Research On The Active Power Precision And Stability Control For Energy Storage Hydraulic Wind Turbines

As a new type of wind turbine,the energy storage hydraulic wind turbine adopts a hydraulic flexible transmission method,which has a series of advantages such as high power to weight ratio,light cabin weight,ground mounted generator,and low installation and maintenance costs.However,wind energy has randomness and volatility,and the hydraulic main transmission system has time-varying and nonlinear characteristics.As the proportion of wind turbines in the power grid increases,the stability of the power grid decreases.It is urgent to solve the problem of precise and stable control of the active power for energy storage hydraulic wind turbines with multi-source disturbances.Therefore,the energy storage hydraulic wind turbines are taken as the research object,and the research on the precise and stable control of active power is conducted under multi-source disturbances.Firstly,based on the power bond graph modeling concept,a power bond graph model for key components is established,such as wind turbines,quantitative pumps,hydraulic pipelines,variable motors,accumulators,variable pumps/motors,generators,etc.,and a complete machine power bond graph model is obtained.The mechanism are clarifyed for power capture,transmission,and conversion.The effects of aerodynamic torque and time-varying hydraulic parameters on the speed and output power are analyzed separately.Secondly,due to the fact that grid connected speed is a prerequisite for achieving active power output,the nonlinear and disturbance characteristics of the grid connected speed control system are analyzed for wind turbine aerodynamic torque,hydraulic main transmission system nonlinearity and uncertainty.The feedback linearization control method is used to linearize the multiplicative nonlinear problem existing in the grid connected speed control system.A nonlinear disturbance state observer is proposed to observe the impact of the time-varying hydraulic parameters,wind power disturbance and generator side disturbance on the grid connected speed.the rapidity and accuracy is verified for the observer.A controller based on matching disturbance compensation is proposed to linearly superimpose the feedback linearization controller and the disturbance compensation controller.The demand for fast and accurate control of grid connected speed is achieved under the disturbance of large inertia and hydraulic parameters.Once again,after the wind turbine is connected to the grid,it cannot generate electricity directly,and active power needs to be controlled,and the impact of internal and external disturbances in the system will be reflected in the active power control.The corresponding relationship between the grid connected speed and output power is analyzed,and the feedback linearization method is used to solve the nonlinear problems existing in the hydraulic main transmission system and hydraulic energy storage system.The nonlinear state observer is used to quickly and accurately observe the impact of the wind turbine aerodynamic torque and hydraulic parameter time-varying on the system output power.The active power compensation controller based on matching disturbance is proposed to accurately compensate the impact of disturbance on the system output power,and the active power control strategy is obtained for energy storage hydraulic wind turbin.The problem of active power fast and accurate control is solved under internal and external disturbances such as wind energy fluctuations and slow hydraulic parameters.Then,the wind turbines need to have the ability to output maximum power smoothly,but the power tracking process leads to fluctuations in output power.Based on the maximum power point tracking principle,with the fixed pump speed as the control output,the linear extended state observer is used to observe the changes of the controller parameters in the sliding mode controller and the output of the hydraulic main transmission system.The power tracking sliding mode control strategy based on the linear extended state observation is proposed to solve the impact of the step mutation of the parameters in the traditional sliding mode controller and the time-varying hydraulic parameters on the power tracking control accuracy.Taking the variable pump/motor torque as the control output,the integrated disturbance nonlinear state observer is used to observe the influence of hydraulic parameter slow change and generator disturbance on the control output of the energy storage system.Combined with the feedback linearization method,a torque compensation control strategy for the hydraulic energy storage system is proposed considering the integrated disturbance,which smoothes the power tracking process and the power disturbance caused by the time-varying hydraulic parameters.Finally,a semi physical simulation experimental platform for a 30 k VA energy storage hydraulic wind turbine is established.Based on this experimental platform,the effectiveness of the proposed control strategies is verified,such as grid speed control,active power control,and maximum power point tracking smooth control,and the energy transmission efficiency is provided under different operating conditions.