Study On Low Voltage Ride Through Control Strategy Of Doubly Fed Induction Generator

With the increasing proportion of large-scale centralized grid-connected wind farms and wind power generation capacity for the power system and the relatively backward grid construction, the impact of wind power on grid security and stability cannot be ignored. A lot of countries have established the low voltage ride-through (LVRT) with their respective national conditions.Using this paper to research the mainstream models of VSCF doubly fed induction generator, analyze its electromagnetic transition process during the voltage dip. And give the corresponding strategy to meet the low voltage ride-through. The main content of this paper are as follows:(1) In order to establish the mathematical models be suitable for operation analysis of DFIG, according to the structure and basic principles of DFIG, considering of the rotor resistance and flux with stator and rotor to establish the mathematical model of voltage dip. From transform to convert to easy analytical matrix algebraic equations. Final, get the high-precision analytical results, which can provide a reliable theoretical basis for LVRT control strategy.(2) Due to the nonlinear electromagnetic transition process, giving a new research idea. Based on the voltage dip mathematical model, get the current variable state-space equations. The state-space equations have linear features, so use the superposition principle to see the voltage dip transient process as the two cases of the operational status of the steady state and reverse voltage. On this basis, according to the requirements of LVRT, analyze the operation characteristics of voltage dip transient characteristics.(3) Through the analysis of operation characteristics during the voltage dip to establish LVRT mathematical model. On the basis, derive the control strategy of controlling the rotor excitation voltage to eliminate the harmonic current. According to the operation indicators of LVRT, analyze the operation characteristics of LVRT.(4) Based on the matlab simulation platform and DFIG LVRT mathematical model to construct the simulation model. Under the LVRT requirements, compared the simulation waveform with numerical computing waveform during the LVRT control strategy to propose the accuracy of the proposed method.Through the above analysis of LVRT control strategy, it can see that this strategy is simple, reliable and will not cause damage to the generator and the converter and have non-rush current and non-harmonics. During the LVRT, the DFIG provide reactive power to support the grid voltage recovery.