  With the increasing penetration of electronic loads and distributed energy
resources (DERs), conventional load models cannot capture their dynamics.
Therefore, a new comprehensive composite load model is developed by Western
Electricity Coordinating Council (WECC). However, this model is a complex
high-order nonlinear system with multi-time-scale property, which poses
challenges on stability analysis and computational burden in large-scale
simulations. In order to reduce the computational burden while preserving the
accuracy of the original model, this paper proposes a generic high-fidelity
order reduction approach and then apply it to WECC composite load model. First,
we develop a large-signal order reduction (LSOR) method using singular
perturbation theory. In this method, the fast dynamics are integrated into the
slow dynamics to preserve the transient characteristics of fast dynamics. Then,
we propose the necessary conditions for accurate order reduction and embed them
into the LSOR to improve and guarantee the accuracy of reduced-order model.
Finally, we develop the reduced-order WECC composite load model using the
proposed algorithm. Simulation results show the reduced-order large signal
model significantly alleviates the computational burden while maintaining
similar dynamic responses as the original composite load model.
