Small disturbance stability estimation method for grid-following type and grid-constructing type series-parallel grid-connected converters

Abstract

The invention provides a small disturbance stability estimation method for a grid-following type and grid-constructing type hybrid grid-connected converter, and relates to the technical field of power grids, and the method comprises the steps: aiming at each preset time period, based on the corresponding control and structure parameters of the grid-following type grid-connected converter and the grid-constructing type grid-connected converter in a small disturbance scene, calculating the stability of the grid-following type and grid-constructing type hybrid grid-connected converter; determining a system stable equilibrium point, a system unstable equilibrium point and equilibrium point stability conditions corresponding to the preset time period; determining a period stability analysis result corresponding to the preset time period based on a balance point linear differential equation, the system stable balance point, the system unstable balance point and the balance point stability condition; and determining a target stability analysis result based on the period stability analysis results corresponding to all the preset time periods. The method is applied to the condition of series-parallel connection of the following grid-connected converter and the construction grid-connected converter, is not influenced by a relatively high model order of the grid-connected converter, and can obtain an accurate stability analysis result.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid, in particular to a small disturbance stability estimation method for grid-connected converter mixed with grid-following and grid-forming. BACKGROUND

[0002] In recent years, new energy power grids dominated by wind power and photovoltaic power have a growing proportion in power sources. The existing new energy power grids are weak in strength, and when subjected to small disturbances, the oscillation problem is prominent, affecting the safe and stable operation of the power grid. New energy power sources have characteristics such as multi-time scale, multi-control strategy, and multi-parameter range, and their transient stability characteristics are quite different from synchronous generators.

[0003] Grid-connected converters are important interfaces for new energy power sources to deliver energy to the grid. The main control strategies for grid-connected converters currently include grid following (GFL) and grid forming (GFM).

[0004] Existing research on small disturbance stability domains mainly focuses on scenarios with single or multiple grid-connected converters of the same type. There is a certain gap in the research on small disturbance stability domains and mechanism analysis for scenarios with GFL and GFM grid-connected converters mixed together. In addition, the research methods for estimating the small disturbance stability domain of grid-connected converters mainly include impedance method and eigenvalue method, but due to the high model order of grid-connected converters, both existing methods are difficult to obtain stability analysis results. SUMMARY

[0005] The present application provides a small disturbance stability estimation method for grid-connected converters mixed with grid-following and grid-forming, which solves the defects in the prior art that there is a certain gap in the research on small disturbance stability domains and mechanism analysis for scenarios with GFL and GFM grid-connected converters mixed together, and due to the high model order of grid-connected converters, both existing methods are difficult to obtain stability analysis results. The technical scheme of the present application is applied to the mixed connection of grid-following grid-connected converters and grid-forming grid-connected converters, determines the periodic stability analysis results corresponding to the preset time period based on the linear differential equation of the equilibrium point, the stable equilibrium point of the system, the unstable equilibrium point of the system, and the equilibrium point stability condition, and finally determines the target stability analysis results under the small disturbance scenario, which is not affected by the high model order of grid-connected converters and can obtain accurate stability analysis results.

[0006] The present application provides a small disturbance stability estimation method for grid-connected converters mixed with grid-following and grid-forming, which solves the defects in the prior art that there is a certain gap in the research on small disturbance stability domains and mechanism analysis for scenarios with GFL and GFM grid-connected converters mixed together, and due to the high model order of grid-connected converters, both existing methods are difficult to obtain stability analysis results. The technical scheme of the present application is applied to the mixed connection of grid-following grid-connected converters and grid-forming grid-connected converters, determines the periodic stability analysis results corresponding to the preset time period based on the linear differential equation of the equilibrium point, the stable equilibrium point of the system, the unstable equilibrium point of the system, and the equilibrium point stability condition, and finally determines the target stability analysis results under the small disturbance scenario, which is not affected by the high model order of grid-connected converters and can obtain accurate stability analysis results.

[0007] For each preset time period, based on the control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario, a system stable equilibrium point, a system unstable equilibrium point and an equilibrium point stability condition corresponding to the preset time period are determined; A period stability analysis result corresponding to the preset time period is determined based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition; the equilibrium point linear differential equation is constructed based on the control and structure parameters, and is used to solve the system stable equilibrium point and the system unstable equilibrium point; A target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario is determined based on the period stability analysis results corresponding to all the preset time periods.

[0008] According to the grid-following and grid-forming hybrid grid-connected converter small disturbance stability estimation method provided by the application, the control and structure parameters include: grid-following side line impedance superimposed filter impedance, grid-forming side line impedance superimposed internal impedance, load impedance, grid-following converter output current, grid-forming converter output current, and grid-forming terminal voltage. The control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario are used to determine the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition corresponding to the preset time period, including: A system admittance matrix is constructed based on the grid-following side line impedance superimposed filter impedance, the grid-forming side line impedance superimposed internal impedance and the load impedance; The system stable equilibrium point and the system unstable equilibrium point corresponding to the preset time period are determined based on the system admittance matrix, the grid-following converter output current, the grid-forming converter output current and the grid-forming terminal voltage; The equilibrium point stability condition is determined based on the system admittance matrix, the grid-following converter output current and the grid-forming terminal voltage.

[0009] According to the grid-following and grid-forming hybrid grid-connected converter small disturbance stability estimation method provided by the application, the period stability analysis result corresponding to the preset time period is determined based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition, including: A system static stability limit is determined based on the equilibrium point stability condition; A small disturbance linearization model corresponding to the equilibrium point linear differential equation is established based on the system stable equilibrium point and the system unstable equilibrium point; determine a small-disturbance synchronous stability damping ratio based on the small-disturbance linearization model; determine a stability analysis result corresponding to the preset time period based on the small-disturbance synchronous stability damping ratio and the system static stability limit.

[0010] According to the small-disturbance stability estimation method for the grid-connected converter in parallel connection of the grid-following type and the grid-forming type provided by the application, the small-disturbance linearization model corresponding to the linear differential equation of the equilibrium point is established based on the system stable equilibrium point and the system unstable equilibrium point, and the small-disturbance linearization model comprises: determine a first system coefficient and a second system coefficient based on the system stable equilibrium point, the system admittance matrix, the grid-following type converter output current and the grid-forming type terminal voltage; establish the small-disturbance linearization model corresponding to the linear differential equation of the equilibrium point based on the first system coefficient and the second system coefficient at the system stable equilibrium point and the system unstable equilibrium point.

[0011] According to the small-disturbance stability estimation method for the grid-connected converter in parallel connection of the grid-following type and the grid-forming type provided by the application, the small-disturbance linearization model is determined based on the small-disturbance linearization model, and the small-disturbance linearization model comprises: determine a characteristic value corresponding to a characteristic equation of the small-disturbance linearization model based on the characteristic equation of the small-disturbance linearization model; determine a small-disturbance synchronous stability damping ratio based on the characteristic value of the linear equation.

[0012] According to the small-disturbance stability estimation method for the grid-connected converter in parallel connection of the grid-following type and the grid-forming type provided by the application, the control and structure parameters further comprise: a droop coefficient corresponding to the grid-forming type grid-connected converter, a phase-locked loop proportional coefficient corresponding to the grid-following type grid-connected converter and a phase-locked loop integral coefficient corresponding to the grid-following type grid-connected converter; determine a stability analysis result corresponding to the preset time period based on the small-disturbance synchronous stability damping ratio and the system static stability limit. determine the stability analysis result corresponding to the preset time period based on a first positive inverse ratio relationship between the small-disturbance synchronous stability damping ratio and the droop coefficient within the preset period, a second positive inverse ratio relationship between the small-disturbance synchronous stability damping ratio and the phase-locked loop proportional coefficient within the preset period, and a third positive inverse ratio relationship between the small-disturbance synchronous stability damping ratio and the phase-locked loop integral coefficient within the preset period within the system static stability limit range.

[0013] The application further provides a small-disturbance stability estimation device for a grid-connected converter in parallel connection of a grid-following type and a grid-forming type, comprising the following modules: The balance point module is configured to determine, for each preset time period, a system stable balance point, a system unstable balance point and a balance point stability condition corresponding to the preset time period based on corresponding control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter in a small disturbance scenario. The first analysis module is configured to determine a period stability analysis result corresponding to the preset time period based on a balance point linear differential equation, the system stable balance point, the system unstable balance point and the balance point stability condition, wherein the balance point linear differential equation is constructed based on the control and structure parameters and is used to solve the system stable balance point and the system unstable balance point. The second analysis module is configured to determine a target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario based on period stability analysis results corresponding to all the preset time periods.

[0014] The application further provides an electronic device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the grid-following grid-connected converter and the grid-forming grid-connected converter small disturbance stability estimation method according to any one of the above when executing the computer program.

[0015] The application further provides a non-transitory computer readable storage medium having a computer program stored thereon, wherein the computer program is executable by a processor to implement the grid-following grid-connected converter and the grid-forming grid-connected converter small disturbance stability estimation method according to any one of the above.

[0016] The application further provides a computer program product comprising a computer program, wherein the computer program is executable by a processor to implement the grid-following grid-connected converter and the grid-forming grid-connected converter small disturbance stability estimation method according to any one of the above.

[0017] The application provides a small disturbance stability estimation method for a grid-connected converter in a follow-grid type and a grid-constructing type, and the method comprises the following steps: for each preset time period, based on the control and structure parameters of the follow-grid type grid-connected converter and the grid-constructing type grid-connected converter in a small disturbance scenario, determining a system stable equilibrium point, a system unstable equilibrium point and an equilibrium point stability condition corresponding to the preset time period; based on an equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition, determining a period stability analysis result corresponding to the preset time period; the equilibrium point linear differential equation is an equation for solving the system stable equilibrium point and the system unstable equilibrium point, which is constructed based on the control and structure parameters; and based on the period stability analysis results corresponding to all the preset time periods, determining a target stability analysis result of the follow-grid type grid-connected converter and the grid-constructing type grid-connected converter in the small disturbance scenario. The technical scheme of the application is applied to the case of the follow-grid type grid-connected converter and the grid-constructing type grid-connected converter in a mixed mode, the period stability analysis result corresponding to the preset time period is determined based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition, and finally the target stability analysis result in the small disturbance scenario is determined, which is not affected by the high model order of the grid-connected converter, and an accurate stability analysis result can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative effort.

[0019] Figure 1 is a flowchart of the small disturbance stability estimation method for the follow-grid type and the grid-constructing type grid-connected converter provided by the application.

[0020] Figure 2 is an equivalent structure diagram of the follow-grid type grid-connected converter and the grid-constructing type grid-connected converter provided by the application.

[0021] Figure 3 is a diagram of the equilibrium point and the corresponding curve provided by the application.

[0022] Figure 4 is a diagram of the change trend of the equilibrium point provided by the application.

[0023] Figure 5 is a column chart of the small disturbance synchronous stability damping ratio under different parameters provided by the application.

[0024] Figure 6This is a graph showing the eigenvalues ​​and small disturbance synchronous stability damping ratio under different parameters provided by the present invention.

[0025] Figure 7 This is a schematic diagram of the small disturbance stability estimation device for grid-connected converters that are hybrid between grid-connected and grid-connected types, provided by the present invention.

[0026] Figure 8 This is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] To address the aforementioned problems in the prior art, this invention provides a method for estimating the small-disturbance stability of grid-connected converters that are hybrid between grid-connected and grid-connected types. Figure 1 This is a flowchart illustrating the small-disturbance stability estimation method for grid-connected converters with both grid-connected and hybrid grid configurations provided by the present invention. Figure 1 As shown, the method includes the following steps 110 to 130.

[0029] Step 110: For each preset time period, based on the control and structural parameters of the grid-connected converter and the grid-connected converter under small disturbance scenarios, determine the system stable equilibrium point, the system unstable equilibrium point, and the equilibrium point stability condition corresponding to the preset time period.

[0030] Specifically, multiple preset time periods can be set in advance, for example, you can set... A preset time period Indicates the first A preset time period This represents the set of all preset time periods. Furthermore, based on the control and structural parameters of grid-connected and grid-connected converters under small disturbance scenarios, the system stable equilibrium point, system unstable equilibrium point, and equilibrium point stability conditions corresponding to this preset time period can be determined. The control and structural parameters can be preset or obtained from the grid-connected and grid-connected converters.

[0031] In one embodiment, the control and structure parameters include: grid-following type side line impedance superimposed filter impedance, grid-forming type side line impedance superimposed internal impedance, load impedance, grid-following type converter output current, grid-forming type converter output current, grid-forming type machine terminal voltage; The control and structure parameters corresponding to the grid-following type grid-connected converter and the grid-forming type grid-connected converter in a small disturbance scenario are used to determine the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition corresponding to the preset time period, which includes: The system admittance matrix is constructed based on the grid-following type side line impedance superimposed filter impedance, the grid-forming type side line impedance superimposed internal impedance and the load impedance; The system stable equilibrium point and the system unstable equilibrium point corresponding to the preset time period are determined based on the system admittance matrix, the grid-following type converter output current, the grid-forming type converter output current and the grid-forming type machine terminal voltage; The equilibrium point stability condition is determined based on the system admittance matrix, the grid-following type converter output current and the grid-forming type machine terminal voltage.

[0032] Specifically, Figure 2 is an equivalent structure schematic diagram of the grid-following type grid-connected converter and the grid-forming type grid-connected converter provided by the present application, and the grid-following type grid-connected converter and the grid-forming type grid-connected converter in a mixed connection state can be equivalent to the structure model shown in Figure 2 , as shown in Figure 2 , GFL represents the grid-following type grid-connected converter, GFM represents the grid-forming type grid-connected converter, SVPWM represents the space vector pulse width modulation, node 3 represents the constant impedance load, and the two dashed boxes respectively represent the control strategy for GFL and GFM. The control and structure parameters can include: grid-following type side line impedance superimposed filter impedance , grid-forming type side line impedance superimposed internal impedance , load impedance , grid-following type converter output current , i.e. the current injected by bus 1 of GFL into the grid system, grid-forming type converter output current , i.e. the current injected by bus 2 of GFM into the grid system, grid-forming type machine terminal voltage . In addition, the control and structure parameters can also include: output power of GFL , output power of GFM , GFM machine-side input power , system rated power , about 100π radians per second (rad / s), phase angle of GFL , phase angle of GFM , first per-unit value of the angular frequency deviation of GFL from the synchronous angular frequency , second unit of the angular frequency deviation of the GFM from the synchronous angular frequency , droop coefficient of the GFM , medium frequency of the low-pass filter , phase-locked loop ratio of the GFL , and integral coefficient .

[0033] Further, the system admittance matrix can be constructed based on the grid-following type side line impedance superimposed filter impedance, the grid-forming type side line impedance superimposed internal impedance, and the load impedance . Further, the system stable equilibrium point and the system unstable equilibrium point corresponding to the preset time period can be determined based on the system admittance matrix, the grid-following type converter output current, the grid-forming type converter output current, and the grid-forming type machine terminal voltage.

[0034] The equilibrium point stability condition can also be determined based on the system admittance matrix, the grid-following type converter output current, and the grid-forming type machine terminal voltage.

[0035] Illustratively, the equilibrium point linear differential equation can be constructed, and to obtain the equilibrium point linear differential equation applicable to the small disturbance synchronous stability theory analysis of the hybrid system, the following assumptions widely used in existing research are adopted when constructing the equation: 1) the influence of frequency dynamics on network impedance is ignored, i.e. , and are constant impedances; 2) based on the multi-time scale theory, it is considered that the elements with a time scale faster than the synchronization control, such as the current control loop of the GFL and the GFM, reach quasi-steady state, which is described by an algebraic equation; 3) the output of the outer loop of the GFL is constant, and in the phase-locked loop dq coordinate system, the output current of the GFL can be expressed as , , where represents the phase of the current, and correspondingly, in the synchronous coordinate system, the output current of the GFL can be expressed as ; 4) the GFM adopts a classical model, which is represented by an equivalent internal reactance and the potential after the reactance; 5) the low-pass filter of the GFM provides a very small inertia to the system. In general, the bandwidth of the low-pass filter is set to tens of hertz, and the time scale is much faster than the synchronization control, so the influence of the inertia is ignored, and the relationship between frequency and active power is mainly determined by .

[0036] Under the above assumption conditions, let the grid-connected point voltage of the GFL be , and the grid-connected point voltage of the GFM be . The system admittance matrix can be represented by the following formula: (1) (2a) (2b) (2c) wherein, , In normal condition and short-circuit fault condition respectively and , represents the short-circuit resistance.

[0037] Considering the characteristics of GFL current source and GFM voltage source, formula (1) can be changed to the following formula (3): (3) Further note , The q-axis component of the phase-locked loop dq coordinate system Can be expressed by the following formula (4): (4) Further output power of GFL and output power of GFM Can be expressed by the following formula: (5) (6) The phase-locked loop control equation of GFL can be shown in the following formula (7): (7) According to formula (4) and formula (7), the derivative of As shown in the following formula (8): (8) The inertialess droop control equation of GFM is shown in formula (9): (9) Combined with formula (7) to formula (9), the linear differential equation of the equilibrium point can be obtained as follows: (10) At steady state, the frequency of GFL and GFM should reach the rated frequency , so , and according to formula (9), at this time . The input of GFL phase-locked loop satisfies , and the equilibrium point exists according to algebraic equation (4): (11) ​In addition to being able to directly obtain the system's stable equilibrium point and unstable equilibrium point using formula (10), they can also be obtained through the following method, analyzed from the perspective of the GFL phase-locked loop. Figure 3 This is a schematic diagram of the equilibrium point and corresponding curve provided by the present invention, denoted as (4) , The drawn curve is as follows Figure 3 As shown, Figure 3 In this context, rad represents radians. When the equilibrium point exists under condition (11), that is, when formula (11) strictly satisfies the condition of being less than a predetermined time period... Inside, and There are two intersection points, corresponding to two equilibrium points. and : The above formula can be obtained by solving formula (10), where Z represents the set of integers.

[0038] Furthermore, the equilibrium point can be analyzed to determine whether it is a stable or unstable equilibrium point. Figure 4 This is a schematic diagram illustrating the changing trend of the equilibrium point provided by the present invention. Figure 4 For example, 1) in There is ,at this time Assuming a small perturbation Increasing the infinitesimal, the following formula (12) shows the changing trend of each variable, and the result after the disturbance can be obtained. There is a downward trend. 1) The system's stable equilibrium point; 2) In There is ,at this time Assuming a small perturbation By adding an infinitesimal, equation (13) shows the changing trends of each variable, and the result after the disturbance can be obtained. The trend is further increasing. This is the unstable equilibrium point of the system. Equations (12) and (13) are shown below: (12) (13) In the above embodiments, based on the control and structural parameters of the grid-connected converter and the grid-connected converter under small disturbance scenarios, the system stable equilibrium point, the system unstable equilibrium point, and the equilibrium point existence conditions corresponding to the preset time period are determined, laying the foundation for the subsequent determination of the periodic stability analysis results.

[0039] Step 120: determining a period stability analysis result corresponding to the preset time period based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition; the equilibrium point linear differential equation is constructed based on the control and structure parameters and is used to solve the equation of the system stable equilibrium point and the system unstable equilibrium point.

[0040] Specifically, the period stability analysis result corresponding to the preset time period can be determined based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition. The equilibrium point linear differential equation is constructed based on the control and structure parameters and is used to solve the equation of the system stable equilibrium point and the system unstable equilibrium point. The construction process of the equilibrium point linear differential equation can refer to the embodiment corresponding to step 110.

[0041] In one embodiment, the determination of the period stability analysis result corresponding to the preset time period based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition comprises: determining a system static stability limit based on the equilibrium point stability condition; establishing a small disturbance linearization model corresponding to the equilibrium point linear differential equation based on the system stable equilibrium point and the system unstable equilibrium point; determining a small disturbance synchronous stability damping ratio based on the small disturbance linearization model; determining the stability analysis result corresponding to the preset time period based on the small disturbance synchronous stability damping ratio and the system static stability limit.

[0042] Specifically, the system static stability limit can be determined based on the equilibrium point stability condition, that is, when the inequality (11) takes the equality, the static stability limit of the hybrid system is obtained, and at this time, the static stability limit It can be seen that the system static stability limit is determined by the network topology and is independent of the coefficients.

[0043] Further, the small disturbance linearization model corresponding to the equilibrium point linear differential equation can be established based on the system stable equilibrium point and the system unstable equilibrium point, and then the small disturbance synchronous stability damping ratio can be determined based on the small disturbance linearization model. After obtaining the small disturbance synchronous stability damping ratio, the stability analysis result corresponding to the preset time period can be determined based on the small disturbance synchronous stability damping ratio and the system static stability limit.

[0044] In the above embodiment, the system static stability limit and the small disturbance synchronous stability damping ratio are solved, and the stability analysis of the grid-connected converter under the small disturbance scenario is performed based on the system static stability limit and the small disturbance synchronous stability damping ratio, and the stability analysis result is obtained.

[0045] In one embodiment, the establishing the small perturbation linearization model corresponding to the linear differential equation of the equilibrium point based on the system stable equilibrium point and the system unstable equilibrium point comprises: determining a first system coefficient and a second system coefficient based on the system stable equilibrium point, the system admittance matrix, the grid-following converter output current and the grid-forming machine terminal voltage; establishing the small perturbation linearization model corresponding to the linear differential equation of the equilibrium point based on the first system coefficient and the second system coefficient at the system stable equilibrium point and the system unstable equilibrium point.

[0046] Specifically, the first system coefficient and the second system coefficient can be determined based on the system stable equilibrium point, the system admittance matrix, the grid-following converter output current and the grid-forming machine terminal voltage. The first system coefficient and the second system coefficient may be represented by the following formula (14): (14) As can be seen from the above formula (14), the first system coefficient and the second system coefficient are determined by the structure parameters in the control and structure parameters, and are independent of the control parameters therein.

[0047] Further, the small perturbation linearization model corresponding to the linear differential equation of the equilibrium point can be established based on the first system coefficient and the second system coefficient at the system stable equilibrium point and the system unstable equilibrium point. The small perturbation linearization model can be shown in the following formula (15): (15) wherein, is a mathematical operator symbol, representing the infinite change of a variable.

[0048] In the above embodiment, the small perturbation linearization model corresponding to the linear differential equation of the equilibrium point is established based on the first system coefficient and the second system coefficient at the system stable equilibrium point and the system unstable equilibrium point, which lays a foundation for the subsequent determination of the small perturbation synchronous stability damping ratio.

[0049] In one embodiment, the determining the small perturbation synchronous stability damping ratio based on the small perturbation linearization model comprises: determining a characteristic value corresponding to a characteristic equation of the small perturbation linearization model based on the characteristic equation; determining the small perturbation synchronous stability damping ratio based on the characteristic value of the linear equation.

[0050] Specifically, an eigen equation of the small perturbation linearization model can be determined, a characteristic value corresponding to the eigen equation of the small perturbation linearization model can be determined based on the eigen equation, and the eigen equation can be represented by the following formula (16): (16) wherein, represents the characteristic value.

[0051] Further, the small perturbation synchronous stability damping ratio can be determined based on the characteristic value of the linear equation, and specifically, the real part of is removed from the negative sign and divided by the modulus of , so that the small perturbation synchronous stability damping ratio is obtained.

[0052] In addition, the small perturbation synchronous stability damping ratio can also be represented by the following formula (17): (17) In the above embodiment, the characteristic value corresponding to the eigen equation of the small perturbation linearization model can be determined based on the eigen equation of the small perturbation linearization model, and the small perturbation synchronous stability damping ratio can be determined based on the characteristic value of the linear equation. The small perturbation synchronous stability damping ratio determined by the above embodiment has high accuracy.

[0053] In one embodiment, the control and structure parameters further include: a droop coefficient corresponding to the network-constructing grid-connected converter, a phase-locked loop proportional coefficient corresponding to the network-following grid-connected converter, and a phase-locked loop integral coefficient corresponding to the network-following grid-connected converter. The determination of the stability analysis result corresponding to the preset time period based on the small perturbation synchronous stability damping ratio and the system static stability limit includes: Within the system static stability limit range, the stability analysis result corresponding to the preset time period is determined based on a first positive inverse ratio relationship between the small perturbation synchronous stability damping ratio and the droop coefficient within the preset period, a second positive inverse ratio relationship between the small perturbation synchronous stability damping ratio and the phase-locked loop proportional coefficient within the preset period, and a third positive inverse ratio relationship between the small perturbation synchronous stability damping ratio and the phase-locked loop integral coefficient within the preset period.

[0054] Specifically, within the system static stability limit range, the stability analysis result corresponding to the preset time period can be determined based on the positive inverse ratio relationships between the small perturbation synchronous stability damping ratio and the droop coefficient, the phase-locked loop proportional coefficient, and the phase-locked loop integral coefficient. The first positive inverse ratio relationship is the positive inverse ratio relationship between the small perturbation synchronous stability damping ratio and the droop coefficient, the second positive inverse ratio relationship is the positive inverse ratio relationship between the small perturbation synchronous stability damping ratio and the phase-locked loop proportional coefficient, and the third positive inverse ratio relationship is the positive inverse ratio relationship between the small perturbation synchronous stability damping ratio and the phase-locked loop integral coefficient.

[0055] For example, when the first system coefficient and the second system coefficient are both greater than zero, the system is small-disturbance stable under typical control parameters, and as the droop coefficient increases, the phase-locked loop proportional coefficient increases or the phase-locked loop integral coefficient decreases, the small-disturbance synchronization stability damping ratio increases, Figure 5 is a column chart of the small-disturbance synchronization stability damping ratio under different parameters provided by the application, Figure 5 demonstrates the change of under different control parameters, Figure 5 With the increase of , that is, with the increase of the droop coefficient.

[0056] In addition, when the network parameters change, the change can cause , and further cause the eigenvalue to cross the imaginary axis, thereby . Figure 6 is a curve graph of the eigenvalue and the small-disturbance synchronization stability damping ratio under different parameters provided by the application, and the change is taken as an example, as shown in Figure 6 (a), when , the system undergoes Hopf bifurcation, and the small-disturbance is unstable. Further observing the change of the GFL and GFM output power in Figure 6 (b), it can be obtained that when , the system damping ratio is maximum, and the excessive GFM or GFL output ratio causes the damping ratio to decrease.

[0057] In the above embodiment, within the system static stability limit range, the stability analysis result corresponding to the preset time period can be determined based on the positive and negative ratio relationship between the small-disturbance synchronization stability damping ratio and the droop coefficient, the phase-locked loop proportional coefficient, and the phase-locked loop integral coefficient, thereby ensuring the accuracy of the periodic stability analysis result in a single preset time period under the small-disturbance scenario.

[0058] Step 130: determining the target stability analysis result of the follow-network type grid-connected converter and the network-constructing type grid-connected converter under the small-disturbance scenario based on the periodic stability analysis result corresponding to all the preset time periods.

[0059] Specifically, the target stability analysis result of the follow-network type grid-connected converter and the network-constructing type grid-connected converter under the small-disturbance scenario can also be determined based on the periodic stability analysis result corresponding to all the preset time periods.

[0060] The application provides a small disturbance stability estimation method for grid-connected converters in a follow-grid type and a grid-constructing type in a mixed connection mode.

[0061] The follow-grid type and grid-constructing type mixed connection grid-connected converter small disturbance stability estimation device provided by the application is described below, and the follow-grid type and grid-constructing type mixed connection grid-connected converter small disturbance stability estimation device described below can be correspondingly referred to the follow-grid type and grid-constructing type mixed connection grid-connected converter small disturbance stability estimation method described above.

[0062] Figure 7 FIG. 7 is a structural schematic diagram of the follow-grid type and grid-constructing type mixed connection grid-connected converter small disturbance stability estimation device provided by the application, as shown in the figure, the follow-grid type and grid-constructing type mixed connection grid-connected converter small disturbance stability estimation device 700 comprises the following modules: Figure 7 The balance point module 710 is configured to determine, for each preset time period, a system stable equilibrium point, a system unstable equilibrium point and an equilibrium point stability condition corresponding to the preset time period based on corresponding control and structure parameters of the follow-grid type grid-connected converter and the grid-constructing type grid-connected converter in a small disturbance scenario. The first analysis module 720 is configured to determine a periodic stability analysis result corresponding to the preset time period based on an equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition; the equilibrium point linear differential equation is constructed based on the control and structure parameters and is used to solve an equation of the system stable equilibrium point and the system unstable equilibrium point. ​The second analysis module 730 is configured to determine the target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter under the small disturbance scenario based on the periodic stability analysis result corresponding to all the preset time periods.

[0063] In one embodiment, the control and structure parameters include: grid-following side line impedance superimposed filter impedance, grid-forming side line impedance superimposed internal impedance, load impedance, grid-following converter output current, grid-forming converter output current, and grid-forming terminal voltage. The equilibrium point module 710 is specifically configured to: construct a system admittance matrix based on the grid-following side line impedance superimposed filter impedance, the grid-forming side line impedance superimposed internal impedance, and the load impedance; determine the system stable equilibrium point and the system unstable equilibrium point corresponding to the preset time period based on the system admittance matrix, the grid-following converter output current, the grid-forming converter output current, and the grid-forming terminal voltage; determine the equilibrium point stability condition based on the system admittance matrix, the grid-following converter output current, and the grid-forming terminal voltage.

[0064] In one embodiment, the first analysis module 720 is specifically configured to: determine a system static stability limit based on the equilibrium point stability condition; establish a small disturbance linearization model corresponding to the equilibrium point linear differential equation based on the system stable equilibrium point and the system unstable equilibrium point; determine a small disturbance synchronous stability damping ratio based on the small disturbance linearization model; determine the stability analysis result corresponding to the preset time period based on the small disturbance synchronous stability damping ratio and the system static stability limit.

[0065] In one embodiment, the first analysis module 720 is specifically configured to further: determine a first system coefficient and a second system coefficient based on the system stable equilibrium point, the system admittance matrix, the grid-following converter output current, and the grid-forming terminal voltage; establish a small disturbance linearization model corresponding to the equilibrium point linear differential equation based on the first system coefficient and the second system coefficient at the system stable equilibrium point and the system unstable equilibrium point.

[0066] In one embodiment, the first analysis module 720 is specifically configured to further: determine a characteristic value corresponding to the characteristic equation based on the characteristic equation of the small disturbance linearization model; determine a small disturbance synchronous stability damping ratio based on the characteristic value of the linear equation.

[0067] In one embodiment, the droop coefficient corresponding to the grid-forming grid-connected converter, the proportional coefficient of the phase-locked loop corresponding to the grid-following grid-connected converter, and the integral coefficient of the phase-locked loop corresponding to the grid-following grid-connected converter; the first analysis module 720 is specifically further used for: Within the static stability limit range of the system, based on the first positive inverse relationship between the small disturbance synchronous stability damping ratio and the droop coefficient within the preset period, the second positive inverse relationship between the small disturbance synchronous stability damping ratio and the proportional coefficient of the phase-locked loop within the preset period, and the third positive inverse relationship between the small disturbance synchronous stability damping ratio and the integral coefficient of the phase-locked loop within the preset period, the stability analysis result corresponding to the preset time period is determined.

[0068] The grid-following grid-connected converter and the grid-forming grid-connected converter are mixed. For each preset time period, based on the control and structural parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter corresponding to the small disturbance scenario, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition corresponding to the preset time period are determined. The linear differential equation of the equilibrium point is constructed based on the control and structural parameters, and is used to solve the equation of the system stable equilibrium point and the system unstable equilibrium point. Based on the periodic stability analysis result corresponding to all the preset time periods, the target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario is determined. The technical scheme of the present application is applied to the mixed connection of the grid-following grid-connected converter and the grid-forming grid-connected converter. The periodic stability analysis result corresponding to the preset time period is determined based on the linear differential equation of the equilibrium point, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition. Finally, the target stability analysis result in the small disturbance scenario is determined. It is not affected by the high model order of the grid-connected converter, and an accurate stability analysis result can be obtained.

[0069] Figure 8 An example of an electronic device is shown in the physical structure diagram of the electronic device, as shown in Figure 8 The electronic device can include a processor 810, a communications interface 820, a memory 830, and a communications bus 840. The processor 810, the communications interface 820, and the memory 830 communicate with each other through the communications bus 840. The processor 810 can invoke the logic instructions in the memory 830 to execute the grid-following grid-connected converter and the grid-forming grid-connected converter small disturbance stability estimation method, which includes: For each preset time period, based on the corresponding control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario, a system stable equilibrium point, a system unstable equilibrium point and an equilibrium point stability condition corresponding to the preset time period are determined; A period stability analysis result corresponding to the preset time period is determined based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition; the equilibrium point linear differential equation is constructed based on the control and structure parameters, and is used to solve the system stable equilibrium point and the system unstable equilibrium point; A target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario is determined based on the period stability analysis results corresponding to all the preset time periods.

[0070] In addition, the logical instructions in the memory 830 described above can be implemented in the form of a software function unit and sold or used as an independent product, and can be stored in a computer readable storage medium. Based on this understanding, the technical solutions of the present application essentially or the parts that contribute to the prior art or parts of the technical solutions can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in the embodiments of the present application. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a magnetic disk or an optical disk, and various storage program codes.

[0071] On the other hand, the present application also provides a computer program product, which comprises a computer program, the computer program can be stored on a non-transitory computer readable storage medium, and when the computer program is executed by a processor, the computer can execute the grid-following and grid-forming hybrid grid-connected converter small disturbance stability estimation method provided by the above-mentioned methods, which comprises: For each preset time period, based on the corresponding control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario, a system stable equilibrium point, a system unstable equilibrium point and an equilibrium point stability condition corresponding to the preset time period are determined; determine the periodic stability analysis result corresponding to the preset time period based on the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition; the equilibrium point linear differential equation is constructed based on the control and structure parameters, and is used for solving the system stable equilibrium point and the system unstable equilibrium point; determine the target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter under the small disturbance scenario based on all the periodic stability analysis results corresponding to the preset time periods.

[0072] In another aspect, the present application also provides a non-transitory computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the grid-following and grid-forming hybrid grid-connected converter small disturbance stability estimation method provided by the above method, and the method comprises: For each preset time period, based on the corresponding control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter under the small disturbance scenario, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition corresponding to the preset time period are determined; determine the periodic stability analysis result corresponding to the preset time period based on the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition; the equilibrium point linear differential equation is constructed based on the control and structure parameters, and is used for solving the system stable equilibrium point and the system unstable equilibrium point; determine the target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter under the small disturbance scenario based on all the periodic stability analysis results corresponding to the preset time periods.

[0073] The device embodiments described above are only schematic, wherein the units described as separate components can or can not be physically separated, and the components displayed as units can or can not be physical units, i.e., they can be located in one place, or distributed on multiple network units. Part or all of the modules can be selected according to actual needs to achieve the purpose of the present embodiment scheme. Those skilled in the art can understand and implement it without creative labor.

[0074] Those skilled in the art can clearly understand the technical solutions of the various embodiments from the above description of the embodiments, and the various embodiments can be implemented by means of software with the necessary general hardware platforms, and of course, can also be implemented by hardware. Based on such understanding, the above technical solutions, essentially or in other words, the part of the prior art that makes a contribution, can be embodied in the form of a software product, which can be stored in a computer readable storage medium, such as a ROM / RAM, a magnetic disk, an optical disk, and the like, and includes a number of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute the methods described in the various embodiments or some parts of the embodiments.

[0075] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for some technical features therein; and these modifications 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 application.

Claims

1. A small signal stability estimation method for a grid-connected converter with mesh-type and construction-type hybrid connection, characterized in that, The method comprises the following steps: For each preset time period, based on the control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition corresponding to the preset time period are determined; Based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition, the periodic stability analysis result corresponding to the preset time period is determined; The equilibrium point linear differential equation is constructed based on the control and structure parameters, and is used to solve the system stable equilibrium point and the system unstable equilibrium point; Based on the periodic stability analysis result corresponding to all the preset time periods, the target stability analysis result of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario is determined.

2. The small signal stability estimation method for grid-connected converter of hybrid grid-forming and grid-forming according to claim 1, wherein, The control and structure parameters include: grid-following side line impedance superimposed filter impedance, grid-forming side line impedance superimposed internal impedance, load impedance, grid-following converter output current, grid-forming converter output current, and grid-forming terminal voltage; The control and structure parameters of the grid-following grid-connected converter and the grid-forming grid-connected converter in the small disturbance scenario are used to determine the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition corresponding to the preset time period, which comprises the following steps: Based on the grid-following side line impedance superimposed filter impedance, the grid-forming side line impedance superimposed internal impedance and the load impedance, a system admittance matrix is constructed; Based on the system admittance matrix, the grid-following converter output current, the grid-forming converter output current and the grid-forming terminal voltage, the system stable equilibrium point and the system unstable equilibrium point corresponding to the preset time period are determined; Based on the system admittance matrix, the grid-following converter output current and the grid-forming terminal voltage, the equilibrium point stability condition is determined.

3. The method of claim 2, wherein, The periodic stability analysis result corresponding to the preset time period is determined based on the equilibrium point linear differential equation, the system stable equilibrium point, the system unstable equilibrium point and the equilibrium point stability condition, which comprises the following steps: Based on the equilibrium point stability condition, a system static stability limit is determined; Based on the system stable equilibrium point and the system unstable equilibrium point, a small disturbance linearization model corresponding to the equilibrium point linear differential equation is established; Based on the small disturbance linearization model, a small disturbance synchronous stability damping ratio is determined; Based on the small disturbance synchronous stability damping ratio and the system static stability limit, the stability analysis result corresponding to the preset time period is determined.

4. The method of claim 3, wherein, The small disturbance linearization model corresponding to the equilibrium point linear differential equation is established based on the system stable equilibrium point and the system unstable equilibrium point, which comprises the following steps: Based on the system stable equilibrium point, the system admittance matrix, the grid-following converter output current and the grid-forming terminal voltage, a first system coefficient and a second system coefficient are determined; Based on the first system coefficient and the second system coefficient, the small disturbance linearization model corresponding to the equilibrium point linear differential equation is established at the system stable equilibrium point and the system unstable equilibrium point.

5. The method of claim 3, wherein, The small-disturbance synchronization stability damping ratio is determined based on the small-disturbance linearization model, including: determining a characteristic value corresponding to the characteristic equation of the small-disturbance linearization model; determining a small-disturbance synchronization stability damping ratio based on the characteristic value of the linear equation.

6. The method of claim 3 to 5, wherein, The control and structure parameters further include: a droop coefficient corresponding to the grid-constructing grid-connected converter, a phase-locked loop proportional coefficient corresponding to the grid-following grid-connected converter, and a phase-locked loop integral coefficient corresponding to the grid-following grid-connected converter; The stability analysis result corresponding to the preset time period is determined based on the small-disturbance synchronization stability damping ratio and the system static stability limit, including: Within the system static stability limit range, the stability analysis result corresponding to the preset time period is determined based on a first positive inverse ratio relationship between the small-disturbance synchronization stability damping ratio and the droop coefficient within the preset period, a second positive inverse ratio relationship between the small-disturbance synchronization stability damping ratio and the phase-locked loop proportional coefficient within the preset period, and a third positive inverse ratio relationship between the small-disturbance synchronization stability damping ratio and the phase-locked loop integral coefficient within the preset period.

7. A small signal stability estimation device for a grid-connected converter of a grid-following and grid-forming hybrid type, characterized in that, including: a balance point module configured to determine, for each preset time period, a system stable balance point, a system unstable balance point, and a balance point stability condition corresponding to the preset time period based on control and structure parameters of a grid-following grid-connected converter and a grid-constructing grid-connected converter under a small-disturbance scenario; a first analysis module configured to determine a period stability analysis result corresponding to the preset time period based on a balance point linear differential equation, the system stable balance point, the system unstable balance point, and the balance point stability condition; The balance point linear differential equation is an equation for solving the system stable balance point and the system unstable balance point, which is constructed based on the control and structure parameters; a second analysis module configured to determine a target stability analysis result of the grid-following grid-connected converter and the grid-constructing grid-connected converter under the small-disturbance scenario based on period stability analysis results corresponding to all the preset time periods.

8. An electronic device comprising a memory, a processor, and a computer program stored on the memory and running on the processor, characterized in that, The processor executes the computer program to implement the grid-following and grid-constructing hybrid grid-connected converter small-disturbance stability estimation method of any one of claims 1 to 6. 9.A non-transitory computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the grid-following and grid-constructing hybrid grid-connected converter small-disturbance stability estimation method of any one of claims 1 to 6.

10. A computer program product comprising a computer program, characterized in that, The computer program is executed by the processor to implement the grid-following and grid-constructing hybrid grid-connected converter small-disturbance stability estimation method of any one of claims 1 to 6.

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