Distributed voltage-driven demand response: flexibility, stability and value assessment

Abstract

The need for operating reserve from energy storage, demand reduction (DR) etc. is expected to increase signifcantly in future low-carbon Great Britain (GB) power system with high penetration of non-synchronous renewable generation. One way to provide the reserve is to use power electronic compensators (PECs) for point-of-load voltage control (PVC) to exploit the voltage dependence of loads. This thesis focuses on the quantifcation of DR capability from PVC in the domestic sector using high-resolution stochastic demand models and generic distribution networks in GB. The effectiveness of utilising PVC in contributing to frequency regulation is analysed and demonstrated through time domain simulations. The techno-economic feasibility of such technology is evaluated considering the investment cost of the PEC deployment as well as the economic and environmental benefts of using PVC. The payback period varies between 0.3 to 6.7 years for different future scenarios considering a range of converter price. It is demonstrated that PVC could effectively complement battery energy storage system towards enhanced frequency response provision in future GB power system. For practical application of PVC for flexible demand and voltage regulation in future distribution networks/microgrids, it is important to investigate the overall small signal stability of the system. In this thesis, the linearised state space model of a distribution network/isolated microgrid with converter-interfaced distributed generators (CDGs) working in grid following mode along with loads with PVC is developed. The stability performance is revealed through both modal analysis and time domain simulations. It is shown that multiple loads with PVC for voltage regulation in distribution networks are not likely to threaten the small signal stability of the system. In the case of a microgrid, the introduction of PVC is shown to have marginal impact on the low frequency modes associated with the droop control of the CDGs. However, there is a trade-off when choosing the droop gain of the loads with PVC. Lower droop gains could ensure better frequency regulation in face of intermittent renewables but at the expense of a lower stability margin for an oscillation mode at a frequency slightly higher than 20Hz.