CN116780634A - Small-disturbance synchronous stability enhancement method for new energy grid-connected system and application of small-disturbance synchronous stability enhancement method - Google Patents
Small-disturbance synchronous stability enhancement method for new energy grid-connected system and application of small-disturbance synchronous stability enhancement method Download PDFInfo
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- CN116780634A CN116780634A CN202310808544.XA CN202310808544A CN116780634A CN 116780634 A CN116780634 A CN 116780634A CN 202310808544 A CN202310808544 A CN 202310808544A CN 116780634 A CN116780634 A CN 116780634A
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- 238000000034 method Methods 0.000 title claims abstract description 36
- 230000001360 synchronised effect Effects 0.000 title claims abstract description 30
- 238000013507 mapping Methods 0.000 claims abstract description 8
- 230000003111 delayed effect Effects 0.000 claims abstract description 5
- 239000011159 matrix material Substances 0.000 claims description 16
- 230000006870 function Effects 0.000 claims description 13
- 230000002708 enhancing effect Effects 0.000 claims description 6
- 230000008569 process Effects 0.000 claims description 4
- 238000005457 optimization Methods 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 5
- 238000004088 simulation Methods 0.000 abstract description 2
- 238000004458 analytical method Methods 0.000 description 6
- 230000010355 oscillation Effects 0.000 description 3
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
Abstract
The method is a new energy grid-connected system small disturbance synchronous stability enhancement method based on delayed embedded Koopman model predictive control, and comprises the following steps of: collecting time sequence data of a new energy grid-connected system; step 2: carrying out delay embedding on the acquired data; step 3: and (3) performing observation space mapping on the acquired data by using an observation function group phi (x), and performing linear least square solution. The invention realizes the state identification and prediction of the network-following new energy grid-connected system under the condition of limited observance quantity, and establishes a Koopman model prediction control method based on time delay embedding; the optimal control of a nonlinear system based on measurement is realized, and the small disturbance synchronization stability of the grid-connected system of the new energy is enhanced; simulation results show that the Koopman model predictive control method based on time delay embedding can remarkably improve the small disturbance synchronous stability of the new energy grid-connected system.
Description
Technical Field
The invention relates to an enhancement method and application thereof, in particular to a method for enhancing small disturbance synchronous stability of a new energy grid-connected system and application thereof, belonging to the field of stable control of power systems.
Background
The new energy unit is generally connected to a power grid through a power electronic converter, and has obvious differences from the traditional synchronous unit in internal structure, electromechanical transient characteristics and control method design. According to the synchronous control strategy adopted by the grid connection of the converters, the converters can be divided into a following-grid converter and a grid-structured converter. The phase-locked loop is utilized to extract the phase of the voltage of the common grid-connected point, so that the synchronization with the power grid is ensured, and the grid-connected converter is the most widely applied grid-connected converter at present. The synchronization characteristic of the new energy grid-connected system is completely determined by the converter control system, the influence of the performance of the controller and the strength of the power grid is large, and the oscillation caused by the synchronization instability is easy to occur. According to the severity of disturbance, the synchronous stability problem can be further divided into a small disturbance synchronous stability problem and a large disturbance synchronous stability problem, and the research of the small disturbance synchronous stability of the new energy source grid-connected system of the grid-connected type alternating current system has important practical significance.
The problem of small disturbance synchronous stability can be usually studied by adopting methods such as impedance analysis, lyapunov analysis, characteristic analysis and the like, and a linear controller is designed on the basis of the problem to enhance the small disturbance synchronous stability of the system. The impedance analysis method is based on a complex variable impedance model of the converter, and on the basis, parameters of a controller of the converter can be optimized, so that the impedance characteristic of the converter can be effectively improved; a voltage feed forward loop may also be added to the controller so that the output admittance of the converter is controllable during periods of disturbance to enhance synchronous stability. The characteristic analysis method can analyze the grid-connected inverter, a high-order small signal model which is favorable for the research of small disturbance stability is established, and on the basis, the small disturbance stability of the doubly-fed fan can be improved by utilizing an additional damping control method. However, in actual engineering, a new energy grid-connected system is difficult to obtain a specific model and detailed parameters due to various reasons such as business confidentiality, belongs to a gray box model or even a black box model, and a control strategy based on model design has failure risk. Meanwhile, due to the problems of weak disturbance resistance, low overload capacity and the like of the power electronic equipment, the running state of the system may deviate far from the balance point when the new energy grid-connected system suffers small disturbance, and at the moment, the accuracy of the linearization model based on the balance point is greatly reduced, which is also unfavorable for the implementation of stable control
Disclosure of Invention
The invention aims to solve the technical problems that: the problem of small disturbance synchronous stability enhancement of a new energy grid-connected system based on system time sequence measurement data is specifically as follows: the new energy grid-connected system is based on a small disturbance synchronous instability mechanism of improper parameter setting or weak AC power grid access, a Koopman system identification method based on delay embedding and a Koopman model prediction control method based on delay embedding.
The invention aims to perform model predictive control of a new energy grid-connected system by means of time sequence measurement data of system state quantity, thereby solving the problem of small disturbance synchronization instability caused by improper parameter setting or weak connection of an alternating current grid system.
The technical scheme of the invention is as follows:
the method is a new energy grid-connected system small disturbance synchronous stability enhancement method based on delayed embedded Koopman model predictive control, and is characterized by comprising the following steps of:
step 1: collecting time sequence data of a new energy grid-connected system;
step 2: carrying out delay embedding on the acquired data;
step 3: and (3) performing observation space mapping on the acquired data by using an observation function group phi (x), and performing linear least square solution.
Advantageous effects
The state identification and prediction of the network-following new energy grid-connected system under the condition of limited observance are realized, and a Koopman model prediction control method based on time delay embedding is established;
the optimal control of a nonlinear system based on measurement is realized, and the small disturbance synchronization stability of the grid-connected system of the new energy is enhanced;
simulation results show that the Koopman model predictive control method based on time delay embedding can remarkably improve the small disturbance synchronous stability of the new energy grid-connected system.
Drawings
Fig. 1 is a diagram showing a control structure of a heel-net type converter;
fig. 2 is a schematic diagram showing oscillation of a grid-connected converter due to improper PLL parameter setting;
FIG. 3 is a graph showing a comparison of the predictions of a Koopman model in a scene of small disturbance instability due to improper setting of PLL parameters for a grid-type converter;
fig. 4 shows the system state of the Koopman MPC after the network converter is put into operation under the condition of improper PLL parameter setting.
Detailed Description
The method for enhancing the small disturbance synchronous stability of the new energy grid-connected system is based on the delayed embedded Koopman model predictive control and comprises the following steps:
step one, collecting time sequence data of a system.
Collecting time sequence data omega (t) 1 ),ω(t 2 ),ω(t 3 ),...,ω(t n ) And delta (t) 1 ),δ(t 2 ),δ(t 3 ),...,δ(t n ) Wherein ω is the angular frequency of the new energy grid-connected system; delta is the angular frequency of the new energy grid-connected system, t is different moments, and n is the total moment number of the acquisition process. .
And step two, carrying out delay embedding on the acquired data.
Based on the embedding theorem proposed by Takes, proper delay embedding dimension n necessarily exists d The phase space of the delay reconstruction can reflect the structural characteristics of the new energy grid-connected system. The data collected can be embedded in a time delay manner to obtain the dimension rising data:
wherein u is the control quantity of the new energy grid-connected system, T is the total time number of the system operation time sequence data, and n d For the dimension of delay embedding, ζ is the dimension-increasing state of the acquired data, so as to obtain a dimension-increasing matrix:
and thirdly, performing observation space mapping on the acquired data by using an observation function group phi (x), and performing linear least square solving.
Assume that there is a specifiable set of observation functions:
wherein the method comprises the steps ofFor specifiable scalar value observation functions, N is the number of scalar value observation functions in the scalar value observation function group. The observation space mapping is performed on the upgoing matrix, and then:
wherein z is the mapping state of the up-dimension matrix χ, U t The sequence formed by all control variables at the time t is represented, and a delay embedded state equation in a formula form can be obtained by solving two linear least square problems of the formula and the formula:
wherein A, B are matrix parameters of the delay embedded state equation, C is matrix parameters of the output equation
And fourthly, designing a controller by using a model predictive control method based on linear quadratic programming, and realizing the linear optimal control of the small disturbance synchronous stability of the new energy grid-connected system.
Let N be the predicted range length, where γ i 、y j I=0, …, N-1, j=1, …, N denotes the input and output sequences in the prediction horizon, a classical convex quadratic cost function suitable for reference signal tracking can be constructed:
wherein Q is i＝1,…,N 、R i＝0,…,N-1 Is a positive definite matrix of real symmetry, so the optimization problem solved by MPC during the prediction time of each closed loop operation is as follows:
matrix E N And the coefficient matrix in the inequality constraint of the power system is represented, so that the limited electric quantity in the system can not exceed the safety range in the system control process. Therefore, the optimal control gamma of each moment can be obtained, and the small disturbance synchronous stability of the new energy grid-connected system is improved.
Examples
Referring to fig. 1, the topology structure of the grid-connected new energy grid-connected system is shown in table 1.
TABLE 1 grid-connected converter model parameters based on Simulink platform
When the system is destabilized by a small disturbance due to improper PLL parameter settings, the output of the system is shown in fig. 2. And (3) collecting time sequence data of the first step, embedding delay of the second step and solving the linear quadratic problem of the third step to the system, and finally obtaining a Koopman model of the system. FIG. 3 is a graph of the comparative predictions of the Koopman model when the PLL parameters are improperly set, the root mean square error of the Koopman model based on measurement and identification is about 4.43%, the reliability of the predictions is high, and FIG. 4 is the system state after MPC control is added. After the MPC control was added by graph analysis, the oscillation of the system was suppressed and stabilized at about 0.45 s.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made therein without departing from the spirit and scope of the invention, which is defined by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (7)
1. The method is a new energy grid-connected system small disturbance synchronous stability enhancement method based on delayed embedded Koopman model predictive control, and is characterized by comprising the following steps of:
step 1: collecting time sequence data of a new energy grid-connected system;
step 2: carrying out delay embedding on the acquired data;
step 3: and (3) performing observation space mapping on the acquired data by using an observation function group phi (x), and performing linear least square solution.
Step 4: and a controller is designed by using a model predictive control method based on linear quadratic programming, so that the linear optimal control of the small disturbance synchronous stability of the new energy grid-connected system is realized.
2. The method for enhancing the small-disturbance synchronous stability of the new energy grid-connected system according to claim 1, wherein the step 1 further comprises the following steps: collecting time sequence data omega (t) 1 ),ω(t 2 ),ω(t 3 ),...,ω(t n ) And delta (t) 1 ),δ(t 2 ),δ(t 3 ),...,δ(t n ) Wherein ω is the angular frequency of the new energy grid-connected system, δ is the angular frequency of the new energy grid-connected system, t is different moments, and n is the total moment number of the acquisition process.
3. The method for enhancing the small-disturbance synchronous stability of the new energy grid-connected system according to claim 1, wherein the step 2 further comprises the following steps: based on the embedding theorem proposed by Takes, proper delay embedding dimension n necessarily exists d The phase space of the delay reconstruction can reflect the new energy grid-connected systemStructural characteristics; the collected data is embedded in a delayed mode to obtain dimension-increasing data:
wherein u is the control quantity of the new energy grid-connected system, T is the total time number of the system operation time sequence data, and n d For the dimension of delay embedding, ζ is the dimension-increasing state of the acquired data, so as to obtain a dimension-increasing matrix:
4. the method for enhancing the small-disturbance synchronous stability of the new energy grid-connected system according to claim 1, wherein the step 3 further comprises the following steps: assume a specified set of observation functions:
wherein the method comprises the steps ofFor specifiable scalar value observation functions, N is the number of scalar value observation functions in the scalar value observation function group. The observation space mapping is performed on the upgoing matrix, and then:
wherein z is the mapping state of the up-dimension matrix χ, U t The sequence formed by all control variables at the time t is represented, and a delay embedded state equation in a formula form can be obtained by solving two linear least square problems of the formula and the formula:
wherein A, B is matrix parameter of the delay embedded state equation, C is matrix parameter of the output equation:
5. the method for enhancing the small-disturbance synchronous stability of the new energy grid-connected system according to claim 1, wherein the step 4 further comprises the following steps:
let N be the predicted range length, where γ i 、y j I=0, …, N-1, j=1, …, N denotes the input and output sequences in the prediction horizon, a classical convex quadratic cost function suitable for reference signal tracking can be constructed:
wherein Q is i＝1,…,N 、R i＝0,…,N-1 Is a positive definite matrix of real symmetry, so the optimization problem solved by MPC during the prediction time of each closed loop operation is as follows:
matrix E N And the coefficient matrix in the inequality constraint of the power system is represented, so that the limited electric quantity in the system can not exceed the safety range in the system control process. Thus, the optimal control γ at each time can be obtainedThereby improving the small disturbance synchronous stability of the new energy grid-connected system.
6. A non-volatile storage medium, characterized in that the non-volatile storage medium comprises a stored program, wherein the program, when run, controls a device in which the non-volatile storage medium is located to perform the method of any one of claims 1 to 5.
7. An electronic device comprising a processor and a memory; the memory has stored therein computer readable instructions for executing the processor, wherein the computer readable instructions when executed perform the method of any of claims 1 to 5.
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