Today's domestic appliances are more and more adapted and controlled by power electronics and processors, and their number is growing. This development can bring both advantages and disadvantages for the power quality in local grids. An advantage for example is the growing number of power supplies that are equipped with a Power Factor Corrector front-end. This type of power supply behaves as a resistive load and has a very good power factor. A disadvantage for example is the constant power load character that comes with a controlled AC to DC power supply with a constant loaded DC output, independent of the applied grid voltage. This type of load has a Negative Differential Impedance (NDI) and can cause voltage instability. This paper discusses the NDI effect that power supplies can bring, and their effect on voltage stability.
SUMMARYToday's electrical appliances are more and more built with and controlled by power electronics and processors, and their number is growing. This development can bring both advantages and disadvantages for the power quality of the electricity supply system. An advantage, for example is the growing number of home appliances that are equipped with a power factor corrector front-end. This type of appliance behaves as a resistive load and has a very good power factor. A disadvantage is the constant power load (CPL) character that shows up when the appliance is stabilized against grid voltage fluctuations by a power electronic frontend. This paper investigates the oscillatory grid voltage effect of certain amounts of CPLs in a small isolated grid system and the impact on the quality of the voltage. Results of computer simulations show that an oscillatory grid voltage due to an interaction of a CPL with the voltage control system of a generator is possible and can be reduced by changing the parameters of the voltage control system.
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