Square-Wave Source with Adjustable dv/dt for Insulation Testing under Mixed-Frequency Stresses

This paper presents an insulation test setup that emulates the mixed-frequency stresses experienced by magnetic devices in solid-state transformers (SSTs). Medium-frequency transformers (MFTs) utilized in SSTs typically face a superim-posed electric stress of two different frequencies, namely the grid frequency and the switching frequency of converter operation. Such mixed-frequency stress is regarded as a new concern for MFTs' insulation design. However, the test environment for such stress has been limited compared to those for traditional transformers. The aim of this paper is to fill this gap by proposing a test setup dedicated to mixed-frequency stresses. A battery-powered square-wave source is developed to be connected in series with an existing insulation test setup to emulate the stress, achieving a wide operating condition including the dv/dt and switching frequency. The details of the design are given, and the key operation is verified in the experiment.