Skip to content
Flash Posts
  • Solar resource distribution and application
  • Sun and solar radiation
  • Future prospects for wind power
  • Problems encountered in the application of wind power engineering
  • The impact of wind farms on the environment
Renewable energy electric power generation technologies engineering and application

The basic principles and implementation methods of renewable energy engineering using various renewable energy technologies for electric power generation are described

  • Home
Renewable energy electric power generation technologies engineering and application

The basic principles and implementation methods of renewable energy engineering using various renewable energy technologies for electric power generation are described

  • Home
Renewable energy electric power generation technologies engineering and application

The basic principles and implementation methods of renewable energy engineering using various renewable energy technologies for electric power generation are described

Grid connection method of asynchronous wind turbines

Grid connection method of asynchronous wind turbines

  • admin
  • January 11, 2022

Generally, there are the following three methods for grid connection of asynchronous wind turbines.

(1) Directly connected to the grid. The conditions for direct grid connection of asynchronous wind turbines are as follows:

①The rotation of the generator rotor is consistent with the direction of the rotating magnetic field, that is, the phase sequence of the generator is the same as that of the power grid. This method must be strictly followed, otherwise, the generator will be in the state of electromagnetic braking after connecting to the grid, and the phase sequence should be adjusted when wiring.

②The speed of the generator is as close to the synchronous speed as possible. The requirements of this method are not very strict, but the smaller the error between the generator’s rotational speed and the synchronous rotational speed when the grid is connected, the smaller the inrush current generated when the grid is connected, and the shorter the decay time.

The direct parallel connection between the asynchronous wind turbine and the grid is shown in Figure 1. When the wind turbine is started under the drive of the wind, when the rotor of the asynchronous generator is brought to the vicinity of the synchronous speed (usually 98%~100%) through the speed-increasing gear box, the speed measuring device gives an automatic grid connection signal, and the closing and grid connection process is completed through the circuit breaker. This grid connection method is simpler than the quasi-synchronous grid connection of synchronous generators, but because the generator itself has no voltage before the grid connection, an inrush current of 5 to 6 times the rated current will be generated during the grid connection process, causing the grid voltage to drop. Therefore, this grid connection method can only be used in occasions where the capacity of the asynchronous generator is below 100 kilowatts and the capacity of the grid is relatively large.

Grid connection method of asynchronous wind turbines
Figure 1 – Direct parallel connection of asynchronous wind turbines to the grid

(2) Step-down and grid connection. This method of grid connection is to connect a resistor or reactor in series between the asynchronous motor and the grid, or connect an autotransformer to reduce the instantaneous impact current amplitude and grid voltage drop when the grid is closed.

(3) Soft grid connection through thyristor. This grid connection method is to connect a bidirectional thyristor in series between the stator of the asynchronous generator and the power grid, and the three phases are controlled by thyristors. Both ends of the bidirectional thyristor are connected in parallel with the moving contact of the grid-connected automatic switch K2 (see Figure 2). The purpose of connecting the triac is to control the inrush current at the moment when the generator is connected to the grid within the allowable limit. The grid connection process is: when the wind turbine generator receives the start command issued by the microprocessor in the control system, it firstly checks whether the phase sequence of the generator is consistent with the phase sequence of the power grid. If the phase sequence is correct, a release command is issued, and the wind turbine starts to start. When the generator speed is close to the synchronous speed (99% to 100% of the synchronous protection speed), the control angle of the triac is gradually opened synchronously from 180° to 0°; at the same time, the conduction angle of the bidirectional thyristor increases gradually from 0 to 180°. At this time, the grid-connected automatic switch K2 does not act, and the moving contact is not closed, and the asynchronous generator is smoothly integrated into the grid through the thyristor; as the generator speed continues to increase. The slip rate of the motor tends to zero gradually. When the slip rate is zero, the grid-connected automatic switching action, the moving contact is closed, the bidirectional thyristor is short-circuited, and the output current of the asynchronous generator will no longer flow through the bidirectional thyristor, but flow into the grid through the closed automatic switching contact. After the generator is connected to the grid, a compensation capacitor should be incorporated at the generator end immediately to increase the power factor (cosφ) of the generator to more than 0.95.

Grid connection method of asynchronous wind turbines
Figure 2 – Schematic diagram of soft grid connection of asynchronous motor via thyristor
Conditions for direct grid-connected asynchronous wind turbines Grid-connected asynchronous wind turbine system

Post navigation

Previous Article
Next Article

Recent Posts

  • Solar resource distribution and application
  • Sun and solar radiation
  • Future prospects for wind power
  • Problems encountered in the application of wind power engineering
  • The impact of wind farms on the environment

Categories

  • Overview of renewable energy power generation technology
  • Solar power generation technology
  • Wind power generation technology

Tag

Acid rain Advantages of offshore wind farms Bottleneck restricting the increase in system capacity Classification of electrical equipment for wind farms Comprehensive performance evaluation of wind turbines Conditions for direct grid-connected asynchronous wind turbines Designed Wind speed Determinants of the best tip speed ratio Efficient way to harness wind energy at scale Factors that determine the torque experienced by a wind turbine Features of brushless doubly-fed generator Four working states of wind turbine General composition of wind power generation system Generator rotor Grid-connected asynchronous wind turbine system Grid-connected synchronous wind turbine system Interference from wind turbines Internal reaction of the sun Low voltage ride through of wind turbines low voltage ride through technology Main features of early fixed pitch wind turbines Main function of the yaw system Main goal of the wind turbine control system Multi-objective optimal control Primary issue in building wind farms Realization of sustainable development of wind power Relationship between air pressure and flow rate Selection of resistance value in Crowbar Source of wind turbine noise Stall phenomenon Stator winding Structure of the sun's atmosphere The most common type of wind turbine The most prominent advantages of vertical axis wind turbines The most promising emerging energy industry Three intervals of ideal power curve Three ways to start wind turbines Traditional wind generator Two main types of airfoil Type of pitch system Various models of horizontal axis wind turbines Ways to solve the problem of wind power grid integration Wind energy capture efficiency Working principle of wind turbines Yaw control system composition

Detailed knowledge of renewable energy technologies and renewable energy engineering for electric power generation.