2. Conventional dc drive system

In this Section the control methodology of the conventional dc drive system is presented.

The drive system consists of the full controlled dc motor connected to the load. At the high power, the controlled six pulses full bridge ac-dc power converter is involved; at the low – medium power the full bridge dc-dc power converter connected in series with the uncontrolled ac-dc power rectifier is used. From the point of view of commutation, there is a substantial difference between the above presented solutions: while at low and medium power, the force commutation is used (based on the high frequency switching power transistors), at high power, the natural commutation is used (based on thyristors).

In order to design the conventional control for fast processes, the entire system should be modeled under certain assumptions:

#### 2.1. Assumptions for mathematical modeling of the dc motor

The magnetizing flux is maintained at the rated value; the permeability of the ferromagnetic core is infinite; the unsaturated magnetic circuit is considered, a compensated dc motor is taken into consideration; there are auxiliaries poles; the brushes are situated on the neutral axis; and the brush droop voltage is neglected.
