Research On Control Techniques Of The Converter For Doubly Fed Wind Power Generation

In recent years, wind power generation experienced rapid development, especially the doubly-fed wind power technique has obtained a wide range of applications in the wind power generation units of 1.5MW and above rating, because of its peculiar advantage.Although doubly-fed wind power generation units have lots of advantage, their operating performance relies on the applied control strategy. In addition, the doubly fed induction generator (DFIG) is quite sensitive to grid voltage disturbance, because of its stator is connected to the grid directly.Firstly, this paper analyzed the resonance phenomenon in the LCL filter based grid side converter, introduced a straightforward and easy to realized active damping control strategy, and then proved its availability via simulation in PSIM.Considering the feature of DFIG that both the magnetic path and the electric circuit of stator and rotor are symmetrical, this paper established the mathematic model of DFIG in the view of space vector. And according to it, this paper analyzed the principle of stator flux oriented and stator voltage oriented vector control strategies. Through a simulation of several situations, this paper showed the advantages of stator voltage oriented vector control strategy. Furthermore, this paper explained why the DFIG is sensitive to grid voltage disturbance.In order to obtain two important angles accurately, which are used to perform the rotating coordinate transformation, this paper researched the theory of three-phase voltages soft phase lock and rotor angle estimating. First the method of rotor angle estimating estimates stator voltage via the measured rotor currents, after that performs closed-loop regulation using the measured stator voltage value as reference, and then the rotor angle is obtained. On the basis of simulations in PSIM, this paper proved the validity of this method.For the convenience of researching on methods of realizing LVRT of doubly fed wind power generation units, this paper analyzed the electromagnetic transient in DFIG when grid voltage disps. Then this paper pointed out conceivable damages, according to simulation results. On the basis of aforementioned analysis and references, this paper introduced the active resistance control strategy. By means of numerical simulation, this paper proved its ability of improving the current control performance, and exposed the limitation of depending on improving control strategy only. For the condition of deep grid voltage dips, this paper analyzed the principal and switching process of the usual used active crowbar circuits. At last, this paper designed and constructed a 1.5kW prototype of doubly fed wind power generation, then introduced it briefly.