Research On Wide Area Information Based Power System Out-of-step Oscillation Detecting Scheme And Out-of-step Protection

As an important part of the last defense line to maintain the safety and stability of power system,the out-of-step protection is indispensable.However,the interconnected power grid scale expansion,the new control technology application and the operation mode diversification brought by the openness of power market make the power grid stability characteristics more complicated,which bring serious challenges to the traditional local measurement based out-of-step protection.The development of wide-area measurement system(WAMS)provides a new platform for the study of new out-of-step protection.Therefore,further analyzing the variation characteristics of electric quantity during the out-of-step oscillation process and utilizing the measurement quantities of electrical components obtained by WAMS to construct novel power system out-of-step oscillation detecting scheme and out-of-step protection owns important theoretical significance and practical value on improving the performance of the last security defense line and the power system safe and stable operation level.A new coordinate transformation is proposed in this dissertation.It transforms a multi-point linkage system into a single-point motion system and owns conformal property.It not only facilitates the analysis on the electric quantity variation characteristic during the out-of-step oscillation process in the complex scene where the potential amplitudes of two equivalent systems are not equal and all electrical component impedance angles are different,but also guarantees the conclusions obtained in the new coordinate system still applicable in the original coordinate system.By the aid of new coordinate transformation,the bus voltage phase angle variation characteristic during the out-of-step oscillation process is analyzed and the conclusion that the absolute values of voltage phase angles of some buses are always smaller than 110?,while the voltage phase angles of the rest buses vary from-180? to 180? is obtained.Utilizing this property,the out-of-step system can be divided into two parts with the bus voltage phase angle information obtained from WAMS,the connecting line of these two parts is the location of out-of-step center.Base on this,a novel bus voltage phase angle based power system wide-area out-of-step oscillation detecting scheme and out-of-step protection are proposed in this dissertation.Since only the bus voltage phase angle information provided by WAMS is applied,this out-of-step protection is easy to implement.Based on the relationship between the bus voltage and system current obtained from WAMS,a novel out-of-step oscillation detecting and oscillation center tracking scheme is proposed in this dissertation.In this scheme,the out-of-step oscillation is detected by the change rate of phase angle difference between bus voltage and system current,and the oscillation center tracking is completed by analyzing the phase angle relationship between the terminal bus voltages of electrical components and system current.It is easy to implement,and the tracking result is not affected by the changes of system structure and operation mode.Even in the scene that the impedances of the electrical components in the whole system are nonuniform and the equivalent system potential amplitudes are not equal,it can still work well.Based on the oscillation center tracking results,a new out-of-step protection is given,in with the location of out-of-step center can be determined dynamically according to the real-time operation state of power system.The bus voltage frequency variation regulation during the out-of-step oscillation process is analyzed in the complex scene where the two terminal potential amplitudes are not equal and all electrical component impedance angles are different,the different voltage frequency characteristics of the buses on different side of out-of-step center are detailed described.In order to use it to construct the out-of-step oscillation detecting criterion and out-of-step protection,a fast frequency calculation algorithm is proposed in this dissertation.Through toggling different frequency calculating formulas at different sampling points and by the aid of CORDIC algorithm,the measurement errors can keep under a low level.Based on this,a bus voltage frequency based wide-area out-of-step protection is proposed.It can quickly detect out-of-step oscillation and determine the electrical components where the out-of-step center locate in the first out-of-step oscillation cycle,which lays the foundation for the determination of out-of-step splitting section in complex power systems.Based on the wide area information,a multi-Agent based power system on-line out-of-step splitting control system is designed in this dissertation.It owns distributed design structure,the Agents with different functions in different control layers cooperates to realize the power system on-line out-of-step splitting control.In order to obtain the optimal out-of-step splitting section,a layer-by-layer search scheme from the inside to the outside which takes the electrical components where the out-of-step centers locate as the initial splitting section and the energy balance in the isolated island as the search target is proposed in this dissertation.Its search difficulty is small and it meets the meshed power system optimal out-of-step splitting section on-line search requirements.