Research On Frequency Prediction And Frequency Control Optimization Of Power System After Disturbance

With the deployment of the national energy strategic vision,it is an inevitable trend to adhere to the power grid reform and transformation to promote energy conservation,environmental protection,and sustainable development.Driven by the rapid development of renewable energy generation and UHVDC transmission technology,various forms of new energy in modern power system are integrated into the power grid,and the asynchronous DC interconnection between regional power grids further leads to the decrease of the moment of inertia and frequency stability of the original power system.Modern low inertia power system is disturbed by power shortage,which leads to frequent frequency collapse events.After the accident,the primary frequency regulation does not achieve the expected effect.With the rapid development of wide area measurement system based on synchronous phasor measurement unit,the real-time and fast online data acquisition of power grid is realized,which provides the basis for online analysis of frequency stability and fast control of frequency offset.According to the results of on-line frequency analysis,the strategy of primary frequency modulation is optimized to provide a new suppression scheme for frequency offset caused by power shortage.The research in this paper is of great significance for the primary frequency modulation system after disturbance to release the regulation capacity quickly,reduce the frequency offset and increase the frequency stability of power system.Firstly,this paper introduces the function and modeling process of the main modules in the primary frequency modulation system model of power system.The BP neural network,support vector regression and Kriging interpolation are introduced.To verify and compare the accuracy and efficiency of different prediction methods,this paper first selects the Schwefel standard test function with high nonlinearity as the test target,and tests three algorithms.In addition,IEEE 10 machine 39 bus system and an asynchronous power grid in China are selected as examples to generate samples for training model and evaluating prediction accuracy by using PSS/E and BPA software,respectively.In the frequency prediction model,the prediction objectives include: the lowest frequency after the power shortage disturbance and the time from the beginning of the disturbance to the lowest frequency.Through the subsequent comparison of frequency offset suppression effect,it is found that the accuracy of the three frequency prediction methods can meet the needs of primary frequency modulation optimization control.Based on the frequency prediction results with two objectives,this paper proposes two optimization schemes of primary frequency regulation: the first scheme uses the predicted time when the disturbance reaches the lowest frequency to formulate the optimization scheme of temporarily closing the dead zone of primary frequency regulation,so that the primary frequency regulation equipment of the unit can act quickly and release the active power in time;In the second scheme,two objectives are used: the predicted minimum frequency and the time to reach the minimum frequency after disturbance.A control system is added to the speed feedback link of the original generator speed control system,so that the predicted frequency and the feedback frequency control the speed input at the same time,and the primary frequency regulation capacity of the unit is released in advance,to suppress the frequency offset after disturbance.Then the single machine system,multi machine system and an asynchronous power grid in China are used to establish the frequency simulation model based on MATLAB / Simulink,and the above two optimization schemes are added to the original primary frequency modulation model.The simulation results show that the two schemes can adjust the output of the generator in advance and suppress the maximum absolute offset and the integrated offset of the frequency.Finally,particle swarm optimization algorithm is used to optimize the control parameters of scheme 2.The simulation results show that the optimized scheme 2 has better frequency offset suppression effect.To sum up,this study provides a theoretical basis for the frequency dynamic analysis and control of modern power system after disturbance.