CN104852404A - Micro-grid system of grid-connected island power grid - Google Patents

Abstract

The invention discloses a micro-grid system of a grid-connected sea-island power grid, which includes an energy storage system connected to the AC bus of the sea-island power grid through a step-up transformer; The solid-state switch is connected to the load transformer of the distribution network; the diesel power generation system, which is used as the main power supply when the microgrid system is in an island operation; the wind power generator system, which includes asynchronous wind power generators, and the output side of the stator of the asynchronous wind power generators is connected in series Back-to-back converters, the output of the back-to-back converters is boosted and then sent to the AC bus of the island power grid; the optical fiber communication network, erecting optical fibers along the transmission and distribution lines in the island power grid, and installing them at each power point, load point and control terminal The optical fiber communication transceiver device forms the optical fiber communication network of the island power grid; the micro grid energy coordination optimization and control system collects the operating data of the island power grid in real time through the optical fiber communication network and issues control instructions.

Description

A microgrid system of grid-connected island power grid

technical field

The invention belongs to the technical field of engineering application of micro-grid technology, and in particular relates to a micro-grid system of a grid-connected sea-island power grid.

Background technique

my country's islands are rich in resources, and most of the islands and surrounding sea areas are rich in renewable resources, such as wind energy, solar energy, wave energy, and tidal current energy. Vigorously developing island power grids and building an efficient and clean island energy system can not only ensure the stable power supply of islands, but also have important significance for protecting the marine environment and promoting energy conservation and emission reduction. my country promulgated the "Island Protection Law of the People's Republic of China" at the end of 2009, and it has clearly pointed out that "in the development and construction of inhabited islands, priority should be given to the use of renewable energy such as wind energy, ocean energy, and solar energy, as well as rainwater harvesting, seawater desalination, and sewage regeneration." Utilize other technologies".

The production and living of island residents, coastal defense and military affairs, and the development of renewable energy on islands depend on the construction of reliable and stable island power grids. At present, island power grids are generally divided into grid-connected island power grids and independent island power grids, which have the following problems:

There is no electrical connection between the independent island power grid and the external large power grid, and diesel generators or gas turbines are generally used as the main power supply for the island's power supply; since the independent island power grid has no power transmission channel, the development scale of wind power, photovoltaic and other renewable energy Limited by maximum load on the island.

The grid-connected island power grid is connected to the external large power grid through submarine cables or overhead lines. The abundant renewable energy such as wind power and photovoltaics on the island can be sent to the large power grid through submarine cables or overhead lines while meeting the power needs of the island. It is suitable for large-scale development and utilization of renewable energy such as offshore wind farms around islands. At present, my country generally adopts grid-connected power access for islands with large areas, many residents, and important coastal defense positions. The stability of power supply is mainly affected by the failure rate of submarine cables or overhead lines.

The maintenance of the submarine cables and overhead lines of the island power grid is difficult and the cycle is long. Especially in the windy winter weather, the failure of the island power grid's sending line often leads to the interruption of power supply for several weeks, which not only affects the normal production and life of the military and civilians on the island, but also It has also caused a great waste of renewable energy such as wind power and photovoltaics on the island.

Therefore, for the grid-connected island power grid, it is necessary to carry out micro-grid construction, so that the island power grid can become a multi-characteristic power source/load unit that can be flexibly and quickly connected to/exited from the large power grid, and realize the stability of the island power grid in both grid-connected and isolated modes. operation, avoiding the dependence of the island power grid on submarine cables or overhead lines, improving the reliability and stability of the island power grid, and at the same time providing a strong power grid transmission channel for the island's abundant renewable energy.

For the construction of grid-connected island microgrid, two methods can be adopted: new microgrid and microgrid transformation of the original grid. The grid-connected island power grid belongs to the actual business area of the power grid. The construction of a new micro-grid will not only lead to unnecessary abandonment of the original grid lines and equipment, but also cause a huge amount of investment and engineering volume. On the basis of the original power grid lines and equipment of the island power grid, the micro-grid engineering transformation can effectively reduce the project scale and shorten the construction period of the micro-grid.

Contents of the invention

Aiming at the objective requirement of guaranteeing the high-quality and high-reliability electric energy supply of the island grid, the present invention proposes a microgrid system of the grid-connected island grid. The system retains the original grid structure and equipment of the grid-connected island grid , completed the large-scale project access of energy storage, photovoltaic, wind power and other types of distributed power sources, the active regulation of grid loads, and the optimization and coordination control of multi-type energy sources in island power grids, and realized the stable operation of grid-connected/isolated dual-modes of island power grids.

To achieve the above object, the specific scheme of the present invention is as follows:

A micro-grid system of a grid-connected sea-island power grid, comprising:

An energy storage system, the energy storage system is connected to the AC bus of the island power grid through a step-up transformer;

Distribution network load system, the distribution network load system includes user loads, the user loads are connected to the low-voltage side of the distribution network load transformer through fast solid-state switches, and the high-voltage side of the distribution network load transformer is connected to the AC distribution network of the island power grid ;

Diesel power generation system, which is used as the main power source when the microgrid system of the island power grid is operating in an isolated state; the diesel power generation system includes diesel generator set A and diesel generator set B, and diesel generator set A is connected to the island power grid through the distribution network load transformer In the low-voltage distribution network, the diesel generator set B is connected to the AC bus of the island power grid through a step-up transformer to participate in the AC bus voltage stability control during the island operation of the island power grid;

A wind power generator system, which includes an asynchronous wind power generator set, the output side of the stator of the asynchronous wind power generator set is connected in series with back-to-back converters to realize low-voltage ride-through and reactive power control of the traditional asynchronous wind power generator set, the back-to-back converter The output side of the inverter is boosted and then sent to the AC bus of the island power grid;

Optical fiber communication network, erecting optical fibers along the power transmission and distribution lines in the island power grid, installing optical fiber communication transceiver devices at preset points of the power transmission and distribution lines, forming an optical fiber communication network of the island power grid;

Micro-grid energy coordination optimization and control system, which collects the operating data of the island power grid in real time through the optical fiber communication network, and issues operation control instructions to each operating equipment in the island power grid, so as to realize the stable operation of the grid-connected/island dual-mode of the island power grid, dual Mode switching is smooth.

When the energy storage system includes several types of hybrid energy storage subsystems, each type of energy storage subsystem is connected to the low-voltage side of the step-up transformer after converging through a branch.

The back-to-back converter includes a machine-side converter and a grid-side converter, the two are connected in parallel through a DC bus, the AC side of the machine-side converter is connected to the generator stator, and the AC side of the grid-side converter is connected to The power grid and the DC bus are connected to the Crowbar circuit to realize the low-voltage ride-through of the generator set, and the machine-side converter can provide reactive power for the start-up of the wind turbine, so that the traditional squirrel-cage asynchronous wind turbine has the ability to participate in the microgrid. Ability to run modally.

Both the machine-side converter and the grid-side converter adopt a three-phase half-bridge VSR topology.

The energy storage system, the diesel power generation system, and the energy coordination optimization and control system of the microgrid all adopt a container structure.

The island power grid AC bus is connected to the external power grid through a submarine cable, and a PCC point switch is provided between the island power grid and the external power grid; when the submarine cable connected to the island power grid and the external power grid fails, the PCC point switch is disconnected, and the island power grid is Grid-connected mode to island mode.

When the island grid is in the transient process of grid-connected/island dual-mode switching or is operating in an island, if the power supply is insufficient, the micro-grid energy coordination optimization and control system controls the load of the island grid by controlling fast solid-state switches. Quick switch.

The beneficial effects of the present invention are:

(1) Through the transformation of the microgrid system of the grid-connected island grid, the grid-connected island grid has the ability to operate in both grid-connected and isolated modes, which enhances the reliability and stability of the power supply of the island grid. It provides a stable and strong grid transmission channel for the island's abundant renewable energy.

(2) The grid-connected island grid microgrid system retains the original lines and equipment of the island grid, and there is no repetitive grid equipment construction in the microgrid transformation process, which reduces the scale of the microgrid project, reduces investment costs, and shortens the construction period .

(3) The diesel generator set is installed on the load side of the distribution network. When the island microgrid is running in isolation, the diesel generator set can provide power supply for the load of the island grid nearby, reducing the loss of power transmission.

(4) By installing a solid-state fast switch on the low-voltage side of the distribution network transformer, not only can the fast and accurate management of the load of the island power grid be realized, but also the impact on the solid-state fast switch during the switching process of the transformer can be avoided.

(5) By connecting the back-to-back converter on the output side of the stator of the traditional squirrel-cage asynchronous wind turbine, the asynchronous wind turbine has reactive power control and low voltage ride-through capability, so that it can participate in the operation control of the microgrid, and It solves the problem of reactive power impact on the grid caused by the grid-connected start of asynchronous wind turbines.

Description of drawings

Figure 1 is a schematic diagram of the microgrid system structure of the island power grid;

Fig. 2 is a structural schematic diagram of a modified squirrel-cage asynchronous wind turbine;

Fig. 3 is a structural diagram of the grid-side/micro-grid side converter.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

The microgrid system of the grid-connected sea-island power grid of the present invention builds an energy storage system, a diesel power generation system, a micro-grid energy coordination optimization and control system, and an optical fiber communication network on the basis of the original grid-connected sea-island power grid architecture. Power grid transformation and asynchronous wind turbine transformation.

As shown in Figure 1, the microgrid construction of the grid-connected island power grid mainly involves the transformation of wind turbines, the construction of diesel power generation systems, the construction of energy storage systems, the transformation of distribution networks, the construction of microgrid energy coordination optimization and control systems, and optical fiber communication. Network construction, etc.

A micro-grid system of a grid-connected sea-island power grid, comprising:

An energy storage system, the energy storage system is connected to the AC bus of the island power grid through a step-up transformer;

Distribution network load system, the distribution network load system includes user loads, the user loads are connected to the low-voltage side of the distribution network load transformer through fast solid-state switches, and the high-voltage side of the distribution network load transformer is connected to the AC distribution network of the island power grid ;

Diesel power generation system, which is used as the main power source of the island micro-grid system when it is operating in an isolated manner; the diesel power generation system includes diesel generator set A and diesel generator set B, and diesel generator set A is connected to the low-voltage distribution network of the island power grid through the distribution network load transformer. Power grid, diesel generator set B is connected to the AC bus of the island power grid through a step-up transformer to participate in the AC bus voltage stability control when the island power grid is running in isolation;

A wind power generator system, which includes an asynchronous wind power generator set, the output side of the stator of the asynchronous wind power generator set is connected in series with back-to-back converters to realize low-voltage ride-through and reactive power control of the traditional asynchronous wind power generator set, the back-to-back converter The output side of the inverter is boosted and then sent to the AC bus of the island power grid;

Optical fiber communication network, erecting optical fibers along the power transmission and distribution lines in the island power grid, installing optical fiber communication transceiver devices at preset points of the power transmission and distribution lines, forming an optical fiber communication network of the island power grid;

Micro-grid energy coordination optimization and control system, which collects the operating data of the island power grid in real time through the optical fiber communication network, and issues operation control instructions to each operating equipment in the island power grid, so as to realize the stable operation of the grid-connected/island dual-mode of the island power grid, dual Mode switching is smooth.

In the transformed island microgrid engineering system, the energy storage system used to undertake tasks such as smooth regulation of renewable energy power, emergency power/energy support, and grid power/energy control in the microgrid is connected to the island grid through a step-up transformer. AC bus. The energy storage system can adopt multi-type sub-hybrid energy storage systems, so as to improve the comprehensive characteristics of the energy storage system in terms of power, energy, and cycle life. Different types of energy storage systems are controlled by their respective energy storage converters and connected through new transformers. Island power grid AC bus. If the energy storage system adopts a multi-type hybrid energy storage method, the low-voltage side of the step-up transformer adopts a multi-branch structure, and the branches of various energy storage systems are connected to the low-voltage side of the step-up transformer after confluence.

Due to the limited energy storage capacity of the energy storage system, diesel generator sets are generally selected as the main power supply for microgrid island operation. The construction of diesel power generation system adopts new diesel generator set B and diesel generator set A in the island power grid. Diesel generator set B is connected to the AC bus of the island power grid through a new transformer, and diesel generator set A is connected to the load side of the island power grid. Diesel generator set A is the main power source when the island power grid operates in isolation. It can be connected to the load side nearby to meet the load power demand, which can reduce the power transmission loss when the island power grid operates in an isolated manner. Its capacity should be equivalent to the load capacity of the island power grid. Diesel generator set B is connected to the AC bus of the island power grid to participate in the AC bus voltage stability control when the island power grid operates in isolation.

The wind turbines connected to the grid-connected island grid are generally direct-drive permanent magnet synchronous wind turbines, double-fed wind turbines and squirrel-cage asynchronous wind turbines. Direct-drive permanent magnet synchronous wind turbines and double-fed wind turbines do not need to be modified in the microgrid because they have low-voltage ride-through capabilities and active and reactive power adjustment capabilities. For squirrel-cage asynchronous wind turbines, since they do not have low-voltage ride-through capability and need to absorb a large amount of reactive power from the grid when they are connected to the grid, they should be modified to have the ability to participate in the operation and control of the micro-grid. The scheme adopted is: connect the back-to-back converter in series on the output side of the stator of the asynchronous wind turbine, the back-to-back converter is composed of the machine-side converter and the grid-side converter; the machine-side converter and the grid-side converter Both adopt the three-phase half-bridge VSR topology, and the two are connected in parallel through the DC bus; the AC side of the machine-side converter is connected to the stator of the generator, the AC side of the grid-side converter is connected to the power grid, and the DC bus is connected to the Crowbar circuit. To realize the low voltage ride through of the generator set, the machine-side converter can provide reactive power for the start-up of the wind turbine.

In order to solve the problem of active load control of the island power grid, fast solid-state switches are connected in series on the low-voltage side of the distribution network load transformer to realize switching management of the island power grid load during the transformation and construction of the distribution network. Connecting the fast solid-state switch to the low-voltage side of the transformer can avoid the inrush current impact generated during the switching process of the transformer, thereby reducing the capacity demand for the fast solid-state switch and reducing the transformation cost.

In order to realize the rapid and accurate collection of operating information of the island power grid and the real-time issuance of remote control instructions, optical fibers are erected along the transmission and distribution lines in the island power grid, and optical fiber communication transceiver devices are installed at preset points of the power transmission and distribution lines to provide a comprehensive solution for the island power grid. Provide channels for real-time data monitoring of various operating equipment and rapid release of control information, and complete the construction of the optical fiber communication network of the island power grid.

Choose a suitable location in the island to build a micro-grid energy coordination optimization and control system. This system is the center of the operation and control of the island micro-grid. It is mainly composed of multiple types of servers, workstations, communication switches, vertical isolation and encryption devices, and energy optimization coordination management software. It is used for real-time collection of micro-grid operation data, operation strategy optimization, and remote control command issuance, and then realizes the functions of operating mode switching, emergency control, renewable energy power smoothing, and economic operation of island micro-grids.

Energy storage systems, diesel power generation systems, and microgrid energy coordination optimization and control systems can adopt container structures to save civil investment, shorten system installation cycles, and facilitate equipment transportation and transfer.

Through the above-mentioned construction, on the basis of retaining the original grid structure and grid equipment of the island grid, the construction of energy storage system, the transformation of wind turbine connection, the construction of diesel generator set, the transformation of distribution network, the construction of communication network and the energy coordination of microgrid have been completed. Optimization and control system construction, etc., enable the island power grid to have the stable operation capability of the grid-connected/island dual mode.

As shown in Figure 2, the back-to-back converter is connected in series between the output side of the stator of the squirrel-cage asynchronous wind turbine and the step-up transformer, and the back-to-back converter is composed of a machine-side converter and a grid-side converter. The generator-side converter and the grid-side converter are connected in parallel through the DC bus. Among the back-to-back converters, the grid-side converter operates in the P/Q mode to control the stability of the DC bus voltage; the machine-side converter operates in the V/F mode to provide the stator of the squirrel-cage asynchronous wind turbine. Stable three-phase AC voltage. When the squirrel-cage asynchronous wind turbine is started, its reactive power demand is provided by the machine-side converter. Due to the DC decoupling effect of the DC bus, the grid-side converter can independently operate in the state of unity power factor, which solves the problem of squirrel-cage asynchronous wind turbines. The problem of reactive power impact on the island power grid when the asynchronous wind turbine starts. The Crowbar circuit connected in parallel to the DC bus is used to solve the low voltage ride-through problem of wind turbines during the transient process of island grid connection/island dual mode switching.

The back-to-back converter is composed of a generator-side converter and a grid-side converter. Both the machine-side converter and the grid-side converter adopt a three-phase half-bridge VSR topology, and the two are connected in parallel through a DC bus. As shown in Figure 3, both the grid-side converter and the micro-grid side converter adopt the three-phase half-bridge VSR topology. The drains of the power switch tubes G1, G3, and G5 are connected together to the positive pole of the DC side capacitor C1, and the sources of the power switch tubes G1, G3, and G5 are respectively connected to the drains of the power switch tubes G2, G4, and G6. The sources of the power switch tubes G2, G4, and G6 are connected together to the negative pole of the DC side capacitor C2. The freewheeling diodes D1, D3, D5, D2, D4, and D6 are connected in antiparallel between the drain and the source of each power switch tube respectively. L1, L2, and L3 are the filter inductors on the AC side. Through the on-off control of the above switching tubes, the fast and flexible conversion of the rectification state and inverter state of the converter and the fast switching of the DC side voltage and the active/reactive power of the AC side can be realized. Precise control.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (7)

1. a micro-grid system for grid type island electrical network, is characterized in that, comprising:

Energy-storage system, described energy-storage system is by step-up transformer access island electrical network ac bus;

Distribution network load system, described distribution network load system comprises customer charge, and customer charge is connected with distribution network load step down side by fast solid-state switches, described distribution network load high voltage side of transformer access island electrical network AC distribution net;

Diesel generating system, main power source when it is in islet operation as island microgrid system; Described diesel generating system comprises diesel generating set A and diesel generating set B, diesel generating set A accesses island electrical network low-voltage network through distribution network load transformer, the ac bus Voltage Stability Control of diesel generating set B when step-up transformer access island electrical network ac bus participates in island electrical network islet operation;

Wind powered generator system, it comprises asynchronous wind driven generator group, the stator outlet side series connection access back-to-back converter of asynchronous wind driven generator group, to realize low voltage crossing and the Reactive Power Control of conventional asynchronous wind turbine generator, described back-to-back converter outlet side delivers to island electrical network ac bus after boosting;

Fiber optic communication network, along electric line fiber plant in the electrical network of island, at the preset points installing optical fibres transceiver communication device of electric line, forms island electrical network fiber optic communication network;

Microgrid energy coordination optimization and control system, it carries out collecting in real time of island operation of power networks data through fiber optic communication network, and assign operation control command to each operational outfit in the electrical network of island, realize island electrical network grid-connected/the double mode stable operation of isolated island, double modely to take over seamlessly.

2. the micro-grid system of a kind of grid type island as claimed in claim 1 electrical network, is characterized in that, when described energy-storage system comprises some class hybrid energy-storing subsystems, accesses step-up transformer low voltage side after each class energy storage subsystem is respectively confluxed by a branch road.

3. the micro-grid system of a kind of grid type island as claimed in claim 1 electrical network, it is characterized in that, described back-to-back converter comprises pusher side current transformer and net side converter, in parallel by DC bus between pusher side current transformer with net side converter, pusher side AC side of converter is connected with asynchronous wind driven generator group stator, net side converter AC access island electrical network ac bus, DC bus place access Crowbar circuit.

4. the micro-grid system of a kind of grid type island as claimed in claim 3 electrical network, is characterized in that, described pusher side current transformer and net side converter all adopt three-phase half-bridge VSR topological structure.

5. the micro-grid system of a kind of grid type island as claimed in claim 1 electrical network, it is characterized in that, described energy-storage system, diesel generating system and microgrid energy coordination optimization and control system all adopt container-like structure.

6. the micro-grid system of a kind of grid type island as claimed in claim 1 electrical network, is characterized in that, described island electrical network ac bus accesses external electrical network by submarine cable, is provided with PCC point switch between island electrical network and external electrical network; When the submarine cable that island electrical network is connected with external electrical network breaks down, PCC point switch disconnects, and island electrical network transfers island mode to by grid-connect mode.

7. the micro-grid system of a kind of grid type island as claimed in claim 1 electrical network, it is characterized in that, when island electrical network in the transient process of the double mode switching of grid-connected/isolated island or islet operation time, if there is the situation of electric power undersupply, described microgrid energy coordination optimization and control system carry out quick-switching by controlling fast solid-state switches to island network load.