A new power grid stability assessment method and device based on damping level

Abstract

The present invention discloses a novel power grid stability assessment method and device based on damping levels. By applying an external excitation to the novel power grid, the voltage at the common coupling point before and after the excitation is applied is obtained, and the voltage response curve is extracted. The amplitude, oscillation frequency, attenuation factor, and initial phase of multiple oscillation modes in the response curve are then identified using the Prony algorithm. The damping ratio of each mode is calculated based on the identified parameters, and the minimum damping ratio is selected to represent the damping level of the novel power grid, thereby assessing the stability of the novel power grid. The present invention does not require the specific structure and parameters of the novel power grid. By applying an external excitation to obtain the voltage response of the novel power grid, the Prony algorithm is used to identify the parameters of the response curve, and the damping level of the novel power grid is calculated to assess its stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of new power grids containing new energy, and in particular relates to a method for measuring the damping level and stability of new power grids. Background Art

[0002] Traditional power system stability analysis typically begins with generator theory, analyzing power angle stability, frequency stability, and voltage stability to reflect power system stability. However, new power grids incorporating renewable energy are power generation and distribution systems comprised of distributed power sources, distributed energy storage, energy conversion devices, and loads. The power electronics interfaces of distributed power sources feature diverse control strategies and complex dynamic characteristics, significantly different from traditional power systems. This diversity of control methods and the high penetration of power electronic converters will significantly impact microgrid stability. Consequently, traditional power system stability analysis methods struggle to effectively adapt to these new power grids.

[0003] Future power grids, primarily based on renewable energy, will incorporate a significant amount of renewable energy and power electronic converters. These systems will have low inertia and are susceptible to oscillations due to disturbances. Therefore, studying the stability of these new grids is essential. Traditional methods for analyzing the stability of power grid systems include the eigenvalue method, frequency domain analysis, and singular perturbation method. Eigenvalue analysis requires solving eigenvalues, and its accuracy depends on the accuracy of the models of all system components, making it computationally complex. Frequency domain analysis results are highly dependent on the interface separating the load and source subsystems and cannot be directly applied to load-side inverters, limiting their applicability. The singular perturbation method ignores smaller parameters, thus failing to ensure accurate stability analysis. These methods all require a large number of parameters and circuit topologies to model the system, resulting in tedious and computationally intensive analysis. In new power grids, input sources and load switching are present, and the structure and parameters of the actual system dynamically change. Traditional stability analysis methods are unlikely to meet the stability analysis requirements of future new power grids. Existing grid stability assessment methods mostly use eigenvalue analysis and impedance analysis. These analysis methods require accurate modeling of the grid, the processing process is relatively complex, and the established models deviate from the actual operating conditions. Summary of the Invention

[0004] In response to the shortcomings of the above-mentioned new power grid stability analysis method, the present invention proposes a new power grid stability assessment method and device based on damping level, so as to obtain the system's damping level and stability information in real time when the structural parameters of the new power grid are unknown, so as to prevent system instability and ensure the stable operation of the new power grid.

[0005] In order to achieve the above-mentioned object, the present invention adopts the following technical solutions:

[0006] The novel power grid stability assessment method and device based on damping level of the present invention are characterized in that the method and device include the following steps:

[0007] Step S1: Inject pulse current into the PCC end of the normally operating new power grid

[0008] Step S2: Real-time detection of the pulse current injected into the PCC end of the new power grid The voltage before and after; wherein, the pulse current is injected The voltage after the pulse current is: the steady-state voltage at the PCC end and the The response voltage caused by injecting the pulse current The voltage before is only the steady-state voltage at the PCC end; The voltage response curve was extracted by subtracting the voltage before and after injection.

[0009] Step S3: selecting the data of the voltage response curve as sample data, and performing parameter identification on the sample data using the Prony algorithm to obtain the amplitude, attenuation factor, initial phase angle and oscillation angular frequency corresponding to the voltage response in each oscillation mode, thereby obtaining the time domain expression of the voltage response.

[0010] Step S4: Calculate the damping ratio of the new power grid in the i-th oscillation mode according to the time domain expression, and select the minimum damping ξ in all oscillation modes. min The ratio is taken as the damping level of the new power grid, and the stability of the new power grid is evaluated according to the damping level.

[0011] The novel power grid stability assessment method and device based on damping level described in the present invention is also characterized in that the pulse current The injection process is as follows:

[0012] According to the pulse current I s The amplitude of the current pulses I with different amplitudes is injected into the new power grid in sequence. s , until the voltage fluctuation generated by the new power grid exceeds Δ% of the fundamental voltage amplitude, and record the current pulse when it exceeds Where Δ is the threshold;

[0013] In step S3, the time domain expression u is obtained using formula (1):

[0014]

[0015] In formula (1), A i represents the amplitude of the i-th oscillation mode, δ i represents the attenuation coefficient of the i-th oscillation mode, ω i represents the oscillation angular frequency of the i-th oscillation mode, θ irepresents the initial phase angle of the i-th oscillation mode, and K is the number of oscillation modes in the voltage response.

[0016] In step S4, the damping ratio ξ under the i-th oscillation mode is calculated using formula (2): i :

[0017]

[0018] In step S4, evaluating the stability of the new power grid according to the damping level includes: if ξ min If it is greater than the set threshold, it means that the new power grid is stable; otherwise, it means that the new power grid is unstable.

[0019] The novel power grid stability assessment device based on damping level of the present invention is characterized in that it includes:

[0020] Pulse generator for injecting pulse current at the PCC end of the new power grid

[0021] Response extractor, used to detect in real time the pulse current injected into the PCC end of the new power grid The voltage before and after; wherein, the pulse current is injected The voltage after the pulse current is: the steady-state voltage at the PCC end and the The response voltage caused by injecting the pulse current The voltage before is only the steady-state voltage at the PCC end; The voltage response curve was extracted by subtracting the voltage before and after injection.

[0022] The parameter identification module is used to select the data of the voltage response curve as sample data and perform parameter identification on the sample data to obtain the amplitude, attenuation factor, initial phase angle and oscillation angular frequency corresponding to the voltage response in each oscillation mode, thereby deriving the time domain expression of the voltage response.

[0023] The stability evaluation module is used to calculate the damping ratio of the new power grid in the i-th oscillation mode according to the time domain expression and select the minimum damping ξ in all oscillation modes. min The ratio is used as the damping level of the new power grid, so as to evaluate the stability of the new power grid according to the damping level.

[0024] The novel power grid stability assessment device based on damping level described in the present invention is also characterized in that it includes: the pulse current in the pulse generator The injection process is as follows:

[0025] According to the pulse current I s The amplitude of the current pulses I with different amplitudes is injected into the new power grid in sequence.s , until the voltage fluctuation generated by the new power grid exceeds Δ% of the fundamental voltage amplitude, and record the current pulse when it exceeds Where Δ is the threshold.

[0026] The parameter identification module uses formula (1) to obtain the time domain expression u:

[0027]

[0028] In formula (1), A i represents the amplitude of the i-th oscillation mode, δ i represents the attenuation coefficient of the i-th oscillation mode, ω i represents the oscillation angular frequency of the i-th oscillation mode, θ i represents the initial phase angle of the i-th oscillation mode, and K is the number of oscillation modes in the voltage response.

[0029] The stability evaluation module calculates the damping ratio ξ under the i-th oscillation mode using formula (2) i , if min If it is greater than the set threshold, it means that the new power grid is stable; otherwise, it means that the new power grid is unstable;

[0030]

[0031] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0032] 1. In step S1 of the present invention, the stability of the system is evaluated by injecting current pulses to obtain the actual response, thereby improving the accuracy of the stability analysis results.

[0033] 2. Steps S3 and S4 of the present invention use an algorithm to identify the damping level of the new power grid when it is online. This is an online evaluation method that overcomes the shortcomings of offline analysis of eigenvalue analysis and impedance analysis. The method is real-time and intuitive.

[0034] 3. During the implementation of the method of the present invention, there is no need to obtain the topology and detailed parameters of the new power grid, nor is there any need for accurate mathematical modeling, which greatly reduces the tedious calculation process and is more concise than the eigenvalue analysis method and the impedance analysis method. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of pulse current injection in a new type of power grid in the prior art.

[0036] Figure 2 Flowchart of the method of the present invention. DETAILED DESCRIPTION

[0037] In conjunction with the accompanying drawings, a new method for evaluating power grid stability based on damping level is presented. Taking a new power grid containing renewable energy as an example, the method injects pulse current, measures and extracts the voltage response curve, uses the Prony algorithm to identify the parameters of the response curve, and calculates the damping level and evaluates the stability of the new power grid based on the identified parameters. Specifically, the method includes:

[0038] Step S1: Inject a programmable current pulse I from outside the new power grid s , according to the pulse current I s The amplitude of the current pulses I with different amplitudes is injected into the new power grid in sequence. s , the position of pulse current injection is as follows Figure 1 As shown; and it is required that the voltage fluctuation caused by the injected pulse current does not exceed 5% of the fundamental amplitude, and the current pulse at this time is recorded Thus, the pulse current is injected into the PCC end of the new power grid.

[0039] Step S2: Real-time detection of the pulse current injected into the PCC end of the new power grid The voltage before and after; the process of extracting the voltage response is as follows Figure 2 As shown. Wherein, the pulse current injected The voltage u1 after the pulse current is composed of the steady-state voltage u2 at the PCC end and the The response voltage u caused by injecting the pulse current The voltage before is the steady-state voltage u2 at the PCC end. The voltage response curve u is extracted by subtracting the voltage before and after injection. The voltage response curve u can be obtained according to formula (1):

[0040]

[0041] Step S3: Perform parameter identification processing on the response curve u separated in step S2. Parameter identification is performed on the sample data based on the Prony algorithm. The response of the new power grid can be regarded as a superposition of K damped oscillations: The Prony algorithm uses a linear combination of p complex exponential functions with arbitrary amplitudes, phases, oscillation frequencies, and attenuation factors to fit equally spaced sampled data u(0), u(1), ..., u(N-1). Its goal is to identify the amplitudes, phases, oscillation frequencies, and attenuation factors corresponding to the p complex exponential functions. The estimated value of the sampled data u(n) is expressed as:

[0042]

[0043] In formula (2): In the formula, A i ,θi , δ i 、ω i Respectively represent the amplitude, initial phase angle, attenuation factor and oscillation angular frequency corresponding to the i-th function. p is the model order. If the model order p is small, the mode in the data may be lost; if the model order p is large, a large number of invalid modes will be generated. It is necessary to select an appropriate model order to increase the speed of data processing. Δt is the sampling time interval. The core of the Prony algorithm is to select appropriate sampling data to solve A i ,θ i , δ i 、ω i The numerical value of .

[0044] The steps for Prony-based parameter recognition are as follows:

[0045] Step a1: First, use the sample data to construct the expansion matrix R, where (i,j=0,1,...,p r )

[0046]

[0047] In formula (3): p r >>p,p r is the order of the expansion matrix R.

[0048] Step a2: Use the singular value decomposition-least squares algorithm (SVD-TLS) to determine the effective rank of the extended matrix R as p, and construct the extended matrix R under the effective rank p , establish the following linear equation and solve the coefficients α1, α2, ..., α p :

[0049] R p [α1 α2 ... α p ] T =[ε p 0 ... 0] T (4)

[0050] In formula (4): p is the minimum error energy.

[0051] Step a3: Based on the coefficients solved in b2, construct the characteristic equation shown below:

[0052] 1+α1z -1 +α2z -2 +…+α p z -p =0 (5)

[0053] The root z of the characteristic equation i It is called the Prony point.

[0054] Step a4: Establish solution b according to formula (6) i The linear equation is:

[0055]

[0056] Step a5: Construct a matrix through the above steps to solve and obtain b i 、z i The parameters of each oscillation mode are calculated according to the following formula:

[0057]

[0058] In formula (7), Im is the imaginary part of the complex number; Re is the real part of the complex number. Based on the oscillation parameters identified by the Prony algorithm, the expression of the response voltage u in step S2 can be obtained. The approximate expression of u is:

[0059]

[0060] In formula (8), A i Indicates the amplitude of the i-th oscillation mode, δ i represents the attenuation coefficient for identifying the i-th oscillation mode, ω i Indicates the oscillation angular frequency of the i-th oscillation mode, θ i represents the initial phase angle for identifying the i-th oscillation mode, and p is the number of oscillation modes in the identified voltage response.

[0061] Step S4: The damping level of a system is an inherent characteristic of the system, which is related to the structure and parameters of the system and has nothing to do with the initial conditions and external effects. The oscillation frequency and attenuation coefficient identified in step S3 can be used to calculate the damping ratio of each oscillation mode in the voltage response. The calculation formula is as follows:

[0062]

[0063] In formula (9), δ i represents the attenuation coefficient of the i-th oscillation mode, ω i Indicates the oscillation angular frequency of the i-th oscillation mode. To ensure its own safe and stable operation, the new power grid must contain a certain amount of damping to suppress oscillations caused by external interference. Damping ratio ξ i It determines the decay rate of the oscillation amplitude and the degree of damping of the system. i,...} represents the system's damping level. According to the "Power System Security and Stability Calculation Code," the critical damping ratio for power grid oscillation modes is 0.03. When the damping ratio is greater than the critical damping ratio, the system is stable under small disturbances; otherwise, it is unstable. This method uses the obtained damping level to assess the small-disturbance stability of a novel power grid and detect instability risks during operation in real time.

[0064] In this embodiment, a novel power grid stability assessment device based on damping level includes:

[0065] Pulse generator for injecting pulse current at the PCC end of the new power grid

[0066] Response extractor, used to detect in real time the pulse current injected into the PCC end of the new power grid The voltage before and after; wherein, the pulse current is injected The voltage after the pulse current is: the steady-state voltage at the PCC end and the The response voltage caused by injecting the pulse current The voltage before is only the steady-state voltage at the PCC end; The voltage response curve was extracted by subtracting the voltage before and after injection.

[0067] The parameter identification module is used to select the data of the voltage response curve as sample data and perform parameter identification on the sample data to obtain the amplitude, attenuation factor, initial phase angle and oscillation angular frequency corresponding to the voltage response in each oscillation mode, thereby deriving the time domain expression of the voltage response.

[0068] The stability evaluation module is used to calculate the damping ratio of the new power grid in the i-th oscillation mode according to the time domain expression and select the minimum damping ξ in all oscillation modes. min The ratio is used as the damping level of the new power grid, so as to evaluate the stability of the new power grid according to the damping level.

[0069] The pulse current in the pulse generator The injection process is as follows:

[0070] According to the pulse current I s The amplitude of the current pulses I with different amplitudes is injected into the new power grid in sequence. s , until the voltage fluctuation generated by the new power grid exceeds Δ% of the fundamental voltage amplitude, and record the current pulse when it exceeds Where Δ is the threshold.

[0071] The parameter identification module uses formula (1) to obtain the time domain expression u:

[0072]

[0073] In formula (1), A i represents the amplitude of the i-th oscillation mode, δ i represents the attenuation coefficient of the i-th oscillation mode, ω i represents the oscillation angular frequency of the i-th oscillation mode, θ i represents the initial phase angle of the i-th oscillation mode, and K is the number of oscillation modes in the voltage response.

[0074] The stability evaluation module calculates the damping ratio ξ under the i-th oscillation mode using formula (2): i , if min If it is greater than the set threshold, it means that the new power grid is stable; otherwise, it means that the new power grid is unstable;

[0075]

Claims

1. A new power grid stability assessment method based on damping level, characterized by: The following steps are involved: Step S1: Inject pulse current into the PCC end of the normally operating new power grid ; The pulse current The injection process is as follows: According to the pulse current The amplitude of the current pulses increases from small to large, and the current pulses of different amplitudes are injected into the new power grid in sequence. , until the voltage fluctuation generated by the new power grid exceeds Δ% of the fundamental voltage amplitude, and record the current pulse when it exceeds ; Where Δ is the threshold; Step S2: Real-time detection of the pulse current injected into the PCC end of the new power grid The voltage before and after; wherein, the pulse current is injected The voltage after the pulse current is: the steady-state voltage at the PCC end and the The response voltage caused by injecting the pulse current The voltage before is only the steady-state voltage at the PCC end; The voltage response curve was extracted by subtracting the voltage before and after injection; Step S3: Select the data of the voltage response curve as sample data, and perform parameter identification on the sample data to obtain the amplitude, attenuation factor, initial phase angle and oscillation angular frequency corresponding to the voltage response in each oscillation mode, and then use formula (1) to obtain the time domain expression of the voltage response : (1) In formula (1), represents the amplitude of the i-th oscillation mode, represents the attenuation coefficient of the i-th oscillation mode, represents the oscillation angular frequency of the i-th oscillation mode, represents the initial phase angle of the i-th oscillation mode, K is the number of oscillation modes in the voltage response; Step S4: Based on the time domain expression, use formula (2) to calculate the damping ratio of the new power grid in the i-th oscillation mode , and select the minimum damping in all oscillation modes The ratio is used as the damping level of the new power grid, and the stability of the new power grid is evaluated according to the damping level: (2)。 2. The novel power grid stability assessment method based on damping level according to claim 1 is characterized in that: The parameter identification method in step S3 is the Prony algorithm.

3. The novel power grid stability assessment method based on damping level according to claim 1 is characterized in that: In step S4, evaluating the stability of the new power grid according to the damping level includes: like If it is greater than the set threshold, it means that the new power grid is stable; otherwise, it means that the new power grid is unstable.

4. A novel power grid stability assessment device based on damping level, characterized in that: include: Pulse generator for injecting pulse current at the PCC end of the new power grid ; The pulse current in the pulse generator The injection process is as follows: According to the pulse current The amplitude of the current pulses increases from small to large, and the current pulses of different amplitudes are injected into the new power grid in sequence. , until the voltage fluctuation generated by the new power grid exceeds Δ% of the fundamental voltage amplitude, and record the current pulse when it exceeds ; Where Δ is the threshold; Response extractor, used to detect in real time the pulse current injected into the PCC end of the new power grid The voltage before and after; wherein, the pulse current is injected The voltage after the pulse current is: the steady-state voltage at the PCC end and the The response voltage caused by injecting the pulse current The voltage before is only the steady-state voltage at the PCC end; The voltage response curve was extracted by subtracting the voltage before and after injection; The parameter identification module is used to select the data of the voltage response curve as sample data, and perform parameter identification on the sample data to obtain the amplitude, attenuation factor, initial phase angle and oscillation angular frequency corresponding to the voltage response in each oscillation mode, thereby obtaining the time domain expression using formula (1): : (1) In formula (1), represents the amplitude of the i-th oscillation mode, represents the attenuation coefficient of the i-th oscillation mode, represents the oscillation angular frequency of the i-th oscillation mode, represents the initial phase angle of the i-th oscillation mode, K is the number of oscillation modes in the voltage response; The stability evaluation module is used to calculate the damping ratio of the new power grid in the i-th oscillation mode according to the time domain expression using formula (2) , and select the minimum damping in all oscillation modes The ratio is used as the damping level of the new power grid, and the stability of the new power grid is evaluated according to the damping level: (2) like If it is greater than the set threshold, it means that the new power grid is stable; otherwise, it means that the new power grid is unstable.

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