many applications for speed control of DC motors were controlled manually.
Frequent speed and direction reversals were handled by combinations
of braking schemes as well as reversing switches and contactors. Since
the majority of these applications were appropriate for full wave,
unidirectional controllers, it is natural that standard motor ratings
evolved for these uses. This resulted in the de facto standards of
90VDC rated armatures for 115VAC power lines and 180VDC rated armatures
for 208/230VAC power lines.
Recent trends in the automation of factory tasks the rise of the microprocessor
and the need for greater industrial productivity have expanded the
requirements for devices that remotely control motive power. Many
of these automation related applications require frequent speed and
direction reversals or regenerative braking. Since the half wave configuration
is statically reversible (e.g. without requiring reversing switches
or relays) it provides the most dependable overall performance for
four quadrant requirements.Reversing and regenerative braking applications,
particularly those under several horsepower, naturally call for the
economical, extremely rugged and reliable performance of the half
wave thyristor DC motor drive.
However, when half wave drives are used with 90VDC and 180VDC rated
motors, they occasionally provide less than desired performance, since
these motors are optimized for full wave applications. In effect,
an impedance mismatch occurs because the half wave instantaneous armature
currents are higher than those produced by corresponding full wave