Cycloconverter with rectifier bank control for smooth switching between rectifier banks

Claim 2

A frequency conversion system for use with a source of alternating current power of varying, indeterminate frequency to provide a fixed frequency output therefrom comprising, frequency conversion means for each of a desired number of output phases, each conversion means including a number of gated power switching devices responsive to the output of the power source so as to be rendered conductive at selected points of the phases of the alternations of the output of said power source, said devices being rendered conductive during power source, alternations of a polarity such that the devices are forward biased thereby and upon application of switching signals thereto, said number of devices in each conversion means being separated into groups of oppositely poled switching devices which are selectively made conductive to supply alternating output current from the conversion means, a reference frequency signal source, gating means for each of said frequency conversion means coupled to the power source and to said reference source for combining the power source output with the reference signal and producing a switching signal for each power switching devIce to control the points in the phase of the output source voltage alternation at which the device conducts in response both to the power source output voltage and the reference signal, biasing means to apply a biasing signal to the gating means so that the output voltages from the oppositely poled groups of switching devices differ from each other by a fixed amount to prevent circulating currents between the groups of switching devices, means responsive to transfer of current conduction from one group of poled switching devices to the opposite poled group of switching devices for changing the output voltages from both groups of switching devices in a direction so that the output voltage from the newly conducting group is made equal to the output voltage from the formerly conducting group while maintaining the difference between the output voltages by said fixed amount to eliminate thereby wave form distortion due to switching.

Claim 3

The system according to claim 1 including means for sensing the point at which current conduction is transferred from one group of switching devices to the other and for producing a control signal in response thereto, means to impress said control signal on said biasing means to shift the output voltages from the two groups of switching devices in a direction and by an amount such that the output voltage of the newly conducting group coincides with the output of the formerly conducting group at the point of current transfer between groups while maintaining the difference in the voltage output between the groups.

Claim 4

The system according to claim 2 in which the switching devices are silicon controlled rectifiers.

Claim 5

The system according to claim 2 wherein the zero crossing of the converter output is sensed indirectly.

Claim 6

The system according to claim 2 wherein each of said frequency conversion means is coupled to a load through an output filter whereby the converter output current must supply a reactive current component to the filter and the load current, and means to sense the zero crossing of the converter current by sensing filtered components of the converter current to eliminate thereby any errors in sensing the zero crossing due to wave form distortions in the converter current.

Claim 7

A frequency conversion system for use with a source of alternating power of varying, indeterminate frequency to produce a fixed frequency output from the varying frequency power, comprising, frequency conversion means including a number of gated power switching devices responsive to the output of the power source so as to be rendered conductive at selected points of the phases of the alternations of the power source output, said devices being rendered conductive during power source output alternations which forward bias the devices and upon the simultaneous application of switching signals thereto, said number of devices being separated into groups of oppositely poled switching devices which are selectively made conductive to supply alternating output current from the conversion means, a reference frequency signal source, gating means for the switching devices coupled to the power source and to the reference source for combining the power source output with the reference signal to produce a switching signal for each power switching device to control the point of conduction in the power source voltage alternation in response both to the power source output voltage and the reference signal, biasing means to apply a biasing signal to the gating means so that the output voltages from the groups of switching devices differ from each other by a fixed amount to prevent circulating currents between groups of switching devices, means for producing a control signal in response to the passage of converter output current through zero to determine transfer of current conduction between groups of switching devices, means to apply said control signal to said gating means to vary the bias applied to said gating means to chAnge the output voltages from both groups of switching devices such that the output voltage from the group of devices newly conducting current is made equal to the output voltage from the group formerly conducting current while maintaining the difference between the output voltages from the groups the said fixed amount to eliminate wave form distortion in spite of the difference in output voltage between the group of switching devices.

Claim 8

A frequency conversion system for use with a source of alternating power of varying, indeterminate frequency to produce a fixed frequency output from the varying frequency power, comprising, frequency conversion means including a number of gated power switching devices responsive to the output of the power source so as to be rendered conductive at selected points of the phases of the alternations of the power source output, said devices being rendered conductive during power source output alternations which forward bias the devices and upon the simultaneous application of switching signals thereto, said number of devices being separated into groups of oppositely poled switching devices which are selectively made conductive to supply alternating output current from the conversion means, a reference frequency signal source, gating means for the switching devices coupled to the power source and to the reference source for combining the power source output with the reference signal to produce a switching signal for each power switching device to control the point of conduction in the power source voltage alternation in response both to the power source output voltage and the reference signal, biasing means to apply a biasing signal to the gating means so that the output voltages from the groups of switching devices differ from each other by a fixed amount to prevent circulating currents between groups of switching devices, means for producing a control signal in response to the passage of converter output current through zero to determine transfer of current conduction between groups of switching devices, means to apply said control signal to said gating means to vary the bias applied to said gating means to chAnge the output voltages from both groups of switching devices such that the output voltage from the group of devices newly conducting current is made equal to the output voltage from the group formerly conducting current while maintaining the difference between the output voltages from the groups the said fixed amount to eliminate wave form distortion in spite of the difference in output voltage between the group of switching devices.

Claim 9

The system according to claim 6 which the switching devices are silicon controlled rectifiers.

Claim 10

The system according to claim 6 wherein the conversion means is coupled to a load through an L-C filter whereby the converter output current must supply the load current and filter capacitor current, and means to sense the zero crossing of the converter current by sensing the filtered components of the converter current to eliminate any errors in sensing zero crossing due to wave form distortion in the converter current.

Claim 11

The system according to claim 8 wherein a signal representing the converter current is reconstructed including, means to produce a signal proportional to the magnitude of the load current, means for producing a signal proportional to the filter capacitor current, means vectorially combining the two signals to produce a reconstructed converter current signal, and means for sensing the zero crossing of the reconstructed signal.

Claim 12

The system according to claim 8 including, means to produce a voltage proportional to the load current flowing at the output of said filter, integrating means coupled to the output of said filter to produce a voltage proportional to the capacitor current flowing in said filter, means to add said signals vectorially to produce a signal representing said converter current, and means to sense the zero crossing of said reconstructed signal to produce said control signal.

Claim 13

The system according to claim 9 including, means coupled to the output of said converter to produce a voltage proportional to the load current magnitude but 180* out of phase therewith, means coupled to the output of the filter to produce a voltage proportional to the magnitude of the capacitor current but 180* out of phase therewith, means to combine said voltages to produce a resultant voltage which is equal to but 180* out of phase with the converter current; means to sense the zero crossing of the converter current to produce a control signal for said gating means.

Claim 14

The system according to claim 11 wherein the means for producing a signal proportional to the capacitor current comprises an integrating circuit.

Claim 15

The system according to claim 12 wherein said means for producing a control signal, includes means for producing a square wave which is applied to the gating means to control and maintain the bias to shift the output voltages during the intervals between zero crossings of the current.

Claim 16

The system according to claim 13 in which said means to produce a square wave includes saturating amplifier means, and means to apply said resulting voltage to said saturating amplifying means, whereby the output of said saturating amplifying means is a square wave having positive and negative alternations for controlling the biasing of said gating means.