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As a result of the increasing integration of renewable energy sources, power system is changing to a low inertia system with intermittent power supply. Frequency stability is therefore difficult to be maintained. Rather than increasing the spinning reserve capacity from conventional fossilfuel generators, the use of Energy Storage System (ESS) for frequency response is considered as a technically viable lowcarbon solution. To facilitate the grid-level study which aggregates a number of widespread small-size ESS, simplified models of multi-type ESSs including batteries and flywheels were developed. A generalized frequency controller was developed and applied to the aforementioned types of ESS. The controller coordinates the response amongst a population of ESS based on the units' State of Charge indicator. An adaptive droop control is combined with the coordinated control to guarantee a linear frequency response provided by a smaller number of ESS units. The number of charging and discharging of each unit is therefore reduced which prolongs the lifetime of the ESS units. Case studies were carried out by connecting a number of multi-type ESSs to a simplified GB power system model. Results show that the grid-scale ESSs are able to provide frequency response similar to but faster than frequency-sensitive generators. Implementation of ESS is therefore technically feasible to support the grid frequency stability with the reduction in the spinning reserve capacity.

The control of multiple battery energy Storage systems (BESSs) to provide frequency response will be a challenge in future smart grids. This paper proposes a hierarchical control of BESSs with two decision layers: the aggregator layer and the BESS control layer. The aggregator layer receives the states of charge (SoC) of BESSs and sends a command signal to enable/disable the BESS control layer. The BESS controller was developed to enable the BESSs to respond from the highest to lowest SoC when the frequency drops, and from lowest to highest when it rises. Hence, the BESS's response is prioritised to reduce the impact on the power system and end-users during the service. The BESS controller works independently when a failure occurs in the communication with the aggregator. The dynamic behaviour of the population of the controllable BESSs was modelled based on a Markov chain. The model demonstrates the value of aggregation of BESSs for providing frequency response and evaluates the effective capacity of the service. The model was demonstrated on the 14-machine SouthEast Australian power system with a 14.5GW load. 254MW of responsive capacity of aggregated batteries was effective in reducing the system frequency deviation below 0.2 Hz following a sequence of disturbances.

The role of ancillary services related to the frequency control have become increasingly important in the smart grids. Demand Side Response is a competitive resource that can be used to regulate the grid frequency. This paper describes the use of heat pumps and fridges to provide ancillary services of frequency response so that to continuously balance the supply with demand. The power consumption of domestic units is usually small and, therefore, the aggregation of large numbers of small units should be able to provide sufficient capacity for frequency response. In this research, dynamic frequency control was developed to evaluate the capacity that can be gathered from the aggregation of domestic heat pumps and fridges for frequency response. The potential of frequency response was estimated at a particular time during winter and summer days. We also investigated the relationship between both loads (domestic heat pumps and fridges) to provide Firm Frequency Response service. A case study on the simplified Great Britain power system model was developed. Based on this case study, three scenarios of load combination were simulated according to the availability of the load and considering cost savings. It was demonstrated that the aggregation of heat pumps and fridges offered large power capacity and, therefore, an instantaneous frequency response service was achievable. Finally, the economic benefit of using an aggregated load for Firm Frequency Response service was estimated.

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