Research On Low Voltage Ride Through Technology Of Doubly-Fed Wind Power System

Since the stator side of the Doubly-Fed Induction Generator(DFIG)is directly connected to the grid,DFIG is highly susceptible to grid voltage drop faults.In this paper,the low voltage ride-through technology of doubly-fed wind power generation system is taken as the research object,and a new control strategy is proposed to solve the problem of low voltage crossover(LVRT)during the doubly-fed wind power generation system,so that DFIG is in low voltage fault.Under the grid can meet the requirements.The paper mainly completed the following work:First,for the electromagnetic transient characteristics of DFIG grid voltage drop,a control strategy with zero harmonic component coefficient is designed to eliminate the influence of harmonic current during the transition period.Adopting this control strategy,the stator-side stator current only has the DC component and the fundamental component during the transition process,which weakens the violent fluctuation of the current,and achieves the purpose of protecting the grid-connected converter,which can effectively improve the low-voltage crossing of the DFIG.Operational ability.Secondly,starting from the rotor-side converter control strategy,the rotor-side sliding mode current control matrix equation is constructed.From the perspective of suppressing energy flow to the rotor side,the rotor-side transformation based on sliding mode is designed.Control strategy.The simulation results show that the designed control strategy can significantly weaken the rotor side overcurrent and electromagnetic torque oscillation,which can effectively improve the LVRT capability of the doubly-fed wind turbine during grid faults.Thirdly,starting from the stator-side converter control strategy,the mathematical model of DC bus voltage,d-axis current and q-axis current sliding mode variable structure controller is established under fault condition,and a sliding mode based on approach law is designed.Control strategy for variable structure control.The designed network side controller works more stably.It can still output the standard-compliant voltage and stabilize the DC bus voltage under fault conditions,effectively improving the LVRT capability of the doubly-fed wind turbine during grid faults.