Electricity: motive power systems – Induction motor systems – Braking
Patent
1984-02-29
1985-06-04
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Braking
318798, 318757, H02P 318
Patent
active
045217246
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. FIELD OF THE ART
The present invention relates to an apparatus for processing energy regenerated by an AC motor and particularly to an apparatus which returns the energy regenerated by the AC motor to an AC power source.
2. BACKGROUND OF THE ART
The energy regenerated by a motor due to the inertial energy thereof or the energy which the motor receives from an external source usually results in the rise of potential of a DC power source to which is connected a motor drive circuit that receives pulse width modulation (PWM) signals. The rise in potential often destroys a smoothing capacitor which is contained in a rectifier circuit or semiconductor switches are contained in the motor drive circuit to drive the AC motor. It is therefore necessary to process the regenerated energy by some means.
As one means for processing the regenerated energy, a system is known which returns the regenerated energy to an AC power source.
In a conventional apparatus for returning the regenerated energy to the AC power source, hereinafter described in detail, voltages between the phases of the AC power source are monitored during the period of deceleration mode of the AC motor, and semiconductor switches for processing the regenerated energy are closed during periods in which voltages between the phases exceed a predetermined value so as to return the electric current of the DC power source to the AC power source. The regenerated energy can be efficiently returned to the AC power source if it is returned during the periods in which voltages between the phases of the AC power source are great.
In the AC motor, however, three operation modes are performed repetitively, i.e., regeneration, circulation, and consumption, and a regenerative condition is not always established even when voltages between the phases are greater than a predetermined value during the deceleration mode. As was mentioned above, since semiconductor switches for processing the regenerated energy are closed whenever the voltages between the phases become greater than a predetermined value, a large amount of electric power must be dissipated by resistors that are inserted, for protecting the semiconductor switches, between the lines of the DC power source and the semiconductor switches. For this purpose, the resistors must be capable of handling a large amount of electric power. Because of this resistors for handling a large amount of electric power are much greater in size than other elements and make the apparatus for processing the regenerated energy bulky.
DISCLOSURE OF THE INVENTION
IN view of the problems inherent in the above-mentioned conventional apparatus, the object of the present invention, which is based on the idea of detecting the regenerative condition of an AC motor by monitoring the direction of the current flowing through the AC motor and the condition of the motor drive circuit, in addition to monitoring the deceleration mode and the condition in which voltages between the phases are greater than a predetermined value of the AC power source, to provide an apparatus for processing energy regenerated by an AC motor, which apparatus instantaneously discriminates whether or not the AC motor is in a regenerative condition and returns the regenerated energy to the AC power source only under a regenerative condition by rendering conductive the semiconductor switches for processing the regenerated energy, so that the power consumption is decreased in the resistors for protecting the semiconductor switches for processing the regenerated energy, resulting in the possibility of reduced power in the resistors and, accordingly, a reduction in the size of the apparatus for processing the regenerated energy.
To achieve the above-mentioned object, the present invention provides an apparatus for processing energy regenerated by an AC motor, which comprises: a rectifier circuit for supplying a direct current to the lines of the DC power source by rectifying an alternating current supplied from an AC power source; a drive circuit including A
REFERENCES:
patent: 4319177 (1982-03-01), Kawada et al.
patent: 4353023 (1982-10-01), Kawada et al.
patent: 4434393 (1984-02-01), Kobari et al.
Sakamoto Keiji
Toyozawa Yukio
Fanuc Ltd.
Smith Jr. David
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