Grid Connected Control Research Of Permanent Magnet Direct-drive Wind Power System Based On Hybrid Energy Storage

With the increase of wind power penetration rate in the power grid, the influencebetween wind power system and power grid is becoming more and more big. Wind powersystem output power has the characteristics of volatility and intermittent, this will producegreat influence to power quality of grid and its stability will; At the same time, the powergrid failure will also bring a series transient process to the wind power system, and evenendanger the safe operation of the whole system. Therefore, the introduction of largecapacity storage system is the increasing grid reserves and increasing wind powerimportant means of access, it has a key role in the respect of new energy acceptance andstable operation of power grid.This paper adopts double tri-level back-to-back converter structure. Through thenetwork side converter DC-side shunt super capacitor and battery energy storage system topromote wind power unit parallel operation stability, by controlling the bi-directionalDC/DC converter and grid inverter, make the direct-drive wind power system has a certainability of low voltage ride through when power grid voltage sags by using charging anddischarging characteristics of the energy storage system, and make the grid side getsmooth output power in the large wind power fluctuations; Making wind turbines preferredto the power grid into a certain reactive current according to the requirements of grid inpower grid voltage failure to help power grid quickly return to normal operation.The mathematical model of direct-drive wind power system and hybrid energy storagesystem is established, and verify the VRB battery charging and discharging characteristics;Design the control strategy of bi-directional DC/DC converter and analyze the dynamicresponse process and operating characteristics of system in the power grid voltage fault.Set up the simulation model of complete system in the environment ofMatlab/Simulink. The simulation results show that according to access hybrid energystorage system in dc side could adjust electric power demand and smooth system generatoroutput power fluctuation, improve the system parallel operation performance and lowvoltage ride through ability. The simulation results verify the correctness and theeffectiveness of the proposed scheme.