Fault current characterisation of single phase inverter systems

With rise in distributed energy resources (DERs) due to increased penetration of roof top solar systems, the collective impacts of their inverters during low and medium voltage grid faults and abnormalities will need to be better understood. The fault characteristics of IBDGs (Inverter Based Distributed Generation) are necessary to be practically measured to reflect on their impacts on the existing protection schemes. Existing literature on fault current contribution of inverters are mainly simulation based, while actual experimental data and associated modelling is limited. In this paper, two particular characteristics, namely LVRT (Low Voltage Ride Through) and short-circuit characteristics are analysed through lab testing and consequently modelled on a suitable platform. During this assessment, the existing standards for interconnection of IBDG on distribution network are compared along with evaluation of commercial inverters for compliance to existing standards. The fault characteristics and LVRT are determined by direct observation, rather than simulation. The experimental set up to quantify fault current contribution of single phase grid connected inverters is explained and the LVRT characteristics of several inverters addressed. The behaviour of the inverters during voltage and frequency based grid anomalies is presented along with possible models found through state estimation.