Electricity: motive power systems – Synchronous motor systems – Hysteresis or reluctance motor systems
Patent
1991-04-30
1992-09-01
Smith, Jr., David
Electricity: motive power systems
Synchronous motor systems
Hysteresis or reluctance motor systems
363124, H02P 540
Patent
active
051442159
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a current supply control apparatus for an inductance load, which is used to control the energizing current of an armature coil of an electric motor with an output of about 30 W or more for a specified waveform when the motor is rotating at high speed.
BACKGROUND ART
In current control for an electromagnet of a magnetic bearing, it is difficult to drastically to change energizing current for floating a rotor, since the inductance of the exciting coil of the bearing is high.
In order to ensure good responsiveness of a chopper circuit for the energizing current of an inductance load, the supply voltage is increased correspondingly if the inductance load is great, so that the rise of the energizing current is quickened, and accumulated magnetic energy attributable to the inductance is returned to the power supply. By doing this, the fall of the energizing current is quickened to improve responsiveness, whereby the energizing current is controlled.
There are means for increasing the supply voltage which are used to ensure high-speed response of the energizing current of a great inductance load by means of a chopper circuit. For higher responsiveness, however, the supply voltage is inevitably increased to an unpractically high level.
In the case of an induction motor of 500-W output or a reluctance-type electric motor, for example, a voltage five to ten times as high as the necessary applied voltage for the driving torque is needed to obtain a pulse width of several microseconds or thereabout for the chopper control of the armature current supply, which is not practical.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a current supply control apparatus for an inductance load, capable of effecting current supply control of the inductance load with satisfactory responsiveness despite the use of a low applied voltage.
The present invention provides a current supply control circuit for an inductance load, which comprises: first and second semiconductor switching elements connected across an inductance load; a dc power source for supplying power to the inductance load through the first and second semiconductor switching elements; a first diode reversely connected to a series junction of the first semiconductor switching element and the inductance load; a second diode reversely connected to a series junction of the second semiconductor switching element and the inductance load; a current sensing circuit for detecting an energizing current for the inductance load, thereby obtaining a detected voltage; a reference voltage including a set voltage with an optional waveform; a third diode for back flow prevention forwardly inserted on the side of the dc power source for supplying power to the inductance load; a small-capacitance capacitor connected in parallel with a series junction of the first and second semiconductor switching elements, the inductance load, and the current sensing circuit; and a chopper circuit adapted to render the first and second semiconductor switching elements nonconducting so that accumulated magnetic energy in the inductance load is prevented from flowing into the plus terminal of the dc power source by means of the third diode for back flow prevention when the reference voltage is exceeded by the detected voltage from the current sensing circuit, to convert the accumulated magnetic energy into electrostatic energy of the small-capacity capacitor by means of the first and second diodes, thereby causing the energizing current to fall rapidly, and to cause the first and second semiconductor switching elements to conduct when the energizing current is lowered to a predetermined value. Thus, the rise of the energizing current is quickened by means of a high voltage of the small-capacitance capacitor.
According to the present invention, when an exciting current of an inductance load 1 (voltage drop in a resistor 9) in FIG. 1(a) exceeds a reference voltage (voltage at a terminal 12), the output of an operational amplif
REFERENCES:
patent: 4933621 (1990-06-01), MacMinn et al.
patent: 5043643 (1991-08-01), Hedlund et al.
Kabushikigaisha Sekogiken
Smith Jr. David
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