High efficiency multi-phase generator
A generator system that includes a six-phase AC machine and an active rectifier bridge employing low on-resistance switches, such as 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 six-phase current flow. The system determines the phase-to-ground voltages of the machine for inputs to the switch control circuit. The control circuit calculates the phase-to-phase voltages from the phase-to-ground voltages. The control circuit uses a specific control scheme to determine 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 six armature coils;
a rectifier circuit electrically coupled to the armature coils, said rectifier circuit including twelve switches where a node between an adjacent pair of the switches defines a phase voltage node for a particular one of the armature coils, wherein the six armature coils are defined as a combination of two three-phase sets of coils where the two sets of coils are oriented relative to each other by a predetermined electrical phase; and
a control circuit providing control signals to the rectifier circuit to switch the switches on and off, said control circuit determining whether phase-to-phase voltages of the machine between each of the nodes are above a first predetermined threshold voltage or below a second predetermined threshold voltage for each of the twelve switches, 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, and 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.
2. The system according to claim 1 wherein the two sets of armature coils are oriented 30° apart in electrical phase.
3. The system according to claim 1 wherein the control circuit determines the phase-to-ground voltages of the armature coils, and calculates the phase-to-phase voltages from the phase-to-ground voltages.
4. The system according to claim 1 wherein the switches are MOSFET switches.
5. The system according to claim 1 wherein the rectifier includes a diode electrically coupled across each switch.
6. The system according to claim 5 wherein the diodes are zener diodes with a voltage clamping capability.
7. The system according to claim 1 wherein the generator system is on a vehicle.
8. The system according to claim 1 wherein each three-phase set of coils can be connected as a star connection.
9. A generator system for a vehicle, said system comprising:
a six-phase machine including six armature coils;
a rectifier circuit electrically coupled to the armature coils, said rectifier circuit including twelve MOSFET switches where a node between an adjacent pair of the switches defines a phase voltage node for a particular one of the armature coils, wherein the six armature coils are defined as a combination of two three-phase sets of coils where the two sets of coils are oriented relative to each other 30° apart in electrical phase, wherein each three-phase set of coils can be connected as star or delta connection; and
a control circuit providing control signals to the rectifier circuit to switch the switches on and off, said control circuit determine the phase-to-ground voltage of the armature coils at six locations in the rectifier circuit and calculating twelve phase-to-phase voltages from the phase-to-phase ground voltages, said control circuit determining whether the phase-to-phase voltages of the machine are above a first predetermined threshold voltage or below a second predetermined threshold voltage for each of the twelve switches, 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.
10. The system according to claim 9 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.
11. The system according to claim 9 wherein the rectifier includes a diode electrically coupled across each switch.
12. The system according to claim 11 wherein the diodes are zener diodes with a voltage clamping capability.
13. The system according to claim 11 where the diodes are integral body-drain diodes within the respected MOSFET switch.
14. A method for rectifying an AC signal from an AC machine, said AC machine including six armature coils, said method comprising:
defining the six armature coils in the machine as a combination of two three-phase sets of coils where the two set of coils are oriented relative to each other by a predetermined electrical phase;
determining the voltage between each phase of the machine and a predetermined ground;
calculating phase-to-phase voltages from the phase-to-phase 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;
turning off the switch if the phase-to-phase voltage for that phase is less than a second predetermined threshold voltage; and
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.
15. The method according to claim 14 wherein determining the voltage between each phase of machine and a predetermined ground includes determining six phase-to-phase ground voltages, and calculating the phase-to-phase voltages includes calculating twelve phase-to-phase voltages.
16. The method according to claim 14 wherein the switches are MOSFET switches.
17. The method according to claim 14 further comprising providing a diode electrically coupled across each switch.
18. The method according to claim 14 wherein the two sets of coils are 30° apart in electrical phase.