High efficiency generator
A generator system that includes a three-phase AC machine and an active rectifier bridge employing low on-resistance MOSFET switches for converting the AC current from the machine to a DC current. The system also includes a switch control circuit to switch the MOSFET switches in synchronization with the three-phase current flow. The system determines the phase-to-ground voltages of the machine as inputs to the switch control circuit. The control circuit calculates the phase-to-phase voltages from the phase-to-ground voltages. The control circuit then determines if each of the phase-to-phase voltages is above or below first and second predetermined threshold voltages, where if the phase-to-phase voltage is above the first threshold voltage, the control circuit closes the switch, and if the phase-to-phase voltage is below the second threshold voltage, the control circuit opens the switch.
1. A generator system comprising:
an AC machine including a plurality of armature coils;
a rectifier circuit electrically coupled to the armature coils, said rectifier circuit including a plurality of switches; and
a control circuit providing control signals to the rectifier circuit to switch the switches on and off to convert an AC signal to a DC signal, said control circuit determining whether phase-to-phase voltages of the machine are above a first predetermined threshold voltage or below a second predetermined threshold voltage, wherein the control circuit turns on a switch associated with a particular phase of the machine if the phase-to-phase voltage for that phase is greater than the first predetermined threshold voltage and turns off the switch if the phase-to-phase voltage for that phase is less than the second predetermined threshold voltage.
2. The system according to claim 1 wherein the control circuit determines the phase-to-ground voltage of the armature coils, and calculates the phase-to-phase voltages from the phase-to-ground voltages.
3. The system according to claim 1 wherein the control circuit directly measures the phase-to-phase voltages of the armature coils.
4. The system according to claim 1 wherein the control circuit determines whether the speed of the machine is below a predetermined speed threshold, and prevents the switches from being turned on if the speed of the machine is below the speed threshold.
5. The system according to claim 1 wherein the switches are MOSFET switches.
6. The system according to claim 1 wherein the machine includes three armature coils.
7. The system according to claim 6 wherein the control circuit calculates six phase-to-phase voltages based on three phase-to-ground voltages of the three phases associated with the armature coils.
8. The system according to claim 6 wherein the control circuit calculates three phase-to-phase voltages based on three phase-to-phase ground voltages of the three phases associated with the armature coils.
9. The system according to claim 6 wherein the three armature coils are electrically substantially symmetric.
10. The system according to claim 1 wherein the first predetermined threshold voltage is a positive value and the second predetermined threshold voltage is different than of the first predetermined threshold voltage.
11. The system according to claim 1 wherein the rectifier circuit includes a diode electrically coupled across each switch.
12. The system according to claim 11 where the diodes are zener diodes with a voltage clamping capability.
13. The system according to claim 11 wherein the switches are MOSFET switches and wherein the diodes are integral body-drain diodes within the respective MOSFET switch.
14. A generator system for a vehicle, said system comprising:
a three-phase AC machine including three armature coils;
a rectifier circuit electrically coupled to the armature coils, said rectifier circuit including six MOSFET switches; and
a control circuit providing control signals to the rectifier circuit to switch the MOSFET switches on and off to convert an AC signal from the machine to a DC signal, said control circuit determining the phase-to-ground voltage of the armature coils and calculating six phase-to-phase voltages from the phase-to-ground voltages, said control circuit further determining whether the phase-to-phase voltages of the machine are above a first predetermined threshold voltage and below a second predetermined threshold voltage where the control circuit turns on a switch associated with a particular phase of the machine if the phase-to-phase voltage for that phase is greater than the first predetermined threshold voltage and turns off the switch if the phase-to-phase voltage for that phase is less than the second predetermined threshold voltage.
15. The system according to claim 14 wherein the control circuit determines whether the speed of the machine is below a predetermined speed threshold, and prevents the switches from being turned on if the speed of the machine is below the speed threshold.
16. The system according to claim 14 wherein the rectifier circuit includes a diode electrically coupled across each switch.
17. The system according to claim 16 where the diodes are zener diodes with a voltage clamping capability.
18. The system according to claim 16 wherein the diodes are integral body-drain diodes within the respective MOSFET switch.
19. The system according to claim 14 wherein the first predetermined threshold voltage is a positive value and the second predetermined threshold voltage is different than the first predetermined threshold voltage.
20. A method for rectifying an AC signal from an AC machine, said method comprising:
determining the voltage between each phase of the machine and a predetermined ground;
calculating phase-to-phase voltages from the phase-to-ground voltages;
comparing the phase-to-phase voltages to a first predetermined threshold voltage and a second predetermined threshold voltage;
turning on a switch associated with a particular phase of the machine if the phase-to-phase voltage for that phase is greater than the first predetermined threshold voltage; and
turning off the switch if the phase-to-phase voltage for that phase is less than the second predetermined threshold voltage.
21. The method according to claim 20 further comprising determining the speed of the machine, and preventing the switches from being closed if the speed of the machine is less than a predetermined speed.
22. The method according to claim 20 wherein the AC machine is a three-phase AC machine including three armature coils.
23. The method according to claim 22 wherein determining the voltage between each phase of the machine and a predetermined ground includes determining three phase-to-ground voltages, and calculating the phase-to-phase voltages from the determining phase-to-ground voltages includes calculating six phase-to-phase voltages.
24. The method according to claim 20 wherein the switches are MOSFET switches.
25. The method according to claim 20 further comprising providing a diode electrically coupled across each switch.
26. The method according to claim 25 wherein the diodes are zener diodes having a voltage climbing capability.
27. The method according to claim 25 wherein the switches are MOSFET switches and wherein the diodes are integral body-drain diodes within the respective MOSFET switch.