Microgrid distributed voltage restoration and power distribution method under event triggering mechanism

Abstract

The application is suitable for the field of micro-grid control, and provides a micro-grid distributed voltage recovery and power distribution method under an event triggering mechanism. Firstly, the DC micro-grid is modeled and analyzed under the event triggering condition, the DC bus error is obtained, and the voltage and current sampling error problem caused by the event triggering is analyzed to obtain the sampling error. Then, an event triggering controller is constructed, the event triggering condition is determined, and finally the control method of DC bus voltage recovery and optimal power distribution is realized. The method of the application breaks the hierarchical boundary of the power grid control model, realizes the optimal power distribution in the three layers while completing the two-layer control. In addition, the method is realized based on the event triggering communication mechanism, greatly reduces the communication burden of the micro-grid system, and improves the stability of the overall system.

Description

Technical Field

[0001] This invention belongs to the field of microgrid control, and particularly relates to a method for distributed voltage recovery and power distribution in microgrids under an event-triggered mechanism. Background Technology

[0002] With the shortage of traditional energy supplies and the increasing demand for reliable electricity, microgrids, based on efficient and clean distributed generation (DG) and combined with energy storage units, loads, and related control devices, have become a flexible and advanced new power supply method and a research hotspot both domestically and internationally in recent years. Microgrids can operate in parallel with the main power grid or in islanded operation during grid faults, independently supplying power to local loads, offering high power supply security and reliability. Furthermore, compared to AC microgrids, DC microgrids offer advantages such as not requiring attention to frequency, reactive power, and power quality, making them more popular in practical applications.

[0003] Inspired by traditional power system control methods, a hierarchical control structure is typically adopted to achieve more efficient energy management of isolated DC microgrids. The entire control system is divided into three layers. The bottom layer mainly uses distributed droop control to achieve proportional current output. The second layer aims to eliminate voltage deviation problems caused by droop function, while the third layer discusses the optimization of the entire energy management system.

[0004] Two-level control plays a crucial role in ensuring the stability of islanded microgrids, thus becoming an important research area. There are three main control strategies in microgrid two-level control: centralized, decentralized, and distributed. Centralized control uses a single integrated controller to control the entire network; decentralized control uses many sub-controllers to control each generator node (DG), with no information exchange between sub-controllers; distributed control uses information from sub-controllers and their neighbors, offering high flexibility and reliability. However, due to the involvement of numerous control decisions and information communication technologies, continuous-time distributed control places a significant burden on communication between generator nodes. Therefore, designing non-continuous-time controllers to reduce the communication burden within the microgrid and improve control efficiency has become a worthy research focus.

[0005] In three-layer control, to address the inflexibility and high computational cost of traditional centralized optimization algorithms, distributed optimization architectures have been proposed in recent years, employing distributed consensus principles to solve energy management optimization problems. However, it is worth noting that the intermittent and variable nature of renewable energy generation means that the operating states of generator units may change frequently, which makes the slow convergence of most algorithms hinder their use in online microgrid implementations. Summary of the Invention

[0006] The purpose of this invention is to provide a microgrid distributed voltage recovery and power allocation method under an event-triggered mechanism. This method relies only on discrete, non-periodic event-triggered communication and considers both secondary voltage recovery error and tertiary power allocation optimization.

[0007] This invention is implemented as follows: a microgrid distributed voltage restoration and power distribution method under an event-triggered mechanism, comprising the following steps:

[0008] S1. Establish a DC microgrid model suitable for event-triggered mechanisms, as follows:

[0009] 11) In droop control, the reference voltage Represented as formula :

[0010]

[0011] in Rated DC voltage This is the droop gain coefficient. It is the first The output current of each DG;

[0012] Due to transmission line impedance The presence of this factor indicates that the voltage at the point of common coupling bus is... With reference voltage Having such a formula The relationship shown is... For output current:

[0013]

[0014] Joint - The DC bus voltage equation can be obtained as follows: As shown:

[0015]

[0016] 12) According to the system block diagram, in order to reduce the system communication cost, the DC bus voltage... and output current Perform aperiodic sampling, and define it as follows: , The event trigger signal shown and :

[0017]

[0018]

[0019] in and exist Updated constantly;

[0020] 13) Define event-triggered sampling error and As shown in the formula As shown:

[0021]

[0022] in Let represent an N-dimensional column vector where all elements are 1. and These are the calculated values ​​for the bus voltage and the output current, respectively.

[0023] S2. Design a distributed voltage recovery and optimal power distribution controller based on an event-triggered mechanism, as follows:

[0024] 21) Based on the above DC microgrid model, design an event-triggered controller. As shown in the formula As shown:

[0025]

[0026] in This represents the cost coefficient of each node in the optimal power allocation;

[0027] 22) Add a controller Afterwards, the overall system can be configured as follows: express:

[0028]

[0029] in ,

[0030]

[0031] It is the Laplace matrix of the power grid communication diagram;

[0032] 23) To facilitate further analysis, the controller can be transformed into the following formula: As shown:

[0033]

[0034] 24) Define the event trigger time Satisfying the following formula Conditions shown:

[0035]

[0036] in The parameter values ​​will be calculated in the controller stability analysis based on Lyapunov's theorem.

[0037] A further technical solution is that the event-triggered controller in S2 is designed to realize the DC bus voltage recovery and optimal power distribution of the DC microgrid under a discrete and discontinuous communication mechanism.

[0038] The microgrid distributed voltage recovery and power allocation method under the event-triggered mechanism provided in this invention first analyzes the DC microgrid system to obtain the bus voltage equation. Simultaneously, considering event-triggered conditions, a system state model is established to obtain the sampling errors of the bus voltage and output current under event-triggered sampling. Furthermore, while considering optimal power allocation, an event-triggered controller is constructed, and the event-triggered conditions are given to achieve bus voltage recovery and optimal power allocation. This invention breaks the hierarchical nature of grid layered control, achieving optimal power allocation in the third layer while realizing second-level DC bus voltage recovery control. In addition, by employing a discontinuous-time communication strategy, this invention significantly reduces the system's communication overhead while achieving the same control objectives as continuous-time communication. Attached Figure Description

[0039] Figure 1 This is a structural diagram of a DC microgrid system;

[0040] Figure 2 This is a block diagram of a control system based on an event-triggered mechanism.

[0041] Figure 3 The control method proposed in this invention relates to the bus voltage and output current before and after activation;

[0042] Figure 4 After load transformation, the control method proposed in this invention activates the bus voltage and output current before and after the load change.

[0043] Figure 5 A comparison chart of bus voltage and output current before and after activation for the control method based on continuous time communication;

[0044] Figure 6 This refers to the communication triggering status of each generator node in the control method proposed in this invention;

[0045] Figure 7 This is a schematic diagram of the test platform used in this invention;

[0046] Figure 8 This is a flowchart illustrating the implementation of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0049] like Figures 1-6 As shown, a microgrid distributed voltage recovery and power distribution method under an event-triggered mechanism provided by an embodiment of the present invention includes the following steps:

[0050] S1. Establish a DC microgrid model suitable for event-triggered mechanisms, as follows:

[0051] 11) In droop control, the reference voltage Represented as formula :

[0052]

[0053] in Rated DC voltage This is the droop gain coefficient. It is the first The output current of each DG;

[0054] Due to transmission line impedance The presence of this factor indicates that the voltage at the point of common coupling (PCC) bus is... With reference voltage Having such a formula The relationship shown is... For output current:

[0055]

[0056] Joint - The DC bus voltage equation can be obtained as follows: As shown:

[0057]

[0058] 12) According to the system block diagram, in order to reduce the system communication cost, the DC bus voltage... and output current Perform aperiodic sampling, and define it as follows: , Event trigger signal shown and :

[0059]

[0060]

[0061] in and exist Updated constantly;

[0062] 13) Define event-triggered sampling error and As shown in the formula As shown:

[0063]

[0064] in Let represent an N-dimensional column vector where all elements are 1. and These are the calculated values ​​for the bus voltage and the output current, respectively.

[0065] S2. Design a distributed voltage recovery and optimal power distribution controller based on an event-triggered mechanism, as follows:

[0066] 21) Based on the above DC microgrid model, design an event-triggered controller. As shown in the formula As shown:

[0067]

[0068] in This represents the cost coefficient of each node in the optimal power allocation;

[0069] 22) Add a controller Afterwards, the overall system can be configured as follows: express:

[0070]

[0071] in ,

[0072]

[0073] It is the Laplace matrix of the power grid communication diagram;

[0074] 23) To facilitate further analysis, the controller can be transformed into the following formula: As shown:

[0075]

[0076] 24) Define the event trigger time Satisfying the following formula Conditions shown:

[0077]

[0078] in The parameter values ​​will be calculated in the controller stability analysis based on Lyapunov's theorem.

[0079] To intuitively verify the effectiveness of the strategy proposed in this invention, the following examples illustrate the results: Table 1 shows the main electrical parameters and controller parameters.

[0080] Table 1: Main Electrical Parameters and Controller Parameters

[0081]

[0082] like Figure 7 As shown, this invention establishes an islanded DC microgrid system consisting of three distributed power sources for testing. These distributed power sources are connected to a common DC bus via resistors that simulate line resistance. In addition to traditional resistive loads, a constant power load (CPL) is also connected to this DC bus. The event-triggered controller and its top-level optimization algorithm proposed in this invention are implemented on the dSPACE1006 control platform. This invention uses a four-channel digital oscilloscope to simultaneously measure the voltage of the point of common coupling bus. and the current output of these three DGs .

[0083] like Figure 3 and Figure 4 As shown, before the proposed secondary control method is activated, each DG shares almost the same current output. Because the initial drop gain is set to the same, i.e. However, the bus voltage at the point of common coupling drops to 90.43V. When the proposed control is activated, the bus voltage... It has been restored to 100.28V. Additionally, as... Figure 3 As shown, the current output is adjusted to the optimal ratio, rather than the reverse droop gain, i.e. .

[0084] Furthermore, the performance of the control strategy proposed in this invention is further tested under varying load conditions. Figure 5 It can be seen that when the CPL load changes from... Become This caused the total load to drop from Become At that time, the voltage at the point of common coupling bus It remains almost unchanged, while the current output reaches a new ratio, namely .

[0085] To demonstrate the effectiveness of our findings, the experimental results of our proposed control method are as follows: Figure 3 As shown, with Figure 5 Signal sampling frequency in The results of continuous-time control are almost identical. In continuous-time control, signal sampling and communication events are triggered with a period of 15k times. In contrast, the event-triggered controller triggers communication non-periodically with a much smaller number of times; the actual number of triggers for both is shown in Table 2. Figure 6 The diagram illustrates the triggering status of the controller proposed in this invention, where "1" indicates triggering and "0" indicates no triggering.

[0086] Table 2: Number of triggers for the two controllers

[0087]

[0088] The experimental results above show that the control method for distributed voltage recovery and optimal power allocation of DC microgrid based on event triggering mechanism proposed in this invention can not only restore the bus voltage while effectively reducing the communication burden, but also allocate the optimal power output among dispatchable distributed power sources under different power sharing ratios.

[0089] The above embodiments of the present invention provide a distributed voltage recovery and power allocation method for microgrids under an event-triggered mechanism. First, the DC microgrid system is analyzed to obtain the bus voltage equation. Simultaneously, a system state model is established considering event-triggered conditions to obtain the sampling errors of the bus voltage and output current under event-triggered sampling. Further, while considering optimal power allocation, an event-triggered controller is constructed, and the event-triggered conditions are given to achieve bus voltage recovery and optimal power allocation. This invention breaks the hierarchical nature of grid layered control, achieving optimal power allocation in the third layer while simultaneously realizing second-layer DC bus voltage recovery control. Furthermore, by employing a discontinuous-time communication strategy, this invention significantly reduces the system's communication overhead while achieving the same control objectives as continuous-time communication.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A microgrid distributed voltage restoration and power distribution method under an event-triggered mechanism, characterized in that, Includes the following steps: S1. Establish a DC microgrid model suitable for event-triggered mechanisms, as follows: 11) In droop control, the reference voltage Represented as formula : in Rated DC voltage This is the droop gain coefficient. It is the first The output current of each DG; Due to transmission line impedance The presence of this factor indicates that the voltage at the point of common coupling bus is... With reference voltage Having such a formula The relationship shown is... For output current: Joint - The DC bus voltage equation can be obtained as follows: As shown: 12) According to the system block diagram, in order to reduce the system communication cost, the DC bus voltage... and output current Perform aperiodic sampling, and define it as follows: , Event trigger signal shown and : in and exist Updated constantly; 13) Define event-triggered sampling error and As shown in the formula As shown: in Let represent an N-dimensional column vector where all elements are 1. and These are the calculated values ​​for the bus voltage and the output current, respectively. S2. Design a distributed voltage recovery and optimal power distribution controller based on an event-triggered mechanism, as follows: 21) Based on the above DC microgrid model, design an event-triggered controller. As shown in the formula As shown: in This represents the cost coefficient of each node in the optimal power allocation; 22) Add a controller Afterwards, the overall system can be configured as follows: express: in , It is the Laplace matrix of the power grid communication diagram; 23) To facilitate further analysis, the controller can be transformed into the following formula: As shown: 24) Define the event trigger time Satisfying the following formula Conditions shown: in The parameter values ​​will be calculated in the controller stability analysis based on Lyapunov's theorem.

2. The microgrid distributed voltage restoration and power distribution method under the event-triggered mechanism according to claim 1, characterized in that, The event-triggered controller designed in S2 realizes DC bus voltage recovery and optimal power distribution of DC microgrid under discrete and discontinuous communication mechanism.

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