Research On Converter Technology And Low Voltage Ride Through For Direct-drive Wind Power Systems

As a kind of fair and renewable energy, wind power is the most important alternative worldwide energy in the21st Century. With the global cry for energy security and lower energy consumption with less pollutants is on the upsurge, more and more countries are attaching importance to wind power.Direct-driven wind power generation system is the hot topic of current research in the industry. As the core technology, converter technology plays a decisive role in the realization of low voltage ride through (LVRT) for direct-driven wind power geneation system.The direct-driven wind power geneation system, with its full power converter’s technical advantages, can make best use of the wind, and also has better fault ride through capability by adding Crowbar protection circuits. In this paper, the research object is back-to-back dual-PWM converter, also the control technology of generator-side and grid-side converter are both discussed in detail, as well as the Crowbar circuits. Firstly, on the basis of the mathematical model for generator-side, the theory of Field OIrientation Control and Direct Torque Control are discussed, with the pros and cons of two strategies being analyzed. Secondly, as to the mathematical model of grid-side PWM converter, technical principle of grid Voltage Orientation Control and Direct Power Control are researched, and common crowbar protection schemes are detailedly analyzed, as well as the elaboration on their principles and realizations, with their own advantages and disadvantages being discussed. Analysis shows that Crowbar circuits in D-C side are the best one. Finally, based on the analysis of several common D-C link crowbar schemes, in the face of grid voltage sag, power-shared load is selected as crowbar circuit. The control principle and cooperation of grid-side converter and power-shared load are explained in detail, and then the sag performances without crowbar and with crowbar are analyzed and compared by simulation. The results show that the control circuit by adopting power-shared load is simple and easily cooperated with grid-side converter, which may effectively strengthen the low voltage ride-through capability of direct-drive wind power system.