Research On Suppression Of Ultra-low Frequency Oscillation Of The Hydropower System By The Self-adaptive Parameter Of The Hydraulic Turbine Governing Side

With the operation of the back-to-back VSC-HVDC of Chongqing and Hubei,the south-west power grid and the Central China Power Grid are connected with the asynchronous network to form the southwest synchronous power grid covering Sichuan,Chongqing and Tibet.The great changes in the scope and scale of the synchronous power grid make the structural contradiction of the power supply more prominent.The installed capacity of hydropower in the south-west power grid accounts for about 70%of the total installed capacity of the whole network.The ultra-low frequency oscillation is an urgent problem in the new grid and power structure.An increasing number of studies have shown that the inverse regulation characteristics of water hammer effect inherent in the hydropower system,and the unreasonable parameter configuration of the governor result in the generation of the ultra-low frequency oscillation.It is of great significance to study in detail the stability influence of hydropower speed regulation system in high duty ratio hydropower system in the process of primary frequency regulation and to take effective measures to reduce the risk of ultra-low frequency oscillation of the system.The main research work of this paper around the above two points is as follows:1.In this paper,the mechanism of ultra-low frequency oscillations by damping torque method based on prime mover side regulation system is analyzed,and the influence of speed regulation system access on the damping of frequency oscillations in ultra-low frequency band is analyzed.The main control parameters of the speed regulation system and the treatment methods of nonlinear components such as deadband and amplitude limiting in stability analysis are analyzed.According to the characteristics of ultra-low frequency oscillation,the multi-machine equivalent modeling is carried out.Based on the theory of traditional frequency analysis method,the influencing factors and the influence on the frequency characteristics of ultra-low frequency band are analyzed in detail according to the inertia of the system,the change of load frequency characteristics of the system and the proportion of hydro power and thermal power units2.In order to study the self-adaptive parameter configuration technology of the PID controller of the speed regulation system,the model of the hydraulic turbine governing system of the PID-type speed regulator is firstly established.And the specific algorithm of the parameter optimization of the speed regulation system and the corresponding objective function are put forward.Combined with the optimization algorithm,the adaptive parameter configuration is carried out,and the simulation is carried out.On the basis of the parameter optimization simulation of the control model,the self-adaptive parameter configuration application is carried out in the actual four-machine two-region system.For the single-phase short-circuit fault on the connecting line,the adjustment of the system stability of the different set of parameters and the self-adaptive parameters is compared.The effect of the configuration of different adaptive parameter groups on the stability of the system is compared under the fault of the cutting machine.3.In view of the ultra-low-frequency oscillation phenomenon in the actual field of the Tibet power grid,the simulation and the oscillation analysis are carried out through the PSASP software based on the actual data of the operation of the Tibet power grid.In order to verify the adaptability and effectiveness of the adaptive PID parameter suppression method for ultra-low frequency oscillation,the proposed method is used to suppress ultra-low frequency oscillations in simulation systems.Based on the actual operation data of the Tibet power grid,the influence of the hydroelectric speed regulation system on the ultra-low frequency oscillation of the power grid in Tibet is studied.The self-adaptive PID parameter control method is used to set up the control model in the simulation program through the user-defined model design interface in the simulation program,and the typical fault disturbance is analyzed based on the actual situation.The ability of primary frequency regulation in Tibet power grid is effectively improved by using adaptive control,and the stability of the system is good.