Wear-out prediction of grid-following converters for two-phase three-wire isolated ac power grids

Electrification in remote communities is mostly based on isolated ac grids with diesel generator, renewables and battery storage system. These latter energy sources are interfaced by power electronics converters that require very high reliability and long lifetime. This paper compares the reliability of two-phase three-wire ($2\Phi 3\mathrm{W}$) PV-inverters considering three different configurations of grid structure in terms of line voltage angle displacement: 90° ($\alpha\beta n$-system); 120° (abn-system) and 180° (xyn-system). A 4.5 kW grid-following inverter is considered in the case study. The wear-out failure probability for the inverter is quantified for the three systems in rated conditions, considering the same hardware design. Then, a sensitivity analysis is performed for the inverters of the $\alpha\beta n$-system and xyn-system, aiming to obtain the same probability of failure of the inverter operating in the abn-system. The obtained results shows that a PV inverter in xyn-system can have its rated power increased (22.22%) or its heatsink volume decreased (58.33%), and even so achieve the same wear-out $B_{10}$ lifetime for abn-system. Such result indicates that xyn-system may be attractive for isolated ac grids to reduce cost and/or extend converters $2\Phi 3\mathrm{W}$ lifespan.

I. Introduction

Portion of the world population is supplied by isolated power systems, which gradually insert renewable sources such as photovoltaics, bio-gas and others in their generation. In isolated power systems, two types of converters are usually presented: i) grid-forming converter, that regulates the voltage amplitude, frequency and phase angle displacement between the lines and ii) the grid-following converter that operates under the conditions imposed by the grid-forming converter, pursuing the main target of injecting active power into the grid.