Asymmetric Overvoltage Protection Levels for DC/DC-Converters

In modern DC-grids a bidirectional power flow is state of the art due to energy storage systems and a high number of volatile sources. The bidirectional power flow is realized by buck-boost DC/DC-converters. Those converter topologies come along with an internal freewheeling diode. In case of a negative transient overvoltage event the built-in freewheeling diode thwarts common surge protection devices (SPD) as spark gaps or varistors. This leads to a destruction of DC/DC-converters. In this paper a categorization of the threatening overvoltage events is shown, risk levels of DC/DC-converter topologies are identified, and protection requirements are specified.