Modeling And Simulation Analysis On Grid-Connected Directly Driven Wind Generator

Nowadays, economic development excessive dependence on oil and coal in the world, as a result, the primary traditional energy increasingly exhausted. In this circumstances, vigorously develop renewable clean energy become the main way to solve the energy problem for the international community. Wind power, which is inexhaustible, widely distributed, green and cleaning, get more attention.In recent years, with power electronic technology rapid development, the device costs continue to reduce, directly driven wind turbine with permanent magnet synchronous generators(D-PMSG) occupy more and more share in wind power market. This system adopts the permanent magnet synchronous generator, the full-scale high power converter is needed as the interface between generator and grid, it has essential distinction with the traditional induction wind-driven generator and doubly-fed wind generators. Therefore, established the model of directly driven wind generator and analyzed its characteristics, becomes the hot research in nearly two years.This paper introduces the mathematical model of directly driven wind generator and control strategy of dual PWM converter, analysis the dynamic characteristics of D-PMSG through simulation. According the randomness of wind speed, the steady-state model of wind farm was established and calculated power system flow, analyze the impact of wind farms on system voltage. Main contents of the paper are summarized as following:(1) The mathematical models of gust wind, ramp wind, and random wind are studied, introduces the basic principle of wind energy conversion, wind machine model and strategy for pitch angle control, through simulation get the relationship curves between wind energy utilization coefficient and pitch angle or tip speed ratio. On this basis expound Maximum wind power captured principle detailedly.(2) The mathematical model of permanent magnetism generators, PWM converter and DC link are established, and designed control strategy of dual PWM converter. According to the permanent magnet motor stator voltage equation and magnetic flux equations, use the vector control methods that generator side converter using rotor magnetic field oriented and grid side converter using grid voltage oriented, realize the active power and reactive power can be controlled independently, and built the simulation model of the whole system including wind speed and wind turbine in Matlab/Simulink platform.(3) simulation of dynamic response of D-PMSG during gust wind, ramp wind, voltage dip of grid and three phase short circuit. The simulation results show that the model may well reflect the dynamic corresponding system. The wind speed disturbance has effects on generator, DC capacitance voltage and grid side converter, but the impact is limited.During grid voltage dips and three-phase short-circuit fault, each physical quantities of generator has changed a little, current of grid side converter and voltage of DC capacitance fluctuations very largely. Fault does not affect the normal operation of the generator, but it is harm to grid side converter and DC capacitance, so we need to take relevant restricted measures to protect devices.(4) Established the steady-state model of wind farm according to the power characteristics of D-PMSG. By IEEE-24 node test system for example, considering the wind speed changed and wind farm connected with power system in different position, calculate power system flow. Based on this result analyze the impact of wind farms on system voltage. The results show that system voltage varied with wind farm output power and connected position, therefore, site selection of wind farm is an important work in planning project.