Generally, the control parameters should be designed based on three main factors:
1- Consumers’ comfort level. Consumers need hot water at a temperature that satisfies them. If they are not satisfied with this temperature, they will not be motivated to participate or continue to participate in DSM programs.
2- The load (EWH) itself. It is very important to consider and study the effect of the control strategy on the EWH. The EWH should not turn ON/OFF frequently in order to avoid reducing the lifetime of EWH switches.
3- Power system requirements. The purpose of using controllable loads in the power system is essentially to regulate it and reduce the frequency or voltage variations.
Unlike the first two factors, power system requirements can be different from one power system to another. Referring to the integrated control of EWHs, Td varies as a function of the system frequency. Therefore, the power system requirement that will be considered is the system frequency.
The acceptable frequency range in the large utility grid can be different from the acceptable frequency range in the mini-grid, although they might have the same nominal value of system frequency (50 Hz or 60Hz).
Much effort has been made in frequency control for large grid systems to allow power flow from multiple sources. An imbalance between generation and demand will lead to increased frequency deviation, destabilize the system, and may even cause blackouts. Therefore, it is highly recommended that system frequency does not exceed (±1%) of its nominal frequency (50 or 60Hz) under normal operation conditions [53].