Electro-thermal analysis of power converter components in low-voltage DC microgrids for optimal protection system design

Bidirectional power converters are considered to be key elements in interfacing the low voltage dc microgrid with an ac grid. However to date there has been no clear procedure to determine the maximum permissible fault isolation periods of the power converter components against the dc faults. To tackle this problem, this paper presents an electro-thermal analysis of the main elements of a converter: ac inductors, dc capacitors and semiconductors. In doing this, the paper provides a methodology for quantifying fault protection requirements for power converter components in future dc microgrids. The analysis is performed through simulations during normal and fault conditions of a low voltage dc microgrid. The paper develops dynamic electro-thermal models of components based on the design and detailed specification from manufacturer datasheets. The simulations show the impact of different protection system operating speeds on the required converter rating for the studied conditions. This is then translated into actual cost of converter equipment. In this manner, the results can be used to determine the required fault protection operating requirements, coordinated with cost penalties for uprating the converter components.