Electricity: motive power systems – Synchronous motor systems – Hysteresis or reluctance motor systems
Patent
1980-06-10
1982-11-23
Smith, Jr., David
Electricity: motive power systems
Synchronous motor systems
Hysteresis or reluctance motor systems
318254, 318138, H02P 516
Patent
active
043607705
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to variable reluctance motor systems of the type including a variable reluctance motor having a main winding for each of a number of phases and a power converter circuit including a main thyristor in series with each main winding of the motor across a d.v. source from which the main windings are supplied with unidirectional current pulses sequentially, and a commutating circuit including a capacitor for commutating the main thyristors.
2. Description of the Prior Art
Known commutating circuits, having performed their turn-off function for a particular thyristor, leave the commutating capacitor or capacitors charged with a polarity which is opposite to that required to turn-off the same thyristor again or to turn-off the next thyristor in the sequence of thyristor conduction. An additional thyristor in series with an inductor is necessary forming a resetting circuit through which a half cycle of current flows whereby the polarity of the capacitors is reversed.
SUMMARY OF THE INVENTION
According to the present invention, the resetting circuit is arranged to resonantly reverse the charge on the said capacitor by passing a current through the motor winding of another phase.
For a range of motor speeds, especially at standstill and at low speed, it is necessary to adopt a chopping mode in which a main thyristor of one phase is fired and turned off several times before that of another phase is fired, so as to maintain current in a particular phase winding between desired limits and thus to develop the desired motor torque.
The present invention is particularly applicable to a system when working in the chopping mode. Thus the commutating circuit may embody one or more commutating capacitors common to two main thyristors connected to opposite source terminals, and commutating thyristors associated respectively with the said main thyristors, and, for operation in a chopping mode, means for firing a main thyristor, means for then firing the associated commutating thyristor to commutate the main thyristor, while reversing the capacitor charge, and, for resetting the capacitor charge, means for firing the commutating thyristor of another phase to effect resonant reversal of the capacitor through the winding of the other phase.
The invention may conveniently be applied to variable reluctance motors having a main winding and a closely coupled auxiliary winding for each phase, or to such motors having a single winding for each phase in which case one end of every winding is connected together and connected to a mid-tapping on the d.v. source.
When the motor has main and auxiliary windings the phase current referred to hereafter is defined as the sum of the main winding current and m times the auxiliary winding current where m is the ratio of the auxiliary to main winding turns. The present invention has the advantage that it avoids the need for a resetting circuit formed by an additional thyristor and inductor in series, and so eliminates the power losses associated with this circuit.
In one form of the invention the commutating circuit common to two phases having main thyristors connected to opposite source terminals has a junction point connected to the junction of the main thyristor and main winding of a first phase through a commutating thyristor arranged when fired to divert current flowing through the winding to flow into the commutating circuit to turn off the main thyristor while making the junction points of the commutating circuit more positive, in preparation for commutating the main thyristor of the second phase, while the junction of the main winding and main thyristor of the second phase is connected to a junction point of the commutating circuit through a commutating thyristor arranged when fired to divert current flowing through the winding to flow out of the commutating circuit to turn off the main thyristor while making the junction points of the commutating circuit more negative, in preparation for commutating the main th
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Davis Rex M.
Ray William F.
Chloride Group Public Limited Company
Smith Jr. David
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