Research On Circulation Suppression Technology Of Parallel Wind Power Converters

In recent years,with the increasingly severe environmental pollution problems,new energy industries such as wind power and solar energy have developed rapidly.Wind power generation technology has become a hot issue in the global power generation field.As the core device of wind power generation,converters are the key to determine the reliability of wind power systems.With the development of power generation technology,6MW capacity wind turbines have been developed,but power electronic switching devices of the same capacity class have not yet been developed.It’s difficult to accomplish such large energy conversion by a set of converters,while parallel converters can double the power level of the converter system and increase the reliability and redundancy of the wind power system.Parallel technology has become a hot topic in wind power technology research.However,the parallel converter solves the large-capacity energy conversion and also introduces the common circulation problem in the parallel system.Because the parameters of each converter are difficult to keep consistent,there is often a circulating current between parallel converters.The circulating current will cause the output current harmonic content to increase and the load current to be unbalanced,which will reduce the performance of the converter and cause economic losses.Therefore,it is necessary to suppress the zero-sequence circulating current in the parallel system to ensure the consistency of the output current among the converters and improve the reliability of the parallel system.Based on this background,this paper develops a study of the suppression of the circulation current in the converter parallel system.Firstly,this paper introduces the development status and trends of wind power generation technology both at home and abroad.It also analyzes commonly used converter paralleling methods and control methods.It analyzes the parallel converter system based on the coordinate system transformation and deduces mathematical equivalent model of zero sequence circulation.Secondly,the effect of carrier phase shifting technology on the zero-sequence circulation in parallel system is analyzed.Firstly,theoretical derivation is carried out.After simulation experiments,it is proved that the carrier phase shifting technology can reduce the harmonic content of the total current of the parallel system,but it will produce larger Zero-sequence currents and increase the harmonic content of the branch current.Finally,a zero-sequence current controller based on PR control is designed.The zero-sequence current is suppressed by zero-sequence voltage compensation of SVPWM modulated wave.In MATLAB/SIMULINK software,the simulation model of parallel converter system is built to verify that the controller can effectively suppress the zero-sequence circulation of the parallel system in many situations,which proves the feasibility and effectiveness of the circulation controller.