Integration of more renewable energy resources introduces a challenge in frequency control of future power systems. This paper reviews and evaluates the possible challenges and the new control methods of frequency in future power systems. Different types of loads and distributed energy resources (DERs) are reviewed. A model representation of a population of the water heater devices for the demand side frequency response is considered. A model representation of a population of battery energy storage system (BESS)-based DERs such as smart electric vehicles (EVs) charging, large-scale BESSs, and residential and non-residential BESSs, are highlighted. The simplified Great Britain power system and the 14-machine South-East Australian power system were used to demonstrate the effectiveness of the new methods in controlling power system frequency following a disturbance. These new methods are effective in recovering the fallen frequency response and present a great potential in controlling the frequency in future power systems.

This paper presents a decentralized scheduling algorithm for electric vehicles charging. The charging control model follows the architecture of a Multi-Agent System (MAS). The MAS consists of an Electric Vehicle (EV)/Distributed Generation (DG) aggregator agent and “Responsive” or “Unresponsive” EV agents. The EV/DG aggregator agent is responsible to maximize the aggregator’s profit by designing the appropriate virtual pricing policy according to accurate power demand and generation forecasts. “Responsive” EV agents are the ones that respond rationally to the virtual pricing signals, whereas “Unresponsive” EV agents define their charging schedule regardless the virtual cost. The performance of the control model is experimentally demonstrated through different case studies at the micro-grid laboratory of the National Technical University of Athens (NTUA) using Real Time Digital Simulator. The results highlighted the adaptive behaviour of “Responsive” EV agents and proved their ability to charge preferentially from renewable energy sources

For a grid-connected inverter requiring the ac volt- age magnitude and the active power control, both vector control and power synchronization control can be applied. The stability comparison based on the dq impedance stability analysis between both control are carried out via three factors including the grid impedance, the inner current loop and the virtual impedance. The dq impedances of the inverter based on both control are derived. The determinant of the impedance ratio is used for the stability analysis. The bode plot of the grid impedance and the inverter impedance are present to assist the stability analysis and explain their interactions. It is found that increasing the grid impedance and the cut-off frequency of the current loop stabilize the inverter with the power synchronization control, which is converse to the vector control. Furthermore, the inverter with the power synchronization control may suffer the instabilities when connecting to a strong grid. The virtual inductor and resistor are proposed to enhance the stability for the vector control and the power synchronization control respectively. The simulation validation using Matlab/Simulink is performed.

The capability of domestic heat pumps to provide dynamic frequency response to an electric power system was investigated. A thermal model was developed to represent a population of domestic heat pumps. A decentralised dynamic control algorithm was developed, enabling the heat pumps to alter their power consumption in response to a system frequency. The control algorithm ensures a dynamic relationship between the temperature of building and grid frequency. The availability of heat pumps to provide low-frequency response, was obtained based on data supplied by Element Energy. Case studies were carried out by connecting a representative model of the aggregated heat pumps to the regional Great Britain (GB) transmission system model, which was developed by National Grid. It was shown that the dynamically controlled heat pumps distributed over GB zones have a significant impact on the GB system frequency and reduce the dependency on frequency services which are currently supplied by expensive frequency-sensitive generators. The rate of change of frequency was also reduced when there is a reduction is system inertia.

The high penetration of inverter-fed renewable energy sources (RESs) in modern energy systems has led to a reduction in the system’s inertial response. This reduction in the rotational inertial response is associated with synchronous generation and might result in a deteriorated frequency response following a power disturbance. This paper investigates the frequency stability of the Kingdom of Saudi Arabia’s (KSA) grid. It includes a description of the changing energy landscape of the KSA’s electricity grid and an investigation of the impact of high penetration levels of inverter-fed RESs on the dynamic behavior of the KSA grid. The impact of RESs has been studied through a simulation of case studies of the future KSA power system using the MATLAB/Simulink simulation software. The frequency stability of the KSA’s power system has been evaluated with various RES levels under peak and base load conditions. The simulation results show that the high penetration levels of RESs dramatically affect the system’s frequency response, especially under off-peak conditions. In addition, the significance of battery energy storage systems (BESSs) for compensating the reduction in the system inertial response has been addressed. The results show the effectiveness of aggregated BESSs for enhancing the system frequency control of the KSA grid.