Speed regulation of DC motor with series excitation by changing of magnetic flux

Scheme for realization of this method have a view represented on figure 4.18.

Figure 4.18 – Scheme with shunting of excitation winding.

Here the shunting resistor is connected in parallel to excitation winding, changing the resistance of which the current of excitation winding, and thus the magnetic flux, can be changed.

As the current, and thus magnetic flux, can be only decreased (under the normal conditions magnetic system of motor is saturated), then the speed regulation will be realized in up direction relatively to the main, and mechanical characteristics of motor will have the view represented on figure 4.19.

Here also for all characteristics ordinate is the asymptote, because as in previous case

І_a®0; М®0; Ф®0; w®.

Figure 4.19 – Mechanical characteristics.

Results of regulation are analogical to speed regulation of DCM IE by field weakening: the method is economical, because losses at the weakened flux are small (resistance is small, so resistance is also small); regulation is realized at constant power, and at speed increasing an admissible loading moment decreases by hyperbolic law; the range of regulation is insignificant – it is limited by commutation quality and mechanical strength of armature. It is used in cases when speed increasing at small loads is necessary. The shunting of excitation winding is used in electric drives of metal-cutting machines.

Дата добавления: 2014-01-05