Control Method Research Based On Unbalanced Voltage Of Three-Level Full Power Wind Power Concerter

Wind energy is a kind of clean and renewable energy. And it has greatpotential with huge reserves in nature. How to develop and make full use ofwind energy will be of great significance to China’s economic development.But power failure occurs frequently with the installed capacity of domesticwind power growing rapidly. Especially the grid voltage fault will seriouslyaffect the normal operation of the unit when it is in an unbalanced state. Tocontrol wind power system better, people take more attentions to three-levelinverter output voltage harmonics, which has the advantage of small outputvoltage harmonics and small switches withstand voltage and so on. Therefore,study of grid voltage imbalance in three-level inverter control strategy is ofgreat importance.In this paper, three-level full power wind power converter as the researchobject focuses to research variable flow control technology around thepermanent magnet direct-drive wind power system.Firstly, the status of the development of wind power technology and itstrends in the future is introduced. The current network control technology ofwind power and its operational problems and control strategies in the gridvoltage unbalance state is analyzed in detail. And the advantages of all kindsof technique are compared to the disadvantages. Then a wind turbine model isbuilt. What’s more, each module of wind machine and its principle areintroduced.Secondly, the structure and principle of three-level full-power converteras well as direct drive permanent magnet synchronous generator is analyzed.Wind power systems has machine side and network side, and the mathematicalmodel which connects both sides is built. On this basis of model, the controlstrategies of the converter are introduced.Thirdly, under the condition of the balanced grid voltage state, three-level control strategy of full-power converter is verified by simulation with the zerod-axis current control belonging to machine side and grid voltage-currentdouble closed-loop control belonging to grid side.Fourthly, the space vector pulse width modulation (SVPWM) controltechnology three-level inverter space is studied. The basic principles of eachpart of the process and its implementation are introduced in detail. Afterwards,according to its midpoint voltage of balance voltage, An improved method isproposed. and a corresponding simulation model is built, to verify theeffectiveness of its improved method.Finally, under the condition of the unbalanced state of three-phase gridvoltage, three-level full-power converter control strategy is studied. Afterexploding unbalanced three-phase voltage into positive and negative sequence.Then, the network side is controled by a dual-current loop control method andproportional resonant control method, and an improved method to acombination of both methods is suggested. By comparing various controlstrategies to verify the correctness and effectiveness of the improved method.