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Historically, 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 drives.

four quadrant analysis half wave vs full wave optimum motor selection