The world faces an energy problem.Oil supply is gradually running out.Therefore,power systems undergo fundamental changes due to the integration of large volumes of wind and other intermittent renewable energy sources.In addition,renewable generation is variable and difficult to predict and cannot provide services needed to balance demand and supply in real time.That is why the requirements for real-time ancillary services such as frequency control,efficiency of system operation,and the ability to absorb intermittent renewable output are increasing.To satisfy these requirements it is more convenient to use demand response strategies instead of regulation conventional generation.Renewable energy sources bring more variability and uncertainty to power systems.This has potential impacts on power system reliability and efficiency.These impacts can in principle be either positive or negative;however,large amount of renewable power usually turn even positive impacts to negative at some stage of penetration level with regards to the cost of integration and will increase the demand for flexibility of the ancillary services associated with system balancing.Especially,wind power production introduces additional variability and uncertainty into the operation of the power system.To meet this challenge,there will be need for more flexibility in the power system.How much extra flexibility is required depends on the one how much wind power is embedded in the system and on the other hand on how flexibility already exists in the power system.The demand response(DR)concept implies the regulation of energy consuming through intelligent and more efficient control strategies for energy users both residential and commercial.That concept includes usage of smart control of thermostatically controlled loads(TCLs)through HVAC(Heating,Ventilation,and Air Conditioning),EWH(Electric water Heaters)etc.and real time electricity pricing environment for loads.These DR strategies can provide frequency response during the peak loads of power system with intermittent renewable sources expelling conventional regulation of generation and hence increase the energy efficiency of power system.Also smart control strategies of electrical energy consumption in commercial and residential fields by HVAC,EWH and other DR strategies can lower the energy consumption and shift the consuming load during peak hours through delaying and shaving loads.That can be great improvement for efficient work of modern power systems facing integration of renewable energy sources.The work done in this thesis named "Integration of Demand Response Strategies to Implement Ancillary Frequency Response and Increase Efficiency of Power Systems with Intermittent Renewable Energy Sources" develops the model of system frequency response and HVAC load control model through several approaches.Simulink(MATLAB)is used to build the frequency response and HVAC load Control models;Adaptive Fuzzy Logic Control(AFLC)and PID Control strategies used to imply the ancillary frequency response to the Power System.To assess from efficiency and the performance of the proposed method;a typical Low-Order Frequency Response Model with Great Britain Power System characteristics is used to integrate the HVAC load to the system and the results are investigated.