Autori: Christian Klumpner

Editorial: Aalborg University, ISBN 87-89179-57-9, 2004.

Rezumat:

In this project, power converter topologies for the next generation of Integrated Adjustable Speed Drives have been investigated. First, in order to select the candidates, it has been necessary to identify their requirements, which are:
– More robustness against voltage supply disturbances (unbalance and distortion);
– Limited variation or stabilized dc-link voltage while the input voltage may vary widely (universal voltage supply) which will allow a better utilization of semiconductors in the motor side inverter in the case of voltage source converter topologies are used;
– Reduced/minimized input current THD under a wider voltage supply quality which requires a sort of active front-end to control the shape of the input currents to be square-wave (dc-link current control) or sinusoidal (individual input current control);
– Allow for size reduction of the converter because it has to be integrated with the motor into a single unit, and one way to achieve this is to minimize the size of passive components;
– Increase the lifetime of the drive, which means the replacement of limited lifetime components such as electrolytic capacitors by film capacitors and elimination of the fans by employing converter topologies with a higher efficiency or higher operating temperature.
Then, a number of 11 power converter topologies have been identified, classified into three groups depending on their most important features: regenerative power capability, which is the most expensive and square wave or sinusoidal input current, while regenerative power converters without sinusoidal input currents have been omitted. Simulation models of the candidates have been developed in Simcad in order to develop their control, to estimate the candidate performance and to identify their loss distribution. Design of the necessary magnetics and estimation of their size and losses have been carried out, as some of the topologies are using inductances that are subject to high frequency core and copper losses. It has been shown that even though some of the converter topologies show low semiconductor losses, the situation changed dramatically after the losses in the passive components are added.
Comparison of the hardware requirements has shown that sinusoidal input current ASD topologies require more semiconductors and magnetics than square wave input current ASDs, while within this group, the situation regarding the consumption of semiconductor devices on one hand and the size of the magnetics on the other hand compensates somehow. A Vienna rectifier requires 3 IGBTs and a back-to back Voltage Source Converter (VSC) requires 6 IGBT in the front-end stage but three boost inductances which are expensive (ferrite or metglass) and bulky (bigger for the regenerative converter) are needed. A matrix converter requires 18 IGBTs and a two-stage Direct Power Converter (DPC) requires 12 IGBTs in the rectification stage, while the high frequency stress on the input filter inductance is reduced which reflects in its size and technology. The best choice has been shown to be the two-stage DPC which employs reverse blocking (RB) IGBTs in the rectification stage.
Additionally, technologies to reduce the size of the power converters, such as the possibility to integrate the power converter inductance into the AC motor magnetic circuit or to use the leakage stator inductance of the motor as a virtual inductance in the power converter circuit have been investigated. Multistage filtering has been shown to provide higher attenuation of the switching frequency ripple, while using the same amount of passive components.
The use of RB-IGBTs in power converters has also been investigated and it has been shown that even though its switching performance isn’t great, there are a few converter topologies that may benefit from using it.
The application aspects of using a DPC, such as ride-through capability or braking capability of an ASD based on a DPC topology (matrix converter) under power grid failure have been investigated and experimentally tested on a lab setup.
New features of the two-stage DPC topology, the possibility to share the rectification stage in a multiple motor drive approach, as well as operating from multiple power grids of different frequencies and smoothly adjusting the fraction of power have for the first time been proposed and investigated. The first mentioned feature has also been prototyped in the lab and experimentally tested. New techniques to interleave the pulse generation of the inversion stages have been shown that allow for reduction of the input current ripple and estimation of the output currents, which are cost effective because are all-software base and does not require an increase of the filter components or extra transducers.
Investigations on the stability of a DPC topology (matrix converter) have been carried out, showing that filtering the two components of the input voltage vector, its magnitude and its angle, have different impact on the stability. The findings have experimentally demonstrated to provide for a more reliable operation and increased performance on the grid side by using as angle for the input current vector reference the filtered angle of the input voltage vector.
The findings of this project have been widely published in 15 papers: four journal papers and 11 conference papers. A webpage of the project has been established at:
http://www.iet.auc.dk/~ck/matrix/dpec.html
which contains a summary of the project, pictures of the prototypes and the list of papers, available in pdf format, which have been published as a result of the work done in this project and which acknowledge the support given by this project.

Cuvinte cheie: direct power conversion, integrated motor-drive