Disclosure of Invention
The invention aims to provide a power distribution network reactive voltage robust control method considering photovoltaic and load uncertainty, which can reduce the influence of uncertain power fluctuation and communication delay of a power distribution network on voltage control, improve the quality of voltage waveform and ensure the safety and stability of the voltage of the power distribution network under the condition of distributed photovoltaic high-proportion access.
The technical scheme adopted by the invention is as follows: a power distribution network reactive voltage robust control method considering photovoltaic and load uncertainty comprises the following steps:
s1, converting the uncertain time lag caused by the communication delay into the confirmed time lag, and establishing a discrete control system model of the controlled node of the power distribution network;
s2, based on the discrete control system model established in S1, the load and the photovoltaic accessed by the node are used as uncertain quantities, and a multi-cell model describing the dynamic characteristics of the voltage control system of the power distribution network is established, so that various values of the uncertain quantities are constrained in the multi-cell model and correspond to each vertex of the multi-cell;
s3, using H∞Robust control principle for converting gain of node voltage disturbance to output into H∞Solving the problem of norm boundary by using a linear matrix inequality optimization method to solve the problem with the gain minimization as the target to obtain a discrete system H which enables all vertexes in the multicellular model to meet the linear matrix inequality∞Control parameters of the robust voltage controller;
s4, collecting voltage vectors of controlled nodes of the power distribution network, and calculating to obtain node voltage deviation as H∞An input quantity of the robust voltage controller; discrete system H determined by using control parameters obtained in S3∞And the robust voltage controller obtains the reactive power regulating quantity corresponding to each photovoltaic access point in the controlled node, and performs reactive voltage control on the distributed photovoltaic accessed by the node according to the reactive power regulating quantity.
Further, discrete system H∞The robust voltage controller comprises a state feedback controller u which minimizes the gain of the disturbance on the outputk=Kxk(ii) a In S3, the discrete system H obtained by the solution∞The control parameter of the robust voltage controller is a control parameter matrix K of the state feedback controller.
Preferably, in S1, the uncertain time lag is converted into a determined time lag which is the control period T of the robust voltage controller, i.e. the control quantity u at the time k-1k-1As a disturbance to the k-th time, namely a discrete control system model:
xk+1=Axk+Buuk+Buuk-1+Bwwk
zk=Cxk (1)
to convert to:
zk=Cxk (2)
wherein x iskA state vector of the control system at the moment k comprises a voltage deviation vector delta V of each photovoltaic grid-connected point; u. ofkControl vectors of a control system at the moment k comprise reactive power regulation vectors delta Q of all the photovoltaic cells; z is a radical ofkThe control output quantity of the controlled node at the moment k is obtained; w is akRepresenting interference items of the voltage of each photovoltaic grid-connected point at the kth moment, namely voltage fluctuation caused by load and photovoltaic active output fluctuation; a is I, C is I, I is an identity matrix; b isuA voltage sensitivity matrix representing the relation between photovoltaic grid-connected point voltage and photovoltaic reactive, BwA voltage sensitivity matrix representing the relation between the photovoltaic grid-connected point voltage and the photovoltaic active power output and load;
order to
The discrete control system model is simplified to:
xk+1=Axk+Buuk+Bw'wk'
zk=Cxk (3)。
preferably, S2 includes:
the photovoltaic active power is output by PpvLoad active power PloadLoaded reactive QloadAs the indeterminate quantity, the definition vector P ═ (P)pv,Pload,Qload) Constrained within a multicellular model;
considering the changes of the load and the photovoltaic output, setting the control vector as u ═ Δ Q and the state vector as x ═ Δ V, and then forming a system multilocular body model by the dynamic characteristics of the control system as follows:
in the formula, coefficient matrix Bu(p)、Bw' (P) by an indeterminate quantity Ppv、PloadAnd QloadDetermining that the uncertainty is contained in a vector P, and Ppv,Pload,QloadConstrained within an interval between respective maximum and minimum values:
defining respective uncertainty P
pv,P
load,Q
loadAre respectively equal to 2
NEach vertex { v
1,...,v
LIn the convex polyhedron, N is the number of groups of uncertain quantity, and each vertex v
iCorresponding to a vector P ═ P (P)
pv,P
load,Q
load) Value of (a) p
iI.e. a matrix [ B ]
u(p
i),B
w′(p
i)]Is taken from the value of
Is the apex of the asperity, then:
preferably, S3 includes:
s31, converting the gain of the disturbance to the output into H∞Problem of norm bound: defining the transfer function of disturbance signal w to output signal z as G (z), corresponding to H∞The norm of (a) is:
wherein | · | purple sweet∞And | · | non-conducting phosphor2Respectively, infinite norm and 2 norm, for a given scalar γ > 0, if | | G (z) | non-conducting phosphor∞If < gamma, the system is said to have H∞Performance γ;
s32, establishing a linear matrix inequality with the gain minimization as a target:
where ρ represents the minimum disturbance suppression degree
Square of (d), superscript T represents the transpose of the matrix;
suppose that for a discrete control system, there is one H∞State feedback controller uk=Kxk(ii) a If and only if the positive matrix X ∈ Rn*n,Y∈Rn*nIf there is a feasible solution Y*,X*If the linear matrix inequality in the expression (9) is satisfied and all the vertices of the multicellular model satisfy the expression (i) in the expression (9), u isk=Y*(X*)-1xkIs a state feedback H of a discrete control system∞A controller, wherein K ═ Y*(X*)-1Namely a control parameter matrix K of the state feedback controller.
I.e. access to all vertices in the multicellular model of load and distributed photovoltaics for nodes of corresponding uncertainty
When the control parameter matrix is solved, the stability problem of different steady-state working points of the system can be solved only by enabling all vertexes of the multilocular body model to satisfy the formula (i) in the formula (9).
The invention also discloses a power distribution network reactive voltage robust control system considering the uncertainty of the photovoltaic and the load, which comprises the following steps:
the discrete control system model building module is used for converting uncertain time lag brought by communication delay into determined time lag and building a discrete control system model of a controlled node of the power distribution network;
the multi-cell model building module is used for building a multi-cell model for describing the dynamic characteristics of the voltage control system of the power distribution network by taking the load and the photovoltaic accessed by the node as uncertain quantities based on the discrete control system model built in the S1, so that various values of the uncertain quantities are constrained in the multi-cell model and correspond to each vertex of the multi-cell;
H∞control parameter solving module of robust voltage controller using H∞Robust control principle for converting gain of node voltage disturbance to output into H∞Solving the problem of norm boundary by using a linear matrix inequality optimization method to solve the problem with the gain minimization as the target to obtain a discrete system H which enables all vertexes in the multicellular model to meet the linear matrix inequality∞Control parameters of the robust voltage controller;
H∞an application module of the robust voltage controller collects voltage vectors of controlled nodes of the power distribution network, and calculates to obtain node voltage deviation as H∞An input quantity of the robust voltage controller; discrete system H determined by using control parameters obtained in S3∞And the robust voltage controller obtains the reactive power regulating quantity corresponding to each photovoltaic access point in the controlled node, and performs reactive voltage control on the distributed photovoltaic accessed by the node according to the reactive power regulating quantity.
Advantageous effects
Compared with the prior art, the invention has the following advantages and progresses:
(1) communication delay possibly existing in the power distribution network level control process is considered, uncertainty time lag is converted into certainty time lag, the control model and the controller design are simplified, effective response of the controller is facilitated, and influence caused by control instantaneity brought by the communication delay is reduced;
(2) by converting the uncertain time lag into the confirmed time lag, the influence of uncertain power change (photovoltaic and load) and uncertain time lag of the power distribution network on voltage control can be reduced, the quality of voltage waveform is improved, and the safety and stability of the voltage of the power distribution network under the condition of distributed photovoltaic high-proportion access are ensured;
(3) the method comprises the steps of considering the changes of load and photovoltaic output, namely the changes of reactive voltage sensitivity, into a system model, establishing the system model by using a multicell model in a convex optimization theory so as to conveniently solve control parameters by adopting an optimization method of a Linear Matrix Inequality (LMI), wherein the method can ensure the stability and the optimal anti-interference capability of the system under different operating conditions;
(4) by means of H∞The voltage control parameter is designed according to the robust control principle, and the gain of the disturbance on the output is converted into H∞The problem of norm boundary is solved by using an optimization method of a Linear Matrix Inequality (LMI), the solving process of the control parameters is simplified, the design process of multiple control parameters can be simplified, and engineering realization is facilitated.
In conclusion, the invention considers the uncertainty of the power distribution network system, simplifies the design of voltage control parameters, is suitable for the power distribution network with distributed photovoltaic multipoint access, can effectively inhibit the fluctuation of the voltage of the power distribution network, and improves the operation safety of the power distribution network.
Detailed Description
The following further description is made in conjunction with the accompanying drawings and the specific embodiments.
Example 1
A power distribution network reactive voltage robust control method considering photovoltaic and load uncertainty comprises the following steps:
s1, converting the uncertain time lag caused by the communication delay into the confirmed time lag, and establishing a discrete control system model of the controlled node of the power distribution network;
s2, based on the discrete control system model established in S1, the load and the photovoltaic accessed by the node are used as uncertain quantities, and a multi-cell model describing the dynamic characteristics of the voltage control system of the power distribution network is established, so that various values of the uncertain quantities are constrained in the multi-cell model and correspond to each vertex of the multi-cell;
s3, using H∞Robust control principle for converting gain of node voltage disturbance to output into H∞Solving the problem of norm boundary by using a linear matrix inequality optimization method to solve the problem with the gain minimization as the target to obtain a discrete system H which enables all vertexes in the multicellular model to meet the linear matrix inequality∞Control parameters of the robust voltage controller;
s4, collecting voltage vectors of controlled nodes of the power distribution network, and calculating to obtain node voltage deviation as H∞An input quantity of the robust voltage controller; discrete system H determined by using control parameters obtained in S3∞And the robust voltage controller obtains the reactive power regulating quantity corresponding to each photovoltaic access point in the controlled node, and performs reactive voltage control on the distributed photovoltaic accessed by the node according to the reactive power regulating quantity.
In S1, the determined time lag converted from the uncertain time lag is the control period T of the robust voltage controller, namely the control quantity u at the k-1 momentk-1As a disturbance to the k-th time, namely a discrete control system model:
xk+1=Axk+Buuk+Buuk-1+Bwwk
zk=Cxk (1)
to convert to:
zk=Cxk (2)
wherein x iskA state vector of the control system at the moment k comprises a voltage deviation vector delta V of each photovoltaic grid-connected point; u. ofkControl vectors of a control system at the moment k comprise reactive power regulation vectors delta Q of all the photovoltaic cells; z is a radical ofkThe control output quantity of the controlled node at the moment k is obtained; w is akRepresenting interference items of the voltage of each photovoltaic grid-connected point at the kth moment, namely voltage fluctuation caused by load and photovoltaic active output fluctuation; a is I, C is I, I is an identity matrix; b isuA voltage sensitivity matrix representing the relation between photovoltaic grid-connected point voltage and photovoltaic reactive, BwRepresenting photovoltaic grid-connected point electricityA voltage sensitivity matrix of the relation between the voltage and the photovoltaic active power output and the load;
order to
The discrete control system model is simplified to:
xk+1=Axk+Buuk+Bw'wk'
zk=Cxk (3)。
s2 includes:
the photovoltaic active power is output by PpvLoad active power PloadLoaded reactive QloadAs the indeterminate quantity, the definition vector P ═ (P)pv,Pload,Qload) Constrained within a multicellular model;
considering the changes of the load and the photovoltaic output, setting the control vector as u ═ Δ Q and the state vector as x ═ Δ V, and then forming a system multilocular body model by the dynamic characteristics of the control system as follows:
in the formula, coefficient matrix Bu(p)、Bw' (P) by an indeterminate quantity Ppv、PloadAnd QloadDetermining that the uncertainty is contained in a vector P, and Ppv,Pload,QloadConstrained within an interval between respective maximum and minimum values:
defining respective uncertainty P
pv,P
load,Q
loadAre respectively equal to 2
NEach vertex { v
1,...,v
LIn the convex polyhedron, N is the number of groups of uncertain quantity, and each vertex v
iCorresponding to a vector P ═ P (P)
pv,P
load,Q
load) Value of (a) p
iI.e. a matrix [ B ]
u(p
i),B
w′(p
i)]Is taken from the value of
Is the apex of the asperity, then:
in the present invention, the discrete system H∞The robust voltage controller comprises a state feedback controller u which minimizes the gain of the disturbance on the outputk=Kxk(ii) a In S3, the discrete system H obtained by the solution∞The control parameter of the robust voltage controller is a control parameter matrix K of the state feedback controller.
Specifically, S3 includes the steps of:
s31, converting the gain of the disturbance to the output into H∞Problem of norm bound: defining the transfer function of disturbance signal w to output signal z as G (z), corresponding to H∞The norm of (a) is:
wherein | · | purple sweet∞And | · | non-conducting phosphor2Respectively, infinite norm and 2 norm, for a given scalar γ > 0, if | | G (z) | non-conducting phosphor∞If < gamma, the system is said to have H∞Performance γ;
s32, establishing a linear matrix inequality with the gain minimization as a target:
where ρ represents the minimum disturbance suppression degree
Square of (d), superscript T represents the transpose of the matrix;
hypothesis pairIn a discrete control system, there is one H∞State feedback controller uk=Kxk(ii) a If and only if the positive matrix X ∈ Rn*n,Y∈Rn*nIf there is a feasible solution Y*,X*If the linear matrix inequality in the expression (9) is satisfied and all the vertices of the multicellular model satisfy the expression (i) in the expression (9), u isk=Y*(X*)-1xkIs a state feedback H of a discrete control system∞A controller, wherein K ═ Y*(X*)-1Namely a control parameter matrix K of the state feedback controller.
I.e. access to all vertices in the multicellular model of load and distributed photovoltaics for nodes of corresponding uncertainty
When the control parameter matrix is solved, the stability problem of different steady-state working points of the system can be solved only by enabling all vertexes of the multilocular body model to satisfy the formula (i) in the formula (9).
Example 2
The embodiment specifically describes a power distribution network reactive voltage robust control method considering photovoltaic and load uncertainty, and the method comprises the following steps:
(1) referring to fig. 1 and 2, the control system acquires voltage data of each photovoltaic grid-connected point from the sensors to obtain voltage vectors V of multiple photovoltaics and voltage reference vectors VrefThe input quantity delta V of the voltage robust controller is obtained through comparison, namely the voltage deviation vector of each photovoltaic grid-connected point, and as a period of time is required from the acquisition of voltage data to the completion of the tracking of each photovoltaic control command to the completion of the voltage control, the control hysteresis problem is brought, so that the uncertainty time lag needs to be converted into the certainty time lag for simplifying the control model and the controller design;
(2) the reactive voltage sensitivity changes along with the change of the power flow due to nonlinearity in the power system, namely the reactive voltage sensitivity changes along with the change of the load and the photovoltaic output, is not a fixed value, and causes certain errors on the control of the system. Therefore, the system model is established by using the multilocular body model in the convex optimization theory, so that the control parameters can be conveniently solved by adopting an optimization method of a Linear Matrix Inequality (LMI), and the method can ensure the stability and the optimal anti-interference capability of the system under different operating conditions;
(3) the invention adopts H∞The robust control principle solves a voltage controller feedback control matrix K by utilizing an optimization method of a Linear Matrix Inequality (LMI), and converts the gain of the disturbance on the output into H∞And in the problem of norm boundary, the voltage deviation vector delta V of each photovoltaic grid-connected point is subjected to robust controller to obtain the output quantity delta Q of the controller, namely the reactive power regulation vector photovoltaic of each photovoltaic, so that the power control of a plurality of distributed photovoltaics in the power distribution network is achieved, the problem of voltage out-of-limit is solved, and the engineering realization is facilitated.
Transition with regard to indeterminate skew:
referring to the voltage control system implementation structure diagram shown in fig. 2, a sensor acquires a distribution network node voltage vector V and a voltage reference vector VrefAfter comparison, the control instruction Q, tau is obtained by a voltage controllers k cRepresenting the time delay, τ, of the sensor to the controllerc k aThe time delay from the controller to the actuator is shown, and the problem of voltage control lag is brought by communication delay, so the invention converts the uncertain time lag into the deterministic time lag, and the specific form is as follows:
referring to fig. 3, due to the existence of the time lag, the control command at the time k-1 may not be completely executed at the time k, and therefore, the discrete control system model may be represented as:
in the formula: x is the number ofkControlling the state quantity of the system at the moment k, and taking the state quantity as a voltage deviation vector delta V of each photovoltaic grid-connected point; u. ofkControlling the control quantity of the system at the moment k, and obtaining a reactive power regulation vector delta Q of each photovoltaic; z is a radical ofkThe output quantity controlled at the moment k; w is akIndicates the k-th timeAnd interference items of the voltage of each photovoltaic grid-connected point, namely voltage fluctuation caused by load and photovoltaic active output fluctuation. And A is I, C is I, and I is an identity matrix. The size of B is determined by the reactive voltage sensitivity between the controlled node and the reactive power control equipment, BuA voltage sensitivity matrix representing the relation between photovoltaic grid-connected point voltage and photovoltaic reactive, BwAnd the voltage sensitivity matrix represents the relation between the photovoltaic grid-connected point voltage and the photovoltaic active power output and load.
It is assumed that the maximum delay time of transmission of the control system in each period is bounded and does not exceed the control period T, i.e. the maximum transmission delay
In this case, the control system can be designed with a communication delay of T, i.e. the control quantity u at the time k-1
k-1Considering as the disturbance amount to the k-th time, the following discrete control system model can be established:
order to
The control model is further simplified to:
regarding establishment of multicellular models:
during modeling, the photovoltaic active power output P is measuredpvLoad active power PloadLoaded reactive QloadAs an uncertainty, i.e. the definition vector P ═ (P)pv,Pload,Qload) Constrained within a multicellular model. Considering the variation of load and photovoltaic output, setting a control vector of a control system as u ═ Δ Q, a reactive regulation vector of each photovoltaic, a state vector x ═ Δ V, and a voltage deviation vector Δ V of each photovoltaic grid-connected point, and then setting the reactive voltage control systemThe dynamic properties of the system may form a multicellular model of the system as follows:
in the formula: x is the number ofkIs the state quantity at the k moment; u. ofkIs the control quantity at the k moment; z is a radical ofkThe output quantity controlled at the moment k; w is akAnd (4) representing interference items of the voltage of the controlled node at the moment k, namely voltage fluctuation caused by fluctuation of load and photovoltaic active output. And A is I, C is I, and I is an identity matrix. Coefficient matrix Bu(p)、Bw(p) is determined by the uncertainty contained in the vector p, which is assumed to consist of N uncertainty, i.e. p ═ p, without loss of generality1,...,pN]Each uncertainty amount piBetween the minimum and maximum values for a bounded variable, i.e. N-3 in the method, the uncertainty quantity Ppv,Pload,QloadConstrained within the interval between its maximum and minimum values, i.e.:
uncertainty P in the inventionpv,Pload,QloadAre known according to the actual application. When the parameter matrix of the feedback controller is solved, the values of the 8 groups of uncertain quantities are determined according to the value intervals of the uncertain quantities.
Definition of p
iIs taken to be 2
NEach vertex { v
1,...,v
LIn the convex polyhedron of which each vertex v is
iCorresponding to the matrix [ B
u(p
i),B
w(p
i)]If, if
Is the pole of the lobe, then:
in the invention, if N is 3, the constructed convex polyhedron has 8 vertexes, and each vertex corresponds to a group of values of the uncertainty.
With respect to H∞Robust controller control parameter solution
Referring to the voltage controller structure shown in FIG. 3, z-1Representing a discrete integrator, if the control vector of the system is set to u ═ Δ Q and the state vector x ═ Δ V, then without loss of generality, equation (4) can be written as:
for the system (7) there is a state feedback controller which acts to minimise the gain of the disturbance to the output. In robust control system design, the gain of the output from the disturbance is usually converted into H∞Problem of norm bound, H∞The norm is valid for problems related to model uncertainty. Smaller norm indicates stronger suppression of disturbance. For a discrete system, the transfer function of the perturbation signal w to the output signal z is G (z), and the corresponding norm is expressed as:
wherein | · | purple sweet∞And | · | non-conducting phosphor2Respectively, infinite norm and 2 norm. For a given scalar γ > 0, if | | G (z) | luminance∞If < gamma, the system is said to have H∞The property γ.
For a discrete system, there is one H∞State feedback controller (u)k=Kxk) If and only if a positive definite matrix X ∈ Rn*nAnd the matrix Y ∈ Rn*nSuch that the matrix inequality (i) in equation (9) holds, if there is a feasible solution Y*,X*Then u isk=Y*(X*)-1xkIs one of a discrete system (7)Individual state feedback H∞A controller, wherein K ═ YX-1Is a feedback control matrix, K in fig. 3.
By solving the following optimization problem:
the optimal solution of the optimization problem can be used for obtaining the optimal H of the system
∞The controller feeds back a control matrix K with a corresponding minimum disturbance rejection degree of
For all vertices in the multicellular model
The stability problem of different steady-state working points of the system can be solved only by satisfying the formula (i) in the formula (9).
The design process of multiple control parameters is simplified through the solving of the convex optimization problem, and engineering realization is facilitated.
Example 3
A power distribution network reactive voltage robust control system that accounts for photovoltaic and load uncertainty, comprising:
the discrete control system model building module is used for converting uncertain time lag brought by communication delay into determined time lag and building a discrete control system model of a controlled node of the power distribution network;
the multi-cell model building module is used for building a multi-cell model for describing the dynamic characteristics of the voltage control system of the power distribution network by taking the load and the photovoltaic accessed by the node as uncertain quantities based on the discrete control system model built in the S1, so that various values of the uncertain quantities are constrained in the multi-cell model and correspond to each vertex of the multi-cell;
H∞control parameter solving module of robust voltage controller using H∞Robust control principle for converting gain of node voltage disturbance to output into H∞The problem of norm boundary is solved by utilizing a linear matrix inequality optimization methodSolving the problem of minimizing gain to obtain a discrete system H which enables all vertexes in the multi-cell model to meet the linear matrix inequality∞Control parameters of the robust voltage controller;
H∞an application module of the robust voltage controller collects voltage vectors of controlled nodes of the power distribution network, and calculates to obtain node voltage deviation as H∞An input quantity of the robust voltage controller; discrete system H determined by using control parameters obtained in S3∞And the robust voltage controller obtains the reactive power regulating quantity corresponding to each photovoltaic access point in the controlled node, and performs reactive voltage control on the distributed photovoltaic accessed by the node according to the reactive power regulating quantity.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.