[0033] The present invention will be further described below in conjunction with the drawings and embodiments:
[0034] The microgrid system of the grid-connected island grid of the present invention constructs an energy storage system, a diesel power generation system, a microgrid energy coordination optimization and control system, and an optical fiber communication network on the basis of the original grid-connected island grid architecture. Power grid transformation and asynchronous wind turbine transformation.
[0035] Such as figure 1 As shown, the construction of a microgrid for the grid-connected island grid mainly involves wind turbine transformation, diesel power generation system construction, energy storage system construction, distribution network transformation, microgrid energy coordination optimization and control system construction, and optical fiber communication network construction, etc. content.
[0036] A microgrid system of a grid-connected island power grid, including:
[0037] An energy storage system, which is connected to the AC bus of the island power grid through a step-up transformer;
[0038] 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 island power grid AC distribution network ;
[0039] Diesel power generation system, which is used as the main power source when the island microgrid system is in island operation; the diesel power generation system includes diesel generator set A and diesel generator set B. Diesel generator set A is connected to the low-voltage distribution network of the island power grid via the load transformer of the distribution network. In the power grid, the diesel generator set B is connected to the AC bus of the island power grid via a step-up transformer to participate in the AC bus voltage stability control of the island power grid during island operation;
[0040] A wind turbine system includes an asynchronous wind turbine, the stator output side of the asynchronous wind turbine is connected in series with a back-to-back converter to realize the low voltage ride-through and reactive power control of the traditional asynchronous wind turbine. The back-to-back converter The output side of the converter is boosted and sent to the AC bus of the island power grid;
[0041] Optical fiber communication network, in the island power grid along the transmission and distribution lines to erect optical fibers, install optical fiber communication transceiver devices at the preset points of the transmission and distribution lines to form the island power grid optical fiber communication network;
[0042] The micro-grid energy coordination optimization and control system, which collects the operation data of the island power grid in real time via the optical fiber communication network, and issues operation control instructions to each operating device in the island power grid, so as to realize the stable operation of the island grid/island dual mode. Smooth mode switching.
[0043] In the transformed island microgrid engineering system, the energy storage system used to undertake tasks such as smooth adjustment of renewable energy power in the microgrid, emergency power/energy support, grid power/energy control, etc., is connected to the island grid through a step-up transformer AC bus. The energy storage system can adopt multiple types of sub-hybrid energy storage systems 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 the new transformer AC bus of island power grid. 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.
[0044] Due to the limited energy storage capacity of the energy storage system, diesel generator sets are generally selected as the main power source for microgrid island operation. The construction of diesel power generation system adopts the newly added diesel generator set B and diesel generator set A in the island grid. Diesel generator set B is connected to the AC bus of the island power grid via 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 for island operation of the island power grid. It is connected to the nearby load side to meet the load power demand and can reduce the power transmission loss during island operation of the island power grid. Its capacity should be equivalent to the load capacity of the island 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 is operating in islands.
[0045] The wind turbines connected to the grid-connected island grid are generally direct-drive permanent magnet synchronous wind turbines, doubly-fed wind turbines, and squirrel cage asynchronous wind turbines. Direct-drive permanent magnet synchronous wind turbines and doubly-fed wind turbines have low voltage ride-through capabilities and active and reactive power adjustment capabilities, so there is no need for modification in the microgrid. For the squirrel-cage asynchronous wind turbine, since it does not have low voltage ride-through capability and needs to absorb a large amount of reactive power from the grid when it is connected to the grid, it should be modified to have the ability to participate in microgrid operation control. The scheme adopted is: connect back-to-back converters in series on the stator output side of asynchronous wind turbines. The back-to-back converters are composed of machine-side converters and grid-side converters; machine-side converters and grid-side converters Both adopt a three-phase half-bridge VSR topology, and the two are connected in parallel through a DC bus; the AC side of the generator-side converter is connected to the generator stator, the AC side of the grid-side converter is connected to the grid, and the DC bus is connected to the Crowbar circuit. Realize the low voltage ride through of the generator set, and the generator-side converter can provide reactive power for the start of the wind turbine.
[0046] In order to solve the problem of active load control of the island power grid, in the reconstruction and construction of the distribution network, fast solid-state switches are connected in series on the low-voltage side of the load transformer of the distribution network to realize the switching management of the island power grid load. Connecting the fast solid-state switch to the low-voltage side of the transformer can avoid the inrush current generated during the switching process of the transformer, thereby reducing the capacity demand for the fast solid-state switch and reducing the cost of transformation.
[0047] In order to realize the rapid and accurate collection of the operation information of the island power grid and the real-time delivery of remote control instructions, optical fibers are installed along the transmission and distribution lines in the island power grid, and optical fiber communication transceivers are installed at the preset points of the transmission and distribution lines. The real-time data monitoring of the operating equipment and the rapid release of control information provide channels to complete the construction of the optical fiber communication network of the island power grid.
[0048] Choose a suitable location in the island to build a microgrid energy coordination optimization and control system. This system is the center of the island microgrid operation and control. 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 operating data, optimization of operating strategies, and remote control command delivery, thereby realizing functions such as operating mode switching, emergency control, renewable energy power smoothing, and economic operation of the island micro-grid.
[0049] The energy storage system, diesel power generation system, and microgrid energy coordination optimization and control system can adopt a containerized structure to save civil construction investment, shorten the system installation cycle and facilitate the transportation and transfer of equipment.
[0050] Through the above construction, on the basis of retaining the original grid structure and grid equipment of the island power grid, the construction of energy storage system, wind turbine integration and transformation, diesel generating set construction, distribution network transformation, communication network construction and microgrid energy coordination have been completed Optimization and control system construction, etc., enable the island grid to have the ability to operate in a grid-connected/islanded dual mode.
[0051] Such as figure 2 As shown, the back-to-back converter is connected in series between the stator output side of the squirrel-cage asynchronous wind turbine and the step-up transformer. The back-to-back converter is composed of a machine-side converter and a grid-side converter. The converter and the grid-side converter are connected in parallel via a DC bus. In the back-to-back converter, the grid-side converter operates in P/Q mode to control the stability of the DC bus voltage; the machine-side converter operates in 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 of the DC bus, the grid-side converter can operate independently in the unit power factor state, which solves the problem of the squirrel-cage type. 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 the island grid/island dual-mode switching.
[0052] 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 both adopt a three-phase half-bridge VSR topology, and the two are connected in parallel through a DC bus. Such as image 3 As shown, the grid-side converter and the micro-grid-side converter both adopt a three-phase half-bridge VSR topology. The drains of the power switch tubes G1, G3, G5 are connected together to the positive electrode of the DC side capacitor C1, and the sources of the power switch tubes G1, G3, G5 are connected to the drains of the power switch tubes G2, G4, G6, respectively. The sources of the power switch tubes G2, G4, and G6 are connected together to the negative electrode of the DC side capacitor C2. Freewheeling diodes D1, D3, D5, D2, D4, and D6 are respectively connected in anti-parallel between the drain and source of each power switch tube. L1, L2, and L3 are the AC side filter inductors. Through the on-off control of the above switch tubes, fast and flexible conversion of the rectifier state and inverter state of the converter, as well as the fast and fast DC side voltage and AC side active/reactive power can be realized. Precise control.
[0053] Although the specific embodiments of the present invention are described above with reference to the accompanying drawings, they do not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solutions 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.
