Impact Analysis Of The Double-fed Machine And Converter Caused By Sudden Short Circuit

With the intensification of energy crisis and the deterioration of the environment, renewableenergy exploration and utilization have been given increased focus by a lot of countries aroundthe world. As a renewable and clean energy source, wind power generation has presented asustainable and rapid trend of development mainly because of its rich storage capacity anddevelopment on a large scale in recent years.With respect to their devices in the current market, the double-fed wind generator systemhas a higher market share. The double-fed wind power generation system which has its statorwinding directly connected to the power grid and its rotor winding indirectly connected to thegrid via the converter is controlled by a dual PWM converter. When a sudden short-circuit faultoccurs on the grid, the double-fed machine and the converter will be affected. In order to clarifythe impact of the sudden short-circuit fault on the double-fed machine and convertor, this paperanalyses the following:（1）The wind turbine model, the working principle and topological structure of thedouble-fed machine and the converter have been sequentially analyzed, the mathematical modelof the double-fed machine and converter are derived. on this basis, the control strategy of thedouble-fed machine and the converter is studied. The control strategy on the grid side adopts thenetwork voltage oriented control with voltage and current dual close-loop strategy, the controlstrategy on the machine side adopts the stator flux oriented with current and power dualclose-loop strategy.（2）The transient characteristics of the double-fed machine and converter during sudden ashort circuit fault are studied. The transient mathematical model of the double-fed machine andconverter are derived using the symmetrical component method. It includes the mathematicalexpressions of the transient rotor flux, transient stator flux, rotor transient current and rotortransient voltage. Simultaneously, the numerical analysis of the above stated mathematicalexpressions is done using Matlab programming. The results indicate that there exists steady-stateDC components, DC transient components, AC transient components in the short-circuit current.The variation of each component is determined by the double-fed machine parameters and thephase angles while the magnitude of the short-circuit current mainly depends on the ACcomponent.（3）The parameters of the doubly-fed machine are provided in this paper,the MatlabSimulink is used to build the simulation platform for the double-fed wind power generationsystem. The single-phase short-circuit fault on the grid side of the double-fed wind power generation system, phase to phase short-circuit fault and three-phase short-circuit faultsimulation analysis was carried out using the same platform. The simulation results shows thatthe stator side and rotor side of the double-fed machine will produce an over-current3~4timesbigger and the DC bus voltage will surge after sudden short-circuit. At this point, if thecorresponding protection measures are not taken, the over-current and voltage surge maybreakdown the winding insulation and bus capacitance, which cause irreparable harm to thedouble-fed machine and converter.