Research Of Fault Control And Energy Dispatching Method For Active Distribution Network

As an important supporting network for “Energy Internet”,the active distribution network(ADN)is an important integration carrier for distributed generation(DG).The ADN can effectively promote the integration and consumption of renewable energy sources(RESs),and further improve the utilization efficiency of RESs.However,due to the large uncertainty caused by the large scale integration of DG units in ADN,the network structure and operation mode of the distribution network are changed,which brings new challenges to the safety,stability and economic operation of the ADN.Fault control and energy dispatching become the key technologies for the safety and economical operation of the ADN.This work was supported in part by the National High Technology Research and Development Program of China(863 Program)“Intelligent SCADA and EMS for New Energy Power Stations on Islands” under Grant 2011AA050203,in part by Sino-US international Science and Technology Cooperation Project “Key Technology Research and Developmentof Networking and Operation Optimization for Enterprise-level Energy Internet” under Grant 2016YFE0105300,in part by National Natural Science Foundation of China “Optimization Theory and Methods for Planning and Operation of Comprehensive Energy Power Systems” under Grant 51722701,in part by Natural Science Foundation of Hunan,China “The Theory and Technology for Networking,Operation and Control of Enterprise-level Energy Internet” under Grant 2017JJ1011,and in part by Hunan Provincial Innovation Foundation For Postgraduate “Key Technology Research for Support Voltage of Industrial Active Distribution Networks” under Grant CX2017B107.The research is conducted from the aspects of fault voltage support,fault current limitation,self-healing and islanding energy dispatching,targeting for solving the key technologies of the fault control and energy dispatching of the ADN,and providing assurance for the safety and economical operation of the ADN.These studies can promote theoretical and practical guidance for the demonstration and application of ADN.The main contributions are summarized as follows.1.To tackle the challenge that the DG inverter can not make a tradeoff between the dynamic and stability performance during voltage support of ADN,a hybrid control method that combined with improved frequency droop control and improved passive based control(PBC)is proposed for voltage support of ADN.Based on the idea of “energy forming” and “damping injection”,the energy control rate of DG inverter is improved,and both dynamic response performance and stability are effectively improved during the voltage support of ADN.Extensive simulation and experimental results have validated the effectiveness of the proposed method with an effective dynamic response performance and stability.2.To tackle the challenge that the the system total fault current of ADN is increased during fault ride-through(FRT)of microgrid(MG),a fault current neutralization strategy is proposed in this paper.The phase angle difference between point of common coupling(PCC)and ADN voltages is considered for calculating a more precise phase angle shifting of DG fault current.A novel inverter current generation strategy is formulated with peak fault current limitation.The nameplate capacity/current of different local inverters is considered for coordinated operation of parallel inverters within grid code requirements.Extensive tests have validated the effectiveness of proposed method with a successful FRT while the MG output fault current has a minute effect on the system total fault current amplitude.3.With views to the differences between the traditional distribution network and ADN in terms of the operation model and structural features,an essential difference can appear in the classification of operating states between these two systems.According to the characteristics of ADN,a new decision tree method based on hierarchical classification is proposed to classify the operating states of ADN.In this method,several important performances reflecting the operating conditions of ADN are regarded as critical attributes,including external stability,reliability,integrity,and economy.Moreover,different transition paths and control targets in different states are proposed to demonstrate the effectiveness of the classification method,which aim at the safety and reliability of ADN.Finally,a control strategy based on state classification is presented to support the decision-making for the self-healing of ADN.A case study demonstrates the feasibility and effectiveness of operating states classification and self-healing control of the ADN.4.To tackle the challenge that the energy dispatching in the islanding model of the ADN,cuased by external grid fault,has the high level of uncertainties by high penetration of volatile clean energy such as wind farms and solar photovoltaic.The uncertainties creates large forecast errors under some conditions and makes low operation of reliability and economy.Thus,a time-scale adaptive dispatch method is developed in this paper.The time-scale for dispatch of islanding ADN is adjusted online according to the intrinsic relationship among confidence coefficient of forecast error,confidence interval of forecast error and spinning reserve capacity.Extensive tests have validated the effectiveness of the poposed method in offsetting the uncertainties in the system and improving the system reliability.