A dissertation submitted to the Facaulty of Engineering and the Built Environment,
University of the Witwatersrand in ful lment of the requirements of the degree of
Master of science in Engineering
September 2016 / Standalone microgrid studies are being done because an expansion of the existing
utility grids to supply power to remote communities is not feasible. Standalone
microgrids can be considered as one of the solutions for remote communities because
power can be generated close to these communities and it minimizes cost related to
power transmission. Renewable energy sources with large
uctuations are frequently
the source of power for these standalone microgrids. The
uctuating nature of these
renewable sources can often lead to frequent blackouts. This research is aimed at
minimizing power
uctuations using controllable energy storage systems. This MSc
focuses on the analysis of the ramp rate and delay time requirements for controllable
energy storage system used in standalone PV microgrids. Measured insolation data
and recorded load demand data for typical domestic appliances are used in this
study to analyze ramp rates present. The ramp rates are then used to determine
the range of energy storage ramp rate and delay time required to maintain the
microgrid voltage within the standardized range of 1pu 5%. From the recorded data
it has been observed that PV power can be sampled from at least 1-second intervals
without losing important information. The 1 second averaged ramp rates obtained
from the insolation data measurements have been found to have the highest value
of 0.12pu/sec. However, this ramp rate increases to 0.3pu/sec when the allowable
microgrid voltage band is narrow (1pu 5%). These insolation ramp rates are very
low compared to the ramp rates of typical loads that can be connected to a microgrid.
This means that, if the energy storage system is speci ed to meet the load ramp rate
requirements, it will be able to respond to the
uctuating PV power. The results
obtained from the simulations con rm that energy storage system ramp rate plays an
important role in the stability of a standalone microgrid. The minimum allowable
energy storage ramp rate was found to be 8.15pu/sec for load transients with a
ramp time of 20ms. This value is 28 times the energy storage ramp rate required to
cancel out insolation
uctuations. This further con rms that energy storage system
ramp rates must be speci ed using the load demand data. The maximum allowable
delay time was also found to be 0.53s to maintain the microgrid voltage within the
standardized range of 1pu 5%. This delay time is applicable when canceling out
only the insolation
uctuations. To cancel out load transient power
uctuations,
there should be no delay time. / MT2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/22674 |
| Date | January 2016 |
| Creators | Horonga, Nyasha |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xii, 82 leaves), application/pdf, application/pdf, application/pdf |
Page generated in 0.0018 seconds