Research On Low Voltage Ride Through Technology Of Doubly Fed Wind Power System

Among all the clean energy sources, wind energy is one of the most widely used energy source. China’s wind turbine assembly capacity has always maintained a sustained growth trend in recent years. Therefore, with the application of wind power become more and more common, the research of grid connected control for wind power generation system, fault detection and fault ride through research has become hot research topics in wind power generation technology. Among all the types of generators, doubly fed induction generator is most widely used. However, the stator side of doubly fed induction generator is directly connected with power grid, so the low voltage fault of the power grid will directly acting on the stator side of doubly fed induction generator, which will cause a great impact on the system. Therefore, the low voltage fault transient process analysis of doubly fed wind power system and the low voltage ride through research has important theoretical significance and practical significance in improving the safety and stability of wind turbines.This thesis takes the doubly fed induction wind power generation system as the research object. Firstly, this thesis theoretically analyzed the main parts of the system, deduced the mathematical models and corresponding control strategies. Secondly, on the basis of the mathematical model of the system, we set up the simulation model of the doubly fed wind power system, which provides a simulation platform for the wind power system’s low voltage fault transient analysis as well as low voltage through. Finally, based on system’s simulation platform, we carried out the simulation experiment under different voltage drop amplitude, got the changes of main parameters. Combined with the practical simulation results, it shows that the theoretical derivation under low voltage condition is correct. After analysis the change of main parameters in the transient process, we use DC-Chopper circuit joint crowbar circuit way to carry out fault ride through, analysis the simulation result to get the fault ride through performance under this kind of strategy. Finally, considering the crowbar circuit will cause the out of control of rotor side’s converter and crowbar resistance will absorb reactive power in the investment process, which is not conducive to the recovery of power grid, we use the rotor cascade resistance array way to replace crowbar circuit, at the same time, parallel DC-Chopper circuit in DC bus side to control the surge of main parameters during fault period. Under this strategy, the rotor side converter is not out of control and always maintain working state during fault period. After the removal of the fault, DFIG system can quickly recover to the steady state and finally achieve the goal of improving DFIG system’s stability.