Manuscript received November 16;
1995;
revised August 12;
1996;
August;
8;
1997;
May;
12;
1998;
and August 3;
1998. Recommended by Associate Editor;
J. C. Spall. This work was supported by the Australian Research Council. E. Weyer is with the Department of Electrical and Electronic Engineering;
University of Melbourne;
Parkville VIC 3052;
Australia. R. C. Williamson is with the Department of Engineering;
Australian National University;
Canberra ACT 0200;
Australia. I. M. Y. Mareels is with the Department of Electrical and Electronic Engineering;
Parkville;
VIC;
3052;
Australia. Publisher Item Identifier S 0018-9286(99)05462-8;