Modelling of Power Electronic Loads in AC Distribution Systems using the Generalized State Space Averaging Method

Most of the loads in AC distribution systems have positive incremental impedance characteristic. However, power electronic loads, when tightly regulated, sink constant power from the system. Therefore, they have negative incremental impedance characteristic. This can even cause negative impedance instability. Power electronic loads usually have a controlled or uncontrolled rectifier at the front end. In this paper, these loads are modelled using the generalized state space averaging method. An assessment of their effects in AC distribution systems is also presented.