Research On Grid-connected Control Strategy Of Vscf Ac Excitation Doubly Fed Wind Energy Generation System

As a kind of green and recycled energy, wind energy has attracted more and more attention. The relative technology on wind energy is becoming much more comprehensive and mature. Comparison with the traditional wind energy generation system, the variable speed constant frequency(VSCF) wind energy generation system(WEGS)with doubly fed induction generator(DFIG) has more advantages, smaller size, lower weight, higher efficiency, and also it can improve the stability of power system. AC excited VSCF with DFIG and its control strategy is studied in this paper.First of all, the steady state mathematical model of the grid side converter(GSC) in the WEGS has been established in the synchronous reference frame. The schematic of GSC vector control structure is studied based on grid voltage orientation. It is analyzed and compared that the influence on the mutation load of the DC capacitor voltage. Also, the relative simulation is given.Secondly, mathematical models of the DFIG in the WEGS under the synchronous reference frame is established which is the foundation of the later discussion on the stand-alone and grid-connection DFIG with stator-flux-oriented scheme. Under the stand-alone DFIG, two traditional control method is shown what are direct voltage control and indirect voltage control. The reason for the final choice and the relative simulations is given.It is a brief introduction that consists the traditional grid-connected way of induction motor, synchronous motor and the anti-islanding grid-connected way of DFIG. The article focuses on the grid-connected way of AC excited VSCF DFIG, which conclude no-load grid- connection, direct grid-connection and grid connection with load. It presents the detailed theoretical analysis and derived formula of the three grid-connected operation mode. It comes to the conclusion that the control strategy of these types of grid-connected method and gives the relevant simulation waveforms. In addition, it mentions the removal way of power system and its simulation waveform.Based on the above theoretical analysis, a set of rated power for the simulation platform and 4kW test bench are established. It shows the experimental researches and theoretical analysis under different conditions and reached the desired results.