Research On Operational Control Methods And Low Voltage Ride Through Of Directly Driven Wind Turbine

As the energy crisis is getting over more acute, wind power that is the resource of green energy is the key to solving the problem. Because of its high effectiveness and high ability of LVRT, PMSG has drawn the most attention. This paper deals with PMSG and studies the control strategy of its machine side converter(MSC) and grid side converter(GSC) when they are in steady-state and the power system fault. The main content of this paper includes the following aspects.(1) The mathematical model of the components in PMSG system was established in detail, and it puts forward the selection condition of component parameters in the main circuit. Based on the analysis of the mathematical model, the various components model in the PSCAD/EMTDC software environment have been established.(2) The MSC of the PMSG control strategy based on the rotor position oriented have been designed. It achieved the torque electric current and magnetic current of the PMSG decoupled, and can achieve the maximum wind energy tracking function. The control strategy has been established in the software of PSCAD in the MSC simply model, the correctness and validity of the control strategy was verified.(3) According to the mathematical model of the GSC, it designed the control strategy of the GSC. The control objective is to achieve active and reactive power decoupling control and stable DC voltage. Converter modulation used SVPWM technology. In PSCAD software, a simulation model of1.5MW PMSG system is established, and it was operated on the step under wind speed. The simulation results show that, the PMSG model can achieve the maximum wind energy tracking, DC voltage is stable, harmonic small, and run in unit power factor.(4) When power grid was symmetrical fault, the LVRT control strategy of generator is put forword. By limiting the power of PMSG, it can achieve the purpose of LVRT. The method compared with the LVRT method now used crowbar switching and DC unloading circuit. When asymmetric fault occurs in power grid, the asymmetric control strategy based on double dq coordinate is put forword. The above two control strategies have been carried out in the PSCAD simulation. The simulation results prove the validity of the control strategy. It gives out the engineering application value.