Pavel Vorel

Advantages of using two-switch forward converter for high-voltage applications

The study and implementation of a two-switch forward converter operating at high frequency for high-voltage applications, in a voltage range up to several kV and in a power range up to several kW, is presented in this paper. Trend is to use a resonant converter in this voltage and power range. However progresses in the development of semiconductor components allow the usage of the two-switch forward converter topology operating at high frequency. Comparison of converters for high-voltage applications is performed. Design details of the converter hardware and the high-voltage high-frequency transformer are given. Simple control and simple auxiliary circuits are the major advantages of this topology. The two-switch forward converter, using SiC based semiconductor components, operating at 100kHz is discussed in the article.

Maximum efficiency of an induction machine operating in a wide range of speed and torque - part 1 (theoretical analysis)

A set of unique equations usable to calculate directly the optimum slip frequency and line voltage of a 3phase squirrel-cage induction machine with respect to maximum efficiency is deduced in this article. An operation in steady state at any requested speed and torque in a wide range is taken into consideration. The proposed calculation is especially useful for independent traction purposes. The requested torque, speed and an extended mathematical model of the machine based on a Γ-network are the inputs of the calculation. The optimum slip frequency and line voltage are the outputs. The calculation results using the deduced analytical formulas were verified with a practical measurement and with a MATLAB simulation. Due to the extensiveness of the problems the correspondence of the theoretical calculation with the practical results will be presented in a separate 2nd part of the article.

Design of small electric car

Paper deals with design of traction drive for small electric car where its primary energy source is realized by two hydrogen cells with nominal power 2 × 1,2 kW. Main attention is paid to find appropriate torque-velocity, resp. power-velocity dependences related to wheel of the small electric car. According to these characteristics an appropriate gear ratio is calculated. Finally, an appropriate traction motor is chosen.

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.

Small electric vehicle drive control according to maximal efficiency criteria

This paper deals with induction drive control implementation according to the requirement of maximal efficiency for a traction application in a small electric car. Optimum setting of the motor slip frequency was found according to the criteria of maximal motor efficiency in a wide range of torque and speed (see [1] and [2]). The traction drive is an application without any extreme dynamic response requirement. It is possible to use scalar control strategies without any significant impact on the vehicle dynamic behavior. An implementation of the optimum motor setting into a scalar control is described in this article. Optimum rotor frequency and stator current look-up tables for any operating point in the used range of desired torque and actual speed were generated and used in common induction machine scalar control schemes.

Maximum efficiency of an induction machine operating in a wide range of speed and torque - part 2 (calculation, simulation and measurement results)

A set of equations usable to calculate directly the optimum slip frequency and line voltage of a 3phase squirrel-cage induction machine with respect to maximum efficiency was deduced in part 1 of this article. An operation in steady state at any requested speed and torque in a wide range is taken into consideration. The requested torque, speed and an extended mathematical model of the machine based on a Γ-network are the inputs of the calculation. The optimum slip frequency and line voltage are the outputs. The calculation results using the deduced analytical formulas are compared with practical measurement results and with a MATLAB simulation of the machine input power in this part 2 of the article.

Identification of Induction Machine Electromagnetic Parameters for a Wide Range of Frequency and Flux Density

The paper deals with the experimental identification of electromagnetic parameters of an induction motor for a wide range of frequency and flux density. The relations for calculation of the iron loss resistance and magnetizing inductance of equivalent circuit alike \(\Gamma \)-network are derived for identification from the no-load measurement. The knowledge of these parameters is necessary for simulation or control of the induction machine over a wide range of speed and torque. Presented procedures were used for identification of induction motor with 600 W rated output power.

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.

Application of acceleration method for evaluation of induction motor torque-speed characteristics

This paper deals with practical application of acceleration method for evaluation of induction machine torque-speed and current-speed characteristics. Influence of measuring time on the shape of evaluated torque-speed characteristics is presented based on the results of measurements. One of the aims of this paper is also calculation and measurement of mechanical losses from deceleration test. A method for determination of distribution of friction and windage mechanical losses from the measurement is described. The influence of a cooling fan on the total mechanical losses is also discussed.

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.