Control scheme for timing the application of limited duration firing signals to power switching devices

Claim 2

In an electrical apparatus including one or more gate controlled ON-OFF power switching devices operatively connected to a voltage source and firing signal control circuit means operatively connected to said gate controlled ON-OFF power switching devices to provide firing signals for a period of time representing a prescribed period of conduction of the ON-OFF power switching devices, the improvement for limiting the firing signals applied to the gate controlled ON-OFF power switching devices to a time less than the prescribed conduction period and further limiting the application of firing signals to a time when forward blocking voltage conditions exists across the ON-OFF power switching devices; said improvement comprising means for monitoring the voltage conditions across said ON-OFF power switching devices and producing an output signal indicative of forward blocking voltage condition, second circuit means having a first input operatively connected to the output of said first circuit means and a second input operatively connected to the output of said firing signal control circuit means; said second circuit means supplying a limited duration firing signal to the gate controlled ON-OFF power switching devices in response to the simultaneous presence of a signal indicative of forward blocking voltage conditions at said first input and a firing signal at said second input, the duration of said limited duration firing signal being substantially the time required to establish said ON-OFF power switching devices in an ON conductive state thereby reducing said forward blocking voltage condition essentially to zero.

Claim 3

In an electrical apparatus as claimed in claim 1 wherein said first circuit means includes a voltage difference detector circuit means operatively connected to said ON-OFF power switching devices and producing a first polarity output signal in response to said forward blocking voltage condition and a second polarity output signal in response to a reverse blocking voltage condition, a comparator circuit means having a first input operatively connected to the output of said voltage difference detection circuit means and means for applying a threshold signal indicative of said forward blocking voltage condition to a second input of said comparator circuit means, said comparator circuit means providing said input sigNal to said first input of said second circuit means when a first output signal from said voltage difference detector circuit means satisfies a predetermined relationship with said threshold signal.

Claim 4

In an electrical power converter apparatus including converter legs having one or more gate controlled ON-OFF power switching devices operatively connecting an input voltage source to an electrical load and firing signal control circuit means operatively connected to said gate controlled ON-OFF power switching devices of each converter leg to sequentially provide firing signals for a period of time representing a prescribed period of conduction of each converter leg, the improvement for limiting the firing signals applied to the gate controlled ON-OFF power switching devices to a time less than the prescribed conduction period and further limiting the application of firing signals to a time when a forward blocking voltage condition exists across the converter leg; said improvement comprising means for monitoring the voltage conditions of each converter leg and producing an output signal indicative of said forward blocking voltage condition, second circuit means having a first input operatively connected to the output of said first circuit means and a second input operatively connected to the output of said firing signal control circuit means; said second circuit means supplying a limited duration firing signal to the gate controlled ON-OFF power switching devices of said converter leg in response to simultaneous presence of a signal indicative of said forward blocking voltage condition at said first input and a firing signal at said second input, the duration of said limited duration firing signal being substantially the time required to establish the ON-OFF power switching devices of said converter leg in an ON conductive state thereby reducing said forward blocking voltage condition essentially to zero.

Claim 5

In an electrical power converter apparatus including converter legs having one or more gate controlled ON-OFF power switching devices operatively connecting an input voltage source to an electrical load and firing signal control circuit means operatively connected to said gate controlled ON-OFF power switching devices of each converter leg to sequentially provide firing signals for a period of time representing a prescribed period of conduction of each converter leg, the improvement for limiting the firing signals applied to the gate controlled ON-OFF power switching devices to a time less than the prescribed conduction period and further limiting the application of firing signals to a time when a forward blocking voltage condition exists across the converter leg; said improvement comprising means for monitoring the voltage conditions of each converter leg and producing an output signal indicative of said forward blocking voltage condition, second circuit means having a first input operatively connected to the output of said first circuit means and a second input operatively connected to the output of said firing signal control circuit means; said second circuit means supplying a limited duration firing signal to the gate controlled ON-OFF power switching devices of said converter leg in response to simultaneous presence of a signal indicative of said forward blocking voltage condition at said first input and a firing signal at said second input, the duration of said limited duration firing signal being substantially the time required to establish the ON-OFF power switching devices of said converter leg in an ON conductive state thereby reducing said forward blocking voltage condition essentially to zero.

Claim 6

In an electrical converter apparatus as claimed in claim 3 wherein said first circuit means includes a voltage difference detector circuit means operatively connected across opposite ends of said converter leg and producing a first polarity output signal in response to said forward blocking voltage condition and a second polarity output signal response to reverse blocking voltage condition across said converter leg, a comparator circuit means having a first input operatively connected to the output of said voltage difference detection circuit means and means for applying a threshold signal indicative of said forward blocking voltage condition to a second input of said comparator circuit means, said comparator circuit means providing said input signal to said first input of said second circuit means when a first output signal from said voltage difference detector circuit means satisfies a predetermined relationship with said threshold signal.