I. Introduction
During recent decades, distributed power generation and storage technologies have been increasingly considered, such as distributed solar farms and large-scale battery energy storage [1]–[3]. In order to interface generated power to the national grid, high voltage grid-connected inverters have been widely used in those distributed generation systems. To protect both the national grid and the end user, the thermal performance and electrical characteristics of the HV side need to be measured and analysed. However, a series of technical problems need to be solved when applying those monitoring methods into a distributed generation system. In a commonly-used system, the bus bar temperature and HV phase angle are normally considered as the critical parameters. For a high-end industrial application, the bus-bar temperature can be measured by infrared temperature sensor and thermometer [4]. However, the poor accuracy, cost and isolation requirement makes this less desirable for distributed generation systems.