Control circuit and method for controlling a resonant converter and power inverter comprising the resonant converter and the control circuit

A method of controlling a resonant converter, comprising:

• providing a full-bridge configuration having two parallel switching branches, each of the two switching branches comprising two series-connected switch members, such that a switch member of one switching branch and a respective member of the other switching branch form a diagonal pair;
• providing a voltage control signal for controlling an output voltage of the resonant converter;
• providing a zero crossing-predicting signal indicating zero crossing-predicting events of a resonant current of the resonant converter, each zero crossing-predicting event leading a respective zero crossing of the resonant current by a predetermined advancing time interval;
• during each half period of a plurality of periods of the resonant current, starting from an initial state in which a diagonal pair is conductive, turning off a first switch member of the diagonal pair based on the voltage control signal;
• turning on, after the turn-off of the first switch member, a switch member in series connection with the first switch member prior to a zero crossing of the resonant current in the half period;
• turning off, after the turn-off of the first switch member, a second switch member of the diagonal pair at a zero crossing-redicting event leading to the zero crossing based on the zero crossing-predicting signal;
• and
• turning on, after the turn-off of the second switch member, a switch member in series connection with the second switch member prior to the zero crossing event.

A power inverter, comprising:

• a resonant converter comprising:
• a full-bridge configuration having two parallel switching branches, each of the two switching branches comprising two series-connected switch members, such that a switch member of one switching branch and a respective member of the other switching branch form a diagonal pair;
• and
• a resonant circuit connected between junctions of the two series-connected switch members of each of the two switching branches;
• and
• a control circuit configured for controlling the resonant converter, comprising:
• an output voltage controller configured for providing a voltage control signal for controlling an output voltage of the resonant converter;
• a zero crossing predictor configured for providing a zero crossing-predicting signal indicating zero crossing-predicting events of a resonant current of the resonant converter, each zero crossing-predicting event leading a respective zero crossing of the resonant current by a predetermined advancing time interval;
• a switch encoder configured for controlling switching events of the switch members, wherein the switch encoder is configured, during each half period of a plurality of periods of the resonant current, starting from an initial state in which a diagonal pair is conductive, to:
• turn off a first switch member of the diagonal pair based on the voltage control signal;
• turn on, after the turn-off of the first switch member, a switch member in series connection with the first switch member prior to a zero crossing of the resonant current in the half period;
• turn off, after the turn-off of the first switch member, a second switch member of the diagonal pair at a zero crossing-predicting event leading to the zero crossing, based on the zero crossing-predicting signal;
• and
• turn on, after the turn-off of the second switch member, a switch member in series connection with the second switch member prior to the zero crossing event.

An x-ray generator, comprising:

• a power inverter comprising:
• a resonant converter comprising:
• a full-bridge configuration having two parallel switching branches, each of the two switching branches comprising two series-connected switch members, such that a switch member of one switching branch and a respective member of the other switching branch form a diagonal pair;
• and
• a resonant circuit connected between junctions of the two series-connected switch members of each of the two switching branches;
• and
• a control circuit configured for controlling the resonant converter, comprising:
• an output voltage controller configured for providing a voltage control signal for controlling an output voltage of the resonant converter;
• a zero crossing predictor configured for providing a zero crossing-predicting signal indicating zero crossing-predicting events of a resonant current of the resonant converter, each zero crossing-predicting event leading a respective zero crossing of the resonant current by a predetermined advancing time interval;
• a switch encoder configured for controlling switching events of the switch members, wherein the switch encoder is configured, during each half period of a plurality of periods of the resonant current, starting from an initial state in which a diagonal pair is conductive, to:
• turn off a first switch member of the diagonal pair based on the voltage control signal;
• turn on, after the turn-off of the first switch member, a switch member in series connection with the first switch member prior to a zero crossing of the resonant current in the half period;
• turn off, after the turn-off of the first switch member, a second switch member of the diagonal pair at a zero crossing-predicting event leading to the zero crossing, based on the zero crossing-predicting signal;
• and
• turn on, after the turn-off of the second switch member, a switch member in series connection with the second switch member prior to the zero crossing event;
• a DC voltage source connected to an input of the power inverter;
• and
• an x-ray tube connected to an output of the power inverter.