Cost-efficient operation and control of isolated power systems

Remote areas and islands isolated from the main electric power system ensure reliability and stability of power supply using diesel generation. Due to the high purchase and transportation costs of diesel fuel, isolated communities are exploring other options for efficient and reliable power supply.

Renewable energy sources (e.g., wind and solar) can reduce operating costs, although are unable to achieve high penetration without expensive and complex enabling technologies such as energy storage. Furthermore, the stochastic and intermittent nature of renewable sources (i.e., wind and solar) makes the control system complex, decreasing power system reliability and requiring highly qualified personnel in local control centres. To satisfy security needs system operators might keep diesel engines in operation even during high renewable energy penetrations consistently reserving some part of system load to diesel generation. The problem becomes particularly acute when diesel engines are forced to operate at partial load extensively, resulting in poor combustion efficiency and potential engine damage.

In the first part of this research, the thesis investigates how forecast-based operational frameworks of an isolated system can facilitate the transition away from fossil fuel dependency towards sustainable electricity generation. Implementation of forecasting into systems traditionally governed by non-predictive algorithms offers opportunities to reduce regulating reserve requirements and displace diesel generation with renewable energy without compromising system reliability. The impact of forecasting error is evaluated and considered in systems of different sizes and with different compositions of renewable resources. Depending on the system configuration a certain increase in renewable energy penetration, reduced operational costs or both can be observed. The findings also suggest that even a simple forecasting system can lead to substantial operational improvements.

Another part of this research is dedicated to the design of control architecture. In the quest to reduce the reliance on diesel fuel, practical isolated power systems employ multiple enabling technologies. The isolated power system with multiple technologies may suffer from some overlap in capability and function, leading to reduced asset utilisation. This thesis suggests a cost-efficient control strategy, adopting low load diesel application to reduce fuel consumption and improve renewable energy penetration without overcomplicating the control architecture. Two common control strategies, minimization of operational cost and maximization of renewable energy penetration, are considered and analysed based on the operation of a real-world isolated power system. A mathematical model is initially developed, then validated against real data, to facilitate the comparative assessment of various control approaches. Optimised control methodologies are shown to deliver significant fuel savings, with increased renewable energy penetration, in comparison to conventional management.