Increasing penetration of non-synchronous generators (e.g. wind) would result
in drastic reduction of the system (effective) inertia in future especially, during the
low demand condition. Moreover, the possibility of larger and more frequent infeed
losses is likely to cause unacceptably large variations in grid frequency and its
rate-of-change (RoCoF). Restricting RoCoF within acceptable limits will be critical
to avoid triggering of mains protection relays based on RoCoF which could lead to
cascading outages and threaten system security. Rapid response from loads could
be crucial in such situations to ensure secure operation of the system.
Flexibility in certain types of loads could be exploited to provide fast and controllable
power reserve if the supply voltage/frequency is controlled using the existing
power electronic interfaces (e.g. motor drives) or additional ones like recently proposed
`Electric Spring' (ES). This thesis investigates the availability of fast shortterm
power reserve from such controllable loads and shows their effectiveness in
collectively contributing to inertial and/or primary frequency control.
The proportion of different types of voltage-dependent loads varies depending
on the time of the day. It is, therefore, important to determine the available reserve
from such loads over the time horizon. The thesis proposes an online estimation
method which can be used by the system operators to estimate available reserve in
real time and schedule other forms of reserves accordingly.
For practical implementation of ES in future distribution networks, it is important
to investigate the operation of multiple such devices and their interaction
with the change in network parameters. This thesis has developed both the time and
frequency-domain models to study the control loop dynamics of ES in order to
mitigate any adverse interaction.