* Corresponding author: Amer Al-Hinai, alhinai@masdar.ac.ae 1 Masdar Institute of Science and Technology, iEnergy Center, P.O. Box 54224, Abu Dhabi, UAE 2 Sultan Qaboos University, Electrical & Computer Engineering, PO Box 33, PC 123, Alkhoud, Oman Copyright © JES 2016 on-line : journal/esrgroups.org/jes Maksymilian Klimontowicz 1 , Amer Al-Hinai 1,2, * , Jimmy C.-H. Peng 1       Regular paper                                                                                                                             !          "       #$%$& Keywords: load frequency control, sliding mode control, distributed energy resources Article history: Received 15 September 2015, Accepted 16 February 2016 1. Introduction Frequency deviation is defined as the difference between current system frequency and the scheduled value [1], [2]. According to the European Network of Transmission System Operators for Electricity (ENTSO-E) regulation policy, [2], the grid frequency is allowed to swing between ±180 mHz or 200 mHz for a system with and without load self-regulation, respectively. In order to reach quasi-steady-state, the grid will continuously drive the integral of frequency deviation trajectory to zero within a predefined timeframe. Such control action is essential for electronic devices, which calculate time based on power supplied frequency. Modern power systems regulatory policies subdivide frequency regulation into three parts: primary, secondary, and tertiary control. Primary control is an intrinsic feature of every power unit. It is responsible for providing local responses to mitigate encountered disturbances. The amount of control effort is proportional to the rating of each device, and does not necessary resolve frequency deviations. The aim of the secondary frequency regulation is to maintain the frequency and/or the scheduled power flows in tie-lines. The input signal to the secondary controller is known as the Area Control Error (ACE), which is a linear combination of frequency and tie-line power deviations. Broader descriptions of modes, states, and organization of the secondary regulation can be referred to [2] and [3]. Usually PI type controller is utilized in each assigned control area in the system [1, 2]. In the European interconnected electrical power system, tertiary control or tertiary reserves are divided into: directly activated and schedule activated. Directly activated can