Department of Engineering

Centre for Advanced Electronically Controlled Drives

POWER ELECTRONICS

This centre and these projects have mostly moved to the Company Technelec Ltd, that was set up
by Professor Pollock to exploit this technology

Laser Power Supplies

The Group has worked on laser power supplies in collaboration with Lumonics Ltd. This is a very demanding application area for power electronic design with very high peak powers.  One project developed a new circuit technique for three phase ac to dc power conversion with unity power factor. A second project developed a constant current capacitor charger, which again had unity power factor.

Design of Welding Power Supplies Employing Resonant Switching Techniques

Many welding power supplies still use bulky transformers with tap changing or thyristors providing a low grade form of current control.  Research in the Group is developing designs of power supplies with a much higher electronic content which will be smaller, lighter, cost less and offer significant performance advantages over existing designs.  Furthermore, forthcoming legislation limiting the amount of distortion caused to the electrical supply will make it illegal for manufacturers to sell the majority of existing welding equipment without major redesign.

Resonant circuit techniques are being used to reduce switching losses in the power semiconductor devices, allowing the devices to switch when the current and/or the voltage is zero.  This allows the switching frequency to be increased without the normal prohibitive increase in switching losses.  In the welding power supply high current IGBTs are being switched at 90 kHz, to produce a sinusoidal current in a high frequency transformer operating at the same frequency.  The high transformer frequency leads to a very compact design and furthermore the ripple current in the rectified output is minimal, removing the need for any output choke.  The soft switching also reduces the levels of radiated electromagnetic interference. 

The welding power supplies are being designed with the help of the SABER simulator from Analogy.  This provides multilevel and mixed mode simulation and can deal with electromagnetic, electromechanical and electrochemical models without requiring electrical equivalent circuits.  Existing mathematical models for welding arcs are being used in conjunction with power electronic circuit simulation to determine the best resonant circuit arrangement for this application with particular emphasis being placed on short circuit and open circuit protection.

Flexible AC Transmission Systems (FACTS)

Flexible A.C. Transmission Systems (FACTS) is the use of power electronic controllers for the control of the electricity supply grid.  A novel PWM controlled series compensation system has been developed and laboratory models have been constructed.  The circuit offers very low levels of harmonic distortion while using switching frequencies well within the capabilities of thyristor and GTO technology.

Design of Integrated Capacitors and Inductors

A Teaching Company Scheme between the Group and Industrial Capacitors Wrexham Ltd. has investigated designs for integrated passive components containing both capacitance and inductance.  Such components could offer a cost saving in applications such as filtering but will be particularly appropriate to resonant converters.

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Author: Ewan Goodier, last updated 17/10/2000.
This document has been approved by the Head of Department.