Component-based aggregate load models for combined power flow and harmonic analysis

Aggregate load models traditionally used for steady state analysis of power systems are based on standard constant impedance/current/power representation of static load component, with induction motor representation of dynamic load component. These traditional load models cannot accurately represent characteristics of non-linear power electronic loads, the impact of local distributed generation (DG) on the aggregate load demand, or the effects of demand-manageable loads. Furthermore, the assessment of the contribution of non-linear loads and inverter-interfaced DG to the flow and propagation of harmonic currents is usually not possible using the traditional aggregate load models. This paper uses a component-based approach to build improved aggregate load models that are capable of preserving full information on electrical characteristics of aggregated load, enabling to use the same load models for both the analysis of power flows and voltage profiles, and analysis of harmonics. Furthermore, by modelling aggregate system load as a composition of general load categories, it is possible to identify the exact portion of available demand-manageable load in the aggregate demand, and then investigate the actual effects of the controlled changes in demand on system performance. The developed load models are implemented in two "sister papers" that accompany this one, where they are combined with the models of small/large DG to perform steady state analysis of network performance (power flows, voltage profiles, overloading of system components, harmonic analysis and a simple case of demand-side management).