Shootthrough fault protection system for a voltage source transistor inverter

• US 4,331,994 A
• Filed: 09/28/1979
• Issued: 05/25/1982
• 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:
  US06/079,853
• Time in Patent Office: 970 Days
• Field of Search: 361/56, 361/57, 361/100, 361/93, 361/91, 363/55, 363/56, 363/57, 363/58, 363/34, 363/37, 363/98, 363/132, 363/123, 363/127, 307/252 M, 307/252 Q
• US Class Current: 361/56
• CPC Class Codes: H02H 3/445 of DC quantities
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/38 Means for preventing simultaneous conduction of switches
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements

Abstract

Faulted 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 a d-c bus, by interposing a small choke in series with the filter capacitor to limit the rate of rise of that fault current. At the same time and in response to a shootthrough fault, a pre-charged capacitor, included in a crowbar circuit connected across the d-c bus, discharges through the faulted transistors in a direction opposite to the fault current in order to effect fast turn-off of the transistors, thereby preventing damage thereto.

Claims

1. A shootthrough fault protection system for a voltage source transistor inverter which is driven by a d-c bus voltage received over a d-c bus, having positive and negative lines, from a d-c voltage source having a filter capacitor shunt-connected across the d-c bus, 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 faulted and are inadvertently conductive at the same time thereby short-circuiting the d-c bus, said protection system comprising:

a choke, interposed in series with the filter capacitor between the positive and negative lines of the d-c bus and therefore normally translating only the capacitor ripple current, for limiting the rate of increase of any shootthrough fault current and causing the fault current to increase linearly along a ramp function;

a crowbar circuit shunt-connected across the d-c bus and having a crowbar capacitor and a series-connected SCR;

means for normally changing said crowbar capacitor with a charge of opposite polarity to the charge on the filter capacitor, the positively-charged side of the filter capacitor being adjacent to the positive line of the d-c bus, while the negatively-charged side of the crowbar capacitor is adjacent to the positive line;

and control means, responsive to a shootthrough fault, for firing said SCR into conduction and discharging said crowbar capacitor to translate high amplitude crowbar current through the faulted transistors in a direction opposite to the fault current from the filter capacitor, the instantaneous amplitude of the crowbar current, at the beginning of a shootthrough fault, being much greater than that of the fault current, thereby producing high amplitude reverse recovery current flow through the faulted transistors which sweeps out the minority carriers and effects fast turn-off of the transistors to prevent the destruction thereof, the crowbar current thereafter decreasing exponentially while the fault current is increasing linearly along a ramp function until the opposing crowbar and fault currents are equal at which time the net transistor current becomes zero, after which the subsequent fault and crowbar currents will both flow through said crowbar circuit in the same direction and will re-charge said crowbar capacitor with the same polarity as the filter capacitor,

the emitter-collector conduction path of each of the transistors being shunted by an oppositely poled feedback diode which conducts the decreasing net transistor current after the minority carriers are swept away and the transistor is turned off.