Optimal scheduling of energy systems incorporating load management schemes

• Main Author: Krishnan, Ashok
• Other Authors: Gooi Hoay Beng
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/85712; http://hdl.handle.net/10220/49894
• Institution: Nanyang Technological University

The advent of enabling smart grid technologies has resulted in the proliferation of heterogeneous power generation networks. In this context, the concept of microgrids has gained popularity in recent years due to their ability to integrate renewable energy sources with the power system. As such, many industrial units are increasingly displaying characteristics similar to grid-connected microgrids. Consequently, the traditional day-ahead scheduling (unit commitment) problem solved in power systems needs to account for the increasingly heterogeneous nature of the generators. Furthermore, deregulated electricity market concepts such as load management need to be incorporated in the scheduling problem. As such, there exists a need to formulate optimization models for modern energy systems which can account for the heterogeneity in the generation and the flexibility in the load. This thesis is broadly divided into four parts. The first part develops accurate scheduling models of the components which constitute the energy systems considered in the later chapters of the thesis. The mixed logical dynamical modelling framework is used to develop scheduling models of the gas turbines, steam turbines, boilers, diesel generators, battery energy storage systems, thermal energy storage systems and interruptible loads. The scheduling models of the gas turbines, the steam turbines and the boilers include the power trajectories followed by these components while undergoing the hot, warm and cold start-up processes. A detailed treatment of the modelling of an exemplar conventional fossil fuel based generating unit using the mixed logical dynamical framework is also provided. The second part of this thesis proposes a shipyard energy management system (SEMS) to optimize the cost of operating a typical shipyard drydock. The SEMS comprises three modules - load forecasting, contracted capacity optimization and optimal scheduling. The load forecasting module uses artificial neural networks (ANN) to generate short term and medium term load forecasts. Historical load demand data and ship arrival schedules are provided as inputs to the ANN. The inclusion of the ship arrival schedule as an input to the ANN enhances the accuracy of the load forecast. The optimal scheduling module minimizes the electricity cost incurred by the drydock operator. A pump scheduling optimization model is proposed within the optimal scheduling module which minimizes the uncontracted capacity cost incurred by the drydock operator. The third part of the thesis enhances the optimal scheduling module of the SEMS. The microgrid considered in this context comprises diesel generators, battery energy storage systems, renewable energy sources, flexible pump loads and interruptible loads. A two-stage energy management system architecture is proposed wherein an optimal, day-ahead scheduling problem similar to that of the SEMS is solved in the first stage. Subsequently, the results from the first stage are used to solve an optimal power flow problem in the second stage. This is done to account for the network losses and to verify the feasibility of the optimal schedule generated in the first stage with respect to the network constraints. This is unlike conventional unit commitment formulations which ignore the AC network constraints. Thereafter, the two stages are coordinated using an iterative procedure. The utility of the proposed optimization model is demonstrated using illustrative case studies. The final part of this thesis proposes a detailed optimal scheduling model for an exemplar multi-energy system comprising combined cycle power plants (each constituted by one gas turbine and one steam turbine), battery energy storage systems, renewable energy sources, boilers, thermal energy storage systems, electric loads and thermal loads. The electric and thermal energy streams are linked through the combined cycle power plants which produce electricity and waste heat. A practical, multi-energy load management scheme is proposed which utilizes the flexibility offered by the flexible electrical pump loads, the electrical interruptible loads and a lumped flexible thermal load to reduce the overall energy cost of the system. The efficacy of the proposed model in reducing the energy cost of the system is demonstrated in the context of a day-ahead scheduling problem using four illustrative scenarios.