Research On Speed Pulling-back And Control Strategy Of Doubly-fed Variable Speed Pumped Storage Units

Pumped storage is currently the most mature,economical and scalable flexible power source in the power system,which can effectively solve the problem of grid integration of renewable energy and support energy transformation.Variable speed pumped storage units of excitation with AC exciter have high efficiency,fast response speed and fine stability.But in the process of power regulation,the response speed of the excitation system and the guide vane is quite different so the power of the rotor side may exceed the converter capacity due to the wide range variation of speed,which may damage the converter and disturb the normal operation of the units.Aiming at this problem,this article firstly selects the variable speed operation scheme of pumped storage unit and establishes the unit model.Then,the speed pulling-back control is added to the active power regulation and the influence of the speed pulling-back control strategy on the power response process is studied.At last,this dissertation will propose improvement strategies to address the shortcoming of speed pulling-back control,ensuring that the rotor side power less than limit during the regulation process and minimizing the adverse impact on power regulation performance as much as possible.The details are as follows:(1)A method of selecting variable speed operation scheme of doubly-fed variable speed pumped storage units is proposed.The power regulation range of different schemes are compared under pump mode,and the efficiency and economy of different schemes are comprehensively considered under turbine mode.The synchronous speed and variable speed range is selected,and the converter capacity is determined according to the variable speed range.(2)The control strategy of speed pulling-back is analyzed and a doubly-fed variable speed pumped storage units model with speed pulling-back is established.The upper and lower limits of speed are set according to the converter capacity,and the influence of speed pulling-back control on the power regulation process is studied.And the influence of different control parameters,methods and system parameters of speed pulling-back control are studied.It is found that the speed pulling-back control can prevent the power of the rotor side from exceeding the converter capacity,but it will cause the active power disturbance and reduce the power regulation performance.(3)In view of the problem existing in the speed pulling-back control,improved strategies are proposed.Firstly,the upper and lower limits of the dead zone in the speed pulling-back control are automatically adapted to the changes in active power during the dynamic process.Secondly,the speed change rate is limited,and the control of speed change rate is added to act together with the speed pulling-back control.The results show that improved strategies can prevent the power of the rotor side from exceeding the converter capacity and reduce the disturbance of the total active power.To further eliminate power disturbance,it is proposed to directly limit the total active power change rate while meeting the power regulation requirements.It can ensure that the active power of the rotor side does not exceed the limit and eliminate the disturbance of total active power in the regulation process.