Research On Some Problems Of Security And Economy Of Power Grid

The interconnection of larger scale power networks and the consummation of power market have become an inevitable trend of modern power system.With the building of Ultra High Voltage(UHV) power system in china,the system is changing into one of the extra large synchronous AC transmission systems in the world.The interconnection of power grids has changed the power system into a high dimensions,strongly nonlinear system,and the complex operating mode brings forward more request to the security of the power grid.On the other hand,the contribution and consummation of power market has proposed more request to the economy of the power grid.As the problems of voltage stability,electromagnetically coupled power loop during the processing of grid fast development,economic of hydro-thermal economic dispatch are more serious of the interconnected power grid.In this paper,correlated problems of the power system security and economy assessment are analyzed,main research work and contributions are summarized as follows:Voltage stability assessment is one of the most important security to power system's secure and stable running.Firstly,the paper proposes a new method of on-line voltage stability analysis based on Ybus form and deduces monotone mode of voltage instability resulted by divergence of voltage iteration.Secondly,a new criteria of on-line voltage stability index based on load margin is proposed by use of the local measurements data of synchronous phase measure uints(PMU),thus indices of active power margin and reactive power margin can be calculated respectively,which can distinguish voltage unstability caused by overload from the lack of reactive power.The third,as the assessment of reactive power sources is a great need for system operators in an open access environment,this paper presents a novel approach to assessment importance of reactive power sources in power market based on risk theory,it accounts for both the uncertainties on the system and the consequences associated with the output of the reactive power sources.The operation of electromagnetically coupled power loop brings more risk to system running.In this paper,a new risk assessment and control method for electromagnetically coupled power loop is provided.Firstly,the security of the grid is assessed.The static risk,the transient risk and the overall risk are obtained.And the change of the risk with and without the using of security and stability equipment are obtained also.Secondly,the economical of electromagnetically coupled power loop and security and stability equipment as well as the value of risk benefit function are calculated.Based on these,the various of economical of risk are analyzed during different system states.The analyzed results provide effective supports for system operators.In order to solve the conservation on economic of a short term hydro-thermal coordinated economic dispatch model,a new short term hydro-thermal coordinated economic dispatch method is proposed.The uncertainty of water value is considered in this method,the fuzzy optimization is used to balance the two objectives,thus the hydro-system and the thermal-system are traded off,and the primal-dual interior point method(PDIPM) is used to solve this multi-objective fuzzy optimization problem for its good convergence probability.Compared with traditional methods,the proposed method improves the system economic to some extent.