DC inverter having reduced switching loss for paralleled phase leg switches
An electrified vehicle propulsion system uses current feedback to modify gate drive signals to suppress voltage spikes and increase switching efficiency. A DC link having a link capacitor and a link inductance is connected to first and second converters. A first converter bridge has a first phase leg with first upper and lower switching devices, each switching device having a respective gate loop. A second converter bridge has a second phase leg with second upper and lower switching devices, each switching device having a respective gate loop. A plurality of gate drivers provide gate drive signals to respective gate loops for turning the respective switching devices on and off. A plurality of gate coils are provided, wherein each gate coil is connected in series between a respective gate driver and a respective gate loop. Each gate coil is respectively inductively coupled to the link inductance.
1. A pulse width modulated (PWM) power converter comprising:
a DC link with positive and negative buses configured to receive a DC supply voltage;
a phase leg comprising a set of parallel upper transistors and a set of parallel lower transistors coupled in series between the buses, wherein a junction between the sets is configured to be coupled to a load, wherein each of the transistors has a gate terminal and an emitter terminal arranged to create a respective enhanced common source inductance; and
an upper gate driver having a plurality of driving stages each coupled to a respective upper transistor gate terminal to activate a respective upper transistor according to a PWM timing signal, wherein during a turn-on event the upper gate driver hard-switches a first subset of the respective upper transistors at a time defined by the PWM timing signal and soft-switches a remaining subset of the respective upper transistors after a predetermined delay time, and wherein the first subset has a selected number of the upper transistors that provides a combined common source inductance which optimizes an aggregate switching loss for the turn-on event.
2. The power converter of claim 1 wherein during a turn-off event the upper gate driver soft-switches a second subset of the respective upper transistors at a time defined by the PWM timing signal and hard-switches a remaining subset of the respective upper transistors after the predetermined delay time, and wherein the remaining subset has a selected number of the upper transistors that provides a combined common source inductance which optimizes an aggregate switching loss for the turn-off event.
3. The power converter of claim 1 further comprising:
a lower gate driver having a plurality of driving stages each coupled to a respective lower transistor gate terminal to activate a respective lower transistor according to the PWM timing signal, wherein during a turn-on event the lower gate driver hard-switches a third subset of the respective lower transistors at a time defined by the PWM timing signal and soft-switches a remaining subset of the respective lower transistors after the predetermined delay time, and wherein the third subset has a selected number of the lower transistors that provides a combined common source inductance which optimizes an aggregate switching loss for the turn-on event.
4. The power converter of claim 3 wherein during a turn-off event the lower gate driver soft-switches a fourth subset of the respective lower transistors at a time defined by the PWM timing signal and hard-switches a remaining subset of the respective lower transistors after the predetermined delay time, and wherein the remaining subset has a selected number of the lower transistors that provides a combined common source inductance which optimizes an aggregate switching loss for the turn-off event.
5. A pulse width modulated (PWM) power converter comprising:
a DC link with positive and negative buses configured to receive a DC supply voltage;
a phase leg comprising a set of parallel upper transistors and a set of parallel lower transistors coupled in series between the buses, wherein a junction between the sets is configured to be coupled to a load, wherein each of the transistors has a gate terminal and an emitter terminal arranged to create a respective enhanced common source inductance;
an upper gate driver having a plurality of driving stages each coupled to a respective upper transistor gate terminal to activate a respective upper transistor according to a PWM timing signal, wherein during switching events the upper gate driver hard-switches a first subset of the respective upper transistors and soft-switches a remaining subset of the respective upper transistors, and wherein the first subset has a first selected number of the upper transistors that provides a combined common source inductance which optimizes an aggregate switching loss for the switching event; and
a lower gate driver having a plurality of driving stages each coupled to a respective lower transistor gate terminal to activate a respective lower transistor according to the PWM timing signal, wherein during switching events the lower gate driver hard-switches a second subset of the respective lower transistors and soft-switches a remaining subset of the respective lower transistors, and wherein the second subset has a second selected number of the lower transistors that provides a combined common source inductance which optimizes an aggregate switching loss for the switching event.
6. The power converter of claim 5 wherein the first and second selected numbers are determined according to a phase current flowing through the junction.
7. The power converter of claim 6 further comprising a controller defining the first and second selected numbers corresponding to a plurality of consecutive ranges of the phase current.
8. The power converter of claim 5 wherein the respective transistors included in the first and second subsets are varied for successive switching events according to a predetermined circulating pattern so that hard-switching is distributed among all the respective transistors.
9. An electric vehicle inverter comprising:
a switching bridge wherein a phase leg comprises ganged parallel switching devices; and
a gate driver for executing PWM switching events wherein a first subset of the devices are hard-switched and a remaining subset of the devices are soft-switched separated from the hard switching by a predetermined interval, and wherein the first subset includes a number of devices determined by a phase leg current magnitude.
10. The inverter of claim 9 wherein the switching events include turn-on events wherein the first subset of devices are turned on prior to turning on the remaining subset of devices, and wherein the predetermined interval comprises a characteristic turn-on time of the devices.
11. The inverter of claim 9 wherein the switching events include turn-off events wherein the first subset of devices are turned off after turning off the remaining subset of devices, and wherein the predetermined interval comprises a characteristic turn-off time of the devices.
12. The inverter of claim 9 wherein the number of devices included in the first subset of devices is selected according to a comparison between the phase leg current magnitude and a plurality of consecutive current ranges.
13. The inverter of claim 9 wherein the respective devices included in the first subsets are varied for successive switching events according to a predetermined circulating pattern so that hard-switching is distributed among all the respective devices.
14. A method of switching a pulse-width modulation (PWM) power converter, comprising the steps of:
determining a PWM timing signal for controlling switching events of switching devices in a phase leg of the power converter, wherein the phase leg is comprised of a set of parallel upper switching devices and a set of parallel lower switching devices coupled in series, and wherein each of the switching devices has a gate terminal and an emitter terminal arranged to create a respective enhanced common source inductance;
determining a phase current flowing between the phase leg and a load of the power converter;
determining a number of switching devices to include in a subset of switching devices for being hard-switched during each switching event according to the phase current, wherein the number of switching device provides a combined common source inductance which optimizes an aggregate switching loss for the respective switching event; and
generating delayed and non-delayed gate drive signals for each respective switching event to provide hard-switching of the subset of switching devices and to provide soft-switching of a remainder of the switching devices, wherein the hard-switching and soft-switching are separated by a predetermined interval.
15. The method of claim 14 wherein the step of determining the number of switching devices to include in a subset of switching devices is comprised of comparing the phase current with a plurality of consecutive current ranges.
16. The method of claim 14 wherein the switching devices selected to be in the subset for hard-switching is varied between successive switching events according to a predetermined circulating pattern so that hard-switching is distributed among all the respective switching devices.