Shootthrough fault protection system for bipolar transistors in a voltage source transistor inverter

• US 4,310,866 A
• Filed: 09/28/1979
• Issued: 01/12/1982
• Est. Priority Date: 09/28/1979
• Status: Expired due to Term

• Current Assignee: Pacsci Motion Control, Inc. (Regal Rexnord Corp.)
• Original Assignee: BorgWarner Incorporated
• Inventors: Wirth, William F.
• Primary Examiner(s): Salce, Patrick R.
• Application Number:
  US06/079,855
• Time in Patent Office: 837 Days
• Field of Search: 361/91, 361/88, 361/110, 361/111, 361/100, 361/98, 361/93, 361/94, 361/58, 363/50, 363/52, 363/53, 363/57, 363/55, 363/56, 363/131, 363/132, 363/135, 363/136, 363/127, 363/128
• US Class Current: 361/88
• CPC Class Codes: H02H 3/445 of DC quantities
• CPC Class Codes: H02M 1/38 Means for preventing simultaneous conduction of switches

Abstract

Faulted bipolar transistors in a voltage source transistor inverter are protected against shootthrough fault current, from the filter capacitor of the d-c voltage source which drives the inverter over the d-c bus, by interposing a small choke in series with the filter capacitor to limit the rate of rise of that fault current while at the same time causing the d-c bus voltage to instantly drop to essentially zero volts at the beginning of a shootthrough fault. In this way, the load lines of the faulted transistors are effectively shaped so that they do not enter the second breakdown area, thereby preventing second breakdown destruction of the transistors.

Claims

1. A shootthrough fault protection system for a voltage source transistor inverter driven by a d-c bus voltage received over a d-c bus from a d-c voltage source having a shunt-connected filter capacitor, where the inverter includes, series-connected across the d-c bus, at least one pair of power bipolar transistors which are subject to undesired shootthrough fault current caused by the discharging of the filter capacitor through the emitter-collector conduction paths of the transistors whenever the transistors are inadvertently conductive at the same time thereby short-circuiting the d-c bus, said protection system comprising:

protection means, including a choke in series with the filter capacitor, for effectively shaping the load lines of the faulted transistors, during a shootthrough fault, to avoid entering the second breakdown area, thereby preventing second breakdown destruction of the transistors,

said choke limiting the rate of increase of shootthrough fault current and causing the fault current to increases linearly along a ramp function and causing the d-c bus voltage, across the d-c bus, to instantly drop to essentially zero volts at the beginning of a shootthrough fault, thereby effectively removing any significant voltage across the faulted transistors and preventing the emitter-collector voltage and the collector current, in each faulted transistor, from producing a peak power of a magnitude which would destroy the transistor;

a fast recovery diode in shunt with said choke to clamp said d-c bus to the filter capacitor voltage and to provide a discharge path for the inductive energy developed in said choke; and

means, responsive to a shootthrough fault, for removing the base drive from the faulted transistors to effect turn-off thereof.

2. A shootthrough fault protection system according to claim 1 wherein each of the faulted transistors is shunted by a snubber network which shapes the load line after the transistor has been turned off.

3. A fault protection system for preventing bipolar transistors, in a voltage source transistor inverter, from suffering second breakdown damage from fault current flowing through faulted transistors, when the output of the inverter is short circuited, from the filter capacitor of the d-c voltage source which drives the inverter over a d-c bus, the filter capacitor being connected across the d-c bus, comprising:

protection means, including a choke in series with the filter capacitor, for effectively shaping the load lines of the faulted transistors, when there is an output short circuit, to avoid entering the second breakdown area, thereby preventing second breakdown destruction of the transistors,

said choke limiting the rate of increase of fault current and causing the fault current to increase linearly along a ramp function and causing the d-c bus voltage, across the d-c bus, to instantly drop to essentially zero volts at the beginning of an output short circuit, thereby effectively removing any significant voltage across the faulted transistors and preventing the emitter-collector voltage and the collector current, in each faulted transistor, from producing a peak power of a magnitude which would destroy the transistor;

a fast recovery diode in shunt with said choke to clamp said d-c bus to the filter capacitor voltage and to provide a discharge path for the inductive energy developed in said choke; and

means, responsive to an output short circuit, for removing the base drive from the faulted transistors to effect turn-off thereof.