Strategies For Control Of Doubly-fed Induction Wind Turbines

The most common operation mode of doubly-fed induction wind turbine(DFIG) is variant-speed constant-frequency. Using dual PWM inverter control can not only adjust active and reactive power generator independently, but also reduce the waste of wind resources. VSCF has a positive effect on the stability of the grid. DFIG control strategy for grid-side and machine-side PWM converter control and influence on stability of the grid were studied.Firstly, the characteristics of DFIG and power relations, as well as electromagnetic relations and VSCF operation principle were studied, a mathematical model of DFIG was build, provide a basis for the control strategy.Secondly, for the grid-side converter, structure and principles were studied. On the basis of the vector control, using fast Terminal sliding mode variable structure control designed control strategy of current loop and coordination of the voltage loop for the grid-side PWM converter. A control model of grid-side converter was built and a grid-side converter simulation system was built using Matlab. The two working ways of grid side PWM converter was analyzed. Dynamic performance and stability of the controller were analyzed in a variety of disturbance. The results show that compared with the traditional control strategy control in this paper has the advantages of fast, small overshoot and strong robustness.Next, for the machine-side converter, structure and principles were studied. On the basis of the vector control, using fast Terminal sliding mode variable structure control designed control strategy of the machine-side converter and the maximum wind energy tracking method. A control model of machine-side converter was built and a simulation system was built using Matlab. The stability of the DFIG during the cutting-in was studied. The results show that decoupling control for active and reactive power of the machine side PWM converter was achieved. Variant-speed constant-frequency was also achieved by control strategy in this paper.Finally, a stand-alone infinite system of DFIG with dual PWM control was built. The stability of DFIG controller based on the fast Terminal synovial variable structure of was verified by simulation. On this basis, the effect of wind farm consisting of DFIG on Jiangsu power grid was analyzed taking Rudong wind farm as an example in the background of East China Power Grid for the data. The results show that wind farm consisting of DFIG has a positive effect on the stability of the grid.