Theoretical Studies On Synergistic Dispatch Of Power Source And Electric Network In Power System

Nowadays, the exhaustible resources are gradually exhausted, and the problems of environmental damage and climate change are gradually serious, which forces the energy-cleaning reform and the promotion of utility and efficiency of power system. Power system is characterized by complex relationship between power source (including power supply and consumption) and electric network, which bright formidable challenges for the operation of power system. And the source power balance is faced with the challenge of the accommodation capability of uncertainties, voltage support capability and power transmission capability of electric network.The realization of source power balance is the target of power system dispatch and control, and how to realize the integration of dispatch and control of power system is the key to accommodate uncertainties. It can promote the capability of accommodating uncertainties to exploit the synergistic capability of frequency regulation characteristics, voltage regulation characteristics as well as the complementarity characteristics between power source and electric network.Under the aforementioned background of accommodating uncertainties, taking system frequency and voltage as the clue, this thesis has investigated the theories of source synergistic dispatch and synergistic dispatch of power source and electric network aiming at dealing with the complex contradictions between power source and electric network. The basic theories and methods of synergistic dispatch of power system focusing on accommodating uncertainties during the process of the balance between generations and loads are studied. The thesis is also the important content of the project entitled ’Theoretical study of power system synergistic dispatch’ and supported by National Natural Science Foundation of China. The main research work and innovation of this thesis are shown as follows:(1) Theoretical frame of power system synergistic dispatch aiming at dealing with uncertainties is proposed. Firstly, definitions of power source and electric network are given for a clear expression of dispatch ideas. Secondly, elaboration on synergistic potential in power system operation and its technical specification are discussed. Then the reason for the theoretic study of synergistic dispatch is proposed, that is the synergistic effect of frequency regulation characteristics and voltage regulation characteristics as well as the flexible control techniques of smart grid. Thus the idea of synergistic dispatch is to exploit the synergistic potentials of frequency regulation effect and voltage regulation effect to realize the seamless integration of dispatch and control. Finally, theory system of synergistic dispatch is proposed, which mainly includes frequency aware source synergistic dispatch, voltage aware network synergistic dispatch, as well as source-network synergistic dispatch with the consideration of coupled frequency and voltage characteristics. This work lays a foundation for the following work.(2) Considering the contradictions between power sources during the process of source power balance under the uncertain circumstance, a novel source synergistic dispatch approach with transmission security constraints is proposed to exploit the synergistic capability of accommodating uncertainties by accounting for both the frequency regulation effect and optimal participation mechanism of secondary regulation reserves of conventional units in response to uncertainties in the robust optimization counterpart of security constrained economic dispatch. The proposed model is formulated as a robust optimization problem with variable uncertainty sets. In order to improve the computational tractability, the dominant constraints that can be candidates of the tight transmission constraints are determined by complementarity constraints. Then the robust optimization problem is simplified to a bilinear programming problem based on duality theory. Finally, the effectiveness and efficiency of the proposed method are illustrated based on several study cases.(3) Considering the effects of voltage support and voltage regulation characteristics on economic dispatch under the uncertain circumstance, the model of synergistic dispatch considering voltage regulation effect is established based upon the mechanism analysis of voltage support affecting source power balance. In the proposed model, the voltage regulation effect and the unit reserve response mechanism are well considered into the decision-making of source power balance. In addition, the source power balance and its voltage support are effectively integrated to exploit the potential synergistic capability of power system to accommodate uncertainties. Then a parallel solution methodology formed by the combination of the fast and elitist non-dominated sorting generic algorithm and the Monte Carlo simulation with nonlinear programming is proposed for the model. Finally, validity and effectiveness analyses are conducted for several cases. Presented analyses demonstrate that the proposed model can take the advantage of voltage regulation effect to keep the balance of source power under uncertainty.(4) The model of unit commitment considering voltage regulation effect is established based upon the analysis of characteristics of unit commitment under uncertainty. In the proposed model, the operation states of generators are well considered into the decision-making of network synergistic dispatch. In addition, the source power balance and its voltage support are effectively integrated. Based on Benders decomposition, the model is decomposed into a master problem and some subproblems. The master problem corresponds to the resolution of unit commitment with direct current power flow constraints, in which the opearation states and generation level of generators are decided to act as the complicating variables to facilitate the interface of master problem and the subproblems. While the subproblems correspond to alternating current power flow voltage support decision for each scenarios to check the feasibility of network security and voltage security constraints. Finally, validity and effectiveness analyses are conducted by case studies to explain the influence mechanism of voltage support and voltage regulation effect on unit commitment.(5) Considering power system voltage support faced with the problems of bidirectional power flow, light load operation and bad voltage support caused by optimal transmission switching on the basis of direct current power flow, the model of voltage support decision-making considering flexible network structure is proposed based upon the analysis of the characteristics of voltage support of power system. The proposed model takes the conditional adjustment of power grid structure as a decision-making variable based on given source power balance mode, and considers the cooperation mechanism of network structure as well as the constraints of transformer over-load tap-changing blocking. The proposed model is solved by the combination of the genetic algorithm and the nonlinear primal-dual interior point method. Case analysis verifies the effectiveness of the proposed method, showing the benefit of network structure optimization to promote the voltage support capability during the process of source power balance.(6) Considering voltage support for the realization of source power balance under the uncertain circumstance, the study of the relationship between network and source power balance is conducted and an optimization model for security economic source-network synergistic dispatch is proposed to deal with the complex contradictions between power source and electric network. The core of the proposed model is that the cooperation mechanism of network structure optimization is incorporated into the coordinated economic dispatch with the consideration of physical law of electric network to deal with voltage security and network constraints to realize the source synergistic dispatch. Then the proposed model is solved by the combination of the genetic algorithm and the nonlinear primal-dual interior point method. Finally, Example analyses are conducted to verify the validity of the proposed model to promote the capability of source power balance and operation efficiency of power system.To sum up, in this paper, some key problems about the synergistic dispatch of power source and electric network are studied, and the corresponding mathematical models and algorithms are proposed and verified by some numerical cases. But it needs to be proved that, many related problems need to be studied deeply to form the full theory system of synergistic dispatch of power system, which can promote the development and enrichment of the dispatch theory series of modern power system.