Comprehensive low-voltage ride-through method for doubly-fed wind turbines based on stator series dynamic reactance

Abstract

The invention relates to a comprehensive low-voltage ride-through method for doubly-fed wind turbines based on stator series dynamic reactance, which includes: when the power grid voltage drop is detected, control is carried out according to transient control mode 1, and control mode 1 is the stator series connection with a large input value. Reactance and RSC adopt the comprehensive ride-through mode of the control strategy of transient flux linkage active attenuation. The setting principle of large reactance in mode 1 is to ensure that the peak value of rotor current does not exceed the limit after a fault occurs; real-time observation of the modulus of transient induced electromotive force When the attenuation reaches the set threshold, switch to control mode 2. The setting principle is to ensure that the rotor current does not exceed the limit after the reactance is switched; when the monitored grid voltage returns to normal, the normal control of the unit will be restored, and the series reactance will be cut off after a delay of 100ms.

Description

technical field [0001] The invention relates to a low-voltage ride-through scheme of a doubly-fed fan, in particular to a comprehensive strategy for improving the low-voltage ride-through performance of a doubly-fed fan by dynamically adjusting the stator series reactance value. Background technique [0002] The ever-increasing energy transformation requirements, the ever-changing wind power generation technology and the abundant wind energy resources have made wind power generation receive strong support and development worldwide. The doubly-fed asynchronous wind generator (DFIG) has become one of the current mainstream wind turbine models due to its small converter capacity and independent decoupling control of active and reactive power. [1] . However, the stator of DFIG is directly connected to the grid and is sensitive to grid-side voltage disturbances. Its low-voltage ride-through technology (LVRT) is still a research hotspot. Especially with the continuous increase o...

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Problems solved by technology

[0004] Research on software control strategies mainly includes control strategies for the purpose of de-excitation [3] , A control strategy dominated by limiting the rotor overcurrent [4] and Transient Nonlinear Controller Design [5] etc. These strategies can play a certain control effect when the voltage drops slightly. However, due to the limited capacity of the converter, it is still necessary to use hardware measures when the grid-side voltage drops deeply; although the mainstream rotor crowbar method in the hardware measures can suppress Fan rotor overcurrent, but it is difficult to effectively solve the problem of DC bus overvoltage and absorbing a large amount of reactive power from the system [6] ;Rotor side series current limiting resistor [7] Uninterrupted control of RSC can be realized, but the current injection capability of the rotor-side converter (RSC) will be reduced; other hardware ride-through methods such as series grid-side converter (SGSC) [8] , dynamic voltage restorer [9] etc. can significantly improve the ride-through performance of DFIG, but the utilization rate of these devices is low, and it is contrary to the low-cost advantage of DFIG; the stator series reactance is a kind of ride-through method with better active performance [10-11] , but it is difficult to suppress the fault overcurrent and give full play to the contradiction of RSC transient control ability at the same time, and the transient impact caused by cutting off the series reactance after the fault will also threaten the operation safety of DFIG, so it is necessary to carry out the stator series reactance method In-depth research and improvement

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