Active discharge circuit for link capacitor using phase leg switches

• US 10,384,561 B2
• Filed: 09/19/2016
• Issued: 08/20/2019
• Est. Priority Date: 09/19/2016
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Yang, Shuitao, Zhou, Yan, Xu, Fan, Alam, Mohammed Khorshed, Chen, Lihua
• Primary Examiner(s): Barnie, Rexford N
• Assistant Examiner(s): Ly, Xuan
• Application Number:
  US15/268,872
• Publication Number:
  US 20180079315A1
• Time in Patent Office: 1,065 Days
• Field of Search: 307 91
• CPC Class Codes: B60L 2210/40 DC to AC converters
• CPC Class Codes: B60L 3/0046 relating to electric energy storage systems, e.g. batteries or capacitors
• CPC Class Codes: B60L 50/14 using DC generators and AC motors
• CPC Class Codes: H02M 1/322 Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock
• CPC Class Codes: H02M 7/46 using discharge tubes without control electrode or semiconductor devices without control electrode
• CPC Class Codes: H02M 7/5387 in a bridge configuration

Abstract

A DC link capacitor in a drive system for an electric vehicle is quickly discharged using only local action within an inverter module and without any extra components to dissipate the charge. The inverter has a phase leg comprising an upper switching device and a lower switching device coupled across the capacitor. A gate driver is coupled to the phase leg to alternately switch the switching devices to ON state according to a PWM signal during pulse-width modulation of the drive system. The gate driver is configured to discharge the link capacitor during a discharge event by simultaneously activating the upper and lower switching devices to transitional states. Thus use of transitional states ensures that the switching devices provide an impedance that dissipates the capacitor charge while protecting the devices from excessive temperature.

Claims

1. A drive system for an electric vehicle, comprising:

a DC link capacitor adapted to be coupled to positive and negative DC busses between a DC power source and an inverter;

a phase leg comprising an upper switching device and a lower switching device coupled across the DC link, wherein a junction between the upper and lower switching devices is configured to be coupled to a load;

a gate driver coupled to the phase leg to switch the upper switching device to an ON state according to an upper gate PWM signal and to switch the lower switching device to an ON state according to a lower gate PWM signal during pulse-width modulation of the drive system, wherein the gate driver is configured to discharge the link capacitor by simultaneously activating the upper and lower switching devices to transitional states, and wherein the gate driver discharges the link capacitor by simultaneously switching the upper and lower switching devices according to synchronous pulse trains having a gate voltage corresponding to the ON state and a duration that is too short to obtain the ON state.

2. The system of claim 1 wherein the pulse trains have a frequency configured to discharge the link capacitor within a predetermined time while maintaining a temperature of the switching devices below a predetermined temperature.

3. The system of claim 2 wherein the frequency is fixed.

4. The system of claim 1 wherein the gate driver discharges the link capacitor by switching the upper and lower switching devices according to inverse-dead-time signals that activate both upper and lower switching devices during periods having a duration that is too short to obtain the ON state.

5. The system of claim 4 wherein the inverse dead-time signals have a frequency configured to discharge the link capacitor within a predetermined time while maintaining a temperature of the switching devices below a predetermined temperature.

6. The system of claim 5 wherein the frequency is fixed.

7. A method of rapid discharge of a DC link capacitor in drive system for an electric vehicle, wherein the drive system includes positive and negative DC busses coupled to a DC power source by contactor switches, and wherein the link capacitor and a plurality of inverter phase legs are connected to the busses, the method comprising:

detecting a discharge event wherein the busses are decoupled from the power source by the contactor switches;

driving upper and lower switching devices in at least one phase leg with gate signals that simultaneously activate the upper and lower switching devices to transitional states, wherein the gate signals are configured to discharge the link capacitor within a predetermined time while limiting a current through the switching devices that maintains a temperature of the switching devices below a predetermined temperature, and wherein the gate signals are comprised of synchronous pulse trains having a gate voltage corresponding to the ON state and a duration that is too short to obtain an ON state of the switching devices.

8. The method of claim 7 wherein the gate signals are comprised of inverse-dead-time signals that activate both upper and lower switching devices during periods having a duration that is too short to obtain an ON state of the switching devices.

9. A capacitor discharge system, comprising:

a phase leg of an inverter comprising upper and lower switching devices configured to invert a DC voltage from a link capacitor to an AC voltage for driving a motor; and

a gate driver simultaneously activating the upper and lower switching devices to transitional states to discharge the link capacitor within a predetermined time during a discharge event while maintaining the switching devices below a predetermined temperature, wherein the transitional states are comprised of simultaneously switching the upper and lower switching devices according to synchronous pulse trains having a gate voltage corresponding to the ON state and a duration that is too short to obtain an ON state of the switching devices.

10. The system of claim 9 wherein the transitional states are comprised of switching the upper and lower switching devices according to inverse-dead-time signals that activate both upper and lower switching devices during periods having a duration that is too short to obtain an ON state of the switching devices.