Electricity: motive power systems – Motor-reversing – Armature or primary circuit control
Patent
1975-03-14
1976-07-27
Rubinson, Gene Z.
Electricity: motive power systems
Motor-reversing
Armature or primary circuit control
318230, 318231, 321 54, H02P 540
Patent
active
039719723
ABSTRACT:
A transistor inverter drive provides variable frequency and variable voltage power to an electric motor and pulse width modulates a predetermined number of harmonic-reduced constant volt/hertz pulses per cycle of motor frequency to selectively vary the motor stator voltage so that constant torque over a wide speed range can be accomplished and increases the number of constant volt/hertz PWM pulses per motor frequency cycle at low motor speeds to boost the stator voltage and thereby compensate for decrease in magnetizing current and in torque which would otherwise occur at low frequencies. Particularly, the drive has first and second oscillators for respectively deriving trains of first and second clock pulses whose frequencies vary at different rates as a function of an analog speed signal; a frequency switch which selects the higher frequency train of clock pulses; a volt/hertz integrator which derives ramp pulses whose leading edges are established by the pulses from the frequency switch and which vary in magnitude as a function of the time integral of the inverter bridge output voltage; a first comparator for deriving a first control pulse when each ramp signal becomes equal to a first reference voltage; a three phase generator for deriving three phase reference waves synchronized to the first clock pulses and displaced 120.degree. and each of whose period includes a predetermined number of first clock pulses; and means for controlling the fundamental output voltages of individual phases of the inverter bridge in accordance with respective reference waves and including pulse width modulation chopping means for controlling conduction of transistors of the bridge inverter by variable width PWM pulses whose leading edges are at the output pulses from the frequency switch and whose trailing edges are at the first control pulses, whereby the number of PWM pulses in each fundamental voltage cycle is controlled by the higher frequency pulse train and provides a boost in motor terminal voltage at low motor speeds.
REFERENCES:
patent: 3346794 (1967-10-01), Stemmler
patent: 3387195 (1968-06-01), Piccand et al.
patent: 3585488 (1971-06-01), Gutt et al.
patent: 3611086 (1971-10-01), Mokrytzki et al.
patent: 3694718 (1972-09-01), Graf et al.
Allis-Chalmers Corporation
Kaiser Lee H.
Rubinson Gene Z.
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