The Effect of Non-Ideal Operating Conditions on Reliability of Inverters in Microgrids

Microgrids are becoming increasingly popular due to modern trends in power consumption and distribution. Power converters are essential in order to ensure the desired function of a microgrid. As with traditional distribution systems, reliability is a major concern since it is one of the main functions of a microgrid [1]. A lot of literature has been published related to microgrid specific reliability. However, literature on the reliability of converters under non-ideal operating conditions is scarce. In this paper, the reliability in terms of failure rate of a three-phase converter operating under non-ideal conditions is investigated. The studied microgrid is derived from the CIGRE LV benchmark system. The study shows that unbalanced conditions have a particularly detrimental effect on converter reliability expressed as its failure rate. Nonlinear conditions also have a negative impact and even more so than the impact of increased RMS currents due to low power factor (pf) loads. In addition, the ambient temperature has a large impact on the system reliability. Temperature swings in the power electronic devices caused by harmonics and imbalanced currents could also cause large failure rate deviations. The results show that failing to include the effect of expected non-ideal operating conditions could lead to a wrong estimation of the system reliability as an effect of worsened failure rates in the power electronic components.