Jan Martis

Power supply for resistive heating of iron components

This paper deals with the design and construction of a switching power supply which is intended for direct resistive heating of iron components. The power supply is especially intended for resistive heating of horseshoes. The supply is able to deliver an output current of up to 1600 A at a power of up to 2500 W. The chosen topology, design parameters and control strategy are included in the contribution. Specific construction of the pulse transformer with respect to minimum leakage and details of the secondary synchronous rectifier are described. Finally measurement results are presented and operation details are introduced and documented with the measurements. The power supply was successfully tested and the required output parameters were met. However some problems do exist, especially with contacting the heated component to the output leads of the supply. The power supply can be used as an alternative solution to classic means of iron heating. The methods and ideas presented in this work can be applied in a design of a similar power supply with high output current, but most of the design rules are valid generally for the given topology.

Push–Pull Converter Transformer Maximum Efficiency Optimization

The contribution describes a maximum efficiency design of a push–pull (full-bridge and half-bridge) DC/DC converter transformer based on straightforward analytical calculations. The input parameters for the optimization are transformer core size, switching frequency and power. The output parameter is the core peak-to-peak flux density, from which all other essential parameters of the transformer (numbers of turns, core loss, winding loss etc.) can be derived. The optimization contains some simplifications which could cause a small error, but the result is an easy-to-use and simple to implement analytical formula, which can be used to quickly design a well-performing transformer or evaluate multiple designs.

Volume Minimization of Power Pulse Transformer for a Two-Switch Forward Converter

Advantages and disadvantages of forward and push-pull converters for a power region of several kW are overviewed in the beginning of the contribution. Further an optimization of the power pulse transformer of the standard two-switch forward converter is proposed. The goal of the optimization is to ensure minimum total transformer volume at constant predefined parameters: maximum core flux density, DC-link voltage of the converter, output voltage of the converter, output power, current densities in the primary and secondary winding and switching frequency. Optimum size and geometrical proportions of the toroidal ferrite core are the results of the optimization. An analytical approach is used in the optimization (searching for a local minimum of a function). Practical results for a converter with output parameters 1 kW/60 V are included to document the optimization task.

Test stand for obtaining power transistors switching characteristics during aging

This paper aims to construction, control and implemented measurement method of laboratory stand in order to acquire insulated gate bipolar transistor transients. The transients waveforms are consequently used to obtain indicators of the transistor age. The lifetime tests of an insulated gate bipolar transistor are introduced. Consequently, a novel architecture of measuring stand in order to provide lifetime tests is designed. Also the control algorithm is presented. A fundamental part of this work is a method of measuring switching waveforms including a high frequency current. Acquired waveforms of transistor switching are presented. Finally, the trend of chosen aging indicator values was obtained from the acquired data. Namely the influence of aging on turn-off time was observed.

Two-switch forward converter efficiency optimization

This contribution presents a mathematical tool for analytical calculation of the optimum switching frequency and transformer parameters of a switching power supply utilizing a two-switch forward converter. The calculations are based on minimization of total power loss of the converter with given switching semiconductors and size of transformer and inductor core. This allows the designer to construct a converter with greatest efficiency using given parts (keeping cost of the components). The results are power saving, less waste heat and possibly smaller size and weight of the converter or power supply. Applications include photovoltaic inverter, electric vehicle charging, industrial power supply and any isolated DC/DC converter in general.

Apparatus for induction heating 2.5 kW using a series resonant circuit

A device for induction heating of smaller iron components was designed and constructed. The shape of the work coil was matched to horseshoe heating. Required simplicity and robustness of the device excludes the use of water cooled work coil (made of copper tube) which is mainly used in the applications of induction heating. A HF Litz-wire was used in the construction of the work coil in our solution. A non-tradition conception of the input rectifier with a low DC-link capacity is used. This way a sufficiently high power factor can be achieved without any additional PFC circuit. A double acting inverter using a MOS-FET half-bridge is used for exciting the series resonant tank. The system description of the designed induction heater is presented including some important details.