Constant power loads are modeled as a speciﬁed quantity of real and reactive power consumed at a bus. For bus , the load is
and denotes the vector of complex loads at all buses. The MW and MVAr equivalents (before conversion to p.u.) of and are speciﬁed in columns PD (3) and QD (4), respectively of row of the bus matrix. These ﬁelds can also take on negative quantities to represent ﬁxed (e.g. distributed) generation.
Constant impedance and constant current loads are not implemented directly, but the constant impedance portions can be modeled as a shunt element described below. Dispatchable loads are modeled as negative generators and appear as negative values in .