Control for frequency converters

Claim 2

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse.

Claim 3

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals dErived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse.

Claim 4

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals dErived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse.

Claim 5

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse.

Claim 6

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse.

Claim 7

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means include sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero-over instant.

Claim 8

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means include sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero-over instant.

Claim 9

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means include sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant.

Claim 10

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means include sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant.

Claim 11

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphaSe lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means include sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage cross-over instant.

Claim 12

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphaSe lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means include sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage cross-over instant.

Claim 13

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said control means including sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant and said control means initiating said starting pulse initiate said pulse within a 0* to 60* range in the first half cycle of the input voltage wave.

Claim 14

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said control means including sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant and said control means initiating said starting pulse initiate said pulse within a 0* to 60* range in the first half cycle of the input voltage wave.

Claim 15

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said control means including sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant and said control means initiating said starting pulse initiate said pulse within a 0* to 60* range in the first half cycle of the input voltage wave.

Claim 16

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said control means including sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant and said control means initiating said starting pulse initiate said pulse within a 0* to 60* range in the first half cycle of the input voltage wave.

Claim 17

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said control means including sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant and said control means initiating said starting pulse initiate said pulse within a 0* to 60* range in the first half cycle of the input voltage wave.

Claim 18

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said control means including sensing means for sensing the instantaneous value of the input voltage, means for initiating a starting pulse directing said pulse to an appropriate solid state switching device at a predetermined phase angle with respect to line to neutral voltage zero cross-over instant and said control means initiating said starting pulse initiate said pulse within a 0* to 60* range in the first half cycle of the input voltage wave.

Claim 19

Control means for an AC to AC frequency converter as claimed in claim 1, wherein said control means include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts output current, and means whereby the time relationship of said envelopes to said line to neutral supply voltage is shifted to provide control of output power.

Claim 20

Control means for an AC to AC frequency converter as claimed in claim 2, wherein said control means include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts output current, and means whereby the time relationship of said envelopes to said line to neutral supply voltage is shifted to provide control of output power.

Claim 21

Control means for an AC to AC frequency converter as claimed in claim 3, wherein said control means include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts output current, and means whereby the time relationship of said envelopes to said line to neutral supply voltage is shifted to provide control of output power.

Claim 22

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of the subsequent firing pulse, wherein said control means also include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts, and means whereby the time relationship of said envelopes and said line to neutral supply voltage is modified by shifting said envelopes ahead in time to reduce output power.

Claim 23

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of the subsequent firing pulse, wherein said control means also include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts, and means whereby the time relationship of said envelopes and said line to neutral supply voltage is modified by shifting said envelopes ahead in time to reduce output power.

Claim 24

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means also include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts, and means whereby the time relationship of said envelopes and said line to neutral supply voltage is modified by shifting said envelopes ahead in time to reduce output power.

Claim 25

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means also include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts, and means whereby the time relationship of said envelopes and said line to neutral supply voltage is modified by shifting said envelopes ahead in time to reduce output power.

Claim 26

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means also include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts, and means whereby the time relationship of said envelopes and said line to neutral supply voltage is modified by shifting said envelopes ahead in time to reduce output power.

Claim 27

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, wherein said control means also include sensing means for sensing the instantaneous value of the line to neutral supply voltage and producing substantially equal envelopes controlling the time period during which each solid state switching device conducts, and means whereby the time relationship of said envelopes and said line to neutral supply voltage is modified by shifting said envelopes ahead in time to reduce output power.

Claim 28

Control means for an AC to AC frequency converter as claimed in claim 13, wherein the power is regulated by sensing of the output voltage and output current and adjusting the phase of the envelope logic.

Claim 29

Control means for an AC to AC frequency converter as claimed in claim 14, wherein the power is regulated by sensing of the output voltage and output current and adjusting the phase of the envelope logic.

Claim 30

Control means for an AC to AC frequency converter as claimed in claim 15, wherein the power is regulated by sensing of the output voltage and output current and adjusting the phase of the envelope logic.

Claim 31

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said tiMe relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control includes a signal proportional to the output voltage providing an input to a voltage limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 32

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the said solid state switching devices during steady state conditions and to automatically modify said tiMe relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control includes a signal proportional to the output voltage providing an input to a voltage limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 33

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control includes a signal proportional to the output voltage providing an input to a voltage limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 34

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control includes a signal proportional to the output voltage providing an input to a voltage limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 35

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control includes a signal proportional to the output voltage providing an input to a voltage limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 36

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control includes a signal proportional to the output voltage providing an input to a voltage limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 37

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from sAid sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control means includes a signal proportional to the output current and provides an input to a current limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 38

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from sAid sensing means to provide a substantially fixed time relationship between initiating of firing pulses for the solid state switching devices during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control means includes a signal proportional to the output current and provides an input to a current limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 39

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control means includes a signal proportional to the output current and provides an input to a current limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 40

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide a fixed time relationship between initiation of each firing pulse for said solid state switching devices and the corresponding output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control means includes a signal proportional to the output current and provides an input to a current limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 41

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control means includes a signal proportional to the output current and provides an input to a current limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.

Claim 42

Control means for an AC to AC frequency converter utilizing solid state switching devices connected to a polyphase lower frequency source to provide single phase power at a higher frequency to a load comprising an induction heating coil and parallel capacitance, said control means including sensing means for sensing the instantaneous values of the output voltage and output current, and means for combining signals derived from said sensing means to provide initiation of firing pulses for said solid state switching devices substantially at each output voltage zero cross-over instant during steady state conditions and to automatically modify said time relationship under transient conditions which results in substantial lengthening of an output current pulse, so as to obtain a safe interval between the cessation of said lengthened output current pulse and the initiation of the subsequent firing pulse, said sensing means are provided to sense instantaneous line to neutral supply voltage and power control is obtained by shifting the time relationship between the envelope and the line to neutral supply voltage and the envelope is shifted forward with respect to the input voltage wave, wherein said control means includes a signal proportional to the output current and provides an input to a current limit circuit which shifts the envelope forward with respect to the line to neutral supply voltage.