Abstract
The insulation of high-frequency transformers (HFTs) has a significant impact on the safety and reliability of high voltage power electronic transformers (PETs). The transient voltages from the rapid turn-off and turn-on of the high voltage power semiconducting device increase the insulation stress and loss, resulting in thermal stress distortion. However, few studies have presented an accurate evaluation of the dielectric loss, especially under high dV / dt square waves. This paper focuses on the dielectric loss calculation in HFT insulation by analyzing the loss from a high-frequency square wave with spike voltages. A step function that is equivalent to spike voltage superposition is proposed for the quantitative calculation of the dielectric loss of epoxy resin. A cutoff frequency ( $f_{\mathrm {c}}$ ) is defined to indicate high dV/dt characteristics. A similar narrow step function is used for simulating spike voltage at the rising/falling edge. The additional dielectric loss increases with the spike voltage and the duration. The electric field and temperature distributions are simulated in a 10 kW, 10 kHz HFT by considering the calculation of dielectric loss. The spike voltages enhance the electric field and temperature in the insulation. The increase in the external temperature (close to the glass transition temperature ( $T_{\mathrm {g}}$ ) of epoxy resin) causes a significant increase in the insulation temperature. This paper is of great importance to the design and application of HFT insulation.
Highlights
A high-frequency transformer (HFT) is a key component in power electronic transformers (PETs) [1,2], which can be used for power transfer, electrical isolation, voltage conversion, and impedance matching
The contribution of this paper focuses on the evaluation of the dielectric loss and electrothermal properties of epoxy insulation used in HFTs
A calculation of dielectric loss under high dV/dt spike voltages coupled with square wave voltages was proposed
Summary
A high-frequency transformer (HFT) is a key component in power electronic transformers (PETs) [1,2], which can be used for power transfer, electrical isolation, voltage conversion, and impedance matching. The PVC/TiO2 nanocomposites indicated that the dielectric loss ranging from 20 to 1.0 MHz can be decreased by surface modification of TiO2 nanofillers [19] These studies play important roles in the dielectric and thermal performance of epoxy insulation for application in HFTs. In this article, the analysis and calculation of the dielectric loss in HFTs and the resulting electric field and temperature distribution are discussed. A new method is proposed for calculating the dielectric loss under square wave voltage with spike voltages, which includes a step function with a rapid rise time to simulate the high dV/dt behavior This method takes into account the handling of spike voltages and the combination of physical field analysis to better estimate the electric and thermal distribution in HFTs. the dielectric loss of the epoxy resin was calculated. The influence of spike voltages on the electric field and the temperature in the HFT insulation structure is discussed
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