Estimation of Exponential and ZIP Load Model of Aggregated Load with Distributed Generation

The voltage dependence of loads plays a major role when the conservation voltage reduction (CVR) is analysed or implemented. This dependence is affected by the amount of distributed generation (DG) included among the load of the aggregated bulk supply point. In this paper, the impact of DG on estimated values of exponential load model and ZIP load model (second order polynomial load model) is analysed based on a measurement-based case study. A new equation is presented for assessing the impact of DG penetration level on the ZIP model of the aggregated load (with DG). Additionally, the modelling accuracy of ZIP and exponential model is compared and the exponential model is shown to provide a better accuracy than the ZIP model for modelling this type of loads. The case study was conducted in a distribution network with significant amount of DG. An on-load tap changer was used for inducing the voltage changes. Both, exponential load models and ZIP load models, were estimated from measurement data for transformer load and aggregated load excluding the DG.