Design method of microgrid distributed stability and control considering transmission impedance characteristics

Abstract

The application discloses a micro-grid distributed stability and control design method considering transmission impedance characteristics, and the method comprises the following steps: for a micro-grid with multiple micro-sources in parallel, equivalent model topology is carried out, a star-shaped micro-grid topology is converted into a more general mesh micro-grid topology, a mapping relationship between equivalent line impedance between micro-sources and single-machine micro-source line impedance is solved, and overall system small-signal modeling and stability analysis are carried out, so that it is found that the key condition for system stability is that the equivalent line impedance angle needs to be greater than the power angle of the steady-state operation between micro-sources, and then, according to the mapping relationship between the equivalent line impedance angle between multiple machines and the single-machine line impedance angle, global stable operation is designed from the perspective of single-machine micro-source stabilization strategy, so that all line impedance information of other micro-sources is avoided to be known, and certain reference is provided for universal application of droop control under different line characteristics. The application improves the reliability of the micro-grid system and ensures stable operation under arbitrary line characteristics.

Description

Technical Field

[0001] This invention relates to the fields of microgrid technology and power control technology, and in particular to a distributed stability and control design method for microgrids that takes into account transmission impedance characteristics. Background Technology

[0002] With the depletion of global non-renewable energy, increasing environmental pollution, and the gradual growth in electricity demand, traditional power systems characterized by centralized large-scale generating units, high-voltage transmission, complex connections, and motor load dominance are no longer sufficient to meet the diverse power supply and high reliability requirements of the demand side. Microgrid technology, as an effective carrier for future distributed energy supply systems, is a crucial component of future smart power distribution systems and a vital foundation for building a global energy internet. It holds milestone significance for promoting national energy conservation and emission reduction and achieving sustainable energy development.

[0003] Unlike traditional power systems, renewable energy sources in microgrids are often intermittent and random, resulting in more significant random disturbances and a greater likelihood of small perturbations. Therefore, the stability of microgrids during small perturbations is more prevalent and warrants further study. Furthermore, micro-sources are often connected to microgrids via converters, and their stability often exhibits characteristics of power electronic systems, such as: 1) fast response speed of power electronic devices and significantly wider control bandwidth; 2) weakened inertia of micro-sources; 3) switching characteristics, easily inducing harmonic stability; and 4) a smaller short-circuit capacity ratio, exhibiting characteristics of a weak grid. Extensive research has been conducted by scholars both domestically and internationally on the stability issues of microgrid systems. However, research on stability analysis considering different types of micro-sources, multi-time-scale converter models, micro-source interactions, and system control strategies remains lacking. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, the purpose of this invention is to propose a distributed stability and control design method and device for microgrids that considers transmission impedance characteristics, thereby improving the reliability of microgrid systems and ensuring their stable operation under arbitrary line characteristics.

[0006] To achieve the above objectives, this invention proposes a distributed stability and control design method for microgrids that considers transmission impedance characteristics, comprising:

[0007] A model topology equivalence processing is performed on a microgrid system with multiple micro-sources connected in parallel to obtain a microgrid topology equivalent model;

[0008] The mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source is solved using the microgrid topology equivalent model.

[0009] Stability analysis of the multi-machine micro-source parallel microgrid system under different line impedances was performed using a small-signal model of droop control. The results showed that the equivalent line impedance angle was greater than the steady-state operating power angle between the micro-sources.

[0010] Based on the mapping relationship and the stability analysis results, the single-machine distributed stability control parameters are designed from the perspective of multi-machine mapping to obtain the control parameter design results.

[0011] To achieve the above objectives, another aspect of the present invention proposes a distributed stabilization and control design device for microgrids that considers transmission impedance characteristics, comprising:

[0012] The equivalent transformation module is used to perform model topology equivalence processing on a microgrid system with multiple micro-sources connected in parallel to obtain a microgrid topology equivalent model;

[0013] The relationship mapping module is used to solve the mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source using the microgrid topology equivalent model.

[0014] The stability analysis module is used to perform stability analysis on the multi-machine micro-source parallel microgrid system under different line impedances using a small-signal model of droop control, and to obtain the stability analysis result that the equivalent line impedance angle is greater than the steady-state operating power angle between the micro-sources.

[0015] The control design module is used to design single-machine distributed stability control parameters from a multi-machine mapping perspective based on the mapping relationship and the stability analysis results to obtain the control parameter design results.

[0016] The distributed stability and control design method and device for microgrids that consider transmission impedance characteristics in the embodiments of the present invention improves the reliability of microgrid systems and ensures their stable operation under arbitrary line characteristics.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0019] Figure 1 A flowchart of a microgrid distributed stability and control design method considering transmission impedance characteristics according to an embodiment of the present invention;

[0020] Figure 2 This is a microgrid structure with multiple machines connected in parallel according to an embodiment of the present invention and its equivalent network topology.

[0021] Figure 3 A schematic diagram showing the variation of the eigenvalues ​​of a dual-machine parallel system according to an embodiment of the present invention with the active power droop coefficient, the reactive power droop coefficient, and the filter parameters, respectively.

[0022] Figure 4 This is a diagram showing the conversion relationship between the equivalent line impedance between micro-sources and the line impedance of a single micro-source according to an embodiment of the present invention.

[0023] Figure 5 This is a simulation diagram of three micro-sources with different line impedance characteristics according to an embodiment of the present invention.

[0024] Figure 6 This is a schematic diagram of a microgrid distributed stabilization and control design device considering transmission impedance characteristics according to an embodiment of the present invention. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0027] The following describes, with reference to the accompanying drawings, a microgrid distributed stability and control design method and apparatus considering transmission impedance characteristics, according to an embodiment of the present invention.

[0028] Figure 1 This is a flowchart of a microgrid distributed stability and control design method considering transmission impedance characteristics, according to an embodiment of the present invention.

[0029] like Figure 1 As shown, the method includes, but is not limited to, the following steps:

[0030] S1, perform model topology equivalence processing on the microgrid system with multiple micro-sources in parallel to obtain the microgrid topology equivalent model;

[0031] S2, using the microgrid topology equivalent model to solve the mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source;

[0032] S3. Using a small-signal model of droop control, stability analysis of a multi-machine micro-source parallel microgrid system under different line impedances is performed, and the stability analysis results show that the equivalent line impedance angle is greater than the steady-state operating power angle between micro-sources.

[0033] S4. Based on the mapping relationship and stability analysis results, design the single-machine distributed stability control parameters from the perspective of multi-machine mapping to obtain the control parameter design results.

[0034] According to embodiments of the present invention, a distributed stability and control design method for microgrids considering transmission impedance characteristics is proposed. For microgrids with multiple micro-sources connected in parallel, the model topology is equivalently transformed, converting the star-shaped microgrid topology into a more general mesh microgrid topology. The mapping relationship between the equivalent line impedance between micro-sources and the line impedance of a single micro-source is solved. A global small-signal model of the system is established, and the stability of the microgrid with multiple micro-sources in parallel under different line impedances is studied, providing guidance for control parameter design. Based on the mapping relationship between the equivalent line impedance angle between multiple micro-sources and the line impedance angle of a single micro-source, a design for globally stable operation is proposed, avoiding the need to know all the line impedance information of other micro-sources. This provides a certain reference for the universal applicability of droop control under different line characteristics.

[0035] Figure 2 This is a diagram of a microgrid structure with multiple machines connected in parallel, according to an embodiment of the present invention. Figure 2 As shown, each micro-source is equivalent to an ideal controlled voltage source, and each inverter-type micro-source is connected in parallel to the point of common coupling (PCC) through the line impedance to supply power to a common RLC load.

[0036] As an example, Figure 2 In (a) of the diagram, the output voltage of the i-th inverter micro-source is The line impedance between the i-th inverter microsource and the common bus is Common bus voltage is The reference voltage of the grounding point is expressed as The common load of the microgrid system is According to Kirchhoff's law of current in a parallel microgrid topology, we can obtain:

[0037]

[0038] Therefore, the voltage at the common node can be calculated:

[0039]

[0040] In the formula, This refers to the system line admittance or load admittance. It is the sum of the admittances of all branches in the star-parallel topology centered on the PCC node.

[0041] As an example, in Figure 2 In (a), there is dynamic impedance interaction between the inverter-type micro-source and the common bus. In order to clearly express the interaction between micro-sources through the line, this embodiment first transforms the microgrid network with n micro-source nodes and 1 load node connected in parallel from the star circuit into a complete grid network, ensuring that the output voltage and current of the n micro-source nodes and 1 load node remain unchanged before and after.

[0042] According to the equivalence condition, if the voltages of micro-source nodes 1 to n and the voltage of load node 0 remain unchanged before and after the transformation, then the current from outside the network must also remain unchanged. For any node i, there exists:

[0043]

[0044] In the formula, It represents the equivalent admittance between any nodes.

[0045] Based on the common bus voltage, we have:

[0046]

[0047] Combining the above formula, we can obtain

[0048]

[0049] This holds true for any voltage node, meaning that the coefficients of any like terms on both its left and right sides are equal. If the coefficient of the j-th term must be equal, then the equivalent admittance between any nodes can be derived as follows:

[0050]

[0051] If we convert it to impedance form, then we have

[0052]

[0053] When j = 0 Represents the equivalent local load of the i-th inverter micro-source to ground; when j∈[1,n], it is defined as follows: Let be the equivalent line impedance between the i-th inverter microsource and the j-th inverter microsource.

[0054] As can be seen from the above derivation, a star circuit with n inverter micro-source branches connected in parallel is equivalent to a complete network circuit with n vertices. In this power supply network, there is direct dynamic interaction between any micro-sources, with a total of n(n-1) / 2 branches, as detailed below. Figure 2 As shown in (b) of the diagram.

[0055] According to the equivalent model, the output power of the i-th inverter micro-source is expressed as:

[0056]

[0057] The active and reactive power outputs of the i-th inverter microsource are respectively:

[0058]

[0059]

[0060] In the formula,

[0061] and

[0062] When all line impedances are purely inductive, θ ij =π / 2; when all line impedances are purely resistive, θ ij =0; when the line impedance is resistive-inductive, θ ij ∈(0,π / 2).

[0063] As an example, a small-signal model of multi-machine micro-source interaction is established, and the steady-state operating point of the system is represented by an uppercase letter (V). i ,δ ij The small-signal interference term is represented as (ΔV). i ,Δδ i ,Δω i ).

[0064] The droop control law for the i-th single-machine microsource is:

[0065]

[0066]

[0067] In the formula, ω i and V i The inner loop control reference angular frequency and voltage amplitude of the inverter voltage source; ω * and V * Represents the angular frequency and voltage amplitude under no-load conditions; m i and n i These are the coefficients of P-ω sagging and QV sagging, respectively; P * and Q * It is the rated power of the inverter-type micro-source; ω max and ω min These are the maximum and minimum allowable angular frequencies of the system; V max and V min These are the maximum and minimum allowable values ​​for the system voltage.

[0068] Based on the small-signal model of droop control and the power transfer characteristics of multi-machine interaction, the system's state equation is:

[0069]

[0070] In the formula:

[0071] Δx=[Δδ1 … Δδ n Δω1 … Δω n ΔV1 … ΔV n ] T

[0072]

[0073] The eigenvalues ​​of the state matrix in the above equation characterize the stability and transient response of the multi-machine micro-source in parallel. To study the adaptability of traditional droop control under different line impedances and the design of stabilization parameters, this invention investigates the influence of active power droop coefficient, reactive power droop coefficient, and filter parameters on system stability for three cases: high-inductance lines, high-resistance lines, and lines with comparable resistance and inductance. Considering the rated capacity and allowable voltage / frequency deviation range of the inverter-type micro-source during steady-state operation, and taking into account the response time scale of the inverter's power outer loop, the range of the first-order filter time constant is given.

[0074] Under three conditions—purely inductive, equally resistive and inductive, and purely resistive—the characteristic roots of a dual-machine parallel system vary with the active power droop coefficient, reactive power droop coefficient, and filter parameters, respectively, as follows: Figure 3 As shown, Figure 3 From top to bottom, the parameters represent the changes in coefficient m, the changes in coefficient n (filtering), and the changes in the time constant τ. In the case of two machines in parallel, the system's eigenvalues ​​include five non-zero eigenvalues ​​and one zero eigenvalue, and only the five non-zero eigenvalues ​​are useful for system stability analysis. The specific analysis and patterns are detailed below:

[0075] Furthermore, if the power outer loop dynamic response time scale (filter time constant) and line impedance characteristics of multiple micro-sources are similar, the root locus analysis results of multi-micro-source interaction are basically similar to those of single-source stability analysis. A general overview is as follows:

[0076] With the line impedance modulus remaining constant, as the line resistance increases, the dominant poles of the system tend to approach the imaginary axis, but all remain within a stable range.

[0077] Under the three line impedances, the active droop factor m mainly affects the transient response of the system: when m is too small, the dominant pole λ1 is negative and close to the imaginary axis, and the system is in an overdamped state; as m increases, conjugate dominant poles λ1 and λ2 appear.

[0078] Under the characteristics of pure inductive and resistive inductive lines, the reactive power droop factor n has almost no effect on the stability and transient performance of the system. However, under high-resistance lines, the reactive power droop factor n determines the stability and transient performance of the system. When n is in the range of 0 to 0.0006, the system has poles in the right half-plane and the system is unstable. As n gradually increases, the system stability gradually improves, a pair of dominant conjugate poles appear, and the transient performance of the system improves. However, when n is too large, the conjugate poles tend to move closer to the imaginary axis, but the approach speed is extremely slow.

[0079] The filtering time constant τ primarily affects the system's transient response: as τ varies from 0.01 to 0.1 (cutoff frequency 1.5Hz-10Hz), the two dominant conjugate poles tend to converge towards the imaginary axis, but remain some distance away (real part less than -5). Therefore, within the normal range of filtering constants, the effect of the filtering time constant τ on system stability can be ignored.

[0080] Based on the above analysis, a reasonable selection of the reactive power droop coefficient n can ensure the application of traditional droop control under any line characteristics, thereby achieving the equal distribution of active power among micro-sources.

[0081] Traditional droop control does not require high sensitivity of control parameters in purely inductive and resistive-inductive circuits, and generally ensures normal system operation within normal value ranges. However, in the most extreme purely resistive conditions, traditional droop control places certain requirements on the reactive power droop factor. This invention will study, from a new perspective, the minimum requirement for the line impedance angle during stable operation of a microgrid based on a reduced-order model when the reactive power droop factor is 0, thereby providing guidance for engineering applications.

[0082] When the droop coefficient of QV is 0, the state equation of a single micro-source is expressed as:

[0083]

[0084] In the formula:

[0085]

[0086] The differential equation for a single micro-source is:

[0087]

[0088] In the formula:

[0089]

[0090] The single-machine small-signal model is:

[0091]

[0092] Considering the dynamic interaction of multiple micro-sources, the small-signal model of the multi-machine parallel system under the reduced-order condition is as follows:

[0093]

[0094] In the formula:

[0095] Δx=[Δδ1 … Δδ n Δω1 … Δω n ] T

[0096]

[0097]

[0098]

[0099] The stability of a system can be analyzed and characterized by solving for its eigenvalues. Generally, the analytical solution to the system matrix is ​​difficult to obtain directly; however, the calculation can be simplified through the following series of transformations. The eigenvalues ​​of the system matrix A are expressed as follows:

[0100]

[0101] The above equation is a quadratic eigenvalue problem, where the coefficient matrices of both the quadratic and linear terms are non-singular identity matrices. For matrix L, according to Schur's diagonalization theorem, any matrix can be transformed into an upper triangular matrix through a unitary transformation, and the diagonal elements of the upper triangular matrix are the eigenvalues ​​of that matrix. By performing a unitary transformation (U... * Let LU = T), then transform it into an upper triangular matrix T whose diagonal elements are all eigenvalues. Therefore, there exists at least one unitary matrix U such that matrix λ 2 I+λω c I+L standardization, meets

[0102]

[0103] In the formula:

[0104]

[0105] The above equation decomposes a polynomial of order 2n into n second-order polynomials.

[0106] λ 2 +λω c +μ i =0; i∈{1,2,…,n}

[0107] The equivalent condition that all eigenvalues ​​of the system matrix are non-positive real parts is that all eigenvalues ​​of matrix L are non-negative; that is, the condition for system stability is that matrix L is a positive semi-definite matrix. Combining this with the inherent characteristics of matrix L, when all off-diagonal elements are negative or zero...

[0108] At that time, matrix L is a weakly diagonally dominated matrix, which has at least one eigenvalue of 0 and at most n-1 positive eigenvalues ​​(μ). n If ≥…μ2≥μ1=0), the system stability condition is satisfied. Therefore, a sufficient condition for system stability is that for any element a in matrix L… ij It is always greater than or equal to zero, and its diagonal elements are always greater than zero, that is, the following formula always holds true:

[0109]

[0110] That is, the operating power angle and equivalent line impedance between any micro-sources must satisfy the following:

[0111] π+δ ji >θ ij >δ ji

[0112] Due to the operating power angle range (δ) of microgrids ji =δ j -δ i Generally, it lies within the interval [-π / 6, π / 6]. Therefore, a more intuitive generalized form is:

[0113] 5π / 6>θ ij >π / 6

[0114] In single-unit stability analysis, the sufficient condition for system stability is that the line impedance angle of a single micro-source is greater than the power angle of steady-state operation (θ>δ), which is independent of the line impedance of other micro-sources. The conclusion is relatively simple and suitable for single-unit grid-connected applications.

[0115] Regarding the stability analysis results for multi-machine interaction, a sufficient condition for system stability is that the equivalent line impedance angle between micro-sources is greater than the power angle (θ) during steady-state operation. ij >δ ji The conclusions are more accurate and suitable for analysis applications in islanded mode, but the stability conditions involve the line impedance characteristics of more other micro-sources.

[0116] Furthermore, comparing the stability conditions of single-unit micro-sources and multi-unit parallel connections, the main difference lies in the correlation between the equivalent line impedance angle between multi-unit micro-sources and the line impedance angle of a single-unit micro-source. Based on the equivalent transformation relationship between the two, the equivalent line impedance angle between micro-sources can be expressed as:

[0117]

[0118] In the formula, It is the admittance angle of the sum of the admittances of all individual branches in a star topology:

[0119]

[0120] For complex microgrid systems, obtaining the line impedance information between all micro-sources is often difficult. Therefore, it is necessary to ensure the overall stability of the multi-source system from the perspective of single-unit stabilization design. By comparing the stability conditions of single-unit micro-sources and multi-unit parallel connections, it can be seen that the two can be transformed into each other under certain conditions, exhibiting consistency, but also some differences. These differences are summarized as follows:

[0121] Since the load impedance is generally much larger than the line impedance, the effect of the load impedance on the equivalent line impedance characteristics is almost negligible. The mathematical process is expressed as follows:

[0122]

[0123] Under the same high, medium, or low voltage level, the output impedance angle of each individual micro-source is generally the same, such as Figure 4 As shown in (a), the equivalent line impedance angle between multiple micro-sources and the output impedance angle of a single micro-source are basically the same. The mathematical process is expressed as follows:

[0124]

[0125] Therefore, in the case of multiple units in parallel, in order to ensure the universal applicability of droop under different impedance angles, we can refer to the stability analysis conclusions based on single-unit micro-sources, increase the reactive power droop coefficient or add virtual inductance to improve the equivalent impedance angle, and carry out the overall system stabilization design from the perspective of single-unit micro-sources.

[0126] For a dual-machine micro-source interactive system, when the line impedance characteristics of the two micro-sources are significantly different, the single-machine stability analysis result is a sufficient condition for the stability of the dual-machine interactive system. The mathematical process is expressed as follows:

[0127]

[0128] For a multi-microsource parallel system, when the line impedance characteristics are significantly different, the equivalent line impedance angle between all microsources must be greater than π / 6 after reshaping each individual microsource to ensure stable system operation. The mathematical process is as follows:

[0129]

[0130] Otherwise, if the output impedance angle of each individual micro-source is an unknown arbitrary impedance angle, the system may be unstable. For ease of understanding, the equivalent impedance vector diagram when the three line impedance angles are significantly different is shown below. Figure 4 As shown in (b) of , if there is a high-sensitivity line with an excessively small modulus, the system is extremely difficult to be stable. The mathematical expression is:

[0131]

[0132] Therefore, in order to improve the system stability of multiple micro-sources under the condition of different line impedance angles, it is necessary to design the virtual impedance or reactive power droop coefficient reasonably to ensure that when the reshaped output impedance angle of each single micro-source is greater than π / 3, the equivalent line impedance angles between multiple micro-sources will all be greater than π / 6, which meets the condition for stable operation of the system. This provides a theoretical basis and engineering reference for the design of virtual impedance and reactive power droop coefficient.

[0133] For a system with multiple parallel micro-sources, when the reshaped output impedance angle of each single micro-source is approximately equal to π / 2, it meets the optimal design for system stability, and the stability margin is the largest. The mathematical process is expressed as:

[0134]

[0135] From Figure 4 (a), it can be seen that when the output impedance angles of each micro-source are substantially the same (θ1≈θ2≈θ3), the equivalent line impedance angles between the micro-sources are also substantially the same (θ 12 ≈θ 23 ≈θ 13 ), and is approximately equal to the output impedance angle of a single micro-source. At this time, the stability condition for multi-micro-source interaction is consistent with the stability condition of a single micro-source, that is, when the output impedance angle of each single micro-source is greater than π / 6, the stability of the overall system can be guaranteed.

[0136] From Figure 4 (b), it can be seen that when the output impedance angles of each micro-source are significantly different (θ1=π / 2; θ2=π / 4; θ3=0), the equivalent line impedance angles between the micro-sources are also significantly different. Especially when the impedance modulus of a purely inductive line is far smaller than the impedance modulus of other micro-sources (Z1<<Z2; Z1<<Z3), it will cause the equivalent total admittance of the system to approach high-capacitance characteristics. Therefore, the line impedance characteristics between micro-sources may exhibit resistance-capacitance characteristics (θ 12 ≈π / 3; θ 13 ≈π / 6; θ 23 ≈-π / 12). For example, it can be seen from the equivalent impedance angle between micro-source 2 and micro-source 3 that resistance dominates and contains a certain amount of capacitance, and its impedance modulus is also relatively large, which is not conducive to system stability. In addition, due to the small line impedance modulus of micro-source 1, the dynamics of the multi-parallel common bus mainly depends on the dynamics of micro-source 1. Therefore, in Figure 2In the equivalent topology of (b), there is mainly interaction between micro-source 1 and micro-source 2 and interaction between micro-source 1 and micro-source 3. The direct interaction capability between micro-source 2 and micro-source 3 becomes very weak, which also explains the reason why the impedance magnitude of the RC equivalent circuit is too large.

[0137] To ensure the stable operation of multi-machine interactive micro-sources, it is necessary to guarantee that any equivalent line impedance angle is greater than the maximum power angle of the system. Therefore, based on the conversion relationship between equivalent line impedance and the line impedance of a single micro-source, when there are significant differences in line impedance, reasonable design parameters are needed to ensure that the output impedance of any single micro-source is greater than π / 3, i.e., the equivalent line impedance angle between multiple machines will be greater than π / 6. Based on the inherent consistency between virtual impedance and droop control, the design principles for single-machine distributed stabilization and control parameters are as follows:

[0138]

[0139] Therefore, for microgrids with multiple generators in parallel, when the line impedance of other micro-sources is unknown, it is necessary to reshape the equivalent output impedance of each micro-source and reasonably select the reactive power droop factor or virtual impedance to ensure stable system operation.

[0140] To investigate the dynamic interaction effects of multiple micro-sources and to verify the applicability of traditional droop reduction to different line impedance characteristics and the effectiveness of parameter design principles, this invention establishes a model of three parallel inverter-type micro-sources based on the Matlab / Simulink platform. The active and reactive droop coefficients of the three micro-sources are both set to m = 1 × 10⁻⁶. -3 n = 5 × 10 -3 The rated operating voltage effective amplitude and frequency are 220V / 50Hz.

[0141] In one embodiment of the present invention, Figure 5 Simulation results are presented for three micro-sources with line impedance characteristics of one high inductance, one with equal resistance and inductance, and one high resistance. In the first 0-1 second, the active power among the micro-sources is precisely evenly distributed, and the reactive power distribution is within an acceptable range. At 1 second, the common load changes, thus altering the equivalent network connection parameters. This primarily affects the local load of each micro-source; the common load has little impact on the equivalent line parameters between the micro-sources, verifying the correctness of the above conclusions. Furthermore, a comparison... Figure 5 Simulation results of the multi-parallel inverter connection structure and the equivalent network microgrid connection structure show that, within the allowable error range, the two have almost the same dynamic response and steady-state performance, verifying the effectiveness of the microgrid topology equivalent structure.

[0142] from Figure 5As can be seen, by reasonably setting the droop coefficient, the stable operation of droop control across different impedances can be ensured, thereby achieving precise distribution of active power. In the multi-parallel inverter topology, the line impedance angles of the three micro-sources are 0.40π, 0.28π, and 0.04π, respectively. Therefore, in the equivalent network microgrid topology, the equivalent line impedance angles between micro-sources are 0.45π, 0.08π, and 0.21π, respectively, which do not fully meet the minimum impedance angle requirement (π / 6) between any two micro-sources. However, the reactive power droop coefficient can be approximated as a virtual inductance, where the value of the virtual inductance is... The reshaped individual line impedance angles are 0.46π, 0.41π, and 0.33π, respectively, which meet the requirement that the individual output impedance angle is greater than π / 3. Therefore, the equivalent line impedance angle between multiple machines will be greater than π / 6, ensuring the stable operation of the system.

[0143] This invention presents a distributed stability and control design method for microgrids considering transmission impedance characteristics. For microgrids with multiple micro-sources connected in parallel, the method performs topological equivalence, transforming the star-shaped microgrid topology into a more general mesh microgrid topology. The mapping relationship between the equivalent line impedance between micro-sources and the line impedance of individual micro-sources is solved. A global small-signal model of the system is established, and the stability of the multi-source parallel microgrid under different line impedances is studied, providing guidance for control parameter design. Based on the mapping relationship between the equivalent line impedance angle between multiple sources and the line impedance angle of individual sources, global stable operation is designed, avoiding the need to know all the line impedance information of other micro-sources. This provides a certain reference for the universal applicability of droop control under different line characteristics. This improves the reliability of the microgrid system and ensures its stable operation under arbitrary line characteristics.

[0144] To achieve the above embodiments, such as Figure 6 As shown, this embodiment also provides a microgrid distributed stability and control design device 10 that considers transmission impedance characteristics. The device 10 includes: an equivalent transformation module 100, a relation mapping module 200, a stability analysis module 300, and a control design module 400.

[0145] The equivalent transformation module 100 is used to perform model topology equivalence processing on a microgrid system with multiple micro-sources connected in parallel to obtain a microgrid topology equivalent model;

[0146] The relation mapping module 200 is used to solve the mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source using the microgrid topology equivalent model;

[0147] The stability analysis module 300 is used to perform stability analysis on a microgrid system with multiple micro-sources in parallel under different line impedances using a small-signal model of droop control, and to obtain stability analysis results where the equivalent line impedance angle is greater than the steady-state operating power angle between micro-sources.

[0148] The control design module 400 is used to design single-machine distributed stability control parameters from a multi-machine mapping perspective based on the mapping relationship and stability analysis results to obtain the control parameter design results.

[0149] Furthermore, the aforementioned equivalent transformation module 100 is also used to construct the structure of a microgrid system with multiple micro-sources connected in parallel; the output voltage of the i-th inverter micro-source is preset to be... The line impedance between the i-th inverter microsource and the common bus is Common bus voltage is The reference voltage of the grounding point is expressed as The common load of the microgrid system is According to Kirchhoff's law of current in parallel microgrid topologies:

[0150]

[0151] Solve for the voltage at the common node:

[0152]

[0153] In the formula, This refers to the system line admittance or load admittance. It is the sum of the admittances of all branches in the star-parallel topology centered on the PCC node;

[0154] A microgrid network with n micro-source nodes and 1 load node connected in parallel is transformed from a star circuit into a fully grid-type network, ensuring that the output voltage and current of the n micro-source nodes and 1 load node remain unchanged before and after.

[0155] According to the equivalence condition, if the voltages of micro-source nodes 1 to n and the voltage of load node 0 remain unchanged before and after the transformation, then the current from outside the network remains unchanged. For any node i, we have:

[0156]

[0157] In the formula, Represents the equivalent admittance between any nodes;

[0158] Based on the common bus voltage, we have:

[0159]

[0160] Combining the above formula, we get:

[0161]

[0162] The equivalent admittance between any nodes is:

[0163]

[0164] Converting to impedance form, we get:

[0165]

[0166] When j = 0 Represents the equivalent local load of the i-th inverter micro-source to ground; when j∈[1,n], it is defined as follows: Let be the equivalent line impedance between the i-th inverter microsource and the j-th inverter microsource.

[0167] Furthermore, the aforementioned stability analysis module 300 is also used to establish a small-signal model of the droop control in multi-machine micro-source interaction, and to represent the steady-state operating point of the microgrid system using uppercase letters (V). i ,δ ij The small-signal interference term is represented as (ΔV). i ,Δδ i ,Δω i );

[0168] The droop control law for the i-th single-machine microsource is:

[0169]

[0170]

[0171] In the formula, ω i and V i The inner loop control reference angular frequency and voltage amplitude of the inverter voltage source; ω * and V * Represents the angular frequency and voltage amplitude under no-load conditions; m i and n i These are the coefficients of P-ω sagging and QV sagging, respectively; P * and Q * It is the rated power of the inverter-type micro-source; ω max and ω min These are the maximum and minimum allowable angular frequencies of the system; V max and V min These are the maximum and minimum allowable values ​​for the system voltage.

[0172] Furthermore, when the droop coefficient of QV is 0, the state equation for a single micro-source is expressed as:

[0173]

[0174] In the formula:

[0175]

[0176] The differential equation for a single micro-source is:

[0177]

[0178] In the formula:

[0179]

[0180] The single-machine small-signal model is:

[0181]

[0182] Furthermore, the relationship mapping module 200 is also used to derive the equivalent line impedance angle between micro-sources as follows, based on the mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source:

[0183]

[0184] In the formula, It is the admittance angle of the sum of the admittances of all individual branches in a star topology:

[0185]

[0186] This invention presents a distributed stability and control design device for microgrids considering transmission impedance characteristics. For microgrids with multiple micro-sources connected in parallel, it performs topological equivalence modeling, transforming the star-shaped microgrid topology into a more general mesh microgrid topology. The mapping relationship between the equivalent line impedance between micro-sources and the line impedance of a single micro-source is solved. A global small-signal model of the system is established, and the stability of the multi-source parallel microgrid under different line impedances is studied, providing guidance for control parameter design. Based on the mapping relationship between the equivalent line impedance angle between multiple sources and the line impedance angle of a single source, global stable operation is designed, avoiding the need to know all the line impedance information of other micro-sources. This provides a certain reference for the universal applicability of droop control under different line characteristics. This improves the reliability of the microgrid system and ensures its stable operation under arbitrary line characteristics.

[0187] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0188] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0189] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A distributed stability and control design method for microgrids considering transmission impedance characteristics, characterized in that, Includes the following steps: A model topology equivalence processing is performed on a microgrid system with multiple micro-sources connected in parallel to obtain a microgrid topology equivalent model; The mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source is solved using the microgrid topology equivalent model. Stability analysis of the multi-machine micro-source parallel microgrid system under different line impedances was performed using a small-signal model of droop control. The results showed that the equivalent line impedance angle was greater than the steady-state operating power angle between the micro-sources. Based on the mapping relationship and the stability analysis results, the single-machine distributed stability control parameters are designed from the perspective of multi-machine mapping to obtain the control parameter design results. Construct the structure of the multi-machine micro-source parallel microgrid system; preset the output voltage of the i-th inverter micro-source to be... The line impedance between the i-th inverter micro-source and the common bus is The common bus voltage is The reference voltage at the grounding point is expressed as The common load of the microgrid system is According to Kirchhoff's law of current in parallel microgrid topologies: Solve for the voltage at the common node: In the formula, This refers to the system line admittance or load admittance. It is the sum of the admittances of all branches in the star-parallel topology centered on the PCC node; A microgrid network with n micro-source nodes and 1 load node connected in parallel is transformed from a star circuit into a fully grid-type network, ensuring that the output voltage and current of the n micro-source nodes and 1 load node remain unchanged before and after. According to the equivalence condition, if the voltages of micro-source nodes 1 to n and the voltage of load node 0 remain unchanged before and after the transformation, then the current from outside the network remains unchanged. For any node i, we have: In the formula, Represents the equivalent admittance between any nodes; Based on the common bus voltage, we have: Combining the above formula, we get: The equivalent admittance between any nodes is: Converting to impedance form, we get: When j=0 This represents the equivalent local load of the i-th inverter micro-source to ground; when j When [1, n], define Let be the equivalent line impedance between the i-th inverter micro-source and the j-th inverter micro-source; Based on the mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source, the equivalent line impedance angle between micro-sources can be expressed as: In the formula, It is the admittance angle of the sum of the admittances of all individual branches in a star topology: 。 2. The method according to claim 1, characterized in that, A small-signal model of the droop control in multi-machine micro-source interaction is established, and the steady-state operating point of the microgrid system is represented by uppercase letters. V i , δ ij The small-signal interference term is represented as... ; No. i The droop control law for a single micro-source is: In the formula, ω i and V i The inner loop control reference angular frequency and voltage amplitude represent the inverter-type voltage source; ω and V Represents the angular frequency and voltage amplitude under no-load conditions; m i and n i They are P-ω sagging and QV The coefficient of droop; P i 、Q i These are the active and reactive power outputs of the i-th inverter micro-source, respectively; P i and Q i It is the rated power of the inverter-type micro source; ω max and ω min These are the maximum and minimum allowable angular frequencies of the system; V max and V min These are the maximum and minimum allowable values ​​for the system voltage.

3. The method according to claim 2, characterized in that, when QV droop coefficient n i When the value is 0, the state equation of a single micro-source is expressed as: Where τ is the filtering time constant, and in the formula: The differential equation for a single micro-source is: In the formula: The single-machine small-signal model is: 。 4. A distributed stabilization and control design device for microgrids considering transmission impedance characteristics, characterized in that, include: The equivalent transformation module is used to perform model topology equivalence processing on a microgrid system with multiple micro-sources connected in parallel to obtain a microgrid topology equivalent model; The relationship mapping module is used to solve the mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source using the microgrid topology equivalent model. The stability analysis module is used to perform stability analysis on the multi-machine micro-source parallel microgrid system under different line impedances using a small-signal model of droop control, and to obtain the stability analysis result that the equivalent line impedance angle is greater than the steady-state operating power angle between the micro-sources. The control design module is used to design single-machine distributed stability control parameters from a multi-machine mapping perspective based on the mapping relationship and the stability analysis results to obtain control parameter design results. The equivalent transformation module is also used to construct the structure of a microgrid system with multiple micro-sources connected in parallel; the output voltage of the i-th inverter micro-source is preset to be... The line impedance between the i-th inverter micro-source and the common bus is The common bus voltage is The reference voltage at the grounding point is expressed as The common load of the microgrid system is According to Kirchhoff's law of current in a parallel microgrid topology: Solve for the voltage at the common node: In the formula, This refers to the system line admittance or load admittance. It is the sum of the admittances of all branches in the star-parallel topology centered on the PCC node; A microgrid network with n micro-source nodes and 1 load node connected in parallel is transformed from a star circuit into a fully grid-type network, ensuring that the output voltage and current of the n micro-source nodes and 1 load node remain unchanged before and after. According to the equivalence condition, if the voltages of micro-source nodes 1 to n and the voltage of load node 0 remain unchanged before and after the transformation, then the current from outside the network remains unchanged. For any node i, we have: In the formula, Represents the equivalent admittance between any nodes; Based on the common bus voltage, we have: Combining the above formula, we get: The equivalent admittance between any nodes is: Converting to impedance form, we get: When j=0 This represents the equivalent local load of the i-th inverter micro-source to ground; when j When [1, n], define Let be the equivalent line impedance between the i-th inverter micro-source and the j-th inverter micro-source; The relationship mapping module is also used to derive the equivalent line impedance angle between micro-sources as follows, based on the mapping relationship between the equivalent line impedance angle between micro-sources and the line impedance angle of a single micro-source: In the formula, It is the admittance angle of the sum of the admittances of all individual branches in a star topology: 。 5. The apparatus according to claim 4, characterized in that, The stability analysis module is also used to establish a small-signal model of the droop control in multi-machine micro-source interaction, and to represent the steady-state operating point of the microgrid system using uppercase letters. V i , δ ij The small-signal interference term is represented as... ; No. i The droop control law for a single micro-source is: In the formula, ω i and V i The inner loop control reference angular frequency and voltage amplitude represent the inverter-type voltage source; ω and V Represents the angular frequency and voltage amplitude under no-load conditions; m i and n i They are P-ω sagging and QV The coefficient of droop; P i 、Q i These are the active and reactive power outputs of the i-th inverter micro-source, respectively; P i and Q i It is the rated power of the inverter-type micro source; ω max and ω min These are the maximum and minimum allowable angular frequencies of the system; V max and V min These are the maximum and minimum allowable values ​​for the system voltage.

6. The apparatus according to claim 5, characterized in that, when QV When the droop coefficient is 0, the state equation of a single microsource is expressed as: Where τ is the filtering time constant, and in the formula: The differential equation for a single micro-source is: In the formula: The single-machine small-signal model is: 。

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