Abstract
In the past, the DC machine was the only motor that could provide easy speed control. Nowadays, since the advent of power electronics, rotating field machines offer cheaper and more powerful possibilities for speed control. Nevertheless, in older industrial installations and environments, DC motor drives may still be used. As a result, and also because of their excellent characteristics, it remains instructive to shortly review the possibilities of DC machines for speed control, including braking in particular.
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Notes
- 1.
The figure only shows the first quadrant, although the characteristics continue in the second quadrant for generator operation (see Sect. 12.2.2).
- 2.
The characteristics to the left are obtained by reversing the connection between armature and series excitation; reversing the polarity of the supply does not affect the characteristics.
- 3.
To prove this, consider operating points with the same flux level and therefore also the same excitation current.
- 4.
Moreover, it can be shown that a series-excited machine is not able to recuperate electrical energy into a voltage supply.
- 5.
A transition from motoring in the first (or third) quadrant to generating in the second (or fourth) quadrant is impossible: for zero load torque the speed goes to infinity, and armature current and excitation current become zero. Even if there were an (artificial) ‘operating point’ with recuperation into a voltage supply, such an operating point would not be stable. Again, this can be proven quite easily.
- 6.
Indeed, the larger \(\alpha \), the smaller the time available to increase the excitation current, and vice versa.
- 7.
This is important for the control of the adhesion between the rail and wheel in trains.
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Melkebeek, J.A. (2018). DC Commutator Motor Drives. In: Electrical Machines and Drives. Power Systems. Springer, Cham. https://doi.org/10.1007/978-3-319-72730-1_12
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DOI: https://doi.org/10.1007/978-3-319-72730-1_12
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