| Frequency is one of the important parameters for the safe operation of the power grid.When there is a major fault in the system,the large-capacity generator units in the system will fall off,which may cause the system to have a biggish power vacancy,and even lead to frequency instability.Therefore,it is essential to study on analysis of system frequency and on-line detection,especially when the frequency of the inertial center is unstable after disturbance.Measuring wrong data of each node in the wide-area during monitoring and analyzing,for instance,when the data are asynchronous,the online analysis,the calculation and the control of the inertial center frequency may generate errors.Therefore,it is significant,for the accuracy and robustness of the on-line system frequency calculation based on the data of wide-area measurement system(WAMS),to study the on-line calculation results of the inertia center frequency of the system when the data collected of WAMS are asynchronous.Based on the existing methods,this paper analyzes the WAMS data and calculates the frequency of the inertial center of the system online.Based on the WAMS data before and right after disturbance,the frequency curves of the inertial center after the disturbance are calculated quickly.This paper utilizes PSS/E simulation software for simulating the real WAMS data,and translating the data asynchronously,then bringing it into the algorithms which has been verified by MATLAB for asynchronous calculation,subsequently,comparing and analyzing it with the PSS/E calculation results under synchronous condition.Firstly,the WSCC3 machine 9-node model,the IEEE10 machine 39-node model and the IEEE5 machine14-node model are established based on PSS/E.Then,the system parameters,such as system inertia,frequency regulation effect coefficient and the time constant of governor will be changed.Finally,when the data sampling rate is 120.5Hz,the adjacent interval of sampling points is 0.0083 seconds,and the simulation asynchronous interval change from 0.0083 seconds to 0.0083N(N?51)seconds,the asynchronous calculation results of the system's inertial center frequency are compared and analyzed with the results of synchronous.The simulation results show that,firstly,calculation of inertial center frequency is very sensitive to the location of the asynchronous measurement data: The asynchronous data of generator node have a great influence on the calculation results;The asynchronous load-node data not zero may be related to the load power,which has a big difference on the calculation results,causing the calculation results to be higher or smaller;When the load power on both sides node of the fault line is not zero,the asynchronous node data has a great effect on the calculation results;When the load power of the line is zero,the asynchronous node data haslittle effect on the calculation results,but when there are more asynchronous data,it still has a great influence on the calculation results.Secondly,the frequency calculation of the on-line inertial center is sensitive to the time when the measuring data asynchronous: The calculation results are greatly influenced by the asynchronous data from steady state to fault occurrence time,before and after fault removal and generator removal.Especially with the system inertia and other parameters changing,as well as the system stability changing,the WAMS asynchronous data may cause the calculation of the inertial center frequency a failure or serious oscillation of the calculated inertial center frequency,eventually,the calculation results are inconsistent with the actual condition.The method of calculating the frequency of the inertial center used in this paper is real-time,but the robustness of the calculation still needs to be improved when handling the WAMS asynchronous data,which shows both the improvement of the real-time algorithm and the robustness of the real-time measurement data are very important. |
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