Dynamic event-triggered dual-layer distributed control method for ac-dc microgrid

Abstract

The application provides a dynamic event-triggered AC / DC microgrid double-layer distributed control method, which comprises the following steps: collecting the operation state quantity of an AC / DC hybrid microgrid system; performing primary control on the distributed power supply in the AC subnetwork and the interconnection converter based on the operation state quantity; performing distributed secondary control on the interconnection converter by the upper layer of the AC / DC hybrid microgrid system; performing leader-follower-based restraint consensus secondary control on the AC subnetwork by the lower layer of the AC / DC hybrid microgrid system, generating a load rate reference value by the interconnection converter, and synchronizing the load rate state through local communication by the multiple distributed power supplies, so as to realize AC frequency recovery and distributed power supply power distribution; through the above technical scheme, the stability, coordination and communication resource utilization efficiency of the system under extreme disturbance and mode switching working conditions are improved.

Description

Technical Field

[0001] This application relates to the field of microgrid power control technology, and in particular to a two-layer distributed control method for AC / DC microgrids based on dynamic event triggering. Background Technology

[0002] With the rapid development of distributed power sources, power electronic converters, and DC loads, AC / DC hybrid microgrid systems have significant application value in terms of renewable energy integration, energy sharing, and improved power supply reliability. Compared to single AC or DC microgrid systems, AC / DC hybrid microgrid systems typically use the DC bus as a common energy channel and connect multiple AC subgrids through interconnecting converters, enabling bidirectional power support between different AC subgrids. However, under islanded operation and complex load disturbance conditions, AC / DC hybrid microgrid systems lack the support of a large power grid, and AC frequency, DC bus voltage, and inter-regional power distribution are prone to coupling fluctuations, affecting the stable operation of the system.

[0003] Currently, AC / DC hybrid microgrid systems mostly employ centralized control or traditional hierarchical control methods. Centralized control relies on a central controller and a global communication network, which suffers from high single-point-of-failure risk and poor system scalability. While traditional hierarchical control methods can improve voltage and frequency recovery and power distribution, they typically require continuous or high-frequency periodic communication, which can easily lead to communication congestion and control delays under conditions such as multi-mode switching and extreme load surges. Furthermore, existing control strategies often handle DC voltage recovery, interconnected converter power distribution, AC frequency recovery, and distributed power allocation separately, making it difficult to simultaneously address both emergency stability support and steady-state precise coordination. Summary of the Invention

[0004] This application provides a two-layer distributed control method for AC / DC microgrids based on dynamic event triggering. This method solves the problems of difficulty in coordinating AC frequency and DC voltage in AC / DC hybrid microgrid systems under complex load disturbances and multi-mode switching processes in related technologies, and improves the stability, coordination and communication resource utilization efficiency of the system under extreme disturbances and mode switching conditions.

[0005] To achieve the above objectives, this application provides a two-layer distributed control method for AC / DC microgrids based on dynamic event triggering, the method comprising: The system collects operational status parameters of the AC / DC hybrid microgrid system, including AC subgrid frequency, DC bus voltage, distributed power output, and interconnected converter transmission power. The AC / DC hybrid microgrid system uses a DC bus as a common backbone, and the DC bus is connected to multiple AC subgrids through interconnected converters. Based on the operating status, a control operation is performed on the distributed power sources and the interconnected converters in the AC subnet, so that the distributed power sources share the load in the AC subnet and the interconnected converters perform bidirectional power mutual assistance according to the AC and DC side operating status. The upper layer of the AC / DC hybrid microgrid system performs distributed secondary control on the interconnected converters, performs DC voltage recovery and interconnected converter power sharing based on the status information of two adjacent interconnected converters, and switches to emergency frequency recovery mode when the AC subgrid frequency exceeds the limit. In the AC / DC hybrid microgrid system, the lower layer performs leader-follower-based constrained consistency secondary control on the AC subgrid. The interconnected converter generates a load rate reference value, and multiple distributed power sources synchronize their load rate status through local communication to achieve AC frequency recovery and distributed power allocation. The communication variables of the local communication are updated using a dynamic event-triggered mechanism. When the trigger condition is met, the current status information is sent; when the trigger condition is not met, the status information of the previous cycle is maintained to reduce continuous communication and redundant data transmission.

[0006] In one possible implementation, the primary control of the distributed power source in the AC subnet is to perform droop control on the distributed power source to achieve primary distribution of load fluctuations within the AC network. The first control operation performed on the interconnected converters in the AC subnet is to perform normalized unified droop control on the interconnected converters to achieve bidirectional power mutual assistance between AC and DC networks.

[0007] In one possible implementation, the upper layer of the AC / DC hybrid microgrid system performs distributed secondary control on the interconnected converters, performs DC voltage recovery and interconnected converter power sharing based on the status information of two adjacent interconnected converters, and switches to emergency frequency recovery mode when the AC subgrid frequency exceeds the limit, including: Based on the power sharing consistency error of the distributed power source and the distributed voltage controller, the rate of change of the voltage correction of the interconnected converter is determined. Based on the rate of change and voltage reference value, and in conjunction with the primary control rate expression, the unified power mutual assistance control rate under the distributed secondary control is determined. Power allocation is performed according to the unified power mutual assistance control rate.

[0008] In one possible implementation, the method further includes: If the load on the AC subnet exceeds a preset load threshold, switch to emergency frequency recovery mode to ensure the AC network does not disconnect; the strong tracking target of the emergency frequency recovery mode is 50Hz. When the interconnected converter restores DC voltage, an integrator-linked reset is used.

[0009] In one possible implementation, the lower layer of the AC / DC hybrid microgrid system performs leader-follower-based constrained consistency secondary control on the AC subgrid. The interconnected converter generates a load rate reference value, and multiple distributed power sources synchronize their load rate states through local communication to achieve AC frequency recovery and distributed power allocation, including: The interconnected converter is used as the leader, and the frequency deviation on the AC subnet side is extracted using a PI regulator to generate a unified load rate reference value for the AC subnet. Multiple distributed power sources are used as followers, and the load rate status is synchronized in a sparse communication network to maintain consistency. The secondary frequency recovery is completed by superimposing the underlying active power reference value of the system based on the synchronized load rate status.

[0010] In one possible implementation, the communication variables are a DC voltage signal, a normalized power signal, a load rate reference value, and a local load rate; the triggering time of the dynamic event triggering mechanism is determined based on the absolute dead zone and the minimum triggering interval for anti-Zeno behavior.

[0011] In one possible implementation, the DC voltage signal uses state decoupling as the trigger condition; the normalized power signal uses strong state coupling as the trigger condition; the load rate reference value uses no spatial error as the trigger condition; and the local load rate uses spatiotemporal constraint coordination as the trigger condition.

[0012] The technical solutions provided in this application embodiment have at least the following technical effects or advantages: Based on the above technical solution, a two-layer control architecture for AC / DC hybrid microgrids was established. The lower layer achieves initial load sharing within the AC subgrid and bidirectional power mutual assistance between the AC and DC sides through primary droop control of the AC subgrid and normalized unified droop control of the interconnected converters. The upper layer achieves DC voltage recovery, capacity-based power allocation of interconnected converters, zero-steady-state-error recovery of AC frequency, and capacity-based power allocation of distributed power sources through distributed secondary control of interconnected converters and constrained consistency secondary control of the AC subgrid. At the same time, a dynamic event triggering mechanism is introduced to update each communication variable on demand, reducing continuous communication and redundant data transmission, and improving the stability, coordination, and communication resource utilization efficiency of the system under extreme disturbances and mode switching conditions. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 A flowchart illustrating a two-layer distributed control method for AC / DC microgrids based on dynamic event triggering, provided in an embodiment of this application; Figure 2 A topology diagram of a simulated AC / DC hybrid microgrid system model provided in this application embodiment; Figure 3 A schematic diagram of the transmission power of each IC provided in an embodiment of this application; Figure 4 A schematic diagram of DC voltage provided for an embodiment of this application; Figure 5 A schematic diagram of the frequency of each AC unit provided in an embodiment of this application; Figure 6 A schematic diagram of the active power of each DG provided in an embodiment of this application; Figure 7 A DC voltage communication triggering timing diagram provided in an embodiment of this application; Figure 8 A power transmission communication triggering time diagram for an interconnected converter is provided in an embodiment of this application; Figure 9 A communication triggering time diagram for a load rate reference value is provided in an embodiment of this application; Figure 10 This is a local load rate communication triggering time diagram provided for an embodiment of this application. Detailed Implementation

[0015] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0016] In the description of the embodiments of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; a mechanical connection or an electrical connection; a direct connection or an indirect connection through an intermediate medium; or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0017] As the background technology describes, existing event-triggered control methods mostly employ fixed thresholds or static triggering conditions, making it difficult to adaptively adjust the communication frequency according to system transient impacts and steady-state operation requirements. When the system experiences frequency exceedances, power direction switching of interconnected converters, or sudden load changes in the AC subgrid, the lack of a reasonable multi-mode switching and dynamic triggering mechanism can easily lead to wasted communication resources, uneven power distribution, or reduced frequency and voltage recovery effectiveness. Therefore, there is an urgent need for a control method for AC / DC hybrid microgrids that can simultaneously achieve multi-mode power mutual assistance, two-layer distributed collaborative control, and on-demand communication triggering.

[0018] To address the aforementioned issues, this application provides a two-layer distributed control method for AC / DC microgrids based on dynamic event triggering. A two-layer control architecture for AC / DC hybrid microgrids is established. The lower layer achieves initial load sharing within the AC subgrid and bidirectional power mutual assistance between the AC and DC sides through primary droop control of the AC subgrid and normalized unified droop control of the interconnected converters. The upper layer achieves DC voltage recovery, capacity-based power allocation of the interconnected converters, zero-steady-state-error recovery of AC frequency, and capacity-based power allocation of distributed power sources through distributed secondary control of the interconnected converters and constrained consistency secondary control of the AC subgrid. Simultaneously, a dynamic event triggering mechanism is introduced to update communication variables on demand, reducing continuous communication and redundant data transmission, and improving system stability, coordination, and communication resource utilization efficiency under extreme disturbances and mode switching conditions.

[0019] Figure 1 This is a flowchart illustrating a two-layer distributed control method for AC / DC microgrids based on dynamic event triggering, provided as an embodiment of this application. Figure 1 As shown, the method may include the following steps.

[0020] S101. Collect the operating status data of the AC / DC hybrid microgrid system.

[0021] Among them, the operating status variables are AC subgrid frequency, DC bus voltage, distributed power output, and interconnected converter transmission power; the AC / DC hybrid microgrid system uses the DC bus as a common backbone, and the DC bus is connected to multiple AC subgrids (AC Microgrid or AC unit) through interconnected converters.

[0022] S102. Based on the operating status quantity, perform a control operation on the distributed power source and the interconnected converter in the AC subnet, so that the distributed power source shares the load in the AC subnet and the interconnected converter performs bidirectional power mutual assistance according to the AC / DC side operating status.

[0023] S103. The upper layer of the AC / DC hybrid microgrid system performs distributed secondary control on the interconnected converter, performs DC voltage recovery and interconnected converter power sharing based on the status information of two adjacent interconnected converters, and switches to emergency frequency recovery mode when the frequency of the AC subgrid exceeds the limit.

[0024] S104. The lower layer of the AC / DC hybrid microgrid system performs leader-follower-based constrained consistency secondary control on the AC subgrid. The load rate reference value is generated by the interconnected converter, and multiple distributed power sources synchronize the load rate status through local communication to achieve AC frequency recovery and distributed power allocation.

[0025] The communication variables in this local communication are updated using a dynamic event-triggered mechanism. When the trigger condition is met, the current status information is sent; when the trigger condition is not met, the status information of the previous cycle is maintained, so as to reduce continuous communication and redundant data transmission.

[0026] Based on the above technical solution, a two-layer control architecture for AC / DC hybrid microgrids was established. The lower layer achieves initial load sharing within the AC subgrid and bidirectional power mutual assistance between the AC and DC sides through primary droop control of the AC subgrid and normalized unified droop control of the interconnected converters. The upper layer achieves DC voltage recovery, capacity-based power allocation of interconnected converters, zero-steady-state-error recovery of AC frequency, and capacity-based power allocation of distributed power sources through distributed secondary control of interconnected converters and constrained consistency secondary control of the AC subgrid. At the same time, a dynamic event triggering mechanism is introduced to update each communication variable on demand, reducing continuous communication and redundant data transmission, and improving the stability, coordination, and communication resource utilization efficiency of the system under extreme disturbances and mode switching conditions.

[0027] In one possible implementation, the aforementioned primary control of the distributed power source in the AC subnet is to perform droop control on the distributed power source to achieve primary distribution of load fluctuations within the AC subnet; the aforementioned primary control of the interconnected converter in the AC subnet is to perform normalized unified droop control on the interconnected converter to achieve bidirectional power mutual assistance between AC and DC networks.

[0028] For example, distributed generation (DG) in an AC subnet can employ classic droop control to achieve primary autonomous distribution of load fluctuations within the AC microgrid. P - f In the (Active Power-Frequency) regulation loop, the first... The first communication subnet within the first The primary frequency regulation characteristic of a distributed power source can be expressed as: ;in, and These are the actual sampling frequency of the distributed power source and the rated operating frequency of the system, respectively. Choose 50Hz; For the first In the first communication subnet Distributed power supply unit P - f Sag coefficient; and These are the actual output active power of the distributed power unit and the given initial active reference power, respectively.

[0029] For example, the above-described normalized unified droop control of the interconnected converter can achieve bidirectional power exchange between AC and DC networks. To eliminate the difference in physical dimensions between AC frequency and DC voltage, a full-range normalized mapping is introduced here to the dimensionless standard interval [-1,1]: ;in, For the first The normalized AC frequency of an Interlinking Converter (IC); For the first Normalized DC voltage of interconnected converters; This is the frequency reference value; This is the voltage reference value; and These are the maximum and minimum values ​​of the AC bus frequency, respectively. and These are the maximum and minimum values ​​of the DC bus voltage; and These represent the AC frequency and DC voltage on both sides of the interconnected converter, respectively.

[0030] Normalized AC frequency of interconnected converters DC voltage normalized with interconnected converter The difference is used as a parameter for the power transmission of the bidirectional AC / DC converter. The positive direction is defined as from DC to AC (inverting to positive). Then the... The unified droop power mutual control law of interconnected converters is expressed as: ;in, For the first The unified droop adjustment coefficient for each interconnected converter is set according to the actual scenario. The active power transmitted by the interconnected converter. In this way, the AC frequency and DC voltage of the interconnected converter can be normalized by full-range normalization mapping; based on the normalized AC frequency and normalized DC voltage, the unified droop power mutual assistance control law of the interconnected converter is determined, thereby realizing bidirectional power mutual assistance between AC and DC networks through the unified droop power mutual assistance control law.

[0031] In one possible implementation, S103 may include: determining the rate of change of the voltage correction of the interconnected converter based on the power sharing consistency error of the distributed power source and the distributed voltage controller; determining the unified power mutual assistance control rate under the distributed secondary control based on the rate of change and the voltage reference value, and in conjunction with the primary control rate expression; and performing power sharing according to the unified power mutual assistance control rate.

[0032] For example, the unified power mutual control law can be determined in the following way. Define the first... Power sharing consistency error of distributed power sources : ;in, A collection of interconnected converter nodes; For the adjacency matrix of the communication network The element, when the node Received by node Information ,otherwise ; For the first The actual transmission power of the interconnected converters; The rated capacity corresponding to the interconnected converter.

[0033] Next, the distributed voltage local controller is defined to be obtained solely through communication matrix calculation. : ;in, Representative node The number of adjacent nodes; This is the power regulation coefficient; This is the integral value of the power sharing error, which is coupled with the voltage target; Distributed voltage local controller; yes V m User-defined reference steady-state value; For the first The actual sampling voltage of the DC bus.

[0034] Based on the power sharing consistency error and distributed voltage local controller of the distributed power source, a distributed control algorithm for the distributed power source is established to determine the rate of change of the voltage correction of the interconnected converter: ;in, This is the local voltage regulation coefficient; For the first Rate of change of local voltage correction for each interconnected converter.

[0035] The voltage correction amount is obtained after the action of the limiting integrator. Superimposed on the voltage reference value Using the above as the new normalized reference value, substituting it into the primary control law expression yields the unified power mutual assistance control law under secondary control: ;in, To unify the power mutual control law, DC voltage This is the voltage reference value. The rate of change of the local voltage correction. and These represent the maximum and minimum values ​​of the DC bus voltage.

[0036] In one possible implementation, the method further includes: switching to an emergency frequency recovery mode when the load on the AC subnet exceeds a preset load threshold to ensure that the AC network does not disconnect; the strong tracking target of the emergency frequency recovery mode is 50Hz; and using an integrator linkage reset when the interconnected converter performs DC voltage recovery.

[0037] For example, when the AC subnet is unable to handle the load during distributed voltage consistency control, an emergency frequency recovery control method with 50Hz as the strong tracking target is used to ensure that the AC system does not disconnect from the grid. Next, The limiting integrator serves as a correction term for the primary frequency reference value of this interconnect converter. : , ;in, The rate of change of the correction amount for the frequency reference value. This is the frequency adjustment coefficient. For frequency recovery reference value, For AC frequency, This is the frequency normalization value under secondary control. As a frequency reference value, and These represent the maximum and minimum AC bus frequencies, respectively.

[0038] When a certain interconnected converter in the system switches from distributed consistent voltage control to emergency frequency recovery, the power control topology changes, and the eigenvalue spectrum of the Laplace matrix in the consensus algorithm jumps. An integrator-linked reset is then implemented. When the state changes, the State signal emits a rising or falling edge pulse signal. During the transient process of receiving this signal, integrator updates are temporarily frozen, and a common pulse signal is immediately applied to the external reset port of the integrator, achieving synchronous reset of all integrators across the network.

[0039] In one possible implementation, S104 may include: using the interconnected converter as the leader and extracting the frequency deviation on the AC subnet side using a PI regulator to generate a unified load rate reference value for the AC subnet; using multiple distributed power sources as followers and performing constraint consistency synchronization of the load rate state through a sparse communication network; reconstructing the active power reference value at the system bottom layer based on the synchronized load rate state, and superimposing it to complete the secondary frequency recovery.

[0040] For example, on the leader's interconnect converter side, a PI regulator is used to extract the AC side frequency deviation and generate a unified load rate reference value for the AC subnet: ;in, This is a global load rate reference instruction; and These are the actual sampling frequency and the system rated frequency, respectively. and For the first k PI controller adjustment parameters for frequency recovery of each AC subnet; s For the Laplace operator.

[0041] Multiple distributed power units act as followers, using a sparse communication network to maintain consistent synchronization of load rate states. Their dynamic evolution state equation is as follows: ;in, The rate of change of the load rate of the AC subnet; For the set of DGs within the communication subnet; and They are nodes Its neighboring nodes The load rate state variable; These are the elements of the adjacency weight matrix of the communication network; To restrain the gain; For consistent convergence gain. Since only nodes that communicate directly with the interconnected converter side obtain global reference information, this is only for the constrained nodes. Other ordinary distributed power nodes Relying on this constraint mechanism, the entire network state eventually converges, that is... .

[0042] Finally, multiple distributed power units reconstruct the underlying active power reference value based on the synchronized load rate state, and then superimpose them to complete the secondary frequency recovery: ;in, This is the updated active power reference value; The initial active power given to this unit; This is the rated capacity of the unit. Substituting it into the primary control loop allows for simultaneous zero-steady-state-error recovery of AC frequency and precise distribution of active power across the entire network according to capacity.

[0043] In one possible implementation, the communication variables are a DC voltage signal, a normalized power signal, a load rate reference set, and a local load rate; the triggering time of the dynamic event triggering mechanism is determined based on the absolute dead zone and the minimum triggering interval to prevent Zeno behavior. For example, Zeno behavior refers to the control system triggering an infinite number of control commands or communication updates within an extremely short period of time.

[0044] In one possible implementation, the DC voltage signal uses state decoupling as the trigger condition; the normalized power signal uses strong state coupling as the trigger condition; the load rate reference value uses no spatial error as the trigger condition; and the local load rate uses spatiotemporal constraint coordination as the trigger condition.

[0045] For example, a DC voltage signal can be represented as: The normalized power signal can be expressed as: The load factor reference value can be expressed as: The local load factor can be expressed as: Using state variables In the system, these four types of communication signals are represented; nodes are defined. The local sampling error is: ;in, The last trigger time Send and maintain discrete state values ​​in the network. for node t Time-based measurement. Define network consistency error. for: ;in, and The first and The triggering time of each converter for node t Time measurement value.

[0046] Combined with absolute dead zone Minimum trigger interval for anti-Zeno behavior Design a unified dynamic event-triggered mechanism (DETM) to determine the next trigger time. for: ;in, This is the trigger time. This is the local error penalty coefficient; For consistency error feedback gain; Dynamic shield weight; As a dynamic auxiliary variable; It is an absolute dead zone.

[0047] The evolution equation of the dynamic term satisfies: ; where the initial value of the dynamic term ; The exponential decay rate governs the tightening of the shield and the elimination of static error in the steady state of the dominant system. Inject gain into the dynamic term error.

[0048] Considering the sensitivity of the bottom-level nodes of the AC subnet to high-frequency noise, for the bottom-level... The channel, dynamic event triggering mechanism, trigger condition, first-order absolute error. Dynamic shield. This causes the measurement error to surge when the system is subjected to large disturbances, leading to... The shield rapidly expands to increase the trigger threshold and intercept communication storms; as the system stabilizes, dissipation items... The dominant effect is the decay of the shield index, forcing the system to approach zero static error. Furthermore, the minimum trigger interval at the bottom layer... In engineering, it also serves as a steady-state heartbeat survival mechanism, used to refresh the dead zone. The system possesses adaptive adjustment capabilities to compensate for the slight steady-state error caused by the error.

[0049] For example, differentiated triggering logic is set for different communication variables: for DC voltage signals It employs state-decoupled triggering, and its triggering condition is unaffected by the state. For normalized power signals... It employs a strongly coupled state triggering mechanism. When State=1, it triggers according to the dynamic event triggering condition; when the frequency exceeds the limit and switches, it triggers once; when State=0, it blocks the communication channel. (For the leader load rate reference value...) It employs a zero-space-error triggering method, with a network consistency error of 0. For follower local load rates... The network error is defined as follows: (The network uses a spatiotemporal constraint-based collaborative triggering mechanism.) ;in, For nodes The neighborhood group, These are the elements of the adjacency weight matrix of the communication network; To control gain, the above settings enable each communication channel to adaptively trigger according to control requirements, thereby reducing redundant communication while ensuring coordinated control of voltage, power, and load rate.

[0050] The workflow of the technical solution of this application will be described below with reference to the embodiments.

[0051] This section uses simulation examples to illustrate the process, demonstrating how to build a simulation platform like MATLAB / Simulink. Figure 2 The diagram shows a hybrid AC / DC microgrid topology model, where each secondary control module in the system's communication network is modeled using the S-Function module in Simulink. Each AC subgrid is connected via a DC bus (DC ring network). Within the AC subgrid's physical layer, each distributed power source is configured with a single bus parallel connection, and all distributed power sources are ideal inverter types. The information layer includes secondary voltage and frequency controllers. Each distributed power source is configured with an intelligent agent to interact with neighboring intelligent agents and uses secondary control to eliminate frequency and voltage errors and allocate active power according to capacity.

[0052] To verify the effectiveness of the method in this application, the system components, control parameters, and dynamic event triggering coefficients in the system are shown in Tables 1 and 2 below. The total runtime of the simulation example is 4 seconds, the DC base load is 150Ω, and the AC base loads are 10kW / 37kW / 12kW / 14kW respectively.

[0053] Table 1: Table 2: The 0-1s droop control phase: The system operates solely based on the underlying droop control. Due to the inherent inherent limitations of droop control, Figure 4 The DC voltage is stable at around 692V (lower than the rated value of 700V). Figure 5 The frequency of each AC unit (AC subnet) is below 50Hz, with the frequency drop being particularly severe in the heavily loaded AC2; meanwhile, Figure 3 The transmission power of each IC (interconnected converter) in the circuit was not evenly distributed.

[0054] 1-2s Interconnected converter secondary voltage and power coordinated control stage: The secondary control of the interconnected converter is connected at 1s. Figure 3 The power transmission curves of each IC (interconnected converter) quickly converge and overlap, achieving precise power allocation; Figure 4 The DC voltage was restored to 700V without error. However, to boost the DC voltage, the interconnect converter needs to draw more power from the AC side, resulting in… Figure 5 The frequency of each AC unit in the middle dropped twice, and the AC2 frequency approached the lower limit risk, which verified the necessity of subsequent emergency frequency control.

[0055] 2-3s Interconnected Converter Frequency Emergency Recovery and Global Mutual Aid Phase: At 2 seconds, the AC2 frequency drops below the 49.9Hz lower limit, triggering emergency recovery control. At this time, Figure 5 The frequency of AC2 was forcibly boosted to 50Hz, at the cost of Figure 3 IC2 significantly altered its power flow to obtain support, while the remaining lightly loaded interconnected converters absorbed the power deficit across the entire network according to their capacity and reconverged. Meanwhile, Figure 5 The frequency of the remaining lightly loaded AC subnets (AC1, AC3, and AC4) is further reduced to provide support. Figure 4 After a brief fluctuation, the DC voltage stabilized again at 700V. This stage fully demonstrates the global high-power mutual support capability of the AC / DC microgrid under extreme operating conditions.

[0056] 3-4s AC subnet secondary frequency recovery and distributed power sharing stage: At 3s, the AC side is connected to the secondary control for consistency, and each DG (distributed power source) in the AC subnet actively takes on the local load. Figure 5 This indicates that the frequency of all AC subnets was smoothly and flawlessly restored to 50Hz; Figure 6 The output power of each distributed generation (DG) within the AC subnet converges to the same value, achieving precise local power allocation. As the output of distributed power sources increases, the cross-regional support burden of interconnected converters is relieved. Figure 3 The transmission power of each IC in the process drops back and converges again to a uniform distribution state. Figure 4 The DC voltage was perfectly maintained at 700V. Thus, the entire AC / DC hybrid microgrid system, under multi-level secondary coordinated control, achieved global error-free recovery of frequency and voltage, and precise power distribution.

[0057] In terms of communication, since the system's trigger control relies on the secondary coordination strategy, the event triggering of the interconnected converters all starts when the secondary control is engaged at 1.0s. For example... Figure 7 and Figure 8The figures show the communication trigger timing distribution for the upper-layer DC voltage and IC power transmission, respectively. During the initial transient phases of 1.0 s coordinated control activation, 2.0 s emergency frequency recovery triggering, and 3.0 s AC subnet secondary control activation, both communication channels exhibit dense triggering characteristics due to the combined effects of sudden changes in local measurement errors and the adaptive adjustment of the internal dynamic shield, in order to quickly respond to the system power redistribution requirements. As the system dynamically approaches a new steady state, the dynamic shield automatically relaxes the trigger threshold to intercept redundant data, the trigger interval gradually lengthens, and eventually smoothly degenerates into a fixed heartbeat keep-alive pulse of 0.1 s. Furthermore, because IC2 activates an AC frequency emergency recovery strategy independent of communication between 2.0 s and 3.0 s, its power channel trigger state is strongly locked, maintaining absolute silence. The remaining interconnected converter nodes generate dense triggering due to the instantaneous break in the communication topology, rapidly reconstructing a new power sharing consensus. Simultaneously, IC2's DC voltage channel is not affected by state locking during this phase and continues to maintain independent triggering communication. The above mechanism effectively ensures the security of global voltage monitoring and realizes efficient compression and on-demand scheduling of communication resources under complex mode switching.

[0058] Figure 9 and Figure 10 The demonstration shows the triggering status of the two communication channels in IC1 after 3 seconds, both exhibiting a significant "dense transient, sparse steady-state" timing characteristic. In the initial 3.0-second control access phase, errors accumulate rapidly due to transient impacts, leading to dense triggering of both channels to ensure tracking speed and control rigidity. As the system converges, the steady-state error is perfectly absorbed by the dead zone, and the communication frequency decreases significantly, degenerating into sparse 0.1-second fixed heartbeat pulses. In terms of spatial topology, Figure 10 The number of triggers exhibits precise adaptive differentiation: DG1 acts as the sole receiver. Figure 9 The reference signal's control center exhibits the most drastic dynamic response and the highest number of triggers. DG2, as a star-shaped hub, experiences increased neighbor divergence errors due to multi-directional pulling; the dynamic event triggering mechanism adaptively increases the trigger threshold, effectively filtering redundant communication at the hub. Meanwhile, DG3 and DG4, located at the topology's ends and perfectly symmetrical, show completely overlapping waveforms and have the fewest triggers. Overall, this dynamic triggering mechanism perfectly achieves on-demand, precise allocation of communication resources in both spatiotemporal dimensions.

[0059] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0060] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A two-layer distributed control method for AC / DC microgrids based on dynamic event triggering, characterized in that, The method includes: The system collects operational status parameters of the AC / DC hybrid microgrid system, including AC subgrid frequency, DC bus voltage, distributed power output, and interconnected converter transmission power. The AC / DC hybrid microgrid system uses a DC bus as a common backbone, and the DC bus is connected to multiple AC subgrids through interconnected converters. Based on the operating status, a control operation is performed on the distributed power sources and the interconnected converters in the AC subnet, so that the distributed power sources share the load in the AC subnet and the interconnected converters perform bidirectional power mutual assistance according to the AC and DC side operating status. The upper layer of the AC / DC hybrid microgrid system performs distributed secondary control on the interconnected converters, performs DC voltage recovery and interconnected converter power sharing based on the status information of two adjacent interconnected converters, and switches to emergency frequency recovery mode when the AC subgrid frequency exceeds the limit. In the AC / DC hybrid microgrid system, the lower layer performs leader-follower-based constrained consistency secondary control on the AC subgrid. The interconnected converter generates a load rate reference value, and multiple distributed power sources synchronize their load rate status through local communication to achieve AC frequency recovery and distributed power allocation. The communication variables of the local communication are updated using a dynamic event-triggered mechanism. When the trigger condition is met, the current status information is sent; when the trigger condition is not met, the status information of the previous cycle is maintained to reduce continuous communication and redundant data transmission.

2. The method according to claim 1, characterized in that, The first control of the distributed power source in the AC subnet is to perform droop control on the distributed power source to achieve the primary distribution of load fluctuations within the AC network. The first control operation performed on the interconnected converters in the AC subnet is to perform normalized unified droop control on the interconnected converters to achieve bidirectional power mutual assistance between AC and DC networks.

3. The method according to claim 1, characterized in that, The upper layer of the AC / DC hybrid microgrid system performs distributed secondary control on the interconnected converters, performs DC voltage recovery and interconnected converter power sharing based on the status information of two adjacent interconnected converters, and switches to emergency frequency recovery mode when the AC subgrid frequency exceeds the limit, including: Based on the power sharing consistency error of the distributed power source and the distributed voltage controller, the rate of change of the voltage correction of the interconnected converter is determined. Based on the rate of change and voltage reference value, and in conjunction with the primary control rate expression, the unified power mutual assistance control rate under the distributed secondary control is determined. Power allocation is performed according to the unified power mutual assistance control rate.

4. The method according to claim 3, characterized in that, The method further includes: If the load on the AC subnet exceeds a preset load threshold, switch to emergency frequency recovery mode to ensure the AC network does not disconnect; the strong tracking target of the emergency frequency recovery mode is 50Hz. When the interconnected converter restores DC voltage, an integrator-linked reset is used.

5. The method according to claim 1, characterized in that, The lower layer of the AC / DC hybrid microgrid system performs leader-follower-based constrained consistency secondary control on the AC subgrid. The interconnected converter generates a load rate reference value, and multiple distributed power sources synchronize their load rate states through local communication to achieve AC frequency recovery and distributed power allocation, including: The interconnected converter is used as the leader, and the frequency deviation on the AC subnet side is extracted using a PI regulator to generate a unified load rate reference value for the AC subnet. Multiple distributed power sources are used as followers, and the load rate status is synchronized in a sparse communication network to maintain consistency. The secondary frequency recovery is completed by superimposing the underlying active power reference value of the system based on the synchronized load rate status.

6. The method according to claim 1, characterized in that, The communication variables are DC voltage signal, normalized power signal, load rate reference value and local load rate; the triggering time of the dynamic event triggering mechanism is determined based on the minimum triggering interval of absolute dead zone and anti-Zeno behavior.

7. The method according to claim 6, characterized in that, The DC voltage signal uses state decoupling as the trigger condition; the normalized power signal uses strong state coupling as the trigger condition; and the load rate reference value uses zero spatial error triggering as the trigger condition. The local load rate is triggered by spatiotemporal constraint coordination.

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