Cycloconverter arrangements which prevent circulating currents

Claim 2

Cycloconverter apparatus for converting a high-frequency electrical multiphase supply having a first predetermined number of phases to a low-frequency supply for a load having a second predetermined number of star-connected phases, including: at least as many controlled-rectifier means as the larger of the said predetermined numbers, each controlled rectifier means being capable of passing current selectively in either direction and control means for providing control signals for the controlledrectifier means to synthesize a low-frequency output having the same number of phases as the load, the controlled-rectifier means being connected to provide a number of bidirectional current paths, one said path for each combination of load phase and supply phase and particular to that combination, and the only paths for substantial currents from the supply, when the load and supply are connected to the cycloconverter apparatus, being by way of the load, even if all the rectifier means were to receive control signals enabling them to conduct.

Claim 3

Cycloconverter apparatus for converting a high-frequency electrical multiphase supply having a first predetermined number of phases to a low-frequency supply, comprising: a plurality of input terminals adapted to be connected to said supply, an AC load having a second predetermined number of star-connected phases including a number of groups of windings equal to said second predetermined number, a number of controlled-rectifier means, one for each combination of one input terminal and one load phase and particular to that combination, each controlled-rectifier means being capable of passing current selectively in either direction, and control means for providing control signals for the controlled-rectifier means to synthesize a low-frequency output having the same number of phases as the load, the only paths for substantial currents from the supply, when the supply is connected to the cycloconverter apparatus, being by way of the load, even if all the rectifier means were to receive control signals enabling them to conduct.

Claim 4

Cycloconverter apparatus for converting a high-frequency electrical multiphase supply having a first predetermined number of phases to a low-frequency supply, comprising: a plurality of input terminals adapted to be connected to said supply, an AC load having a second predetermined number of star-connected phases including a number of groups of windings equal to said second predetermined number, a number of controlled-rectifier means, one for each combination of one input terminal and one load phase and particular to that combination, each controlled-rectifier means being capable of passing current selectively in either direction, and control means for providing control signals for the controlled-rectifier means to synthesize a low-frequency output having the same number of phases as the load, the only paths for substantial currents from the supply, when the supply is connected to the cycloconverter apparatus, being by way of the load, even if all the rectifier means were to receive control signals enabling them to conduct.

Claim 5

Apparatus aCcording to claim 2 including a plurality of capacitor means one for each supply phase and connected in series with an input terminal of that phase, the total reactance of all the capacitor means being substantially equal but opposite to the reactance of the leakage inductance of the apparatus.

Claim 6

Electrical apparatus adapted to be supplied from a high-frequency supply, including a plurality of input terminals adapted to be connected to a multiphase AC supply having a first predetermined number of phases, a load requiring a low-frequency supply, having a second predetermined number of star-connected phases, a number of controlled-rectifier means at least equal to the larger of the said predetermined numbers, each controlled-rectifier means being connected between an input terminal particular thereto and the common connection between the load phases, and each controlled-rectifier means being capable of passing current selectively in either direction, and control means for providing control signals for the controlled-rectifier means to synthesize a low-frequency output having the same number of phases as the load, the only paths for substantial currents from the supply when connected to the apparatus, being by way of the load, even if all the rectifier means were to receive control signals enabling them to conduct.

Claim 7

Electrical apparatus adapted to be supplied from a high-frequency supply, including a plurality of input terminals adapted to be connected to a multiphase AC supply having a first predetermined number of phases, a load requiring a low-frequency supply, having a second predetermined number of star-connected phases, a number of controlled-rectifier means at least equal to the larger of the said predetermined numbers, each controlled-rectifier means being connected between an input terminal particular thereto and the common connection between the load phases, and each controlled-rectifier means being capable of passing current selectively in either direction, and control means for providing control signals for the controlled-rectifier means to synthesize a low-frequency output having the same number of phases as the load, the only paths for substantial currents from the supply when connected to the apparatus, being by way of the load, even if all the rectifier means were to receive control signals enabling them to conduct.

Claim 8

Apparatus according to claim 4 wherein the load has a number of groups of pairs of windings equal to the first predetermined number, the numbers of pairs of windings in each group equals the second predetermined number, and the number of controlled rectifier means equals the number of windings, each pair of windings being connected in star with the other pairs of windings in the group, and each rectifier means being connected in series with a winding particular thereto, and associated therewith between an input terminal and the common connection between phases.

Claim 9

Apparatus according to claim 5 wherein, in each star connection two common input terminals are provided, and the controlled-rectifier means coupled to the windings of each pair, are coupled to the common input terminals, respectively, between the windings and the input terminals.

Claim 10

Apparatus according to claim 6 including a two-phase alternator forming the AC supply, wherein the load is a three-phase induction motor with two pairs of windings for each phase, each pair connected in star with one pair from each other phase.

Claim 11

Apparatus according to claim 5 wherein each controlled-rectifier means includes a pair of oppositely poled thyristors connected in parallel.

Claim 12

Apparatus according to claim 5 wherein the load is three-phase star connected and each rectifier means is connected in series with a load phase particular thereto.

Claim 13

Apparatus according to claim 6 wherein the control circuit includes means for providing first and second control signals to cause the controlled-rectifier means connected to the input terminals for each supply phase to pass currents for equal alternate intervals in the one and the other directions, respectively, in each load phase, the changeover in current direction in the phases being separated by the said interval divided by the second predetermined number.

Claim 14

Apparatus according to claim 10, wherein the means providing the first and second signals applies the first signal alternately to the controlled-rectifier means associated with the windings in each pair during each alternate interval, and applies the second signal alternately to the controlled-rectifier means associated with the windings in each pair for the other intervals.

Claim 15

Apparatus according to claim 11 wherein the control circuit includes a clock pulse generator coupled to a shift register having a number of stages equal to twice the second predetermined number, and a logic circuit so coupling the shift register to the controlled-rectifier means the first and second control signals are applied to a different combination of the controlled-rectifier means while each different staGe is in a predetermined conduction state.

Claim 16

Apparatus according to claim 11 wherein the control circuit includes a logic circuit connected to receive input signals from sensing means for sensing the direction of current flow in the thyristors, from synchronizing means for sensing the polarity and start of each half-cycle of the supply voltage, and from polarity-indicating means for indicating the polarities of the load phase voltages.

Claim 17

Apparatus according to claim 13 wherein, in operation, logic circuit provides the second and first control signals for one controlled-rectifier means in each phase if the sensing means indicates that the other rectifying means of that same phase are not conducting in the said one or the said other direction respectively and if the polarity of the supply voltage and the load phase voltage are the same, and for the other controlled-rectifier means in each phase if the sensing means indicates that the other rectifying means of that phase are not conducting in the said one or the said other direction, respectively, and if the polarity of the supply voltage and the load phase voltage are opposite.

Claim 18

Apparatus according to claim 12 wherein the logic circuit includes first and second AND gates for each phase adapted to be opened if the rectifying means associated with the pair of windings of that phase are not conducting in the one and the other directions, respectively.

Claim 19

Apparatus according to claim 15 wherein each controlled-rectifier means includes a pair of oppositely poled controlled rectifiers connected in parallel, each controlled rectifier is associated with the phase of the winding whose current it controls, and the logic circuit includes a number of OR gates each with inputs coupled to a pair of AND gates, there being one OR gate and one pair of AND gates for each controlled rectifier, and the AND gates in each pair being coupled to receive output signals from that first or second AND gate of the phase associated with that controlled rectifier which indicates that current in that phase is not in forward direction of that controlled rectifier, one AND gate in each pair receiving enabling signals from the synchronizing means and the polarity-indicating means when the load phase voltage and the supply voltage have first and second polarities, respectively, and the other gate of that pair receiving enabling signals when the said voltages have the opposite polarities, the first and second polarities being the same for the controlled rectifiers in the controlled-rectifier means associated with one winding in each pair, but opposite for the controlled rectifiers in the controlled-rectifier means associated with the other winding in each pair.