Reliability management of microgrids with renewal energy sources
Koh, Leong Hai
Date of Issue2014
School of Electrical and Electronic Engineering
Operational challenges of classical electric utilities, evolutionary changes in the regulatory and the emergence of smaller generating systems (e.g. micro turbines, wind turbines, hydroelectric generators etc.) have unlocked new prospects for distributed generation at site by electricity users. Distributed energy resources (DERs), i.e. small power generating systems which are typically located in the vicinity of end-users, have materialized as a favourable route in meeting the growing electric power needs of end-users and the increasing emphasis on power quality, reliability and energy resilience. DERs are integrated with load demand and energy storage systems (ESSs) providing an opportunity for an entirely new approach in establishing a microgrid. Such a microgrid can provide a lot of benefits to the end-users as it is designed and implemented to meet the immediate power and heat needs of the immediate site. The microgrid can provide uninterruptible power supply, decrease feeder cable losses, enhance local reliability and improve power quality. The energy resources connected to the microgrid include stable sources such as micro turbines, fuel cells and diesel generators; and intermittent energy resources such as photovoltaic system (PVS). A microgrid can be operated as a stand-alone electrical grid, or grid-tied when connected to the main utility grid. In remote villages, islands, emergency situations (e.g. refugee camps, tsunamis, earthquakes etc.), remote mining operations and military command posts, stand-alone microgrids would be a natural choice to provide electricity. This thesis serves to establish the probabilistic reliability of hierarchical level I (HL I) of stand-alone microgrid operational adequacy taking into considerations of uncertainties in ESSs, PVSs and conventional generators (CGs). The IEEE Reliability Test System (IEEE-RTS) constant intra-hour load model is modified and used to include a minutely random rapid-ramp microgrid demand model. Instead of using the classical constant intra-hour or intra-day time step, an operating period of one-minute time step to incorporate the effect of fast ramp up (or down) of system components is considered for microgrid operating adequacy due to load and resource variations. The ESS model is proposed with time dependent state-of-charge (SOC) in order to determine the output power from cell to system level. The PVS reliability is modelled using the basic solar photovoltaic cell to form the PV system in various different configurations and different penetration levels. The interaction between the variability of PVSs and random rapid-ramp demand; and between the variability of PVSs and ESSs are evaluated. The two reliability indices used for the stand-alone microgrid considered are the expected energy not supplied (EENS) and the expected energy not used (EENU).
DRNTU::Engineering::Electrical and electronic engineering::Electric power