Research On Control Strategy Of Urban Power Grid Black-start Based On Distributed Generators

China power system has developed into a AC interconnection,DC interconnection,AC-DC hybrid muti-class voltage complex systems.The system has the characteristics of scale-free,small-world effect,self-organized criticality which lead to the inevitability of power system cascading failures.In the event of a large blackout accident,the rapid recovery of urban power grids is particularly important.Restricted by the territorial environment such as hydropower units,pumped storage units,black-start is not available in some cities,other solutions are needed.In recent years,with the widespread use of distributed generator(DG),new explorations on urban power grids black start could be provided.Black-start is lacking for theoretical support,for instance,wind and storage are integrated for power grid black-start of northern Liaoning Province,Systematic theory research is needed urgently.This dissertation conducted an in-depth study on urban power grid black start based on DG as black start source,including the selection strategy of the being started generator,on and off-grid switching control strategy,reboot strategy of DG etc.The main research work are as follows:(1)Research on the selection strategy of the being started generator of the urban power grid.Comprehensive black-start effect of power grid generators are evaluated by using a hybrid algorithm of combining data envelope analysis algorithm and normalization arithmetic algorithm,so as to select the first urban generator.Comprehensive black-start effect of the rest power grid generators are evaluated by using the same hybrid algorithm for the overall system restore.(2)In order to solving switching failure between DG and power grid because of lack of system frequency,voltage reference during the DG off-grid switching,A new smooth switching strategy of Power systems is first proposed.The smooth transition of DG is realized based on fuzzy algorithm.The strategy has three control curves with different droop characteristics.Three control functions(PQ control,droop control and V/f control)are implemented in one control mode.Three different control functions can switch flexibly by using fuzzy algorithm.Compared with switching strategy based on the islanding detection,it not only avoids the loss of frequency and voltage reference during the islanding,but also reduces the impact of DG on the island.(3)Splitting schematic design of urban power grid based on spectral clustering algorithm considering the black-start.By combining the weight coefficients of the black-start in the power constraints,the partition considering the black start of the urban power grids is achieved,so that the splitting and the black start are well connected.Even if the system splitting failure,black start can reboot quickly within the subsystem,reducing the dimension of the power system,speeding up system recovery.(4)A double master-slave control strategy(consisting of DG and SVG)is first proposed according to small capacity,weak resistance to shock loads for DG as the black start source.By adopting different droop control,DG meets the active power,SVG meets the reactive power of the dynamic changes of loads.The strategy not only increases the capacity of the black start source,but also realize de-coupled control of active and reactive power in the power supply.Compared with the control strategy which only achieves power decoupling control through feedforward compensation in the control structure of the system,the complexity of power coupling is reduced,and enhance the resistance to shock loads.With the other slave power help,DG may further increase the capacity of the black start source which make up for the shortcomings of its capacity.(5)Research on urban power grids black start in Longkang LiaoNing province.Adopting smooth splitting strategy and double master-slave control strategy of this dissertation,the feasibility of urban grid black start by using Longkang DG is studyed.According to the ratio between the capacity of the wind and storage,the black-start scheme on how to restart Diaobingshan power plant is proposed.Providing a novel way for the urban power grid black start.