| Under the background of structured and market-oriented electric power reform,random renewable energy such as wind-solar power will be absorbed more and more by power system.As an important role of peak and frequency regulation,hydropower will face two more important development trends of more frequent transition condition and non-optimal condition.Accurately understanding the dynamic changes of hydropower units under non-optimal operating conditions is of great scientific significance for improving the flexibility of hydropower generating systems and maintaining the safety and reliability of regional power systems.In the non-optimal working area of the hydraulic unit,the shaft system vibrates violently.The traditional PID governor control in the hydraulic turbine regulating system as the core cannot guarantee the stability of the angular speed of the generator,which seriously threatens the power supply reliability of hydraulic unit in the non-optimal working area.The thesis focuses on the interaction between the generator angular velocity control and the vibration of the shafting system as a key scientific issue and improves the traditional turbine control system model to study the reliability and comprehensive performance evaluation of the hydropower unit.The following three research results have been obtained:1.Three new methods coupling the models of the hydro-turbine governing system and the shafting system of the hydro-turbine generator unit.The coupling mechanism and parameter transfer relationship between the hydraulic turbine regulating system and the hydro-generator shaft system are discussed and analyzed systematically.Through in-depth study of the three coupling methods,the simulation accuracy of the hydraulic turbine regulating system under part load or overload conditions is further improved.The calculated results include:(1)Using the first-order derivative of the angular velocity of the generator and the centroid offset of the generator rotor as the coupling interface parameters in the governing system,the model unification of the interaction between governor control and shaft vibration is realized.Choose different hydraulic turbine governing system models and hydro-generator shaft system models for comparison to explore the model simulation accuracy.The comparison results show: the first-order vibration modal error of the hydro-generator shaft system vibration is 1.38%,and the second-order vibration modal simulation error is 1.59%.The dynamic response simulation error of the governing system has no difference at a stable value,and the simulation error exceeds 10%.It can be seen that the coupled system model can better reflect the interaction between the turbine control system and the shaft vibration during the transient process.(2)The hydraulic imbalance force and the hydraulic moment of the turbine were used as the coupling interface parameters,and different hydraulic turbine adjustment system models were selected.Based on the on-site measurement of the peak-to-peak value of the shafting offset of the Nazixia Hydropower Station,the simulation accuracy of the model was investigated.The results show that thecentroidal offset of the unit's shafting is not affected by the change in flow,that is,the centroidal offset value of the unit remains unchanged,but the natural frequency of the shafting remains basically unchanged.It can be seen that the system coupled by the hydraulic imbalance force and the hydrodynamic moment of the water wheel has a poor interaction under different working conditions,and the simulation accuracy on the axis offset is poor.(3)Using hydraulic excitation force,hydraulic imbalance force,and turbine torque as the coupling section parameters.A comparison is performed based on laboratory shafting vibration experiments to measure the axis trajectory and vibration frequency under misalignment faults from the established model.It was found that the simulation error of the natural frequency of the unit was less than 3%.It can be seen that the system model through the coupling of hydraulic excitation force,hydraulic imbalance force and water wheel maneuvering torque also showed good simulation accuracy when simulating misalignment failure.2.New ideas on using power sensitivity and reliability analysis tools to simulate unit power supply reliability——Power supply reliability index and its preliminary application1.Study the sensitivity ordering of model parameters under stable and transient conditionsFrom the perspective of hydropower station parameter design,the unit model parameters are randomly defined,and the generator angular velocity and generator centroid offset are selected as the output values of the adjustment system and shafting system model to obtain the unit's stable operating conditions and transition conditions.In this case,the single-parameter sensitivity ranking of the model and the sensitivity ranking of the interaction between parameters further establish the scenario design principles for the reliability of the hydropower system's power supply.2.Selection and simulation analysis of power supply reliability indexes of units in different scenariosBy designing different renewable energy proportions,different wind speed interference and other scenarios,the five dynamic indicators of minimum adjustment value,maximum adjustment value,overshoot,undershoot,and peak are selected as power supply reliability evaluation indicators to study the fault response,the adjustment performance of the hydropower system,and the dynamic characteristics of harmonic propagation.The research results show that the regulation capacity of hydropower systems is extremely sensitive to the low standard deviation of random wind and the average low standard deviation of gradient wind high.In contrast,the adjustment sensitivity to gust attribute indicators(ie,wind speed frequency,amplitude,and offset)is weak.In addition,the evaluation of the dominant factors between fast response(represented by adjustment time and peak time)and stable response(represented by minimum adjustment value,maximum adjustment value,overshoot,undershoot,and peak value)is more complicated.However,when the fast response is consistent with the stable response,it is easy to evaluate dynamic regulation performance of the unit.3.An economic evaluation scheme based on the second scale dynamic model--Analysis of resource utilization,flatness and comprehensive benefitsMulti-scale effects of time and space scales of wind power resources are analyzed,and a simple equivalent method of space-time scale is given.Then,a method of calculating wind speed variation coefficient,fluctuation coefficient and suppression coefficient based on a second-scale wind-water hybrid power generation system model is proposed.Further,by designing scenarios such as different renewable energy proportions and different wind speed disturbances,the dynamic response of the wind-water complementary system is obtained,and the annual operation includes electricity sales benefits,peak shaving benefits,energy savings benefits,unit start-up and shutdown costs,Leaf fatigue loss cost,maintenance cost(no guide vane loss),etc.Preliminary trial results show that the economic evaluation scheme of the hydro-wind complementary system based on the second-level scale is feasible. |
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