Study On Optimal Power Factor And Minimal Capacitance Control Algorithm In Wind Turbine

As the high-power electronic device such as IGBT and control technique become more and more mature, more and more dual PWM converters are used in mega-watt variable-speed constantfrequency wind power generation system. Dual PWM converters have better input and output performances, less harmonic currents and a wider frequency adjustment range. The rotor-side converter is responsible for maximal wind energy capturing and independent regulation of reactive power output from the stator of the doubly-fed induction generator (DFIG) through vector control. The grid-side converter diverts the rotor power to or from the grid using a DC-link between the two converters. Large aluminum electrolytic capacitors are normally installed to reduce the DC-link voltage fluctuation. But the aluminum electrolytic capacitor has several drawbacks from the viewpoints of size, weight, cost, and reliability which become the fatal shortcoming of extending the lifespan of the whole system. In this thesis, a control strategy of dual PWM converters based on fuzzy PI control is proposed to minimize the DC-link capacitor, reduce the bus-bar capacitance.Firstly, based on the analysis of the dynamic mathematical model of DFIG and its stator-fluxoriented vector control, a traditional dual-dosed-loop PI control scheme is developed Simulation study is carried out on the platform of MATLAB/SIMULINK and validates the proposed strategy, which will guide designing and debugging the practical software and hardware systems.Secondly, based on the mathematical model of the grid-side PWM converter and according to the engineering design method of dual-closed-loop system, a voltage-current dual-closed-loop control system of grid-side PWM converter which is in grid-voltage-oriented synchronous rotating reference is designed, it bottomed for seeking control algorithm of minimum capacitance value, and also provide the basis of selecting control system parameter in later experiment.Lastly, it introduced the load current feed forward control scheme and the predictive current control scheme of three-phase PWM converters, and pointed out the reason why those two control scheme can't be used in the wind turbine specific load, then put forward the control scheme based on fuzzy PI control, carried out the comparative simulation study to evaluate the performance of the traditional dual-closed-loop PI control scheme and the flirty PI control scheme, Simulation results demonstrates the superiority of the fuzzy PI control scheme over its counterparts in less DClink voltage fluctuation and faster stabilization. Thus, with the same fluctuation voltage allowed, if adopt the fuzzy control scheme, can greatly reduce the bus-bar capacitance, which has quite important practical application value.