See A Supplemental Report, Edward Herbert, Co-chairman, PSMA Magnetics Committee, December 14, 2011. Fortunately, they are of the same format and file structure, so one set of tools could examine all of the data. The raw data of the Pilot Project and the Phase II data were used. Accordingly, a supplemental report was undertaken to see if additional information could be extracted from the data. The Pilot Project and the Phase II Project took massive amounts of data, far more than could be analyzed under the Phase II time and budget constraints. The Phase II Project data can be downloaded from Sullivan and John H.Harris Thayer School of Engineering at Dartmouth. He showed that core loss of non-sinusoidal waveforms cannot be accurately predicted by separately examining the Fourier components of the waveform.įor more information, see Testing Core Loss for Rectangular Waveforms, Phase II Final Report, 21 September 2011 by Charles R. Sullivan analyzed Fourier expansion and its applicability to core losses. Unlike the traditional Steinmetz equations for sine wave data, one set of parameters can be used over a very wide range of voltages and pulse widths.ģ. Sullivan applied square wave data to a Steinmetz-like equation for estimating core losses. It is unlikely that the hippo waveform will be used in practical power converter circuits, but its use for testing will be invaluable.Ģ. This may be the most important achievement of the Phase II Project. The current returns nearly to zero during the off-time. A pulse of one polarity is immediately followed by a pulse of the opposite polarity and the same pulse width, followed by an off-time. The Dartmouth team developed a "hippo waveform" as a test excitation.
There were several important by-products of the study:ġ. Flux migration is seen in the drilled core experiments, but its timing and magnitude suggests that it is not an important factor in the off-time losses. The Phase II study confirmed that the off-time phenomenon is seen on a variety of cores of different shape and material. To test a core that had been drilled through with sense windings installed, to see if flux migration may contribute to the off-time loss phenomenon. To test the composite waveform hypothesis on a variety of cores of different materials, with emphasis on ensuring that the off-time loss phenomenon was not just a test rig or test procedure artifact.Ģ. The Phase II project had two principle objectives:ġ. The Phase II Project was approved by PSMA and a purchase order to Dartmouth was issued in the Spring of 2010. Power Electronic Systems Laboratory, Zurich, Switzerland See: Improved Core Loss Calculation for Magnetic Components Employed in Power Electronic Systems, Muhlethaler, J. Jonas identified two off-time loss mechanisms, a "relaxation phenomenon" that has a fairly short time constant immediately following turn-off, and a longer effect due to circuit impedance. Jonas' paper was not sponsored by PSMA, but it is mentioned here because it is an important contribution to the study of the "off-time phenomenon." The importance of this paper is that it confirmed the off-time loss using a different core on different test apparatus. The Pilot Project data can be downloaded from Harris, Thayer School of Engineering at Dartmouth and Edward Herbert. However, it was observed that increasing off-time between excitation pulses increased the loss per cycle.įor more information, see Testing Core Loss for Rectangular Waveforms, Februby Charles R. The composite waveform hypothesis was partly validated, and shown to be an improvement over other approximations, both for accuracy and for ease of use. Data was taken on one ferrite core and one powdered metal core. The Pilot Project was approved by PSMA and a purchase order to Dartmouth was issued in the Spring of 2009. Most core loss data is taken with sine-wave excitation, but most power converters use rectangular excitation, often with reduced duty-ratio.Ī hypothesis, later dubbed the "Composite Waveform Hypothesis" proposed that the core loss with low duty-ratio rectangular excitation could be derived from square-wave data.įor more information, see User-friendly Data for Magnetic Core Loss Calculations, Edward Herbert, Canton, CT. For a magnetic component, there is no need to use dimensional factors, any more than one would buy a resistor using the resistivity and dimensions of its core.ģ. Core loss calculations can use voltage, current and time.Ģ. There is no need to use the unfamiliar magnetic parameters. The PSMA Core Loss studies have their roots in frustration with the traditional core loss estimations.ġ.