
254 Electric Motors and Drives
Steps per Sec
Figure 8.12 Steady-state operating region with ideal constant-current drive.
(In such idealized circumstances there would be no limit to the stepping rate,
but as Figure 8.14 shows any real drive circuit imposes an upper limit.)
turned fully on, or they are
cut-off.
A brief description of
each is given below, and the pros and cons of each type are
indicated. In order to simplify the discussion, we will con-
sider one phase of a 3-phase VR motor and assume that it can
be represented by a simple R-L circuit, though in practice
the inductance will vary with rotor position, giving rise to
motional
e.m.f ...