| Against the backdrop of profound changes in the global energy system,China’s energy system is evolving from a thermal power-dominated electricity system towards a large-scale and high-proportion new energy system.Due to its flexible regulation and fast response characteristics,hydropower has become the main force for frequency regulation in the new power system.However,the hydropower system will face more complex operating conditions and more stringent grid assessment requirements due to the dual effects of power system load characteristics and its own water-turbine-generator coupling characteristics.The pursuit of faster response speed will weaken the system damping characteristics,leading to lowfrequency oscillations and other faults,which seriously endanger the safety and stability of the units and the frequency regulation effect.This paper aims to reveal and balance the contradictory relationship between the frequency regulation performance and damping characteristics of the hydropower system during the primary frequency regulation process.For the primary frequency regulation process,this paper focuses on studying the active power regulation performance,optimizing the damping quantification method and frequency control strategy,and evaluating the comprehensive dynamic characteristics of the operation.This paper has achieved the following three research results.(1)To reflect the evolution law of the stability of the hydropower unit and power grid during the primary frequency regulation process,while considering the influence of both hydraulic and grid structure factors on the unit stability,this paper takes a three-generator and one-pipe hydropower unit grid-connected system as the research object and establishes a coupled model of the turbine control system(governor and servo system)and the controlled system(water intake system and turbine).From the perspective of nonlinear modeling,the stability and transient performance of the system are studied,exploring the impact mechanism of water hammer effect on the coupling nonlinear hydropower system.The water turbine characteristic curve reflecting the characteristics of the water turbine is discretized and the continuity processing is combined with the water intake system.From the perspective of the balance of source-load supply and demand,the speed control system is regarded as the main control system of the hydropower unit.The power system stabilizer and synchronous motor physical model are built on the MATLAB/Simulink platform.Finally,the hydropower unit single-machine and grid-connected model are built for the study of primary frequency regulation dynamic stability.(2)To overcome the limitations of damping quantification methods in solving highdimensional state space equations and fill the gap in real-time damping quantification methods,this paper optimized the speed-power trajectory damping quantification method and used the reference unit of the No.2 unit of an actual power station as an example to reveal the mechanism by which the main operating parameters such as controller parameters,head,deadzone,and load affect the regulation performance and damping characteristics of the hydraulic turbine unit during the primary frequency regulation process.This provides theoretical basis and technical support for the optimization range and operating range of hydraulic turbine unit parameters.The results showed that the damping characteristics of the system were directly related to its stability.The better the damping characteristics,the stronger the ability to resist external disturbances.For hydraulic power generation systems,the size of damping reflects the degree of response of power output to speed changes.Specifically,the trends of damping performance and regulation performance are contradictory as the head,controller parameters,head,and dead-zone change.The larger the head,the more favorable it is for the hydraulic turbine unit to quickly regulate.However,under high head conditions,the unit’s damping characteristics are poor due to the impact of regulation sensitivity,and the unit should avoid running below 0.7 times its rated head.As the regulation system parameters increase,the regulation time continues to shorten,and the damping coefficient shows a decreasing trend.As the dead-zone size increases,the regulation time gradually decreases and then gradually increases,and the overshoot first decreases and then increases.As the load shedding value gradually increases,the regulation time gradually increases,and the damping characteristics gradually deteriorate.These results indicate that head,controller parameters,load shedding,and adjustment dead-zone are important ways to affect the regulation performance of hydraulic turbine units.(3)To simulate a primary frequency regulation process in a hydro-dominated power system,this paper incorporates a hydroelectric generator system into a two-area interconnected simulation model.Using a regional power system simulation model,numerical simulations are conducted on both an isolated grid system and a two-area interconnected system to verify the effectiveness of the TD3 segmented optimization control algorithm and the hydroelectric unit dispatch strategy.Three dispatch strategies for the units are developed and their corresponding damping characteristics under different initial water heads are analyzed.These strategies provide reference for operation and fault conditions of actual power stations and have far-reaching engineering significance.The results show that in the isolated grid system,the action of the TD3 segmented optimization controller can increase system damping and extend the regulation time.For the frequency regulation unit dispatch strategies in the two-area interconnected power generation system,when operating at lower water heads,running all three units with frequency regulation capability can provide good damping characteristics for the units.However,when the operating water head is higher,the damping characteristics of the system can be improved by withdrawing one or two units from frequency regulation. |
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