Electric power conversion systems – Current conversion – Using semiconductor-type converter
Patent
1994-04-08
1995-07-25
Dougherty, Thomas M.
Electric power conversion systems
Current conversion
Using semiconductor-type converter
363 17, 363 98, H02M 75387
Patent
active
054368251
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the invention
The invention concerns an electronic control-circuit for the supply of ohmic-inductive loads by means of direct-current pulses with variable pulse duty-ratio--in particular of electronic motors, preferably those in whose stator or rotor a magnetic unidirectional field is produced; with a regulator that features a transformer; wherein on the primary side the transformer is connected in push-pull arrangement--via electronic switches that are bridged by freewheeling diodes--to a source of d.c. voltage; and on the secondary side is in connection--via electrical switches that are symmetrically connected to the transformer and[are bridged by freewheeling diodes--to the load; and wherein the transformer is preferably designed as an autotransformer with single continuous winding with center tap and taps that are symmetrical to the latter.
2. Description of the Prior Art
So-called step-down regulators [choppers], which consist of bipolar transistors, MOS field-effect transistors, or thyristors make it possible to achieve economically a partial-load operation of consumers, with supply from a source of d.c. voltage with constant voltage, because in this case one avoids losses such as those that occur in adjustable resistances which are inserted in the circuit ahead of the arrangement. This is of importance in such cases as, for instance, the operation of electric vehicles from batteries carried along, because by means of a low-loss partial-load operation such vehicles can greatly improve the autonomy achievable with one and the same battery charge.
In the most simple case, an electronic switch is in series with the source of d.c. voltage and with the electric motor, with an additional freewheeling-diode connected in parallel with the motor. The electrical energy which is supplied to the motor via the switch can be controlled by means of the pulse duty-ratio, between the closed and open condition of the switch. This is the most simple mode of operation, which corresponds to one-quadrant operation.
If the motor lends itself to being operated as a generator, independently of its speed of rotation, a two-quadrant operation is possible. In this case, the motor is not only electrically driven, but can also be braked electrically. In that case, the control circuit for supplying the motor encompasses a series-circuit of two electronic switches that is connected to the source of d.c. voltage, the electric motor being connected in parallel to one of these two switches. At any given moment, only one of the two electronic switches may be made conductive, while the other one must be blocked. The electronic switch connected in series with the source of d.c. voltage and with the motor is used for driving operation, as described earlier. For braking operations, the switch that is connected in series with the source of d.c. voltage and with the motor is opened, the motor operating as a generator; it may be short-circuited with the electronic switch that is in parallel with it. Assuming that the exciting fields stay the same, the voltage of the generator has the same polarity. However, the flow direction of the current is opposite to the one that occurs during operation as a motor. This means that in the case of-a d.c. series-wound motor, the field winding must have its poles reversed for braking purposes. On the other hand, in the case of a motor with shunt characteristics--such as, for instance, a permanent-field motor--no special measures must be taken. By means of the short-circuiting of the motor which is functioning as a generator, a current that rises with time flows from the generator through the smoothing choke (which may be made up, for instance, by the motor winding); when the current circuit is opened, a self-induced voltage appears at the smoothing choke, which voltage, together with the generator voltage, exceeds the voltage of the source of d.c. voltage. This causes a flow of current which diminishes with time, flowing via the freewheeling diode of the other electro
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Patent Abstract of Japan for JP 58-046874.
Beszedics Geza
Pavuza Franz
Toriser Walter
Wawra Manfred
Winkler Werner
Dougherty Thomas M.
Nguyen Matthew V.
Silent Motors
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