CN113206500B - Micro-grid distributed secondary control clock synchronization method based on event triggering - Google Patents

Micro-grid distributed secondary control clock synchronization method based on event triggering Download PDF

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CN113206500B
CN113206500B CN202110492131.6A CN202110492131A CN113206500B CN 113206500 B CN113206500 B CN 113206500B CN 202110492131 A CN202110492131 A CN 202110492131A CN 113206500 B CN113206500 B CN 113206500B
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distributed power
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power supply
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CN113206500A (en
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楼冠男
洪吟秋
谢吉华
顾伟
蒋啸宇
李山林
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Southeast University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L67/00—Network arrangements or protocols for supporting network services or applications
    • H04L67/01—Protocols
    • H04L67/12—Protocols specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
    • H04L69/28—Timers or timing mechanisms used in protocols
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

Abstract

The invention discloses a micro-grid distributed secondary control clock synchronization method based on event triggering, which comprises the following steps: s1, establishing a local clock model of the distributed power supply, and introducing frequency and offset correction parameters to correct the clock model; s2, designing event trigger conditions, judging at local sampling time, and only when the trigger conditions are met, sampling local correction parameter information and transmitting the local correction parameter information to a neighbor node; s3, optimizing and selecting a holddown clock and establishing a distributed clock synchronization protocol based on a holddown consistency theory; and S4, determining local sampling time according to the corrected clock, establishing micro-grid distributed secondary control, and realizing synchronous information interaction among the distributed power supplies. The invention focuses on the clock synchronization problem in distributed secondary control, establishes a distributed power local clock model, realizes synchronous information interaction among distributed power, has better synchronous economy and faster synchronous convergence speed, and effectively improves the stability and the convergence precision of the system.

Description

Micro-grid distributed secondary control clock synchronization method based on event triggering
Technical Field
The invention belongs to the technical field of microgrid operation control, and particularly relates to a microgrid distributed secondary control clock synchronization method based on event triggering.
Background
With the gradual depletion of earth resources and the concern of people on environmental problems, the access of renewable energy resources is more and more emphasized by countries in the world. The microgrid is an emerging energy transmission mode for increasing the permeability of renewable energy sources and distributed energy sources in an energy supply system, and its components include various kinds of distributed energy sources (DER, including micro gas turbines, wind generators, photovoltaics, fuel cells, energy storage devices, etc.), user terminals of various electrical and/or thermal loads, and related monitoring and protection devices.
The power supply in the micro-grid is mainly used for energy conversion by power electronic devices and provides necessary control; the micro-grid is represented as a single controlled unit relative to an external large grid, and can simultaneously meet the requirements of users on electric energy quality, power supply safety and the like. Energy exchange is carried out between the micro-grid and the large grid through a public connection point, and the micro-grid and the large grid are mutually standby, so that the reliability of power supply is improved. Because the micro-grid is a small-scale decentralized system and is close to the load, the reliability of local power supply can be improved, the grid loss is reduced, the energy utilization efficiency is greatly increased, and the micro-grid is a novel power supply mode which meets the development requirements of the future intelligent power grid.
Under normal conditions, the micro-grid is in grid-connected operation, and the large power grid provides voltage and frequency support; when an unexpected or planned event occurs to cause the microgrid to be disconnected, the microgrid will operate in an autonomous state. Droop control strategies have gained widespread attention because there is no need to dominate the distributed power supply and the inter-tie connections. When the micro-grid is required to be switched from a grid-connected mode to an independent operation mode, each distributed power supply can automatically share load power in the micro-grid. However, since droop control is proportional difference control, which causes steady-state deviation of voltage and has undesirable reactive power distribution effect, it is necessary to adopt secondary control to assist voltage recovery and reactive power equalization. In an actual distributed structure, because a global centralized clock does not exist, the information updating and transmission process of secondary control is triggered by a local clock, and the amount of information for control decision acquired at the sampling time is continuously misplaced in consideration of the difference between the local clocks of the heterogeneous distributed power supplies, so that steady-state errors are introduced and even the system is unstable. Therefore, it is necessary to research a clock synchronization method for secondary control of the microgrid, so that the synchronization of information interaction among the distributed power supplies is guaranteed, and the operation stability and convergence accuracy of the microgrid are improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a microgrid distributed secondary control clock synchronization method based on event triggering, which comprises the steps of establishing a local clock model of distributed power supplies, introducing a frequency and offset correction parameter correction clock model, designing an event triggering condition, sampling local correction parameter information when the triggering condition is met, transmitting the local correction parameter information to a neighbor node, optimally selecting a holddown clock and establishing a distributed clock synchronization protocol on the basis of the holddown consistency theory, determining local sampling time according to the corrected clock, establishing microgrid distributed secondary control, realizing synchronous information interaction among the distributed power supplies with higher economy, and improving the stability and convergence accuracy of a system.
The purpose of the invention can be realized by the following technical scheme:
a micro-grid distributed secondary control clock synchronization method based on event triggering is used for realizing control of an information interaction mode of an island micro-grid in a droop operation mode, and specifically comprises the following steps:
s1, establishing a local clock model of the distributed power supply, and introducing frequency and offset correction parameters to correct the clock model;
s2, designing event trigger conditions, judging at local sampling time, and only when the trigger conditions are met, sampling local correction parameter information and transmitting the local correction parameter information to a neighbor node;
s3, optimizing and selecting a holddown clock and establishing a distributed clock synchronization protocol based on a holddown consistency theory;
and S4, determining local sampling time according to the corrected clock, establishing micro-grid distributed secondary control, and realizing synchronous information interaction among the distributed power supplies.
Further, in S1, for each distributed power source, a local clock model is established:
τi(t)＝ait+bi (1)
in the formula (1), τiDenotes the local clock of the ith distributed power supply, t denotes absolute time, a denotes a frequency drift coefficient, and b denotes a clock offset.
On this basis, the introduction corresponds toCorrection factor alpha of frequencyiCorrection coefficient beta of sum offsetiTo obtain a corrected clock τ'i：
τ′i(t)＝αi(t)(ait+bi)+βi(t) (2)。
Further, in S2, event triggering conditions are designed for the correction parameters α and β respectively as follows:
Figure BDA0003052818670000031
Figure BDA0003052818670000032
in the formulas (3) and (4),
Figure BDA0003052818670000033
correction factor representing the event trigger time sampled, cα，cβThe error threshold value is indicated as being indicative of,
Figure BDA0003052818670000034
representing the h-th sampling instant of the ith distributed power supply,
Figure BDA0003052818670000035
representing the most recent event trigger time prior to the sampling time.
And at each sampling moment of the distributed power supply, judging whether the event triggering condition is met, and sampling local corresponding correction parameter information and transmitting the local corresponding correction parameter information to the neighbor node only when the condition is met.
Further, in S3, based on the containment consistency theory, with the goal of obtaining better convergence performance, the following containment point optimization indexes are set:
Figure BDA0003052818670000036
in formula (5), p represents an existing holddown set, I represents a corresponding non-holddown set, deg represents holddown set out degree, and l (I, j) represents the shortest path for transmitting information from node I to node j.
And calculating the optimization indexes of the distributed power nodes aiming at the distributed power nodes, selecting the local clock corresponding to the node with the maximum optimization index as a holdover clock, and setting the local clock as an absolute clock.
Further, in S3, the following distributed clock synchronization protocol is established:
Figure BDA0003052818670000041
Figure BDA0003052818670000042
in the formulas (6) and (7), ρα，ρβ，ρα0And ρβ0Indicating the control intensity; tau'0Representing the local time of the holdback clock;
Figure BDA0003052818670000043
representing the local time sampled at the event trigger time; mu.si0Indicating the communication connectivity, mu, between the ith distributed power source and the holddown node i01 denotes information of the ith distributed power supply reception holdover node, μi0If the value is 0, the ith distributed power supply does not receive the information of the holdover node; etai0＝a0/ai，a0A frequency drift coefficient representing a holdover clock; etaij＝aj/aiCan be obtained by obtaining the absolute time t1And t2The ith and jth distributed power local clocks corresponding to the time are according to the following formula
Figure BDA0003052818670000044
And (4) indirectly calculating.
Further, in S4, for each distributed power source, according to the corrected local clock, the following formula is used:
Figure BDA0003052818670000045
the local sampling instant is determined, in equation (9),
Figure BDA0003052818670000046
t represents a set quadratic control update period for the local sampling instant.
And further establishing micro-grid distributed secondary control:
Figure BDA0003052818670000047
in the formula (10), uiFor the secondary control input of the ith distributed power supply, ki1，ki2，ki3In order to integrate the coefficients for the controller,
Figure BDA0003052818670000048
representing the observed value of the average voltage, niIs the droop coefficient, V, of the ith distributed power supplyiIs the output voltage, Q, of the ith distributed power supplyiReactive power, T, for the ith distributed power supply outputiDenotes the control period, T, of the ith distributed power supplyi＝T/(aiαi)。
The invention has the beneficial effects that:
1. the invention provides a micro-grid distributed secondary control clock synchronization method based on event triggering, which mainly focuses on the clock synchronization problem in distributed secondary control, establishes a distributed power local clock model, designs event triggering conditions, samples local correction parameter information and transmits the local correction parameter information to a neighbor node when the triggering conditions are met, optimizes and selects a holddown clock and establishes a distributed clock synchronization protocol by combining a holddown consistency theory on the basis, further determines local sampling time according to the corrected clock, establishes micro-grid distributed secondary control, realizes synchronous information interaction among all distributed power supplies, has better synchronous economy and faster synchronous convergence speed, and can effectively improve the stability and convergence accuracy of a system.
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In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a flow chart of the overall process of the present invention;
FIG. 2 is a schematic diagram of a microgrid simulation system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a distributed communications topology of an embodiment of the present invention;
FIG. 4 is a diagram of an active power waveform when no clock synchronization strategy is applied according to an embodiment of the present invention;
FIG. 5 is a graph of a reactive power waveform when no clock synchronization strategy is applied according to an embodiment of the present invention;
FIG. 6 is a graph of output voltage waveforms when no clock synchronization strategy is applied according to an embodiment of the present invention;
FIG. 7 is a diagram of a counter waveform when no clock synchronization strategy is applied according to an embodiment of the present invention;
FIG. 8 is a diagram of an active power waveform after applying a clock synchronization strategy in accordance with an embodiment of the present invention;
FIG. 9 is a graph of a reactive power waveform after applying a clock synchronization strategy according to an embodiment of the present invention;
FIG. 10 is a graph of output voltage waveforms after applying a clock synchronization strategy according to an embodiment of the present invention;
FIG. 11 is a diagram of a counter waveform after applying a clock synchronization strategy according to an embodiment of the present invention;
FIG. 12 is a schematic diagram of the triggering time when the clock synchronization policy applies the time-triggered communication mechanism according to the embodiment of the present invention;
FIG. 13 is a graph of the average voltage and reactive power waveforms when the clock synchronization strategy applies the time triggered communication mechanism according to an embodiment of the present invention;
FIG. 14 is a schematic diagram of the triggering time when the clock synchronization policy applies the event to trigger the communication mechanism according to the embodiment of the present invention;
fig. 15 is a waveform diagram of average voltage and reactive power when the clock synchronization strategy applies the event-triggered communication mechanism according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an event-triggered distributed secondary control clock synchronization method for a microgrid based on an event trigger is used for realizing control in an information interaction manner of an island microgrid in a droop operation mode, and specifically includes the following steps:
s1, establishing a local clock model of the distributed power supply, and introducing frequency and offset correction parameters to correct the clock model;
for each distributed power supply, establishing a local clock model:
τi(t)＝ait+bi (1)
wherein, tauiDenotes the local clock of the ith distributed power supply, t denotes absolute time, a denotes a frequency drift coefficient, and b denotes a clock offset.
On the basis of the frequency correction factor alpha, correction factors alpha corresponding to the frequency and the offset are respectively introducediAnd betaiTo obtain a corrected clock τ'i：
τ′i(t)＝αi(t)(ait+bi)+βi(t) (2)
S2, designing event trigger conditions, judging at local sampling time, and only when the trigger conditions are met, sampling local correction parameter information and transmitting the local correction parameter information to a neighbor node;
for the correction parameters α and β, event triggering conditions are respectively designed as follows:
Figure BDA0003052818670000071
Figure BDA0003052818670000072
wherein the content of the first and second substances,
Figure BDA0003052818670000073
correction factor representing the event trigger time sampled, cα，cβThe error threshold value is indicated as being indicative of,
Figure BDA0003052818670000074
representing the h-th sampling instant of the ith distributed power supply,
Figure BDA0003052818670000075
representing the most recent event trigger time prior to the sampling time.
And at each sampling moment of the distributed power supply, judging whether the event triggering condition is met, and sampling local corresponding correction parameter information and transmitting the local corresponding correction parameter information to the neighbor node only when the condition is met.
S3, optimizing and selecting a holddown clock and establishing a distributed clock synchronization protocol based on a holddown consistency theory;
based on a containment consistency theory, aiming at obtaining better convergence performance, the following containment point optimization indexes are set:
Figure BDA0003052818670000076
wherein p represents the existing holdback set, I represents the corresponding non-holdback set, deg represents the holdback set out degree, and l (I, j) represents the shortest path for transferring information from node I to node j.
And calculating the optimization indexes of the distributed power nodes aiming at the distributed power nodes, selecting the local clock corresponding to the node with the maximum optimization index as a holdover clock, and setting the local clock as an absolute clock.
On the basis, the following distributed clock synchronization protocol is established:
Figure BDA0003052818670000081
Figure BDA0003052818670000082
where ρ isα，ρβ，ρα0And ρβ0Indicating the control intensity; tau'0Representing the local time of the holdback clock;
Figure BDA0003052818670000083
representing the local time sampled at the event trigger time; mu.si0Indicating the communication connectivity, mu, between the ith distributed power source and the holddown node i01 denotes information of the ith distributed power supply reception holdover node, μi0If the value is 0, the ith distributed power supply does not receive the information of the holdover node; etai0＝a0/ai，a0A frequency drift coefficient representing a holdover clock; etaij＝aj/aiCan be obtained by obtaining the absolute time t1And t2The ith and jth distributed power local clocks corresponding to the time are according to the following formula
Figure BDA0003052818670000084
And (4) indirectly calculating.
And S4, determining local sampling time according to the corrected clock, establishing micro-grid distributed secondary control, and realizing synchronous information interaction among the distributed power supplies.
Aiming at each distributed power supply, according to the corrected local clock, the following formula is adopted:
Figure BDA0003052818670000085
a local sampling instant is determined. Wherein the content of the first and second substances,
Figure BDA0003052818670000086
t represents a set quadratic control update period for the local sampling instant.
And further establishing micro-grid distributed secondary control:
Figure BDA0003052818670000087
wherein u isiFor the secondary control input of the ith distributed power supply, ki1，ki2，ki3In order to integrate the coefficients for the controller,
Figure BDA0003052818670000088
representing the observed value of the average voltage, niIs the droop coefficient, V, of the ith distributed power supplyiIs the output voltage, Q, of the ith distributed power supplyiReactive power, T, for the ith distributed power supply outputiDenotes the control period, T, of the ith distributed power supplyi＝T/(aiαi)。
The technical scheme of the design is applied to the reality, as shown in fig. 2, the simulation system comprises 5 distributed power supplies in the microgrid, DG1, DG2 and DG3 are respectively connected to the voltage bus 1 through respective connecting impedances, DG4 and DG5 are respectively connected to the voltage bus 2 through respective connecting impedances, the rated active and reactive capacities of the 5 distributed power supplies are equal, and the load in the system adopts an impedance type load. The 5 distributed power supplies communicate through the topology shown in fig. 3, and the DG1 is selected as the holdback clock according to the holdback point optimization selection principle. The initial DG2, DG3, DG4 and DG5 have local clock frequency drift coefficients and offsets of a2＝0.5，a3＝0.67，a4＝1，a50.67 and b2＝5*10-3，b3＝1*10-3，b4＝4*10-3，b5＝2*10-3。
According to the event-triggered microgrid distributed secondary control clock synchronization method, a local clock is corrected, the local sampling time is determined, the microgrid distributed secondary control is established, a simulation microgrid model is established based on an MATLAB/Simulink platform, the secondary control effects before and after clock synchronization are compared, the important function of the method in system control performance improvement is verified, the method is further compared with a clock synchronization strategy under a time-triggered communication mechanism, and the synchronization economy of the method is demonstrated.
Fig. 4 to 7 are simulation waveforms when the clock synchronization strategy is not applied in this embodiment, where at the initial time, the system operates in the droop control mode, 2s is used for the secondary control of the microgrid, and 3.5s is used for increasing the load. Fig. 7 shows the waveform of the counter at this time, and it can be known from the figure that the secondary control time of each distributed power source is asynchronous due to the difference between the local clocks of different distributed power sources.
Fig. 4 and 5 show waveforms of active power and reactive power output by each distributed power supply respectively, active power is equally divided among the distributed power supplies under the effect of droop control at the initial moment, while the reactive power distribution effect is not ideal, after 2s, reactive power of each distributed power supply is gradually equally divided under the effect of distributed cooperative control, and when about 2.5s, the system is stable, but the active power and the reactive power are lower than normal values due to the fact that information amount is staggered caused by different sampling moments of secondary control among the distributed power supplies. And 3.5s, increasing the output active power and reactive power of the system along with the increase of the load, and sharing the reactive power again under the action of secondary control, wherein the reactive power is still lower than a normal operation value.
Fig. 6 shows the output voltage waveform, at the initial moment, under the effect of droop control, the output voltage of each distributed power supply is obviously lower than the rated value, after 2 seconds, under the effect of secondary control, the output voltage gradually rises, and the system is stable in about 2.5 seconds, but because the information amount dislocation caused by the difference of secondary control sampling moments among the distributed power supplies, the average output voltage is still lower than the rated value. The output voltage of the distributed power supply is reduced due to the increase of the system load at 3.5s, the system is stabilized again at about 4 s, and the output voltage is recovered again but the average value is still lower than the rated value.
Fig. 8 to fig. 11 are simulation waveforms after the clock synchronization strategy is applied in this embodiment, where at 0.5s, the clock synchronization control is applied, at the initial time, the system operates in the droop control mode, at 2s, the microgrid secondary control is applied, and at 3.5s, the load increases. Fig. 11 shows the waveform of the counter at this time, and it can be known from the figure that the initial time is asynchronous between the secondary control times of the distributed power supplies due to the difference between the local clocks of different distributed power supplies, after 0.5s, the clocks are synchronously controlled to be switched in, the local clocks of the distributed power supplies gradually reach synchronization, and when the 2s secondary control is switched in, the secondary control times are basically consistent.
Fig. 8 and 9 show waveforms of active power and reactive power output by each distributed power supply respectively, active power of each distributed power supply is equally divided under the effect of droop control at the initial moment, and the reactive power distribution effect is not ideal, after 2s, reactive power of each distributed power supply is gradually equally divided under the effect of distributed cooperative control, and the system is stable about 2.5 s. And 3.5s, increasing the active power and the reactive power output by the system along with the increase of the load, and sharing the reactive power again under the action of secondary control.
Fig. 10 shows the output voltage waveform, at the initial moment, under the action of droop control, the output voltage of each distributed power supply is obviously lower than the rated value, after 2 seconds, under the action of secondary control, the output voltage gradually rises, and about 2.5 seconds, the system is stable, and the average output voltage is restored to the rated value. And when the system load is increased in 3.5s, the output voltage of the distributed power supply is reduced, the system is stabilized again in about 4 s, and the average value of the output voltage is restored to the rated value again.
As can be seen from comparison of fig. 4-7 with fig. 8-11, after the clock synchronization control provided by the present invention is applied, synchronization of the sampling time of the secondary control of each distributed power supply can be realized, so as to effectively improve the steady-state control accuracy of the system, and facilitate the safe and stable operation of the system.
Fig. 12 and fig. 13 are simulation waveforms when the clock synchronization strategy applies the time-triggered communication mechanism according to the embodiment of the present invention, where 0.5s is the clock synchronization control input, and 2.5s to 3s is the DG2 clock frequency disturbed, and the clock period thereof gradually changes from 0.02s to 0.025 s. At the initial moment, the system operates in a droop control mode, the secondary control of the micro-grid is started when 2s is needed, and the load is increased when 3.5s is needed. Fig. 12 shows the communication triggering time in the time synchronization control, and it can be known that the local clock correction parameter needs to be transmitted to the neighboring node at each sampling time of the distributed power supply. Fig. 13 shows the control effect of the average voltage and the output reactive power, and it can be seen from the figure that, under the action of the secondary control after the clock synchronization is performed by applying the strategy, the average voltage can be accurately recovered to the rated value of 311V, meanwhile, the reactive power equalization is realized, and higher control precision can be still maintained under the conditions of clock frequency fluctuation and load increase.
Fig. 14 and fig. 15 are simulation waveforms when the clock synchronization strategy applies the event-triggered communication mechanism according to the embodiment of the present invention, where 0.5s is a clock synchronization control input, and 2.5s to 3s is a DG2 clock frequency disturbance, and the clock period thereof gradually changes from 0.02s to 0.025 s. At the initial moment, the system operates in a droop control mode, the secondary control of the micro-grid is started when 2s is needed, and the load is increased when 3.5s is needed. Fig. 14 shows the communication triggering time in the time synchronization control, where x and ° respectively indicate the time when the local clock frequency drift coefficient and the offset transmission occur, and it can be seen from the figure that the clock synchronization control no longer triggers communication at each sampling time, and the communication frequency is significantly reduced, especially for the frequency drift coefficient, when it converges to the required accuracy, the sampling and communication of the corresponding information will be terminated, and after 2.5s, due to the disturbance of the clock frequency, the communication of the clock frequency drift amount will be triggered again, and the communication will be stopped after the accuracy requirement of convergence is reached again. Fig. 15 shows the control effect of the average voltage and the output reactive power, and it can be seen from the figure that, under the action of the secondary control after the clock synchronization is performed by applying the strategy, the average voltage can still be accurately recovered to the rated value of 311V, meanwhile, the reactive power equalization is realized, and higher control precision can be maintained under the conditions of clock frequency fluctuation and load increase.
Comparing fig. 12 and 13 with fig. 14 and 15, it can be seen that the event triggered clock synchronization method provided by the present invention effectively reduces the communication frequency while ensuring the synchronization accuracy, and has better economy compared with the conventional time triggered clock synchronization method.
The micro-grid distributed secondary control clock synchronization method based on event triggering establishes a local clock model, and corrects the local clock model by respectively introducing frequency and offset correction parameters; an event trigger condition is designed, so that local correction parameter information is sampled and transmitted to a neighbor node only at the moment when the trigger condition is met; further combining with a containment consistency theory, optimally selecting a containment clock and providing a distributed clock synchronization protocol; on the basis, the local sampling time is determined according to the corrected clock, and then the distributed secondary control of the micro-grid is established.
Aiming at solving the problem that the existing micro-grid secondary control research does not pay attention to and solve the asynchronous problem of the distributed clocks, the invention provides the distributed secondary control clock synchronization method, which is used as an important component of a secondary control strategy to realize the synchronization of the local clocks of different distributed power supplies with higher economy, and effectively avoids the adverse effects of asynchronous information interaction on the stability and control precision of the system.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed.

Claims (4)

1. A micro-grid distributed secondary control clock synchronization method based on event triggering is used for realizing control of an information interaction mode of an island micro-grid in a droop operation mode, and is characterized by specifically comprising the following steps:
s1, establishing a local clock model of the distributed power supply, and introducing frequency and offset correction parameters to correct the clock model;
s2, designing event trigger conditions, judging at local sampling time, and only when the trigger conditions are met, sampling local correction parameter information and transmitting the local correction parameter information to a neighbor node;
s3, optimizing and selecting a holddown clock and establishing a distributed clock synchronization protocol based on a holddown consistency theory;
s4, determining local sampling time according to the corrected clock, establishing micro-grid distributed secondary control, and realizing synchronous information interaction among distributed power supplies;
the correction parameter α in S2iAnd betaiRespectively designing the following event triggering conditions:
Figure FDA0003510377190000011
Figure FDA0003510377190000012
in the formulas (3) and (4),
Figure FDA0003510377190000013
representing eventsCorrection factor sampled at the moment of triggering, cα，cβThe error threshold value is indicated as being indicative of,
Figure FDA0003510377190000014
representing the h-th sampling instant of the ith distributed power supply,
Figure FDA0003510377190000015
representing the most recent event trigger time prior to the sampling time;
judging whether an event trigger condition is met at each sampling moment of the distributed power supply, and sampling local corresponding correction parameter information and transmitting the local corresponding correction parameter information to a neighbor node only when the condition is met;
in S4, for each distributed power supply, according to the corrected local clock, the following formula is shown:
Figure FDA0003510377190000016
the local sampling instant is determined, in equation (9),
Figure FDA0003510377190000017
t represents a set secondary control updating period at the local sampling moment;
and further establishing micro-grid distributed secondary control:
Figure FDA0003510377190000021
in the formula (10), uiFor the secondary control input of the ith distributed power supply, ki1，ki2，ki3In order to integrate the coefficients for the controller,
Figure FDA0003510377190000022
representing the observed value of the average voltage, niIs the droop coefficient, V, of the ith distributed power supplyiFor the ith distributed power supplyOutput voltage, QiReactive power, T, for the ith distributed power supply outputiDenotes the control period, T, of the ith distributed power supplyi＝T/(aiαi)。
2. The method according to claim 1, wherein in S1, for each distributed power source, a local clock model is established:
τi(t)＝ait+bi (1)
in the formula (1), τiDenotes the local clock of the ith distributed power supply, t denotes absolute time, aiRepresenting the frequency drift coefficient, biRepresents a clock offset;
on the basis of the frequency correction coefficient alpha is introduced corresponding to the frequencyiCorrection coefficient beta of sum offsetiTo obtain a corrected clock τ'i：
τ′i(t)＝αi(t)(ait+bi)+βi(t) (2)。
3. The method according to claim 2, wherein the constraint consistency theory is used as a basis in S3 to achieve better convergence performance, and the following constraint point optimization indexes are set:
Figure FDA0003510377190000023
in the formula (5), p represents an existing holddown set, I represents a corresponding non-holddown set, deg represents holddown set out degree, and l (I, j) represents the shortest path for transmitting information from a node I to a node j;
and calculating the optimization indexes of the distributed power nodes aiming at the distributed power nodes, selecting the local clock corresponding to the node with the maximum optimization index as a holdover clock, and setting the local clock as an absolute clock.
4. The distributed secondary control clock synchronization method for the microgrid based on the event trigger as claimed in claim 3, characterized in that the following distributed clock synchronization protocol is established in the step S3:
Figure FDA0003510377190000031
Figure FDA0003510377190000032
in the formulas (6) and (7), ρα，ρβ，ρα0And ρβ0Indicating the control intensity; tau'0Representing the local time of the holdback clock;
Figure FDA0003510377190000033
representing the local time sampled at the event trigger time; mu.si0Indicating the communication connectivity, mu, between the ith distributed power source and the holddown nodei01 denotes information of the ith distributed power supply reception holdover node, μi0If the value is 0, the ith distributed power supply does not receive the information of the holdover node; etai0＝a0/ai，a0A frequency drift coefficient representing a holdover clock; etaij＝aj/aiBy obtaining the absolute time t1And t2The ith and jth distributed power local clocks corresponding to the time are according to the following formula
Figure FDA0003510377190000034
And (4) indirectly calculating.
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