Impedance ratio sensing-based multi-grid-connected inverter instability source positioning analysis method and device

Abstract

The invention discloses a multi-grid-connected inverter instability source positioning analysis method and device based on impedance ratio perception, and the method comprises the steps: obtaining the output impedance of a grid-connected inverter and the input impedance of a power grid side through a multi-sine wave injection impedance measurement technology under a dq system in combination with an online impedance measurement strategy of power adaptive stable operation; a multi-grid-connected inverter parameter model is constructed; node equivalent impedance aggregation is carried out through an impedance model obtained through measurement, and node stability analysis based on the impedance ratio is achieved by dividing the two ends of each inverter node into a source sub-module and a load sub-module. According to the method provided by the invention, efficient online positioning of the instability source of the multi-machine system can be quickly and accurately realized, so that the stability of the subsequent system is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of stability of new energy grid-connected inverter systems, and in particular relates to a method and device for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio sensing. Background Art

[0002] With the continuous development of new energy, grid-connected inverters, as an efficient power electronic interface device, have been widely used in new power systems. However, due to the long-distance and large-scale transmission characteristics of renewable energy power generation, there is a non-negligible line impedance between the output port of the grid-connected inverter and the grid. This interaction between the inverter and the grid impedance leads to system oscillation instability, which significantly affects the stable operation of the renewable energy grid-connected system.

[0003] Impedance stability criterion plays a key role in the stability analysis of grid-connected inverters and power grid cascades. In a single-machine grid-connected inverter system, the impedance analysis method divides the system into source submodules and load submodules, and then calculates the ratio of the grid-side input impedance to the inverter-side output impedance to verify whether it meets the Nyquist stability criterion, thereby evaluating the system stability. The core of this analysis method is to accurately obtain the port impedance characteristics of the inverter and the power grid.

[0004] At present, the acquisition of impedance mainly relies on two methods: analytical modeling and impedance measurement. Although the analytical modeling method is feasible in theory, it requires a deep understanding of the internal structural parameters of the inverter. However, since the actual commercial inverter system is often regarded as a "black box system", its internal parameters are difficult to obtain directly, so it faces great challenges in actual operation. Therefore, the impedance measurement method is more commonly used to obtain the required impedance information due to its practicality and operability.

[0005] However, in the scenario of a centralized grid-connected power station with renewable energy, when the system is expanded from a single-machine mode to a large-scale grid-connected system containing multiple inverters, the system instability mechanism becomes complicated, which directly increases the difficulty of instability analysis using traditional impedance analysis methods.

[0006] In response to the instability problem caused by the interaction between multiple grid-connected inverters and the power grid, this patent proposes an instability strategy based on impedance ratio perception. This strategy uses power adaptive stabilization operation technology to achieve effective acquisition of port impedance when the multi-machine system is online and not shut down. Subsequently, based on the measured impedance model, the node equivalent impedance is aggregated. By clearly dividing each inverter node into source submodules and load submodules, a node stability analysis based on impedance ratio is implemented to accurately identify the main instability sources and potential instability sources. Summary of the invention

[0007] The purpose of the present invention is to provide a method and device for locating and analyzing the instability source of multiple grid-connected inverters based on impedance ratio perception. The method can quickly and accurately realize efficient online positioning of the instability source of a multi-machine system, so as to provide an effective reference for subsequent system stabilization adjustment.

[0008] In order to achieve the first objective of the present invention, a technical solution is provided as follows: a method for locating instability sources of multiple grid-connected inverters based on impedance ratio sensing, comprising:

[0009] Step 1: Based on the online impedance measurement strategy of power adaptive stabilization operation, the inverter and grid port impedance acquisition is realized when the multi-grid-connected inverter system is online and does not stop. The inverter impedance and grid-side input impedance are expressed in the form of qq-axis impedance;

[0010] Step 2: performing equivalent impedance aggregation of multiple grid-connected inverter nodes based on the impedance model measured in step 1, and dividing the two ends of each inverter node into a source submodule and a load submodule to obtain the impedance ratio of each inverter node of the multi-inverter system;

[0011] Step 3, draw a Nyquist curve of the node impedance ratio obtained in step 2;

[0012] Step 4: judging the stability of the grid-connected current at the node where the inverter is located according to whether the Nyquist curve of the node impedance ratio drawn in step 3 surrounds (-1, j0);

[0013] Step 5, repeating step 1 to step 4 until the stability result of the grid-connected current of the inverter node of the multi-grid-connected inverter system is obtained;

[0014] Step 6: According to the node current stability analysis results in step 5, based on the basic circuit principles, the nodes of the multi-grid-connected inverter are divided into main unstable nodes, stable nodes and potential unstable nodes.

[0015] The present invention uses a multi-sine wave injection impedance measurement technology under a dq system combined with an online impedance measurement strategy of power adaptive stabilization operation to obtain the output impedance of the grid-connected inverter and the input impedance of the grid side, so as to construct a parameter model of multiple grid-connected inverters; and performs node equivalent impedance aggregation through the impedance model obtained by measurement, and realizes node stability analysis based on impedance ratio by dividing the two ends of each inverter node into a source submodule and a load submodule, thereby locating the main unstable nodes and potential unstable nodes, providing an effective reference for subsequent system optimization and stabilization strategy.

[0016] Specifically, the specific process of the online impedance measurement strategy for power adaptive stabilization operation is as follows:

[0017] Step 1-1: Bus-level stability monitoring of new energy systems;

[0018] Step 1-2: divide the new energy multi-grid-connected inverter system into two inverter systems, A and B, with similar capacities according to power levels;

[0019] Step 1-3, adaptively reduce the operating conditions of the inverter system of group A until the new energy multi-grid-connected inverter system becomes stable again;

[0020] Step 1-4: Under the working condition of step 1-3, the inverter impedance of group B is measured online based on the multi-sine dq impedance measurement technology;

[0021] Step 1-5, restore the inverter working condition of group A. Similarly, adaptively reduce the operating condition of the inverter system of group B, and measure the inverter working condition of group A according to the process of steps 1-1 to 1-4;

[0022] Specifically, the specific process of the multi-sine wave injection impedance detection method under the dq system is as follows:

[0023] Step 2-1, connecting the grid-connected inverter in series with the voltage disturbance source;

[0024] Step 2-2, injecting two sets of linearly independent multi-sinusoidal voltage disturbance signals into each frequency point in the dq system through the disturbance source, and recording the voltage and current responses of the inverter and the grid side at each frequency point respectively;

[0025] Step 2-3, according to the two groups of voltage and current responses, calculate the dq impedance value of the converter and the power grid at each frequency point;

[0026] Step 2-4: Perform transfer function fitting on the dq impedance values ​​at each frequency point to obtain the dq impedance expression of the grid-connected inverter output impedance and the grid-side input impedance.

[0027] Specifically, the expression of the multi-sinusoidal voltage disturbance signal is as follows:

[0028]

[0029] Among them, f k represents the frequency of the kth frequency component of the multi-sine wave disturbance, A k represents the amplitude of the kth frequency component of the multi-sine wave disturbance, represents the phase of the kth frequency component of the multi-sine wave disturbance, and N represents the number of sine waves in the multi-sine wave disturbance.

[0030] Specifically, the equivalent impedance aggregation process of multiple grid-connected inverter nodes is as follows:

[0031] Step 3-1, determine the equivalent aggregate component type, equate the grid-connected inverter component to a Y-type component (Norton circuit), and equate the grid component to a Z-type component (Thevenin circuit);

[0032] Step 3-2, determine the equivalent aggregation principle, connect Y-type components in parallel with Y-type components to form a new Y-type component, and connect Z-type components in parallel with Y-type components to form a new Z-type component;

[0033] Step 3-3: According to the aggregation principle of step 3-2, impedance aggregation processes are performed from left to right and from right to left on any node in the multi-inverter system to obtain the aggregated admittance Y on the right side of the node and the aggregated impedance Z on the left side;

[0034] Step 3-4: Based on the node aggregate impedance result obtained in step 3-3, construct the corresponding equivalent circuit impedance equivalent circuit at any node of the multi-inverter system.

[0035] Specifically, the expression of the impedance equivalent circuit is as follows:

[0036]

[0037] Among them I K is the node entry current, is the aggregate impedance on the left side of the node, is the equivalent voltage source on the left side of the node, is the equivalent current source on the right side of the node, Represents the aggregate admittance on the right side of the node.

[0038] In order to achieve the second purpose of the present invention, the technical solution provided is as follows: a device for locating and analyzing the instability source of multiple grid-connected inverters based on impedance ratio perception, comprising a computer memory, a computer processor, and a computer program stored in the computer memory and executable on the computer processor, wherein the processor executes the above-mentioned method for locating and analyzing the instability source of multiple grid-connected inverters based on impedance ratio perception when executing the computer program.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The multi-sine based dq impedance measurement technology is used to avoid the complex calculation of the theoretical analytical model, which is suitable for occasions where key information such as the grid-connected converter structure, parameters, and control method are unknown;

[0041] The stable operation impedance measurement method with power adaptive strategy can realize the online measurement of the port impedance of the multi-machine unstable system without stopping the system.

[0042] The proposed impedance ratio-aware instability source location strategy can realize efficient online location of instability sources in multi-machine systems and has strong universality and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The Norton equivalent model of the inverter system provided in this embodiment;

[0044] Figure 2 A flow chart of a method for locating instability sources of multiple grid-connected inverters based on impedance ratio sensing provided in this embodiment;

[0045] Figure 3 A flow chart of the online impedance measurement strategy for power adaptive stabilization operation provided in this embodiment;

[0046] Figure 4 A schematic diagram of the impedance measurement principle in the dq system provided in this embodiment;

[0047] Figure 5 Flowchart of component aggregation of any node of the multi-inverter system provided for this embodiment: (a) from left to right (b) from right to left;

[0048] Figure 6 Impedance equivalent circuit diagram of a node of a multi-inverter system provided in this embodiment DETAILED DESCRIPTION

[0049] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] like Figure 1 As shown, a method for analyzing the sensitivity of stability parameters of a grid-connected converter based on impedance measurement is provided in this embodiment, and the specific process is as follows:

[0051] Step 1: Based on the online impedance measurement strategy of power adaptive stabilization operation, the inverter and grid port impedance acquisition is realized when the multi-grid-connected inverter system is online and does not stop. The inverter impedance and grid-side input impedance are expressed in the form of qq-axis impedance;

[0052] Going a step further, Figure 4As shown in the figure, based on the impedance measurement principle in the dq system, the converter is connected to the grid in series with the voltage disturbance source. First, while keeping the q-axis disturbance at 0, a disturbance sinusoidal signal is generated on the d-axis, and the corresponding voltage and current response in the dq system is measured. Then, while keeping the d-axis disturbance at 0, a second disturbance is injected into the q-axis, and the above process is repeated, thereby obtaining two groups of response signals in the dq system. The first group is [v d1 ,v q1 ]、[v gd1 ,v gq1 ] and [i d1 ,i q1 The second group is [v d2 ,v q2 ]、[v gd2 ,v gq2 ] and [i d2 ,i q2 ]. Then the inverter impedance Z l With grid impedance Z g There are the following expressions.

[0053] Step 2: Based on the impedance model measured in step 1, perform equivalent impedance aggregation of multiple grid-connected inverter nodes, and divide the two ends of each inverter node into a source submodule and a load submodule to obtain the impedance ratio of each inverter node in the multi-inverter system.

[0054] Furthermore, any node in the multi-inverter system performs impedance aggregation from left to right and from right to left as follows: Figure 5 (a) and (b) show:

[0055] Among them Figure 5 In (a), step 1 is the Norton circuit With line impedance Z K Aggregate to (in Represents slave node N K+1 The equivalent Norton circuit looking from the right side to the left side, Representative node N K Norton circuit on the left), step 2 is With node N K The inverter GCI#K below is aggregated into

[0056] exist Figure 5 In (b), step 1 means With line impedance Z K Aggregation (Among them Representative node N K Thevenin circuit on the right. Represents slave node N K-1The equivalent Thevenin circuit looking from the left side to the right side). Step 2 means Aggregated with inverter GCI#K

[0057] Furthermore, based on the impedance analysis principle, the two ends of each inverter node are divided into source submodules and load submodules, and the left aggregate admittance Y and the right aggregate impedance Z of the obtained node are used to construct the following Figure 6 (a) and (b) show the equivalent circuits, where I K is the node entry current, is the aggregate impedance on the left side of the node, is the equivalent voltage source on the left side of the node, is the equivalent current source on the right side of the node, Represents the aggregate admittance on the right side of the node.

[0058]

[0059] Step 3, draw a Nyquist curve of the node impedance ratio obtained in step 2;

[0060] Step 4: judging the stability of the grid-connected current at the node where the inverter is located according to whether the Nyquist curve of the node impedance ratio drawn in step 3 surrounds (-1, j0);

[0061] Step 5: Repeat step 1 to step 4 until the stability results of the grid-connected currents of all inverter nodes of the multi-grid-connected inverter system are obtained;

[0062] Step 6: According to the node current stability analysis results in step 5, based on the basic circuit principles, the nodes of the multi-grid-connected inverter are divided into main unstable nodes, stable nodes and potential unstable nodes.

[0063] Furthermore, the classification of instability types at each node of the multi-inverter system is based on Kirchhoff’s current law, e.g. Figure 6 (a) shown in which I K For node N K The grid current on the right side, I K+1 For node N K+1 The current on the left side (its stability can be judged in the same way), I' K N K At the inverter port current, from formula (6), we can know that I' K is the difference between the two currents. The three currents may have the following relationship:

[0064] (1) When the current I K and I K+1 are stable, so I' K Stable, that is, the inverter GCI#K at this node is stable.

[0065] (2) When I K Unstable, I K+1 Stable, the difference between unstable current and stable current is also unstable, so I' K Unstable, that is, the inverter GCI#1 of this node is unstable and is recorded as having the main instability risk source.

[0066] (3) When I K+1 When unstable, the current I of the previous node K It is also bound to be affected by the unstable current I K+1 The influence of I' K It is also unstable. At this time, the current I' K The stability of the inverter cannot be determined, so the inverter is marked as a potential source of instability risk.

[0067] This embodiment also provides an apparatus for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception, comprising a computer memory, a computer processor, and a computer program stored in the computer memory and executable on the computer processor. When the processor executes the computer program, the method for locating instability sources of multiple grid-connected inverters based on impedance ratio perception provided in the above embodiment is executed.

[0068] In addition, the terms "upper", "lower", "inner", "outer", "front", "rear" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. Unless otherwise specifically stated, the relative steps, numerical expressions and values ​​of the components and steps described in these embodiments do not limit the scope of the present invention.

[0069] Of course, the above description is only a specific embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. All equivalent changes or modifications made according to the structure, characteristics and principles described in the patent application scope of the present invention should be included in the patent application scope of the present invention.

[0070] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above-described embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-described embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for locating instability sources of multiple grid-connected inverters based on impedance ratio perception, characterized in that: include: Step 1: Based on the online impedance measurement strategy of power adaptive stabilization operation, the impedance of the inverter and the grid port is obtained when the multi-grid-connected inverter system is online and not shut down; the inverter impedance and the grid-side input impedance are expressed in the form of qq-axis impedance; Step 2: performing equivalent impedance aggregation of multiple grid-connected inverter nodes based on the impedance model measured in step 1, and dividing the two ends of each inverter node into a source submodule and a load submodule to obtain the impedance ratio of each inverter node of the multi-inverter system; Step 3, draw a Nyquist curve of the node impedance ratio obtained in step 2; Step 4: judging the stability of the grid-connected current at the node where the inverter is located according to whether the Nyquist curve of the node impedance ratio drawn in step 3 surrounds (-1, j0); Step 5, repeating step 1 to step 4 until the stability result of the grid-connected current of the inverter node of the multi-grid-connected inverter system is obtained; Step 6: According to the node current stability analysis results in step 5, based on the basic circuit principles, the nodes of the multi-grid-connected inverter are divided into main unstable nodes, stable nodes and potential unstable nodes.

2. The method for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception according to claim 1 is characterized in that: In step 1, the specific process of the online impedance measurement strategy based on power adaptive stabilization operation is as follows: Step 1-1: Bus-level stability monitoring of new energy systems; Step 1-2: divide the new energy multi-grid-connected inverter system into two inverter systems, A and B, with similar capacities according to power levels; Step 1-3, adaptively reduce the operating conditions of the inverter system of group A until the new energy multi-grid-connected inverter system becomes stable again; Step 1-4: Under the working condition of step 1-3, the inverter impedance of group B is measured online based on the multi-sine dq impedance measurement technology; Step 1-5, restore the inverter working condition of group A. Similarly, adaptively reduce the operating condition of the inverter system of group B, and measure the inverter working condition of group A according to the process of steps 1-1 to 1-4.

3. The method for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception according to claim 2 is characterized in that: The specific process of multi-sine dq impedance measurement technology is as follows: Step 2-1, connecting the grid-connected inverter in series with the voltage disturbance source; Step 2-2, injecting two sets of linearly independent multi-sinusoidal voltage disturbance signals into each frequency point in the dq system through the disturbance source, and recording the voltage and current responses of the inverter and the grid side at each frequency point respectively; Step 2-3, according to the two groups of voltage and current responses, calculate the dq impedance value of the converter and the power grid at each frequency point; Based on the impedance measurement principle in the dq system, the converter is connected to the grid in series with the voltage disturbance source. First, a disturbance sinusoidal signal is generated on the d-axis while keeping the q-axis disturbance at 0, and the corresponding voltage and current response in the dq system is measured. Then, a second disturbance is injected into the q-axis while keeping the d-axis disturbance at 0. The above process is repeated to obtain two groups of response signals in the dq system. The first group is [v d1 ,v q1 ]、[v gd1 ,v gq1 ] and [i d1 ,i q1 The second group is [v d2 ,v q2 ]、[v gd2 ,v gq2 ] and [i d2 ,i q2 ]. Then the inverter impedance Z l With grid impedance Z g There are the following expressions. Therefore, the inverter impedance Z l With grid impedance Z g It can be calculated as follows: Step 2-4: Perform transfer function fitting on the dq impedance values ​​at each frequency point to obtain the dq impedance expression of the grid-connected inverter output impedance and the grid-side input impedance.

4. The method for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception according to claim 3 is characterized in that: The expression of the multi-sinusoidal voltage disturbance signal is as follows: Among them, f k represents the frequency of the kth frequency component of the multi-sine wave disturbance, A k represents the amplitude of the kth frequency component of the multi-sine wave disturbance, φ k represents the phase of the kth frequency component of the multi-sine wave disturbance, and N represents the number of sine waves in the multi-sine wave disturbance.

5. The method for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception according to claim 1 is characterized in that: The equivalent impedance aggregation process of multiple grid-connected inverter nodes is as follows: Step 3-1, determine the equivalent aggregate component type, and equate the grid-connected inverter component to a Y-type component, i.e., a Norton circuit, and the grid component to a Z-type component, i.e., a Thevenin circuit; Step 3-2, determine the equivalent aggregation principle, connect Y-type components in parallel with Y-type components to form a new Y-type component, and connect Z-type components in parallel with Y-type components to form a new Z-type component; Step 3-3: According to the aggregation principle of step 3-2, impedance aggregation processes are performed from left to right and from right to left on any node in the multi-inverter system to obtain the aggregated admittance Y on the right side of the node and the aggregated impedance Z on the left side; Step 3-4: Based on the node aggregate impedance result obtained in step 3-3, construct an equivalent circuit of the impedance at any node of the corresponding equivalent circuit multi-inverter system.

6. The method for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception according to claim 5 is characterized in that: The expression of the equivalent circuit is as follows: Among them I K is the node entry current, is the aggregate impedance on the left side of the node, is the equivalent voltage source on the left side of the node, is the equivalent current source on the right side of the node, Represents the aggregate admittance on the right side of the node.

7. A device for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception, comprising a computer memory, a computer processor, and a computer program stored in the computer memory and executable on the computer processor, characterized in that: When the processor executes the computer program, the method for locating and analyzing instability sources of multiple grid-connected inverters based on impedance ratio perception is performed as described in any one of claims 1 to 6.

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