Island microgrid distributed fixed time secondary control method for non-ideal communication

Abstract

The invention relates to a non-ideal communication island micro-grid distributed fixed time secondary control method. A primary control layer sets a droop control strategy of an ith DG at a t moment; determining a communication network for information interaction between the DG and the adjacent DG in the island micro-grid, and describing a switching form of a topological structure in a communication process; introducing an integral compensation item into the controller; designing a distributed event triggering mechanism; a secondary voltage and frequency control strategy is designed, a multi-agent system structure is adopted, a fixed time consistency control algorithm containing communication time delay and topology switching is designed in a secondary control layer, the frequency and voltage of the micro-grid system under the non-ideal communication condition are recovered to reference values, and the secondary control layer designs an edge-based controller. And the upper bound of system voltage or frequency stabilization time can be obtained conveniently.

Description

Technical Field

[0001] The invention relates to a distributed fixed-time secondary control method for an island microgrid with non-ideal communication. Background Art

[0002] With the development of renewable energy (such as solar energy and wind energy), traditional centralized power systems are difficult to fully utilize these distributed energy sources. Microgrids can effectively integrate and optimize distributed energy resources to achieve reliability and flexibility of power systems. There are two operating modes for microgrids, namely grid-connected mode and island mode. In grid-connected mode, it is regarded as a whole and connected to the main grid through a point of common coupling (PCC). When the PCC is damaged and disconnected due to interference, the microgrid will switch to island mode and operate autonomously to independently supply power to ensure the stability of the grid. In order to enable the microgrid system to operate stably under small-scale load fluctuations, the concept of hierarchical control is proposed. The control structure is divided into three levels: primary control, secondary control and tertiary control. Among them, secondary control is used to correct the problem of system frequency and voltage deviating from the reference value caused by the droop control strategy of primary control.

[0003] Traditional secondary control uses asymptotic consistency control method, and the convergence time is close to infinity. In practical systems, it is a challenge to reach a consensus within a specific time. Therefore, due to its high accuracy, fast convergence speed and good robustness, finite time consistency control is widely used in secondary control of microgrids to ensure that the system frequency and voltage converge quickly within a finite time. However, the convergence time of the finite time is affected by the initial state of the microgrid system and is difficult to determine, so fixed time consistency is proposed to overcome this problem.

[0004] Communication networks play a vital role in information exchange and coordinated control between distributed generators (DGs). The communication environment of isolated microgrids is often non-ideal, but there are still few studies on various communication constraints. Communication delay is first considered as an inherent communication constraint, and the Artstein model reduction method can effectively solve the delay problem. In addition, due to the "plug-and-play" characteristics of DGs or unexpected events such as environmental interference and link failures, the links between adjacent DGs may be disconnected or connected, thereby causing changes in the topology of the microgrid. Therefore, it is particularly important to design a suitable distributed secondary control algorithm to ensure the stable operation of the microgrid system.

[0005] At present, in the research of microgrids in non-ideal communication environments, distributed secondary control algorithms are overly dependent on communication, however, the communication bandwidth is limited. To solve the problem of limited communication bandwidth, a distributed event trigger mechanism is introduced, which is only executed under specific event conditions, reducing the communication burden and excessive consumption of communication resources. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an isolated island microgrid distributed secondary control method under non-ideal communication based on an event trigger mechanism.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The distributed fixed-time secondary control method of an island microgrid with non-ideal communication is characterized by comprising the following steps:

[0009] Step 1) The primary control layer sets the droop control strategy of the i-th DG at time t. The control layer adopts the droop control method to maintain the frequency and voltage of the island microgrid system within the set range by adjusting the active and reactive power output of the power generation unit;

[0010] Step 2) determine the communication network for information exchange between the DG and its adjacent DG in the isolated microgrid, and describe the switching form of the topology structure during the communication process;

[0011] Step 3) Using the Artstein model reduction method, an integral compensation term is introduced into the controller to solve the communication delay;

[0012] Step 4) Considering the limited communication bandwidth, design a distributed event triggering mechanism;

[0013] Step 5) Design the secondary voltage and frequency control strategy, adopt a multi-agent system structure, and design a fixed-time consistency control algorithm including communication delay and topology switching in the secondary control layer to restore the frequency and voltage of the microgrid system under non-ideal communication conditions to the reference value. Design an edge-based controller in the secondary control layer to obtain the upper bound of the system voltage or frequency stabilization time.

[0014] Furthermore, in the above-mentioned non-ideal communication isolated microgrid distributed fixed-time secondary control method, in which, in step 1), the control layer adopts a droop control method to adjust the active and reactive power outputs of the power generation unit so that the frequency and voltage of the isolated microgrid system are maintained within a set range. The droop control equation is expressed as follows:

[0015]

[0016] In the formula, ω i (t) and v i(t) represent the frequency and voltage of DG respectively; and Respectively represent the reference values ​​of frequency and voltage, which are given by the secondary control layer; P i (t) and Q i (t) are the active power and reactive power actually measured at the inverter end; and They are the droop control systems for active power and reactive power respectively;

[0017] The reference values ​​of frequency and voltage are given by the secondary control layer:

[0018]

[0019] Among them, setting u vi (t),u ωi (t),u pi (t) are the auxiliary controllers of the voltage, frequency and active power of the ith DG, respectively, satisfying

[0020] Further, the above-mentioned distributed fixed-time secondary control method for an island microgrid with non-ideal communication, wherein, in step 2), a communication network for information exchange between a DG in the island microgrid and its adjacent DGs is determined;

[0021] Let G = (V, E) represent the undirected graph of the island microgrid communication network, where the vertex set V = {ν i |i=1,…,N} represents the N nodes of the microgrid system, and the edge set Represents the communication link between nodes; represents the number of distributed generation units, where σ(t) = M (m∈1,2,…,s) is the random switching signal and s is the number of communication topologies; set Represents the adjacency matrix of the system. When (i, j)∈E, the i-th DG and the j-th DG are adjacent and exchange information with each other, that is, on the contrary During the communication process, due to the plug-and-play characteristics of DG or external interference and link failure factors, the communication topology of the microgrid will change, that is, the communication link between the two DGs will be temporarily interrupted, and other backup communication links will be established.

[0022] Furthermore, the above-mentioned non-ideal communication isolated island microgrid distributed fixed-time secondary control method, wherein step 3), adopts ξ vi (t-τ) is used as a reduced-order model of voltage, and an integral compensation term is introduced Solve the communication delay. The delay τ has an unknown upper bound and satisfies is a positive constant.

[0023] Furthermore, in the above-mentioned non-ideal communication isolated microgrid distributed fixed-time secondary control method, in which, in step 4), the voltage event triggering mechanism g of the i-th DG unit vi (t) is:

[0024]

[0025] In the formula, the control gain α v is a normal number; parameters m, n, υ, μ are four positive odd numbers, satisfying m>n, μ>υ; represents the state of DGi at the triggering time k; e vi (t) represents the voltage state error of the i-th DG; ε vi (t) represents the voltage tracking error of the ith DG, defined as ε vi (t) = ξ i (t)-v ref ; φ vi (t), is the defined intermediate variable.

[0026] Furthermore, in the above-mentioned distributed fixed-time secondary control method of the isolated island microgrid with non-ideal communication, in which the system voltage is used as a state variable in the event triggering, the proof process is as follows:

[0027] Before the voltage reaches the reference value, there is a positive constant χ such that the following inequality holds:

[0028]

[0029] exist The state error satisfies:

[0030]

[0031] Trigger condition vi (t)>0, the next event of the ith DG is at g vi Not triggered before (t) = 0

[0032]

[0033] From equations (7) and (8), we can deduce:

[0034]

[0035] This indicates that there is no Zeno behavior.

[0036] Furthermore, in the above-mentioned distributed fixed-time secondary control method for isolated island microgrid with non-ideal communication, in step 5), the auxiliary controller for constructing the voltage is:

[0037]

[0038] In formula (10), the control gain α v is a positive number; parameters m, n, υ, μ are four positive odd numbers, satisfying m>n, μ>υ; Indicates that DGi is in k th The state at the time of the trigger.

[0039] Furthermore, in order to verify the effectiveness of the fixed-time quadratic control method for an isolated microgrid with non-ideal communication, an isolated microgrid system is built in the MATLAB / Simulink environment. The system includes four DGs communicating in an undirected graph, four loads, and three transmission lines. DG 1 is used as the only node to receive system reference information, where the frequency reference value is set to 50Hz and the voltage reference value is set to 311V; the corresponding matrix data of G1 is as follows:

[0040]

[0041] The performance of the isolated island microgrid system is tested under topology switching and communication delay. The running time is 20s, and the communication delay is set to τ = 0.01s. The corresponding simulation process is divided into the following four parts:

[0042] 1) When t = 0 ~ 5s, it only works in the primary control layer;

[0043] 2) When t = 5-10s, under topology G1, the control algorithm is applied to the secondary control layer;

[0044] 3) At t = 10-15s, DG 4 is disconnected from the microgrid, the communication topology changes from G1 to G2, and the Laplace matrix L 2 The calculation is as follows:

[0045]

[0046] 4) At t = 15-20s, DG 4 is reconnected, and the communication topology changes from G2 to G3. The Laplace matrix L 3 The calculation is as follows:

[0047]

[0048] Compared with the prior art, the present invention has significant advantages and beneficial effects, which are specifically embodied in the following aspects:

[0049] ① The present invention takes into account multiple communication constraints, communication delays, topology switching and limited communication bandwidth issues at the same time. By establishing the frequency and voltage droop control law, introducing the integral compensation term, designing the distributed event triggering mechanism, and reconstructing the edge-based secondary control algorithm, the frequency and voltage of the power grid are maintained stable, and the consumption of communication resources is significantly reduced;

[0050] ② Considering both switching and communication delays, a distributed secondary control method is designed with strong robustness to quickly restore the frequency and voltage of each DG to the reference value; compared with the node-based controller, the designed edge-based controller has a certain symmetry, which helps to estimate the setting time considering the switching;

[0051] ③ The distributed event trigger mechanism solves the continuous communication problem, significantly reduces the number of system triggers, and alleviates the communication burden; in addition, it is confirmed that the island microgrid system considering communication delay can establish a positive minimum trigger interval, thereby avoiding Zeno behavior;

[0052] ④ Fixed-time consistency control provides an accurate convergence time given by the Lyapunov method; this convergence time is independent of any initial state of the system and ensures fast and accurate convergence of system frequency and voltage.

[0053] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or be understood by practicing the specific embodiments of the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 : Specific flow diagram of the present invention;

[0056] Figure 2 : The control structure block diagram of the distributed power generation unit based on the inverter of the isolated island microgrid of the present invention;

[0057] Figure 3 : Communication topology switching diagram of the isolated island microgrid of the present invention;

[0058] Figure 4 : Simulation test diagram of isolated island microgrid system of the present invention;

[0059] Figure 5a : Frequency response curve of island microgrid considering topology switching and communication delay;

[0060] Figure 5b : Active power response curve of isolated microgrid considering topology switching and communication delay;

[0061] Figure 5c : Voltage response curve of island microgrid considering topology switching and communication delay;

[0062] Figure 6a : Frequency response curve of island microgrid without delay compensation;

[0063] Figure 6b : Active power response curve of island microgrid without delay compensation;

[0064] Figure 6c : Voltage response curve of island microgrid without delay compensation;

[0065] Figure 7a : Timeline diagram of frequency event triggering of each distributed generation unit;

[0066] Figure 7b : Timeline diagram of active power event triggering of each distributed generation unit;

[0067] Figure 7c : Timeline diagram of voltage event triggering of each distributed generation unit. DETAILED DESCRIPTION

[0068] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0069] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, in the description of the present invention, directional terms and order terms are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0070] Considering the isolated microgrid in a non-ideal communication environment, a distributed fixed-time secondary control method based on event trigger mechanism is designed. Meanwhile, multiple communication constraints are taken into account, including communication delay, topology switching and limited communication bandwidth. By establishing the frequency and voltage droop control law and introducing the integral compensation term, a distributed event trigger mechanism is designed, and the edge-based secondary control algorithm is reconstructed to maintain the frequency and voltage stability of the power grid and significantly reduce the consumption of communication resources.

[0071] like Figure 1 As shown, the distributed secondary control method of the isolated island microgrid under non-ideal communication based on the event trigger mechanism includes the following steps:

[0072] Step 1) The primary control layer sets the droop control strategy of the i-th DG at time t. The control layer adopts the droop control method to maintain the frequency and voltage of the island microgrid system within the set range by adjusting the active and reactive power output of the power generation unit;

[0073] Step 2) determine the communication network for information exchange between the DG and its adjacent DG in the isolated microgrid, and describe the switching form of the topology structure during the communication process;

[0074] Step 3) Using the Artstein model reduction method, an integral compensation term is introduced into the controller to solve the communication delay;

[0075] Step 4) Considering the limited communication bandwidth, design a distributed event triggering mechanism;

[0076] Step 5) Design the secondary voltage and frequency control strategy, adopt a multi-agent system structure, and design a fixed-time consistency control algorithm including communication delay and topology switching in the secondary control layer to restore the frequency and voltage of the microgrid system under non-ideal communication conditions to the reference value. Design an edge-based controller in the secondary control layer to obtain the upper bound of the system voltage or frequency stabilization time.

[0077] DG is composed of an inverter 105, an LC filter 106, an output connector 107, a power calculation module 104, a current controller 102, a voltage controller 101, etc. A droop control strategy is adopted for primary control to maintain the stability of the power system by adjusting the power output of the power generation unit, but this will cause the frequency and voltage to deviate from their reference values; secondary control provides reference values ​​for the primary control layer by designing corresponding controllers. The control structure is as follows: Figure 2 .

[0078] like Figure 2 The control structure of the distributed generation unit (DG) in the isolated island microgrid based on the voltage source inverter (VSI) is divided into primary control and secondary control. The voltage controller 101 is used to adjust the output voltage of the inverter 105 according to the real-time voltage v oiand reference voltage signal The comparison is performed to generate the required voltage regulation amount, and its output is connected to the current controller 102 to provide the required current reference signal, which provides a control basis for the current controller 102, thereby indirectly regulating the current output by the inverter 105. The current controller 102 is based on the current reference signal provided by the voltage controller 101. Control the output current i of the inverter 105 oi , ensuring that the output current meets the set value. The power controller 103 is connected to the power calculation module 104 and receives the P i and Q i The power calculation module 104 collects the output voltage v of the inverter 105. oi and current i oi , calculate the active power P of the current DG unit i and reactive power Q i The inverter 105 converts the DC power into AC power according to the output signal of the current controller 102, and is connected to the LC filter 106 to filter out high-frequency harmonics and output a smoother AC voltage v oi and current i oi ; The filtered voltage and current are transmitted to the load end of the microgrid or other distributed generation units through the output connector 107. Distributed secondary control, since the droop control strategy adopted by the primary control layer causes the frequency and voltage of the system to deviate from the rated value, the distributed secondary control can provide the primary control with a frequency / voltage reference value to eliminate the deviation. The primary control adjusts the output voltage and current of the inverter 105 through the voltage controller 101 and the current controller 102 to ensure the stable operation of the system, and at the same time realizes the regulation of active power and reactive power through the power calculation module 104 and the power controller 103. After the output of the inverter 105 passes through the LC filter 106, it is connected to the microgrid through the output connector 107. The secondary control is used to coordinate local and adjacent DG units, provide frequency and voltage reference values ​​for the primary control, ensure the voltage and frequency recovery and proportional power distribution of the microgrid, and achieve overall coordination and stable operation of the system.

[0079] Step 1), the control layer adopts the droop control method to maintain the frequency and voltage of the island microgrid system within the set range by adjusting the active and reactive power output of the power generation unit. The droop control equation is expressed as follows:

[0080]

[0081] In the formula, ω i (t) and v i(t) represent the frequency and voltage of DG respectively; and Respectively represent the reference values ​​of frequency and voltage, which are given by the secondary control layer; P i (t) and Q i (t) are the active power and reactive power actually measured at the inverter end; and They are the droop control systems for active power and reactive power respectively;

[0082] The reference values ​​of frequency and voltage are given by the secondary control layer:

[0083]

[0084] Among them, setting u vi (t),u ωi (t),u pi (t) are the auxiliary controllers of the voltage, frequency and active power of the ith DG, respectively, satisfying Design accordingly in subsequent steps.

[0085] Step 2), determine the communication network for information exchange between the DG in the isolated microgrid and its adjacent DGs;

[0086] Let G = (V, E) represent the undirected graph of the island microgrid communication network, where the vertex set V = {ν i |i=1,…,N} represents the N nodes of the microgrid system, and the edge set Represents the communication link between nodes; represents the number of distributed generation units, where σ(t) = M (m∈1,2,…,s) is the random switching signal and s is the number of communication topologies; set Represents the adjacency matrix of the system. When (i, j)∈E, the i-th DG and the j-th DG are neighbors and can exchange information with each other, that is, on the contrary During the communication process, due to the plug-and-play characteristics of DG or external interference and link failure factors, the communication topology of the microgrid will change, that is, the communication link between the two DGs (between DG 3 and DG 4) is temporarily interrupted, and other backup communication links (between DG 2 and DG 4) are established, such as Figure 3 As shown, the original communication topology of DG is Figure 3 The G1 part.

[0087] Taking the design process of system voltage as an example, the controller design process of frequency and active power is similar.

[0088] Step 3) (taking the design process of system voltage as an example, the design of integral compensation items of frequency and active power is similar), using ξ vi(t-τ) is used as a reduced-order model of voltage, and an integral compensation term is introduced Solve the communication delay. The delay τ has an unknown upper bound and satisfies is a positive constant.

[0089] Step 4) (taking the design process of system voltage as an example, the event trigger mechanism design of frequency and active power is similar), the voltage event trigger mechanism g of the i-th DG unit vi (t) is:

[0090]

[0091] In the formula, the control gain α v is a normal number; parameters m, n, υ, μ are four positive odd numbers, satisfying m>n, μ>υ; represents the state of DGi at the triggering time k; e vi (t) represents the voltage state error of the i-th DG; ε vi (t) represents the voltage tracking error of the ith DG, defined as ε vi (t) = ξ i (t)-v ref ; φ vi (t), It is a defined intermediate variable; using a distributed event trigger mechanism, the controller updates only use its own information, reducing the communication burden.

[0092] In event triggering, the existence of Zeno behavior is excluded. Taking voltage as an example, the system voltage is used as a state variable. The detailed proof process is as follows:

[0093] Before the voltage reaches the reference value, there is a positive constant χ such that the following inequality holds:

[0094]

[0095] exist The state error satisfies:

[0096]

[0097] Trigger condition vi (t)>0, the next event of the ith DG is at g vi Not triggered before (t) = 0

[0098]

[0099] From equations (7) and (8), we can deduce

[0100]

[0101] This indicates that there is no Zeno behavior.

[0102] Step 5) (taking the design process of the voltage controller as an example, the design of the frequency and active power controllers is similar), construct the auxiliary controller of the voltage as:

[0103]

[0104] In formula (10), the control gain α v is a positive number; parameters m, n, υ, μ are four positive odd numbers, satisfying m>n, μ>υ; Indicates that DGi is in k th Status at the time of triggering

[0105] To verify the effectiveness of the fixed-time quadratic control algorithm considering multiple communication constraints simultaneously, an island microgrid system is built in the MATLAB / Simulink environment. The system includes four DGs communicating in an undirected graph, as well as four loads and three transmission lines, e.g. Figure 4 As shown, let DG 1 be the only node receiving system reference information, where the frequency reference value is set to 50Hz and the voltage reference value is set to 311V; Figure 3 The corresponding matrix data of G1 is as follows:

[0106]

[0107] The performance of the isolated island microgrid system is tested under topology switching and communication delay. The running time is 20s, and the communication delay is set to τ = 0.01s. The corresponding simulation process is divided into the following four parts:

[0108] 1) When t = 0 ~ 5s, it only works in the primary control layer;

[0109] 2) When t = 5-10s, under topology G1, the control algorithm is applied to the secondary control layer;

[0110] 3) At t = 10-15s, DG 4 is disconnected from the microgrid, and the communication topology changes from Figure 3 G1 in the transformation to G2, the Laplace matrix L 2 The calculation is as follows:

[0111]

[0112] 4) At t = 15 to 20 seconds, DG 4 is reconnected and the communication topology changes from Figure 3 G2 in the transformation to G3, the Laplace matrix L 3 The calculation is as follows:

[0113]

[0114] Figure 5a to 5c The response curves of DG frequency, active power and voltage considering communication delay and topology switching are shown. The simulation results show that the proposed fixed-time quadratic control algorithm quickly achieves frequency and voltage recovery and proportional distribution of active power within the theoretical convergence time (frequency 0.65s, voltage 0.55s). The results show that the control method of the present invention has good robust performance. Figure 6a-6c The frequency and voltage response curves of the controller with no delay compensation term introduced within 5 to 5.1 seconds are shown. It can be seen that the simulation results fail to converge to a value, but diverge, which may lead to unexpected performance and potential DG failure. At the same time, considering the limited communication bandwidth, a distributed event trigger mechanism is added to the controller. Figures 7a to 7c The triggering times of frequency, active power and voltage of each DG are shown (6 to 6.1s, where 1 indicates triggering and 0 indicates not triggering). The results show that the introduction of event triggering mechanism effectively reduces the triggering times and relieves the communication pressure.

[0115] In summary, the present invention considers both switch switching and communication delays, designs a distributed secondary control method with strong robustness, and quickly restores the frequency and voltage of each DG to the reference value; compared with the node-based controller, the designed edge-based controller has a certain symmetry, which helps to estimate the setting time considering switch switching.

[0116] The distributed event triggering mechanism solves the continuous communication problem, significantly reduces the number of system triggering times, and alleviates the communication burden; in addition, it is confirmed that the isolated microgrid system considering the communication delay can establish a positive minimum triggering interval, thereby avoiding Zeno behavior.

[0117] Fixed-time consistency control provides an exact convergence time, given by the Lyapunov method; this convergence time is independent of any initial state of the system and ensures fast and accurate convergence of system frequency and voltage.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention. It should be noted that similar numbers and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0119] The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0120] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

Claims

1. A distributed fixed-time secondary control method for an island microgrid with non-ideal communication, characterized by: The following steps are involved: Step 1) The primary control layer sets the droop control strategy of the i-th DG at time t. The control layer adopts the droop control method to maintain the frequency and voltage of the island microgrid system within the set range by adjusting the active and reactive power output of the power generation unit; Step 2) determine the communication network for information exchange between the DG and its adjacent DG in the isolated microgrid, and describe the switching form of the topology structure during the communication process; Step 3) Using the Artstein model reduction method, an integral compensation term is introduced into the controller to solve the communication delay; Step 4) Considering the limited communication bandwidth, design a distributed event triggering mechanism; Step 5) Design the secondary voltage and frequency control strategy, adopt a multi-agent system structure, and design a fixed-time consistency control algorithm including communication delay and topology switching in the secondary control layer to restore the frequency and voltage of the microgrid system under non-ideal communication conditions to the reference value. Design an edge-based controller in the secondary control layer to obtain the upper bound of the system voltage or frequency stabilization time.

2. The distributed fixed-time secondary control method for an isolated island microgrid with non-ideal communication according to claim 1 is characterized in that: Step 1), the control layer adopts the droop control method to maintain the frequency and voltage of the island microgrid system within the set range by adjusting the active and reactive power output of the power generation unit. The droop control equation is expressed as follows: In the formula, ω i (t) and v i (t) represent the frequency and voltage of DG respectively; and Respectively represent the reference values ​​of frequency and voltage, which are given by the secondary control layer; P i (t) and Q i (t) are the active power and reactive power actually measured at the inverter end; and They are the droop control systems for active power and reactive power respectively; The reference values ​​of frequency and voltage are given by the secondary control layer: Among them, setting u vi (t),u ωi (t),u pi (t) are the auxiliary controllers of the voltage, frequency and active power of the ith DG, respectively, satisfying 3. The distributed fixed-time secondary control method for isolated island microgrid with non-ideal communication according to claim 1 is characterized in that: Step 2), determine the communication network for information exchange between the DG in the isolated microgrid and its adjacent DGs; Let G = (V, E) represent the undirected graph of the island microgrid communication network, where the vertex set V = {ν i |i=1,…,N} represents the N nodes of the microgrid system, and the edge set Represents the communication link between nodes; represents the number of distributed generation units, where σ(t) = M (m∈1,2,…,s) is the random switching signal and s is the number of communication topologies; set Represents the adjacency matrix of the system. When (i, j)∈E, the i-th DG and the j-th DG are adjacent and exchange information with each other, that is, on the contrary During the communication process, due to the plug-and-play characteristics of DG or external interference and link failure factors, the communication topology of the microgrid will change, that is, the communication link between the two DGs will be temporarily interrupted, and other backup communication links will be established.

4. The distributed fixed-time secondary control method for an island microgrid with non-ideal communication according to claim 1 is characterized in that: Step 3), using ξ vi (t-τ) is used as a reduced-order model of voltage, and an integral compensation term is introduced Solve the communication delay. The delay τ has an unknown upper bound and satisfies is a positive constant.

5. The distributed fixed-time secondary control method for an isolated island microgrid with non-ideal communication according to claim 1 is characterized in that: Step 4), the voltage event triggering mechanism g of the i-th DG unit vi (t) is: In the formula, the control gain α v is a normal number; parameters m, n, υ, μ are four positive odd numbers, satisfying m>n, μ>υ; represents the state of DGi at the triggering time k; e vi (t) represents the voltage state error of the i-th DG; ε vi (t) represents the voltage tracking error of the ith DG, defined as ε vi (t) = ξ i (t)-v ref ; φ vi (t), is the defined intermediate variable.

6. The distributed fixed-time secondary control method for an island microgrid with non-ideal communication according to claim 5 is characterized by: In the event triggering, the system voltage is used as the state variable, and the proof process is as follows: Before the voltage reaches the reference value, there is a positive constant χ such that the following inequality holds: exist The state error satisfies: Trigger condition vi (t)>0, the next event of the ith DG is at g vi Not triggered before (t) = 0 From equations (7) and (8), we can deduce: This indicates that there is no Zeno behavior.

7. The distributed fixed-time secondary control method for an island microgrid with non-ideal communication according to claim 1 is characterized by: Step 5), construct the auxiliary controller of voltage as: In formula (10), the control gain α v is a positive number; parameters m, n, υ, μ are four positive odd numbers, satisfying m>n, μ>υ; Indicates that DGi is in k th The state at the time of the trigger.

8. The distributed fixed-time secondary control method for isolated island microgrid with non-ideal communication according to claim 1 is characterized by: In order to verify the effectiveness of the fixed-time quadratic control method considering multiple communication constraints at the same time, an island microgrid system is built in the MATLAB / Simulink environment. The system includes four DGs communicating in an undirected graph, four loads, and three transmission lines. DG 1 is used as the only node to receive system reference information, where the frequency reference value is set to 50Hz and the voltage reference value is set to 311V; the corresponding matrix data of G1 is as follows: The performance of the isolated island microgrid system is tested under topology switching and communication delay. The running time is 20s, and the communication delay is set to τ = 0.01s. The corresponding simulation process is divided into the following four parts: 1) When t = 0 ~ 5s, it only works in the primary control layer; 2) When t = 5-10s, under topology G1, the control algorithm is applied to the secondary control layer; 3) At t = 10-15s, DG 4 is disconnected from the microgrid, the communication topology changes from G1 to G2, and the Laplace matrix L 2 The calculation is as follows: 4) At t = 15-20s, DG 4 is reconnected, and the communication topology changes from G2 to G3. The Laplace matrix L 3 The calculation is as follows:

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