The paper presents an inductor with reduced self-capacitance, designed and evaluated with fast-switching SiC transistors in dc-dc converters. A conventional inductor with the same core and number of turns was also build for comparison. The two inductors are tested experimentally on two different 2 kW, 100 kHz dc-dc converters with silicon carbide switches-one with a junction field-effect transistor (JFET) and the other with a bipolar junction transistor (BJT). Replacing the conventional inductor with the one that has lower self-capacitance improved the switching performance of the converter and reduced its electromagnetic emissions. Furthermore, the efficiency of the converter is improved-in the case of the JFET boost converter the power losses were reduced by 16% and by 20% in the case of BJT.

In this paper issue of pulse width modulation (PWM) methods for bidirectional/high-performance Z-source inverter (ZSI) is presented. Due to additional switch operating with the Z-network frequency an approach is different than in basic version of ZSI. Three various PWM methods are discussed: the state-of-the-art maximum constant boost control (MCBC), maximum constant boost control with discontinuous reference (DMCBC) and highly optimized minimum switching number (MSN). All methods are described in details and compared on the base of simulation test in SABER package and investigations of laboratory model of bidirectional ZSI. Impact of applied PWM method on inverter design process is also analysed - key issue is selection of passive elements (especially Z-network and line filter inductors).

This paper presents the implementation of a thermal camera for the quantitative estimation of power losses in a high frequency planar transformer (100 kHz/ 5600 VA). The methodology is based on the observation of the transient temperature rise and determination of the power losses by means of curves representing the derivative of temperature as a function of power losses dissipated in the transformer. First, the thermal calibration characteristics had to be obtained from a simple experiment, where power losses are generated by DC current in the ferrite core and windings. Next, experimental investigations focused on the determination of the transformer power losses for a short circuit and no load, with a resistive load and with the rectifier as a load were carried out. Finally, to verify the obtained results, analytical calculations based on Dowell’s and modified Steinmetz’s equations were additionally made, which showed a good convergence. The proposed method is easy to implement and can be used as an alternative to the calorimetric method which is time-consuming and requires a complicated measurement setup.

This paper presents an analysis of the power transfer between two DC circuit by use a single phase galvanically isolated dual active bridge - DAB. The analytical description of instantaneous values of the currents in both DC and in AC circuits of the DAB is done. The influence of the dead time as well as voltage drops across the transistors and diodes of the bridges is examined. The different relations between voltages of the DC circuits coupled through DAB and various phase shift ratios are considered. The analytical relations describing the average values of the currents in DC circuits are derived. These currents can be used to predict the power in both DC circuits and power losses generated in semiconductor devices of the converter. It is assumed that the voltage drops across these devices in conduction states are constant. The calculation of the transferred power as well as power losses and energy efficiency for the DAB converter power rated 5600 VA which is used to energy transfer between DC circuits 280 V and 51 V±20% is presented. The proposed relations and calculation results can be useful for preliminary evaluation of power losses generated in semiconductor devices and for design of the cooling system. Due to the high switching frequency of 100 kHz, the phase shift modulation for the control of DAB is used. To validate the theoretical investigations a few experimental results are presented.

In this paper, results of laboratory investigation of representative samples of semiconductor silicon and silicon carbide power devices, such as PiN diode, Shottky diode, IGBT and JFET, are presented. With use of a thermal chamber the characteristics of temperature sensitive parameters for selected types of devices were determined by measurements within the range 25 - 150degC. The measurement was done using short pulses, which are not able to change measured temperatures. The results have to enable identification of junction temperature in the case of other tests, especially those oriented on energy losses, efficiency, and thermal management.

This paper proposes a model of a coupled inductor which takes into account the influence of frequency, temperature, and a constant component, I_DC, of currents in the windings on the parameters of the considered element. A description of the model and methods of measuring parameters of the inductor using an impedance analyzer and a chamber for thermal measurements is given. The obtained results of measurements are compared with the results of calculations proving a satisfactory match.