Distributed stability method of grid-connected renewable energy power generation system based on passivity

Abstract

The present invention discloses a distributed stability method for a network-forming new energy power generation system based on passivity, belonging to the field of electrical engineering. The stability method of the present invention includes establishing a control model of a network-forming inverter, giving the output differential passivity index σ of each network-forming inverter, and giving the input differential passivity index σ of network coupling net , and performing the stability judgment of the network-forming inverter. The present invention is proposed under the background of high-penetration new energy power generation, aiming at the characteristics of strong dynamic characteristics and poor stability of the new energy power generation system, and based on the passivation of the feedback system of the power loop control of the network-forming inverter and network coupling, the non-linear distributed stability condition of the network-forming new energy power generation system is obtained. The present invention is not only simple to implement, but also solves the problem that the traditional linear passivation method is difficult to meet the transient stability of the system under large-signal disturbances.

Description

Technical Field

[0001] The invention belongs to the field of electrical engineering and relates to a distributed stabilization method of a grid-type new energy power generation system based on passivity. Background Art

[0002] In the context of high penetration of new energy, a large number of distributed devices with power electronic converters as interfaces are continuously connected to the power system, which makes the new energy power generation system often show weak grid characteristics, which has a negative impact on system stability. Under weak grid, the stability margin of grid-connected inverter decreases or even becomes unstable. Compared with the traditional current source mode grid-connected inverter, the grid-connected inverter can operate stably under weak grid. Therefore, more and more research is based on grid-connected inverter.

[0003] The article entitled "Research on Impedance Adaptive Dual-Mode Control of Grid-connected Inverter for High Penetration Renewable Energy Generation" (Li Ming. Research on Impedance Adaptive Dual-Mode Control of Grid-connected Inverter for High Penetration Renewable Energy Generation [D]. Hefei University of Technology, 2020.) introduces the characteristics of different modes of inverter control under weak power grids. Among them, the traditional grid-following inverter has low stability margin and is prone to instability under weak power grids, while the grid-connected mode can operate stably under weak power grids.

[0004] In addition, the structure and parameters of the equivalent power grid at the grid-connected inverter point in renewable energy systems such as wind power and photovoltaic power generation often show nonlinear changes due to factors such as failures, maintenance and expansion. As the penetration rate of new energy increases, the nonlinear dynamic characteristics will become more complex, and the stability and safety of the system will be severely challenged.

[0005] In response to high grid impedance and nonlinear grid structure / parameter changes, some scholars have proposed passive control based on nonlinear control theory. For example:

[0006] Titled "Low-Frequency Passivity-Based Analysis and Damping ofPower-Synchroni zat ion Control 1ed Grid-Forming Inverter" (F.Zhao, SelectedTopics in Power Electronics, vo1.11, no.2, pp.1542-1554, April 2023)(《Damping Analysis of Power Synchronous Control Grid-Connected Inverter Based on Low-Frequency Passivity》)(Zhao Fangzhou, Wang Xiongfei and Zhu Tianhua, Damping Analysis of Power Synchronous Control Grid-Connected Inverter Based on Low-Frequency Passivity[J], IEEE Journal of Emerging Topics in Power Electronics, Vol. 11, No. 2, Pages: 1542-1554, April 2023.) Based on the linear angle, the inverter is made passivated, which can guarantee stability and certain dynamic performance under small disturbances, but cannot guarantee its transient stability under large disturbances.

[0007] In addition, the centralized stability analysis of traditional power generation systems requires overall modeling, which is not suitable for plug-and-play equipment because the large system needs to be remodeled. For example:

[0008] The paper entitled “Direct stability analysis of electric power systems using energy functions: theory, applications, and perspective” (Hsiao-Dong Chang, Chia-Chi Chu and G. Cauley, Direct stability analysis of electric power systems using energy functions: theory, applications, and perspective, in Proceedings of the IEEE, vol. 83, no. 11, pp. 1497-1529, Nov. 1995) uses a direct method to analyze the stability of the entire system, which has a heavy computational burden. At the same time, when the system structure changes due to plug-and-play, the system needs to be re-analyzed in a centralized stability model, which is not suitable for the current high-penetration renewable energy power generation system.

[0009] In summary, the prior art has the following problems:

[0010] (1) Traditional grid-connected inverters based on grid-following control have poor stability under weak grid conditions, while the stability performance of grid-connected inverters is also challenged under nonlinear system conditions.

[0011] (2) The existing technology can only solve the stability problem of small signal disturbances by replacing the traditional PI control of the inverter with a passive controller, but it is difficult to solve the transient stability problem under large signal disturbances.

[0012] (3) The traditional centralized stability analysis method is not suitable for the current high-penetration new energy power generation system that is frequently plug-and-play. Summary of the invention

[0013] The technical problem to be solved by the present invention is that the transient stability under large signal disturbance cannot be solved under traditional passive control of the inverter, and a distributed stability method for a grid-type new energy power generation system based on passivity is proposed.

[0014] The purpose of the present invention is achieved in this way. The present invention provides a distributed stabilization method for a grid-type new energy power generation system based on passivity, wherein the grid-type new energy power generation system refers to a new energy power generation system composed of n grid-type inverters; the distributed stabilization method refers to a method for adjusting the parameters of each grid-type inverter until the conditions are met to achieve the overall stability of the grid-type new energy power generation system;

[0015] The steps of the distributed stabilization method are as follows:

[0016] Step 1: Establish a control model of the grid-connected inverter and record it as the control model, whose expression is:

[0017]

[0018] Among them, P is the instantaneous value of the active power output of the grid-connected inverter, Q is the instantaneous value of the reactive power output of the grid-connected inverter, and P * The reference value of the active power output of the grid-connected inverter is given, Q * is the reference value of reactive power output by the grid-connected inverter, θ is the instantaneous value of the output voltage phase of the grid-connected inverter, θ * is the reference value of the output voltage phase of the grid-type inverter, V is the instantaneous value of the output voltage amplitude of the grid-type inverter, V * Give a reference value for the output voltage amplitude of the grid-connected inverter. is the differential of the instantaneous value θ of the output voltage phase of the grid-connected inverter, K is the differential of the instantaneous value V of the output voltage amplitude of the grid-connected inverter, p is the active power loop droop coefficient, K q is the reactive power loop droop coefficient, τ1 is the active power loop time constant, τ2 is the reactive power loop time constant;

[0019] Define the input variable of the control model as u, and Define the output variable of the control model as y, and y = (θ, V) T , (θ, V) T Where, represents the transpose of (θ, V);

[0020] Step 2: According to the control model established in step 1, define the interconnection relationship between each grid-type inverter as network coupling, that is, the grid-type new energy power generation system is a whole of n grid-type inverters connected to each other through network coupling; calculate the input differential passivity index σ of the network coupling net ;

[0021] Step 3: According to the control model established in step 1, the output differential passivity index σ of each grid-connected inverter is given. The specific steps are:

[0022] Define the storage function S(x) of the grid-connected inverter, and its expression is:

[0023]

[0024] The Hessian matrix of the storage function S(x) of the grid inverter is recorded as the first Hessian matrix Its expression is:

[0025]

[0026] In the formula, is the Hamiltonian operator;

[0027] make And at the same time satisfy The active power loop droop coefficient K p And reactive power loop droop coefficient K q is an adjustable value;

[0028] Step 4: Define the distributed stability condition of the grid-connected renewable energy power generation system as σ+σ net ≥0, specifically, calculate σ+σ for each grid-connected inverter net The value of and make the following judgment:

[0029] If σ+σ is satisfied net ≥0, it is considered that the grid-connected inverter meets the stability conditions;

[0030] If σ+σ net <0, it is determined that the grid-type inverter does not meet the stability condition, and returns to step 3 to reduce the active power loop droop coefficient K p And reactive power loop droop coefficient K q The value of the output differential passivity index σ of the grid-connected inverter is increased until σ+σ is satisfied. net ≥0;

[0031] Step 5: When all n grid-type inverters in the grid-type new energy power generation system meet the stability condition σ+σ net When ≥0, the distributed grid-connected new energy power generation system is deemed to be stable and the operation is completed.

[0032] Preferably, the input differential passivity index σ of the network coupling in step 2 is net The given steps are:

[0033] Step 2.1, record the grid-connected new energy power generation system as a system;

[0034] Define each grid-connected inverter in the system and the grid connected to the system as a node, that is, the system includes n+1 nodes, and any one of the n+1 nodes is recorded as node i, i=1, 2, ..., n+1;

[0035] Define the network coupling potential energy function W B (y), Among them, B ii is the self-admittance of the ith node, B ij is the mutual admittance between the i-th node and the j-th node, j = 1, 2, ..., n + 1, and i ≠ j; V i is the voltage amplitude of the ith node, V j is the voltage amplitude of the jth node, θ ij is the phase angle difference between the i-th node and the j-th node;

[0036] Step 2.2: The network coupling potential energy function W B The Hessian matrix of (y) is recorded as the second Hessian matrix A is the active phase angle relationship matrix, D is the coupling matrix, C is the reactive voltage relationship matrix, D T is the transpose of D, and its expressions are:

[0037]

[0038] Among them, N i is the set of all nodes adjacent to the i-th node, and the set N i Any node in is recorded as adjacent node k, k = 1, 2, ..., N i ; B ik is the mutual admittance between the ith node and the adjacent node k, V k is the voltage amplitude of the adjacent node k, θ ik is the phase difference between the ith node and the adjacent node k;

[0039] Step 2.3, define the input differential passivity index σ of the network coupling net , Among them, λ min is the minimum eigenvalue, is the second Hessian matrix The minimum eigenvalue of .

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. The present invention is based on grid-type droop control, which makes the inverter more stable in the low-inertia new energy power generation system.

[0042] 2. The present invention adopts a grid-type droop control method that satisfies output differential passivity. It is based on a nonlinear passive design of the power loop. It is different from the traditional linear passive control based on a voltage and current double closed-loop design, and can meet the transient stability of the new energy power generation system under large signal disturbances;

[0043] 3. The distributed stabilization method adopted by the present invention uses the Lyapunov stability criterion to obtain the conditions for system stability. The implementation method is simple and only requires modifying the inverter control parameters according to the corresponding conditions to achieve the overall stability of the system.

[0044] 4. The stability analysis method proposed in the present invention is not only applicable to traditional centralized power generation new energy systems, but also to heterogeneous distributed new energy power generation systems. The proposed distributed stability analysis decomposes the overall stability conditions of the new energy power grid into each subsystem, thereby completing the stability analysis of the interconnected system in a weakly centralized or even decentralized manner.

[0045] 5. The stability analysis method proposed in the present invention only needs to focus on the impact of subsystem changes on the overall stability of the system. There is no need to re-model the entire system for analysis and stability control design. The complexity of analysis and control does not need to be increased, so it has high scalability.

[0046] 6. The distributed stability judgment method based on passivity index adopted by the present invention intuitively quantifies the system stability status, is applicable to new energy power generation systems with different structures, and enhances the scalability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a flow chart of the distributed stabilization method described in the present invention.

[0048] Figure 2 This is a structural diagram of the three-machine parallel new energy power generation system used in the simulation of the present invention.

[0049] Figure 3 for Figure 2 Dynamic waveform diagram of the phase angles of the three machines in the system when σ=6.25.

[0050] Figure 4 for Figure 2 Dynamic waveform diagram of the phase angles of the three machines in the system when σ=7. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0052] The present invention provides a distributed stabilization method for a grid-type new energy power generation system based on passivity. The grid-type new energy power generation system refers to a new energy power generation system composed of n grid-type inverters. The distributed stabilization method refers to a method for adjusting the parameters of each grid-type inverter until the conditions are met to achieve overall stability of the grid-type new energy power generation system.

[0053] Figure 1 is a flow chart of the distributed stabilization method of the present invention, comprising Figure 1 It can be seen that the steps of the distributed stabilization method are as follows:

[0054] Step 1: Establish a control model of the grid-connected inverter and record it as the control model, whose expression is:

[0055]

[0056] Among them, P is the instantaneous value of the active power output of the grid-connected inverter, Q is the instantaneous value of the reactive power output of the grid-connected inverter, and P * The reference value of the active power output of the grid-connected inverter is given, Q * is the reference value of reactive power output by the grid-connected inverter, θ is the instantaneous value of the output voltage phase of the grid-connected inverter, θ * is the reference value of the output voltage phase of the grid-type inverter, V is the instantaneous value of the output voltage amplitude of the grid-type inverter, V * Give a reference value for the output voltage amplitude of the grid-connected inverter. is the differential of the instantaneous value θ of the output voltage phase of the grid-connected inverter, K is the differential of the instantaneous value V of the output voltage amplitude of the grid-connected inverter, p is the active power loop droop coefficient, K q is the reactive power loop droop coefficient, τ1 is the active power loop time constant, and τ2 is the reactive power loop time constant.

[0057] Define the input variable of the control model as u, and Define the output variable of the control model as y, and y = (θ, V) T , where (θ, V) T represents the transpose of (θ, V).

[0058] Step 2: According to the control model established in step 1, define the interconnection relationship between each grid-type inverter as network coupling, that is, the grid-type new energy power generation system is a whole of n grid-type inverters connected to each other through network coupling; calculate the input differential passivity index σ of the network coupling net .

[0059] In this embodiment, the input differential passivity index σ of the network coupling in step 2 is netThe given steps are:

[0060] Step 2.1, record the grid-connected new energy power generation system as a system;

[0061] Define each grid-connected inverter in the system and the grid connected to the system as a node, that is, the system includes n+1 nodes, and any one of the n+1 nodes is recorded as node i, i=1, 2, ..., n+1;

[0062] Define the network coupling potential energy function W B (y), Among them, B ii is the self-admittance of the ith node, B ij is the mutual admittance between the i-th node and the j-th node, j = 1, 2, ..., n + 1, and i ≠ j; V i is the voltage amplitude of the ith node, V j is the voltage amplitude of the jth node, θ ij is the phase angle difference between the i-th node and the j-th node.

[0063] Step 2.2: The network coupling potential energy function W B The Hessian matrix of (y) is recorded as the second Hessian matrix A is the active phase angle relationship matrix, D is the coupling matrix, C is the reactive voltage relationship matrix, D T is the transpose of D, and its expressions are:

[0064]

[0065] Among them, N i is the set of all nodes adjacent to the i-th node, and the set N i Any node in is recorded as adjacent node k, k = 1, 2, ..., N i ; B ik is the mutual admittance between the ith node and the adjacent node k, V k is the voltage amplitude of the adjacent node k, θ ik is the phase difference between the ith node and its adjacent node k.

[0066] According to the value of coupling matrix D, we can get the transposed D T Then according to the active phase angle relationship matrix A, reactive voltage relationship matrix C, coupling matrix D and transpose D T The value of matrix.

[0067] Step 2.3, define the input differential passivity index σ of the network coupling net , Among them, λmin is the minimum eigenvalue, is the second Hessian matrix The minimum eigenvalue of .

[0068] Step 3: According to the control model established in step 1, the output differential passivity index σ of each grid-connected inverter is given. The specific steps are:

[0069] Define the storage function S(x) of the grid-connected inverter, and its expression is:

[0070]

[0071] The Hessian matrix of the storage function S(x) of the grid inverter is recorded as the first Hessian matrix Its expression is:

[0072]

[0073] In the formula, is the Hamiltonian operator;

[0074] make And at the same time satisfy The active power loop droop coefficient K p And reactive power loop droop coefficient K q is an adjustable value;

[0075] Step 4: Define the distributed stability condition of the grid-connected renewable energy power generation system as σ+σ net ≥0, specifically, calculate σ+σ for each grid-connected inverter net The value of and make the following judgment:

[0076] If σ+σ is satisfied net ≥0, it is considered that the grid-connected inverter meets the stability conditions;

[0077] If σ+σ net <0, it is determined that the grid-type inverter does not meet the stability condition, and returns to step 3 to reduce the active power loop droop coefficient K p And reactive power loop droop coefficient K q The value of the output differential passivity index σ of the grid-connected inverter is increased until σ+σ is satisfied. net ≥0;

[0078] Step 5: When all n grid-type inverters in the grid-type new energy power generation system meet the stability condition σ+σ net When ≥0, the distributed grid-connected new energy power generation system is deemed to be stable and the operation is completed.

[0079] In order to verify the inverter grid droop control method based on differential passivity provided by the present invention, simulation was carried out.

[0080] Figure 2 This is a structural diagram of the three-machine parallel new energy power generation system used in the simulation of the present invention. As can be seen from the figure, the inverter three-machine parallel new energy power generation system includes a distributed power source connected to the system through three grid-type inverters, that is, n=3. The line impedances of the three grid-type inverters are Z1, Z2 and Z3 respectively, and the grid impedance is Z grid , three grid-connected inverters are connected to the common coupling point (PCC) through their own line impedance and grid impedance for grid-connected power generation.

[0081] Considering each grid-type inverter and the grid as nodes, the input differential passivity index σ of the network coupling can be calculated. net In this embodiment, σ is calculated net =-6.2.

[0082] In the simulation, Figure 2 A three-phase short-circuit fault simulation is performed at the common coupling point of the three-machine parallel new energy power generation system shown. The fault occurs at 1 second and is cleared after 0.04 seconds to observe the stability of the system under large signal disturbance.

[0083] Figure 3 The dynamic waveform of the three-machine phase angle when the node output differential passivity index σ=6.25 satisfies σ+σ net ≥0, it can be seen from the figure that after the fault is removed, the system gradually becomes stable.

[0084] Figure 4 The dynamic waveform of the three-machine phase angle when the node output differential passivity index σ = 7, which also satisfies σ + σ net ≥0 distributed stability condition. It can be seen from the figure that after the fault is removed, the system gradually tends to be stable. At the same time, because the output differential passivity index of the node is higher at this time, the node provides more damping, so after the fault is removed, the system fluctuates less and stabilizes faster.

[0085] In summary, Figure 3 , Figure 4 The simulation waveform shown is consistent with the distributed stability result of the present invention.

Claims

1. A distributed stabilization method for a grid-type new energy power generation system based on passivity, wherein the grid-type new energy power generation system refers to a new energy power generation system composed of n grid-type inverters; the distributed stabilization method refers to a method for adjusting the parameters of each grid-type inverter until the conditions are met to achieve overall stability of the grid-type new energy power generation system; It is characterized in that The steps of the distributed stabilization method are as follows: Step 1: Establish a control model of the grid-connected inverter and record it as the control model, whose expression is: Among them, P is the instantaneous value of the active power output of the grid-connected inverter, Q is the instantaneous value of the reactive power output of the grid-connected inverter, and P * The reference value of the active power output of the grid-connected inverter is given, Q * is the reference value of reactive power output by the grid-connected inverter, θ is the instantaneous value of the output voltage phase of the grid-connected inverter, θ * is the reference value of the output voltage phase of the grid-type inverter, V is the instantaneous value of the output voltage amplitude of the grid-type inverter, V * Give a reference value for the output voltage amplitude of the grid-connected inverter. is the differential of the instantaneous value θ of the output voltage phase of the grid-connected inverter, K is the differential of the instantaneous value V of the output voltage amplitude of the grid-connected inverter, p is the active power loop droop coefficient, K q is the reactive power loop droop coefficient, τ1 is the active power loop time constant, τ2 is the reactive power loop time constant; Define the input variable of the control model as u, and Define the output variable of the control model as y, and y = (θ, V) T , where (θ, V) T represents the transpose of (θ, V); Step 2: According to the control model established in step 1, define the interconnection relationship between each grid-type inverter as network coupling, that is, the grid-type new energy power generation system is a whole of n grid-type inverters connected to each other through network coupling; calculate the input differential passivity index σ of the network coupling net ; Step 3: According to the control model established in step 1, the output differential passivity index σ of each grid-connected inverter is given. The specific steps are as follows: Define the storage function S(x) of the grid-connected inverter, and its expression is: The Hessian matrix of the storage function S(x) of the grid inverter is recorded as the first Hessian matrix Its expression is: In the formula, is the Hamiltonian operator; make And at the same time satisfy The active power loop droop coefficient K p And reactive power loop droop coefficient K q is an adjustable value; Step 4: Define the distributed stability condition of the grid-connected renewable energy power generation system as σ+σ net ≥0, specifically, calculate σ+σ for each grid-connected inverter net The value of and make the following judgment: If σ+σ is satisfied net ≥0, it is considered that the grid-connected inverter meets the stability conditions; If σ+σ net <0, it is determined that the grid-type inverter does not meet the stability condition, and returns to step 3 to reduce the active power loop droop coefficient K p And reactive power loop droop coefficient K q The value of the output differential passivity index σ of the grid-connected inverter is increased until σ+σ is satisfied. net ≥0; Step 5: When all n grid-type inverters in the grid-type new energy power generation system meet the stability condition σ+σ net When ≥0, the distributed grid-connected new energy power generation system is deemed to be stable and the operation is completed.

2. The distributed stabilization method of a grid-type new energy power generation system based on passivity according to claim 1 is characterized in that: The input differential passivity index σ of the network coupling described in step 2 net The calculation steps are: Step 2.1, record the grid-connected new energy power generation system as a system; Define each grid-connected inverter in the system and the grid connected to the system as a node, that is, the system includes n+1 nodes, and any one of the n+1 nodes is recorded as node i, i=1, 2, ..., n+1; Define the network coupling potential energy function W B (y), Among them, B ii is the self-admittance of the ith node, B ij is the mutual admittance between the i-th node and the j-th node, j = 1, 2, ..., n + 1, and i ≠ j; V i is the voltage amplitude of the ith node, V j is the voltage amplitude of the jth node, θ ij is the phase angle difference between the i-th node and the j-th node; Step 2.2: The network coupling potential energy function W B The Hessian matrix of (y) is recorded as the second Hessian matrix A is the active phase angle relationship matrix, D is the coupling matrix, C is the reactive voltage relationship matrix, D T is the transpose of D, and its expressions are: Among them, N i is the set of all nodes adjacent to the i-th node, and the set N i Any node in is recorded as adjacent node k, k = 1, 2, ..., N i ; B ik is the mutual admittance between the ith node and the adjacent node k, V k is the voltage amplitude of the adjacent node k, θ ik is the phase difference between the ith node and the adjacent node k; Step 2.3, define the input differential passivity index σ of the network coupling net , Among them, λ min is the minimum eigenvalue, is the second Hessian matrix The minimum eigenvalue of .

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