Boosted rotor supply circuit and method for improving pulsed electric machine efficiency
A boost circuit and method is described for supplying a boost voltage to a rotor of the electric machine, just as the electric machine is pulsed on, the boost voltage aids the rotor in quickly overcoming its start-up inductance, rapidly turn on the rotor. As a result, much faster transition times are realized each time the electric machine transitions from the off state to the on state at the start of a pulse. By reducing the transition time, the overall efficiency of the electric machine is significantly improved.
1. An electric machine comprising:
a stator;
a rotor;
a power converter configured to energize one or more windings of the stator;
a pulse controller configured to pulse the electric machine between an off state and an on state by controlling the power converter to selectively energize the one or more windings of the stator; and
a boost circuit configured to store a boost voltage on a storage device when the electric machine is in the off state between on pulses and to provide the boost voltage stored on the storage device to the rotor during a transition of the electric machine from the off state to the on state,
the boost voltage causing the rotor to turn-on faster, thereby reducing a transition time of the electric machine during the transition from the off state to the on state, relative to if the boost voltage is not provided to the rotor during the transition.
2. The electric machine of claim 1 , wherein the rotor is further configured to generate an AC voltage following transitions of the electric machine from the on state to the off state.
3. The electric machine of claim 2 , further comprising a rectifier configured to rectify the AC voltage generated by the rotor and to store a DC voltage on the storage device of the boost circuit.
4. The electric machine of claim 3 , wherein the rectifier is an H-bridge rectifier including four transistor-diode pairs arranged in an H-bridge configuration.
5. The electric machine of claim 1 , wherein the storage device of the boost circuit is a capacitor.
6. The electric machine of claim 1 , wherein the boost circuit further comprises a controller configured to clamp the storage of the boost voltage on the storage device once the storage device has achieved a target boost voltage and to prevent the boost voltage from exceeding the target boost voltage.
7. The electric machine of claim 1 , wherein the boost circuit further comprises a controller configured to direct the power converter to energizing the one or more windings of the stator following an on pulse for a sufficient period of time to allow the storage device to be charged to a target boost voltage.
8. The electric machine of claim 7 , wherein the one or more of the windings of the stator are energized until the storage device is charged to the target boost voltage using one of the following:
(a) a reverse multi-phase sinusoidal voltage waveform that is the opposite of what was used to drive the electric machine during a given on pulse;
(b) statically; or
(c) energized using a different frequency or speed compared to the rotation of the rotor.
9. The electric machine of claim 1 , wherein the boost circuit further comprises a controller configured to:
cause the rotor to generate an AC voltage between the on pulses by directing the power converter to energize the one or more windings of the stator when the electric machine is in the off state; and
stop the rotor from generating the AC voltage once the storage device is charged to a target boost voltage by directing the power converter to stop energizing the one or more windings of the stator until the electric machine begins a transition to a next on pulse.
10. The electric machine of claim 1 , wherein the stator, the rotor and the power converter are electrically coupled between a first power rail and a second power rail, and a supply voltage is provided on the first power rail by a DC power source.
11. The electric machine of claim 1 , wherein the stator has three windings, and the power converter provides:
three phase power to the three windings of the stator during the on pulses when the electric machine is in the on state; and
selective power to the one or more of the windings of the rotor between the on pulses when the electric machine is in the off state.
12. The electric machine of claim 1 , wherein the boost circuit includes a rectifier coupled between the rotor and the storage device.
13. The electric machine of claim 1 , wherein the boost circuit comprises a controller configured to control the re-charging of the storage device in the off state between the on pulses of the electric machine and to stop the re-charging of the storage device when a target boost voltage has been reached.
14. The electric machine of claim 1 , wherein the boost circuit maintains the boost voltage stored on the storage device electrically isolated from a power rail that provides supply voltage to the power inverter.
15. The electric machine of claim 1 , wherein the boost voltage applied to the rotor during transitions of the electric machine from the off state to the one state aids in overcoming a turn-on inductance of the rotor so that the rotor can turn on faster relative to if the boost voltage is not applied to the rotor.
16. The electric machine of claim 1 , wherein the electric machine is one of the following:
an Alternating Current electric machine;
a Direct Current electric machine;
a synchronous electric machine;
an asynchronous electric machine;
an induction electric machine;
a switched reluctance electric machine;
a synchronous re reluctance electric machine;
permanent magnet synchronous reluctance electric machine;
hybrid magnet synchronous reluctance electric machine;
externally excited synchronous electric machine;
Permanent Magnet Synchronous electric machine;
an eddy current electric machine;
AC linear electric machine;
an AC mechanically commutated electric machine;
a DC mechanically commutated electric machine;
an axial flux electric machine; or
any of brushless, electrically excited, permanent magnet, series wound, shunt, brushed, or compound type DC electric machines.
17. A method for controlling pulsed operation of an electric machine, the method comprising:
applying a first voltage to a rotor of the electric machine when transitioning the electric machine from an off state to an on state when pulsing the electric machine on; and
applying an additional boost voltage to the rotor of the electric machine when transitioning the electric machine from the off state to the on state when pulsing the electric machine on,
the additional boost voltage aiding in overcoming a turn-on inductance of the rotor so that the rotor can turn on faster relative to if the boost voltage is not applied to the rotor.
18. The method of claim 17 , wherein the boost voltage is generated by:
inducing the rotor to generate an AC voltage between on pulses of the electric machine when in the off state;
rectifying the AC voltage to a DC voltage; and
storing the DC voltage on a storage device between the on pulses when the electric machine is in the off state,
wherein the stored DC voltage on the storage device is used as the boost voltage during the transitions of the electric machine from the off state to the on state.
19. The method of claim 18 , further comprising stopping the storage of the DC voltage on the storage device when the storage device has reached a target boost voltage.
20. The method of claim 19 , wherein the stopping of the storage of the DC voltage on the storage device because the storage device has reached the target boost voltage occurs in three (3) milliseconds or less.
21. The method of claim 17 , further comprising:
(a) energizing at least one winding of a stator when the electric machine is in the off state between on pulses;
(b) generating an AC voltage in the rotor in response to the energization of the at least one winding of the stator when the electric machine is in the off state between on pulses;
(c) rectifying the AC voltage into a DC voltage; and
(d) storing the DC voltage on a storage device, the DC voltage on the storage device used as the boost voltage applied to the rotor when transitioning the electric machine from the off state to the on state when pulsing the electric machine on.
22. The method of claim 21 , further comprising terminating (a) through (d) when the storage device has been charged to a target boost voltage.
23. The method of claim 21 , wherein the energizing of at least one winding of a stator when the electric machine is in the off state between on pulses includes one of the following:
(a) a reverse sinusoidal voltage waveform that is the opposite of what was used to drive the electric machine during a given on pulse;
(b) statically; or
(c) energized using a different frequency or speed compared to the rotation of the rotor.
24. The method of claim 17 , wherein the turn-on of the rotor with the boost voltage occurs in three (3) milliseconds or less.
25. The method of claim 17 , wherein the electric machine is one of the following:
an Alternating Current electric machine;
a Direct Current electric machine;
a synchronous electric machine;
an asynchronous electric machine;
an induction electric machine;
a switched reluctance electric machine;
a synchronous re reluctance electric machine;
permanent magnet synchronous reluctance electric machine;
hybrid magnet synchronous reluctance electric machine;
externally excited synchronous electric machine;
Permanent Magnet Synchronous electric machine;
an eddy current electric machine;
AC linear electric machine;
an AC mechanically commutated electric machine;
a DC mechanically commutated electric machine;
an axial flux electric machine; or
any of brushless, electrically excited, permanent magnet, series wound, shunt, brushed, or compound type DC electric machines.