High Frequency Power Supply System with Closely Regulated and Monitored Output for Heating a Workpiece and Providing Process Feedback

A high frequency power supply system for heating a workpiece load in an induction heating application having monitored output to provide process feedback, the high frequency power supply system comprising:

• a full bridge inverter or a half-bridge inverter comprising a plurality of bridge switching devices and a pair of inverter output leads forming a single-phase inverter output;
• an inverter output impedance adjusting and frequency control network having a control network input connected to the pair of inverter output leads and a control network output connected to the workpiece load;
• a system microprocessor controller having one or more inverter control outputs to the plurality of bridge switching devices and one or more variable impedance control outputs to one or more variable impedance elements in the inverter output impedance adjusting and frequency control network for an adjustable power transfer from the pair of inverter output leads to the workpiece load and a variable output frequency from the pair of inverter output leads to the workpiece load independent of a workpiece impedance of the workpiece load;
• wherein the one or more variable impedance elements comprise:
• one or more variable reactors electrically connected to the inverter output leads and the workpiece load, each of the one or more variable reactors producing a variable energy field when electrically energized;
• wherein each of the one or more variable reactors comprise a motion stage selectively moveable relative to a stationary variable reactor element via one or more motors, each motor of the one or more motors comprising position feedback elements calibrated to report a relative distance between the motion stage and the stationary variable reactor element associated with each motor;
• whereupon movement of the motion stage relative to the stationary variable reactor element adjusts a reactance of the associated variable reactor;
• a software processor operably connected to the position feedback elements of each of the one or more motors controlling the motion stage of the one or more variable reactors and the system microprocessor controller, wherein the software processor identifies a current workpiece load inductance value by performing the steps:
• (a) defining a load inductance relationship corresponding to a circuit topology of the inverter output impedance adjusting and frequency control network, the load inductance relationship corresponding to one or more known reactances and an operating frequency;
• (b) receiving the relative distance between the motion stage and the stationary variable reactor element of each of the one or more variable reactors from the position feedback elements;
• (c) receiving a current operating frequency from the system microprocessor controller;
• (d) determining an effective reactance of each of the one or more variable reactors via the relative distance;
• (e) applying the load inductance relationship to determine a current load inductance using the effective reactance of each of the one or more variable reactors and the current operating frequency.

A method for continuously monitoring a current load inductance and providing process feedback in a high frequency power supply system for heating a workpiece load in an induction heating application over an operation time, the high frequency power supply system having an inverter output impedance adjusting and frequency control network having one or more variable reactors, the method comprising the steps of:

• (a) defining a load inductance relationship corresponding to a circuit topology of the inverter output impedance adjusting and frequency control network, the load inductance relationship corresponding to one or more known reactances and an operating frequency;
• (b) identifying a relative distance between a motion stage of each of the one or more variable reactors and a stationary variable reactor element of each of the one or more variable reactors, each motion stage selectively moveable relative to each stationary variable reactor element via a motor having a position feedback element, wherein the relative distance is reported by the position feedback element of the associated motor;
• (c) receiving a current operating frequency from a system microprocessor controller of the inverter output impedance adjusting and frequency control network, the system microprocessor maintaining the current operating frequency at an instantaneous resonant frequency of a workpiece load circuit via a phase-locked-loop;
• (d) determining an effective reactance of each of the one or more variable reactors via previously collected empirical data relating the relative distance to a previously measured reactance;
• (e) applying the load inductance relationship to determine a current load inductance using the effective reactance of each of the one or more variable reactors and the current operating frequency.