Research On Direct Torque Control Strategy Applied To Variable Speed Constant Frequency Wind Power Generating System

The wind energy, a kind of regenerated energy, has already been paid more and moreattention to countries all over the world presently. In order to make full use of wind energy andenhance generating efficiency and quality in the wind power generating system, applying directtorque control (DTC) strategy to variable speed constant frequency (VSCF) wind power generatingsystem has been studied in this paper.In the wind power generation domain, the VSCF wind generation system has graduallyplayed an important part with the rapid developments of controlling technologies of wind turbinegenerator. It can capture the greatest wind energy and make the system work at the highestefficiency in the large range of wind speed. Comparing several methods of control in VSCFsystem, the paper reaches a conclusion that adopting doubly-fed electrical machine in VSCF windgeneration system can make full use of wind power and enhance the efficiency of the generator.Therefore, on the basis of the doubly-fed VSCF method and the work principle of the doubly-fedelectrical machine, rotating speed can be able to change with wind turbine, and the electricalmachine can maintain a constant frequency output by controlling the low frequency excitingsource of the rotor side. It has a special vital significance to combine DTC strategy developed inthe middle of 1980's with the doubly-fed electrical machine applied together to VSCF windpower generating system. The control method of rotor magnetic flux DTC is used to regulaterotor side AC flux exciting, reaching the aim of controlling stator side output. This paper hasanalyzed the work principle of the doubly-fed electrical machine, built its mathematical model,and then analyzed the principle of DTC, put forward control strategy, and draw the controldiagram of the system. At last, the paper has analyzed the structure and function of VSCFequipment ACS800-67, set up a 30kW test platform, and verified the performance of the DTCstrategy during the process of synchronization and getting connected to the grid.According to the test results, we fred that applying DTC to doubly-fed electrical machine inVSCF wind power generating system has the advantage of enhancing the efficiency and qualityof generated power, and high speed and small surge current during connect-grid synchronization. The accuracy and feasibility of this control strategy has been verified successfully by theexperimental study.