storage is switched to power oscillation resonance control mode, specifically through the following process:

[0058] 1) Determine the direction of oscillation propagation based on the energy flow direction factor of the energy storage grid connection point. If the direction is positive, the resonant control proportional coefficient is set to a positive number; if the direction is negative, the resonant control proportional coefficient is set to a negative number.

[0059] 2) The difference between the power transmission power (oscillation frequency) of the power grid and the power before oscillation is calculated. The difference is adjusted by the resonant controller to obtain the active power reference value for energy storage control, thereby completing the control of energy storage output.

[0060] As an optional example, if it is a generalized forced oscillation, the input signal of the resonant controller is first modified according to the direction of oscillation propagation, and then the resonant coefficient is iteratively updated to make the oscillation amplitude less than the threshold.

[0061] In the specific adjustment and control process, power oscillation resonance control is performed through the following process:

[0062] 1) Determine the direction of oscillation propagation based on the energy flow direction factor of the energy storage grid connection point. If the direction is positive, the resonant control proportional coefficient is set to a positive number; if the direction is negative, the resonant control proportional coefficient is set to a negative number.

[0063] 2) The difference between the power transmitted by the power grid line and the power before oscillation is calculated, and the difference is used to obtain the active power reference value for energy storage control through the resonant controller.

[0064] 3) Track the power of the line that needs to be suppressed. If the oscillation amplitude is greater than the preset threshold, increase the resonance coefficient of the resonance controller and update the active power reference value of the energy storage control until the oscillation amplitude is lower than the threshold, thereby completing the control of the energy storage output.

[0065] The aforementioned resonant controller is expressed as follows:

[0066]

[0067] In the formula, ω c K R These represent the resonant center frequency and the resonant coefficient, respectively.

[0068] The following uses a typical four-generator, two-zone system as an example to describe in more detail the implementation and / or effects of certain embodiments of the present invention. The four generators each have a rated capacity of 900MW, a rated voltage of 20kV, a rated frequency of 60Hz, and the inherent oscillation frequency of the system tie line is 0.64Hz. Energy storage is connected to node 7.

[0069] Online Data Monitoring

[0070] Referring to the attached diagram, in step 1 above, at 1s, an excitation voltage step disturbance with an amplitude of 0.05pu lasting for 0.2s, a mechanical power periodic disturbance with an amplitude of 0.01pu and a frequency of 0.64Hz lasting for 19s, and a mechanical power random disturbance with an amplitude of 0.01pu and a frequency band of 0.5-1.5Hz lasting for 99s are applied to generator 1. Based on the WAMS system, the power oscillation signal occurring at the node where the energy storage is located is monitored and collected.

[0071] [Fitting and Classification of Oscillation Data]

[0072] Combined with appendix Figure 1 When low-frequency power oscillations are detected in the system, in steps 2 and 3 above, the dominant mode waveform of the oscillation is obtained through the EMD algorithm, and then fitted with the envelope expressions for negative damped oscillations and forced oscillations, respectively. The specific expressions are as follows:

[0073]

[0074]

[0075]

[0076] Equation (1) represents the envelope of negative damped oscillation; Equations (2) and (3) represent the envelope of forced oscillation.

[0077] If the fitting result error is less than the preset threshold, for example, the threshold value is 5%, then the oscillation is determined to be the corresponding oscillation type; if the fitting result error exceeds the threshold, then the oscillation is determined to be a generalized forced oscillation.

[0078] [Oscillation Direction Determination and Suppression Control Selection]

[0079] Combined with appendix Figure 1 In step 4 above, when the oscillation type is determined to be negatively damped low-frequency oscillation, Prony calculates the oscillation frequency to be 0.634Hz and the damping to be 0.007. At this time, the energy storage control mode switches to power oscillation damping control, with the input being the difference between the collected line power value and the line power value before oscillation, and the output being a reference value for the active power of the energy storage.

[0080] After the energy storage system was put into operation, the oscillation damping increased to 5.781, and the suppression effect is shown in the attached figure. Figure 2 As shown, the low-frequency oscillations of the system are well suppressed.

[0081] When the oscillation type is determined to be forced oscillation, the propagation direction of the oscillation is first determined based on the energy flow direction factor, the expression of which is as follows:

[0082]

[0083] The calculated energy flow direction factor is negative, indicating that the oscillation propagates from region one to region two, and the control direction is positive at this time.

[0084] Prony's calculations show the oscillation frequency to be 0.64Hz. Therefore, the center frequency of the resonant controller is set to 0.64Hz, and the resonant coefficient is set to 80. The expression for the resonant controller is as follows:

[0085]

[0086] The forced oscillation suppression effect before and after energy storage deployment is shown in the attached figure. Figure 3 As shown, the low-frequency oscillations of the system are well suppressed.

[0087] When the oscillation type is determined to be a generalized forced oscillation, the determination of the oscillation direction and the selection of the control direction are the same as the methods for forced oscillation described above, and will not be repeated here.

[0088] At this point, the center frequency of the resonant controller is set to the average value of the oscillation band, 1Hz, and the resonant coefficient is continuously increased until the threshold of 0.005pu oscillation amplitude is reached, at which point the resonant coefficient is 1000.

[0089] The effects of suppressing generalized forced oscillations before and after the energy storage system is shown in the attached figure. Figure 4 As shown, the low-frequency oscillations of the system are well suppressed.

[0090] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for suppressing low-frequency oscillations through energy storage based on a damping controller and a resonant controller, characterized in that, include: Step 1: Based on the WAMS system, monitor and record the low-frequency power oscillations in the system. Step 2: Extract the dominant oscillation mode based on the EMD algorithm; Step 3: Perform envelope fitting analysis on the extracted oscillation waveforms to identify and classify low-frequency oscillations into three categories: negative damped oscillations, forced oscillations, and generalized forced oscillations. Step 4: Based on the identification type of low-frequency oscillations, apply different oscillation suppression measures: (1) If it is a negative damped oscillation, then switch the energy storage to the additional damping control mode; (2) If it is forced oscillation, switch the energy storage to power oscillation resonance control mode, determine the direction of oscillation relative to energy storage and modify the input signal of the resonance controller accordingly; (3) If it is a generalized forced oscillation, first modify the input signal of the resonance controller according to the direction of oscillation propagation, and then iteratively update the resonance coefficient to make the oscillation amplitude less than the threshold. In step 3 above, the following conditions are used as criteria for determining the type of low-frequency oscillation: ; ; ; In the formula, A 1. A 2. A 3 represents the envelope of negative damped oscillation, resonance, and beat frequency oscillation, respectively; ξ Indicates the system damping ratio; δ Indicates the generator power angle; Specifically, the envelope of the oscillation waveform extracted based on the EMD algorithm as the dominant mode is compared with the above criteria. A 1. A 2. A 3. Perform fitting. The one with a fitting error less than the threshold represents the type of oscillation. If the fitting errors of all three are greater than the threshold, it is a generalized forced oscillation. In step 4 above, the determination of the propagation direction of forced oscillation and generalized forced oscillation is achieved by calculating whether the value of the energy flow direction factor is within a threshold, and its expression is: ; In the formula, Δ P mij Δ ω mi These represent the branch power and frequency variation amplitude, respectively; φ 1 φ 2 represents the initial phase of the branch power and frequency, respectively; Wherein, when the energy flow direction factor is less than 0, it indicates that potential energy flows out of the node; when the energy flow direction factor is greater than 0, it indicates that potential energy flows into the node. In step 4 above, the additional damping control mode is set to be implemented through power oscillation damping, and its control process includes the following steps: 1) The difference between the line transmission power and the power before oscillation is calculated and then amplified to obtain the power oscillation component; 2) The obtained power oscillation component is filtered out by a low-pass filter to remove the stable component and retain the oscillation component; 3) Perform phase compensation on the filtered oscillation components, with the phase of each compensation element being less than 60 degrees; Specifically, for generalized forced oscillation, power oscillation resonance control is achieved through the following process: 1) Calculate the energy flow direction factor at the energy storage grid connection point to determine the direction of oscillation propagation. If the direction is positive, the resonant control proportional coefficient is set to a positive number; if the direction is negative, the resonant control proportional coefficient is set to a negative number. 2) The difference between the power transmitted by the power grid line and the power before oscillation is calculated, and the difference is used to obtain the active power reference value for energy storage control through the resonant controller. 3) Track the power of the line that needs to be suppressed. If the oscillation amplitude is greater than the preset threshold, increase the resonance coefficient of the resonance controller and update the active power reference value of the energy storage control until the oscillation amplitude is lower than the threshold, thereby completing the control of the energy storage output.

2. The method for suppressing low-frequency oscillations based on a damping controller and a resonant controller according to claim 1, characterized in that, In step 4 above, the power oscillation resonance control mode is set to be implemented through a resonance controller, and its expression is: ; In the formula, ω c 、K R These represent the resonant center frequency and the resonant coefficient, respectively.

3. A computer-readable medium for storing software, characterized in that: The software includes instructions executable by one or more computers, which, upon execution, cause the one or more computers to perform operations including the flow of the method as described in claim 1.

4. A computer system, characterized in that, include: One or more processors; A memory that stores operable instructions that, when executed, cause the one or more computers to perform operations, including the flow of the method as described in claim 1.

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