Peter Wallmeier

Improved analytical modeling of conductive losses in gapped high-frequency inductors

An improved method to predict conductive losses in gapped high frequency inductors is presented and used for parametrization of an equivalent small signal circuit model. The method is based on the superposition of power losses resulting from the well known one-dimensional field calculation and losses due to eddy currents caused by the fringing field of airgaps determined from new analytical 2D-field calculations. Losses due to reactive currents in the windings caused by the self capacitance are also considered An accuracy improvement of at least 50% percent compared to the known methods is proved by measurements.

Resonant transition switching welding power supply

By means of parallel connected passive networks, charged only modestly by energy for commutation, resonant transition switching is ensured for this modified full-bridge topology used in a welding power supply. A new driving scheme adapts the resulting power circuitry for both the droplet and the short-circuiting transfer welding modes occurring in the gas metal arc welding process. Less voluminous and cheaper magnetic components together with lower conduction losses of transistors and diodes yield a cost-effective, lightweight power supply for 12 kW/350 A. The analysis of the circuit, the design and the verification results are presented.

Automated optimization of high frequency inductors

The methods, structures modeling techniques, algorithms and results of a computer aided optimization (CAO) software-tool developed for the automated optimization of high frequency inductors used in switched mode power supplies (SMPS) are presented. The software tool represents a design expert suitable for integration in an expert system under development for the design and optimization of switched mode power supplies.

A modular multilevel converter based high-power high-current power supply

This paper presents a power supply for high power and high current DC applications. Presently thyristor rectifiers along with passive filters are used in these applications, which suffer from poor input power factor and input current quality problems. The proposed power supply utilizes a modular multilevel rectifier and inverter, medium-frequency transformer and diode rectifier to convert medium-voltage AC to low-voltage DC via a medium-frequency AC link. Configuration provides unique advantages like high efficiency, high input power factor, good input current quality and controlled output current over the full operating range. Circuit configuration, design, control and performance of the proposed system are discussed in detail. Simulation results are presented to verify the performance and effectiveness of the system.

A high efficiency single-phase power factor corrected switched mode rectifier

The computer aided design and optimization of a single-phase power factor corrected (PFC) switched mode rectifier (SMR) based on the boost topology applying ZVS at turn-on and soft-transition (ST) at turn-off is presented. An industrial prototype rectifier switched at 110 kHz is described having an efficiency larger than 92% at worst case operating conditions. These are low line input voltage of 90 VAC and a maximum output power of 1.2 kW and 400 V regulated output voltage.

Magnetic shielding applied to high-frequency inductors

A new method to reduce power losses in high-frequency inductors based on magnetic shielding is presented. The working principle is derived from analytical investigations of the governing field equations and further investigated by finite element simulations. The improvement of power loss reduction of about 30% is proven by measurements.

Computer aided optimization of multi-winding transformers for SMPS considering HF-effects

Physical models of multi-winding transformers for SMPS with modern standard or variable core geometries and solenoidal windings arranged side by side or planar spiral windings are presented, suitable for computer aided optimization under consideration of skin and proximity effects. The winding layers are composable to interleaved or arbitrary composited windings to reduce losses. The height of ferrite cores for planar transformers in power modules can be assigned, while core losses are approximately accounted for. The selection of an objective function, the initial values and algorithms are guided by the aim to integrate the nonlinear optimization program into a CAE package for SMPS, run on PCs.<<ETX>>

Analysis, design and control of 1MW, high power factor and high current rectifier system

This paper presents a 1MW, 12-pulse thyristor rectifier with passive filter and DSTATCOM for low voltage, high current industrial dc loads. The considered process act (electrically) as a current controlled, variable voltage load. Moreover the load characteristic varies extensively with number of hours of operation. Variable compensation capabilities are required to provide harmonic and reactive power compensation for such kind of loads. A Distribution Static Compensator (DSTATCOM) is used to provide variable reactive power compensation. Along with it an 11th harmonic passive filter with substantial amount of reactive power support is provided to reduce required rating of DSTATCOM. Design and control of system are carried out such that input power factor remains greater than 0.98 and THD remains below 5%. Simulation results are presented to verify the effectiveness of the system.

Comparison of PWM AC chopper topologies

In this paper, a commonly reported single-phase four-switch AC chopper topology is compared with a six-switch topology in terms of the total harmonic distortion (THD) of the input current, power factor (PF), commutation behavior, robustness and efficiency. Working principles of both topologies are presented along with simulation results. Based on a comparison of the findings, the four-switch topology is found to be better choice for the given application. Thus, the implementation of a four-switch topology is carried out at a power level of 10 kW. Experimental evaluation is carried out in order to verify the suitability of the circuit for the intended application. The experimental setup validates the findings of the simulations. Thus, the proposed approach is a practical way to improve input current THD and PF compared to thyristor choppers.

A critical comparison of boost-topologies for single-phase switched mode rectifiers

A detailed comparison of boost-derived topologies operated at 90-265 V/400 V-1.3 kW is presented. They are utilized for single phase power factor corrected rectifiers serving as front-ends of DC/DC-converters in telecommunication equipment. The comparison is based on component stress quantities occurring at worst case operating conditions, which are derived by analytical and simulative analysis. Theoretical results were proved experimentally on selected circuits.