Electricity: motive power systems – Reciprocating or oscillating motor – Energizing winding circuit control
Patent
1983-04-06
1986-01-07
Smith, Jr., David
Electricity: motive power systems
Reciprocating or oscillating motor
Energizing winding circuit control
318254, H02K 2902
Patent
active
045636192
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electric power converter circuits for variable-speed, switched reluctance motors.
Such motors, and controlled power converter circuits for them, are known, and reference may be had to the papers in I.E.E. Proceedings, Volume 127, Part `B` No. 4, July, 1980, between pages 253 and 265 entitled "Variable Speed Switched Reluctance Motors", and I.E.E. Proc. Vol. 128, Part `B`, No. 2, March, 1981 entitled "Inverter Drive for Switched Reluctance Motor; Circuits and Component Ratings" for a summary of what may be the state of the art at the date of this application. The second of those papers is by three Authors, two of which are the Inventors in the present application.
Such motors and converters involve the use of phase windings on the stator poles, which are connected in series with thyristors across a D.C. supply, with the thyristors being switched on in synchronism with the movement of the rotor in relation to the stator to provide driving torque. The thyristors are switched off, or commutated, at appropriate instants during rotor rotation, and after commutation, current in the windings can be free-wheeled, or can be returned to the supply depending upon the circuit and the method of control.
An object of the invention is to improve the efficiency and/or economy of a multi-phase switched variable-reluctance motor having a number of phase windings each connected in series with at least one main thyristor across a D.C. supply, commutating means arranged to commutate the various thyristors, and timing means responsive to the current in the different windings and/or in response to the angular position of the rotor in particular by reducing the number of switching devices such as thyristors which are required for producing a range of possible operating conditions and by providing timing and sequencing means for activating the switching devices so as to obtain maximum benefit from the system.
The improvement in efficiency can be achieved in two related ways which constitute two different aspects of the present invention.
According to one of those aspects, for a reluctance motor where each phase winding is energised in sequence, during the transition of energisation from one phase to the next phase the timing means is arranged to independently control at least one commutation and refiring of the main thyristor of the incoming phase winding before the final refiring and commutation of the main thyristor of the outgoing phase winding.
The idea of commutating and refiring the main thyristor of a phase more than once during the period for which that phase is energised in sequence with the other phases is a method of operation known as "chopping" but in the past it has only been known to chop in one phase winding at a time unless two windings are placed in series so that the current in the first also flows through the second, the windings thereby being treated as one, and separate control of the currents in each being impossible.
The present invention in its first aspect is based on the discovery that a considerable advantage can be achieved if chopping is performed in two adjacent phases simultaneously, the chopping actions in the two phases being independent of each other. Thus, it is quite possible for two adjacent phases to produce torque simultaneously but the ideal current may be different in the two phases, and accordingly independent control of the chopping enables very efficient operation to be achieved.
According to the second aspect of the present invention, the timing means is arranged during a part of a rotor revolution, in which a rotor pole passes a stator pole, to fire at least one main thyristor to cause the phase winding on that stator pole to draw current from the supply; then to commutate at least one main thyristor and if necessary fire a free-wheeling thyristor to cause the current in that phase winding to free-wheel and then to commutate a second main thyristor or the free-wheeling thyristor to cause the current in that phase winding to flow to return energy to the supply.
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Davis Rex M.
Ray William F.
Chloride Group Public Limited Company
Smith Jr. David
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