1. Chapter One: Introduction
1.9 Outline
The thesis is organised into eight chapters. The first chapter contextualises the problem scope under investigation. The main subjects of this chapter introduce the motivation behind this research, describe the proposed modular structure under investigation, and delineate the thesis aims and set of objectives to achieve these aims. The chapter identifies the main challenges facing the power system grid and suggests decentralising the power system operation towards the microgrid as a solution. The control and management hierarchical strategy main contributions and outlines of this thesis are presented. A brief summary of the contents of the following chapters is given below and explained in Figure 1-15 whereas a brief summary of Thesis’ Structure, Aim and objectives, Tasks, and Novelties by chapters are presented in Figure 1-16.
Figure 1-15: Outline of the thesis structure
Microgrid constructor (chapter three)
Electric vehicle operator (chapter six) Charging station operator (chapter five)
Microgrid operator (chapter four)
Photovoltaic model Solar irradiation Temperature Wind turbine model
Wind Speed Temperature
Fuel cell model FC cost Operating cost Maintenance cost Start-up cost Efficiency Emission: (types, Factors, and treatment cost) Microturbine model Fuel cost Operating cost Maintenance cost Start up cost Efficiency Emission: (types, factors, and
treatment cost)
Diesel Engine model Fuel cost Operating cost maintenance cost
Start-up cost Efficiency Emission: (types, factors, and treatment cost) Electric vehicles model Utility grid model
Purchase tariffs Sell tariffs Emission: (types, factors, and treatment cost Microgrid operator agency (Hourly execution) Constrains: Generation consumption balance
Ramp rate limit Generating capacity Exchange power with utility grid
Charging station limit Emission limit Starts and Stops limit
Output PV_out WT_out FC_out MT_out DE_out UG_out CSO_out Voltage variation Frequency variation Charging station operator agency (Secondly execution)
Battery states for each vehicle: voltage Initial state of charge Desired state of charge Discharging minimum state of charge
Rated capacity Charging schedule curve Discharging schedule curve Supercapacitor states for each vehicle:
voltage Initial state of charge Desired state of charge Discharging minimum state of charge
Rated capacity Charging schedule curve Discharging schedule curve
EVs states: Number of EV connected
Electricity Tariff Time connection and period of
parking Rated power of inverters
Operation mode Output of each vehicle: Battery charging power supercapacitor charging power
battery discharging power Battery discharging power battery state of charge supercapacitor state of charge
supercapacitor discharging power Operation mode Microgrid three phase voltage Microgrid three phase current
Measured frequency Nominal voltage Nominal frequency Active power required Reactive power required Energy management shell: Positive sequence voltage
detector Droop controller
Vector controller Power management shell: Power arbitrating of duel source in EV based
on fuzzy controller
Power electronic shell: Switching modulation based
on SVPWM Switching
response to operate the resources of EVs via electric vehicle agency Microgrid structure Effective location of distributed generator Voltage stability analysis model Case study description Modelling of integrating EV within microgrid Energy storage devices of EV Effects of EV on: Voltage stability Voltage Power SIL Load Demand
Experimental layout (chapter seven) Experimental rig description Online
implementation using Lab View software Results
description
Conclusion and future work (chapter
Figure 1-16 Thesis’ Structure, Aim and objectives, Tasks, and Novelties
(chapter four) Microgrid operator
(chapter five) Charging station operator
(chapter six) Electric vehicle operator
Task and novelty:
Design a holistic, systematic management and control framework constructed from three
tiers (MGO, CSO, and EVO) to
include the operation of each element connected to the
microgrid.
Objective:
The CSO determines either minimise the cost of charging power or maximise the cost of discharging power of aggregated
EVs connected to the CSS of the microgrid.
Objective:
The EVO synchronises the power conversion system of the EV to either
provide standard waveforms or consume specific energy, based on the
resources’ states of the EV. Objective:
The MGO determines the optimal scheduling operation of several types
of DGs to minimise the total combined operation and treatment
emission costs of the microgrid.
PMS task and novelty:
Design Power conversion circuitry to operate the duel resources of EV: battery and bank of supercapacitors
based on multilevel inverter.
PMS Objective:
To maintain the voltage balance of the microgrid as well as achieve good performance, high power and high
efficiency.
PES task and novelty:
Design modified SVPWM to do switching modulation of
inverter switches.
PES Objective:
To operate the inverter at minimum transition, losses, and harmonics
(chapter seven) Experimental layout
Task:
Presents the available kinds of literature involving in microgrid and
EVs technologies.
Objective:
To explore an existing literature and state of the art have been arose
electricity system and EVs dimensions. Output PV_out WT_out FC_out MT_out DE_out UG_out CSO_out Voltage variation Frequency variation Microgrid
operator agency Output of each vehicle:Battery charging power
Supercapacitor charging power Battery discharging power Supercapacitor discharging power
Battery state of charge Supercapacitor state of charge
EMS process: Positive sequence
voltage detector Droop controller
Vector controller PMS process:
Power arbitrating of duel source in EV based on fuzzy controller PES process: Switching modulation based on M-SVPWM
Task and novelty:
Laboratory implementation and testing of the multilevel inverter
operation
Objective:
To determines the experimental validation and specification of switching the
multilevel inverter based on CompactRio devices and
Labview software. Charging station operator agency (chapter three) Microgrid constructor Microgrid structure
Task and novelty:
Construct a microgrid considering the advantages of uniform integrating distributed generators based
on voltage stability analysis and intigrating EVs within microgrid.
Objective:
To determine the importance of microgrid’ operation and integration
EV within microgrid (chapter eight) Discussion, Conclusion and Future work Electric vehicle operator agency Centralised operation Decentralised operation
Chapter two provides reviews of the state of art of the power system, smart grid concept,
microgrid concept, energy storage system, control of power electronic devices, and topologies of the converters. The research trends focus on the modular framework structure of integrating the EVs into the microgrid. The main components of the microgrid, the impact of the EV operation, and the charging station infrastructure are investigated to gain an understanding of the microgrid and EV. This follows with a review of a charging station infrastructure, and energy storage technologies. The various techniques of power electronic interface including bidirectional isolated and non-isolated converters, switching modulation strategy, and control strategies of the connected converter to the microgrid. A proposed multilevel inverter topology to manage and control multiple energy storage systems in EVs are also presented.
Chapter three discusses the integrating distributed generators and EVs within the microgrid
and evaluates the microgrid operation from the view of voltage stability. The chapter determines the effective location of distributed generators in the microgrid based on finding the most sensitive bus to the voltage stability. It also evaluates the microgrid operation in island mode operation compared with the traditional grid, from the view of voltage stability, by using a case study. Furthermore, some obstacles preventing the spreading of microgrids are illustrated. Modifying the electric parameters of a distribution line with the characteristic equations of the energy storage system of EVs is suggested as a solution of the generalised mathematical equations of integrating EVs within a microgrid. This follows studying the effect of EV compensation on the critical receiving end voltage and power values. The impact of the compensation of the EV within the microgrid is discussed using an example of the compensation scheme and numerical analysis of the distribution network case study that has a fleet of EVs connected to the specific bus of the distribution network.
Chapter four focuses on the optimal scheduling of the distributed generators using a mixed
integer quadratic programming approach that implements using the MATLAB environment and Cplex package. This chapter discusses the long-term management of the microgrid (MGO) which is responsible for balancing the supply and load to keep the microgrid operationally stable. A multiobjective optimisation algorithm is conceptualised/designed and implemented to schedule the generation of each distributed generator based on the optimisation model, operating cost, set of constraints for each unit, and variable electricity pricing to minimise the operation cost and the emission pollution of the microgrid energy cost. The model of the EVs is implemented as a fleet of EVs connected to the charging station. The medium-term management of the microgrid (CSO) is responsible for informing the MGO about the consumption demand of the EVs and the surplus power that could discharge from the EVs according to the energy storage limit. A case study of the proposed microgrid is analysed using different scenarios of operation that depend on the four parameters to investigate the impact of the MGO. These parameters are status mode (island or connected mode) and unit commitment strategy (applied or not applied).
Chapter five introduces and describes the operation of CSO regarding management charging
or discharging the fleet of EVs connected to it. This chapter discusses the medium-term of hierarchical management strategy of the microgrid which should be operated in minutes. The CSO is responsible for satisfying the owner of the EV in terms of several options. These options are charging the EV at minimum cost, reaching the energy storage of the EV to the desired state of charge at the leaving recorded time, metering the charging cost and revenue the discharging cost of each EV. The discharging EVs within CSO are limited to owner choice, frequency deviation, voltage deviation, and a predefined state of charge limit for energy resources. To minimise the charging cost or maximise the discharging cost of the EV, two optimisation algorithms are proposed/designed and implemented to schedule the operation of the inverter of each EV according to the available power from MGO, a period of connection, desired leaving state of charge, and predefined state of charge limit of the energy storage system. Scheduling the charging or discharging operation of the EV is optimised using a mixed integer linear programming approach using the MATLAB environment and Cplex package. Subsequently, charging and discharging many EVs from a different company are tested at the various demands of the MGO. Each EV has two energy resources: the battery as the main energy resource and the supercapacitor as the main power supply.
Chapter six introduces and describes the operation of the EVO regarding management and
control of the charging or discharging of the battery and the supercapacitors of the EV. It provides the modelling and application of the battery and supercapacitor for the EV system. A comparison between the traditional bidirectional converter topology and multilevel converter topology of EV application is discussed to find a suitable topology for connecting the EV to the microgrid and hybridization battery with a supercapacitor. The modified algorithm details of a multilevel SVPWM modulation of a suitable inverter for EV application is presented. A decomposition of the energy management and control of the EVO into a structured and modular framework is discussed. The framework of the EVO is accomplished by three sectors: EMS, PMS, and PES. The sectors are then demonstrated in the complete design of processing the charging and discharging dual resources of the EV. An exemplification of the proposed system at the different current range for charging and discharging is discussed along with the simulation results. The power sharing between the battery and the supercapacitor to support the microgrid is also discussed along with the simulation results.
Chapter seven describes the details of the physical experimental setup, the practical circuit
diagrams of the rig, and the experimental results to validate the PES operation of the modified cascade multilevel inverter at different output voltages using CompactRio devices and Lab VIEW software.
Chapter eight concludes this thesis. Key areas and some remarks and suggestions that require
further investigation are presented in this chapter.
The appendices provide formula derivation details, explanatory tables of chapters, graphs of simulation software, and graphs of practical software.