Page 228 - Electric Drives and Electromechanical Systems

224 Electric Drives and Electromechanical Systems

Table 8.3 Half step sequence.

Step A B C D
1 On Off Off Off
2 On On Off Off
3 On On Off Off
4 Off On On Off
5 Off Off On Off
6 Off Off On On
7 Off Off Off On
8 On Off Off On

In half-stepping, the phases are energised at the rated current. If the current in each
phase is controlled, it is possible to produce further equilibrium points, leading to
further subdivisions of a motor’s basic step; this approach is termed mini-stepping.
While this approach will result in a greater resolution, each phase’s current must be
individually controlled, leading to additional complexity in the drive system; the
switching pattern is given in Table 8.3.

FIG. 8.11 The use of a zener diode to modify the delay characteristics of the winding current. The winding
voltage is shown is the dotted line. The winding characteristics are identical to those used in Fig. 8.7A. (A) Circuit
diagram. (B) The current and winding voltage.