Low Voltage Ride Through Control Strategy Of Doubly-fed Wind Power System And Model Validation

Developing wind power vigorously is one of the effective ways to solveenvironmental pollution and energy crisis. With the strong development of windpower at home and abroad, the impact of wind power on power system is becomingmore and more important. It is necessary to develop wind turbine model for powersystem stability studies to analyze the interaction between wind power and powersystem. This wind turbine model should be able to meet the grid code requirementon wind turbine characteristics, the level of detail of this model should take intoaccount both the complexity and the accuracy of the response to achieve the bestcombination point. This paper take the doubly-fed variable speed and constantfrequency wind turbine widely applied in wind farms as the research object andstudy its mathematical model, control and low voltage ride through ability.Firstly, the paper describes the structure of the doubly-fed wind powergeneration system, and establishes its mathematical model. The wind turbine anddoubly-fed generator control system is established on basis of this. Through thestator flux oriented and grid voltage oriented vector control strategy, both thepower decoupling control of rotor-side converter and grid-side converter areestablished. The doubly-fed wind turbine power decoupling control is verified bysimulation. Basis on the analysis of the transient characteristics of doubly-fed windturbine during grid voltage drop, its protection system is established according tosome requirements and verified by simulation. Secondly, the crowbar circuitinstalled in the rotor side is adopted by doubly-fed induction generator toimplement its low voltage ride through ability. According to active power andreactive power feature required in wind power grid-connected code and basis on theinvestigation of the doubly-fed wind turbine manufacturers common active powerrecovery characteristics, the reactive power control, active power control andcrowbar circuit control of doubly-fed wind turbine is researched and the doubly-fedwind turbine RMS model with low voltage ride through ability is established basedon circuit crowbar circuit on the software platform. Compare the simulation resultswith the measured doubly-fed wind turbine characteristics to ensure the validity and accuracy of the doubly-fed wind turbine RMS model by amending the relevantparameters. Finally, the characteristics of the doubly-fed wind turbine low voltageride through are researched. The selection of crowbar resistance value and crowbarcircuit input lasting time is analyzed and the impact of different crowbar resistancevalues and its input lasting time on low voltage ride through characteristics ofdoubly-fed wind turbine is also researched. In addition, for the wind turbinecapacity becoming large and its flexible become large as well, the impact of windturbine flexible characteristics on doubly-fed wind turbine low voltage ride throughcharacteristics is researched by establishing the equivalent model of wind turbinethrough equivalent mass method.