It was found from the transfer-functions of the separately excited DC-machine that modification of the torque needs control of the armature current and modification of the speed requires control of either the armature voltage or the excitation voltage. Changing the speed-torque characteristic using series resistors is possible in principle but leads to losses; the torque and speed cannot be adjusted independently from each other and the control velocity is relatively low, especially when using mechanical switches. Power electronic converters offer considerable advantages. There are two basic solutions of the power supply of DC-machines. The first solution is the transformation of a constant direct voltage into the direct voltage required by the DC-machine: these are the DC-DC-converters. The second solution is the conversion of an alternating or three-phase-voltage into the direct voltage required, in which case the circuitry are line commutated converters or naturally commutated converters. This chapter deals with the principles of operating these two types of converters and their open- and closed-loop control.
KeywordsTorque Expense Abate Hine Dmax
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