Online Setting Scheme System Of Under Frequency Load Shedding

Nowadays,most of the under frequency load shedding(UFLS)schemes are formulated off-line and the schemes based on a certain power system operation can not be adapted to the load variations in power system.With the increasing penetration of non-traditional energy power generation,the overall inertia of the power system decreases.The UFLS schemes considering new energy generation emerges as the times require.With the continuous development of power system informatization and intellectualization,the UFLS based on online power grid structure and state has been widely concerned.Given the above background,some relevant research work is carried out in this thesis and summarized as follows.1)The single generator with concentrated load model of traditional UFLS scheme is analysed and discussed.The equivalent inertia time constant and load frequency factor in the model are emphatically studied.Then the common methods of UFLS scheme formulation,such as linear method,maximum available load shedding method and frequency recovery method,are introduced.New energy generation such as wind power generater and photovoltaic power generator affects the first and last start-up frequencies of UFLS schemes.The UFLS optimization considering wind power generators and photovoltaic power generation is proposed.From the point of view of mathematical model,because of power electronic devices in the non-traditional energy generation,the inertia transmission between power system and wind power generator is separated.The unconventional generators reduces the overall inertia of the power system.The power system frequency decline is more severe when there is a power shortage.2)An optimized UFLS scheme based on system frequency respose(SFR)model is proposed.Compared with the traditional single generator with concentrated load model,the governor are considered in the improved SFR model.At the same time,the upper and lower limits of the generator reserve are considered.By introducting the UFLS module,the improved SFR model can more accurately reflect the change of inertia center frequency when the UFLS devices act in a power system fault.The parameters ot the improved SFR model are optimized b y multi-machine system simulation,in which the load variations and power reserves are considered in the model.Then the improved SFR model is estanbilished.This paper proposes a UFLS optimization algorithm based on the improved SFR model and PSO.The penalty function of the UFLS scheme is estanblished.The inertia center frequency of multi-machine is simulated by improved SFR and the opyimum schem of minimizing load shedding is obtained.The effectiveness of the new UFLS schem is verified by simulation analysis.3)The online setting scheme system of UFLS is estanblished.From the point of view of online information measurement and UFLS scheme transmission,the online setting scheme system is estanbilished based on the existing devices of power system.As the "eyes and hands"of power system automation,remote terminal unit(RTU)collected the information of traditionanl generator and station and transmits it to supervisory control and data acquisition system(SCADA).The integrated energy management system(EMS)not only receives information from traditional power generators and stations,but also receives information from new energy EMS.The integrated EMS complete the information collection of new energy generation,load variation and power reserves.The information are used in the multi-machine simulation of the UFLS controller.The UFLS scheme optimization results are obtained based on the improved SFR and PSO.The transmission of the UFLS schemes are through the power system security and stability control system.The stabilization sub-station transmits the information to the UFLS control station.The calculation time of UFLS controller satisfies the requirement of online calculation of UFLS devices in power system.Thus the online UFLS management system has obvious practicality and economy.Finally,the research work is summarized and future research prospects in this filed are pointed out.