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This paper summarises and evaluates in detail aggregate models of plug-in electric vehicles (PEVs) for primary frequency control (PFC) through dynamic simulations. A basic aggregate model of PEVs for PFC is introduced and then gradually developed in the following steps: 1) technical characteristics of PEVs are incorporated into the model; 2) technical characteristics of distribution networks are formulated and added; 3) a strategy is described to well-design the frequency-droop controller of PEVs for PFC. Moreover, from an economic point of view, a method is presented to assess the benefits which could result from PEVs for PFC. Four simulation scenarios are defined to evaluate the impact of: 1) different PEV's penetration levels; 2) PEV's operating modes and constraints; 3) power consumed in the network during the PFC; 4) well-designed frequency droop controller, on the frequency response following a contingency event. Simulation results show that aggregate PEVs have a great potential not only to improve the frequency response, while preserving the overall stability, but also to save some costs associated with PFC.

This paper introduces the exergy hub approach, a framework that can be used for the optimisation of multi–carrier energy supply systems. Moreover, this paper presents a comparison between the results of the optimal dispatch (which defines how much power should be produced by each generation unit) obtained from an exergetic efficiency optimisation and the optimal dispatch obtained from an energetic efficiency optimisation. Finally, a scheduling optimisation (which defines when to turn on or turn off a unit) is performed to identify which combination of available units gives the best exergy and energy performance for different load ratios according to the outside temperature. The results provide valuable insights about the influence of using exergy analysis as an assessment tool in the optimisation of energy supply systems with multiple energy carriers, particularly regarding the difference with respect to an energy optimisation and the effect of the outside temperature.