Anal Ytical Identification Method Of Thevenin Equivalent Parameter And Its Application In Voltage Stability Of Electric Power System

Promoting the energy production and consumption revolution,constructing of a new clean low-carbon system and speeding up the pace of electric energy replacement are the major strategic choice of China in new era.With the rapid growth of load,part of grid is forced to operate with heavy load.In the low-carbonization process of power system,large-scale wind power connecting to grid brings new challenges to the safe and stable operation of power system.How to evaluate the voltage stability and preventively control the power system with high penetration wind power and ensure the system operating safely,stably,and efficiently and in low-carbon state become an urgent problem.This dissertation takes the discussion of Thevenin equivalent(TE)in the view of power flow as the starting point and research in TE analysis and its simplification,voltage stability margin index construction based on analytic impedance ratio index and its total differential,under-voltage load shedding control strategy,and wind-gas hybrid power system(WGS)capacity planning and grid connected control strategy considering voltage stability deeply.The accuracy of TE parameters identification has been troubling people,this dissertation revisits the mechanism of TE in the view of power flow,and the accurate tracking of power route is the premise of reliable identification.Sensitivity analysis can track the distribution and flowing of power in “source-grid-load” clearly.Deriving the analytical expression based on sensitivity can evaluate system parameters,characteristics of source,non-linear load and load increasing mode quantifiably,improve accuracy of identification,and make the results reliable and usable.The simulation results shows that the TE parameters identification method proposed in this dissertation can avoid the effect of change in grid side and non-linear characteristic of both source and load on TE parameters,and the accuracy of method is high.In order to achieve the goal of TE fast identification,reducing the dependence on whole grid data,satisfying the need of different scenario,this dissertation proposes a TE fast identification method based on reduced order self-sensitivity.The method sort the branch by the branch transmission power index,filtrates the transmission power leading routes,and makes leading grid built by the buses and branches of the transmission power leading routes as the shrink grid.The simulation results shows that the fast identificatio n method suits the strong large scale grid whose internal connection tight,and has a higher identification accuracy with different simplification.Voltage weak bus fast identification is an important content of the safe and stable operation of the power system.This dissertation dissects the analytical impedance ratio index,and proofs the impedance match in multi-machines system.It constructs novel voltage stability margin index based on impedance ratio index and its total differential,uses the first order Taylor expansion to describe non-linear relationship impedance ratio index and power margin index in order to improve the linearity of the index.And the novel margin index can calculate the margin under different load increasing mode.The simulation results shows that the index can identify the weak bus effectively.This dissertation derives the analytical expression of under-voltage shed load based on impedance ratio index and its total differential.The expression can calculate the shed load accurately and minimize the consumer lose under the given target of voltage control.As the capacity limit of interruptible load connected to one bus,which may not cover the need of voltage control,this dissertation proposes a control strategy which can joint control interruptible load and reserve units.To maintain system voltage stable.The strategy sheds the interruptible load of adjacent buses and request the enabled reserve units' support,rises the impact of control method in the region and uses the market to optimize the control to maintain system voltage stable at low price.The simulation results show that the strategies are effective and be able to reach the goal.The high proportion installed capacity of gas turbines in the traditional WGS rises the construction cost.And the constant output power grid connected control strategy has not consider the active peak-adjustment and decreasing the fuel cost.This dissertation analyzes the levelized cost of energy of WGS,and proposes a gas turbine capacity optimization strategy and a grid connected control strategy considering the voltage stability constraint based on active impedance ratio index in the condition that the installed capacities of wind farm and compensation device are given.The simulation results shows that the strategies can suppress fluctuation of wind power,improve consumptive ability for wind power,decrease the investment and the operation cost,adjust the system peaking and increase the level of safe and economical operation of WGS.