Study On The Coordinated Control Strategy Of Dual PWM Converter In DFIG System

Nowadays, with the increasing energy consumption, the serious resource shortage aswell as the prominent environmental issue, wind energy, as a renewable, non-pollutinggreen energy, has attracted great attention of the world, and wind power technology hasalso become hotspot researched by scholars. VSCF doubly fed wind power generationsystem is universally used in wind power generation system, due to its good dynamicperformance, high power factor, wide speed range, small capacity of power electronicconverter, achievement of maximum wind energy extraction, etc. In nature, the wind speedis not static. The wind speed mutation could cause the sudden change of power generation,thus causing the DC bus voltage fluctuation of the dual PWM converter. The value of DCside capacitance is generally increased, in order to reduce the DC bus voltage fluctuation.But the bulk capacitor is large in volume as well as quality, and low in reliability, whichbecome the bottleneck of the whole system in reliability and service life. To solve thisproblem, this paper proposes a coordinated control strategy of the dual PWM converter.In this subject, the fundamental principle of DFIG was formulated firstly, themathematical model of DFIG in static three-phase coordinates was established and themathematical model in two-phase synchronous coordinates was deduced by coordinatetransformation theory. According to the power generation characteristics of DFIG, thestator flux oriented control strategy is used, in order to realize the decoupling control ofactive and reactive power as well as the maximum power point tracking feature. Then amathematical model of the grid side PWM converter is established and the control strategyof outer voltage, endocyclic electric is adopted. In order to reduce the DC voltagefluctuation, this paper analyzes the existing fundamental problems in non-coordinatedcontrol and coordinatedcontrol with load current feedforward, by using the analyticalmethod of small-signal model. And new control strategy is developed on the basis of loadcurrent feedforward and then MATLAB/Simulink simulation model is set up. Threecontrol strategies are compared by simulation to obtain the effectiveness of the improvedcontrol strategy. Finally, a control system with the digital signal processor TMS320F2407A DSP asthe core is adopted to design the control system, compose the C language program andverify the control strategy. The simulation platform of 11 kW doubly-fed wind powergeneration is used in the experiment, and the simulation analysis and experimental resultsconfirm the feasibility and correctness of the using control scheme.