Regarding high penetration of distributed energy resources into the medium and low voltage level, power systems undergo challenges with respect to their reliability, security and stability. Aspects of microgrids, including their architecture, distributed generation, storage, and control schemes, are widely researched across the globe, as they have a promising future to integrate distributed energy resources into power systems, thereby reducing greenhouse gas emissions and increasing the reliability and security of power systems with a large amount of distributed generation. Microgrids can be described as decentralized electrical power systems comprising distributed generation, local loads and storage. They can be operated both in grid-parallel and islanded mode. Frequency stability is a common issue to be addressed, especially in islanded microgrids. The focus of this thesis is the development and investigation of a control method for islanded microgrids to regulate their frequency. In islanded mode, microgrids tend to have a low inertia in comparison to large traditional power systems, especially when there is a high penetration of power electronic interfaced power sources in the microgrid. Thus, frequency changes more quickly when there is a power mismatch between generation and demand. In large power systems, frequency control is an important task. For this thesis, its implementation in islanded microgrids to regulate and maintain the frequency is investigated. However, frequency control is much more difficult to be achieved without the support from the utility grid. An additional control method, including load step pre-announcement and a bang-bang controller, is developed in this thesis to assist frequency control to keep frequency stable within islanded microgrids. The concept of the proposed control method is to anticipate active power changes, which result in imbalances between load and generation, by proactively delaying them for a specific time interval, so that any dynamic effect on frequency deviations caused by them is smoothed. Active power infeed of conventional generation based on directly coupled rotating machines can be controlled, and thus, frequency control in islanded microgrids is supported. In this thesis, a simulation model of an islanded microgrid, including a conventional generator, a photovoltaic generator and a lumped load, is used as a study case. Dynamic simulation results of the islanded microgrid are presented and analyzed. The results between the islanded microgrids with and without the proposed control method are compared. The feasibility and effectiveness of the implementation of load step pre-announcement and bang-bang controller are validated using simulation results. Set values of the two time parameters, preset and total time, of the control method regarding different cases are optimized. A discussion regarding still existing problems is given. This includes the influence of frequency measurement time delay on the proposed control method as well as frequency oscillation that may be caused by repeated reconnection of distributed generation.