Microgrid control method and system based on event-triggered directed communication topology

Abstract

The application discloses a micro-grid control method and system based on event triggering under a directed communication topology, relates to the technical field of micro-grid control, and adopts droop control of an analog synchronous generator to realize primary control of the micro-grid; secondary control in the micro-grid is designed, including secondary frequency modulation and active power distribution; specifically, local PI control is adopted for secondary frequency modulation, frequency deviation adjustment is realized by adjusting a frequency set point; a control strategy of a micro-grid distributed active power distribution controller under the directed communication topology is designed based on an event triggering mechanism, active power distribution is carried out, the number of control triggering and communication is reduced, and the convergence of the control method is proved by using a Lyapunov stability analysis method. The application greatly reduces the communication resource cost of the controller, improves the efficiency of the control system, and is suitable for the directed communication topology.

Description

Technical Field

[0001] This invention relates to the field of microgrid control technology, and more specifically to a microgrid control method and system based on event-triggered directed communication topology. Background Technology

[0002] Microgrid technology is an important way to promote the consumption of renewable energy. To achieve flexible operation of microgrids, distributed cooperative control technology, with its good flexibility, reliability, and scalability, is often used to manage distributed renewable energy within microgrids. However, with the large-scale penetration of distributed renewable energy, traditional distributed control strategies based on continuous triggering greatly waste the valuable communication resources of the control system, reducing its efficiency. Moreover, traditional distributed control strategies often require the construction of undirected communication topologies (or "bidirectional communication topologies"). Therefore, how to reduce communication requirements and improve the efficiency of the control system under directed communication topologies (or "unidirectional communication topologies") is of great significance for promoting the further consumption of renewable energy and is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0003] In view of this, the present invention addresses the efficiency problem of traditional distributed control methods for microgrids, especially active power distribution control, by providing a microgrid control method and system based on event-triggered directed communication topology.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A microgrid control method based on event-triggered directed communication topology includes the following steps: Step 1: The microgrid uses droop control of a simulated synchronous generator to achieve primary control; Step 2: Design the secondary control in the microgrid, including secondary frequency regulation and active power distribution. Specifically: use local PI control for secondary frequency regulation, and adjust the frequency setpoint to achieve frequency deviation adjustment; based on the event triggering mechanism, design the control strategy of the distributed active power distribution controller of the microgrid under the directed communication topology to perform active power distribution.

[0005] Optionally, in step 1, primary control is achieved using droop control of a simulated synchronous generator, specifically as follows: ; in, For distributed power sources i The output angular frequency, which is related to the frequency The relationship is: ; For distributed power sources i . output active power; For distributed power sources i Active power / frequency droop factor; This is the reference frequency or frequency setpoint for droop control, and also the angular frequency of the inverter when it is running under no-load. The secondary frequency regulation of the system is achieved by adjusting this parameter.

[0006] Optionally, in step 2, local PI control is used for secondary frequency modulation. By adjusting the frequency setpoint, the frequency deviation is adjusted. Specifically: Differentiating the active power / frequency droop relationship yields: ; Solve for the reference frequency: ; in, This is the control input for the distributed frequency recovery controller. For the control input of the distributed active power distribution controller; The system frequency is restored by controlling each distributed power source to track the reference frequency, specifically as follows: ; in, Hz For the rated frequency, For distributed power sources i The output angular frequency, and These are the proportional and integral control coefficients, respectively.

[0007] Optionally, in step 2, the control strategy of the distributed active power distribution controller of the microgrid under the directed communication topology is specifically as follows: Through control rate To control distributed power sources in microgrids i of efforts, ; in, To control the gain; n This refers to the number of distributed power sources. For distributed power sources i The estimated utilization rate, i.e., the estimated active power output ratio. for Distributed power supply i The actual power; For distributed power sources i Actual utilization rate For distributed power sources i The output active power, For distributed power sources i Maximum output; For distributed power sources i The first distributed active power distribution controller k Triggering time: ; in, Trigger function for distributed active power distribution controller: ; in, To estimate the error, For flexibility adjustment coefficient, For distributed power sources i The number of neighbors.

[0008] This strategy can significantly reduce the number of control triggers and communications.

[0009] Optionally, the method further includes step 3, verifying the convergence of the distributed active power distribution controller of the microgrid under the directed communication topology using Lyapunov stability theory.

[0010] A microgrid control system based on event-triggered directed communication topology, comprising: The primary control module is used to achieve primary control of the microgrid by employing droop control of a simulated synchronous generator; The secondary control module is used to design secondary control in the microgrid, including secondary frequency regulation and active power distribution. Specifically, it adopts local PI control for secondary frequency regulation and adjusts the frequency setpoint to achieve frequency deviation adjustment. Based on the event triggering mechanism, it designs the control strategy of the distributed active power distribution controller of the microgrid under the directed communication topology to perform active power distribution.

[0011] Optionally, the system further includes a convergence verification module, used to verify the convergence of the distributed active power distribution controller of the microgrid under the directed communication topology using Lyapunov stability theory.

[0012] As can be seen from the above technical solution, the present invention provides a microgrid control method and system based on event-triggered directed communication topology, especially innovating the active power allocation strategy, and has the following beneficial effects compared with the prior art: (1) Based on the traditional distributed control method, this invention designs an event triggering mechanism, derives the triggering function and triggering conditions, and allocates active power, which reduces the number of controller triggers and communications, greatly improves the efficiency of the control system, and reduces the overhead of the control system on communication resources.

[0013] (2) The convergence of the distributed active power distribution controller of the microgrid under the designed directed communication topology was analyzed by Lyapunov stability analysis method, and it was proved that the proposed triggering mechanism can guarantee that the output power ratio of each distributed power source converges asymptotically to a consistent level.

[0014] In summary, compared with traditional microgrid distributed power distribution control methods, this invention greatly reduces the overhead of controller communication resources, improves the efficiency of the control system, and is applicable to directed communication topologies. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a microgrid system consisting of four distributed power sources and two integrated loads in a specific embodiment; Figure 2(a) is a graph showing the change in active power output of the distributed power source of the microgrid under the control method of the present invention in a specific embodiment; Figure 2(b) is a frequency variation curve of the distributed power supply output of the microgrid under the control method of the present invention in a specific embodiment; Figure 3 This is a schematic diagram of the triggering time sequence of the active power distribution controller of the microgrid under the control method of the present invention in a specific embodiment; Figure 4(a) is a curve showing the change in active power output of the distributed power source of the microgrid under traditional distributed secondary control in a specific embodiment. Figure 4(b) is a schematic diagram of the triggering time sequence of the active power distribution controller of the microgrid under the traditional distributed secondary control in a specific embodiment; Figure 5 This is a flowchart illustrating the control method steps of the present invention; Figure 6 This is a schematic diagram of the system modules of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention discloses a microgrid control method based on event-triggered directed communication topology, see [link to relevant documentation]. Figure 5 This includes the following steps: Step 1: The microgrid uses droop control of a simulated synchronous generator to achieve primary control.

[0019] In islanded operation of microgrids, distributed generation often employs droop control, simulating synchronous generators, for primary control. Taking active frequency droop control as an example, it characterizes the relationship between frequency and active power in the system. For distributed generation... i Specifically, it can be described as: ; (1) in, For distributed power sources i The output angular frequency, which is related to the frequency The relationship is: ; For distributed power sources i . output active power; For distributed power sources i Active power / frequency droop factor; This is the reference frequency for droop control, or the frequency setpoint, and also the angular frequency of the inverter when it is running under no-load. The system can be further frequency-regulated by adjusting this parameter.

[0020] Step 2: Design the secondary control in the microgrid, including secondary frequency regulation and active power distribution.

[0021] Through droop control, distributed generation can adjust its output according to the droop relationship in response to disturbances such as load changes, output fluctuations, or operating mode switching in the microgrid, thereby achieving rapid frequency stabilization of the system. However, as can be seen from the droop relationship, the system frequency may deviate from the rated value after stabilization. Therefore, secondary frequency regulation is required for further adjustment.

[0022] Typically, microgrid secondary control has two main objectives: first, to restore the frequency deviation caused by droop control; and second, to achieve precise distribution of active power, usually configured to ensure that distributed generation sources output power at the same utilization rate. Therefore, the two main objectives of microgrid secondary control can be expressed as: ; (2) in, This is the system's reference frequency; p i For distributed power sources i Utilization rate , This means that distributed power sources can output power at the same utilization rate.

[0023] Secondary frequency modulation restores the frequency to the normal operating range by adjusting the frequency setpoint, which can be achieved through local PI control.

[0024] Differentiating the active power / frequency droop relationship yields: ; (3) Solve for the reference frequency: ; (4) in, This is the control input for the distributed frequency recovery controller. For the control input of the distributed active power distribution controller; Since the primary goal of a microgrid during islanded operation is to maintain supply and demand balance, it can be assumed that each distributed generation source maintains a frequency of 50 Hz by default during islanded operation. Therefore, system frequency recovery can be achieved by having each distributed generation source track the reference frequency through local control. Specifically: ; (5) in, Hz For the rated frequency, For distributed power sources i The output angular frequency, and These are the proportional and integral control coefficients, respectively.

[0025] In distributed secondary control of microgrids, achieving global control objectives relies heavily on distributed communication networks. These communication networks can be represented by directed graphs. It indicates. Among them. It is a collection of distributed power sources. A set of communication links. A communication link can be defined as... This means distributed power sources i Distributed power sources can be received j Information, namely distributed power sources j For distributed power sources i The information is sent to the neighbors. Define distributed power sources. i The information sent to the neighbor set is Conversely, distributed power sources. i For distributed power sources j The information receiving neighbors. To characterize the communication network, a weighted adjacency matrix is ​​defined. , among which when hour, , usually take ,otherwise Define distributed power sources. i The out-degree and in-degree are respectively and So, the Laplace matrix L Defined as: ,in If there is an information path between any two distributed power sources, the communication network is said to be strongly connected. If it also satisfies... If so, the communication network is called a weighted balanced network.

[0026] For active power distribution control, the traditional distributed control law is generally: ; (6) in, This is the control factor.

[0027] Based on the control design and system dynamic characteristics, and combined with primary droop control, frequency synchronization and fair allocation of active power can be achieved in a distributed manner under an ideal undirected communication topology. However, since the triggering of the controller and the communication between distributed power sources are continuous, communication resources are wasted, thereby reducing the efficiency of the distributed control system. Therefore, this embodiment proposes a control strategy for the distributed active power allocation controller of a microgrid under a directed communication topology, specifically as follows: Through control rate To control distributed power sources in microgrids i of efforts, ; (7) in, To control the gain; n This refers to the number of distributed power sources. For distributed power sources i The utilization rate estimate, i.e., the active power output ratio estimate, for Distributed power supply i The actual power; For distributed power sources i Actual utilization rate For distributed power sources i The output active power, For distributed power sources i Maximum output; For distributed power sources i The first distributed active power distribution controller k Triggering time: ; (8) in, Trigger function for distributed active power distribution controller: ; (9) in, To estimate the error, For flexibility adjustment coefficient, For distributed power sources i The number of neighbors.

[0028] Step 3: Verify the convergence of the distributed active power distribution controller of the microgrid under the directed communication topology using Lyapunov stability theory.

[0029] Define the Lyapunov function: ; (10) Here, bold lowercase letters represent column vectors, where, A constant vector, .

[0030] Differentiating (10) gives: ; (11) This is used The estimation error Substituting (11) into the equation, we get: (12) Expanding (12) yields: (13) Using Young's inequality: , Then for any (13) can be scaled down to: (14) Therefore, for the controller to converge, the following must be satisfied: ; (15) Right now (16) Note that when hour, Finding the maximum value yields the optimal convergence condition: (17) Introducing a flexibility adjustment coefficient Define a trigger function (9) that triggers the system when it violates the convergence condition. The controller will only be triggered at that time. Proof complete.

[0031] Another embodiment also discloses a microgrid control system based on an event-triggered directed communication topology, see [link to relevant documentation]. Figure 6 ,include: The primary control module is used to achieve primary control of the microgrid by employing droop control of a simulated synchronous generator; The secondary control module is used to design secondary control in the microgrid, including secondary frequency regulation and active power distribution. Specifically, it adopts local PI control for secondary frequency regulation and adjusts the frequency setpoint to achieve frequency deviation adjustment. Based on the event triggering mechanism, it designs the control strategy of the distributed active power distribution controller of the microgrid under the directed communication topology to perform active power distribution. The convergence verification module is used to verify the convergence of the distributed active power distribution controller of the microgrid under the directed communication topology using Lyapunov stability theory.

[0032] The system modules disclosed in this embodiment are described in a relatively simple manner because they correspond to the methods disclosed in the embodiments. For relevant details, please refer to the method section.

[0033] The present invention will be further described below through specific embodiments.

[0034] In such Figure 1 The effectiveness of the distributed active power distribution controller in the microgrid system shown is verified. This microgrid contains four distributed power sources and two integrated loads (the sum of load demands connected to the same bus). System parameters are shown in Table 1.

[0035] Table 1

[0036] Assuming that the microgrid operates independently of the main grid, the output power of distributed generation in the islanded microgrid always meets the load demand.

[0037] The simulation process is as follows: 1) Initially, the system operates independently from the main power grid. At this time, the distributed generation operates through droop control; 2) At 1 second, secondary control is initiated; 3) At 3 seconds, the load Load1 suddenly decreases by 10 kW; 4) At 5 seconds, the load Load1 suddenly increases by 10 kW. The entire simulation process lasts 7 seconds.

[0038] Figure 2(a), Figure 2(b) and Figure 3 Experimental results are presented, and Figures 4(a) and 4(b) show the results of the traditional distributed control method for comparison.

[0039] The experiment screenshots are as follows: (1) As can be seen from Figures 2(a) and 2(b), when the microgrid is isolated from the main grid, the load in the microgrid is entirely borne by the four distributed generation sources. Due to the droop control, the system achieves power balance and frequency stability in a very short time, and the distributed generation sources share the load according to their respective droop coefficients. Note that it is precisely because of the droop mechanism that the frequency deviates from the rated frequency of 50 Hz after stabilization. When the secondary control is started at 1 s, under the action of the secondary control, the output frequency of the distributed generation sources synchronizes to the rated frequency of 50 Hz after about 0.5 s, and the distributed generation sources can still share the load according to their respective droop coefficients. When load disturbances occur at 3 s and 5 s respectively, the system can still achieve the control objective. This proves the effectiveness of the proposed distributed secondary control of the microgrid based on trigger control.

[0040] (2) Figure 3 The trigger time series of the active power distribution controller is presented, with the numbers on the right representing the number of triggers. It is clear from the figure that the trigger time series of the active power distribution controller of the distributed power source is very sparse, exhibiting aperiodicity and intermittency. Within 6 seconds of the secondary controller's startup, although three transient processes occur, the number of triggers for each distributed power source's controller does not exceed 100. Figure 1 As shown in the communication topology, each distributed power source has only one neighbor. Therefore, the controller of each distributed power source only needs to communicate with its neighbor once per trigger, meaning the number of communications for each controller is the same as the number of triggers. Furthermore, careful observation reveals that controller triggers are relatively frequent in the early stages of disturbances (including secondary control startup), but become relatively sparse after the system reaches a steady state (control convergence). The reason controller triggering still occurs after the system reaches stability is that the refined model of the distributed power source produces output errors, which can cause the system to occasionally meet the triggering conditions even in a steady state. It should be noted that in actual microgrid systems, measurement errors and noise can both cause some triggering even in a steady state. Therefore, the simulation results in this experiment are closer to reality than the results showing no triggering in steady state.

[0041] (3) Figure 4(a) shows the active power output of the distributed power source in the microgrid under traditional distributed secondary control, demonstrating a similar convergence effect to the proposed method. A closer look reveals that, since traditional distributed secondary control is based on continuous control and communication (in practice, continuous control systems need to be discretized, and the sampling period is usually very small; this experiment sets it to 1 ms), the transient process after a disturbance is smoother than that of the proposed method. However, the convergence effect is essentially the same. Figure 4(b) shows the triggering time sequence of the active power distribution controller under traditional distributed secondary control. It can be seen from the figure that the active power distribution controller of each distributed power source is triggered according to time, triggering 6000 times within 6 seconds after the secondary control starts, nearly 27 times more than the number of triggers in the proposed method. Since traditional distributed secondary control uses the same communication topology as the proposed control strategy, it requires more communication resources. In other words, for active power distribution control, the proposed trigger-based distributed controller reduces the number of controller triggers and communications by 99% compared to the traditional distributed controller, significantly reducing the communication burden.

[0042] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0043] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A microgrid control method based on event-triggered directed communication topology, characterized in that, Includes the following steps: Step 1: The microgrid uses droop control of a simulated synchronous generator to achieve primary control; Step 2: Design the secondary control in the microgrid, including secondary frequency regulation and active power distribution. Specifically: use local PI control for secondary frequency regulation, and adjust the frequency setpoint to achieve frequency deviation adjustment; based on the event triggering mechanism, design the control strategy of the distributed active power distribution controller of the microgrid under the directed communication topology to perform active power distribution. The event triggering mechanism determines whether to trigger using the following trigger function: ； in, To estimate the error, For flexibility adjustment coefficient, For distributed power sources i The number of neighbors; when At that time, the active power distribution controller is triggered; For distributed power sources i The utilization rate estimate, i.e. the active power output ratio estimate; For distributed power sources i Actual utilization rate; This is an estimate of the utilization rate of distributed power source j.

2. The microgrid control method based on event-triggered directed communication topology according to claim 1, characterized in that, In step 1, primary control is achieved using droop control of a simulated synchronous generator, specifically as follows: ； in, For distributed power sources i The output angular frequency, which is related to the frequency The relationship is: ; For distributed power sources i ; For distributed power sources i Active power / frequency droop factor; This is the reference frequency for droop control, or the frequency setpoint, and also the angular frequency of the inverter during no-load operation.

3. The microgrid control method based on event-triggered directed communication topology according to claim 1, characterized in that, In step 2, local PI control is used for secondary frequency modulation. By adjusting the frequency setpoint, the frequency deviation is adjusted. Specifically: Differentiating the active power / frequency droop relationship yields: ； Solve for the reference frequency: ； in, This is the control input for the distributed frequency recovery controller. For the control input of the distributed active power distribution controller; The system frequency is restored by controlling each distributed power source to track the reference frequency, specifically as follows: ； in, Hz For the rated frequency, For distributed power sources i The output angular frequency, and These are the proportional and integral control coefficients, respectively.

4. The microgrid control method based on event-triggered directed communication topology according to claim 1, characterized in that, In step 2, the control strategy of the distributed active power distribution controller of the microgrid under the directed communication topology is as follows: Through control rate To control distributed power sources in microgrids i of efforts, ； in, To control the gain; n This refers to the number of distributed power sources. For distributed power sources i The estimated utilization rate, i.e., the estimated active power output ratio. for Distributed power supply i The actual power; For distributed power sources i Actual utilization rate For distributed power sources i The output active power, For distributed power sources i Maximum output; For distributed power sources i The first distributed active power distribution controller k Triggering time: 。 5. A microgrid control method based on event-triggered directed communication topology according to claim 1, characterized in that, It also includes step 3, which verifies the convergence of the distributed active power distribution controller of the microgrid under the directed communication topology using Lyapunov stability theory.

6. A microgrid control system based on event-triggered directed communication topology, characterized in that, include: The primary control module is used to achieve primary control of the microgrid by employing droop control of a simulated synchronous generator; The secondary control module is used to design secondary control in the microgrid, including secondary frequency regulation and active power distribution. Specifically, it employs local PI control for secondary frequency regulation, adjusting the frequency setpoint to regulate frequency deviation. Based on an event-triggered mechanism, it designs a control strategy for the distributed active power distribution controller in a directed communication topology to perform active power distribution. The event triggering mechanism determines whether to trigger using the following trigger function: ； in, To estimate the error, For flexibility adjustment coefficient, For distributed power sources i The number of neighbors; when At that time, the active power distribution controller is triggered; For distributed power sources i The utilization rate estimate, i.e. the active power output ratio estimate; For distributed power sources i Actual utilization rate; This is an estimate of the utilization rate of distributed power source j.

7. A microgrid control system based on event-triggered directed communication topology according to claim 6, characterized in that, It also includes a convergence verification module, which is used to verify the convergence of the distributed active power distribution controller of the microgrid under the directed communication topology using Lyapunov stability theory.

Images