Abstract: A fault tolerant power supply circuit for a series resonant load having an inductive impedance. The power supply circuit includes alternately conducting first and second sets of switches for supplying current to the load in alternating directions. One terminal of the load is connected to a point intermediate the switches. A protective coil is connected in series with the load and the point intermediate said switches. In one embodiment of the invention, a di/dt reactor is connected in series between the switches. In that embodiment, one end of the protective coil is connected to the load and the other end of the protective coil is connected to the di/dt reactor at a point intermediate the switches.

Abstract: A control system for controlling overshoot and undershoot power values when switching power from a single inverter power source to a plurality of inductive loads, or a single load having a plurality of zones, having different resonant frequencies. The control system causes a preselected amount of power to be drawn from the inverter power source and delivered to the loads, or zones in a time-shared manner. The control system varies the phase shift between load voltage and load current and selectably adjusts the amount of variation in response to overshoot and/or undershoot of power drawn from the inverter and delivered to a load or zone which can occur when switching between loads or zones.

Abstract: A system for simultaneously melting metal and holding molten metal for treatment and the like comprises a plurality of separate induction furnaces, each having an induction coil. The induction coil of each furnace is arranged to inductively heat metal in its associated furnace. A plural-output power supply is operatively connected to the induction coils for supplying ac power to the coils. The power supply comprises at least one rectifier section having an output and a plurality of high-frequency inverter sections equal to the number of separate induction furnaces Each inverter section has an input operatively associated with the rectifier section output for receiving power from said at least one rectifier section and an output operatively connected to a respective one of the induction coils for supplying ac power to the induction coil. Switches are provided for selectably interrupting power from selected ones of said plurality of inverter sections to their associated induction coils.

Abstract: A control system for power delivered to an inductive load includes automatic control with a manual override for emergency situations. The system monitors the power delivered to the load and varies the power delivered to the inductive load by controlling the phase difference between the voltage and current delivered to the load. Feedback to the control system automatically controls the phase difference between voltage and current in response to the measured power delivered to the load. Provision is made for introducing an external signal into the feedback circuit, whereby the external signal supersedes the automatic control of the power delivered to the load.