Abstract: Apparatus and process for heating and melting a material in a susceptor vessel are provided wherein phase synchronized ac voltage is supplied from a separate power source to each one of at least two induction coils in separate zones around the vessel. Power magnitude from each source to an induction coil is controlled by pulse width control of the source's output voltage. Output frequency from each source is either fixed or variable based upon the electrically conductive state of the material. Optional electromagnetic stirring is achieved by establishing a phase shift between the voltage outputs of the power supplies after the material in the susceptor vessel has melted.

Abstract: A dual frequency output is provided from a DC to AC inverter. An H-bridge inverter is provided with switching arranged to reconfigure the inverter from half-bridge to full bridge so that the inverter's output can be switched from high frequency to low frequency, respectively. A resonant load tuning capacitance is utilized across the input of the inverter subsequent to the DC link input (for example from an AC utility fed rectifier) to the inverter. The inductive load circuit at the output of the inverter may be one or more induction coils surrounding a crucible in which an electrically conductive material is placed, or susceptor, or one or more inductors used to heat treat an electrically conductive material. In an alternative arrangement an H-bridge inverter is utilized in both the high and low frequency modes while a tank capacitance is in the circuit, or shorted out of the circuit, respectively, in the high or low frequency modes.

Abstract: An apparatus and process are provided for gradient induction heating or melting of a workpiece with a plurality of induction coils, each of the plurality of induction coils is connected to a power supply that may have a tuning capacitor connected across the input of an inverter. The plurality of induction coils are sequentially disposed around the workpiece. The inverter has a pulse width modulated ac power output that may be in synchronous control with the pulse width modulated ac power outputs of the other power supplies via a control line between the controllers of all power supplies.

Abstract: An apparatus and process are provided for gradient induction heating or melting of a workpiece with a plurality of induction coils, each of the plurality of induction coils is connected to a power supply that may have a tuning capacitor connected across the input of an inverter. The plurality of induction coils are sequentially disposed around the workpiece. The inverter has a pulse width modulated ac power output that may be in synchronous control with the pulse width modulated ac power outputs of the other power supplies via a control line between the controllers of all power supplies.

Abstract: Apparatus and process for heating and melting a material in a susceptor vessel are provided wherein phase synchronized ac voltage is supplied from a separate power source to each one of at least two induction coils in separate zones around the vessel. Power magnitude from each source to an induction coil is controlled by pulse width control of the source's output voltage. Output frequency from each source is either fixed or variable based upon the electrically conductive state of the material. Optional electromagnetic stirring is achieved by establishing a phase shift between the voltage outputs of the power supplies after the material in the susceptor vessel has melted.

Abstract: Molten metal, or other electrically conductive material, in a vessel can be inductively heated, and simultaneously inductively stirred. A single-phase ac supply provides induction heating power to at least one set of three induction coil sections surrounding the vessel. A three-phase ac supply provides induction stirring power to at least one set of three induction coil sections surrounding the vessel. The single-phase ac supply is capacitively connected to the coil sections to form a heat resonance circuit, and the three-phase ac supply is inductively connected to the coil sections to form a stir resonance circuit. The heat circuit capacitive elements provide a sufficient impedance to the output of the three-phase ac supply to block power transfer from its output to the input of the single-phase supply. The stir circuit inductive elements provide a sufficient impedance to the output of the single-phase supply to block power transfer from its output to the input of the three-phase supply.

Abstract: A rectifier/inverter power supply for use with induction heating or melting apparatus includes a tuning capacitor connected across the output of the rectifier and input of the inverter. The tuning capacitor forms a resonant circuit with an inductive load coil at the operating frequency of the inverter. Additionally, the load coil may be formed from an active load coil connected to the output of the inverter and a passive load coil, in parallel with a resonant tuning capacitor.

Abstract: Molten metal, or other electrically conductive material, in a vessel can be inductively heated, and simultaneously inductively stirred. A single-phase ac supply provides induction heating power to at least one set of three induction coil sections surrounding the vessel. A three-phase ac supply provides induction stirring power to at least one set of three induction coil sections surrounding the vessel. The single-phase ac supply is capacitively connected to the coil sections to form a heat resonance circuit, and the three-phase ac supply is inductively connected to the coil sections to form a stir resonance circuit. The heat circuit capacitive elements provide a sufficient impedance to the output of the three-phase ac supply to block power transfer from its output to the input of the single-phase supply. The stir circuit inductive elements provide a sufficient impedance to the output of the single-phase supply to block power transfer from its output to the input of the three-phase supply.

Abstract: A fault current tolerant power supply circuit having a dc power source and switching devices for inverting dc current from the source into ac load current includes a protective circuit for protecting the switching devices from overvoltage conditions when an inductive load is short-circuited. The protective circuit uses a capacitive component to absorb charge during a short circuit to protect non-conducting switching devices from an overvoltage condition.

Abstract: Molten metal, or other electrically conductive material, in a vessel can be inductively heated, and simultaneously inductively stirred. A single-phase ac supply provides induction heating power to at least one set of three induction coil sections surrounding the vessel. A three-phase ac supply provides induction stirring power to at least one set of three induction coil sections surrounding the vessel. The single-phase ac supply is capacitively connected to the coil sections to form a heat resonance circuit, and the three-phase ac supply is inductively connected to the coil sections to forma a stir resonance circuit. The heat circuit capacitive elements provide a sufficient impedance to the output of the three-phase ac supply to block power transfer from its output to the input of the single-phase supply. The stir circuit inductive elements provide a sufficient impedance to the output of the single-phase supply to block power transfer from its output to the input of the three-phase supply.

Abstract: An induction furnace system has an active induction coil surrounding a crucible. A passive induction coil also surrounds the crucible. The passive induction coil is connected in parallel with a capacitor to form an L-C tank circuit. A source of ac current is provided to the active induction coil to produce a magnetic field that inductively heats and melts an electrically conductive material in the crucible. The magnetic field also magnetically couples with the passive induction coil to induce a current in the passive induction coil. This induced current generates a magnetic field that inductively heats and melts the material. The resistance of the L-C tank circuit is reflected back into the circuit of the active induction coil to improve the overall efficiency of the induction furnace system. The crucible may be open-ended to allow the passage of the electrically conductive material through the crucible during the heating process.

Abstract: A rectifier/inverter power supply for use with induction heating or melting apparatus includes a tuning capacitor connected across the output of the rectifier and input of the inverter. The tuning capacitor forms a resonant circuit with an inductive load coil at the operating frequency of the inverter. Additionally, the load coil may comprise an active load coil connected to the output of the inverter and a passive load coil, in parallel with a resonant tuning capacitor, for an improved efficiency circuit.

Abstract: A fault current tolerant power supply circuit having a dc power source and switching devices for inverting dc current from the source into ac load current includes a protective circuit for protecting the switching devices from overvoltage conditions when an inductive load is short-circuited. The protective circuit uses a capacitive component to absorb charge during a short circuit to protect non-conducting switching devices from an overvoltage condition.

Abstract: Molten metal, or other electrically conductive material, in a vessel can be inductively heated, and simultaneously inductively stirred. A single-phase ac supply provides induction heating power to at least one set of three induction coil sections surrounding the vessel. A three-phase ac supply provides induction stirring power to at least one set of three induction coil sections surrounding the vessel. The single-phase ac supply is capacitively connected to the coil sections to form a heat resonance circuit, and the three-phase ac supply is inductively connected to the coil sections to forma a stir resonance circuit. The heat circuit capacitive elements provide a sufficient impedance to the output of the three-phase ac supply to block power transfer from its output to the input of the single-phase supply. The stir circuit inductive elements provide a sufficient impedance to the output of the single-phase supply to block power transfer from its output to the input of the three-phase supply.

Abstract: An induction furnace system has an active induction coil surrounding a crucible. A passive induction coil also surrounds the crucible. The passive induction coil is connected in parallel with a capacitor to form an L-C tank circuit. A source of ac current is provided to the active induction coil to produce a magnetic field that inductively heats and melts an electrically conductive material in the crucible. The magnetic field also magnetically couples with the passive induction coil to induce a current in the passive induction coil. This induced current generates a magnetic field that inductively heats and melts the material. The resistance of the L-C tank circuit is reflected back into the circuit of the active induction coil to improve the overall efficiency of the induction furnace system. The crucible may be open-ended to allow the passage of the electrically conductive material through the crucible during the heating process.