Demand response through point-of-load voltage control

Abstract

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.