Abstract
M.Ing.
Variable liquid resistors are utilised in the rotor circuit, to control mine winders using slipring
induction machines. These liquid resistors have a number of disadvantages, therefore a
new drive technology is required to replace liquid controllers.
A number of machine drives are discussed and a comparative study is made.
A 22kW resistively loaded buck chopper in the rotor, is used as a case study. Full design
details and procedures are given for the chopper. These designs are verified by simulations
and experimental results. A current control was designed and implemented for the buck
chopper in the rotor, using a PI controller and pulse width modulation. The 22kW resistively
loaded buck chopper operated exceptionally well and it is evident that it could be a viable
method for replacing liquid controllers.
The oscillation generated in the hoist cables are discussed and a possible counter acting
acceleration method of removing these oscillations is described. A rotating oscillation system
was designed and constructed for experimental purposes. From the tests undertaken on the
experimental system, it was evident that by the implementation of the counter action
process, it is possible to remove the oscillations in the hoist ropes.