Research on Low Voltage Ride Through Technology of the Grid Connected Doubly Fed Wind Generator
|School||Shanghai Jiaotong University|
|Keywords||doubly fed wind generator low voltage ride through(LVRT) Crowbar protection SVG dynamic simulation|
As a kind of renewable energy, wind energy, which has many advantages such as safe and reliable operation, low maintenance cost comparing with nuclear energy and coal, gains widespread concern and attention. As a kind of variable-speed constant-frequency generators, doubly fed wind generator, which has the advantages as follows: capable of variable speed operation, high utilization coefficient of wind energy, able to absorb energy generated by the mutational energy fluctuations of wind in order to avoid the large torque and stress of the main shaft and driving mechanism, improving the power factor of system, etc, becomes one of most widely used models.Due to the developing of wind power, the wind power capacity becomes larger and larger. Wind grid-connected power generation provides a way of power generating, but it brings new problems to the stable operation of electric power system. When the grid voltage drops, the wind generator will operate unconnected to the grid considering its security, cause the partial active power balance, reduce the power system frequency after voltage recovery, bring the threat to power system stability and power quality, and result in tremendous economic loss. So the effective LVRT protection measures are required.This paper establish the motor mathematical model combining with doubly fed wind turbine mechanism and basic principle, analyze the motor transient process when the grid voltage drops, use Crowbar protection to achieve wind power system low voltage ride through operation. Crowbar protection is effective after simulation and experiment validation.As the important reactive compensation device, SVG gains a wide range of application. After improving the control strategy and using energy stored by DC side capacitor, it can maintain the load voltage stability for a short time. When the load voltage is stable, SVG exports dynamic reactive power needed in the state of compensating dynamic var of the load. When the system voltage drops deeply caused by system voltage sag connected to the compensating area or increasing load of the compensating area, SVG is used to compensate reactive power of the load and keep the steady of the load voltage, so voltage of the compensating area is guaranteed. It shows that dynamic response is fast and the system has good dynamic characteristics according to the result of simulation. The control strategy has certain practical value for solving low voltage ride-through technique of wind generators. Especially it provides a good solution for wind generators installed but not considering about the Crowbar protection, which has very good technical feasibility.