Synchronous flux weakening control method for stator and rotor flux linkage of doubly-fed wind turbine under grid fault

Abstract

The invention discloses a method for synchronous flux weakening control of the stator and rotor flux linkage of a doubly-fed wind power generator under a power grid fault. The key points of the technical solution of the present invention are: when the grid voltage fails, the rotor-side converter of the doubly-fed wind power generator adopts a high control frequency stator-rotor flux linkage synchronous flux-weakening control method. All variables of the control method of the present invention are based on a two-phase synchronous rotating coordinate system. When a fault occurs, the rotor flux linkage is adjusted by controlling the rotor-side converter to realize the synchronous control of the rotor flux linkage and the stator flux linkage, and weaken the influence of the stator flux linkage. The fault impact of the rotor flux linkage, thereby reducing the rotor fault overcurrent. This method can control the fault current of the rotor to be 1.5-1.6 times of the rated current, and the electromagnetic torque ripple is small during the fault period, which reduces the impact on the unit during the fault period, and the active power and reactive power fluctuation of the stator side are small, which can Effectively improve the non-off-grid operation capability of doubly-fed wind turbines under grid voltage faults.

Description

technical field [0001] The invention belongs to the technical field of doubly-fed wind power generator control, and in particular relates to a method for synchronous flux-weakening control of the stator-rotor flux linkage of a doubly-fed wind power generator under a grid voltage drop fault, which ensures that the grid does not run off-grid during a fault. Background technique [0002] As an inexhaustible, inexhaustible and non-polluting renewable energy in nature, wind energy is one of the best ways to solve the energy crisis by effectively utilizing it. In wind power generation technology, doubly-fed wind turbines can operate at variable speed and constant frequency, realizing the flexible connection between the unit and the power grid, and relieving the mechanical stress on the shafting of the unit to a certain extent. The stator winding of the double-fed wind turbine is connected to the power grid, and the rotor winding is supplied with three-phase excitation current by a...

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Problems solved by technology

[0003]When the power grid fails, the rotor short circuit protection is mainly used to maintain the uninterrupted operation of the doubly-fed wind power generation system, and the energy is released through the rotor bypass protection resistor to reduce the Rotor overcurrent, this method increases the hardware cost, the motor operates as an induction motor when a fault occurs, absorbs a large amount of reactive power from the grid, affects the stability of the grid, and is very harmful to the transient electromagnetic impact on the grid and the mechanical impact of the wind turbine. serious

At present, some literatures have reported the modeling and control research of doubly-fed wind turbine excitation frequency converter under grid fault conditions. The main modeling methods are mostly based on instantaneous power theory, and the control methods are mostly positive and negative sequence dual d q Vector control, this method can achieve a variety of optional control objectives in asymmetric fault ride-through, but the double PI closed-loop control greatly affects the dynamic performance of the control system, and the separation and control of positive and negative sequence power make the control structure of the system more efficient. Complicated and more serious is that the time delay required for phase sequence separation reduces the response speed to grid faults, and there is a danger of high voltage and high current damage at the moment of faults, and a small stator voltage imbalance will cause a large stator Current unbalance and electromagnetic torque, active power and reactive power fluctuations will deteriorate the operation performance of doubly-fed wind turbine generators. When the power grid voltage falls by 90% in single-phase or 70% in three-phase symmetrical failure, most of the current control Method It is difficult to control the rotor current value within 2 times of its rated current during the fault period, and the electromagnetic torque fluctuation is relatively large, which has a great impact on the unit

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