Research On Suppression Measures Of Subsynchronous Oscillation In Power System

The reverse distribution between energy endowments and electricity demand determines the current power supply pattern of "West-to-East Electricity Transmission","North-South mutual supply" and "National Interconnection" in China.To cope with the above problems,China has vigorously developed line series compensation and HVDC transmission technologies to improve the capability of long-distance and large-capacity transmission of power systems.However,the resulting subsynchronous oscillations in the power system also have widespread security risks.The analysis and control of the subsynchronous oscillation problem has become one of the technical problems that China needs to solve urgently.Firstly,this paper briefly introduces the research background and status quo of the subsynchronous oscillation problem,as well as the subsynchronous problems and characteristics existing in our country.Then,the generation mechanism,analysis method and the main application of suppression measures are explained in detail.Based on this,the research on suppression of the subsynchronous oscillation of power system is studied.This paper is based on the simplified model of the IEEE First Benchmark model,taking the turbine generator set with the most subsynchronous oscillation problems as the object,the shaft section between the turbine and the generator is discussed.Based on the characteristics that static synchronous series compensator(SSSC)can provide more damping than the fixed series compensator and does not exacerbate the oscillation,replace the fixed capacitance with SSSC in stand-alone infinity system.Considering the orthogonality between the injected voltage and the line current of the SSSC device,establish a controllable voltage function with m,Udc and ?sc.Based on the linear optimal control theory,and taking the modulation factor m and phase angle ?sc of SSSC as the most direct control quantity to design the control law.The torsional vibration of the turbine shafting system under subsynchronous oscillation is actively controlled.The simulation results show that the designed controller can effectively suppress the subsynchronous oscillation of the power system.For the active controller designed in Chapter three of this paper,when the SSSC uses Phasor Measurement Unit to obtain the remote unit signal for state feedback control,the time delay generated during the transmission,exchange,and processing of each signal cannot be ignored and should establish the time-delay power system model to analysis.In this paper,the time-delay utilization technique proposed in structural dynamics is used to further study the subsynchronous oscillation of power systems with time-delay.Combining multiple types of time delay sets in each stage of the system into the one and considering that the transmission delay of each state signal is the same,then model the system as a single-delay power system.Clustering Treatment of Characteristic Roots(CTCR)is used to analyze the stability margin of the time-delay system.According to the calculation result of the stability margin,the controller is not redesigned but the appropriate time delay is introduced into the control law,to achieve the purpose of improving controller performance and system stability.The time domain simulation results show that the controller designed based on the time-delay technology can suppress the subsynchronous oscillation of the power system better and faster after the system is disturbed.