Low voltage ride through control strategy and simulation of doubly-fed wind turbine
Generally, due to the small proportion of DFIG wind turbines in the power grid, in order to ensure grid voltage stability when the grid fails, the strategy of directly cutting off the wind turbine is usually adopted, and the proportion of DFIG wind turbine assembly machine capacity in the power system is increasing. Large, when the grid voltage dips, if it is directly dissociated from the grid will lead to violent fluctuations in the power grid, and even cause large-scale power outages, etc., which seriously affect the stability of the power system and the recovery of the grid [1] Aiming at the goals and specifications of DFIG to achieve low voltage traversal, experts and scholars from various countries have proposed a series of different technical methods in a large number of documents. At present, there are two main implementation strategies: one is to improve the control method of the inverter [2]; the other is to install a hardware protection circuit to change the topology of the DFIG [3]. The former is suitable for the case where the grid is not obvious, and the latter is suitable for the fall of the large grid. Both methods have their own application range, advantages and disadvantages, so they should be reasonably traded when used, and the grid voltage drop is small. In this paper, the stator flux orientation control (SFO) strategy is adopted.
The DFIG system is mainly composed of a wind wheel, a gearbox, a doubly-fed generator, a dual PWM inverter, a DC side capacitor and a transformer. In the figure, the stator side of DFIG is directly integrated into the power grid through the transformer. The rotor side is connected to the double PWM inverter with adjustable current frequency, phase and amplitude of the rotor. The two-way reversible special frequency converter is used to realize the two-way excitation and slip power. flow. In addition, the grid side PWM can keep the DC bus voltage stable, and the rotor side PWM can indirectly control the active and reactive power on the stator side [4][5]. However, this structure also causes the DFIG to be quite sensitive to the disturbance of the grid voltage. The small capacity of the inverter also makes it less able to cope with the grid fault. Therefore, when the voltage drop is small, the corresponding control strategy is needed to overcome the shortcomings of the DFIG.
