Modeling And Grid-control Of Doubly Fed Induction Machine Based On Fractional Order Theory

Doubly-fed induction machines are widely used in the wind energy systems for its simple structure,relatively well-developed technology,widely adjustable speed and its decoupling control of power.However,due to stochastic nature of wind and massive use of plug-in electronics,wind energy integration would bring huge impact to a power system.The fractional theory applied in the wind energy system control can help to solve the above problems.The fractional PIλDμ controller introduced two adjustable order λ and μ,which guaranteed a faster response,less overshot and more precise control results.In this thesis,the potential application of fractional order theory was conducted.Based on the Grunwald-Letnikov fractional order definition and the advanced Oustaloup filtering algorithm,a special optimized algorithm for doubly-fed induction machine was presented.The fractional order operator was applied in machine modeling,particularly in the capacitors’ section,which solved the problem that the integral models failed to simulate in the transient period;A fractional order PI controller was designed and used in the wind energy integration control,and the simulation results showed that the fractional order PI control method would significantly reduce the power oscillation during the starting period.At the same time,the anti-interference in system was improved as well regarding short-circuit faults.The main content is shown as the following:(1)Fractional order operator realization.According to the feature of doubly-fed induction machines,several adjustable parameters in the advanced Oustaloup filtering algorithm were modified,which simplified the process to choose the best orders.(2)Fractional order theory in motor modeling.The situation of Doubly-fed induction machines’ single-phase operating period was discussed.And the traditional simulating model failed to present it.Therefore,the fractional order modeling was brought out.The nature characteristics of inductance and capacitance were investigated.With the help of earlier packaged fractional order block,the fractional order induction machine model with two capacitors was established to simulate the transient process under short-circuits fault.The simulation results proved the validity of the fractional order model.(3)Fractional order PI controller in wind energy integration control.Because of the integral order λ,one more control dimension was introduced in fractional order PI controller.So,it was designed and then replaced the traditional PI controller in the power outer loop.With a series grid-connected simulation,the results showed this new PI controller could significantly reduce the power oscillation during the starting period,which also reduced the power oscillation during the stable period when a three-phase short-circuit fault happened.