Research On Coordinated Optimal Control Of Front-End Speed Regulated Wind Turbine

The development of energy Internet is an important focus for the country to boost the economy and promote the transformation.In view of the important characteristics of wide distribution of energy and transportation network in China,making full use of the openness of the transportation network to realize the local and nearby utilization of distributed renewable energy,and exploring the new mode of energy supply of the transportation system,so as to building the transportation energy Internet,which is an effective way to achieve the goal of "Carbon Peak and Carbon Neutralization " in the transportation field.Considering the uneven spatial distribution,intermittent and time-varying characteristics of renewable energy,how to improve the power quality to better meet the needs of the development of transportation energy Internet is an urgent problem to be solved.The front-end speed regulated wind turbine is a new type of source-grid friendly unit.It uses the hydraulic speed regulating device to realize the constant speed at the front-end,the electrically excited synchronous generator is coupled to the power grid through a boost transformer,which overcomes the limitations of variable speed and constant frequency turbines due to the use of converters for grid connection.On the basis of analyzing the structural characteristics,operation principle and coordinated control mechanism of front-end speed regulated wind turbine,aiming at the shortcomings of the wind turbine in optimal control,the following work has been carried out:(1)Construction of hybrid automata model of front-end speed regulated wind turbine.The hybrid automata model of front-end speed regulated wind turbine is established.The basic structure,operation principle and coordination and optimization control mechanism of the unit are deeply analyzed.The wind turbine model,flexible transmission chain model(including main gearbox and hydraulic torque converter),brushless excitation system model and electric excitation synchronous generator model are established.Based on the hybrid system theory,according to the wind turbine model,empirical knowledge and system logic relationship,a hybrid automaton model suitable for the intelligent coordinated optimal control of the wind turbine power is established,which lays a foundation for the research on the coordinated optimal control of the wind turbine.(2)Hierarchical coordinated control of the active power of the wind turbine.The idea of hierarchical,multi-objective and multi constraint intelligent optimization and coordination control is integrated into the active power coordinated optimal control of the wind turbine.The control system of the wind turbine is divided into two layers,the upper layer is the power coordination and optimization control system(single machine output management).The two subsystems of pitch system and torque system(single machine control)are the lower layer.The two subsystems work together to realize the coordinated and optimal control of the wind turbine active power.Taking the minimum output speed fluctuation of the flexible transmission chain and the minimum output power fluctuation of the wind turbine as the control objective,the improved NSGA-Ⅱ algorithm and the improved CMOPSO algorithm are used to optimize the pitch angle and guide vane opening of the wind turbine,and the fuzzy comprehensive evaluation is used to obtain the best solution from the non-inferior solutions,which effectively suppresses the fluctuation of the output active power and improves the output stability of the active power.(3)Hierarchical coordinated control of the reactive power of wind turbine.The adaptive multi-objective hierarchical control method is integrated into the coordinated optimal control of reactive power control.The reactive power control of the wind turbine is divided into upper and lower layers.The upper layer is the coordinated and optimal control of reactive power,and the lower layer is the coordinated control of three control subsystems of pitch,torque and excitation,so as to realize the reliable regulation of reactive power of wind turbine in structure and function.A multi-objective optimization function is constructed,which aims at the stability of generator terminal voltage and the minimum fluctuation of output active power.The improved NSGA-Ⅱ algorithm is used to optimize the pitch angle,guide vane opening and excitation current of the wind turbine,and the objective relative dominance strategy is introduced to solve the Pareto optimal solution,so as to give full play to the voltage/reactive power regulation capability of the wind turbine,improve the grid friendliness of wind turbines.At the same time,the three closed-loop excitation control system of power loop,voltage loop and current loop is designed by using vector control.(4)Hierarchical coordinated control of wind turbine fault ride-through.The hierarchical vertical structure is integrated into predictive control method of the traditional model,and a model predictive controller based on multiple time scales is designed.According to different time scales,the system is divided into two layers,the upper layer is the rolling plan layer,and the lower layer is the real-time base point tracking layer.The long-time scale rolling optimization aims at minimizing the deviation between the actual active power output and the planned active power output,and determines the planned base point according to the long-time prediction results of wind turbine’s active power and grid voltage.The short-time rolling optimization takes the minimum grid voltage fluctuation as the goal,and obtains the control command according to the planning base point,the current actual operating state of wind turbine,the active power output of wind turbine and the short-time predicted value of the grid voltage.At the same time,a synergetic control method that can improve the fault ride-through capability of wind turbine is proposed.The dynamic analysis of the proposed algorithm is carried out,and the large-scale stability constraints that satisfy the fault ride-through are given,the Monte Carlo method is used to solve the range of parameters that satisfy the constraints,so that the generator can send or absorb a larger amount of reactive power to provide reactive power support for the grid and improve the fault ride-through capability of the front-end speed regulated wind turbine.To deal with the problems existing in the optimal control of the wind turbine,the above research work puts forward the coordinated optimal control method of the wind turbine under different working conditions,which lays a certain foundation for the application of intelligent optimal control theory,technology and method of the front-end speed regulated wind turbine.