Research On Low Voltage Ride Through Technology Improvement Of Doubly-fed Wind Power System

At present, the energy demand kept rising. The general conventional energy's multiple causes, such as high consumption and large pollution, result in that the wind power, the one of the emerging green energy, is attracted more and more attention,development and utilization around the world.With the innovation and development of wind power technology, the utilization of wind power is growing. The worldwide installed capacity of wind power occupancy ratio in the power network is rapidly expanding, that leading to the impact of wind power in the whole power network more and more prominent. The most in need of improvement of technology are included the ability of the low voltage ride through(LVRT), etc.Firstly, it introduced the development of wind power technology, and summarized the research status of high-profile double-fed induction wind power generation system(DFIG) of LVRT technology. Then, it analyzed the working principle of the doubly-fed induction generator, and it established the mathematical model in the three-phase static coordinate system and the two-phase rotating coordinate system. The rotor-side PWM converter of DFIG system is used grid voltage vector control strategy. And the grid-side PWM converter of DFIG system is used dual closed-loop control strategy.It established the network models of DFIG system in the Matlab / Simulink environment. By changing voltage drop extent, different grid failure, it studied the dynamic characteristics of DFIG system. The simulation results indicate that the voltage and current of DFIG system is too high when the grid voltage drops in different degrees. So it requires take protective measures, to keep the system stable and the network normal working. Commonly used hardware protection is adopted Crowbar or series of dynamic resistance(SDR) protection circuit methods. The innovation of this paper is research on low voltage ride through technology improvement of DFIG System, which uses a combination of Crowbar and SDR circuit protection to improve LVRT ability.Compared the different simulation result of the system without any protection circuit, just with Crowbar, just with SDR, and with combinational improvedprotection when the voltage drop under 80% and two-phase asymmetrical short circuit fault occurred.The results show that the combinational improved protection can better reduce the maximum current, maximum voltage peaks, and can shorter LVRT time,and can greatly improve the LVRT ability, and can verify the superiority of the combination improved protection. Finally, it simulate the system with combination improved protection under three failure modes, different voltage level drops, and simulation results show that the combinational improved protection under the different fault conditions have increased the LVRT ability of DFIG system all the time.