Hardware Reference
In-Depth Information
Figure 4.37: The EMF output from the brushes of commutation system.
Figure 4.38: The equivalent circuit of a DC motor.
4.2.6 Electrical Degree and Mechanical Degree
In the analysis of an electric motor, both electrical and mechanical perfor-
mances must be taken into consideration. In motor operation, these perfor-
mances vary cyclically. For motors with one magnetic pole-pair, i.e., p =1,
the electrical cycle matches with the mechanical cycle, or in other words, the
electrical signal varies one cycle in one revolution of the motor, as shown in
Figure 4.39. For such a motor, analysis in the mechanical domain is equivalent
to the analysis in electrical domain. However, if the magnetic pole-pair p is
more than one, then the variation of electrical signal will complete p cycles
in one mechanical revolution. Figure 4.40 shows the variation in back-EMF
of a motor with 3 magnetic pole-pairs (p =3)inonerevolution. Inorderto
relate the results of analysis in the electrical domain to those in the mechanical
domain, the terminology of electrical degree and mechanical degree are jointly
