Power electronics, control of theelectromechanical energy conversionprocess and some applications

Prof. J.D. Van Wyk, Dr.sc.tech., Prof. H.-Ch. Skudelny, Dr.Ing., and

A. Muller-Hellmann, Dr.Ing.

Professor: Ming-Shyan WangStudent: Hao-Chun Chu

Published in:Electric Power Applications, IEE Proceedings B (Volume:133 , Issue: 6 )

Date of Publication:November 1986

Outline Electronic processing of power Power electronics: a proposed systematic approach Development of the subject of machine electronics Development of ideas to control electrical machines Growth of power electronics in rail drives as an example

of application in the control of electric machines State of the art and future trends in power and machine

electronics

Electronic processing of powerPower electronics covers a much wider field encompassing the application of switching power to all types of loads. Electric machines form but a small fraction of the loads found for power electronic convertors.

Power electronics: a proposed systematic approach

It has already been noted that efficiency and loss requirements dictate the control of power in a switching mode in power electronics. For a systematic approach the technology of the specific types of power switches, as well as particular peculiarities of behaviour should be omitted. These characteristics — such as switching speed, switching

This leads to the fundamental possibility to control power flow as shown in Fig. By operation of the switches Si and S2, the switching function s(t) is generated, so that the load voltage becomes

uL{t) = s(t)us(t)

Development of the subject of machine electronics

The oldest known switch used in the control of electrical machines is the mechanical commutator. This was followed by a mechanical switching arrangement to control the field of generators, the Tirrill controller. Subsequently the gaseous valves showed promise for generating the switching functions necessary to control machines. These devices had some disadvantages and at a time it appeared that the mechanical metallic rectifier (a modified commutator!) was the future promise. Almost simultaneously it was succeeded by a device developing in parallel, the transductor or magnetic amplifier. The era of semiconductor switches then dawned, an era from which we, being still concerned in its development, are able to derive but limited historical perspective.

Development of ideas to control electrical machines

Ideas to use electronic elements to control, regulate or augment electrical machines appear to have been put into practice for the first time around 1920. It is possible that these contributions may not be characterised as machine electronics as it is known today, yet may be considered as the very beginning of the subject.

One of the ideas being applied at present is the use of thyristor frequency changers in conjunction with squirrelcage induction machines for electric traction purposes.

Growth of power electronics in rail drives as an example of application in the control of

electric machinesThis last locomotive, representing a very important state in the development, was equipped by the AEG Company. The convertor was built in a particularly interesting circuit arrangement. Four groups of four anodes worked on different taps of the main transformer. Additionally a zero anode was also available. The 18 anodes of a mercury-arc rectifier in a steel tank were connected as shown in the Figure.

State of the art and future trends in power and machine

electronicsAlthough the art and science of electrical machines have for some time been considered well known, the future possibilities for power conditioning and conditioning and control of the electromechanical energy conversion process is being affected profoundly by the present and future developments in semiconductor technology, especially with regard to power semiconductor devices and control electronics, which have been aided by the developments in the field of microelectronics. The discussion in the following sections will centre on the different switching devices, the present and future power convertor topologies, the present and future situation regarding the use of convertors as machine actuators in control systems, the present and future situation regarding control of DC and AC machine drives, including adaptive control ideas, and, finally, the interface between power and machine electronics and power system technology.

ConclusionNew directions of development regarding the electronic conditioning of the electromechanical energy conversion process concerning the elimination of undesirable effects and losses are important. The implementation of these trends by utilising the improved switching characteristics of power electronic switches and the information processing capability of microprocessors is discussed. This is then extended toward control aspects, where both these characteristics enable solutions not possible hitherto. Field control of AC machines imparts control characteristics equal to, or better than, those obtainable with DC machines to the systems, while the processing capability of microprocessors allows the configuration of adaptive machine electronic systems. Finally attention is given to the interfacing of power electronic and machine electronic systems to the power supply network. If the exponential growth of the installed capacity of equipment in the future is to be handled, active compensation of the distorted currents drawn from the supply by this equipment will have to be considered seriously.

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