Research On Power Control Strategy Of Doubly Fed Induction Small Hydropower Unit

Under the background of vigorously developing clean energy and striving to be “carbon neutral”,China has put forward higher requirements for energy supply system.Small hydropower stations have the advantages of green and clean energy supplying,which is conducive to the promotion of energy supply side structural reform and the alleviation of power supply tension.Due to historical reasons,small hydropower stations have some problems,such as out-dated technology and equipment,low level of automation,inadequate management,which lead to insufficient competitiveness and slow development.In order to solve the problems of out-dated technology and insufficient competitiveness of small hydropower station,this paper focuses on the application of doubly fed induction generator in small hydropower station,and studies its power control strategy.Considering the low efficiency and operation level of small hydropower station,this paper puts forward the doubly fed asynchronous operation and monitoring scheme of small hydropower unit: doubly fed asynchronous hydropower unit is used to replace the traditional synchronous hydropower unit to track the maximum power point and effectively improve the generating efficiency;the monitoring system of small hydropower station based on Internet of things is designed to remotely monitor the the operation of power units,water condition and station safety,aiming to improve the operation and management of small hydropower station.Considering the characteristic of doubly fed induction generator(DFIG)power control,the mathematical model of DFIG control system is established,which lays the foundation for power decoupling control.Under the condition of small transients,the models of turbine,water diversion system,governor and electro-hydraulic servo system in the turbine governing system are established and the mathematical model of doubly fed generator in dq coordinate system is established through coordinate transformation,which provides a model basis for subsequent power decoupling control.Considering that DFIG is a complex nonlinear and uncertain system involving multiple controlling units,the traditional PI control method based on approximate linearization design at a certain equilibrium point is not effective.A sliding mode power control method for DFIG based on variable exponential reaching law is proposed.This control method takes the current error as the state variable,and changes the gain of the reaching law according to the state variable,so as to weaken the chattering phenomenon of sliding mode control.It has the advantages of fast response,small overshoot,strong robustness,small steady-state error,etc.It is suitable for the power decoupling control of DFIG.Considering the engineering practice,the DFIG asynchronous transformation of a small hydropower station is carried out to verify the feasibility and effectiveness of the operation and monitoring scheme for DFIG asynchronous small hydropower units.The synchronous generators are replaced by double fed asynchronous generators;Based on the Internet of things,the monitoring system of small hydropower station is established.The maximum power point operation experiment of doubly fed induction generator unit is carried out,and the experimental data are analyzed.The results show that doubly fed induction generator unit can effectively improve the generating ability through the maximum power point tracking,which has obvious advantages compared with synchronous machine.The transformation project and operation examples effectively improve generating efficiency and operation management,which verifies the feasibility of doubly fed asynchronous operation scheme.The scheme should have great engineering application value.