CN110416991B - Modularized multi-terminal flexible direct-current micro-grid networking and layered control method thereof - Google Patents
Modularized multi-terminal flexible direct-current micro-grid networking and layered control method thereof Download PDFInfo
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/14—Balancing the load in a network
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/14—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
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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
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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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
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Abstract
The invention discloses a modularized multi-terminal flexible direct current micro-grid networking, which comprises a direct current bus, a controllable module, an uncontrollable module and a large power grid of a multi-terminal flexible direct current micro-grid; the controllable module comprises one or more controllable distributed power supplies, storage battery energy storage, direct current load and alternating current load, wherein each controllable distributed power supply is integrated into a direct current bus through a distributed power supply grid-connected device, the storage battery energy storage is connected into the direct current bus through the energy storage grid-connected device, the direct current load is directly connected with the direct current bus, and the alternating current load is connected with the direct current bus through the alternating current load grid-connected device; the invention simplifies the control target into the busbar voltage control of the direct current micro-grid, thereby facilitating the selection of the control mode; meanwhile, the micro-grid is subjected to modularized treatment, the traditional design micro-grid is changed into the assembly micro-grid, and the direct-current micro-grid is divided into a plurality of controllable modules and uncontrollable modules, so that the construction cost of the micro-grid is conveniently saved, the occupied area is reduced, and the subsequent expansion construction of the micro-grid is conveniently realized.
Description
Technical Field
The invention belongs to the field of micro-grid modular design and operation control, and particularly relates to a modular multi-terminal flexible direct-current micro-grid networking and a layered control method thereof.
Background
The micro-grid is a small power generation and distribution system formed by integrating a distributed power supply, an energy conversion device, a load, a monitoring and protecting device and the like, and is an autonomous system capable of realizing self-control and management. The micro-grid has a good energy management function, so that the optimal distribution and balance of energy in the micro-grid can be effectively maintained, and the running economy of the micro-grid is ensured; the micro-grid can play a role of load peak shifting and valley filling for the grid through the coordinated control of the output power of the distributed power supply in the grid, so that the fixed value or the fixed range control of the power exchange quantity between the micro-grid and the external power distribution network is realized, the influence of fluctuation of the power generation power of the distributed renewable energy source on the external power distribution network and peripheral users is reduced, and the operation scheduling difficulty of system operators is effectively reduced. The micro-grid generally has the advantages of high energy utilization efficiency, high energy supply reliability, less pollutant emission, good operation economy and the like.
However, the document "design and research of a new modular microgrid" indicates that: the development of the micro-grid is supported from the political strategy level, but the construction of the micro-grid project is not fully spread except a small amount of demonstration projects, and the main reason is that the public grid in China has better power supply reliability and economy after being developed for decades; the existing micro-grid has the disadvantages of complex structure, inconvenient switching of control modes, inconvenient subsequent expansion construction, large one-time investment of projects, slow output and relatively complex technology, so that the internal requirements of construction and the driving force of an economic layer are insufficient. Therefore, a new dc micro-grid networking structure needs to be studied.
The invention application with publication number of CN103219726A discloses a micro-grid topological structure based on energy storage, which comprises an alternating current bus connected with a main power grid; the alternating current bus is connected with a plurality of power generation units and a plurality of load units; the power generation unit comprises a distributed power supply, a micro-grid converter, an energy storage, a grid-connected converter and a unit controller. According to the micro-grid topological structure, the energy storage device is used as a pivot for micro-grid energy conversion, the generated energy of different distributed power supplies is stored in the energy storage device, and then the generated energy is intensively output to the alternating current bus through the energy storage device, so that the number of the distributed power supplies integrated into a main grid is reduced, the impact of the fluctuation of the output voltage of the distributed power supplies in the existing micro-grid structure on the main grid is effectively eliminated, and the stability of a micro-grid system is improved; meanwhile, the invention can intelligently adjust the working state of each micro-grid power generation unit according to different load power requirements, control the storage and output of electric energy, facilitate intelligent management and improve the controllability of a micro-grid system. However, the application of the invention does not classify the distributed power supply according to whether the distributed power supply is controllable, which is not beneficial to reducing the construction cost, the occupied area and the subsequent expansion construction.
The invention application with publication number of CN103236713A discloses a micro-grid networking and a control method thereof, and a bidirectional converter for the micro-grid, wherein the bidirectional converter for the micro-grid comprises a storage battery pack, an inversion module, a DSP control system, a first inductor, a capacitor, a second inductor, a first tie switch and a second tie switch, the direct current input end of the bidirectional converter for the micro-grid is connected with an energy storage battery pack, the alternating current output of the inversion module is filtered through the first inductor and the capacitor, on one hand, the local load is grounded through the first tie switch, and on the other hand, the second inductor and the second tie switch are connected to the micro-grid. By adopting the method, on one hand, the controllable flow of active power and reactive power in the micro-grid is realized, the configuration of an energy storage system is optimized, the service life of an energy storage battery pack is prolonged, and the energy in each region of the micro-grid is reasonably distributed; on the other hand, the existing power converter device and technology are fully utilized, the modularized networking and distributed access are realized, the capacity expansion is simple, and the popularization and the application of the micro-grid technology are facilitated. However, the distributed power supply module classification method still does not carry out module classification on the distributed power supply according to whether the distributed power supply module classification method is controllable, so that the construction cost is reduced, the occupied area is reduced, and the subsequent expansion construction is not facilitated.
Disclosure of Invention
In view of the above, the present invention aims to overcome the shortcomings of the prior art, and provides a modular multi-terminal flexible dc micro-grid networking and a hierarchical control method thereof, which simplifies the control objective into the control of the busbar voltage of the dc micro-grid, thereby facilitating the selection of the control mode; on the other hand, the micro-grid is subjected to modularized treatment, the traditional design micro-grid is changed into the assembly micro-grid, the direct-current micro-grid is divided into a plurality of controllable modules and uncontrollable modules according to the principle of nearby module division, so that the construction cost of the micro-grid is conveniently saved, the occupied area is reduced, and the subsequent expansion construction of the micro-grid is conveniently carried out.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a modularized multi-terminal flexible direct current micro-grid networking comprises a direct current bus of a multi-terminal flexible direct current micro-grid, a controllable module, an uncontrollable module and a large power grid;
the controllable module comprises one or more controllable distributed power supplies, storage battery energy storage, direct current load and alternating current load, wherein each controllable distributed power supply is integrated into a direct current bus through a distributed power supply grid-connected device, the storage battery energy storage is connected into the direct current bus through the energy storage grid-connected device, the direct current load is directly connected with the direct current bus, and the alternating current load is connected with the direct current bus through the alternating current load grid-connected device;
the uncontrollable module comprises one or more uncontrollable distributed power sources, direct current loads and alternating current loads, wherein each uncontrollable distributed power source is connected to a direct current bus through an uncontrollable distributed power source grid-connected device, the direct current loads are directly connected with the direct current bus, and the alternating current loads are connected with the direct current bus through an alternating current load grid-connected device;
the bidirectional converter of the multi-terminal flexible direct current micro-grid is connected with the isolation transformer of the large power grid through an alternating current bus.
Further, the controllable distributed power supply is a diesel generator, a single-shaft micro gas turbine, a wind power plant with energy storage or a photovoltaic power station with energy storage, can continuously supply power for self load and a direct-current micro power grid, and regulates active power and reactive power output by the controllable distributed power supply.
Further, the uncontrollable distributed power source is an MPPT controlled wind power plant or an MPPT controlled photovoltaic power station;
and the bidirectional converter internally receives instructions sent by the central controller of the multi-terminal flexible direct-current micro-grid, judges the running mode and the control mode of the direct-current micro-grid and controls the interaction of the direct-current micro-grid and the large power grid.
Further, the control mode adopted by the energy storage grid-connected device is droop control;
the uncontrollable distributed power source grid-connected device adopts an MPPT control or constant frequency/constant speed control mode.
Further, the operation modes of the modularized multi-terminal flexible direct current micro-grid networking comprise the following three modes: the large power grid and the controllable module in the grid-connected state coordinate control mode, the controllable module independent control mode and the island mode in the island state.
Further, the coordination control mode of the large power grid and the controllable module is applied to a grid-connected state, and the controllable parts of the large power grid and the direct-current micro power grid jointly control the bus voltage balance of the direct-current micro power grid; the bidirectional converter receives signals sent by the top central controller, when all the large power grids run normally, the bidirectional converter receives signals, droop control is selected, and when the sent power is larger than the required power, the micro power grid can transmit the power to the large power grids; when the generated power is smaller than the required power, purchasing power to the large power grid, namely realizing bidirectional transmission of the power, wherein the large power grid participates in voltage regulation of the bus; when the bus voltage rises, the storage battery stores energy to absorb power, the single-shaft micro gas turbine acts to reduce output, and if the storage battery stores energy SOC reaches the upper limit, the single-shaft micro gas turbine sends out zero power, and when the bus voltage still rises, the bidirectional converter sags to control and absorb redundant power; when the busbar voltage drops, the storage battery stores energy and discharges, the power emitted by the single-shaft micro gas turbine is increased, after the busbar voltage is stabilized by the sagging control of the bidirectional converter, the direct-current micro power grid is not supplied with power, the maximization of the utilization of resources in the direct-current micro power grid is ensured, the dependence on a large power grid is reduced, and the running cost of the direct-current micro power grid is reduced.
Furthermore, the independent control mode of the controllable module is applied to the grid-connected state, and the large power grid has requirements on the direct-current micro power grid and does not participate in the busbar voltage regulation of the direct-current micro power grid; the bidirectional converter receives signals sent by the top central controller, and inputs reference values Pref and Qref controlled by PQ according to requirements, and a large power grid at the moment is equivalent to an uncontrollable module; when the bus voltage rises, the storage battery stores energy to absorb power, the single-shaft micro gas turbine reduces output, and if the output power of the single-shaft micro gas turbine is zero and the storage battery stores energy SOC reaches the upper limit, the distributed motor in the uncontrollable module discards wind or light; when the busbar voltage drops, the storage battery stores energy to generate power, the single-shaft micro gas turbine increases the output, and if the storage battery stores energy SOC reaches the lower limit and the single-shaft micro gas turbine reaches the upper limit of the output, the three-level load in the uncontrollable module is cut off.
In the grid-connected state, the large power grid and the controllable module coordinate control mode and the controllable module independent control mode are switched by a central controller to send instructions of a bidirectional converter control mode. When the bidirectional converter control mode is the droop control mode, the control mode is a coordination control mode of the large power grid and the controllable module, and when the bidirectional converter control mode is the PQ control mode, the control mode is an independent control mode of the controllable module.
Further, the island mode is that under the normal operation of the networking state, if the large power grid fails or the electric energy quality does not meet the requirement, the direct current micro power grid receives the instruction of the central controller MGCC, the large power grid is disconnected from the direct current micro power grid, and the bidirectional converter plays an isolating role. The direct current micro-grid consists of a controllable module and an uncontrollable module at the moment, and the control strategies of the two modes are the same because the direct current micro-grid in the independent operation mode of the controllable module also consists of the two parts.
In addition, the invention also provides a layered control method of the modularized multi-terminal flexible direct current micro-grid networking, which is a three-layer control method comprising a central control layer, a module layer and an original layer, wherein,
the central control layer is controlled by signals of the large power grid, judges whether the large power grid has requirements on the direct current micro power grid and whether the electric energy quality of the large power grid reaches the standard, and sends out signals to control a control mode of the bidirectional converter to determine the running mode of the direct current micro power grid;
the module layer controls coordination control in each module, the controllable module must ensure that response is given to fluctuation of an external uncontrollable module on the basis of meeting internal load power, the voltage stability of a direct current bus is ensured, and when the voltage of the bus exceeds +/-5% of rated voltage and the stored energy exceeds the limit, the module layer controls load removal or distributed generator removal in each module;
the element layer mainly determines the control mode of each device in each module, adjusts the internal control parameters of droop control and constant voltage control, and ensures the stable voltage speed.
The beneficial effects of the invention are as follows:
a typical micro-grid networking structure is proposed by CERTS, wherein the structure comprises two micro-source connection modes, one is that all micro-sources are connected to the same feeder line, and the initial end of the feeder line is connected to a micro-grid bus; and the other is that each micro source and the local load form a small power generation system which is commonly connected to the micro-grid bus and has a parallel structure. The concept and structure of the micro-grid proposed by CERTS are widely accepted at home and abroad, and are the most popular micro-grid structure at present. In the structure, the load, the energy storage system and the distributed power supply are in parallel operation in a current source mode when the micro-grid is in grid-connected operation, so that transient oscillation of the busbar voltage of the micro-grid is difficult to avoid in the process of converting the grid-connected state into the island state (particularly in the process of generating an unintended island), and the load and the distributed power supply are off-grid in the process of converting, namely seamless switching of the grid-connected state and the island state is difficult to realize. The documents Advantages and circuit configuration of a DC microgrid, A benchmark LV microgrid for steady state and transient analysis and An update on Sendai demonstration of multiplepower quality supply system respectively propose networking schemes such as a direct current micro-grid, an alternating current micro-grid and an alternating current/direct current hybrid micro-grid. The micro-grid structure basically takes over the micro-grid networking thought of CERTS, and has the control difficulty in the state transition process.
The invention patent of the clear water construction company and the Tokyo university application, "a method for constructing a micro-grid system", proposes a method for constructing a network for uniformly monitoring a plurality of types of distributed power sources, thereby supplying power to a specific area, the method comprising: a step of measuring a load fluctuation of the specific region, and performing frequency analysis on data of the load fluctuation; the frequency of the load fluctuation is analyzed based on the frequency response characteristics of the multiple types of power supplies, and the frequency of the load fluctuation is distributed to the power supplies. The method relies on the optimal design of the control strategy to realize the stability and schedulability of the state transition of the micro-grid, so that the method has high requirements on the accuracy and the response speed of the monitoring system. The serial micro-grid provided by literature 'a micro-source inverter serial connection type micro-grid characteristic research' can reduce output harmonic content, reduce the influence on a power distribution network and a load, and effectively solve a plurality of problems of circulation, harmonic, frequency and the like in an alternating current micro-grid and a direct current micro-grid, but the structure cannot solve the problems of plug-and-play and stable scheduling of the micro-grid. The university of Zhejiang applies for an invention patent of an energy storage-based micro-grid topological structure (publication No. CN 103219726A), and an energy storage device is used as a hub for energy conversion of the micro-grid, so that the impact of fluctuation electric energy output by a distributed power supply on a main grid is reduced and eliminated. However, the patent of the invention does not solve the problem of dual-mode seamless switching of micro-grid connection/island. Aiming at the fact that no effective networking design exists at present for a direct-current micro-grid, so that the structure is simplified, the control mode is convenient to select, the construction cost of the micro-grid is saved, the occupied area is reduced, and the subsequent expansion construction of the micro-grid is convenient; moreover, even if the skilled person realizes the above problems, the design characteristics of the existing micro-grid networking structure are that the existing micro-grid networking structure cannot be thoroughly designed and broken through, the modular design of the modules according to the controllability and uncontrollability cannot be considered, and the skilled person is limited and lacks the power to break through the convention in the prior art, and cannot deeply study the new micro-grid networking.
Aiming at the problems that the existing micro-grid structure is complex, the control mode is inconvenient to switch and the follow-up expansion construction is inconvenient, the invention provides a modularized multi-terminal flexible direct current micro-grid networking which comprises a direct current bus, a controllable module, an uncontrollable module and a large power grid of the multi-terminal flexible direct current micro-grid; the controllable module comprises one or more controllable distributed power supplies, storage battery energy storage, direct current load and alternating current load, wherein each controllable distributed power supply is integrated into a direct current bus through a distributed power supply grid-connected device, the storage battery energy storage is connected into the direct current bus through the energy storage grid-connected device, the direct current load is directly connected with the direct current bus, and the alternating current load is connected with the direct current bus through the alternating current load grid-connected device; the uncontrollable module comprises one or more uncontrollable distributed power sources, direct current loads and alternating current loads, wherein each uncontrollable distributed power source is connected to a direct current bus through an uncontrollable distributed power source grid-connected device, the direct current loads are directly connected with the direct current bus, and the alternating current loads are connected with the direct current bus through an alternating current load grid-connected device; the bidirectional converter of the multi-terminal flexible direct current micro-grid is connected with the isolation transformer of the large power grid through an alternating current bus.
Compared with the traditional direct-current micro-grid, the flexible multi-terminal direct-current micro-grid has the advantages that the structure is simplified, and the later construction is convenient; and the control target is simplified into busbar voltage control of the direct-current micro-grid, so that the selection of a control mode is facilitated. The micro-grid is subjected to modularized treatment, the traditional design micro-grid is changed into the assembly micro-grid, the direct-current micro-grid is divided into a plurality of controllable modules and uncontrollable modules according to the principle of nearby module division, so that the construction cost of the micro-grid is conveniently saved, the occupied area is reduced, and the subsequent expansion construction of the micro-grid is conveniently realized.
In addition, the control of the invention adopts a layered control method, the control layer number is three, and the control layers are respectively: a central control layer, a module layer and an element layer. The central control layer is controlled by signals of a large power grid, controls the running mode of the whole power grid, and belongs to upper control; the module layer controls the coordination of devices in each module, ensures the stability of each module, and belongs to middle-layer control; the element layer mainly determines the control method of each device in each module, adjusts the internal control parameters of droop control and constant voltage control, and ensures the stable voltage speed.
In addition, the controllable part of the invention must ensure that the internal load of the module layer and the output power of the generator can be self-balanced, and no fluctuation is brought to the DC bus voltage of the central control layer micro-grid. On the basis, the controllable module simulates primary regulation and secondary regulation in a large power grid, the storage battery energy storage and the single-shaft micro gas turbine are ensured to be double, and under the state of normal operation, the power fluctuation of an uncontrollable part can be quickly stabilized and enough supporting margin exists subsequently. The distributed generator in the uncontrollable part directly adopts MPPT control or constant frequency/constant speed control, so that the overall control of the distributed generator is simplified, the whole of the distributed generator and the load is regarded as net load, and the bus voltage is influenced by power fluctuation.
In addition, the three operation modes of the invention can cope with various operation conditions, when the large power grid participates in adjustment, the sagging control is selected to limit the power purchase size to the large power grid, and on the basis of meeting balance stability, the micro power grid self-output is as reliable as possible, thereby saving the operation cost. The large power grid does not participate in two states of regulation, and is operated as an uncontrollable module under the condition that the power quality of the large power grid is normal, the control modes are the same, the control modes are simplified, and bus voltage fluctuation caused by excessively complex control means is avoided. When the electric energy quality of the large power grid is in a problem, the central control center sends out a signal, the bidirectional converter cuts off the connection with the large power grid, so that the micro power grid is protected, and the problem of the micro power grid is prevented from being transmitted to the large power grid.
In addition, the distributed power supply, the energy storage device, the load and the like in the system are structurally connected to the direct current bus, and the direct current network is connected to an external alternating current network through the power electronic inversion device, so that the system has strong adaptability; dividing the operation mode into three modes of a large power grid and controllable module coordination control mode in a grid connection state, a controllable module independent control mode and an island mode in an island state in operation; and a layered modularized control method comprising three layers of a central control layer, a module layer and an element layer is adopted on the simultaneous control. According to the controllability of different modules, the multi-terminal flexible direct current micro-grid is divided into three types of controllable modules, uncontrollable modules and large power grid modules, and the types and control methods of distributed power sources and energy storage inside the modules are determined. The structure of the DC micro-grid after multi-terminal flexible simplification is that all modules are connected to a DC bus, and the control aim is to ensure the voltage stability of the DC bus. Aiming at controllable modules in the micro-grid, the internal load of the controllable modules can be completely consumed, the self-balancing of the interiors of the controllable modules is completed, and the controllable modules are externally used as controllable power sources to ensure that the power requirements of uncontrollable modules are met when a large power grid does not participate in regulation; under the grid connection condition, the controllable module and the large power grid jointly maintain the stability of the busbar voltage, and the large power grid can also put requirements on the DC micro-grid side; under island operation, the autonomy of the direct current micro-grid can ensure that the direct current micro-grid is stable within a certain time.
The micro-grid modular design can be basically divided into two main types, the first type is functional type division, so that the balance and control of the micro-grid inside are facilitated, and the number of times of communication with a central controller is reduced. The document "novel modularized AC/DC hybrid micro-grid topology optimization design and research" is to modularize the AC/DC hybrid micro-grid into three types, namely, all energy storage devices, all AC devices and all DC devices. Therefore, only the balance inside each module is required to be ensured, and unbalanced power inside the modules is uniformly balanced by the energy storage device. The topological structure can more easily realize all functions in the micro-grid, the module structure divided by the current transformer can be applied to various different application occasions, the modification quantity is small, and the full-modularized circuit design has the advantages of convenience in manufacturing, transportation, installation, maintenance, capacity expansion and upgrading and the like. Meanwhile, the efficiency of the system can be improved. The second category is to divide according to the geographical environment where each device is located, so that coordination balance stability in each region of the micro-grid is facilitated, occupied area is reduced, and nearby balance control of the region is more convenient. The document "Hybrid AC_ DC microgrid architecture with comprehensive control strategy for energy management of smart building" uses a building as a module to coordinate the distributed motors in the building, balance the DC energy storage and the AC/DC loads, and then access a large power grid. The dividing mode reduces energy transmission loss, is efficient and quick, and is convenient to control. The modularized scheme is beneficial to the accurate calculation of the investment yield of the project construction party, the construction mode and the economic mode have good repeatability, the traditional construction of a micro-grid project is changed into the purchase of a micro-grid, and the construction cost and the management cost of a project main body and various risks in the process are effectively reduced.
The multi-terminal flexible direct current micro-grid is characterized in that a novel converter is adopted to connect a distributed power supply, an energy storage device, a load and the like in the system to a direct current bus, and the direct current network is connected to an external alternating current network through a power electronic inversion device. This connection simplifies the control objective, for controlling the voltage stabilization of the bus. The literature 'flexible multi-state switch improved droop control strategy research' adopts a flexible multi-state switch SOP to replace a traditional interconnection switch, has the advantages of continuous and controllable power, flexible control mode and the like, is beneficial to flexible interconnection and dynamic reconstruction of an active power distribution network, can effectively improve voltage level, and promotes coordination control and absorption of a distributed power supply.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.
Drawings
FIG. 1 is a schematic diagram of a modular multi-terminal flexible DC micro-grid networking architecture of the present invention;
FIG. 2 is a control flow diagram of the present invention in a controllable module independent control mode and an island mode;
fig. 3 is a flow chart of the switching control of the bidirectional converter receiving the central controller signal in the present invention.
Detailed Description
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. It should be understood that, for the sake of clarity, terms such as "front, back, left, right, up, down," etc. used herein are terms such as orientation with respect to fig. 1, and are not intended to be changed over by the conversion of the views.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which are obtained by a person skilled in the art based on the described embodiments of the invention, fall within the scope of protection of the invention.
Example 1:
as shown in fig. 1, a modular multi-terminal flexible dc micro-grid networking comprises a dc bus 1, a controllable module 2, an uncontrollable module 3 and a large power grid 13 of the multi-terminal flexible dc micro-grid.
The controllable module 2 comprises one or more controllable distributed power supplies 4a, a storage battery energy storage 5, a direct current load 6a and an alternating current load 7a, wherein each controllable distributed power supply 4a is integrated into the direct current bus 1 through one distributed power supply grid-connected device 8a, the storage battery energy storage 5 is connected into the direct current bus 1 through an energy storage grid-connected device 9, the direct current load 6a is directly connected with the direct current bus 1, and the alternating current load 7a is connected with the direct current bus 1 through an alternating current load grid-connected device 10 a.
The uncontrollable module 3 comprises one or more uncontrollable distributed power sources 4b, a direct current load 6b and an alternating current load 7b, wherein each uncontrollable distributed power source 4b is connected to the direct current bus 1 through one uncontrollable distributed power source grid-connected device 8b, the direct current load 6b is directly connected with the direct current bus 1, and the alternating current load 7b is connected with the direct current bus 1 through an alternating current load grid-connected device 10 b; the uncontrollable module cannot control the output power of each part, namely cannot maintain the voltage stability of the direct current bus, so that the whole uncontrollable module can be treated as a net load.
The bidirectional converter 11 of the multi-terminal flexible direct current micro-grid is connected with the isolation transformer 14 of the large power grid 13 through the alternating current bus 12, wherein the bidirectional converter 11 is an external interface of the multi-terminal flexible direct current micro-grid.
The controllable distributed power supply 4a is a single-shaft miniature gas turbine, can continuously supply power for self loads and a direct-current micro-grid, and regulates active power and reactive power output by the controllable distributed power supply.
In the embodiment, the controllable distributed power supply adopts a single-shaft micro gas turbine, and of course, a wind power plant with energy storage of a diesel generator or a photovoltaic power station with energy storage of the diesel generator can also be adopted; the single-shaft micro gas turbine is integrated into a direct-current micro power grid system through a rectifier, the rectifier uses direct-current side voltage and reactive power as reference variables, and a pressure-current double ring is adopted to control the output power of the single-shaft micro gas turbine, so that the output power not only meets the internal load demand, but also ensures that the direct-current bus voltage is in a stable range. The storage battery energy storage adopts sagging control, simulates the primary frequency modulation characteristic of a large power grid, can be immediately adjusted when the busbar voltage fluctuates, can absorb power when the system energy is excessive, and can meet the requirement of short-time rapid charge and discharge due to the self characteristic of the storage battery energy storage. The droop control is rapid in adjustment but belongs to poor adjustment and cannot serve as a continuous power supply, and the characteristics of the single-shaft micro gas turbine can ensure continuous energy support for the direct-current micro power grid, so that the single-shaft micro gas turbine is required to perform power balance, voltage deviation caused by droop control is compensated, and internal load of the single-shaft micro gas turbine and the direct-current micro power grid are supplied with power. The controllable module belongs to a small self-balancing micro-grid, and responds to power fluctuation of an upper micro-grid on the basis of on-site load elimination.
The uncontrollable distributed power source 4b is an MPPT controlled wind power plant or an MPPT controlled photovoltaic power station; the photovoltaic in the uncontrollable distributed power supply is connected into a direct current micro-grid through a DC/DC chopper, and the output power of the photovoltaic generator can be changed by adopting an MPPT control mode and the temperature and illumination intensity in uncontrollable factors; the wind driven generator adopts constant frequency/constant speed control, is connected into a direct current micro-grid through a rectifier, and changes of wind speed influence the value of output active power. The alternating current load is integrated into the direct current micro-grid through the rectifier, and the direct current load is directly connected. The uncontrollable module cannot control the output power of each part, namely cannot maintain the voltage stability of the direct current bus, so that the whole uncontrollable module can be treated as a net load.
And the bidirectional converter internally receives instructions sent by a central controller of the multi-terminal flexible direct-current micro-grid, judges the running mode and the control mode of the direct-current micro-grid and controls the interaction between the direct-current micro-grid and the large power grid 13.
The energy storage grid-connected device 9 adopts a control mode of sagging control;
the uncontrollable distributed power source grid-connected device 8b adopts an MPPT control mode, and a constant frequency/constant speed control mode can be adopted.
Table 1 different module distributed power energy storage system types
| Module name | Distributed power supply | Energy storage system |
| DC micro-grid regulation | Diesel generator, single-shaft miniature gas turbine, wind power plant or photovoltaic power plant with energy storage function and the like | Accumulator energy storage |
| Direct current micro-grid is not adjustable | MPPT controlled wind power plant, photovoltaic power station and the like | Without any means for |
Since the different modules play different roles in the direct current micro-grid, the types of distributed power sources and energy storage in the different modules are different. The distributed power supply in the direct current micro-grid controllable module is required to continuously supply power for the load of the direct current micro-grid controllable module and the micro-grid, and the active power and the reactive power output by the direct current micro-grid controllable module can be regulated, so that the selected distributed power supply can be a single-shaft micro-gas turbine, a diesel generator, an energy storage wind power plant, a photovoltaic power station and the like. The module stores energy to cope with rapid fluctuation of the busbar voltage of the direct current micro-grid, and the distributed generator is used for continuously compensating power subsequently. The module with uncontrollable DC micro-grid has no regulation function, so the distributed motor in the module adopts MPPT controlled wind power plant, photovoltaic power station, etc.
As shown in fig. 2, in the independent control mode and the island mode of the controllable module, the specific flow of judging whether the current state is the limit running state is as follows: initial set value U for setting DC bus voltage dcref Maximum and minimum output Pmax and Pmin of the gas turbine, and detecting the DC bus voltage value U at the moment dc Judging the voltage value U of the direct current bus dc Initial set value U of voltage of direct current bus dcref If U is the size of dc >1.05U dcref When the energy storage SOC value and the output P of the gas turbine are detected, if the energy storage SOC value is higher than the set upper limit and the output P of the gas turbine is lower than the minimum output, the distributed motor of a part of uncontrollable modules needs to be cut off when the system runs in the limit state of surplus energy output of the direct current micro-grid, and the stable running of the system is ensured; conversely, if U dc >0.85U dcref And when the stored SOC value and the output P of the gas turbine are detected, and the stored SOC value is higher than a set lower limit and the output P of the gas turbine is lower than a maximum output, the system is ensured to stably operate by cutting off three types of loads of a part of uncontrollable modules when the system is operated in a limit state of insufficient energy output of the direct current micro-grid.
As shown in fig. 3, the bidirectional converter control method includes droop control and PQ control, and the control mode is switched according to a command signal sent by the top central controller. The direct current micro-grid detects an instruction signal sent by the central controller, and when the electric energy quality of the large power grid is in a problem or the bus voltage in the micro-grid is in a huge fluctuation, the central controller sends out a cutting instruction in order to prevent faults from affecting the rest parts, the bidirectional converter plays an isolating role, and the direct current micro-grid is converted into island operation; when the large power grid has a requirement on the direct-current micro power grid, the central controller sends out a command, the bidirectional converter is controlled by PQ, and the direct-current micro power grid adopts an independent control mode of a controllable module; under other conditions, the direct-current micro-grid adopts a coordination control mode of a large power grid and a controllable module.
Example 2:
the layered control method of the modularized multi-terminal flexible direct current micro-grid networking is a three-layer control method comprising a central control layer, a module layer and an original layer, wherein,
the central control layer is controlled by signals of the large power grid, judges whether the large power grid has requirements on the direct current micro power grid and whether the electric energy quality of the large power grid reaches the standard, and sends out signals to control a control mode of the bidirectional converter to determine the running mode of the direct current micro power grid;
the module layer controls coordination control in each module, the controllable module must ensure that response is given to fluctuation of an external uncontrollable module on the basis of meeting internal load power, the voltage stability of a direct current bus is ensured, and when the voltage of the bus exceeds +/-5% of rated voltage and the stored energy exceeds the limit, the module layer controls load removal or distributed generator removal in each module;
the element layer mainly determines the control mode of each device in each module, adjusts the internal control parameters of droop control and constant voltage control, and ensures the stable voltage speed.
Finally, it is noted that the above-mentioned embodiments are merely for illustrating the technical solution of the present invention, and that other modifications and equivalents thereof by those skilled in the art should be included in the scope of the claims of the present invention without departing from the spirit and scope of the technical solution of the present invention.
Claims (5)
1. A modularized multi-terminal flexible direct current micro-grid networking is characterized in that: the system comprises a direct current bus of a multi-terminal flexible direct current micro-grid, a controllable module, an uncontrollable module and a large power grid;
the controllable module comprises one or more controllable distributed power supplies, storage battery energy storage, a first direct current load and a first alternating current load, wherein each controllable distributed power supply is integrated into a direct current bus through a distributed power supply grid-connected device, the storage battery energy storage is connected into the direct current bus through the energy storage grid-connected device, the first direct current load is directly connected with the direct current bus, and the first alternating current load is connected with the direct current bus through the alternating current load grid-connected device;
the uncontrollable module comprises one or more uncontrollable distributed power sources, a second direct current load and a second alternating current load, wherein each uncontrollable distributed power source is connected to a direct current bus through an uncontrollable distributed power source grid-connected device, the second direct current load is directly connected with the direct current bus, and the second alternating current load is connected with the direct current bus through an alternating current load grid-connected device;
the bidirectional converter of the multi-terminal flexible direct current micro-grid is connected with the isolation transformer of the large power grid through an alternating current bus;
the controllable distributed power supply is a diesel generator, a single-shaft miniature gas turbine, a wind power plant with energy storage or a photovoltaic power station with energy storage;
the bidirectional converter internally receives an instruction sent by a central controller of the multi-terminal flexible direct current micro-grid, judges the running mode and the control mode of the multi-terminal flexible direct current micro-grid and controls the interaction between the multi-terminal flexible direct current micro-grid and a large power grid;
the operation modes of the modularized multi-terminal flexible direct current micro-grid networking comprise the following three modes: a large power grid and a controllable module in a grid-connected state coordinate control mode, a controllable module independent control mode and an island mode in an island state;
the coordination control mode of the large power grid and the controllable module is applied to a grid-connected state, and the controllable parts of the large power grid and the multi-terminal flexible direct current micro power grid jointly control the voltage balance of the direct current bus; the bidirectional converter receives signals sent by the central controller, when all the large power grid works normally, the bidirectional converter receives signals, droop control is selected, and when the sent power of the multi-terminal flexible direct current micro-grid is larger than the required power, the power is transmitted to the large power grid; when the generated power is smaller than the required power, purchasing power to a large power grid, realizing bidirectional transmission of power, and enabling the large power grid to participate in voltage regulation of a direct current bus; when the voltage of the direct current bus rises, the storage battery stores energy to absorb power, the single-shaft micro gas turbine acts to reduce output, if the storage battery stores energy SOC reaches the upper limit, the single-shaft micro gas turbine sends out power to be zero, and when the voltage of the direct current bus still rises, the bidirectional converter sags to control and absorb redundant power; when the voltage of the direct current bus is reduced, the storage battery stores energy and discharges, the power emitted by the single-shaft micro gas turbine is increased, and after the voltage of the direct current bus is stabilized by the sagging control of the bidirectional converter, the power supply to the multi-terminal flexible direct current micro power grid is not performed any more;
the controllable module independent control mode is applied to a grid-connected state, and the large power grid has requirements on the multi-terminal flexible direct current micro power grid and does not participate in direct current bus voltage regulation; the bidirectional converter receives signals sent by the top central controller, and inputs reference values Pref and Qref controlled by PQ according to requirements, and a large power grid at the moment is equivalent to an uncontrollable module; when the voltage of the direct current bus is increased, the storage battery stores energy to absorb power, the single-shaft micro gas turbine reduces output force, and if the output power of the single-shaft micro gas turbine is zero and the storage battery stores energy SOC reaches the upper limit, the distributed motor in the uncontrollable module discards wind or light; when the voltage of the direct current bus is reduced, the storage battery stores energy to generate power, the single-shaft micro gas turbine increases the output, and if the storage battery stores energy SOC reaches the lower limit and the single-shaft micro gas turbine reaches the upper limit of the output, the three-level load in the uncontrollable module is cut off.
2. The modular multi-terminal flexible dc micro-grid networking of claim 1, wherein: the uncontrollable distributed power source is an MPPT controlled wind power plant or an MPPT controlled photovoltaic power station.
3. The modular multi-terminal flexible dc micro-grid networking of claim 2, wherein: the control mode adopted by the energy storage grid-connected device is droop control;
the uncontrollable distributed power source grid-connected device adopts an MPPT control or constant frequency/constant speed control mode.
4. The modular multi-terminal flexible dc micro-grid networking of claim 1, wherein: the island mode is that under the normal operation of networking state, if the large power grid fails or the electric energy quality does not meet the requirement, the multi-terminal flexible direct current micro-grid receives the instruction of the central controller MGCC, the large power grid is disconnected from the multi-terminal flexible direct current micro-grid, and the bidirectional converter plays an isolating role.
5. The hierarchical control method of modular multi-terminal flexible direct current micro-grid networking of any one of claims 1-4, wherein: the layered control method is a three-layer control method comprising a central control layer, a module layer and an original layer, wherein,
the central control layer is controlled by signals of the large power grid, judges whether the large power grid has requirements on the multi-terminal flexible direct current micro-grid and whether the electric energy quality of the large power grid reaches the standard, and sends out signals to control a control mode of the bidirectional converter to determine the operation mode of the multi-terminal flexible direct current micro-grid;
the module layer controls coordination control in each module, the controllable module must ensure that response to fluctuation of an external uncontrollable module is given on the basis of meeting internal load power, voltage stability of the multi-terminal flexible direct current bus is ensured, and when the voltage of the direct current bus exceeds +/-5% of rated voltage and energy storage exceeds a limit, the module layer controls load removal or distributed generator removal in each module;
the element layer mainly determines the control mode of each device in each module, adjusts the internal control parameters of droop control and constant voltage control, and ensures the stable voltage speed.
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| CN115992372B (en) * | 2023-03-23 | 2023-06-06 | 国家电投集团云南国际电力投资有限公司 | Flexible direct current micro-grid-based aluminum electrolysis system |
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