High-Efficiency High-Reliability Pulsed Power Converters for Industrial Processes

This paper considers monitoring of semiconductor thermal cycling in high-power resonant converters. For the experiments, a dedicated single-phase resonant converter rated at 1 kV, 250 A (250-kW peak power, duty ratio 10%, 25-kW average power, AND pulse length 1 ms) was been developed. This converter represents one phase of a multiphase resonant power supply designed for long-pulse modulation (typically 1-2 ms) when equipped with a suitable output transformer. Pulsed operation is obtained by direct modulation of the high-frequency power supply. The main aim of the study reported here is to develop a methodology to assess performance and reliability issues related to the use of standard commercially available power switch technology, relying on a physics-based multichip insulated gate bipolar transistor (IGBT) structure model, and to experimentally monitor the chip temperature using high-speed thermal imaging, during the pulse, to identify any limitations of the proposed modulator technology. First, an overview of the converter, including its nominal electrical design, is provided. Optimization of the turn-OFF snubber capacitance is performed through a series of experiments, employing calorimetrically measured losses, to determine a value, which minimizes the overall power losses. Accurate calorimetric measurements of the switching losses and infrared measurements of the IGBT surface temperatures during transient operation are presented. Simulations including multichip structures, experimental results, and high-quality chip thermal images are provided to validate the effectiveness of the proposed approaches.