Uwe Rädel

Comparative investigation on power grid perturbations caused by DC-link converters and matrix converters

In recent years, the matrix converter has been discussed as a competitive alternative to the state-of-the-art DC-link converter. The matrix converter is considered to be superior due to the absent DC-link capacitor and therefore being fully integrable in silicon. Several publications deal with comparative views on power losses, efforts for realization or control strategies for both converter types. But the comparative study of the power grids perturbation is a further viewpoint which has to be considered since both converters have to comply to electromagnetic compatibility standards. Therefore both converters are modeled with generic assumptions made on the switching functions and the modulation strategy to ensure a fair-handed basis of comparison. For both converters the spectrum influencing factors are identified and discussed.

The synchronous switching of motor power supply from frequency converter to grid for an AC drives with field-oriented vector control

The report is dedicated to the closed-loop design for a phase locking and a magnitude balancing of the three-phase inverter voltages to the three-phase grid voltages when the AC motor stator windings are switched to the AC power supply from the power frequency converter and backwards. The proposed control strategy for the AC drive with IGBT-inverter allows to decrease an inductance of current-balancing reactor and to avoid the operation under fault conditions after current surges.

A generic approach for comparing input filter efforts of voltage- and current source converters

Matrix converters are said to redeem the very well established DC-link converter in some fields of application. One general idea behind the matrix converter approach is the absent DC-link capacitor which is referred as one reason for the matrix converter being superior to the DC-link converter regarding its size and lifespan. On the other hand, the input filter of the matrix converter is said to be larger than the input filter of DC-link converters undermining the afore mentioned advantage of the matrix converter concerning the size. In this paper a general approach regarding the input filter design is applied to both converter types to perform a fair-handed filter comparison which also takes into account the parasitic series resistances of the reactances. A first theoretical investigation based on a simplified spectrum is performed for a DC-link converter and a matrix converter both designed for 3 kVA apparent output power.

Increasing the efficiency of the Modular Multilevel Converter with MOSFET switches using Lagrange multipliers

This work proposes an approach to minimize the power losses of the Modular Multilevel Converter with MOSFET switches by applying a circulating current reference calculated using Lagrange multipliers. The optimized circulating current changes the loss distribution between the converter elements and improves the total converter efficiency. For the considered 25kW converter designs, an efficiency increase of 0.3 to 0.6 per cent was achieved which corresponds to the loss reduction of 6 to 11 per cent.

AC side parallel-series active filter with DC voltage control capability of a diode rectifier

This paper discusses a parallel-series active power filter (APF) for a three-phase diode rectifier. In addition to power quality improvement, the proposed APF can control the DC voltage of the diode rectifier. A new control strategy by the series APF generates an adjustable constant DC voltage. The simulation results show that the DC voltage can be decreased or increased.