Page 426 - Power Electronics Handbook

Electrochemical 415
magnitude of this current and the time for which it flows. The supply must
be d.c. although ripples in the current are acceptable, so a three-phase
rectified source can be used. Generally, the magnitude of the voltage is
also low, varying from 5 V to 100 V, and this is usually provided by the use
of a thyristor bridge.
Electrolysis consists of extracting metals such as aluminium from a
solution. Usually a low d.c. voltage is required, in the region of 5 V, but as
the process proceeds this needs to rise to about 50V. Several such
electrolysis baths can be connected in series, so that the overall voltage
requirements can reach in the order of 1 kV. High currents are necessary,
often between 50 kA and 100 kA, and these are obtained by three-phase
12-pulse or 24-pulse rectifier systems, using parallel-connected thyristors.
Current feedback is used to control the voltage and current supplied to the
load, by adjusting the power thyristor conduction periods.
Some electrolysis processes require periodic reversal of the current flow,
for a few seconds every few minutes, to prevent film formation at the
electrodes, and this can be done by a reversing bridge arrangement.
Electrochemical forming is the reverse process to electroplating, where
material is selectively removed from areas of the target. Low voltages are
again required, in the region of 1OV to 30V, and the current drawn by the
load is high, in the region of several kilo-amperes. Therefore the drive
circuits for these loads are similar to the d.c. power supplies used for
electrolysis.

14.7 References
Allegro (1995) Allegro SMPS modules outperform monolithics, Electronic Engineering,
January, pp. 9-10.
Bush, S. (1995) A switch in time, Electronics Weekly, 24 May, pp. 23-24.
Chowanietz, E.G. (1995) Automobile electronics in the 1990s. Electronics and Communication
Engineering. April, pp. 53-58.
Dallimore, P. and Carter, M. (1995) Simplifying power control system design, New Electronics.
10 January, pp. 23-24.
Dewan, S.B. et al. (1994) Power Semiconductor Drives, John Wiley.
Emerald, P. (19%) PWM stepper motor control using PMCMS. Electronic Producr Design,
September, pp. 28-34.
Goodenough, E (I 994) Off-line and one-cell IC converters up efficiency, Electronic Design. 27
June, pp. 55-64.
Goodenough, E (1995) 90% efficient 1.5 A IC switchers run at 1 MHz, Electronic Design. 30
May, pp. 17-84.
Mosley, J.D. (1992) Spin chips whirl into nondrive applications, EDN, 23 April. pp. 43-50.
Peters, D. and Harth, I. (1993) ICs provide control for sensorless d.c. motors, EDN, 29 April,
pp. 85-94.
Pilla, S.K. (1995) Analysis of Thyristor Power-Conditioned Motors, Sangam Books Ltd.
Sax, H. (1995) Mosfets add to car power, What’s New in Electronics, February, pp.
102-103.
Shepherd, W. et al. (1996) Power Electronics and Motor Control, Cambridge University
Press.