Research On Maximum Power Tracking Control Of Variable Speed Constant Frequency Hydropower System Based On Active Disturbance Rejection

As an important construction of hydropower in China,small hydropower stations can improve the power generation capacity and power supply.The maximum power tracking algorithm is often used in variable speed constant frequency hydropower system to adjust the speed of hydraulic turbine and improve the utilization rate of water resources and power generation.In the process of turbine maximum power tracking,the variable speed constant frequency hydropower generation system is vulnerable to external interference,which makes the turbine speed fluctuate.Stable speed is the prerequisite for accurate maximum power tracking.At the same time,the traditional maximum power tracking algorithm has the problem of contradiction between tracking speed and accuracy under low head and variable water flow.Therefore,this paper studies the ADRC suitable for the turbine side speed outer loop of hydropower system,improves the system anti-interference performance and speed control performance,and improves the speed quality.It also proposes a maximum power tracking control algorithm based on improved cloud model to ensure fast and accurate tracking to the maximum power of hydraulic turbine under variable water flow.Firstly,the grid connection structure of variable speed constant frequency hydropower generation system and the working principle of axial flow fixed pitch turbine are introduced,and the relationship between water flow,efficiency and speed of axial flow fixed pitch turbine under constant head is studied.According to the principle of vector transformation,the mathematical models of permanent magnet synchronous generator,generator side and grid side PWM converter,DC bus link and power grid are established,and the control strategy of generator side and grid side PWM converter is analyzed.The generation mechanism of internal and external aperiodic disturbance and periodic disturbance on the generator side of variable speed constant frequency hydropower system is analyzed.Secondly,aiming at the problem of machine side disturbance in hydropower system,an improved speed loop disturbance control strategy of SOGI-LADRC is proposed.The decoupled linear ADRC is adopted for the outer loop of the engine side speed,which improves the observation ability and tracking ability of the linear extended state observer to the disturbance,and has better disturbance rejection performance compared with the structure of the linear ADRC.In order to improve the medium frequency disturbance suppression ability of the decoupled linear ADRC,the second-order generalized integrator SOGI is introduced into the decoupled linear extended state observer structure to improve the medium frequency periodic disturbance suppression ability.At the same time,the stability analysis and parameter discussion of the improved controller are carried out.The simulation results show that the improved controller can effectively suppress the periodic and aperiodic disturbances of the system and improve the speed quality.Finally,the basic principle of MPPT control of variable speed constant frequency hydropower system is studied,and the advantages and disadvantages of different MPPT control methods are analyzed.This paper expounds the basic principle of cloud model,studies the algorithm flow and reasoning rules of cloud model generator,and constructs a cloud model MPPT controller suitable for water turbine.The control method solves the problem of step size under variable flow,and the accurate membership function is not used in the design.At the same time,an improved scaling factor is proposed to make up for the deficiency that the control domain cannot change with hydrological conditions,and expand the domain rules of cloud model.Finally,the simulation verifies the effectiveness of the improved cloud model controller in maximum power tracking under variable water flow.Compared with P & O control and fuzzy control,the results show that the improved cloud model maximum power tracking control strategy can track the maximum power point of the turbine more quickly and accurately,and improve the efficiency of the turbine.