The simulation results show that the supercapacitor energy storage system and the appropriate control strategy can improve the low voltage ride through capability of the permanent magnet direct drive wind turbine.
With the continuous increase of energy demand and the continuous reduction of non-renewable energy, the development of renewable energy has become an important part of the sustainable development of all countries. Wind power has been widely used in recent years due to its mature technology. Among them, the permanent magnet direct-drive wind turbine has the advantages of small mechanical loss, high power generation efficiency and low maintenance cost due to its structural characteristics, and has a good development prospect in the field of wind turbines.
The unit is connected to the grid through the back-to-back converter. Therefore, when the grid voltage drops, the generator is decoupled from the grid, and the operating characteristics of the unit are not affected, so it has better low voltage ride through (LVRT) capability [1] ]. As the grid-connected capacity of wind power generation continues to increase, the mutual influence between the wind power generation system and the power grid becomes larger. The wind power grid-connected guideline requires that the grid-connected wind turbines must have certain LVRT capabilities.
In [2], the LVRT capability of the system is improved by adding an unloading branch on the DC bus. When the voltage at the grid point drops, the unloading resistor branch is turned on, and the unbalanced power on the DC side is flattened by the form of thermal energy. Thereby maintaining the DC bus voltage stability. This method increases the heat dissipation design of the system, and the unbalanced power on the DC bus is wasted.
Reference [3] uses the battery energy storage system to connect to the DC bus. When the voltage at the grid connection falls, the unbalanced power on the DC bus is stored by controlling the energy storage system to maintain the stability of the bus voltage and improve the LVRT capability of the system. However, the proposed grid-side converter control strategy does not consider the grid-side voltage drop to provide reactive power compensation to the grid to support the grid voltage, and the battery has limited number of charge and discharge cycles, short service life and high maintenance costs.
Reference [4] uses the control method of changing the grid side when the grid is faulty. It can help the system to “traverse†the low-voltage region when the voltage drop at the grid-connected point is not high, but when the voltage drop is large, the method is controlled. The effect is not ideal.
In [5], the superconducting energy storage system is connected to the DC side, and the power fluctuation on the DC side is stabilized by controlling the superconducting energy storage system to stabilize the bus voltage. However, the investment operation cost of the superconducting energy storage system is too high and the cooling system needs to be installed when designing the system, which increases the design difficulty.
In view of the shortcomings of the above methods, this paper gives full play to the advantages of fast response, high recyclability and high power density of supercapacitors. The supercapacitor energy storage system is connected to the DC bus side, and the control of a suitable energy storage system is proposed. The strategy is combined with a comprehensive grid-side converter control method to improve the LVRT capability of the wind turbine.
Figure 1: Permanent magnet wind turbine with grid connection with super capacitor
Conclusion
For the traditional permanent magnet direct drive wind power system, based on the analysis of its model, the super capacitor energy storage system is applied to the DC side. By controlling the energy storage system to quickly stabilize the power imbalance on the DC bus, and the integrated grid-side converter control strategy, the LVRT capability of the permanent magnet direct-drive wind power system can be significantly improved.
Indoor Lift,Indoor Elevator,Indoor Escalator,Indoor Home Escalator
XI'AN TYPICAL ELEVATOR CO., LTD , https://www.chinaxiantypical.com