1. Chapter One: Introduction
1.3 Methodology
An important aspect of this research that has a direct impact on the research objective is the choice of the system under investigation. A pragmatic approach in this applied research project is adopted to gain and contribute implementation insight to the problem of managing and control balancing between the supplies and loads at minimum cost and high efficiency in the microgrid. The research begins by constructing the microgrid infrastructure and evaluating the advantages of the microgrid from the view of the voltage stability analysis until implementing the signals of the energy storage system of the EV through three levels of hierarchical control strategies. The long-term, medium-term and short-term objectives are the strategy, policy and process of the system, which take place within the MGO controller, CSO controller, and EVO controller respectively.
In this research, an attempt is made to include all relevant components and subsystems to produce results that are directly relevant to the practical design. The practical system is deployed in a geographical location feeding residential, commercial, and industrial demands through the long connection between various distribution network components such as circuit breakers, cables and secondary equipment such as protection relay, distribution automation, and communications equipment. Therefore, it is expected that there is some significant constraint that is not considered using a purely theoretical approach but could be uncovered when the practical system is applied. A realistic distribution network with all cables and load characteristics, a variety of existing EVs, and existing parameters of distributed generators, are considered in control and management aggregated EVs connected to a microgrid in order to mitigate unattainable constraints.
The management and control research of a microgrid begins by constructing the microgrid from the existing distribution network by adding all necessary equipment. The case study investigated integrates some distributed generators into the distribution network to decentralise the distribution network operation and add all necessary power electronic devices and communication links to transfer the distribution network into the microgrid network. The revenue of the microgrid operation is measured by monitoring the voltage stability indicator of the traditional grid compared to the modification grid. Voltage stability model analysis depends on identifying the magnitude of the eigenvalues that provide a relative measurement of proximity to instability and the eigenvectors that present information related to the mechanism of losing voltage stability.
For insight into the effect of the EV on the microgrid, the study proposes appropriate mathematical equations to integrate the EV into a line of the microgrid based on a modification of the characteristic equation of the distribution feeder which carries the EVs. The effective location of the charging station in the microgrid is located using the identification of the most sensitive bus bar to voltage stability analysis in the network compared to the minimum voltage bus bar.
The study proposes a hierarchical management and control strategy from three sections which are MGO, CSO, and EVO to ensure the flexible, stable, and reliable operation of the microgrid and EVs. The MGO sets the objective function to minimise the power cost of distributed
generators and treatment pollutant emissions. The CSO sets the objective function either to minimise the cost of charging the power or maximise the cost of discharging the power of the EV. The EVO function is to operate a smart charger to decentralise charging and discharging the EV. The EV has two energy storage systems: battery and supercapacitors. The baseline design parameters of the energy storage systems are obtained through iterative simulation and reference of literature. The fuzzy logic theory is used to implement the heuristic reasoning of energy management by incorporating the use of battery and supercapacitors in synergistic operations. Modified multi-level space vector modulation control is implemented effectively to design the modified cascade multilevel inverter to control the charging and discharging operation of the battery and bank of supercapacitors with the microgrid. As the modelling platform, the MATLAB environment tools with Matpower and Cplex package are used extensively. The schematic diagrams of the inverter have drawn using Altium designer whereas the LabVIEW software control the laboratory experiment of the inverter. Some graphs are drawn using PSIM simulation software.
The research into power and energy management of a microgrid, including hybrid battery- supercapacitors energy storage systems, is a big challenge because:
The microgrid has bidirectional power flow in nature. It has different distributed generators’ characteristics. It has different load characteristics.
It has two modes of working: island and connected mode. It has a broad network of the communication system.
It has many EVs with a different capacity and driving style, whereas each EV has two different storage system characteristics.
All of these uncertainties result in very different energy, power, frequency, voltage, and current characteristics. The interactions between these bidirectional power flow components that have a different dynamic reaction are not obvious without exploration of all components’ technologies and performing some empirical verification. This involves adopting a holistic research strategy, embracing all subsystems of distributed generators, EVs, loads, and hierarchical control strategy, rather than narrowly focusing on specific frameworks that adopted other researchers’ work. The approach provides a comprehensive perspective and adds value to this applied research topic. Figure 1-11 illustrates the research framework diagrammatically. The operation of a modular, hierarchical controller operates periodically according to predefined times for each term based on the sequential decision process.
Chapter three (construction MG) Chapter six (EVO_1) Chapter five (CSO_1) Chapter four (MGO) Balancing power of DG 1-N
and load demand 1-N Energy storage systems 1 & 2
Operating constraints of distributed generators 1-N and calculate the total demand and losses
using power flow analysis
Operating constraints of energy storage systems 1 & 2
Optimization function to coordinate the power sharing
between the distributed generators
Synchronizing with microgrid, coordinate power
split, and switching modulation States of the EVs 1-N
Operating constraints of electric vehicles 1-N
Optimization function to charging or discharging the
electric vehicles 1-N
Power interfacing methods
Overall challenge and research problem Physical, electrical, and dynamic prosperities Problem classification Implementation issues Problem refinement Holistic and pragmatic approach
Power interfacing methods
EVO_N CSO_N
Structured power and energy management methodology
Implementation framework (quantitative description)
Voltage stability analysis and Capacity of MG available
Impact of EV on MG & Number of EV connected
Microgrid power requirements
Vehicle power and energy requirements
Chapter one
Problem investigation
Chapter two Problems and challenges in
the research domain
Chapter seven
PES validation
Power interfacing methods
Chapter eight
Dissection, Conclusion and Future work