High-Bandwidth Isolated Voltage Measurements With Very High Common Mode Rejection Ratio for WBG Power Converters
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Date
2022
Publication Type
Journal Article
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Abstract
Galvanically isolated voltage measurements are becoming increasingly important for the characterization of converter systems with fast switching Wide-Bandgap (WBG) semiconductors. A very high Common Mode Rejection Ratio (CMRR) > 80dB for frequencies up to several tens of MHz is required to accurately measure, e.g., the high-side gate-source or drain-source voltage in a half-bridge, or voltages on floating potentials as, e.g., found in multi-level converters. Common to all listed measurement scenarios is the fast changing reference potential, which acts as Common Mode (CM) disturbance. This article derives the minimum necessary CMRR at different frequencies to constrain the time-domain measurement error below a certain limit. Thereby, only the switched voltage and the voltage transition rate (dv/dt) of the CM disturbance have to be considered and not the actual converter switching frequency f(sw). Afterwards, a galvanically isolated measurement system with a CMRR > 100 dB up to 100 MHz and an analog measurement bandwidth of 130 MHz is presented. Critical design aspects to achieve this performance are investigated. Compared to commercially available isolated voltage probes, the presented measurement system does not require any additional equipment like an oscilloscope to perform and visualize measurements, since the data is already digitized/sampled and thus can be transmitted directly to a host device (e.g., computer or monitoring system) with corresponding Graphical User Interface (GUI) software. Experimental verification in frequency- and time-domain confirms that the performance is on par with the best commercially available isolated voltage probes.
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published
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Journal / series
Volume
3
Pages / Article No.
651 - 664
Publisher
IEEE
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Subject
Gate drivers; Isolation technology; Measurement techniques; Power semiconductor switches; Power system measurements; Voltage measurement
Organisational unit
03573 - Kolar, Johann W. (emeritus) / Kolar, Johann W. (emeritus)