Klaus F. Hoffmann

A novel control concept for high-efficiency power conversion with the bidirectional non-inverting buck-boost converter

This paper presents a novel control concept for the bidirectional non-inverting buck-boost converter to achieve extreme high-efficiency power conversion. The duty cycle, duty ratios and time delays of the PWM control signals for the switches are modulated depending on operating points to minimize the power losses in the converter. A 3kW prototype of the converter using SiC MOSFETs has been designed and tested for the verification of the control concept. Measurement results show that the prototype achieves power efficiency between 97.79% and 99.60% over a power range “input voltage from 300V to 500V, output voltage from 200V to 600V and output current from 1A to 5A”.

Comparison of driving concepts for silicon carbide bipolar junction transistors

This paper presents a comparison between conventional base driver concepts for bipolar silicon carbide transistors and an approach based on utilizing a buck-converter-IC to drive the bipolar transistor. The different concepts are simulated and compared with respect to switching performances and driving losses. The results are validated by corresponding measurements.

Control of a hybrid filter topology for the reduction of high frequency harmonics

The Digital Chain is realized as an adaptive finite impulse response filter (FIR). FIR filters with the order of N consist of (N-1) time delay elements, adder and filter coefficients w(n). Based on the measured harmonics in the voltage of ZLoad the filter coefficients are adjusted using the Filtered x Least Mean Square (FxLMS) algorithm [2]. The FxLMS is a stochastic gradient descent method producing the least mean squares of the detected harmonics by updating the filter coefficients with the given formula: w(n +1) = w(n) + μe(n)x(n).

Concept for a Modular Class-D Amplifier for MPI Drive Field Coils

This paper studies the performance of a modular class-D switching amplifier to supply the drive field coils of a magnetic particle imaging scanner with a high quality sinusoidal voltage. While a class-A or class-AB amplifier is capable of delivering such a sinusoidal voltage, its low efficiency does not qualify for an economic solution. Therefore, a class-D amplifier has been used. The modular amplifier consists of commercially available class-D amplifier chips, which are connected in parallel, to achieve the required output power. This paper describes the simulation model and a hardware setup of the modular amplifier which consists of 10 chips connected in parallel.

A Hybrid Filter Topology for a Reduction of High Frequency Harmonics

In this paper a hybrid filter topology for the reduction of the total harmonic distortion in AC sources is introduced. The hybrid filter contains active and passive components. The structure of the digital filter influencing the signals gain and phase will be explained. Furthermore an analytical consideration of optimal filter coefficients is shown. For the validation of the concept a matlab/plecs simulation is presented.