Reliability prediction of new improved current source inverter (CSI) topology for transformer-less grid connected solar system

Abstract

Solar inverters are mainly classified as voltage source based solar inverter and current source based solar inverter. The comparison of voltage source inverter (VSI) and current source inverter (CSI) is presented in this paper. Conventional CSI generate high earth leakage current into the grid. Therefore, conventional CSI requires an intermediate isolation transformer to feed power to the grid. The use of transformer makes the system bulky. To overcome these limitations, a modified CSI without transformer is analyzed from reliability point of view in this paper. The failure rates, Mean Time Between Failures (MTBF) and hence the reliability of various components of conventional VSI, CSI and proposed CSI are calculated using methods discussed in Military Handbook (MILHDBK 217F). It is found that conventional CSI is more reliable than VSI as it requires smaller dc link capacitor.The failure rate for proposed CSI is found to be less compared to conventional CSI, thus MTBF and reliability of proposed transformer less CSI is more than conventional CSI and VSI. The reliability of these inverters is calculated in benign environment.