The overall structure of the wind turbine
A wind turbine is a device that converts the kinetic energy of the wind into mechanical energy through a wind turbine, and then into electrical energy through a generator. The wind turbine blades generate aerodynamic force under the action of the wind to rotate the wind wheel, convert kinetic energy into mechanical energy, and then convert the mechanical energy into electrical energy through the transmission system and electrical system. The complete set of equipment that realizes the conversion of “wind energy-mechanical energy-electrical energy” is called a wind power generation system or a wind power generation unit. The general composition of a wind power generation system is shown in Figure 1. According to the function in the energy conversion process, it mainly includes wind turbine and its control system, transmission and braking mechanism, generator and its control system, electric energy conversion device (optional), etc.
On the whole, wind turbines generally include three parts: wind turbine, nacelle, and tower. There is a rotating body between the nacelle chassis and the tower, so that the nacelle can rotate horizontally. At present, the more mature grid-connected wind turbines in the world mostly use horizontal-axis wind turbines, and the mainstream wind turbines have a capacity from several hundred kilowatts to 1.5MW. From a technical point of view, the single-unit power of the current largest operating unit has reached 8MW, and 10MW or even 15MW wind turbines are being designed.
For a typical large-scale wind turbine, in addition to the externally visible wind wheel, nacelle, and tower, the wind device (also called steering device, yaw device), speed regulating device, transmission device, braking device, generator, controller and other parts are all concentrated in the engine room.
In addition, it is necessary to mention the measures to prevent lightning strikes on the tower. The metal tower or wind turbine unit itself has the possibility of being struck by lightning. In addition, from the point of view of the installation location, wind turbines installed on the top of a mountain or standing in isolation on the flat ground are likely to be targets of lightning strikes. When directly struck by lightning, it will not only damage the wind turbine installation, but also cause casualties. Therefore, lightning protection measures should be taken seriously.
The electrical energy produced by wind turbines will eventually be sent to the grid or users through the electrical system. As shown in Figure 2, a schematic diagram of the connection between the wind turbine generator set and the outside is given.
The working state and conversion of wind power generating set
Under normal circumstances, a wind turbine generator has four working states, namely running state, pause state, shutdown state and emergency shutdown state. Each working state can be regarded as an activity level of the wind turbine, the operating state is the highest level, and the emergency shutdown state is the lowest level. In order to be able to clearly understand how the control system of the wind turbine generator works in various states, it is necessary to make precise definitions for each working state so that the control system can control the yaw, pitch, hydraulic, and braking systems according to the state of the unit according to the set control strategy, and realize the conversion between different states. In order to ensure the safe operation of wind turbines, the level of improving the working status can only be increased layer by layer, while the level of reducing the working status can be one layer or across layers. For example, if the working state of a wind turbine generator is to be transformed to a higher level, it must rise layer by layer. When the system detects a fault during the state transition process, it will automatically switch to the shutdown state. When the system detects a fault in the running state, and this fault is fatal, then the working state will directly enter the emergency stop without going through the pause and stop state.