Power electronic loads with negative differential impedance in a low voltage distribution system

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.