Search

The level of electricity consumption usually can reflect the level of development of a society. With the development of social industrial technology, the demand for electricity and other energy sources is increasing. Meanwhile, the control measures for carbon emissions have become an important social issue that needs to be solved urgently cause a series of problems such as environmental pollution has become more and more serious with the large-scale use of traditional fossil energy. Renewable energy provides new ideas for solving this issue. Recently, some renewable energy sources, including solar and wind energy, have been widely used. However, as renewable energy has some shortages such as instability, inflexibility, it can not replace traditional fossil energy completely. Due to consumers usually having different energy demands, the concept of an integrated energy system including traditional fossil energy and renewable energy has been proposed. The efficiency of energy usage can be improved, and energy losses can be reduced through coordinated planning and optimal operation method. Thus, integrated energy systems become an effective method to solve the current social issues. With the increasing penetration of renewable energy injection in the electric power grid, the impact of uncertainty and fluctuation in renewable energy generation on the grid performance cannot be ignored. Integrated energy networks with the Power-to-Gas (PtG) system have been used to maintain the stability of the system by employing the efficient conversion of different energy forms (electricity and gas) and massive energy storage. Meanwhile, the wave energy converter system can make full use of wave energy to improve the use of renewable energy in the integrated energy system. An economic receding horizon control strategy that solves the constrained optimization problem of the wave energy converter system is analyzed in this research. The Model Predictive Control (MPC) method is adopted to focus on tracking system cost function, and the system state is steered to the steady-state at the end of the optimization horizon by using terminal equality constraint, and the non-convex optimization problem is solved by the controller in real-time. As a form of a hybrid multi-energy system, the integrated energy system usually contains different forms of energy such as electric power, thermal, and gas while meeting the load of various energy forms. Therefore, the model building and optimal operation of the integrated energy system are the key points of the research. The appropriate models established for the integrated energy system can not only reduce the calculation and power dispatch times but can help the entire system reach the optimal state faster. The main work of this thesis is as follows： In chapter 2, various energy conversion systems, including power-to-gas systems and combined heat and power (CHP) systems have been analyzed. A method for optimal operation of a microgrid that contains the PtG system with rolling horizon strategy is proposed, and it applied the power and gas cooperative accommodation to solve the deviation between the forecast load and real load as well as reduce the overall microgrid operation cost in a corrective manner. Models of various components in a microgrid are introduced, and a mixed-integer linear program (MILP) mathematical optimization problem is formulated to describe the day-ahead operation problem. The rolling horizon strategy is adopted to reduce the impact of intermittence natural of the renewable energy sources, and the benefits of cooperative accommodation of electric power and gas in a corrective manner are discussed as well. In chapters 3 and 4, the different energy models in the integrated energy system have been analyzed. The dist-flow method is applied to quickly calculate the power flow, and the gas system model is built by the analogy of the power system model. Meanwhile, the piecewise linearization method is applied to solve the quadratic Weymouth gas flow equation, and the Alternating Direction Method of Multipliers(ADMM) method is applied to narrow the optimal results of each subsystem at the coupling point. Simulation-based calculations and comparison of results under different scenarios are proved that the power-thermal-gas integrated energy system enhances the flexibility and stability of the system as well as reduces system operating costs to some extent. In chapter 5, an economic receding horizon control strategy that solves the constrained optimization problem of the wave energy converter system is proposed. Generally, the standard Model Predictive Control focuses on tracking system cost function. However, in economic MPC, a general economic cost function is established, which contains the objective of maximizing the energy extracted from ocean waves and minimizing the operation cost, as well as directly reflecting the economic indicators of the Wave Energy Converter (WEC). Meanwhile, the system state is steered to the steady-state at the end of the optimization horizon by using terminal equality constraint, and the non-convex optimization problem is solved by the controller in real-time. The auxiliary optimization problem is applied to the stability analysis, while the convergence of the system can be proved by the Lyapunov technique. And several numerical simulation results are presented to demonstrate the effectiveness of the proposed algorithm.

The thermal behaviour of crystal phases of 3-ethyl-5-(2-(3-ethyl-2-benzo-thiazolinylidene)-ethylidene)-rhodanine (commercial name AGFA 10) has been studied. The transition temperatures and transition heats for its crystals were determined by DSC. The entrophy changes for those crystals were calculated. Few previously unknown crystalline phases of this compound, have been identified from the DSC study. One of the new crystals found by DSC has been identified with X-ray diffraction.