A micro-grid stability analysis method, device, equipment and storage medium

Abstract

The application relates to the technical field of power grid operation, and particularly discloses a micro-grid stability analysis method, device, equipment and storage medium, which comprises the following steps: obtaining operation data of a micro-grid and a distributed photovoltaic cluster, wherein the distributed photovoltaic cluster is composed of multiple distributed photovoltaic units; a small signal model of a single distributed photovoltaic unit in a dq synchronous rotating coordinate system is established based on the operation data, and the small signal model is solved to obtain an alternating-current side output impedance; a Norton equivalent circuit of the distributed photovoltaic cluster accessing the micro-grid is constructed according to the alternating-current side output impedance of each distributed photovoltaic unit in the photovoltaic cluster; according to the generalized Nyquist criterion, the Norton equivalent circuit is sequentially checked for single-distributed-photovoltaic-strong-grid access stability, cluster total admittance and grid admittance matching stability and cluster unit admittance interaction stability, and a micro-grid stability state is obtained. The application is suitable for a micro-grid with a high proportion of photovoltaic access and improves the stability of the micro-grid.

Description

Technical Field

[0001] This application relates to the field of power grid operation technology, and in particular to a microgrid stability analysis method, apparatus, equipment and storage medium. Background Technology

[0002] With the large-scale integration of high-proportion distributed photovoltaic clusters into microgrids, traditional synchronous generators are gradually being replaced by photovoltaic grid-connected power electronic devices. This replacement process directly leads to a significant reduction in the inertia of the microgrid system, and a substantial decrease in the system's anti-interference capability and operational stability.

[0003] The complex interaction between the output impedance matrix of a distributed photovoltaic (PV) cluster and the inherent inductive impedance of a microgrid further exacerbates the microgrid's oscillation problem, seriously threatening the overall safety and stability of the microgrid's operation. As the proportion of distributed PV grid connection continues to increase, the structural complexity of distributed PV cluster grid-connected systems continues to rise, and the significant randomness and volatility of PV output further amplify its impact on the stable operation of the microgrid. Summary of the Invention

[0004] The main purpose of this application is to provide a microgrid stability analysis method, which aims to solve the technical problem of unstable operation analysis of microgrids with a high proportion of photovoltaic access in the prior art.

[0005] To achieve the above objectives, this application provides a microgrid stability analysis method, the method comprising the following steps: The system acquires operational data from microgrids and distributed photovoltaic clusters, wherein the distributed photovoltaic clusters consist of multiple distributed photovoltaic units. Based on the aforementioned operational data, a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system is established, and the AC side output impedance is obtained by solving the small-signal model. The Norton equivalent circuit for connecting the distributed photovoltaic cluster to the microgrid is constructed based on the AC output impedance of each distributed photovoltaic unit in the photovoltaic cluster. Based on the generalized Nyquist criterion, the stability of the microgrid is obtained by sequentially verifying the stability of a single distributed photovoltaic grid connection, the stability of the cluster total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units.

[0006] In one embodiment, the step of establishing a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system based on the operating data, and solving the small-signal model to obtain the AC-side output impedance, includes: Small disturbance modeling is performed on the front-end DC boost circuit, the voltage and current dual closed loop of the back-end inverter, and the phase-locked loop contained in the distributed photovoltaic unit to establish the small signal model. Based on the small-signal model, the DC-side and AC-side transfer function matrices are constructed, and the AC-side output impedance of a single distributed photovoltaic unit is calculated based on the DC-side and AC-side transfer function matrices.

[0007] In one embodiment, the step of constructing the Norton equivalent circuit for connecting the distributed photovoltaic cluster to the microgrid based on the AC-side output impedance of each distributed photovoltaic unit in the photovoltaic cluster includes: The microgrid is equivalent to an inductive impedance with a resistor and an inductor connected in series, and the distributed photovoltaic unit is equivalent to an equivalent circuit form with a controlled current source and an output impedance connected in parallel. The Norton equivalent circuit of the distributed photovoltaic cluster is formed by converting the equivalent circuit form to the same microgrid voltage level.

[0008] In one embodiment, the step of sequentially performing single distributed photovoltaic grid connection stability verification on the Norton equivalent circuit includes: Determine whether the AC-side output impedance of a single distributed photovoltaic unit has a right-half-plane zero. When there is no zero point in the right half-plane, the microgrid is determined to be in a stable state.

[0009] In one embodiment, the step of performing a cluster total admittance and grid admittance matching stability verification on the Norton equivalent circuit includes: Calculate the first ratio between the equivalent admittance of the microgrid and the sum of the output admittances of each unit in the photovoltaic cluster; If the number of loops in the eigenvalue trajectory of the first ratio does not encircle the feature points of the complex plane is verified by the generalized Nyquist criterion, the microgrid is determined to be in a stable state.

[0010] In one embodiment, the step of performing inter-cell admittance interaction stability verification on the Norton equivalent circuit includes: For any distributed photovoltaic unit within the distributed photovoltaic cluster, calculate the second ratio of the sum of the output admittances of the remaining distributed photovoltaic units to the output admittance of that unit; If the number of loops in the eigenvalue trajectory of the second ratio does not encircle the feature points of the complex plane is verified by the generalized Nyquist criterion, the microgrid is determined to be in a stable state.

[0011] In one embodiment, after the step of sequentially verifying the stability of the Norton equivalent circuit based on the generalized Nyquist criterion for individual distributed photovoltaic grid connection stability, cluster total admittance matching stability with grid admittance, and inter-cluster admittance interaction stability, to obtain the microgrid stability state, the method further includes: If any one of the following checks fails in the Norton equivalent circuit's sequential verification of the stability of a single distributed photovoltaic grid connection, the stability of the cluster's total admittance matching with the grid admittance, and the stability of admittance interaction between cluster units, the microgrid is determined to be in an unstable state.

[0012] Furthermore, to achieve the above objectives, this application also provides a microgrid stability analysis device, the device comprising: The data acquisition module is used to acquire the operating data of the microgrid and the distributed photovoltaic cluster, which is composed of multiple distributed photovoltaic units; The model building module is used to establish a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system based on the running data, and to solve the small-signal model to obtain the AC side output impedance. The equivalent calculation module is used to construct the Norton equivalent circuit for the distributed photovoltaic cluster to access the microgrid based on the AC side output impedance of each distributed photovoltaic unit in the photovoltaic cluster. The state judgment module is used to perform sequential verification of the stability of a single distributed photovoltaic grid connection, the stability of the cluster total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units on the Norton equivalent circuit according to the generalized Nyquist criterion, so as to obtain the stability state of the microgrid.

[0013] In addition, to achieve the above objectives, this application also provides a microgrid stability analysis device, which includes: a memory, a processor, and a microgrid stability analysis processing program stored in the memory and executable on the processor. When the microgrid stability analysis processing program is executed by the processor, it implements the steps of the above-described microgrid stability analysis method.

[0014] In addition, to achieve the above objectives, this application also proposes a storage medium, which is a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the steps of the microgrid stability analysis method described above.

[0015] The above-mentioned one or more technical solutions provided in this application may have the following advantages or at least achieve the following technical effects: This application discloses a microgrid stability analysis method, apparatus, device, and storage medium. The method includes: acquiring operational data of a microgrid and a distributed photovoltaic (PV) cluster, wherein the distributed PV cluster consists of multiple distributed PV units; establishing a small-signal model of a single distributed PV unit in a dq synchronous rotating coordinate system based on the operational data, and solving the small-signal model to obtain the AC-side output impedance; constructing a Norton equivalent circuit for the distributed PV cluster connected to the microgrid based on the AC-side output impedance of each distributed PV unit in the PV cluster; and performing sequential verifications on the Norton equivalent circuit based on the generalized Nyquist criterion, including the stability of a single distributed PV unit connected to the grid, the stability of the cluster's total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units, to obtain the microgrid stability state. Impedance modeling is used instead of solving high-order state matrices, making it suitable for microgrids with a high proportion of PV access. Through three-layer stability verification, considering the PV unit itself, the grid matching between the cluster and the grid, and the interaction between units, the stability of the microgrid is improved. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating the first embodiment of the microgrid stability analysis method of this application; Figure 2 This is a flowchart illustrating the second embodiment of the microgrid stability analysis method of this application; Figure 3 This is a schematic diagram of the small-signal circuit of the distributed photovoltaic inverter in the dq coordinate system in the second embodiment of the microgrid stability analysis method of this application; Figure 4 This is a block diagram of the AC-side impedance transfer function of a two-stage distributed photovoltaic system in the second embodiment of the microgrid stability analysis method of this application; Figure 5 This is a flowchart illustrating the third embodiment of the microgrid stability analysis method of this application; Figure 6 This is the Norton equivalent circuit diagram of the output impedance of the third embodiment of the microgrid stability analysis method of this application; Figure 7 This is a block diagram of the output current transfer function of the third embodiment of the microgrid stability analysis method of this application; Figure 8 This is an equivalent schematic diagram of a distributed photovoltaic cluster connected to a weak power grid, according to the third embodiment of the microgrid stability analysis method of this application. Figure 9 This is a schematic diagram of the module structure of the microgrid stability analysis device of this application; Figure 10 This is a schematic diagram of the microgrid stability analysis equipment structure, which is part of the hardware operating environment of the microgrid stability analysis method described in this application.

[0018] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0022] It should be noted that the executing entity in this embodiment can be a computing service device with data processing, network communication, and program execution functions, such as a tablet computer, personal computer, or mobile phone, or a microgrid stability analysis device capable of performing the above functions. The following description uses a microgrid stability analysis device as an example to illustrate this embodiment and the subsequent embodiments.

[0023] Based on this, embodiments of this application provide a microgrid stability analysis method, referring to... Figure 1 , Figure 1 This is a flowchart illustrating the first embodiment of the microgrid stability analysis method of this application.

[0024] Step S10: Obtain operational data for the microgrid and distributed photovoltaic clusters.

[0025] It should be noted that the operational data may include the microgrid's grid parameters (resistance, inductance, and voltage levels), the number of units in the distributed photovoltaic cluster, the control parameters of each photovoltaic unit, and basic data such as the grid connection point voltage / current. The distributed photovoltaic cluster can be a photovoltaic power generation group composed of multiple distributed photovoltaic units.

[0026] Step S20: Based on the operating data, establish a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system, and solve the small-signal model to obtain the AC side output impedance.

[0027] It should be noted that the dq synchronous rotating coordinate system can convert AC quantities into DC quantities, simplifying the derivation of small-signal models and reflecting the dynamic characteristics of phase-locked loops. The small-signal model can be a linearized mathematical model established near the steady-state operating point for distributed photovoltaic units, used to analyze the system's dynamic response under small-amplitude disturbances.

[0028] It is understandable that the AC output impedance can be the small-signal impedance characteristic of the AC grid-connected port of a single distributed photovoltaic unit, reflecting the interaction characteristics between the photovoltaic unit and the power grid.

[0029] Step S30: Construct the Norton equivalent circuit for the distributed photovoltaic cluster to access the microgrid based on the AC output impedance of each distributed photovoltaic unit in the photovoltaic cluster.

[0030] It should be noted that the Norton equivalent circuit can be a simplified equivalent circuit for distributed photovoltaic clusters and microgrids, used to analyze the oscillation and stability characteristics of grid-connected clusters. The Norton equivalent circuit can be constructed based on the aforementioned operating data and AC-side output impedance.

[0031] Step S40: Based on the generalized Nyquist criterion, the Norton equivalent circuit is sequentially checked for the stability of a single distributed photovoltaic grid connection, the stability of the cluster total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units to obtain the microgrid stability status.

[0032] It should be noted that the generalized Nyquist criterion can be used to determine the stability of a multi-input multi-output system by judging whether the trajectory of the loop gain eigenvalues ​​encloses the complex plane feature point (-1, j0) and thus determining whether the system is stable.

[0033] It should be understood that the stability of a single distributed photovoltaic (PV) grid connection can be verified to determine whether a single PV unit possesses stable operating capabilities when connected to an ideal grid; the stability of the cluster's total admittance matching the grid admittance can be verified to determine the degree of matching between the PV cluster's total admittance and the microgrid's equivalent admittance, judging whether the overall grid connection is stable; the stability of admittance interaction between cluster units can be verified to check the interaction of admittances between different PV units within the cluster, avoiding system oscillations caused by parameter differences. The final conclusion of the microgrid's stability state is obtained after these three layers of verification. If any verification fails, it indicates that the microgrid is in an unstable state.

[0034] In this embodiment, the microgrid stability analysis method includes: acquiring operational data of the microgrid and distributed photovoltaic (PV) clusters, wherein the distributed PV clusters consist of multiple distributed PV units; establishing a small-signal model of a single distributed PV unit in a dq synchronous rotating coordinate system based on the operational data, and solving the small-signal model to obtain the AC-side output impedance; constructing a Norton equivalent circuit for the distributed PV cluster connected to the microgrid based on the AC-side output impedance of each distributed PV unit in the PV cluster; and performing sequential verifications on the Norton equivalent circuit based on the generalized Nyquist criterion, including the stability of a single distributed PV unit connected to the grid, the stability of the cluster's total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units, to obtain the microgrid stability state. Using impedance modeling instead of solving high-order state matrices is suitable for microgrids with a high proportion of PV access. Through three-layer stability verification, considering the PV unit itself, the matching between the cluster and the grid, and the interaction between units, the stability of the microgrid is improved.

[0035] Based on the first embodiment of this application, in the second embodiment of this application, the content that is the same as or similar to that in Embodiment 1 above can be referred to the above description, and will not be repeated hereafter. Please refer to Figure 2 , Figure 2 This is a flowchart illustrating the second embodiment of the microgrid stability analysis method of this application. In this embodiment, step 20 includes: Step S201: Perform small-interference modeling on the front-end DC boost circuit, the voltage and current dual closed loop of the back-end inverter, and the phase-locked loop contained in the distributed photovoltaic unit, and establish the small-signal model.

[0036] Step S202: Construct the DC-side and AC-side transfer function matrices based on the small-signal model, and calculate the AC-side output impedance of a single distributed photovoltaic unit based on the DC-side and AC-side transfer function matrices.

[0037] It should be noted that the front-end DC boost circuit can be a Boost converter circuit that achieves Maximum Power Point Tracking (MPPT) and contains a PI control loop. The back-end inverter's dual voltage and current closed loop can be a dual PI control structure with an outer voltage loop and an inner current loop on the AC side of the inverter, used to stabilize the output voltage and quickly track current commands. The phase-locked loop can be a control loop that enables synchronous tracking between the inverter control coordinate system and the grid system coordinate system.

[0038] It should be understood that small-disturbance modeling can be a linearized model performed near the system's steady-state operating point, used to analyze the dynamic characteristics under small disturbances and obtain a small-signal model. The DC-side and AC-side transfer function matrices can be matrices used to describe the small-signal relationship between the DC-side and AC-side electrical quantities of the photovoltaic unit.

[0039] Understandably, for impedance modeling of a single distributed photovoltaic (PV) system, the control circuit is mainly divided into a front-end DC circuit and a back-end AC circuit. The front-end DC circuit primarily consists of a DC boost circuit with PI control embedded in the MPPT algorithm, while the back-end inverter circuit mainly comprises voltage and current dual closed-loop control and a phase-locked loop (PLL) control section. The small-signal model can be calculated by constructing an equivalent small-signal circuit, referring to... Figure 3 , Figure 3 This is a schematic diagram of the small-signal circuit of the distributed photovoltaic inverter in the dq coordinate system in the second embodiment of the microgrid stability analysis method of this application. In the small-disturbance stability analysis, the difference between the control coordinate system and the system coordinate system caused by the phase-locked loop cannot be ignored. Therefore, the superscript 's' in the figure indicates the system coordinate system, and the superscript 'c' in the subsequent analysis indicates the control coordinate system. 'md' and 'mq' are the dq-axis components of the inverter modulation, respectively. Uppercase letters indicate the components during steady-state operation, and 'Δ' represents the small-disturbance analysis.

[0040] according to Figure 3 The small-signal circuit diagram shown yields the small-signal model of the inverter under small disturbances. Connecting these in parallel into a matrix equation, we can obtain:

[0041] Equation (1);

[0042] Equation (2);

[0043] Equation (3);

[0044] Equation (4);

[0045] Equation (5); Among them, P i P m K m K v G c Z RL1 Z Rc Z L2 All are vector matrices. To analyze the relationship between the inverter input and output, equations (1), (3), and (5) are first combined to obtain the inverter DC side current Δi. dc With grid-side current Δi2 s Grid-side voltage Δv pcc s Harmony and adjustment system Δm s The relationship between them:

[0046] Equation (6); In the formula, I is the identity matrix.

[0047] Furthermore, by combining equations (2), (3), (4) and (5) above, we can obtain the inverter DC-side voltage Δvdc and the grid-side current Δi2. s Grid-side voltage Δv pcc s Harmony and adjustment system Δm s The relationship between them is shown in equation (7):

[0048] Equation (7); Next, small-disturbance modeling is performed on the voltage and current dual closed-loop control of the inverter, based on... Figure 1 As shown in the control block diagram, the small-signal model of the inverter control circuit in the phase-locked loop control coordinate system is as shown in equations (8) and (9):

[0049] Equation (8);

[0050] Equation (9); In the above formula, h dc =k pdc +k idc / s represents the PI controller for the outer voltage loop, h i =k pi +k ii / s represents the transfer function of the inner-loop PI regulator. When analyzing small-disturbance stability, the inverter DC-side voltage v... dc and q-axis current reference value i 2qrefc The change in can be considered zero, therefore equations (8) and (9) are combined and rearranged into a matrix equation:

[0051] Equation (10); In phase-locked loop (PLL) control, the system coordinate system and the PLL coordinate system variables have the following relationship:

[0052] Equation (11); Therefore, when considering the dynamics of the phase-locked loop, the transformation relationship between the grid-connected point voltage in the system coordinate system and the control coordinate system is as follows:

[0053] Equation (12);

[0054] Equation (13); Equation (13) is the transfer function of the phase-locked loop when a small disturbance occurs. Next, the modulation index Δm will be... c and grid-side current Δi2 c Transformation from controller coordinate system to system coordinate system:

[0055] Equation (14);

[0056] Equation (15); Therefore, by substituting equations (14) and (15) into equation (10), the small-signal model of the inverter control circuit can be transformed from the control coordinate system to the system coordinate system:

[0057] Equation (16); Next, substituting equation (16) into equation (6) yields the inverter DC side current Δi. dc DC side voltage Δv dc Grid-side current Δi2 s and grid-side voltage Δv pcc s The transfer function matrix between them.

[0058]

[0059] Equation (17); Substituting equation (16) into equation (7) yields the inverter DC side voltage Δv. dc Grid-side current Δi2 s and grid-side voltage Δvpcc s The transfer function matrix between them.

[0060]

[0061] Equation (18); Next, we analyze the output impedance model of the DC side of the distributed photovoltaic system. Based on the relationship between the output current and output voltage of the photovoltaic array, the small-signal model under small disturbances can be obtained as follows:

[0062] Equation (19); Let y pv This is the coefficient between the output current and output voltage of the photovoltaic array in the small-signal model.

[0063] Based on the DC-side output impedance model of the photovoltaic system, an overall impedance model of the distributed photovoltaic system is constructed. To facilitate the establishment of this model, for the MPPT control algorithm, the nonlinear part during the maximum power point control process is ignored, and only the dynamic characteristics at the maximum power point are considered. Let the voltage corresponding to the maximum power point of the photovoltaic array be v. max According to the control strategy of the perturbation-observation method, v max With output current i pv The relationship is shown in the following formula:

[0064] Equation (20); Therefore, substituting equation (19) into equation (20) yields the mathematical model of MPPT control under small disturbances:

[0065] Equation (21); Similarly, y max This is the coefficient between the output voltage and output current at the maximum power point of the photovoltaic array in the small-signal model.

[0066] Next, based on the control strategy of the DC boost circuit, a model of the Boost circuit under small disturbances, as shown in equation (22), can be established, where D and I... L and V dc These represent the duty cycle of the Boost converter circuit and the inductor current i. L and inverter DC side voltage v dc The steady-state value.

[0067]

[0068] Equation (22); The control loop of the Boost converter is PI control, and its small-signal model is shown in equation (23):

[0069] Equation (23); In the formula, h B =k pB +k iB / s,k pB and k iB These are the PI control parameters for the Boost converter circuit.

[0070] Before solving for the impedance of the DC side of the distributed photovoltaic system, first transform equation (22) to the frequency domain coordinate system:

[0071] Equation (24); By combining equations (22), (23), and (24), the DC-side voltage Δv of the inverter can be obtained. dc With DC side current Δi dc The relationship is that the DC-side output impedance z of the distributed photovoltaic system is... dc .

[0072]

[0073] Equation (25); In the formula, λ = 1 - y pv y max Q = 1 - D.

[0074] Finally, the overall output impedance model of the distributed photovoltaic system on the AC side is solved. As the above analysis shows, the AC side impedance model of the distributed photovoltaic system is established in the dq synchronous rotating coordinate system. Therefore, it is necessary to first convert the newly established DC side impedance z... dc Convert to the form of a second-order matrix:

[0075] Equation (26);

[0076] Equation (27); Equation (17) represents the DC-side current Δi of the inverter. dc DC side voltage Δv dc Grid-side current Δi2 s and grid-side voltage Δv pcc s The transfer function matrix between them means that, by substituting equation (26) into equation (17), the variable Δi can be eliminated first. dc As shown in equation (27).

[0077] Equation (18) represents the DC-side voltage Δv of the inverter. dc Grid-side current Δi2 s and grid-side voltage Δv pcc s The transfer function matrix between them is used to obtain the grid-side current Δi2 by relating equation (18) and equation (27). s and grid-side voltage Δv pcc s The relationship between them, namely the output impedance Z of the AC side of the distributed photovoltaic system. pv :

[0078] Equation (28); In the formula, Mi and Ni (i=1,2,3) are different combinations of the vector matrices in the above analysis, as shown in formula (29):

[0079] Equation (29); Therefore, refer to Figure 4 , Figure 4 This is a block diagram of the AC-side impedance transfer function of a two-stage distributed photovoltaic system in the second embodiment of the microgrid stability analysis method of this application.

[0080] In this embodiment, small-interference modeling is performed on the front-end DC boost circuit, the voltage and current dual closed loop of the rear-end inverter, and the phase-locked loop included in the distributed photovoltaic unit to establish the small-signal model. Based on the small-signal model, the DC-side and AC-side transfer function matrices are combined to calculate the AC-side output impedance of a single distributed photovoltaic unit. Distinguishing between the system coordinate system and the control coordinate system eliminates phase errors and improves the reliability of analysis in high-proportion grid connection scenarios. By combining the AC and DC transfer function matrices, the AC-side output impedance of the entire unit is directly obtained, providing a reliable input for subsequent stability criteria. The small-signal model more closely reflects the actual photovoltaic control logic.

[0081] Based on the above embodiments of this application, in the third embodiment of this application, the same or similar content as the above embodiments can be referred to the above description, and will not be repeated hereafter. Based on this, please refer to... Figure 5 , Figure 5 This is a flowchart illustrating the third embodiment of the microgrid stability analysis method of this application. In this embodiment, step 30 includes: Step S301: Equivalently represent the microgrid as an inductive impedance with resistors and inductors connected in series, and equivalently represent the distributed photovoltaic unit as an equivalent circuit form with a controlled current source and an output impedance connected in parallel.

[0082] Step S302: Based on the equivalent circuit form, convert it to the same microgrid voltage level to form the Norton equivalent circuit of the distributed photovoltaic cluster.

[0083] It should be noted that, considering the oscillation mechanism after connection to a microgrid, for example, when a distributed photovoltaic power generation system is connected to a 10kV microgrid through a 380V / 10kV transformer, and taking into account the weak characteristics of the microgrid, the equivalent impedance of the grid in this application analysis is mainly the grid inductance L. g and grid resistance R g Transforming it to the dq synchronous rotating coordinate system yields:

[0084] Equation (30); Since distributed photovoltaic inverters are typical current-source inverters, they can be equivalently represented as a Norton circuit with a controlled current source in parallel with an impedance. Therefore, referring to... Figure 6 and Figure 7 , Figure 6 This is the Norton equivalent circuit diagram of the output impedance of the third embodiment of the microgrid stability analysis method of this application; Figure 7 This is a block diagram of the output current transfer function of the third embodiment of the microgrid stability analysis method of this application.

[0085] It is understandable that Δi pv To convert to the equivalent controlled current source of a 10kV distributed photovoltaic system, Z pv-10 To calculate the AC output impedance referred to the 10kV side, Δi 2d Z is the output current at the grid connection point of the distributed photovoltaic system. g For the grid-side equivalent impedance, v g This is the grid-side voltage. (By...) Figure 7 The grid connection point current can be obtained:

[0086] Equation (31); Therefore, the ratio of the grid impedance to the output impedance of the distributed photovoltaic system in the above formula is defined as the minimum loop gain of the grid-connected system:

[0087] Equation (32); Furthermore, when analyzing the stability of a distributed photovoltaic grid-connected system using the generalized Nyquist criterion, the system is considered stable when the number of poles in the right half-plane of the minimum loop gain L equals the number of counterclockwise rotations of the trajectory of the eigenvalue around the complex plane eigenpoint (-1, j0). Further discussion reveals that when the distributed photovoltaic system connected to an ideal grid can maintain stability, Z... pv-10There are no zeros in the right half-plane, meaning the minimum loop gain L also has no poles in the right half-plane. Since weak grids are generally inductive, the minimum loop gain of a distributed photovoltaic system connected to an inductive grid in this case also does not have poles in the right half-plane. Therefore, the stability criterion can be simplified to whether the trajectories of the two eigenvalues ​​of L enclose the point (-1, j0). The system is in a stable state when neither eigenvalue encloses the point (-1, j0).

[0088] For the stability criterion of distributed photovoltaic (PV) clusters, when a distributed PV cluster is connected to a microgrid, each distributed PV unit is connected in parallel to a 10kV busbar via a transformer. Where, v pcc Let i be the voltage at point PCC. pcc i represents the total grid-connected current of the distributed photovoltaic cluster. 2di (i=1, 2, ..., n) represents the grid-connected output current of each photovoltaic unit in the distributed photovoltaic cluster. To make the analysis more closely resemble actual conditions, the system parameters of different photovoltaic power generation units in the distributed photovoltaic cluster analyzed in this study are different.

[0089] As derived in the previous two sections, the AC output impedance of a distributed photovoltaic system depends only on its own system parameters and is not affected by the grid side or other parallel units. Therefore, according to equation (28), the AC output impedance of each distributed photovoltaic unit can be calculated separately, and after converting them all to the 10kV side, as shown below. Figure 8 As shown, Figure 8 This is an equivalent schematic diagram of a distributed photovoltaic cluster connected to a weak power grid, according to the third embodiment of the microgrid stability analysis method of this application. Wherein, Δi pvi (i=1,2,…,n) represents the equivalent current source of each photovoltaic unit in the distributed photovoltaic cluster, Y pvi (i=1, 2, ..., n) represents the AC-side output admittance of each distributed photovoltaic system. Admittance is used here to account for the parallel connection of distributed photovoltaic systems, facilitating subsequent calculations and analysis. The grid admittance Y... g =1 / Z g ,Δi 2di (i=1,2,…,n) represents the output current of the distributed photovoltaic cluster.

[0090] It is understandable that the output current Δi of the distributed photovoltaic system i 2di As shown in the following formula:

[0091] Equation (33); Therefore, according to the superposition theorem, the voltage Δv at the grid connection point of the distributed photovoltaic cluster is... pcc As shown in equation (34):

[0092] Equation (34); In the formula, Yg is the equivalent admittance of the power grid. Therefore, substituting equation (34) into equation (33) yields:

[0093] Equation (35); As can be seen from the above equation, the output current of the distributed photovoltaic system i is not only related to its own equivalent current source Δi pvi Equivalent admittance Y pvi Grid admittance Y g and grid voltage v g Regarding the equivalent current source Δi of other distributed photovoltaic units in the cluster... pvj and equivalent admittance Y pvj It will also affect the output current of the distributed photovoltaic system i.

[0094] Therefore, it can be known that the output current Δi of unit i in the distributed photovoltaic cluster is... 2di It consists of two parts, the first of which can be called its own output current Δi 2diu The magnitude of its value is determined by the distributed photovoltaic cluster as a whole; the second part is called the interactive current Δi. 2div Its value is determined by the interaction of the output admittance within the distributed photovoltaic cluster, as shown in the following formula:

[0095] Equation (36); Now, the distributed photovoltaic cluster is divided. First, when the system parameters of the photovoltaic power generation units in the distributed photovoltaic cluster are the same, it can be seen from equation (36) that Δi 2d1v =Δi 2d2v =…=Δi 2dnv =0, meaning the interaction current between units within the distributed photovoltaic cluster is zero, and the total output current at the grid connection point is equal to the output current Δi of each distributed photovoltaic unit itself. 2diu The sum of , therefore, equation (36) is rewritten as equation (37).

[0096]

[0097] Equation (37); As can be seen from the above analysis, when the parameters of each power generation unit in a distributed photovoltaic cluster are the same, only the output current Δi of each unit is affected. 2diu The stability of the entire system can be determined by judging its stability. From equation (37), we can obtain that the equivalent current source Δi of the distributed photovoltaic system i is... pviIt is stable, meaning that the distributed photovoltaic system i is stable when connected to a strong power grid (without considering grid admittance). Secondly, the generalized Nyquist criterion is used to determine the ratio of the sum of the output admittances of all units in the distributed photovoltaic cluster to the equivalent admittance of the grid. When both of the above conditions are met, the distributed photovoltaic cluster grid-connected system can be determined to be in a stable state.

[0098] When the parameters of each power generation unit in a distributed photovoltaic cluster are different, it can be seen from equation (36) that there must be an interactive current between the photovoltaic units. The influence of the interactive current must be considered when judging the stability of the system. Furthermore, in the interactive current, there is a relationship with Δi pvi The relevant components can also be considered as stable components, therefore the remaining components can be rewritten as:

[0099] Equation (38); As can be seen from equation (38), when judging the stability of the interactive current, it is necessary to first determine the ratio of the grid equivalent admittance to the sum of the output admittances of all units in the distributed photovoltaic cluster, and secondly, it is necessary to determine the ratio of the sum of the output admittances of the remaining units in the distributed photovoltaic cluster to the output admittance of the distributed photovoltaic system i. When both of the above conditions are met, it can be determined that the grid-connected system of the distributed photovoltaic cluster is in a stable state.

[0100] In summary, to address the stability issues of distributed photovoltaic (PV) clusters connected to weak power grids, the following three stability criteria must be met: 1. Each PV system within the distributed PV cluster can operate stably when connected to a strong power grid; 2. The ratio of the grid's equivalent admittance to the sum of the AC-side output admittances of each unit within the distributed PV cluster satisfies the generalized Nyquist stability criterion; 3. The ratio of the sum of the equivalent admittances of the remaining units within the distributed PV cluster to the output admittance of distributed PV i (i=1, 2, ..., n) satisfies the generalized Nyquist stability criterion. A distributed PV cluster grid-connected system that simultaneously satisfies all three stability criteria can be considered to be in a stable state. If any one of the three stability criteria is not met, the distributed PV cluster grid-connected system is considered to be at risk of instability.

[0101] This application establishes an AC-side output impedance model for a single distributed photovoltaic power generation unit in the dq synchronous rotating coordinate system, further derives the grid-connected Norton equivalent circuit of a distributed photovoltaic cluster system, and proposes a stability analysis applicable to the connection of a distributed photovoltaic cluster system to a microgrid based on the generalized Nyquist criterion.

[0102] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent scope of this application.

[0103] This application also provides a microgrid stability analysis device; please refer to [reference needed]. Figure 9 The microgrid stability analysis device includes: The data acquisition module 10 is used to acquire the operating data of the microgrid and the distributed photovoltaic cluster, wherein the distributed photovoltaic cluster is composed of multiple distributed photovoltaic units; Model building module 20 is used to establish a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system based on the running data, and to solve the small-signal model to obtain the AC side output impedance; The equivalent calculation module 30 is used to construct the Norton equivalent circuit for the distributed photovoltaic cluster to access the microgrid based on the AC side output impedance of each distributed photovoltaic unit in the photovoltaic cluster. The state judgment module 40 is used to perform sequential verification of the stability of a single distributed photovoltaic grid connection, the stability of the cluster total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units on the Norton equivalent circuit according to the generalized Nyquist criterion, so as to obtain the stability state of the microgrid.

[0104] The microgrid stability analysis device provided in this application, employing the microgrid stability analysis method in the above embodiments, can solve the technical problem of unstable operation analysis in microgrids with a high proportion of photovoltaic access. Compared with the prior art, the beneficial effects of the microgrid stability analysis device provided in this application are the same as those of the microgrid stability analysis method provided in the above embodiments, and other technical features in the microgrid stability analysis device are the same as those disclosed in the methods of the above embodiments, and will not be repeated here.

[0105] This application provides a microgrid stability analysis device, which includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, which are executed by the at least one processor to enable the at least one processor to perform the microgrid stability analysis method in Embodiment 1 above.

[0106] The following is for reference. Figure 10 The diagram illustrates a structural schematic of a microgrid stability analysis device suitable for implementing embodiments of this application. The microgrid stability analysis device in these embodiments may include, but is not limited to, mobile terminals such as mobile phones, laptops, digital broadcast receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Description), PMPs (Portable Media Players), and in-vehicle terminals (e.g., in-vehicle navigation terminals), as well as fixed terminals such as digital TVs and desktop computers. Figure 10 The microgrid stability analysis device shown is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of this application.

[0107] like Figure 10 As shown, the microgrid stability analysis device may include a processing unit 1001 (e.g., a central processing unit, a graphics processing unit, etc.), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 1002 or a program loaded from a storage device 1003 into a random access memory (RAM) 1004. The RAM 1004 also stores various programs and data required for the operation of the microgrid stability analysis device. The processing unit 1001, ROM 1002, and RAM 1004 are interconnected via a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Typically, the following systems can be connected to the I / O interface 1006: input devices 1007 including, for example, a touchscreen, touchpad, keyboard, mouse, image sensor, microphone, accelerometer, gyroscope, etc.; output devices 1008 including, for example, a liquid crystal display (LCD), speaker, vibrator, etc.; storage devices 1003 including, for example, magnetic tape, hard disk, etc.; and communication devices 1009. Communication device 1009 allows the microgrid stability analysis device to communicate wirelessly or wiredly with other devices to exchange data. Although the figure shows a microgrid stability analysis device with various systems, it should be understood that implementation or possession of all the systems shown is not required. More or fewer systems may be implemented alternatively.

[0108] Specifically, according to the embodiments disclosed in this application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments disclosed in this application include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device, or installed from storage device 1003, or installed from ROM 1002. When the computer program is executed by processing device 1001, it performs the functions defined in the methods of the embodiments disclosed in this application.

[0109] The microgrid stability analysis device provided in this application adopts the microgrid stability analysis method in the above embodiments. Compared with the prior art, the beneficial effects of the microgrid stability analysis device provided in this application are the same as the beneficial effects of the microgrid stability analysis method provided in the above embodiments. Moreover, other technical features of the microgrid stability analysis device are the same as the features disclosed in the method of the previous embodiment, and will not be repeated here.

[0110] It should be understood that the various parts disclosed in this application can be implemented using hardware, software, firmware, or a combination thereof. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0111] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0112] This application provides a computer-readable storage medium having computer-readable program instructions (i.e., a computer program) stored thereon, which are used to execute the microgrid stability analysis method in the above embodiments.

[0113] The computer-readable storage medium provided in this application may be, for example, a USB flash drive, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to: electrical connections having one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, system, or device. The program code contained on the computer-readable storage medium may be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0114] The aforementioned computer-readable storage medium may be included in the microgrid stability analysis device; or it may exist independently and not be assembled into the microgrid stability analysis device.

[0115] Computer program code for performing the operations of this application can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a Local Area Network (LAN) or a Wide Area Network (WAN)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0116] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0117] The modules described in the embodiments of this application can be implemented in software or hardware. The names of the modules do not necessarily limit the functionality of the unit itself.

[0118] The readable storage medium provided in this application is a computer-readable storage medium that stores computer-readable program instructions (i.e., a computer program) for executing the above-described microgrid stability analysis method, which can solve the technical problem of unstable operation analysis in microgrids with a high proportion of photovoltaic access. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided in this application are the same as the beneficial effects of the microgrid stability analysis method provided in the above embodiments, and will not be repeated here.

[0119] The above description is only a part of the embodiments of this application and does not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. A microgrid stability analysis method, characterized in that, The microgrid stability analysis method includes the following steps: The system acquires operational data from microgrids and distributed photovoltaic clusters, wherein the distributed photovoltaic clusters consist of multiple distributed photovoltaic units. Based on the aforementioned operational data, a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system is established, and the AC side output impedance is obtained by solving the small-signal model. The Norton equivalent circuit for connecting the distributed photovoltaic cluster to the microgrid is constructed based on the AC output impedance of each distributed photovoltaic unit in the photovoltaic cluster. Based on the generalized Nyquist criterion, the stability of the microgrid is obtained by sequentially verifying the stability of a single distributed photovoltaic grid connection, the stability of the cluster total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units.

2. The microgrid stability analysis method as described in claim 1, characterized in that, The step of establishing a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system based on the operating data, and solving the small-signal model to obtain the AC side output impedance, includes: Small disturbance modeling is performed on the front-end DC boost circuit, the voltage and current dual closed loop of the back-end inverter, and the phase-locked loop contained in the distributed photovoltaic unit to establish the small signal model. Based on the small-signal model, the DC-side and AC-side transfer function matrices are constructed, and the AC-side output impedance of a single distributed photovoltaic unit is calculated based on the DC-side and AC-side transfer function matrices.

3. The microgrid stability analysis method as described in claim 2, characterized in that, The step of constructing the Norton equivalent circuit for connecting the distributed photovoltaic cluster to the microgrid based on the AC-side output impedance of each distributed photovoltaic unit in the photovoltaic cluster includes: The microgrid is equivalent to an inductive impedance with a resistor and an inductor connected in series, and the distributed photovoltaic unit is equivalent to an equivalent circuit form with a controlled current source and an output impedance connected in parallel. The Norton equivalent circuit of the distributed photovoltaic cluster is formed by converting the equivalent circuit form to the same microgrid voltage level.

4. The microgrid stability analysis method as described in claim 1, characterized in that, The steps of sequentially performing single distributed photovoltaic grid connection stability verification on the Norton equivalent circuit include: Determine whether the AC-side output impedance of a single distributed photovoltaic unit has a right-half-plane zero. When there is no zero point in the right half-plane, the microgrid is determined to be in a stable state.

5. The microgrid stability analysis method as described in claim 1, characterized in that, The steps for verifying the stability of the Norton equivalent circuit by matching the cluster total admittance with the grid admittance include: Calculate the first ratio between the equivalent admittance of the microgrid and the sum of the output admittances of each unit in the photovoltaic cluster; If the number of loops in the eigenvalue trajectory of the first ratio does not encircle the feature points of the complex plane is verified by the generalized Nyquist criterion, the microgrid is determined to be in a stable state.

6. The microgrid stability analysis method as described in claim 1, characterized in that, The steps for performing inter-cell admittance interaction stability verification on the Norton equivalent circuit include: For any distributed photovoltaic unit within the distributed photovoltaic cluster, calculate the second ratio of the sum of the output admittances of the remaining distributed photovoltaic units to the output admittance of that unit; If the number of loops in the eigenvalue trajectory of the second ratio does not encircle the feature points of the complex plane is verified by the generalized Nyquist criterion, the microgrid is determined to be in a stable state.

7. The microgrid stability analysis method according to any one of claims 4 to 6, characterized in that, After the step of performing sequential verifications on the Norton equivalent circuit based on the generalized Nyquist criterion to determine the stability of a single distributed photovoltaic grid connection, the stability of the cluster total admittance matching with the grid admittance, and the stability of admittance interaction between cluster units, to obtain the microgrid stability state, the method further includes: If any one of the following checks fails in the Norton equivalent circuit's sequential verification of the stability of a single distributed photovoltaic grid connection, the stability of the cluster's total admittance matching with the grid admittance, and the stability of admittance interaction between cluster units, the microgrid is determined to be in an unstable state.

8. A microgrid stability analysis device, characterized in that, The device includes: The data acquisition module is used to acquire the operating data of the microgrid and the distributed photovoltaic cluster, which is composed of multiple distributed photovoltaic units; The model building module is used to establish a small-signal model of a single distributed photovoltaic unit in the dq synchronous rotating coordinate system based on the running data, and to solve the small-signal model to obtain the AC side output impedance. The equivalent calculation module is used to construct the Norton equivalent circuit for the distributed photovoltaic cluster to access the microgrid based on the AC side output impedance of each distributed photovoltaic unit in the photovoltaic cluster. The state judgment module is used to perform sequential verification of the stability of a single distributed photovoltaic grid connection, the stability of the cluster total admittance matching with the grid admittance, and the stability of the admittance interaction between cluster units on the Norton equivalent circuit according to the generalized Nyquist criterion, so as to obtain the stability state of the microgrid.

9. A microgrid stability analysis device, characterized in that, The microgrid stability analysis device includes: a memory, a processor, and a microgrid stability analysis processing program stored in the memory and executable on the processor. When the microgrid stability analysis processing program is executed by the processor, it implements the steps of the microgrid stability analysis method as described in any one of claims 1 to 7.

10. A storage medium, characterized in that, The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, it implements the steps of the microgrid stability analysis method as described in any one of claims 1 to 7.

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