The Arklow offshore wind farm is located in Wicklow County, Ireland. It has a planned capacity of 200 wind turbines from about 7 to 12 km east of Ireland, with a total installed capacity of 500 MW. The current site selection and demonstration work has been completed and the project will be carried out in stages, to 200. It will be put into production in 7 years and will become the world's largest offshore wind power project. The first phase of the project was commissioned in 2003 and will provide approximately 25 MW of electricity to the Irish power system. In this phase of the project, seven CE 3.6MW wind turbines will be installed. It is the largest single-unit wind turbine that is currently in commercial operation. It uses a frequency converter such as doubly-fed asynchronous generator, 丨CBT control, pitch control and dynamic voltage. And a series of the latest practical technologies such as reactive power compensation. At the same time, the wind farm has reached an access grid agreement with the Irish Power Supply Board (ESB). The wind farm will be connected to ESB's existing 38kV substation via submarine cable. 1. Because Ireland has a short history of developing wind power and lacks relevant experience, especially the experience of grid-connected operation of large wind farms, it is urgent to carry out relevant research. Analyze the interaction between large wind farms and the Irish national grid, especially the dynamic stability of the system and the ability of the wind farm to resist system accidents.
1Doubly-fed asynchronous generator model The doubly-fed induction generator has a wound rotor. The voltage source inverter controlled by ICBT is connected to the grid. The IGBT is operated in four quadrants. The module uses pulse width modulation technology to output sine wave voltage. This feature ensures that the generator voltage and frequency remain constant and is not affected by the rotor speed, thereby achieving efficient use of slip power and reducing heat loss. If the traditional inductive generator is regarded as a special case of rotor short circuit, then the doubly-fed asynchronous generator model can be written as: the converter double-fed motor works the rectifier circuit part, the fake iS inverter is the ideal inverter . In order to prevent model distortion, it is necessary to consider the stability of the DC link in the inverter circuit, so a low-voltage protection mechanism with inverse time action is added to the model. When the system voltage drops and continues for a period of time, such as 90% of the normal voltage value, then the delay 1~2nhn cuts off the wind turbine. The lower the voltage, the shorter the delay. If the voltage drops very low and reaches the critical value, instantaneously cut off the wind turbine: where: fang=5+æˆ, transient potential, rotor voltage; terminal voltage, eighty L, stator current t', mechanical power, rE=- Rs丨丨, on the stator. Electromagnetic power; A =, f is the system frequency; rotor slip; rotor speed; X = equivalent reactance; transient reactance, 2 redundant A rotor loop time constant.
The model has been simplified on the basis of the asynchronous motor model, ignoring the stator transient process and is suitable for general transient stability analysis. This kind of generator uses a pulse width modulation voltage source inverter only in the rotor circuit, and the power to be processed only accounts for 20% of the total power generation, so the efficiency is quite high. In order to save simulation time, the speed and offset are simplified in the model; the wind power is captured by the fan and the power transmitted by the fan to the generator; respectively, the fan shaft angle and the generator rotor angle; ZCS is the torsional moment coefficient; P is the air density ;r is the fan swept area radius; V is the wind speed; cp is the fan efficiency coefficient, is the tip speed ratio 5V = and the pitch angle of the Deng Yue function 8. Through the variable speed drive, the fan speed can be achieved Accurate adjustments to track the optimal tip speed ratio over a fairly wide range, ensuring that the fan operates at optimum efficiency. In accordance with this operating strategy, the combination of the pitch angle adjustment and the inverter control allows the fan to freely switch between the three synchronous speeds, the synchronous speed and the super synchronous speed. As shown, the pitch angle adjustment can be achieved by a proportional-integral controller with the generator rotor speed as a feedback signal.
I Asia: Arklow Offshore Wind Farm and the Transylvanian Grid Interacting Gearbox Ray Asia: Arklow Offshore Wind Farm and the Transylvanian Grid Interaction Speed ​​Feedback Pitch Control Mechanism Wind Farm and Grid Connection 3 and Grid Connection as shown In order to efficiently transfer the electric energy of the wind farm to the national grid of Ireland, it is necessary to establish a 38kV booster station on the Arklow shoal and connect it to the ESB38kV Arklow substation through a submarine cable of about 12km. Because the charging capacity of the submarine cable is quite large, it will bring harmful high voltage to the wind farm during low load. Therefore, a static var compensator (SVC) is installed near the substation, and the reactive power absorbed during normal operation. Provides dynamic reactive support to the system (and wind farm) in an emergency.
However, the compensation capacity of the SVC is closely related to the voltage level of the system. When the terminal voltage is reduced, the output reactive power is reduced in a square relationship. Therefore, support for wind turbines is limited during system failures.
4 Example Analysis The pitch-controlled variable-speed doubly-fed asynchronous wind turbine model developed on the PSS/E dynamic simulation platform can realize seamless connection with the PSS/E transient simulation module.
Wind turbine speed and pitch angle rate curve. It is the curve of fan angular velocity, generator angular velocity and pitch angle. Because the wind farm 3 pong fault location is far away, the fan terminal voltage drops not much, and it can smoothly resume normal operation from the fault without de-networking.
For comparison, a 220kV substation busbar is selected as the fault point in the QWin area of ​​the western and southern power grids and the load center. The simulation results are shown in Table 1. Although the timely removal of the fault (150ms) can avoid the synchronous generator set out of step, in the case of a single fault in three of the locations, the wind turbine terminal voltage may be too low and off-grid. These three points of failure are all near the Dublin area, so when analyzing the impact of the system on the Arklow wind farm, you need to consider Dublin and the nearby grid in detail.
4.125MW wind farm Arklow-phase wind farm installed capacity 25MW, after the interconnection of 7 GE3.6MW wind turbines, after 38kV boost and then connected to the ESB main system through the submarine cable. In the main power grid Cork area, a 220kV substation takes the transient three-phase short-circuit fault (Lin about 150ra), the wind turbine's terminal voltage and its output (or absorption) work meter 125MW wind farm transient stability analysis regional fault Busbar wind turbine synchronous generator resumes stable off-grid stability recovery stable off-grid stable off-network stability
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