Calorimetric Loss Measurement Research Articles

Research on Losses of PCB Parasitic Capacitance for GaN-Based Full Bridge Converters

The utilization of wide band-gap semiconductor devices provides the possibility of higher switching frequency and power density for power converters. However, the influence of parasitic parameters becomes more significant. It deteriorates the converter performance and leads to extra loss. In this article, the extra loss caused by the parasitic capacitance of printed circuit boards (PCBs) is studied. The mechanism is explained, and the model of full bridge topology with PCB parasitic capacitance is proposed as an example. Both the capacitance in power loops and control circuits are considered in the proposed model. Besides the capacitive loss in power loops, losses are also introduced by the capacitive coupling between the power and control circuits due to the potential pulsation of the control ground. This potential pulsation is analyzed and the calculation method of corresponding losses is presented. The formation of PCB parasitic capacitance is analyzed in detail and corresponding layout optimization methods are proposed. Theoretical analyses are verified on a gallium nitride based full bridge prototype with calorimetric loss measurement. The comparison of calculated and measured losses is presented, which shows a switching loss deviation of 26% without the consideration of parasitic capacitance and a 40% reduction on the extra losses after the proposed optimization.

An Accurate Calorimetric Loss Measurement Method for SiC MOSFETs

An accurate measurement of conduction and switching losses in the power semiconductor devices is necessary in order to design and evaluate the thermal management system of modern converter systems. Conventionally, electrical measurement methods, such as the double-pulse tests (DPTs), are used for measuring the switching losses. However, with the advent of wide-bandgap (WBG) devices that have fast switching transients, it is rather difficult to capture the waveforms accurately during switching transitions, and consequently, the measurement of switching loss becomes inaccurate. In addition, the measurement of switching waveforms depends on the voltage and current probes, as well as the oscilloscope used for the measurement, which makes this method prone to errors. This necessitates the use of measurement methods, which can provide much higher accuracy than the existing conventional electrical methods. Calorimetric methods are based on comparatively slow temperature measurements and do not rely on the measurements of fast switching transitions of voltages and currents, thus eliminating the demand for measuring fast switching transitions. This paper presents an accurate calorimetric method for measuring the device losses, which can be used to determine individual loss components accurately (conduction, turn-on, and turn-off losses). In addition to the turn-on and turn-off losses, this method can evaluate the charging and discharging losses of the device. The novelty of the method lies in the fact that a single setup can be used to measure all possible losses that can occur in a device during converter operation. The calorimetric test setup is described, and a novel modulation scheme is introduced, which enables the segregation of the individual losses. The experimental test setup is built and the method is verified by measuring the losses of a 900-V, 23-A Wolfspeed C3M0120090D SiC MOSFET.

Effect of Multilevel Inverter Supply on Core Losses in Magnetic Materials and Electrical Machines

The effect of multilevel inverter supply on power losses in magnetic cores and electrical machines is studied. A dynamic numerical model for the hysteresis, eddy current, and excess losses in a core lamination is first developed. By both measurements and simulations for a ring-core inductor, we demonstrate how increasing the number of inverter voltage levels decreases the iron losses when compared with traditional two-level supply. Although the switching frequency has a significant impact on the iron losses in the case of a traditional two-level inverter, using three or five voltage levels makes the losses almost independent of the switching. Finally, finite-element simulations show that similar reductions are also possible for the core losses of 150-kVA and 12.5-MW wound-field synchronous machines, in which rather low switching frequencies are typically used. Calorimetric loss measurements are also presented for the 150-kVA machine in order to confirm the significant effect of switching frequency on the core losses with two-level inverter supply.

Experiment Setup for Calorimetric Measurements of Losses in HTS Coils Due to AC Current and External Magnetic Fields

We present a design and details of construction of two calorimetric systems that allow us to measure the total loss in high temperature superconducting coils or linear samples carrying alternating current while exposed to a strong alternating magnetic field. This measurement technique is based on the boil-off of liquid nitrogen. The first system is designed to measure ac losses in superconducting coils in self-field generated by AC transport current. The second system contains a permanent magnet rotor and simulates the environment of an electric motor or generator. The sensitivity of the system is such that it can measure low losses from a few milliwatts to several hundred milliwatts, in either a static or dynamic magnetic field.

Apparatus for calorimetric measurements of losses in MgB2 superconductors exposed to alternating currents and external magnetic fields

Inexpensive superconducting wires with low AC losses would open up for a large superconductor market in AC electrical power applications. One candidate for this market is the MgB2 conductor. In the development of an AC optimized superconductor, high-quality measurements of the AC losses under application-like conditions must be available. This article describes an apparatus built for this purpose. The measurement method is calorimetric. The temperature increase of the superconductor sample is measured and compared to the temperature increase due to a heater with known heat input. The system is designed for measurements of losses due to magnetic fields combined with transport currents. Results from tests verifying the capabilities of the system are given, as well as from initial AC loss measurements on a tape-shaped MgB2 superconductor.

Experimental setup for precise measurement of losses in high-temperature superconducting transformer

A simple cryogenic system for testing of the superconducting power transformer was constructed. Thermal shielding is provided by additional liquid nitrogen bath instead of super-insulation. The system, together with use of a precise nitrogen liquid level meter, permitted calorimetric measurements of losses of the 8 kVA HTS transformer with a resolution of the order of 0.1 W.

Calorimetric measurements of losses in HTS cables

A calorimetric test rig is used to investigate various loss components in a 10 m long superconducting cable model. A calorimetric technique, based on thermocouple measurements, is used to measure the losses of the 10 m long superconducting cable model. The current dependent losses are also measured electrically and compared with the losses obtained with the calorimetric method. The results obtained by the two methods are consistent. Based on an I/sup 2/ (current) fitting procedure, the loss, caused by the eddy current generated in the stainless steel cryostat housing, and the hysteresis loss generated in the conductor can be separated. From this result, it appears that the two contributions are roughly equal in size.

Calorimetric measurements of losses in mineral wool

Measurements of the heat generated in mineral wool during a steady-state single-frequency dynamic process are presented. A microcalorimeter is used to register the heat. The calorimeter consists of a heat sink, i.e., a large water container held at constant temperature, a measurement volume, and a temperature gradient sensor in between. The temperature gradient is then related to the heat flux. The sensitivity of the equipment is on the order of 1 microwatt. A small rod is connected to a shaker outside the calorimeter and to a mineral wool specimen in the other end. The dissipated energy in mineral wool can then be measured during a steady-state single-frequency dynamic process. In order to obtain a value of the reversible energy, one can also measure the acceleration and the voltage to the shaker. Dry friction will cause measurement errors, but if a measurement without any sample is performed, this can partly be compensated for. The heat flux can be related to the dissipation in the mineral wool.

AC loss behaviour of the high-current NbTi- superconductor for the Swiss LCT fusion coil

The results of calorimetric loss measurements in perpendicular and also parallel pulsed magnetic fields performed on the cabled 13000 A superconductor for the Swiss LCT coil are reported. These losses are compared to those of two other different test superconductors developed in the past for the same purpose. Some aspects of our ac loss reduction method are reported.