Power inverter

Claim 1

In a power inverter for converting direct current from a constant current supply into alternating current, for use in applications requiring frequent energizations of serial loads having varying Q characteristics, said power inverter including a starter inverter providing initial energization of each said load, said starting inverter having a direct current input from said supply and an alternating current output which may be selectively applied across each load, means responsive to an energization level of said load to remove said starting inverter from said load when a preselected energization level is reached, and means to energize said power inverter in timed relationship with the removal of said starting inverter with said load, said power inverter having an output voltage level below which there is starting instability, the improvement comprising: means in said power inverter for increasing the apparent Q of the load to be energized, whereby the voltage level of output instability of the power inverter is substantially reduced to a lower output voltage; and, means providing an output voltage at said starting inverter at least as high as said lower output voltage, whereby commutation failure of said power inverter is precluded.

Claim 7

A method of operating a power inverter to reduce commutation failure in operation, the inverter of the type used in induction heat treating of sequential loads, having a constant current power supply and a starting inverter removably connectable across each load to initiate energization thereof until a preselected energization value is achieved whereupon said power inverter is energized and said starting inverter is removed from said load, said power inverter having an output voltage level below which there is starting instability, said method comprising the steps of: (a) reducing the output voltage of starting instability to a new output voltage by increasing the apparent Q of the load; and, (b) providing a voltage energization level of said starting inverter at least as great as the new output voltage of starting instability in said power inverter.

Claim 8

A method of operating a power inverter to reduce commutation failure in operation, the inverter of the type used in induction heat treating of sequential loads, having a constant current power supply and a starting inverter removably connectable across each load to initiate energization thereof until a preselected energization value is achieved whereupon said power inverter is energized and said starting inverter is removed from said load, said power inverter having an output voltage level below which there is starting instability, said method comprising the steps of: (a) reducing the output voltage of starting instability to a new output voltage by increasing the apparent Q of the load; and, (b) providing a voltage energization level of said starting inverter at least as great as the new output voltage of starting instability in said power inverter.

Claim 12

A method of operating a current source power inverter to prevent starting instability when used to provide power for heating cycles of an induction heating load, said inverter having a constant current power supply input and a small starting inverter with an output voltage removably connectable across the output of said power inverter during each heating cycle whereby said power inverter has an output voltage level below which there is starting instability and whereby said output voltage of said starting inverter is less than said instability voltage level of said power inverter, said method comprising increasing the inductance at the constant current input by an amount sufficient to reduce said instability output voltage level to a voltage only slightly below output voltage of said small starting inverter whereby the size of said inductance is minimized.

Claim 13

A method of operating a current source power inverter to prevent starting instability when used to provide power for heating cycles of an induction heating load, said inverter having a constant current power supply input and a small starting inverter with an output voltage removably connectable across the output of said power inverter during each heating cycle whereby said power inverter has an output voltage level below which there is starting instability and whereby said output voltage of said starting inverter is less than said instability voltage level of said power inverter, said method comprising increasing the inductance at the constant current input by an amount sufficient to reduce said instability output voltage level to a voltage only slightly below output voltage of said small starting inverter whereby the size of said inductance is minimized.