The Research On Low Voltage Ride Through For Wind Power Generation System

In recent years, the development of new energy policy has been proposed in China, and the proportion of wind power compared to power energy is increasing year by year, the impact of wind power generation on power system can be no longer ignored. In the conventional wind power generation systems, when the grid votage malfunctions, in order to eliminate the impact on power system, required the wind power system must not be moved from the grid when the grid voltage falls to a constant value, for some small wind power systems could be moved, but for larger capacity power systems, moving wind turbines from power system will cause the collapse of voltage and frequency as well as leading to huge economic losses. Therefore, with the steady increase in wind power generation, wind power generation moved automatically from power system will be no longer suit to the new rules of network, which requires to built a stable and reliable wind power systems, keeping wind power systems uninterrupted operating. Wind power technology-leading countries have issued the new standards for low voltage ride through, requiring wind power systems keep on uninterrupted operating, meanwhile providing reactive power to grid in order to help resuming the normal operation of power grid.In this paper, the research and analysis on low voltage ride through technology focus on direct drive wind power system, also over-voltage protection of the DC side and the grid-side power control strategy for network as well as related technologies are discussed. The framework of wind power system include wind machine, rectifier, Boost circuit, Crowbar circuit, inverter circuit.First of all, this paper describe the basic characteristics of wind turbine, including wind speed , output mechanical torque of wind turbine, and power conversion process. The simulation model of wind turbines is build in MATLAB7.0, making simulation studies on basic characteristics of the wind turbine ,which provides the theoretical basis of low voltage ride through for direct drive wind power system.Secondly, making research on algorithm concerning the output pulse of SVPWM, achieving the modeling and simulation of the boost circuit, rectifier circuit as well as inverter circuit under unity power factor output. And then using the AC side power voltage oriented vector control to achieve the adjustable of power factor, active power and reactive power decoupling of grid-side are better at controlling. Doing the detailed analysis of grid-side converter dynamic operation when three-phase grid voltages drop symmetrically in direct drive wind power system. The direct drive permanent magnet synchronous wind turbines could be able to "pass through" voltage failure period and keep the system uninterrupted operating by increasing energy consumption crowbar circuit in DC side and grid-side inverter operating in STATCOM model. Also analyzing power transfer characteristics of direct drive permanent magnet synchronous wind generator when grid-side converter takes place asymmetric fault, a strategy of grid positive and negative sequence voltage controlled respectively is proposed to inhibit the fluctuations of DC bus voltage.Finally, the driving circuit design of IPM15RSH120 is completed in Protel DXP, some hardware circuit analysis of direct drive wind power system are done under the TMS320F28335 platform.