CN110797855B - Uncertainty direct-current micro-grid fuzzy switch control method with constant power load - Google Patents
Uncertainty direct-current micro-grid fuzzy switch control method with constant power load Download PDFInfo
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
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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
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Abstract
The invention provides a fuzzy switch control method of an uncertainty direct-current micro-grid with a constant power load, which is used for designing injection current of a storage unit based on a fuzzy model and a parallel distributed compensation scheme so as to solve the problem of uncertainty of the constant power load. The proposed fuzzy switch controller can fuse more system information because of more complex construction forms, and the gain can obtain a control design feasible solution with remarkably reduced conservation by using a developed relaxation Linear Matrix Inequality (LMI) design method, thereby being beneficial to the online implementation of a fuzzy control scheme. The direct current micro-grid with constant power load can solve the technical problems caused by inaccuracy in a system model, and controller errors caused by calculation delay, quantization effect and calculation approximation by any type of parameter uncertainty.
Description
Technical Field
The invention belongs to the technical field of power system automation, and particularly relates to an uncertainty direct-current micro-grid fuzzy switch control method with constant power load.
Background
With the great application of sustainable power sources in modern power networks, the idea of combining them into a micro-grid structure to simplify power management and control is receiving increasing attention from researchers. Since the conventional power system network relies on an ac system, research into micro-grids is mainly focused on its ac architecture. However, compared with an alternating-current micro-grid, the direct-current micro-grid consists of a plurality of power supplies and DC/AC exchange loads, and is connected together through a power electronic converter and a filter, so that the direct-current micro-grid has the advantages of high efficiency, reactive power, no harmonic wave and the like. The study of constant power load in a DC micro-grid is of great importance to marine power grids, automotive and spacecraft applications and induction motor drives. For this purpose, a new control strategy needs to be designed so that the constant power load output in the direct current micro-grid can meet the control and stability requirements.
Both current distribution and voltage regulation are used to stabilize the dc microgrid, but the negative impedance characteristics of a constant power load can destabilize the entire microgrid system. At present, the control based on the T-S fuzzy model is widely applied to a complicated nonlinear control system and achieves an effective control effect. Since the dc micro grid has a nonlinear property, the stability of the micro grid system is usually studied by using the property to mitigate the adverse effect of the dc micro grid system to obtain a good effect. In particular, the theory of control gain design based on techniques such as a linear state feedback controller and a Linear Matrix Inequality (LMI) has led to widespread use of the theory of linear control using closed-loop system stability. However, these all require injection of a stabilizing current for use on the desired constant power load to mitigate the effects of instability. Moreover, due to uncertainty of parameters on constant power load, inaccuracy in the energy storage system model and controller errors caused by calculation delay, quantization effect and calculation approximation all make the designed controller difficult to resist, and cause system instability. There is a need to study the robustness of a designed controller against system uncertainty and implementation against controller errors to mitigate the impact on constant power load.
Disclosure of Invention
Aiming at the defects of the background technology, the invention further provides an uncertainty direct current micro-grid fuzzy control method with constant power load, which is used for solving the problem of uncertainty of the constant power load by designing the injection current of a storage unit based on a fuzzy model and a parallel distributed compensation scheme; it should be noted that the proposed fuzzy switch controller can fuse more system information because of its more complex construction form, and its gain can be solved with a control design feasibility that is significantly reduced in conservation by using the developed relaxed linear matrix inequality design method, which is beneficial to the on-line implementation of the fuzzy control scheme. In addition, the direct current micro-grid with constant power load can solve the technical problems caused by inaccuracy in a system model and controller errors caused by calculation delay, quantization effect and calculation approximation by any type of parameter uncertainty.
A fuzzy switch control method for an uncertainty direct-current micro-grid with constant power load comprises the following steps:
step 1, establishing a dynamic model of a single direct current micro-grid system;
step 2, constructing an integral dynamic model of the single direct current micro-grid according to the model of the single direct current micro-grid;
step 3, constructing a corresponding T-S fuzzy model according to the model of the direct-current micro-grid;
step 4, designing a direct-current micro-grid fuzzy control law based on a switch controller;
step 5, solving gains of a controller and an observer related to the fuzzy control law;
and 6, assigning control gains of the controller and the observer obtained by solving to the loop to realize the optimal constant power load and the energy storage system on the direct current micro-grid.
Further, in step 1, the direct current micro grid system includes a constant power load CPL, a direct current source DC and an energy storage system ESS;
in order to obtain the overall dynamic characteristics of a direct current micro-grid with a plurality of constant power loads, firstly, the characteristics of one constant power load with a direct current power supply and a power subsystem are studied; the constant power load is modeled by a voltage controlled current source, and considering the j-th constant power load connected to the dc link, the nonlinearity of its value depends on the power and voltage of the constant power load;
in the circuit of the j-th constant power load system connected in series with the RLC filter and the direct current link, a dynamic model shown by the constant power load is as follows:
wherein ,iL,j and vC,j Representing the inductor current and capacitor voltage, r, respectively, on the jth constant power load L,j Representing the inductance resistance, L, at the jth constant power load j Inductance representing the jth constant power load, C j Represents the jthCapacitance of constant power load, V e Representing a dc link voltage;
P j represents constant power on the jth constant power load and must meet the following constraints: for balance point i L0,j v C0,j ]The method comprises the following steps:
wherein ,iL0,j and vC0,j Inductor current and capacitor voltage, P, respectively representing balance position on jth constant power load max,j Representing the maximum constant power on the jth constant power load, V dc Representing a direct current power supply;
the RLC filter is connected through a voltage source of the energy storage system, and the energy storage system is connected through a current source i es Modeling is carried out, and the state space representation form of the direct current micro-grid energy storage system is as follows:
wherein ,iL,s and vC,s Representing the inductor current and capacitor voltage, r, respectively, on an energy storage system s Representing the resistance of the energy storage system, L s Representing the inductance of the energy storage system, C s Representing the capacitance, i, of an energy storage system es Representing a current source;
in order to obtain a new nonlinear dynamic characteristic with an origin as a balance point, a power system is needed to perform stability analysis and controller synthesis on a nonlinear system of Lyapunov stability theory, and the balance point of the power system is located at the origin. By changing the coordinates, the power models (1) and (3) can be converted into:
wherein , and />Respectively representing the inductor current and the capacitor voltage on the jth constant power load at the point of equilibrium,/> and />Respectively representing the inductor current and the capacitor voltage on the energy storage system at the point of equilibrium, +.>Representing the current source at the point of equilibrium.
Further, in step 2, based on a single constant power load connected to the dc link and an energy storage system connected to the dc power supply, deriving an integral micro-grid with multiple constant power loads, the energy storage system and the dc power supply connected through RLC filters, decoupling the integral dc micro-grid into q+1 subsystems;
the state space representation of a constant power load is:
where j= {1,2 …, Q } and s=q+1 represent the state of the dc source filter, x j ＝[i L,j v C,j ] T and xs ＝[i L,s v C,s ] T Representing the state of the jth constant power load and the state of the DC source filter respectively;
the dc source subsystem state space may be described by:
wherein ,
also, a coordinate of an operation point is changed, and a DC current source i is provided es As a control input, the entire dc micro-grid with the balance point at the origin is rewritten as follows:
wherein ,
when h= [ h ] 1 … h Q ] T In the time-course of which the first and second contact surfaces,
further, in step 3, based on the T-S fuzzy model, systematically calculating an equivalent T-S fuzzy model of the nonlinear system by a sector nonlinear method to obtain a local linear system and a fuzzy membership function; entering each nonlinear term of the original system into two linear sectors; acquiring a membership function and a local matrix of TS fuzzy by aggregating all groups of two sectors;
converting a microgrid having a plurality of constant power loads into a microgrid having one equivalent constant power load and modeling the nonlinearities of a model (10) in which only one nonlinear term is present; for a given regionCalculation sector => and />Make->Wherein the lower slope U min And upper slope U max Drawing a nonlinear term h 1 And its corresponding sector;
by combining the sector inequalityConversion to min-max inequality +.>To calculate the slope, there are:
based on the sector non-linearity method, consider:
solving (14) to obtain a membership function M 1 and M2 ：
Substituting (14) into (10) can obtain an equivalent T-S fuzzy model:
wherein ：
discretizing the T-S fuzzy model (16) to obtain a discrete T-S fuzzy model (18); discretized fuzzy model forThe expression is as follows:
wherein ,i∈N r = {1, …, r }, r represents a control rule of fuzzy control;a state variable representing a constant power load and a dc source filter control input, respectively.
Further, in step 4, a new fuzzy switch controller is proposed to better control the stable input of its current;
assuming that the precondition variables are not clear, there must be one n ε {1,2, …, r } for any one sample point k, so that h n ≥h m Where m ε {1,2, …, r }, n+.m; the expression of the fuzzy system is as follows:
the switch controller input of the DC source filter is made as follows:
then there isi,j∈N r ＝{1,…,r}。
For fuzzy control, a positive fuzzy Lyapunov function is selected: wherein Pθ As a positive definite function, ++>
Then for the ith fuzzy rule, which corresponds to the design rule of the controller, the Lyapunov function is utilized to obtain the expected value, and the relaxation variable is selectedThen there are: />
Applying equation (21) to expression (20) there is
wherein ：i,j,l∈N r ＝{1,…,r}
further, in step 5, the controller gain involved in the control law of the switch controller is obtained by solving the following LMI problem;
given i, j, l, n, a matrix is soughtX n The following LMIs are satisfied:
wherein ：
based on the obtainedObtaining a matrix by solving (25) - (29)>Q ijl ，/>
And because of the fact that,the controller gain is +.>
Further, in step 6, the gain K of the controller is solved by the above expression using the linear matrix inequality LMI i And substituting the optimal constant power load on the direct-current micro-grid and the optimal value of the energy storage system to ensure that the direct-current micro-grid can always stably and efficiently operate.
The technical scheme adopted by the invention has the following advantages: the fuzzy control method of the uncertainty direct current micro-grid with the constant power load based on the fuzzy model is provided, and the fuzzy model and the parallel distributed compensation scheme are used for designing the injection current of the storage unit so as to solve the problem of uncertainty of the constant power load. And the proposed fuzzy switch controller can fuse more system information because of more complex construction forms, and the gain of the fuzzy switch controller can obtain a control design feasible solution with remarkably reduced conservation by using a developed relaxation Linear Matrix Inequality (LMI) design method, thereby being beneficial to the online implementation of a fuzzy control scheme. The direct current micro-grid with constant power load can solve the technical problems caused by inaccuracy in a system model, and controller errors caused by calculation delay, quantization effect and calculation approximation by any type of parameter uncertainty.
Drawings
Fig. 1 is a circuit diagram of a jth constant power load system in series with an RLC filter and a dc link in an embodiment of the present invention.
FIG. 2 shows an energy storage system passing through a current source i according to an embodiment of the present invention es And modeling the circuit diagram.
Fig. 3 is a schematic diagram of a dc micro-grid sector nonlinear method with a constant power load in an embodiment of the invention.
Fig. 4 shows a flowchart of an uncertainty dc micro-grid fuzzy switch control method with constant power load in an embodiment of the invention.
Detailed Description
The technical scheme of the invention is further described in detail below with reference to the attached drawings.
A fuzzy switch control method for an uncertainty direct-current micro-grid with constant power load comprises the following steps:
step 1, establishing a dynamic model of a single direct current micro-grid system;
step 2, constructing an integral dynamic model of the single direct current micro-grid according to the model of the single direct current micro-grid;
step 3, constructing a corresponding T-S fuzzy model according to the model of the direct-current micro-grid;
step 4, designing a direct-current micro-grid fuzzy control law based on a switch controller;
step 5, solving gains of a controller and an observer related to the fuzzy control law;
and 6, assigning control gains of the controller and the observer obtained by solving to the loop to realize the optimal constant power load and the energy storage system on the direct current micro-grid.
Step 1, establishing a dynamic model of a single direct current micro grid system, wherein the direct current micro grid system comprises a Constant Power Load (CPL), a direct current source (DC) and an Energy Storage System (ESS), introducing the constant power load by strictly regulating the direct current or alternating current load, and realizing the constant power load on the input side of a converter. In addition, it is assumed that the voltage of the direct current source is constant and uncontrollable. The dc link is provided by a constant dc power supply.
In order to obtain the overall dynamic characteristics of a dc micro grid with a plurality of constant power loads, the characteristics of one constant power load with a dc power supply and a power subsystem were first studied. The constant power load is modeled by a voltage controlled current source and considering the j-th constant power load connected to the dc link, the nonlinearity of its value depends on the power and voltage of the constant power load.
The circuit diagram of the j-th constant power load system connected in series with the RLC filter and the direct current link, wherein the dynamic model shown by the constant power load is as follows:
wherein ,iL,j and vC,j Representing the inductor current and capacitor voltage, r, respectively, on the jth constant power load L,j Representing the inductance resistance, L, at the jth constant power load j Inductance representing the jth constant power load, C j Capacitance representing the jth constant power load, V e Representing the dc-link voltage (for simplicity of the model, the dc-link voltage is represented by a voltage source V e Modeling).
P j Represents constant power on the jth constant power load and must meet the following constraints: for balance point i L0,j v C0,j ]The method comprises the following steps:
wherein ,iL0,j and vC0,j Inductor current and capacitor voltage, P, respectively representing balance position on jth constant power load max,j Representing the maximum constant power on the jth constant power load, V dc Indicating a dc power supply.
The RLC filter is connected through a voltage source of the energy storage system, and then the energy storageCan pass through the current source i es Modeling is carried out, and the state space representation form of the direct current micro-grid energy storage system is as follows:
wherein ,iL,s and vC,s Representing the inductor current and capacitor voltage, r, respectively, on an energy storage system s Representing the resistance of the energy storage system, L s Representing the inductance of the energy storage system, C s Representing the capacitance, i, of an energy storage system es Representing a current source.
In order to obtain a new nonlinear dynamic characteristic with an origin as a balance point, a power system is needed to perform stability analysis and controller synthesis on a nonlinear system of Lyapunov stability theory, and the balance point of the power system is located at the origin. By changing the coordinates, the power models (1) and (3) can be converted into:
wherein , and />Respectively representing the inductor current and the capacitor voltage on the jth constant power load at the point of equilibrium,/> and />Representing inductor current and capacitor, respectively, on an energy storage system at a point of equilibriumVoltage (V)>Representing the current source at the point of equilibrium.
And 2, constructing an integral dynamic model of the single direct current micro-grid according to the model of the single direct current micro-grid, and deriving the integral micro-grid with a plurality of constant power loads, the energy storage system and the direct current power supply connected through the RLC filter based on the single constant power load connected to the direct current link and the energy storage system connected to the direct current power supply. We can decouple the entire dc micro-grid into q+1 subsystems (i.e., Q constant power loads and one dc power supply).
The state space representation of a constant power load is:
where j= {1,2 …, Q } and s=q+1 represent the state of the dc source filter, x j ＝[i L,j v C,j ] T and xs ＝[i L,s v C,s ] T Representing the state of the jth constant power load and dc source filter, respectively.
The dc source subsystem state space may be described by:
wherein ,
also, it is assumed that the coordinates of an operating point are changed and the DC current source i is allowed to operate es As control inputThe entire dc micro-grid with the balance point at the origin can be rewritten as follows:
wherein ,
when h= [ h ] 1 … h Q ] T In the time-course of which the first and second contact surfaces,
and 3, constructing a corresponding T-S fuzzy model according to the model of the direct current micro-grid, and systematically calculating an equivalent T-S fuzzy model of the nonlinear system based on the T-S fuzzy model by a sector nonlinear method to obtain a local linear system and a fuzzy membership function. Each nonlinear term of the original system is entered into two linear sectors. And (3) obtaining a membership function and a local matrix of TS fuzzy by aggregating all groups of the two sectors.
A micro-grid with multiple constant power loads may be converted to a micro-grid with one equivalent constant power load. To calculate the TS fuzzy model, the nonlinearity of the model (10) needs to be modeled. There is only one nonlinear term in the dynamic model (e.g., h 1 ). For a given regionThe sector +.> and />So thatWherein the lower slope U min And upper slope U max Drawing a nonlinear term h 1 And its corresponding sector.
The slope is typically complex to calculate by taking the sector inequalityConversion to min-max inequality +.>To simply calculate the slope, then there are:
based on the sector nonlinear method, consider
Solving (14) to obtain a membership function M 1 and M2 :
Substituting (14) into (10) can obtain an equivalent T-S fuzzy model:
wherein ：
discretizing the T-S fuzzy model (16) to obtain a discrete T-S fuzzy model (18). Discretized fuzzy model forThe expression is as follows:
wherein ：i∈N r = {1, …, r }, r denotes a control rule of the fuzzy control.A state variable representing a constant power load and a dc source filter control input, respectively. />
In step 4, in the design of the fuzzy control law of the direct current micro-grid based on the switch controller, for a more general constant power load, the constant power load is effectively controlled, and a new fuzzy switch controller is provided for better controlling the stable input of the current.
Assuming that the precondition variables are not clear, there must be one n ε {1,2, …, r } for any one sample point k, so that h n ≥h m Where m ε {1,2, …, r }, n+.m. The expression of the fuzzy system is as follows:
the switch controller input of the DC source filter is made as follows:
then there isi,j∈N r ＝{1,…,r}。
For fuzzy control, a positive fuzzy Lyapunov function is selected: wherein Pθ As a positive definite function, ++>
Then for the ith fuzzy rule, which corresponds to the design rule of the controller, the Lyapunov function is utilized to obtain the expected value, and the relaxation variable is selectedThen there are: />
Applying equation (21) to expression (20) there is
wherein ：i,j,l∈N r ＝{1,…,r}
in step 5, the gains of the controller and the observer related to the fuzzy control law are solved, and the gains of the controller related to the switch controller control law can be obtained by solving the following LMI problem.
Given i, j, l, n, a matrix is soughtX n The following LMIs are satisfied:
/>
wherein ：
based on the obtainedThe matrix can be obtained by solving (25) - (29)>Q ijl ，/>
And because of the fact that,the controller gain is +.>
Step 6, assigning the control gains of the controller and the observer obtained by solving to a loop to realize the optimal constant power load on the direct current micro-grid and the energy storage system, solving by using a Linear Matrix Inequality (LMI) through the expression, and obtaining the gain K of the controller i And substituting the optimal constant power load on the direct-current micro-grid and the optimal value of the energy storage system to ensure that the direct-current micro-grid can always stably and efficiently operate.
In summary, the technical problem to be solved by the present invention is to provide a fuzzy control method for an uncertainty dc micro-grid with constant power load based on a fuzzy model, and to provide an injection current for designing a memory cell based on the fuzzy model and a parallel distributed compensation scheme for coping with the uncertainty of the constant power load. It should be noted that the proposed fuzzy switch controller can fuse more system information because of its more complex construction form, and its gain can be significantly reduced conservatively using the developed relaxed Linear Matrix Inequality (LMI) design method to obtain a control design feasible solution, which is beneficial to the on-line implementation of the fuzzy control scheme. It should be noted that the direct current micro-grid with constant power load, which is aimed at by the present invention, can be any type of direct current micro-grid with parameter uncertainty, and can solve the technical problems caused by inaccuracy in a system model and controller errors caused by calculation delay, quantization effect and calculation approximation.
In addition, as is clear from the description of the above embodiments, a person skilled in the relevant art can implement the technical effects pointed out in the present invention by means of software plus necessary hardware platforms.
The above description is merely of preferred embodiments of the present invention, and the scope of the present invention is not limited to the above embodiments, but all equivalent modifications or variations according to the present disclosure will be within the scope of the claims.
Claims (4)
1. A fuzzy switch control method for a direct-current micro-grid with constant power load is characterized by comprising the following steps of: the method comprises the following steps:
step 1, establishing a dynamic model of a single direct current micro-grid system;
step 2, constructing an integral dynamic model of the single direct current micro-grid according to the model of the single direct current micro-grid;
step 3, constructing a corresponding T-S fuzzy model according to the model of the direct-current micro-grid;
step 4, designing a direct-current micro-grid fuzzy control law based on a switch controller;
in step 4, a new fuzzy switch controller is provided to better control the stable input of the current;
assuming that the precondition variables are not clear, there must be one n ε {1,2, …, r } for any one sample point k, so that h n ≥h m Where m ε {1,2, …, r }, n+.m; the expression of the fuzzy system is as follows:
the switch controller input of the DC source filter is made as follows:
then there is
For fuzzy control, a positive fuzzy Lyapunov function is selected: wherein Pθ Is a positive definite function;
then for the ith fuzzy rule, which corresponds to the design rule of the controller, the Lyapunov function is utilized to obtain the expected value, and the relaxation variable is selectedThen there are: />
Applying equation (21) to expression (20) there is
wherein ：
step 5, solving gains of a controller and an observer related to the fuzzy control law;
in step 5, the controller gain involved in the control law of the switch controller is obtained by solving the following LMI problem;
given i, j, l, n, a matrix is soughtX n The following LMIs are satisfied:
wherein ：
based on the obtainedX n General purpose medicineSolving (25) - (29) to obtain matrix +.>Q ijl ，/>
The controller gain is
Step 6, assigning control gains of the controller and the observer obtained by solving to the loop to realize the optimal constant power load and the energy storage system on the direct current micro-grid;
in step 6, the gain K of the controller is solved by using the linear matrix inequality LMI i And substituting the optimal constant power load on the direct-current micro-grid and the optimal value of the energy storage system to ensure that the direct-current micro-grid can always stably and efficiently operate.
2. The method for controlling the fuzzy switch of the direct current micro-grid with the constant power load according to claim 1, wherein the method comprises the following steps of: in step 1, the direct current micro-grid system comprises a constant power load CPL, a direct current source DC and an energy storage system ESS;
in order to obtain the overall dynamic characteristics of a direct current micro-grid with a plurality of constant power loads, firstly, the characteristics of one constant power load with a direct current power supply and a power subsystem are studied; the constant power load is modeled by a voltage controlled current source, and considering the j-th constant power load connected to the dc link, the nonlinearity of its value depends on the power and voltage of the constant power load;
in the circuit of the j-th constant power load system connected in series with the RLC filter and the direct current link, a dynamic model shown by the constant power load is as follows:
wherein ,iL,j and vC,j Representing the inductor current and capacitor voltage, r, respectively, on the jth constant power load L,j Representing the inductance resistance, L, at the jth constant power load j Inductance representing the jth constant power load, C j Capacitance representing the jth constant power load, V e Representing a dc link voltage;
P j represents constant power on the jth constant power load and must meet the following constraints: for balance point i L0,j v C0,j ]The method comprises the following steps:
wherein ,iL0,j and vC0,j Inductor current and capacitor voltage, P, respectively representing balance position on jth constant power load max,j Representing the maximum constant power on the jth constant power load, V dc Representing a direct current power supply;
the RLC filter is connected through a voltage source of the energy storage system, and the energy storage system is connected through a current source i es Modeling is carried out, and the state space representation form of the direct current micro-grid energy storage system is as follows:
wherein ,iL,s and vC,s Representing the inductor current and capacitor voltage, r, respectively, on an energy storage system s Representing the resistance of the energy storage system, L s Representing the inductance of the energy storage system, C s Representing the capacitance, i, of an energy storage system es Representing a current source;
in order to obtain a new nonlinear dynamic characteristic with an origin as a balance point, a power system is needed to perform stability analysis and controller synthesis on a nonlinear system of Lyapunov stability theory, and the balance point is located at the origin; by changing the coordinates, the power models (1) and (3) can be converted into:
wherein , and />The inductor current and capacitor voltage on the jth constant power load at the balance point are shown, and />Respectively representing the inductor current and the capacitor voltage on the energy storage system at the point of equilibrium, +.>Representing the current source at the point of equilibrium.
3. The method for controlling the fuzzy switch of the direct current micro-grid with the constant power load according to claim 1, wherein the method comprises the following steps of: in step 2, based on a single constant power load connected to a direct current link and an energy storage system connected to a direct current power supply, deriving an integral micro-grid with a plurality of constant power loads, the energy storage system and the direct current power supply connected through an RLC filter, and decoupling the integral micro-grid into Q+1 subsystems;
the state space representation of a constant power load is:
where j= {1,2 …, Q } and s=q+1 represent the state of the dc source filter, x j ＝[i L,j v C,j ] T and xs ＝[i L,s v C,s ] T Representing the state of the jth constant power load and the state of the DC source filter respectively;
the dc source subsystem state space may be described by:
wherein ,
also, a coordinate of an operation point is changed, and a DC current source i is provided es As a control input, the entire dc micro-grid with the balance point at the origin is rewritten as follows:
wherein ,
when h= [ h ] 1 … h Q ] T In the time-course of which the first and second contact surfaces,
4. the method for fuzzy switching control of a dc micro-grid with constant power load of claim 3, further comprising: in the step 3, based on a T-S fuzzy model, systematically calculating an equivalent T-S fuzzy model of a nonlinear system by a sector nonlinear method to obtain a local linear system and a fuzzy membership function; entering each nonlinear term of the original system into two linear sectors; acquiring a membership function and a local matrix of TS fuzzy by aggregating all groups of two sectors;
converting a micro-grid with a plurality of constant power loads into a micro-grid with one equivalent constant power load, and modeling the nonlinearity of the formula (10), wherein only one nonlinearity term exists in the dynamic model; for a given regionCalculate sector-> and />Make->Wherein the lower slope U min And upper slope U max Drawing non-pointsLinear term H 1 And its corresponding sector;
by combining the sector inequalityConversion to min-max inequality +.>To calculate the slope, there are:
based on the sector non-linearity method, consider:
solving (14) to obtain a membership function M 1 and M2 ：
Substituting (14) into formula (10) can obtain an equivalent T-S fuzzy model:
wherein ：
T-SDiscretizing the fuzzy model (16) to obtain a discrete T-S fuzzy model (18); discretized fuzzy model forThe expression is as follows:
wherein ,r represents a control rule of fuzzy control;a state variable representing a constant power load and a dc source filter control input, respectively.
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