Analysis Of Low Head Operation Characteristics Of Pumped Storage Unit And Study On Fuzzy Fractional Order Control

In recent years,with the rapid development of the national scientific and technological level,the demand for industrial electricity and the peak-to-valley difference of the power grid has been increasing,resulting in the problem of frequency modulation or compensation of peak load in power grid.In order to improve the economic benefits of power grid and ensure the safe and stable operation of power grid,China is vigorously developing the construction of pumped storage power station.Compared with traditional hydro-generators,pumped storage units start and stop quickly and respond quickly.They mainly perform tasks such as peak and valley filling,frequency modulation,phase modulation,and emergency backup in the electricity website.However,the structure of the pumped storage unit is complicated,and the operating conditions are frequently switched,especially under low head conditions,it is easy to generate unit vibration,resulting in grid frequency fluctuations.Therefore,it is necessary to accelerate the research in the field of stable operation of the regulation system of pumped storage units and improve the control performance of the units.In order to improve the quality of the control of the frequency of the pumped storage unit under low head conditions,and reduce the fluctuation of water hammer pressure during the transient process.In this paper,based on the consideration of elastic water hammer,a non-linear pumped storage regulation system model is established,and a fuzzy fractional-order proportional integral differential controller based on fuzzy theory is proposed.At the same time,it conducts in-depth research on the optimization of the controller,introduces a multi-objective optimization strategy,uses a multiobjective gravitational search algorithm to optimize the controller parameters to improve the control quality of the pumped storage unit’s adjustment system and increase operating stability of the pumped storage unit.The main research results and innovations of the paper are as follows:(1)Focusing on the problem of low head operation stability of pumped storage units,a nonlinear model of frequency disturbance and load fluctuations of the unit’s regulation system was established,and the transient characteristics of the unit under frequency head disturbance and load reduction were analyzed.Since the regulation system of the pumped storage unit is a complex nonlinear system,for pumped storage power stations with long diversion pipes,the influence of the elastic water hammer on the pipeline must be considered.Therefore,this paper considers the influence of the pipe wall elasticity and friction force of the water diversion system on the pipe pressure,and uses the characteristic line method to establish the water diversion system model.Further,it is considered that there is a non-linear relationship between the relative value of the change in the guide vane opening of the pumped storage unit and the relative value of the displacement of the servo motor.(2)Based on fuzzy theory,a fuzzy fractional order proportional-integral-derivative controller suitable for optimal operation of pumped storage units with low head is proposed.When the regulation system of the pumped-storage unit performs frequency modulation under low head conditions,the unit speed value of the unit is relatively large,and it is easy to enter the "S" characteristic region,causing low-frequency oscillations.A new controller is proposed to replace the traditional proportionalintegral-derivative controller has certain research significance and engineering application value.Compared with traditional integer-order proportional-integralderivative controllers and fractional order proportional-integral-derivative controllers,fuzzy logic control has proved to be a successful control method for many complex nonlinear systems and even non-analytical systems.Effectively improve the stability of the regulation system.(3)Multi-objective optimization strategy and intelligent optimization algorithm are introduced to set the parameters of fuzzy fractional order controller.During the transition between primary frequency regulation and load reduction of pumped storage units,the optimal control mainly considers two factors: One is the stable time of the rotation speed of the pumped storage unit,which reflects the regulating time of the frequency;the other is the fluctuation degree of the rotation speed,which reflects the change of the water hammer pressure in the regulating system.In order to obtain the comprehensive index between the regulation time and the change of water hammer pressure,the multi-objective gravity search optimization algorithm is used to optimize the controller parameters and obtain the optimal control effect.