Presentation Description: It is difficult to avoid unclamped inductive load effects in power electronic systems because even small stray inductances can store high energies depending on the current to be controlled and to be turned off. Such effects are dominant for solid-state relays (SSRs) being configured as AC switches. As there is no freewheeling path for the inductive energy, the dimensioning of suitable clamping circuits is important for the safe operation and the longevity of SSRs. Particularly the occurrence of advanced solid-state isolators that are able to perform turn-on and turn-off within a few 100 nanoseconds enable the use of modern MOSFET’s switching performance. However, it also means that considerations regarding dissipation of unclamped inductive energy gets more dominant. Several aspects of power electronic engineering, such as circuit layout including the power transistor part and the component placement of the clamping circuit, play an important role for smooth switching performance and low electromagnetic interference (EMI). This work explains first the test circuit that is used for evaluating an advanced alternative current solid-state relay. Then, different properties of selected clamping elements are compared to each other with respect to the use in a.c. switching SSRs. In a third part, the presentation shows turn-off waveforms of SSRs using different types of clamping components.
