Generalized Predictive Control Study Of Doubly-fed Variable-speed Pumped Storage Units

In recent years,in order to accelerate the green and low-carbon transformation of energy,a large number of new energy sources have been connected to the power grid,and the construction of a new power system with new energy sources as the mainstay requires the construction of a large number of regulating power sources.Pumped storage has the advantages of mature technology and good economic performance,and has the potential for large-scale development.Variable speed pumped storage has better regulation performance and stable operation capability than ordinary pumped storage,and can undertake key tasks such as peak regulation,frequency regulation and accident backup in the new energy grid with high penetration rate.Doubly-fed variable-speed pumped storage units are a highly coupled hydraulic,mechanical and electrical system with strong nonlinear structure,which differs greatly from the traditional unit control structure,and the traditional control strategy can hardly meet the requirements of fast response and high precision operation in the new grid.In this paper,the advanced generalized predictive control is combined with the doubly-fed variable-speed pumped storage unit to design an incremental nonlinear generalized predictive controller.The specific work is as follows:(1)A detailed mathematical modeling of the doubly-fed variable speed pumped storage unit is carried out.The mathematical model of the unit consists of pump turbine,governor and follower system,diversion system,doubly-fed motor and converter.The full characteristic curve is processed by the logarithmic projection method for the multi-valued phenomenon of the pump turbine operation in the "S" zone,and the mathematical model of the doubly-fed motor in the two-phase dq coordinate system is established.The control strategy of the doubly-fed variablespeed pumped storage unit is introduced in detail to lay the foundation for the following study.(2)A transient linearization scheme is adopted for the doubly-fed variable-speed pumped storage unit,a strongly nonlinear system,and a generalized predictive control strategy is proposed.For the unknown parameters of the transient linearized system,the recursive least squares method with forgetting factor is chosen for real-time parameter identification with rapid computation,and incremental generalized predictive control is introduced to improve the controller performance.The incremental generalized predictive control is applied to the current inner loop in the double-fed motor rotor-side double closed-loop control to improve the regulation performance.Power step simulation experiments of different magnitudes are carried out under turbine and pump conditions.The simulation results show that the designed incremental generalized predictive controller has the advantages of shorter regulation time,smaller overshoot and fewer oscillations than the traditional PI controller..(3)In order to improve the control quality of the turbine regulation system as well as to increase the system operation reliability,an incremental nonlinear generalized predictive speed control strategy in fixed-speed hydro units and doubly-fed variable-speed hydro units is proposed.A reasonable linear simplification is performed in the study in order to obtain a transient linearized model of the doubly-fed variable-speed pumped storage unit.Finally,the simulation results show that the designed incremental generalized predictive controller outperforms the conventional PID controller for different power step disturbances at different operating points and greatly improves the unit performance.