Today’s Distributed Generators (DG) and load appliances are increasingly build up with power electronics. This trend is expected to grow further in the future. Also developments are ongoing to improve the performance and efficiency of grid components by means of power electronics and several grid components might be replaced by power electronics based versions in the future. One of the nice properties of power electronics based grid components is the possibility of voltage control. This feature is very welcome to keep voltage levels within prescribed limits while implementing large numbers of DG. Load appliances often use internal circuits that work on a controlled direct voltage level and this is achieved by using power electronics. In this way the performance of such appliances is much higher today than in the past. Besides this and other advantages, disadvantages will also show up. The disadvantages that are studied in this thesis are the increased harmonics caused by resonances and oscillatory voltages caused by non-linear constant power loads. Beside existing resonances in the grid, new ones will be added by large numbers of capacitances used in Electro Magnetic Interference (EMI) filters of power electronics based appliances. These capacitances can interact with inductances in the grid and bring significant resonances that can amplify harmonic currents and voltages to a high level, even in the lower harmonic frequency range. Oscillatory voltages can be caused by improper stabilization actions. etc.