Controllable rectifier circuits with energy recovery networks

Claim 2

A controllable rectifier circuit including input terminals, output terminals, controllable rectifier means for intermittently supplying current from input terminals in one direction to output terminals through a current limiting inductance, means including a commutating capacitance and switching means connected in series therewith for intermittently initiating a turn-off process in which current flow in the inductance is diverted from the controllable rectifier means to enable the controllable rectifier means to acquire a forward blocking condition, a unidirectionally conductive reactive current path connected between the output and input terminals for returning reactive energy in a load to the input terminals when a load is connected across the output terminals, and a saturable transformer means having a first winding connected in a path across the inductance and a second winding coupled through a unidirectionally conductive path to the input terminals, said saturable transformer undergoing a similar voltage time integral to that which the inductance undergoes during the said turn-off process and thereby enabling a return of surplus energy acquired by the inductance to the input terminals during the resetting thereof towards saturation.

Claim 3

An inverter circuit embodying a controllable rectifier circuit as claimed in claim 1 including further controllable rectifier means for operating intermittently and alternately with the first mentioned controllable rectifier means to supply current from the input terminals in the other direction to the output terminals through a further current limiting inductance, further switching means for intermittently initiating a turn-off process for the further controllable rectifier means by connecting said capacitor to divert current in said further inductance from the further controllable rectifier means to enable the said further controllable rectifier means to acquire a forward blocking condition, a further unidirectionally conductive reactive current path connected between the output and input terminals for returning reactive energy in the load to the input terminals and a further saturable transformer means having one winding connected in a path across the further inductance and another winding connected in a

Claim 4

An inverter circuit as claimed in claim 2 wherein the said unidirectionally conductive reactive current paths include windings of the respective saturable transformer means.

Claim 5

An inverter cirCuit as claimed in claim 2 wherein the said unidirectionally conductive reactive current paths include said another windings of the respective saturable transformer means.

Claim 6

An inverter circuit as claimed in claim 2, further comprising biassing means for biassing the saturable transformers towards remanent saturation to reduce the likelihood of incomplete remanent saturation following recovery of energy in the respective inductance to a precommutation level.

Claim 7

An inverter circuit as claimed in claim 5 wherein said biassing means comprises a current conductive path between a biassing source and the respective said another windings of the transformers.

Claim 8

An inverter circuit as claimed in claim 2 wherein the respective another windings of the saturable transformers are coupled through their respective unidirectionally conductive paths across respective halves of an input circuit fed from the inverter input terminals.

Claim 9

An inverter circuit as claimed in claim 2 wherein the respective said paths across the inductances include a resistor.

Claim 10

An inverter circuit as claimed in claim 8, further comprising respective diodes connected in series with the resistors and of such polarity as to conduct during commutation when the commutation capacitor voltage exceeds the input terminal voltage.

Claim 11

An inverter circuit as claimed in claim 2 wherein the respective said paths across the inductances each include a unidirectionally conductive device and a biassed saturable transformer. ll. An inverter circuit as claimed in claim 10 further comprising respective biassing windings connected in series with the corresponding inductance for biassing said biassed saturable transformers such that these transformers function to support a commutation voltage during a turn-off interval but permit reactive load current flow in intervals following a turn-off operation.

Claim 12

A circuit as claimed in claim 1 including at least one controllable switching device connected in a path through which the inductance and the transformer primary winding are connectable in series at a predetermined overswing voltage of the capacitor so as to limit the capacitor voltage.

Claim 13

An inverter circuit embodying a controllable rectifier circuit as claimed in claim 1, wherein the said switching means in series with the commutating capacitance comprises further controllable rectifier means for operating intermittently and alternately with the first-mentioned controllable rectifier means to supply current from the input terminals to the output terminals in a direction opposite to said one direction through a further current limiting inductance, the first-mentioned controllable rectifier means, on being rendered conducting, operating to connect the capacitance to divert current flow from the further controllable rectifier means to enable the latter to acquire a forward blocking condition, said circuit further comprising a further unidirectionally conductive current path connected between the output and the input terminals for returning reactive energy in the load acquired during conduction of the further controllable rectifier means to the input terminals, the saturable transformer means having a further winding connected in a path across the further inductance, said saturable transformer undergoing a similar voltage time integral to that which the further inductance undergoes during a turn-off process of the first-mentioned controllable rectifier means and enabling, during resetting thereof towards a saturation condition, a return of surplus unidirectionally conductive path across the input terminals, said further saturable transformer undergoing a similar voltage time integral to that which the further inductance undergoes during the second-mentioned turn-off process and thereby enabling a return of surplus energy acquired by the further inductance to the input terminals.

Claim 14

An inverter circuit as claimed in claim 13, wherein the saturable transformer means comprises individual transformers, the transformer through which surplus energy is recoverable from the further inductance also having another winding connected to the input terminals through a unidirectionally conductive path.

Claim 15

An inverter circuit as claimed in claim 14 wherein, the unidirectionally conductive paths through which the said another windings are connected to the input terminals are the same.

Claim 16

An inverter circuit as claimed in claim 14 wherein, the unidirectionally conductive reactive current paths include the respective said another windings of the transformer means.

Claim 17

An inverter circuit as claimed in claim 13 wherein, said saturable transformer means comprises a composite saturable transformer through which surplus energy is returnable from each said inductance.