Research On Simplified Model Of Direct-drive Permanent Magnet Synchronous Generator Wind Turbines And Equivalent Model Of Wind Farms

With the rapid development of wind power the structures and characteristics of traditional power system have been influenced and changed to some extent. Researchers need to study the friendly relationship between wind power and power grid by means of simulation analysis. It’s difficult for power system simulation software to simulate wind farms model that have very high order. Equivalent model of wind farms is the foundation of grid-connected wind farm analysis. This paper studies modeling,simplification modeling of wind turbine and equivalent model of wind farm, based on direct-drive permanent magnet synchronous generator(PMSG) wind turbine which has great prospects and potential.Aiming at the problems that the actual control strategy of low voltage ride through(LVRT) is difficult to obtain and the validity of electromagnetic transient simulation model is insufficient, this paper focuses on the problem of LVRT after exploring the mathematical model and control strategy of PMSG wind turbine. Based on the measured data of LVRT across wind farm, this paper summarizes the typical power control law of converter and control function of active current and reactive current at low voltage period. Then this paper establishes a electromagnetic transient simulation model of PMSG wind turbine in PSCAD/EMTDC platform. It confirms the validity of model by measured data of LVRT and related standard. The verification results show the LVRT characteristics of simulation model are in accordance with actual wind turbine,and deviations meet the requirement of standard, which can provide a reliable model for further research.The simplified model of PMSG wind turbine is focused on, which is to reduce the pressure of computation. According to different requirements of study, the components that have little inertia constant can be ignored selectively. This paper establishes electromagnetic transient simplified model and electromechanical transient simplified model of PMSG wind turbine. The performance of simplified model is tested from response characteristics and calculation time, and the results show that simplified model can reflect the output characteristics of wind turbine and have obvious advantage on saving simulation time.This paper proposes equivalent method for PMSG wind farm based on transient response characteristics of wind turbine and decomposition of active power transient response curves. The PMSG wind farm, whose wind turbines are slant to recover active power, uses multi-machine equivalent model. This paper proposes the following clustering strategy: firstly, wind speed region is divided first time according to the trend of wind turbine active power transient response curves, next, the possible “hidden”segmentation point is searched in every wind speed region, lastly, the factors that impactthe dominant and recessive of “hidden” segmentation point is explored by setting cases that have different wind speed distribution. Researches show that three groups can generally meet accuracy requirements and the wind farm will be divided again at the equivalent wind speed of middle wind speed region if the wind speed is more in the middle wind speed region. The PMSG wind farm, whose wind turbines are instant to recover active power, uses single-machine equivalent model, due to the overall unity of active power transient response curves. The equivalent method is verified by the measured wind speed data. Simulation results show that the equivalent method in this paper for wind farm, which uses two kinds of power recovery control strategies, have good equivalent effect.