Study On Electro-thermal Coordination Theory Of Power Grid Operation

For the restriction of power grid's transmitting capacity, the consumption of electricity cannot coordinate with power generation economically and that will bring negative influence to the development of electric industry and even the whole society. So both academic and engineering members have focused on how to exploit the transmission components'potential capacity sufficiently under the exiting grid operation conditions to relieve transmitting capability inadequacy or to postpone new transmission corridors'construction.At present, dynamic thermal rating (DTR) technology has well developed which can track in real time and calculate the running temperatures and ratings of transmission components. However, it hasn't been organically combined with power grid operation decisions and still has huge potential for its efficiency which needs to be fully developed. Therefore, the research on electro-thermal coordination theory in power grid operation which reflects the essence of transmission components' transfer capability in power grid's operation dispatch and control decisions has significant theoretical and realistic meanings for utilizing exiting grid efficiently, energy saving and emission reduction and adaptation to market competition.With this understanding, this dissertation presents the research of power grid's electro-thermal coordination theory. The core idea is integrating electro-thermal coupling law into grid power flow, optimizing power flow, static security assessment and real-time security corrective control. Then the electro-thermal coordination theory of power grid operation is formed and finally the theories and algorithms of power grid analysis and optimizing dispatching will be enriched and developed well. The main research work and innovative achievements can be summed up as follows:(1) Considering the combination of DTR technology and power grid's operation dispatch and control decisions, the concept of advanced thermal rating is put forward. The aim is to utilize transmission components' inertia predictably by dispatching and coordinating the dynamic electro-thermal coupling process, in which the power grid optimizing and dispatching theories with electro-thermal coordination are reflected and well developed.(2) This dissertation analyzes the coupling relationship between electro-thermal coupling laws of transmission components and power flow, introduces the transmission components'heat balance equation into the power flow model, presents a process power flow calculation model which takes into account electro-thermal coupling law. Furthermore, the simultaneous algebraic differential equations of this model become algebraization through implicit trapezoidal difference method and in allusion to Jacobi matrix an electro-thermal decoupling method is proposed based on the modified equations by Newton method. The proposed model and algorithm make power flow reflect not only electrical information but also the temperature varying tracks of the transmission components and perfect the traditional power flow models and algorithms. Simulation results in different situations illustrate the effectiveness of this model and algorithm.(3) Based on the concept of advanced thermal rating, electro-thermal coupling law is introduced into optimized power flow model and then the dynamic optimized power flow model with electro-thermal coupling is established. The model aims at the minimization of generation and operation cost, introduces electro-thermal coupling power flow equation as restraint and transmission components' temperatures as decision parameters, sets temperature as transmission components' thermal limit. It realizes the organic coordination of the dynamic electro-thermal coupling dynamic process and makes full use of transmission components'thermal inertia. Differencing the model, the algebraic dynamic optimized power flow problem is formed and then can be solved by interior point method. On the basis of features of Newton modified matrix for KKT equations, a decoupling calculation method is put forward which can simplify the optimizing calculation. Comparisons in three simple scheduling modes validate the effectiveness of the proposed model and algorithm.(4) For the problem of electro-thermal coupling dynamic optimized power flow model's complexity, a simplified model is presented by simplifying heat balance equation under conservative assumed condition and neglecting the influence of temperature variation on power folw. The temperature variation is presented by integration of current carrying functions then heat balance equation and temperature variable are eliminated and the complexity of the model is reduced. A comparison between the original and the simplified model shows the effectiveness of the latter.(5) A static security assessment method under electro-thermal coordination is proposed. It simplifies the heat balance equation based on electro-thermal coupling power flow model, obtain its analytic solutions, then decouples the electro-thermal coupling power flow by neglecting the influence of temperature variation and achieves a fast calculation of a stable state temperature and permitted temperature increasing time in case of anticipated accident. According to the calculation results above, anticipated accidents are screened and sequenced by importance and complete static security assessment system under electro-thermal coordination is established. The assessing results can reflect the asynchronism between transmission components'carrying current and temperature varying under anticipated accident, offer early-warning information of permitted temperature increasing time and the severity list of failures, help dispatching center select severe failures reasonably and provide reference for security control measures.(6) For the real-time security corrective control problem when transmission components'carrying current are out of limit by fault, the law electro-thermal coupling is introduced, a process optimized controlling model which can realize real-time security corrective control by electro-thermal coordination is proposed and mechanism Analysis is provided accordingly. The model sets the minimization of security corrective control cost after fault as the objective, introduces electro-thermal coupling power flow equation and transmission components' temperatures as decisive variables, can hold temperature variation of transmission components in process control. On condition of power grid's security operation, this model can make full use of transmission components'thermal inertia as well as economy of control. Simulation results under different load-up conditions show the effectiveness of the model.