Speed regulation of DC motor with series excitation by changing of supply voltage

Regulation is realized accordingly to scheme, where energizing of armature is provided by controlled rectifier CR, creating the system converter - motor (figure 4.20).

Figure 4.20 – Changing of supply voltage with the help of controlled rectifier.

The output voltage of converter is regulated correspondently to input control signal .

Mechanical characteristics of DCM SE have a view represented on the figure 4.21.

If the small internal resistance of converter CR is neglected (at ) the characteristic 1 can be considered as natural. At voltage decreasing the speed of DCM SE decreases, and artificial characteristics are situated lower than natural one. The rigidity of characteristics doesn’t change at voltage decreasing, and as early was considered the abscissa axis is asymptote of characteristics, because І_a®0; М®0; Ф®0; w®.

Results of regulation mostly correspond to speed regulation by voltage changing of DCM IE.

Figure 4.21 – Mechanical characteristics.

The modification of speed regulation for DCM SE by supply voltage changing of motor is changing of DCM SE switching on scheme in the multimotor drive, when a number of same DCM SE are operating on the single shaft. Such system is applied in transport (electric and diesel locomotives, trams and so on), high power metallurgical cranes and other heavy metallurgical equipment, for example, blast-furnace hoist.

Changing of voltage applying to each motor is realized due to scheme of parallel-series motor connection (рисунок 4.22).

a – parallel connection of motors;

b – series connection of motors.

Figure 4.22 – Changing of supply voltage with the help of scheme of motor connection.

So for two-motor electric drive at parallel connection of motors (fragment а of the figure) to the each motor the total (nominal) voltage is applied and motors rotate with the corresponding speed, and at series connection of motors (fragment b of the figure) to the each motor half voltage is applied, and motors rotate with the speed less in half. Thus this method is graduated regulation. Below characteristics of such regulation are mentioned, see figure 4.23.

In such a way, there are two values of speed without additional energy losses for regulation. At ED starting motors are connected in series to have the less speed for relieving of starting conditions.

To use the motors completely regulation should be provided at constant loading moment which is equal to nominal.

Figure 4.23 – Mechanical characteristics.

Дата добавления: 2014-01-05