Study On The System Frequency Stability Influence Considering Doubly Fed Wind Turbine Into Grid

Now the most widely used doubly fed induction wind turbine(DFIG wind turbine), relying on converter makes this doubly fed induction generator’s (DFIG) rotor connect with the grid, the structure will make rotor speed with the grid frequency decoupling, and the inertia of the whole system will be reduced, but also will increase the difficulty the entire grid frequency modulation, to ensure that system frequency stability after wind power incorporates in grid has become an important research topic.Firstly, this paper analyzes the operating characteristics of DFIG wind turbine, studies DFIG wind turbine’s main components and the mathematical model; based on PSCAD/ EMTDC platform designes the wind turbine model and PWM inverter model and the inverter’s control model; based on hysteresis loop vector control and SPWM control, designes PI controller under dual loop control strategy;Secondly, article builts 3 machine 9-bus and 2MW DFIG wind turbine model on PSCAD/EMTDC platform, researches the system frequency stability influence after equivalent doubly fed wind turbine into the grid, including the certain factors such as the wind speed, grid disturbances, wind farm capacity, rotary spare capacity change to frequency stability influence; simulation results are that the grid-side occurres the worst failures or disturbances to the impact of the system frequency fluctuations,which is greater than the wind farm can withstand the maximum wind speed fluctuation to the impact of the system frequency, the conventional DFIG wind turbine is not frequency control module, synchronous generator spinning reserve capacity increase can effectively suppress the frequency fluctuations and also can reduce the burden on the system once FM;Finally, the paper simulation analyzes without low voltage ride through capability of doubly fed induction wind turbine incorporates into the grid to system frequency stability influence in detail, the paper improves original doubly fed induction wind turbine model, uses the way the rotor converter side parallels Active Crowbar circuit and the DC bus capacitors side parallel DC-chopper in order to protect the converter, designs control scheme of Active Crowbar circuit and DC-chopper; during grid serious faults, in order to solve the problem that crowbar circuit into makes the demand of the reactive power increase and isn’t conducive to the grid voltage recovery; grid side converter in the range of power capacity, a new control strategy for grid side converter reactive power is proposed to achieve the reactive power support to help the recovery of the grid faults; after the recovery of the grid faults,DFIG also issues the reactive power to help the recovery of the stator voltage, in order to achieve low voltage ride through’s the reactive power requirements, ultimately based on improved 2MW DFIG wind turbine model, the paper simulation shows that the way can help the recovery of the grid faults and the stator voltage, and possess good usability.