Research On Control Strategy Of Parallel Three-Phase Inverters In Wind Power Generation System

Energy is essential thing for human being. As the consumption of world oil and coal continue to rise, people pay more and more attention on the development of renewable energy. The technology of wind power generation is mature, which makes it possible to apply wind power generation to the production of large-scale industry. With the capacity expansion of the stand-alone wind turbine, the level of inverter has increased to MW-class. Constrained by the level of stand-alone device, the capacity cannot meet the desired level. It is well known that parallel inverters can enlarge power level, improve efficiency, reliability, as well as decrease the cost. In view of this, take grid-connected inverters in direct parallel operation as the object of the study.First, the math model of grid-connected parallel three-phase inverters based on voltage source inverters is given. According to this math model, we can get the coupling characteristics about parallel inverters. The math model also shows that the circulating current path exists while inverters are in direct parallel operation. Circulating current, which can lead to current distortion, is generated when the parameters of the two inverters are different. Proper control strategy must be taken to avoid this current.Secondly, the following two measures should be taken to avoid the circulating current:first, the system should include a link of current of sharing; in the second place, the strategy to inhibit the zero-sequence circulating current should be applied to the system. A master-slave mode is used to realize current-sharing. A zero-sequence current loop is introduced in to inhibit the zero-sequence circulating current. Simulation results in Matlab/Simulink are presented to prove the effectiveness of this method.At last, the experimental platform based on TMS320F28335is built. The experiment is done on this platform.