CN108767900B - Micro-grid system and hierarchical control system thereof - Google Patents

Micro-grid system and hierarchical control system thereof Download PDF

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CN108767900B
CN108767900B CN201810679857.9A CN201810679857A CN108767900B CN 108767900 B CN108767900 B CN 108767900B CN 201810679857 A CN201810679857 A CN 201810679857A CN 108767900 B CN108767900 B CN 108767900B
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grid
amplitude
microgrid
voltage
frequency
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CN108767900A (en
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葛木明
陈亚东
邹绍琨
胡兵
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Sungrow Renewables Development Co Ltd
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Hefei Sungrow Renewable Energy Sci & Tech Co ltd
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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
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
    • H02J13/00019—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using optical means
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/70—Smart grids as climate change mitigation technology in the energy generation sector
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/12—Monitoring or controlling equipment for energy generation units, e.g. distributed energy generation [DER] or load-side generation

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Abstract

The invention provides a microgrid system and a hierarchical control system thereof.A primary droop controller realizes the distribution of output power of a corresponding distributed micro-source energy conversion device based on a droop control theory, a secondary micro-source controller compensates the fluctuation of the frequency and amplitude of the output voltage of the corresponding distributed micro-source energy conversion device introduced by droop control, and a three-level coordination controller regulates the bus voltage of a corresponding sub-microgrid grid-connected point according to the voltage of the main grid-connected point through PI closed-loop feedback regulation control; and further, voltage amplitude and frequency fluctuation caused by droop control are repaired, and the electric energy quality of the micro-grid is improved.

Description

Micro-grid system and hierarchical control system thereof
Technical Field
The invention relates to the technical field of microgrid control, in particular to a microgrid system and a hierarchical control system thereof.
Background
At present, the control modes for the micro-source in the micro-grid mainly include a constant voltage and constant frequency mode (V/F mode), a constant power mode (P/Q mode), and a droop control mode.
When the micro-grid is in an island operation state, the micro-source is controlled in a constant voltage and constant frequency mode to maintain the voltage and the frequency of the micro-grid system at a constant voltage and a constant frequency; when the micro-grid is in a grid-connected operation mode, the system is electrically pressed against the large main grid support, and the micro-source is controlled through a constant power mode to output constant power; the droop control mode is to change the active and reactive power variations of the distributed micro-sources by adjusting the voltage amplitude and frequency of the micro-sources.
The droop control theory has been studied because it can change its active power output in response to an increase or decrease in load, and because it can achieve internal adjustment of voltage and current distribution between the underlying micro-source inverter and converter, many micro-grid systems employ this control method. However, the active and reactive power regulation of each distributed micro-source is completed by the droop control, which affects the amplitude and frequency of the output voltage, resulting in the reduction of the power quality.
Disclosure of Invention
The invention provides a micro-grid system and a layered control system thereof, which aim to solve the problem of low power quality in the prior art.
In order to achieve the purpose, the technical scheme provided by the application is as follows:
a hierarchical control system for a microgrid system, comprising: the system comprises a plurality of primary droop controllers, a plurality of secondary micro-controllers and a plurality of three-level coordination controllers; wherein:
the primary droop controller is used for realizing the distribution of the output power of the corresponding distributed micro-source energy conversion device based on a droop control theory;
the secondary micro-source controller is used for compensating the fluctuation of the frequency and the amplitude of the output voltage of the corresponding distributed micro-source energy conversion device introduced by droop control;
and the three-level coordination controller is used for regulating the bus voltage of the corresponding sub-microgrid grid-connected point through PI closed loop feedback regulation control according to the voltage of the main microgrid grid-connected point.
Preferably, the primary droop controller is configured to, when implementing the distribution of the output power of the corresponding distributed micro-source energy conversion device based on the droop control theory, specifically:
and generating a closed-loop instruction of an internal voltage and current loop through droop control calculation so as to realize active power and reactive power distribution of distributed micro-source output of each energy conversion device interface through adjusting the frequency and amplitude of output voltage of each energy conversion device.
Preferably, the formula adopted by the droop control calculation is as follows:
ω＝ω*-Gp(s)(P-P*)；
E＝E*-GQ(s)(Q-Q*)；
where ω is a frequency set value of the output voltage of the energy conversion device, E is an amplitude set value of the output voltage of the energy conversion device, and ω is*Frequency reference value for output voltage of energy conversion device, E*For the energy conversion deviceReference value of amplitude of output voltage, Gp(s) droop conversion coefficient for frequency, GQ(s) is the droop conversion coefficient of the amplitude, P is the actual value of the active power output by the distributed micro-source of the energy conversion device interface, Q is the actual value of the reactive power output by the distributed micro-source of the energy conversion device interface, P is the actual value of the reactive power output by the distributed micro-source of the energy conversion device interface*Reference value of active power, Q, for distributed micro-source output of an interface of an energy conversion device*And the reference value of the reactive power output by the distributed micro source of the interface of the energy conversion device.
Preferably, the secondary micro-source controller is configured to, when compensating for fluctuations in the frequency and amplitude of the output voltage of the corresponding distributed micro-source energy conversion device introduced by droop control, specifically:
monitoring the frequency and amplitude of the output voltage of the corresponding distributed micro source;
comparing and calculating the frequency of the output voltage of the corresponding distributed micro-source with the voltage frequency reference value of the corresponding sub-micro-grid to obtain a secondary frequency error; comparing and calculating the amplitude of the output voltage of the corresponding distributed micro source with the reference value of the voltage amplitude of the sub-micro grid corresponding to the amplitude of the output voltage of the corresponding distributed micro source, so as to obtain a secondary amplitude error; the sub-microgrid voltage frequency reference value is the frequency of the bus voltage of the corresponding sub-microgrid grid-connected point; the sub-microgrid voltage amplitude reference value is the amplitude of the bus voltage of the corresponding sub-microgrid grid-connected point;
and transmitting the secondary frequency error and the secondary amplitude error to a local controller of the corresponding distributed micro source for PI closed loop feedback control, so that the frequency and the amplitude of the output voltage of the corresponding distributed micro source return to stable values again.
Preferably, the formula for obtaining the secondary frequency error and the secondary amplitude error is as follows:
Figure BDA0001710122850000031
Figure BDA0001710122850000032
where Δ ω is the secondary frequency error, Δ E is the secondary amplitude error, ωSMGFor the actual value of the frequency of the distributed micro-source output voltage, ESMGFor the actual value of the amplitude of the distributed micro-source output voltage,
Figure BDA0001710122850000033
is a sub-microgrid voltage frequency reference value,
Figure BDA0001710122850000034
is a sub-microgrid voltage amplitude reference value, kpw、kiw、kpE、kiEIs a secondary compensation control parameter.
Preferably, the three-level coordination controller is configured to, when adjusting the bus voltage of the corresponding sub-microgrid grid-connected point by PI closed-loop feedback adjustment control according to the voltage of the main grid-connected point, specifically:
monitoring the amplitude, frequency and phase of the voltage of the grid-connected point of the main power grid;
comparing and calculating the frequency of the bus voltage of the corresponding sub-microgrid grid-connected point with the frequency of the voltage of the main grid-connected point to obtain a three-level frequency error; comparing and calculating the amplitude of the bus voltage of the corresponding sub-microgrid grid-connected point with the amplitude of the voltage of the main grid-connected point to obtain a three-level amplitude error;
and carrying out PI closed loop feedback control on the three-level frequency error and the three-level amplitude error to enable the bus voltage of the corresponding sub microgrid grid-connected point to be the same as the voltage of the main grid-connected point.
Preferably, the formula for obtaining the three-level frequency error and the three-level amplitude error is as follows:
Figure BDA0001710122850000035
Figure BDA0001710122850000036
wherein, Δ ω is the error of three-level frequency, Δ E is the error of three-level amplitude, ωMGActual frequency value of grid-connected point bus voltage of sub-microgrid, EMGThe actual value of the amplitude value of the grid-connected point bus voltage of the sub-microgrid,
Figure BDA0001710122850000037
for the actual value of the voltage frequency of the grid-connected point of the main grid,
Figure BDA0001710122850000038
is the actual value of the voltage amplitude of the grid-connected point of the main power grid, kpw1、kiw1、kpE1、kiE1The control parameters are compensated for in three stages.
Preferably, the three-level coordination controller is further configured to implement information sharing among multiple piconets.
Preferably, the method further comprises the following steps:
and the four-stage optimization controller is used for improving the economic low carbon performance of the micro-grid system and maintaining the balance of supply and demand.
Preferably, the four-stage optimization controller is used for improving the economic low carbon performance of the microgrid system and maintaining the balance of supply and demand, and is specifically used for:
the method comprises the steps of taking fuel price data, power price of a main power grid, static data and characteristics, load prediction, power generation prediction, initial state and optimization targets as input, taking output of an optimization unit set, an optimization unit static plan, a carbon emission plan, a cost plan, an energy storage release plan and a distributed micro-source output plan as output, and establishing an economic low-carbon operation model;
and obtaining an optimization target according to the economic low-carbon operation model and the actual demand.
Preferably, the economic low-carbon operation model has the calculation formula as follows:
Min[α∑Cost+(1-α)∑Emissions]；
where Cost is economic Cost, emissitions is carbon emission, and a is the actual demand weight value for economic Cost and carbon emission.
Preferably, when the optimization target is the optimal point of economic operation, the four-stage optimization controller is according to a formula
Figure BDA0001710122850000041
And
Figure BDA0001710122850000042
obtaining a four-level frequency error and a four-level amplitude error; PI closed loop feedback control is carried out on the four-level frequency error and the four-level amplitude error, so that the output power of the micro-grid system is the same as the optimization target;
where Δ ω is the fourth order frequency error, Δ E is the fourth order amplitude error, PMGActual value of active power, Q, for grid-connected points of main gridMGIs the actual value of the reactive power of the grid-connected point of the main power grid,
Figure BDA0001710122850000043
is the active power reference value of the grid-connected point of the main power grid,
Figure BDA0001710122850000044
reference value of reactive power, k, for the grid-connected point of the main gridpP、kiP、kpQ、kiQThe control parameters are compensated for four levels.
A microgrid system comprising: a plurality of sub-piconets and a hierarchical control system of a microgrid system as described in any one of the preceding claims.
Preferably, the method further comprises the following steps: at least one transformer arranged between the power grid and the corresponding sub-microgrid grid-connected point;
a plurality of sub-micro-grids with the same output voltage share one three-level coordination controller, and are connected to a power grid or corresponding transformers through the same sub-micro-grid-connected point.
Preferably, when the hierarchical control system of the microgrid system comprises a four-level optimization controller, the four-level optimization controller realizes communication with each three-level coordination controller, the microgrid master station, the communication server and the real-time server through an optical fiber ring network.
According to the hierarchical control system of the microgrid system, after a primary droop controller realizes the distribution of output power of corresponding distributed micro-source energy conversion devices based on a droop control theory, fluctuation of frequency and amplitude of output voltage of the corresponding distributed micro-source energy conversion devices introduced by droop control is compensated through a secondary micro-source controller, and then a three-level coordination controller adjusts bus voltage of corresponding sub-microgrid grid-connected points through PI closed-loop feedback adjustment control according to the voltage of the main grid-connected points; and further, voltage amplitude and frequency fluctuation caused by droop control are repaired, and the electric energy quality of the micro-grid is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a microgrid system provided by an embodiment of the invention;
fig. 2 is a four-layer control block diagram of a microgrid system provided by an embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, 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 application.
The invention provides a hierarchical control system of a micro-grid system, which aims to solve the problem of low power quality in the prior art.
Referring to fig. 1, the microgrid system includes a plurality of sub-microgrids, each sub-microgrid is connected to a power grid or a corresponding transformer through a corresponding sub-microgrid grid-connected point (such as PCCA, PCCB, and PCCC shown in fig. 1); each sub-microgrid comprises: distributed micro-sources (photovoltaic modules, wind power generation devices, energy storage systems, etc.) and their energy conversion devices (inverters 101, converters, rectifiers, etc.);
the hierarchical control system of the microgrid system comprises the components shown in figure 1: a plurality of primary droop controllers, a plurality of secondary micro controllers 102, and a plurality of tertiary coordinating controllers 103; wherein:
the primary droop controller is used for realizing the distribution of the output power of the corresponding distributed micro-source energy conversion device based on a droop control theory;
specifically, when the distributed micro-source energy conversion devices are connected in parallel, circulating active power and reactive power can appear, primary control is calculated based on a droop control method, a closed-loop instruction of an internal voltage and current loop is completed, and distribution of the active power and the reactive power output by the distributed micro-source of each energy conversion device interface is achieved through adjustment of the frequency and the amplitude of output voltage of each energy conversion device.
The formula adopted when calculating by the droop control method is as follows:
ω＝ω*-Gp(s)(P-P*)；
E＝E*-GQ(s)(Q-Q*)；
where ω is a frequency set value of the output voltage of the energy conversion device, E is an amplitude set value of the output voltage of the energy conversion device, and ω is*Frequency reference value for output voltage of energy conversion device, E*Reference value of amplitude of output voltage for energy conversion device, Gp(s) droop conversion coefficient for frequency, GQ(s) is the droop conversion coefficient of the amplitude, P is the actual value of the active power output by the distributed micro-source of the energy conversion device interface, Q is the actual value of the reactive power output by the distributed micro-source of the energy conversion device interface, P is the actual value of the reactive power output by the distributed micro-source of the energy conversion device interface*Reference value of active power, Q, for distributed micro-source output of an interface of an energy conversion device*And the reference value of the reactive power output by the distributed micro source of the interface of the energy conversion device.
In practical applications, the primary droop controller may be a controller inside a corresponding distributed micro-source energy conversion device (such as the inverter 101 or the converter in fig. 1), and is not particularly limited herein; of course, an additional controller may be provided, depending on the application environment, and is within the protection scope of the present application.
The primary droop control completes the distribution of the output power of the distributed micro-source energy conversion device through the adjustment of the frequency and the amplitude, and can better respond to the phenomenon of unequal active and reactive demands caused by sudden changes of the load, but the fluctuation of the amplitude and the frequency of the output voltage can be indirectly caused by the active and reactive changes of the output of the energy conversion device, the converter and the like, so in order to enable the frequency and the amplitude to return to the rated values again, the secondary micro-source controller 102 is required to compensate the fluctuation of the frequency and the amplitude of the output voltage of the corresponding distributed micro-source energy conversion device introduced by the droop control.
Specifically, in the control of the present layer, the secondary micro-controller 102 monitors the frequency and amplitude of the output voltage of the corresponding distributed energy source in the micro-grid to obtain the actual frequency value ω of the output voltage of the distributed micro-sourceSMGAnd the actual value of the amplitude ESMG(ii) a Then, comparing and calculating the frequency of the output voltage of the corresponding distributed micro-source with the voltage frequency reference value of each corresponding sub-micro-grid to obtain a secondary frequency error; comparing and calculating the amplitude of the output voltage of the corresponding distributed micro source with the reference value of the voltage amplitude of the sub-micro grid corresponding to the amplitude of the output voltage of the corresponding distributed micro source, so as to obtain a secondary amplitude error; the sub-microgrid voltage frequency reference value is the frequency of bus voltage of a corresponding sub-microgrid grid-connected point (such as PCCA, PCCB or PCCC shown in fig. 1), and the sub-microgrid voltage amplitude reference value is the amplitude of the bus voltage of the corresponding sub-microgrid grid-connected point; finally, transmitting the secondary frequency error and the secondary amplitude error to a local controller of the corresponding distributed micro source for PI closed-loop feedback control, so that the frequency and the amplitude of the output voltage of the corresponding distributed micro source return to stable values again, and paving the foundation for the next three-level coordination control; specifically, the formula for obtaining the secondary frequency error and the secondary amplitude error is as follows:
Figure BDA0001710122850000071
Figure BDA0001710122850000072
where Δ ω is the secondary frequency error, Δ E is the secondary amplitude error, ωSMGFor the actual value of the frequency of the distributed micro-source output voltage, ESMGFor the actual value of the amplitude of the distributed micro-source output voltage,
Figure BDA0001710122850000073
is a sub-microgrid voltage frequency reference value,
Figure BDA0001710122850000074
is a sub-microgrid voltage amplitude reference value, kpw、kiw、kpE、kiEIs a secondary compensation control parameter.
Considering the emergency state of the main power grid, the frequency deviation should be corrected within an allowable range by the secondary micro-source control, and in China, the frequency deviation is +/-0.5 HZ. In this case, Δ ω, Δ E must be defined in order not to exceed the maximum deviations allowed for frequency and amplitude.
In addition, since the primary droop control and the secondary micro-source control are only for a single distributed micro-source, and the influence of the combined action of the distributed micro-source and the load in one sub-microgrid on the sub-microgrid grid-connected point is not considered, the three-level coordination controller 103 is further required to adjust the bus voltage of the corresponding sub-microgrid grid-connected point through PI closed-loop feedback adjustment control according to the voltage of the main grid-connected point (such as PCCD shown in fig. 1).
Specifically, the three-level coordination control mainly aims at the bus voltage where the sub-microgrid grid-connected point (such as PCCA, PCCB or PCCC shown in fig. 1) is located, and adjusts the frequency and amplitude of the bus voltage. Firstly, the amplitude, the frequency, the phase and the like of the voltage of the grid-connected point of the main power grid need to be monitored, then the amplitude, the frequency, the phase and the like of the voltage of the grid-connected point of the main power grid need to be monitored, and then the amplitude, the frequency, the phase and the like of the voltage of the grid-connected point of the main power grid need to be sent to each sub-microgrid according to the monitored data information to be compared and synchronized with the frequency phase of the voltage of the grid-connected point of the main power grid; specifically, comparing and calculating the frequency of the bus voltage of the corresponding sub-microgrid grid-connected point with the frequency of the main grid-connected point voltage to obtain a three-level frequency error; comparing and calculating the amplitude of the bus voltage of the corresponding sub-microgrid grid-connected point with the amplitude of the voltage of the main grid-connected point to obtain a three-level amplitude error; then, the three-level frequency error and the three-level amplitude error are transmitted to the three-level coordination controller 103 of each sub-microgrid for PI closed loop feedback regulation control; meanwhile, the three-level coordination controller 103 is also responsible for information sharing among a plurality of sub-micro grids, so as to ensure that the voltage and frequency among the sub-micro grids are regulated to be resynchronized, and once the fact that the amplitude and frequency of the bus voltage of a grid connection point of a certain sub-micro grid are greatly different from those of other sub-micro grids or the voltage of the grid connection point of the main grid is greatly different from those of the other sub-micro grids is detected, the sub-micro grids continue to carry out three-level control error regulation until the bus voltage of the grid connection point of the corresponding sub-micro grid is the same as that of the grid connection point of the main grid.
The formula adopted by the three-level coordination controller 103 to obtain the three-level frequency error and the three-level amplitude error is as follows:
Figure BDA0001710122850000081
Figure BDA0001710122850000082
wherein, Δ ω is the error of three-level frequency, Δ E is the error of three-level amplitude, ωMGActual frequency value of grid-connected point bus voltage of sub-microgrid, EMGThe actual value of the amplitude value of the grid-connected point bus voltage of the sub-microgrid,
Figure BDA0001710122850000083
for the actual value of the voltage frequency of the grid-connected point of the main grid,
Figure BDA0001710122850000084
is the actual value of the voltage amplitude of the grid-connected point of the main power grid, kpw1、kiw1、kpE1、kiE1The control parameters are compensated for in three stages.
In this case, Δ ω, Δ E must be defined in order not to exceed the maximum deviations allowed for frequency and amplitude.
In the hierarchical control system of the microgrid system provided in this embodiment, after the primary droop controller implements distribution of output power of the corresponding distributed type micro-source energy conversion devices based on a droop control theory, fluctuation of frequency and amplitude of output voltage of the corresponding distributed type micro-source energy conversion devices introduced by droop control is compensated by the secondary micro-source controller 102, and then the bus voltage of the corresponding sub-microgrid grid-connected point is adjusted by the tertiary coordination controller 103 through PI closed-loop feedback adjustment control according to the main grid-connected point voltage; voltage amplitude and frequency fluctuation among all distributed micro sources and between the distributed micro sources and loads are coordinated and controlled on the level of a single sub-microgrid; and then realized the restoration to voltage amplitude and frequency fluctuation that the droop control brought, improved the electric energy quality of microgrid, promoted the voltage of microgrid layered structure and frequency control's accuracy and stability, promoted the power consumption efficiency.
Another embodiment of the present invention further provides another hierarchical control system for a microgrid system, and based on the above embodiment, preferably, referring to fig. 1, the hierarchical control system for the microgrid system further includes:
and the four-stage optimization controller 104 is used for improving the economic low carbon property of the micro-grid system and maintaining the balance of supply and demand.
When the micro-grid is connected to the power grid, the power flow can be controlled by adjusting the frequency and amplitude of the voltage of the micro-grid, the primary droop control in the embodiment can complete the response to the sudden change of the load, the secondary micro-source control can improve the voltage and frequency deviation brought by the primary control distributed micro-source so as to improve the quality of electric energy, and the three-level coordination control can improve the stability of the sub-micro-grid and the synchronous consistency of the voltage amplitude and frequency of the sub-micro-grid and the grid-connected point of the main grid, and can also realize the information sharing among the sub-micro-grids; and the four-stage control redistributes the power of the micro-grid system on the basis of the three-stage control, maintains the balance of supply and demand, and improves the overall economy, low carbon and reliability of the micro-grid.
Specifically, four-level optimization control is mainly aimed at the demand state, the fuel price, the main grid electricity price, the distributed energy storage state of the current load, the predicted output and the actual output of distributed photovoltaic, wind power, nuclear power, biomass and other micro sources, a multi-objective optimization function is comprehensively considered, fuel price data, main grid electricity price, static data and characteristics, load prediction, power generation prediction, an initial state and optimization targets are used as input, the output of an optimization unit, an optimization unit static plan, a carbon emission plan, a cost plan, an energy storage release plan and a distributed micro source output plan are used as output, and an economic low-carbon operation model is established;
the refining overall formula is as follows:
Min[α∑Cost+(1-α)∑Emissions]；
where Cost is economic Cost, emissitions is carbon emission, and a is the actual demand weight value for economic Cost and carbon emission.
The value range of a is 0 to 1, the ratio of economy to carbon emission is changed by controlling the value of a, and a desired optimization target is obtained according to actual requirements at different moments. Specifically, when a is 0, the economic low-carbon operation model is the lowest carbon model, economic cost is not considered, the low-carbon weight ratio is 1, and the system operates in a low-carbon target mode; when a is 1, the economic low-carbon operation model is the most economic model; and a is 0.5, which represents half of each economic and low-carbon weight, and the system operates in an economic low-carbon target mode.
From the above, the four-stage optimization control is to form an optimal operation target according to an optimal operation analysis algorithm, further form a forced execution instruction, and reasonably distribute the power of the distributed micro-source in the micro-network again. The optimal point of economic operation is that the marginal cost of all distributed power supplies in the microgrid is equal, and when the optimization target is the optimal point of economic operation, the four-stage optimization controller 104 performs optimization according to a formula
Figure BDA0001710122850000101
And
Figure BDA0001710122850000102
obtaining a four-level frequency error and a four-level amplitude error; and by applying a fourth frequencyCarrying out PI closed loop feedback control on the rate error and the four-level amplitude error so as to enable the output power of the microgrid system to be the same as an optimization target;
where Δ ω is the fourth order frequency error, Δ E is the fourth order amplitude error, PMGActual value of active power, Q, for grid-connected points of main gridMGIs the actual value of the reactive power of the grid-connected point of the main power grid,
Figure BDA0001710122850000103
is the active power reference value of the grid-connected point of the main power grid,
Figure BDA0001710122850000104
reference value of reactive power, k, for the grid-connected point of the main gridpP、kiP、kpQ、kiQThe control parameters are compensated for four levels.
The microgrid system has a decentralized characteristic, each controller must have the capability of self-regulation according to local information and does not depend on external information as much as possible, so that the four-level optimization control in the embodiment is controlled by depending on the local load condition and the information of the distributed energy sources, and meanwhile, the operation management of microgrid optimization is completed by receiving overall scheduling from an upper layer.
The rest of the principle is the same as the above embodiments, and is not described in detail here.
Fig. 2 is a schematic block diagram of the four-layer control provided in this embodiment, where G1 is a proportional-integral function of output voltage amplitude at outlets of energy conversion devices such as an inverter and a converter, G11 is a proportional-integral function of output frequency at outlets of energy conversion devices such as an inverter and a converter, G2 is a proportional-integral function of bus voltage amplitude at a grid-connected point of a sub-microgrid, G22 is a proportional-integral function of bus voltage frequency at a grid-connected point of a sub-microgrid, G3 is a proportional-integral function of reactive power at a grid-connected point of a main grid, and G33 is a proportional-integral function of active power at a grid-connected point of a main grid. The primary droop control of each energy conversion device (inverter, rectifier bridge or converter) in the sub-microgrid is the same as that in the prior art, and the details are not repeated herein; the control of the secondary micro-source needs to be carried out on each distributed micro-source in the sub-micro-gridCarrying out U/I calculation on current acquisition signals of (distributed wind power, distributed energy storage, distributed photovoltaic or load), and then carrying out U/I calculation according to the obtained frequency actual value omega of the distributed micro-source output voltageSMGAnd the actual value of the amplitude ESMGCombined with sub-microgrid voltage frequency reference value
Figure BDA0001710122850000111
And amplitude reference value
Figure BDA0001710122850000112
Two proportional integral functions G1 and G11 are obtained through corresponding control; the three-level coordination control needs to perform U/I calculation on current acquisition signals at the sub-microgrid grid-connected point, and the frequency actual value omega of the voltage of the sub-microgrid grid-connected point bus is obtainedMGAnd the actual value of the amplitude EMGAnd simultaneously, the actual value of the voltage frequency of the grid-connected point of the main power grid is obtained by combining a voltage acquisition signal between the static bypass switch and the power grid and passing through a phase-locked loop (PLL)
Figure BDA0001710122850000113
And the actual value of the amplitude
Figure BDA0001710122850000114
Two proportional integral functions G2 and G22 are obtained through corresponding control; the four-stage optimization control needs to carry out P/Q calculation on a voltage acquisition signal and a current acquisition signal at a main power grid-connected point to obtain an active power actual value P of the main power grid-connected pointMGAnd actual value of reactive power QMGCombining active power reference value of grid-connected point of main power grid
Figure BDA0001710122850000115
And a reactive power reference value
Figure BDA0001710122850000116
G3 and G33 are obtained by corresponding control.
The four-layer control model of the micro-grid layered structure, namely primary droop control, secondary micro-source control, tertiary coordination control and four-level optimization control, stabilizes the voltage frequency and amplitude of the micro-grid system within a safe and controllable range through layer-by-layer control from bottom to top, improves the electric energy quality, and improves the power utilization efficiency, economy, low carbon and reliability.
Another embodiment of the present invention further provides a microgrid system, referring to fig. 1, including: a hierarchical control system for a plurality of sub-piconets and a microgrid system as described in any of the above embodiments.
Preferably, the microgrid system further comprises: at least one transformer arranged between the power grid and the corresponding sub-microgrid grid-connected point;
a plurality of sub-micro grids with the same output voltage share one three-level coordination controller 103, and are connected to a power grid or corresponding transformers through the same sub-micro grid connection point.
According to the above embodiment, the hierarchical control of the microgrid system mainly comprises four layers: the method comprises the following steps of distributed micro-source primary control based on a droop control theory, secondary control for adjusting and recovering deviation generated by the distributed micro-source primary control, three-level control for synchronizing the frequency and amplitude of sub-microgrid grid-connected points formed by a plurality of distributed micro-sources and load coordination control with a main power grid and coordination control of sub-microgrid grid-connected points of a plurality of sub-microgrids with different voltage levels, and four-level control for controlling connection between a microgrid system and an external power distribution system and aiming at improving the overall economic low carbon performance and supply and demand balance of the microgrid. The specific architecture of the microgrid system for realizing the four-layer control is shown in fig. 1, and it can be clearly seen in the figure that for a microgrid system comprising a mixture of high voltage 35KV, medium voltage 10KV, low voltage 400V and the like, local sub-microgrids are established nearby through distributed microgroudes and loads at the same voltage level, so that the modularization of the microgrid system is ensured, and the microgrid system complements the four-layer control architecture provided by the embodiment of the invention.
That is, in this embodiment, for the characteristics of distributed micro-sources and loads inside the microgrid, the four-level hierarchical control architecture in the above embodiment is suitable for a hybrid microgrid system composed of different power levels, such as high voltage, medium voltage, and low voltage, by providing a modeling logic that sub-microgrids are established nearby at different voltage levels.
Preferably, when the hierarchical control system of the microgrid system comprises the four-level optimization controller 104, the four-level optimization controller 104 realizes communication with each three-level coordination controller 103, the microgrid master station, the communication server and the real-time server through an optical fiber ring network, so as to realize information intercommunication.
The rest of the principle is the same as the above embodiments, and is not described in detail here.
The embodiments of the invention are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments can be referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims (15)

1. A hierarchical control system for a microgrid system, comprising: the system comprises a plurality of primary droop controllers, a plurality of secondary micro-controllers and a plurality of three-level coordination controllers; wherein:
the primary droop controller is used for realizing the distribution of the output power of the corresponding distributed micro-source energy conversion device based on a droop control theory;
the secondary micro-source controller is used for compensating the fluctuation of the frequency and the amplitude of the output voltage of the corresponding distributed micro-source energy conversion device introduced by droop control;
and the third-level coordination controller is used for adjusting the bus voltage of the corresponding sub-microgrid grid-connected point according to the voltage of the main grid-connected point through PI closed-loop feedback adjustment control after the primary droop controller realizes the distribution of the output power of the corresponding distributed micro-source energy conversion device and the secondary micro-source controller realizes the compensation of the fluctuation of the frequency and the amplitude of the output voltage of the corresponding distributed micro-source energy conversion device introduced by the droop control, so as to ensure that the bus voltage of the corresponding sub-microgrid grid-connected point is the same as the voltage of the main grid-connected point.
2. The hierarchical control system for the microgrid system of claim 1, wherein the primary droop controller is configured to, when implementing the distribution of the output power to the corresponding distributed micro-source energy conversion devices based on a droop control theory, specifically:
and generating a closed-loop instruction of an internal voltage and current loop through droop control calculation so as to realize active power and reactive power distribution of distributed micro-source output of each energy conversion device interface through adjusting the frequency and amplitude of output voltage of each energy conversion device.
3. The hierarchical control system for the microgrid system of claim 2, wherein the droop control calculation employs the formula:
ω＝ω*-Gp(s)(P-P*)；
E＝E*-GQ(s)(Q-Q*)；
where ω is a frequency set value of the output voltage of the energy conversion device, E is an amplitude set value of the output voltage of the energy conversion device, and ω is*Frequency reference value for output voltage of energy conversion device, E*Reference value of amplitude of output voltage for energy conversion device, Gp(s) droop conversion coefficient for frequency, GQ(s) is the droop conversion coefficient of the amplitude, P is the actual active power value of the distributed micro-source output of the interface of the energy conversion device, and Q is the energyActual value of reactive power, P, of distributed micro-source output of interface of conversion device*Reference value of active power, Q, for distributed micro-source output of an interface of an energy conversion device*And the reference value of the reactive power output by the distributed micro source of the interface of the energy conversion device.
4. The hierarchical control system for the microgrid system as claimed in claim 1, wherein the secondary micro-controller is configured to compensate for fluctuations in frequency and amplitude of output voltages of corresponding distributed micro-source energy conversion devices introduced by droop control, and is specifically configured to:
monitoring the frequency and amplitude of the output voltage of the corresponding distributed micro source;
comparing and calculating the frequency of the output voltage of the corresponding distributed micro-source with the voltage frequency reference value of the corresponding sub-micro-grid to obtain a secondary frequency error; comparing and calculating the amplitude of the output voltage of the corresponding distributed micro source with the reference value of the voltage amplitude of the sub-micro grid corresponding to the amplitude of the output voltage of the corresponding distributed micro source, so as to obtain a secondary amplitude error; the sub-microgrid voltage frequency reference value is the frequency of the bus voltage of the corresponding sub-microgrid grid-connected point; the sub-microgrid voltage amplitude reference value is the amplitude of the bus voltage of the corresponding sub-microgrid grid-connected point;
and transmitting the secondary frequency error and the secondary amplitude error to a local controller of the corresponding distributed micro source for PI closed loop feedback control, so that the frequency and the amplitude of the output voltage of the corresponding distributed micro source return to stable values again.
5. The hierarchical control system for a microgrid system of claim 4, characterized in that the secondary frequency error and the secondary amplitude error are derived using the formula:
Figure FDA0003158237680000021
Figure FDA0003158237680000022
where Δ ω is the secondary frequency error, Δ E is the secondary amplitude error, ωSMGFor the actual value of the frequency of the distributed micro-source output voltage, ESMGFor the actual value of the amplitude of the distributed micro-source output voltage,
Figure FDA0003158237680000023
is a sub-microgrid voltage frequency reference value,
Figure FDA0003158237680000024
is a sub-microgrid voltage amplitude reference value, kpw、kiw、kpE、kiEIs a secondary compensation control parameter.
6. The hierarchical control system for the microgrid system as claimed in claim 1, wherein the tertiary coordination controller is configured to adjust the bus voltage of the grid-connected point of the corresponding sub-microgrid through PI closed-loop feedback regulation control according to the voltage of the grid-connected point of the main grid after the primary droop controller implements distribution of the output power of the corresponding distributed micro-source energy conversion devices and the secondary micro-controller implements compensation for fluctuations in the frequency and amplitude of the output voltage of the corresponding distributed micro-source energy conversion devices introduced by droop control, so as to ensure that the bus voltage of the grid-connected point of the corresponding sub-microgrid is the same as the grid-connected point voltage of the main grid, and is specifically configured to:
monitoring the amplitude, frequency and phase of the voltage of the grid-connected point of the main power grid;
comparing and calculating the frequency of the bus voltage of the corresponding sub-microgrid grid-connected point with the frequency of the voltage of the main grid-connected point to obtain a three-level frequency error; comparing and calculating the amplitude of the bus voltage of the corresponding sub-microgrid grid-connected point with the amplitude of the voltage of the main grid-connected point to obtain a three-level amplitude error;
and carrying out PI closed loop feedback control on the three-level frequency error and the three-level amplitude error to enable the bus voltage of the corresponding sub microgrid grid-connected point to be the same as the voltage of the main grid-connected point.
7. The hierarchical control system for a microgrid system of claim 6, characterized in that the formula for obtaining three levels of frequency error and three levels of amplitude error is:
Figure FDA0003158237680000031
Figure FDA0003158237680000032
wherein, Δ ω is the error of three-level frequency, Δ E is the error of three-level amplitude, ωMGActual frequency value of grid-connected point bus voltage of sub-microgrid, EMGThe actual value of the amplitude value of the grid-connected point bus voltage of the sub-microgrid,
Figure FDA0003158237680000033
for the actual value of the voltage frequency of the grid-connected point of the main grid,
Figure FDA0003158237680000034
is the actual value of the voltage amplitude of the grid-connected point of the main power grid, kpw1、kiw1、kpE1、kiE1The control parameters are compensated for in three stages.
8. The hierarchical control system for the microgrid system of claim 6, wherein the three-level coordination controller is further configured to implement information sharing among a plurality of sub-microgrid.
9. The hierarchical control system for a microgrid system of any of claims 1-8, further comprising:
and the four-stage optimization controller is used for improving the economic low carbon performance of the micro-grid system and maintaining the balance of supply and demand.
10. The hierarchical control system for the microgrid system as recited in claim 9, wherein the four-level optimization controller is configured to, when the four-level optimization controller is used for improving economic low carbon of the microgrid system and maintaining supply and demand balance, specifically:
the method comprises the steps of taking fuel price data, power price of a main power grid, static data and characteristics, load prediction, power generation prediction, initial state and optimization targets as input, taking output of an optimization unit set, an optimization unit static plan, a carbon emission plan, a cost plan, an energy storage release plan and a distributed micro-source output plan as output, and establishing an economic low-carbon operation model;
and obtaining an optimization target according to the economic low-carbon operation model and the actual demand.
11. The hierarchical control system for the microgrid system of claim 10, wherein the economic low-carbon operation model is calculated by the formula:
Min[a∑Cost+(1-a)∑Emissions]；
where Cost is economic Cost, emissitions is carbon emission, and a is the actual demand weight value for economic Cost and carbon emission.
12. The hierarchical control system for a microgrid system of claim 10, wherein the quaternary optimization controller is formulated according to a formula when the optimization objective is an optimum point for economic operation
Figure FDA0003158237680000041
And
Figure FDA0003158237680000042
obtaining a four-level frequency error and a four-level amplitude error; PI closed loop feedback control is carried out on the four-level frequency error and the four-level amplitude error, so that the output power of the micro-grid system is the same as the optimization target;
where Δ ω is the fourth order frequency error, Δ E is the fourth order amplitude error, PMGActual value of active power, Q, for grid-connected points of main gridMGIs the actual value of the reactive power of the grid-connected point of the main power grid,
Figure FDA0003158237680000043
is the active power reference value of the grid-connected point of the main power grid,
Figure FDA0003158237680000044
reference value of reactive power, k, for the grid-connected point of the main gridpP、kiP、kpQ、kiQThe control parameters are compensated for four levels.
13. A microgrid system, comprising: a hierarchical control system for a plurality of sub-piconets and a microgrid system as claimed in any of claims 1 to 12.
14. The microgrid system of claim 13, further comprising: at least one transformer arranged between the power grid and the corresponding sub-microgrid grid-connected point;
a plurality of sub-micro-grids with the same output voltage share one three-level coordination controller, and are connected to a power grid or corresponding transformers through the same sub-micro-grid-connected point.
15. The microgrid system of claim 13, wherein when the hierarchical control system of the microgrid system comprises a fourth-level optimization controller, the fourth-level optimization controller realizes communication with each of the third-level coordination controller, the microgrid master station, the communication server and the real-time server through a fiber ring network.
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