Research On Low Voltage Ride Through Of The Hydraulic Wind Turbine

With the process development of large-scale wind turbine,the proportion of wind power is increasing gradually in the grid. To ensure stability,safety and reliability of power after the access of large-scale wind power to network,countries in the world have been proposed strict regulations for networking technology on the wind farm/wind turbine. Among them,low voltage ride through(LVRT) is the biggest challenge of the stable operation in wind turbines,as well as the current important problem for wind farms connected to the grid.In this paper,taking a hydraulic wind turbine as the research object,the unit transport power from wind turbine to generator by quantitative pump-variable motor closed hydraulic system,reducing cabin weight,improveing power quality and reducing the impact on power. The same with traditional wind turbine,hydraulic wind turbines also need LVRT capability.The control method of LVRT for hydraulic wind turbine was researched,the models of wind turbine,hydraulic system,synchronous generator and excitation system were established by the method of mechanism modeling. The state-space models of the unit were researched and the coupling mathematical models were established,considering load characteristics of generator and energy capture inputing of wind turbine.Taking the hydraulic transmission system of unit as the research object,nonlinear of system was studied. Energy transfer and dissipation mechanism were explored. The linearization and decoupling methods were determined,after the analysis of coupling characteristics. The LVRT control method was proposed by controlling output torque and speed of hydraulic system,through proportional throttle valve opening and variable motor swing angle. The control law of variable motor swing angle and proportional throttle valve opening were derived and analyzed by based on dynamic surface control and Energy dissipation laws,to achieving rapid adjustment of transmission power during LVRT,while ensuring stability in the generator on frequency speed and network operation.The three-phase voltage amplitude drops,two relatively short circuit fault and single-phase short-circuit fault under low voltage operation were simulated analyzed,by simulation models on MATLAB/Simulink. Transient response parameters and operating characteristics under different grid failure were obtained. The proposed control method was validated by simulation based on low voltage operation characteristics.Finally,the experimental research of LVRT for hydraulic wind turbine was carried out,based on the 24 kW semi-physical simulation platform in yanshan university,with network simulator simulating fault forms of LVRT. Simulation characteristics of network simulator were analyzed,and The feasibility of LVRT control method for hydraulic wind turbine was verified.