CN117200363A - Control method for AC/DC coordinated interaction micro-grid group - Google Patents

Abstract

The invention provides a control method of an alternating current/direct current coordinated interaction micro-grid group, which is applied to a scene that a plurality of low-voltage stations are flexibly interconnected to form the micro-grid group, and realizes micro-grid group control under four main operation modes including an on-line control mode, an off-line control mode, a scheduled maintenance mode and a grid fault mode based on a cloud-side-end integrated three-layer cooperative control architecture. The flexible resources such as distributed light, storage, charging and the like in the micro-grid group are considerable, measurable, adjustable and controllable, and the aims of transparent power grid, main-distribution coordination and source-load interaction are realized. The invention realizes the strategy optimization decomposition of the equipment-level control layer, the district autonomous control layer and the main station coordination control layer, realizes the layered cooperative regulation and control independent of the on-site lateral communication, improves the cooperative interaction capability of the distributed resource consumption capability and the source network charge storage, and has the popularization advantages of strong scale expansibility and good function reusability.

Description

A control method for AC and DC coordinated interactive microgrid groups

Technical field

The invention relates to the field of power system operation and control, specifically a control method for AC and DC coordinated interactive microgrid groups.

Background technique

The future distribution network will show the following basic characteristics: large-scale access to distributed power sources (DG), large-scale access to energy storage systems, a large number of construction and application of charging stations and charging piles, and the gradual application of flexible AC and DC hybrid connections. wait. The traditional distribution network is a binary structure based on "grid (network) - load (load)". Simply put, it is a one-way power distribution network between the power supply of the grid and the power consumption of users. With the new form of distribution network in the future, the binary structure of traditional distribution network will gradually transition to the four-element structure of "source-grid-load-storage", which also provides a strong foundation for the development of microgrids. Microgrids rely on distributed new energy power generation and can operate independently. Their power sources are dispersed and their loads are also dispersed. They mainly consume electric energy locally. With the development of power electronics technology, multiple microgrids can rely on flexible interconnection devices to form a microgrid group with AC and DC coordination and interaction functions, maximizing on-site consumption of distributed power sources, and for areas that cannot be reached by large power grids. Solve the problem of flexible and stable electricity consumption for local users.

At this stage, there are still several issues that need to be resolved in the interactive application of source-grid-load-storage in microgrid groups:

First, the accommodation capacity of distributed power sources still needs to be improved. When the distributed power system is put into operation and the load in local areas is low, such as holidays, the voltage of the distribution line will rise or even exceed the warning line. The distribution network lacks flexible adjustment methods and can only roughly limit power or shut down machines, which lengthens the construction payback period of distributed power sources and damages users' construction benefits.

Second, the application function of energy storage devices is single, energy storage systems operate independently, and equipment utilization still needs to be improved. Most of the energy storage devices that have been built are only configured and applied for a single problem. They do not effectively meet the needs of users for improving power quality and reducing electricity costs, and do not give full play to the advantages of energy storage devices.

Third, the orderly management and control of random loads such as electric vehicles still need to be improved. The fast charging time of electric vehicles is getting shorter and shorter, the charging power is getting larger and larger, and large-scale charging stations have an increasing impact on the load fluctuation of the power grid. System-level analysis and management of a large number of charging stations within the regional distribution network will effectively improve the impact of user charging behavior on the distribution network.

Fourth, there is a lack of mutual coordination at the distribution network level between the source, grid, load and storage. At this stage, the mutual coordination between source, grid, load and storage is relatively sufficient at the microgrid level, but the mutual coordination and interaction at the distribution network level is still very weak. Source, load and storage basically carry out independent operation control or interact with the power grid according to their own goals. There is no To form an overall effective coordination and cooperation, that is, the potential of flexible regulation of source, load and reservoir has not been fully utilized.

In summary, there is an urgent need to invent a control method suitable for microgrid groups to maximize the consumption of distributed energy, give full play to the regulation potential of flexible loads such as energy storage and electric vehicles, and achieve coordinated control of source, grid, load and storage. Best results.

Contents of the invention

In order to solve the problems existing in the interactive application of source, grid, load and storage in microgrid groups, such as insufficient distributed energy consumption capacity, lack of full exploration of flexible resource regulation potential, and insufficient coordination and interaction capabilities, the present invention provides an AC-DC coordinated interactive micro-system. Control methods for power grid groups.

A control method for an AC and DC coordinated interactive microgrid group, which is applied to a scenario where multiple low-voltage stations are flexibly interconnected to form a microgrid group. The microgrid group has an AC and DC coordinated and interactive function, and the microgrid group adopts an integrated Three-layer collaborative control architecture and three-layer information interaction architecture adopt different control strategies in four main operating modes: online control mode, offline control mode, planned maintenance mode and power grid failure mode.

Further, the microgrid group consists of multiple low-voltage stations in the 10kV medium-voltage AC line. The multiple low-voltage AC stations form a flexible interconnection on the DC side through flexible interconnection devices, and each station has microgrid autonomy. Capability; Each station area is equipped with a microgrid controller, which sends control instructions downward to the adjustable resources in the station area, collects resource information in the station area, and receives control instructions issued by the cloud master station upwards; all The microgrid controller in the Taiwan area establishes communication with a common cloud master station and accepts the unified coordination and deployment of the cloud master station; the Taiwan area includes ordinary AC and DC loads as well as optical, storage and charging flexible loads.

Further, the three-layer collaborative control architecture includes: equipment-level control layer, station area autonomous control layer, and master station coordination control layer;

The equipment-level control layer includes: adjustable resources connected to the flexible interconnection device and its DC output port, and other adjustable resources in the station area;

The self-made control layer in the Taiwan area consists of the microgrid controller receiving the master station instructions and control mode or autonomous strategy to form control instructions and issuing them to adjustable resources;

The master station coordination control layer relies on real-time power consumption data and optimization models to formulate and issue control instructions or receive the needs of the station area, and form and issue control instructions according to the needs.

Further, the three-layer information interaction architecture is a cloud-edge-end integrated three-layer information interaction architecture;

Among them, the end includes: a flexible interconnection device, a primary and secondary standard interface cabinet, and an energy storage vehicle. The flexible interconnection device is responsible for collecting the basic information of the body and the DC equipment information connected in the station area; the primary and secondary standard interface cabinet is responsible for collecting Collect access energy storage vehicle information and access switch information;

The side includes the microgrid controller configured in each station area, which is responsible for collecting end device information, completing the autonomous coordination control function in the station area, transmitting all end device information and status in the station area to the main station, and receiving the information from the main station at the same time. control instructions to form and issue control instructions;

The cloud includes a cloud master station of the microgrid group. The cloud master station is responsible for monitoring station area information and coordinating control between stations, and issuing regulatory instructions to the microgrid controller.

Further, the online control mode is defined as: the power grid is operating normally, the communication between the station area and the cloud master station is normal, normal information interaction, control instruction issuance, reception and execution can be carried out, under the unified coordination and deployment of the cloud master station , to realize the optimal economic operation of each station, the maximum consumption of distributed resources, and the optimization and management of power supply quality.

Further, the offline control mode is defined as: the power grid is operating normally, the communication between the main station and the microgrid controller is abnormal, the main station cannot receive microgrid control information within 15 minutes, and the offline station area relies on the microgrid control of the station area. The network controller completes the microgrid autonomy in the Taiwan area and maximizes local photovoltaic consumption.

Further, the planned maintenance mode is defined as: the main station issues maintenance instructions to a single station area in advance, and the rest of the operations are completed by the microgrid controller and local interface cabinets, using flexible interconnection devices to transfer power to support the local load of the maintenance station area. way to achieve zero power outage maintenance in the Taiwan area.

Furthermore, the grid-side fault mode is defined as: when the medium-voltage side line fails, the cloud master station controls the microgrid controller to promptly remove the relevant station area in the fault section, and completes power mutual assistance through the flexible interconnection device to support the station. load within the area to achieve the shortest possible power outage in the removed station area.

Further, the conventions and constraints of the control strategy are:

1) When the Taiwan area does not need external support, it operates autonomously according to the Taiwan area. When external support is needed, the Taiwan microgrid controller sends a request to the main station, and the main station forms a control command and issues it;

2) Autonomous operation in the Taiwan District includes the following operating modes: a) Economic operation: Line loss optimization in the Taiwan District; b) Low-carbon operation: Prioritize the consumption of clean energy in the Taiwan District; c) Power supply quality optimization: Control of low voltage, harmonics and other electric energy Quality, improve the quality level of power supply;

3) Power mutual assistance between stations includes: a) heavy load transfer mode, which realizes that when one station area is heavily loaded, another station area can transfer power supply and mutual assistance through flexible interconnection; b) zero power outage maintenance mode, realizes the maintenance of station area Zero power outage; c) Cross-region low-carbon operation mode to realize the cross-region consumption of distributed photovoltaics under the situation of large-scale photovoltaic development.

Further, the initial operating conditions, command sending and power matching principles of the microgrid group are:

1) In terms of primary equipment, both AC and DC in the Taiwan area are connected to the grid, the power electronic transformer is the VF node, and the rest are PQ nodes;

2) In terms of secondary equipment, there are n microgrids controlled online, where 1≤n≤5;

3) The master station issues the node voltage range of each station area. The node voltage range of each station area comes from the power flow calculation and state estimation results, or the voltage qualification rate range +7% to -10%, or the manually set range;

4) Microgrid controller uploads: 15 minutes to upload the power demand, AC and DC power supply situation, and load classification supply situation of the station area in 15 minutes. Among them, the AC and DC power supply situation is classified according to the supply stability, which is predefined in TTU. Main network power is level 1, energy storage is level 2, photovoltaic is level 3, and V2G is level 4. The load classification supply situation is graded according to load importance, with important load being level 1, general load being level 2, and interruptible load being level 3. class;

5) The principles of power matching between stations are: priority for a single station area, priority for the opposite 10kV line station area, and priority for power supply-load stability;

6) The main station performs power matching in the following manner: it is sent to the TTU of station A, and station A sends a certain kW power to the DC bus; it is sent to the TTU of station B, and station B absorbs a certain kW power from the DC bus; The flexible interconnection device is controlled by the TTU of each station participating in the matching;

7) The master station switches the control mode of the station area: online and offline control mode;

8) In response to the failure of the flexible interconnection device, pre-make a table of the VF node switching sequence, and when the power electronic transformer fails, switch the online flexible interconnection device in sequence.

This invention is mainly applied to microgrid groups with AC and DC coordination and interaction functions. Based on the three-layer collaborative control architecture of cloud-edge-end integration, it realizes four main modes including online control mode, offline control mode, planned maintenance mode and power grid failure mode. Microgrid group control in operation mode; realizes the optimal decomposition of strategies at the equipment level control layer, station area autonomous control layer, and master station coordination control layer, realizes hierarchical collaborative regulation that does not rely on local side lateral communication, and fully exploits It improves the potential of flexible resource regulation, improves distributed resource consumption capabilities and source network load storage collaborative interaction capabilities, and has the promotion advantages of strong scale scalability and good function reusability.

Description of the drawings

Figure 1 is a three-layer information interaction architecture diagram of cloud-edge-device integration according to the embodiment of the present invention;

Figure 2 is the overall topology diagram of the AC-DC coordinated interactive microgrid group demonstration project in a certain place;

Figure 3 is the control strategy flow chart of online control mode;

Figure 4 is a flow chart of the offline control mode control strategy;

Figure 5 is a flow chart of the planned maintenance mode control strategy taking the T5 station area as an example according to the embodiment of the present invention;

Figure 6 is a flow chart of the grid-side fault mode control strategy taking the T5 station area as an example according to the embodiment of the present invention;

Figure 7 shows the simulation verification results of T5 station area;

Figure 8 shows the simulation verification results of the T4 station area.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present invention.

The present invention is explained by taking a certain AC-DC coordinated interactive microgrid group demonstration project as an example.

This microgrid group builds flexible low-voltage DC interconnection devices on the low-voltage side of five Taiwan areas. It also deploys an on-load capacity-adjusting and voltage-regulating transformer to replace the existing transformer and a power electronics transformer, with the flexible low-voltage DC interconnection device as the core. , build a DC distribution station area of a certain scale and create an active distribution network with flexible switching and mutual power support. The specific topology is shown in Figure 2. The T4 and T5 station areas are led from the 122# and 124# towers of the 10kV Liu 611 line respectively. The T1, T2, T3 and non-interconnected station areas are led from the 74# tower of the 10kV East 14 line. The 4 station areas pass a branch switch connected. T1, T2, and T3 stations are connected through ring main units. The No. 124 tower of the 10kV Liu 611 line is connected to the No. 74 tower of the 10kV East 14 line through a contact switch. T1, T2, T3, T4, and T5 stations form a flexible interconnection through a DC bus. The configuration of photovoltaics, energy storage, charging piles, and flexible interconnection devices in each station area is detailed in Figure 2. The energy storage vehicles are connected through primary and secondary standard interface cabinets. The microgrid group adopts a three-layer collaborative control architecture, including a device-level control layer, a station autonomous control layer, and a master station coordination control layer. The microgrid group adopts a three-layer information interaction architecture, which is a three-layer cloud-edge-end integration. Information interaction architecture is shown in Figure 1.

The control strategies of various control modes in this embodiment will be introduced in detail below.

1. Online control mode

Step 1: The master station first issues the voltage range instructions for each station area during normal operation.

Step 2: The microgrid controller of each station calculates the photovoltaic output power, energy storage, charging pile and load power in the station.

Judgment 1: Determine whether the voltage in the station area exceeds the limit. If so, go to step 3. If not, go to judgment 3.

Step 3: The microgrid controller calculates the reactive power supplement or harmonic supplement command value of the station area.

Judgment 2: Whether the flexible interconnection device and other adjustable converters connected to the wire have excess capacity. If not, raise your hand and ask the main station for help to transfer power. The flexible interconnection device releases capacity and participates in node voltage regulation. If so, proceed to step 4.

Step 4: The microgrid controller issues reactive power compensation or harmonic compensation command values.

Judgment 3: Determine whether the photovoltaic output Ppv is greater than the load demand Pload. If so, enter judgment 4, otherwise enter judgment 9.

Judgment 4: Determine whether the energy storage meets the charging conditions. If so, charge the energy storage, otherwise go to step 5.

Step 5: The microgrid controller raises his hand to inform the cloud master station that it needs to actively transfer power. The cloud master station looks for the power shortage station area. The next step is to enter judgment 5.

Judgment 5: Determine whether there is a power shortage in the non-identical 10kV power supply station area. If so, go to Judgment 6, otherwise go to Judgment 7.

Judgment 6: Determine whether the transfer conditions are met. If so, the cloud master station issues a transferred instruction to the microgrid controller of the transferred station. The microgrid controller controls the received power of the flexible interconnection device to complete the overload transfer. If not, go to judgment 7.

Judgment 7: Check whether there is a power shortage in the same 10kV power supply station area. If so, enter Judgment 8, otherwise the overload transfer cannot be completed.

Judgment 8: Determine whether the transfer conditions are met. If so, the cloud master station issues the transferred instruction to the microgrid controller of the transferred station. The microgrid controller controls the received power of the flexible interconnection device to complete the overload transfer. Otherwise, the reload transfer cannot be completed.

Judgment 9: Does the energy storage meet the conditions for discharge? If so, the energy storage is discharged and the charging pile stops charging. If not, go to step 6.

Step 6: The microgrid controller raises its hand to inform the cloud master station to request power mutual assistance from other stations, and the cloud master station looks for power surplus stations. The next step is to enter judgment 10.

Judgment 10: Determine whether there is power surplus in the non-identical 10kV power supply station area. If so, enter judgment 11, otherwise enter judgment 12.

Judgment 11: Determine whether the conditions for transfer are met. If so, the cloud master station issues a power transfer instruction to the power transfer area microgrid controller, and the microgrid controller controls the flexible interconnection device to transfer power to complete heavy load transfer. If not, go to judgment 12.

Judgment 12: Determine whether there is power surplus in the same 10kV power supply station area. If so, proceed to Judgment 13, otherwise the overload transfer cannot be completed.

Judgment 13: Determine whether the conditions for transfer are met. If so, the cloud master station issues a power transfer instruction to the power transfer area microgrid controller, and the microgrid controller controls the flexible interconnection device to transfer power to complete heavy load transfer. Otherwise, the reload transfer cannot be completed.

The specific control strategy logic diagram is shown in Figure 3.

2. Offline control mode

Take T5 Taiwan District as an example

Step 1: The T5 microgrid controller calculates the photovoltaic output power and load power. The next step is to enter judgment 1.

Judgment 1: Determine whether the photovoltaic output in the Taiwan area is 0. If so, the photovoltaic output will not be output. The next step will be judgment 4. Otherwise, judgment 2 will be entered.

Judgment 2: Determine whether the photovoltaic output is greater than the load power demand. If yes, go to step 2; if not, go to judgment 4.

Step 2: The photovoltaic output is sent to the T5 station area and the charging vehicle is guided to charge. The next step is to enter judgment 3.

Judgment 3: Determine whether the energy storage is fully charged. If it is, the photovoltaic will charge the energy storage; if not, the photovoltaic will send power to the 10kV power grid in reverse direction. After the communication is normal, the microgrid controller will raise its hand and send a power output request to the main station.

Judgment 4: Determine whether the energy storage is discharged. If so, enter judgment 5; if not, the energy storage stops discharging.

Judgment 5: Determine whether the voltage of the energy storage supporting the load is qualified. If so, enter judgment 6, if not, enter energy storage and stop discharging.

Judgment 6: Determine whether the frequency of energy storage supporting load is qualified. If so, the energy storage is discharged to station area 5, otherwise the energy storage stops discharging.

The specific control strategy logic diagram is shown in Figure 4.

3. Planned maintenance mode

1) Take the maintenance of T5 station area as an example

Step 1: The master station issues planned maintenance instructions in advance.

Step 2: The T5 station area microgrid controller calculates the photovoltaic power Ppv5, charging pile power Pv2g5 and DC load power Pload5 in the station area, and reports the calculation results to the main station. The next step is to enter judgment 1.

Judgment 1: Determine whether Ppv5 is greater than Pv2g5+Pload5? If not, go to step 3, if so, go to step 6.

Step 3: The T5 station area microgrid controller requests the station area power mutual assistance from the main station.

Step 4: The microgrid controller of T5 station area calculates the power deficit Pc5=Ppv5-Pv2g5-Pload5 of this station area and reports it to the main station.

Step 5: The master station issues instructions to the microgrid controllers of the stations participating in the mutual assistance of functions, and uses the flexible interconnection device to transfer PC5 power to other stations. Next go to step 8.

Step 6: The photovoltaics in the control area of the microgrid controller in the T5 station area actively support the DC loads and charging piles in the station area. The next step is to enter judgment 2.

Judgment 2: Determine whether the energy storage can be charged? If so, store energy and charge, if not, go to step 7.

Step 7: The microgrid controller of the T5 station area raises its hand to request support from the cloud master station to transfer the redundant PV in the T5 station area to other station areas.

Step 8: The T5 microgrid controller monitors the transformer incoming side current Iac5, and the next step is to enter judgment 3.

Judgment 3: Determine whether Iac5 is less than the breakable value I0. If yes, go to step 9, otherwise go to step 8.

Step 9: The microgrid controller issues a mode switching instruction to the flexible interconnection device, and the flexible interconnection device switches to the V/F control mode.

Step 10: The microgrid controller sends a command to disconnect the transformer outlet switch to the primary and secondary interface cabinets, and the primary and secondary interface cabinet controls to disconnect the transformer outlet switch.

Step 11: Enter planned maintenance. The next step is to enter judgment 4.

Judgment 4: Determine whether the maintenance is completed. If yes, go to step 12; if not, go to step 11.

Step 12: The microgrid controller sends a request to the main station to inform that the maintenance has been completed.

Step 13: The master station issues a command to restore the normal state to the microgrid controller. The microgrid controller sends a command to close the transformer outlet switch to the primary and secondary interfaces. The primary and secondary interfaces forward the command to check the synchronous closing transformer outlet switch.

Step 14: The low-voltage flexible interconnection device switches to P/Q mode and returns to the main station control state. The maintenance is completed and the system is restored.

The specific control strategy logic diagram is shown in Figure 5.

The maintenance of T4 and other station areas is similar to the control strategy of T5 station area (as shown in Figure 6). The principle followed is that other station areas support their local load power, and then disconnect the AC side power supply to achieve zero power outage maintenance. This No further details will be given here, but the control strategies are within the scope of patent protection.

4. Grid side failure mode

Take the AC 10kV side fault in T5 Taiwan area as an example

Step 1: A phase-to-phase short circuit fault occurs on the medium-voltage side of the power grid. The photovoltaic anti-islanding protection in the T5 station area is activated and the photovoltaic AC grid connection switch is immediately disconnected.

Step 2: Set the active power adjustment command of the flexible interconnection device to zero.

Step 3: The T5 station microgrid controller disconnects the low-voltage side circuit breaker and DC bus switch of the transformer in this station through the primary and secondary standard interface cabinet.

Step 4: The T5 station area microgrid controller switches the energy storage vehicle into the V/F working mode through the primary and secondary standard interface cabinets, supports the station area voltage, and discharges to support the AC load in the station area.

Step 5: The microgrid controller of the T5 station controls the photovoltaic AC grid-connected switch to close and connect to the grid, and the photovoltaic participates in supporting the load of the station.

Judgment 1: Determine whether the energy storage vehicle output + photovoltaic output is greater than the station load. If so, go to step 9, otherwise go to step 6.

Step 6: The T5 microgrid controller controls the flexible interconnection device to switch to V/F mode, closes the DC bus switch at the same time, and requests power mutual assistance from the master station. The cloud master station looks for power surplus station areas. The next step is to enter judgment 2.

Judgment 2: Whether there is power surplus in the non-identical 10kV power supply station area. If so, go to judgment 3, otherwise go to judgment 4.

Judgment 3: Determine whether the transfer conditions are met. If so, the cloud master station issues a transfer power instruction to the power transfer area microgrid controller. The microgrid controller controls the flexible interconnection device to transfer power and enters step 7. If not, go to judgment 4.

Judgment 4: Whether there is power surplus in the same 10kV power supply station area. If so, enter judgment 5, otherwise power mutual assistance cannot be completed.

Judgment 5: Determine whether the conditions for transfer are met. If so, the cloud master station issues a power transfer instruction to the power transfer area microgrid controller, and the microgrid controller controls the flexible interconnection device to transfer power, and enters step 7. Otherwise, power mutual aid cannot be completed.

Step 7: Wait for the grid fault to clear.

Judgment 6: Determine whether the power grid fault has been cleared. If yes, go to step 8, otherwise go to step 7.

Step 8: The T5 station area microgrid controller controls the low-voltage flexible interconnection device to switch to P/Q mode. The T5 station area microgrid controller passes the first and second standard interface cabinet inspection and closes the low-voltage outlet circuit breaker of the station area transformer at the same time. Failure Recovery complete.

Step 9: The T5 microgrid controller controls the flexible interconnection device to switch to V/F mode, raises hands to the cloud master station, applies to transfer the photovoltaic surplus power, and closes the DC bus switch at the same time. The cloud master station looks for power shortage stations. The next step is to enter judgment 7.

Judgment 7: Determine whether there is a power shortage in the non-identical 10kV power supply station area? If so, go to judgment 8, otherwise go to judgment 9.

Judgment 8: Whether the conditions for transfer are met. If yes, go to step 10, otherwise go to judgment 9.

Judgment 9: Determine whether there is a power shortage in the same 10kV power supply station area? If so, proceed to judgment 10, otherwise the photovoltaic surplus power transfer cannot be completed.

Judgment 10: Determine whether the conditions for transfer are met. If so, proceed to step 10; otherwise, the photovoltaic surplus power transfer cannot be completed.

Step 10: The cloud master station issues the transferred instruction to the microgrid controller of the transferred station area, and the microgrid controller controls the flexible interconnection device to complete the transfer of photovoltaic surplus power in the T5 station area. Recovery complete. The specific control strategy logic diagram is shown in Figure 6.

Simulation

In order to effectively verify the specific implementation effect, according to the specific implementation method, a medium and low-voltage active distribution network with AC and DC coordinated interactive microgrids is relied on, relying on the RT-LAB real-time simulation system, to build a discrete simulation model to comprehensively verify both fault and maintenance. control strategy in this scenario.

(1)Power grid failure mode

In the simulation, the 10kV power grid fault of Taiwan District T4 and T5 occurred at 0.438s. In this scenario, when the grid side of Taiwan District T4 and Taiwan District T5 failed, the switch on the grid side was disconnected and entered off-grid operation. The flexibility of Taiwan District T4 The interconnection device changed from constant power mode to AC voltage mode to supply AC loads in the Taiwan area, and the T4 power electronic transformer in the Taiwan area stopped operating. The station area T1 changes from constant power mode to constant voltage mode to control the total DC bus voltage to maintain a stable 750V. The DC loads of station areas T4 and T5 are all powered by the main DC bus. Station area T2 and T3 are still running in constant power mode.

After the power grid faults in Taiwan District T4 and T5 were restored, the power electronic transformer in Taiwan District T4 resumed operation, the flexible interconnection device in Taiwan District T1 was converted from constant voltage mode to constant AC power mode, and Taiwan District T5 was converted from AC voltage mode to constant power mode. Track the grid voltage, control its AC output voltage to be consistent with the grid voltage amplitude, frequency, and phase, and then close the AC side switch of the station area. The overall system of T5 in the station area will switch from off-grid to grid-connected and the overall system will resume normal operation. In the simulation, the 10kV power grid fault recovered at 0.76s, the station area T5 was ready to connect to the grid, and the station area T5 flexible interconnection device completed the off-grid connection transition at 0.789s. The simulation results are displayed with the relevant waveforms of station area T5, as shown in Figure 7. They are consistent with the expected results, proving the correctness of the implementation method.

(2) Maintenance mode

In the simulation, the main station issued a maintenance control command at 0.832s, and the T4 power electronic transformer in the Taiwan area stopped running. The flexible interconnection devices in the other Taiwan areas independently controlled the magnitude and direction of their power flow, so that the power and current on their respective grid sides gradually reduced to 0. After the grid-side port power meets the requirements, the grid-side switches are turned off respectively, and the constant AC power mode is converted to the AC voltage mode to enter the off-grid state. At this time, the DC bus of each station area is supported by energy storage or photovoltaics.

In the simulation, the maintenance ended at 0.957s. When the power grid maintenance was completed, the master station issued a control command, and the Taiwan District T4 power electronic transformer was put into operation to support the total DC bus voltage. All flexible interconnection devices tracked the grid voltage and controlled its grid-side output. After the voltage is synchronized with the grid voltage, the grid-side switches are closed respectively, and the AC voltage mode is converted to the constant power mode, and then transferred to grid-connected operation, and the system returns to normal operation. The simulation results are displayed with the relevant waveforms of station area T4, as shown in Figure 8. They are consistent with the expected results, proving the correctness of the implementation method.

The invention has the following advantages:

1. The present invention realizes the policy optimization and decomposition of the equipment level control layer, the station autonomous control layer, and the master station coordination control layer, realizes hierarchical collaborative regulation that does not rely on local side lateral communication, and fully taps the potential of flexible resource regulation. , which improves distributed resource consumption capabilities and source network load storage collaborative interaction capabilities.

2. Based on the analysis of the above embodiments, it can be concluded that the control method of the present invention is universal and rational, can be applied in microgrid groups with AC and DC coordination and interaction functions, has strong scalability and reusable functions. Good promotion advantages.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. All are covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (10)

1. A control method of an alternating current-direct current coordinated interaction micro-grid group is characterized by being applied to a scene that a plurality of low-voltage stations are flexibly interconnected to form the micro-grid group, the micro-grid group has an alternating current-direct current coordinated interaction function, the micro-grid group adopts an integrated three-layer cooperative control architecture and a three-layer information interaction architecture, and different control strategies are adopted in four main operation modes of an online control mode, an offline control mode, a planned maintenance mode and a grid fault mode.

2. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the micro-grid group consists of a plurality of low-voltage transformer areas in a 10kV medium-voltage alternating-current circuit, the plurality of low-voltage alternating-current transformer areas form flexible interconnection on a direct-current side through a flexible interconnection device, and each transformer area has micro-grid autonomous capability; each station area is provided with a micro-grid controller, and is used for issuing control instructions to adjustable resources in the station area downwards, collecting the resource information in the station area and receiving the control instructions issued by the cloud master station upwards; the micro-grid controllers of all the transformer areas establish communication with a common cloud master station, and receive unified coordination allocation of the cloud master station; the platform area contains common AC/DC load and light, storage and charging flexible load.

3. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the three-layer cooperative control architecture comprises: a device-level control layer, a district autonomous control layer and a master station coordination control layer;

wherein the device level control layer comprises: the flexible interconnection device is connected with adjustable resources and other adjustable resources in the station area through the direct current output port;

the micro-grid controller receives a main station instruction and a control mode or an autonomous strategy forming control instruction from the platform area homemade control layer and issues the control instruction to the adjustable resource;

the main station coordination control layer relies on real-time power generation data, relies on an optimization model to form a demand for issuing a regulation and control command or receiving a station area, and forms a control command for issuing according to the demand.

4. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the three-layer information interaction architecture is a cloud-side-end integrated three-layer information interaction architecture;

wherein the end comprises: the system comprises a flexible interconnection device, a secondary standard interface cabinet and an energy storage vehicle, wherein the flexible interconnection device is responsible for collecting basic information of a body and direct current equipment information connected in a local area; the secondary standard interface cabinet is used for collecting information of the access energy storage vehicle and information of the access switch;

the side comprises a micro-grid controller configured for each area, is responsible for collecting terminal equipment information, completes an autonomous coordination control function in the area, transmits all terminal equipment information and states in the area to a master station, and simultaneously receives a regulation command of the master station to form a issuing control command;

the cloud comprises Yun Zhuzhan of a micro-grid group, and a cloud master station is responsible for monitoring platform area information and coordinated control among the platforms and sends out regulation and control instructions to a micro-grid controller.

5. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the online control mode is defined as: the power grid normally operates, communication between the station areas and the cloud master station is normal, normal information interaction, control instruction issuing, receiving and executing can be performed, and under unified coordination and allocation of the cloud master station, the functions of economic optimal operation, distributed resource maximized consumption and power supply quality optimization management among the station areas are realized.

6. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the offline control mode is defined as: the power grid normally operates, communication between the master station and the micro-grid controller is abnormal, the master station cannot receive information of micro-grid control within 15 minutes, and the off-line platform area finishes the autonomous of the micro-grid in the platform area by means of the micro-grid controller of the platform area, so that the local photovoltaic maximum absorption is realized.

7. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the planned overhaul mode is defined as: the main station issues maintenance instructions to a single platform area in advance, other operations are completed by the micro-grid controller and the local interface cabinet, and the flexible interconnection device is utilized to transfer power to support a mode of maintaining the local load of the platform area, so that the zero power failure maintenance of the platform area is realized.

8. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the grid-side failure mode is defined as: the medium-voltage side line breaks down, the cloud master station controls the micro-grid controller to timely cut off relevant transformer areas in the fault section, and the transformer areas are mutually balanced through the flexible interconnection device, so that loads in the transformer areas are supported, and the shortest power failure of the cut-off transformer areas is realized.

9. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the conventions and constraints of the control strategy are:

1) When the platform area does not need external support, the platform area micro-grid controller automatically operates according to the platform area, and when the external support is needed, the platform area micro-grid controller sends a request to the master station, and the master station forms a control instruction to issue;

2) The autonomous operation of the platform area comprises the following operation modes: a) Economic operation: optimizing the line loss of the transformer area; b) Low carbon operation: preferentially absorbing clean energy in the station area; c) Optimizing power supply quality: the electric energy quality such as low voltage, harmonic wave and the like is treated, and the power supply quality level is improved;

3) Inter-station power comprises: a) A heavy load transfer mode, wherein when a certain area is heavy load, another area can be mutually used by flexible interconnection transfer; b) The zero power failure maintenance mode realizes the zero power failure of a maintenance platform area; c) And under the condition of large photovoltaic heat, the cross-platform low-carbon operation mode of the cross-platform region realizes the cross-platform region absorption of the distributed photovoltaic.

10. The method for controlling an ac/dc coordinated interactive micro grid group according to claim 1, wherein:

the initial running conditions, instruction sending and power matching principles of the micro-grid group are as follows:

1) In the aspect of primary equipment, the alternating current and the direct current of the transformer area are all connected in a grid mode, the power electronic transformer is a VF node, and the rest is a PQ node;

2) In the aspect of secondary equipment, n micro-grid control lines are arranged, wherein n is more than or equal to 1 and less than or equal to 5;

3) The master station transmits node voltage ranges of each platform region, wherein the node voltage ranges of each platform region are derived from power flow calculation and state estimation results, or voltage qualification rate ranges of +7% to-10%, or manually set ranges;

4) Uploading by a micro-grid controller: the power demand of the power supply area, the grading supply condition of the AC/DC power supply and the grading supply condition of the load are sent up for 15min, wherein the grading supply condition of the AC/DC power supply is graded according to the supply stability, the power of an AC main network is predefined in TTU to be 1 grade, the energy storage is 2 grade, the photovoltaic is 3 grade, the V2G is 4 grade, the grading supply condition of the load is graded according to the importance of the load, the important load is 1 grade, the general load is 2 grade, and the interruptible load is 3 grade;

5) The principle of inter-station power matching is as follows: preferentially meeting a single station area, preferentially selecting a side 10kV line station area, preferentially meeting power supply-load stability;

6) The main station performs the power matching in the following manner: the power is issued to a TTU of an A station area, and the A station area sends out certain kW power to a direct current bus; the power is sent to a TTU of a B station area, and the B station area absorbs certain kW power from a direct current bus; the TTU of each platform region participating in the matching controls the flexible interconnection device to execute;

7) Switching of a master station to a station control mode: an online and offline control mode;

8) And (3) prefabricating a table of VF node switching sequences aiming at the faults of the flexible interconnection device, and switching the flexible interconnection device on line according to the sequences when the power electronic transformer fails.