Boosted rotor supply circuit and method for improving pulsed electric machine efficiency
A pulsed control of an Externally Excited Synchronous Machines (EESM), including a boost circuit and method for (1) harvesting the field energy stored in rotor winding when the EESM is transitioning to the off state following an on pulses, (2) storing the harvested field energy on a storage device, (3) optionally “topping” up the harvested field energy stored on the storage device, and (4) supplying the harvested and stored field energy as a “boost voltage” to the rotor, just as the EESM is transitioning on for the next pulse, the boost voltage aiding the rotor in quickly overcoming it's start-up inductance, rapidly turning on the rotor, resulting in a much faster transition time from the off state to the on state at the start of the next pulse.
1 . An electric machine comprising:
a pulse controller configured to pulse the electric machine between an on state during on pulses of the electric machine and an off state between the on pulses;
a rotor having a rotor winding configured to be energized during the on pulses when the electric machine is in the on state and to be de-energized when in the off state between the on pulses; and
a boost circuit configured to harvest energy maintained in the rotor winding when energized in the on state during on pulses, the boost circuit further configured to store the harvested energy as a “boost” voltage on a storage device and to provide the boost voltage to the rotor during transitions of the electric machine from the off state to the on state at the start of next on pulses respectively,
the boost voltage causing the rotor to turn on faster, by energizing the rotor sooner, thereby reducing a transition time for the electric machine to transition from the off state to the on state for the next on pulses, relative to if the boost voltage were not provided to the rotor during the transition.
2 . The electric machine of claim 1 , further configured to operate in a regulation mode in which hysteresis or any other type of on/off control is used to maintain a target operating current through the rotor winding at a desired level when the machine is in the on state during the on pulses.
3 . The electric machine of claim 1 , further configured to operate in a harvesting mode wherein the energy maintained in the rotor winding is harvested and stored on the storage device during transitions of the electric machine from the on state during on pulses to the off state between the on pulses.
4 . The electric machine of claim 1 , further comprising a “topping” up mode wherein an additional energy, from a power supply, is added to the boost voltage stored on the storage device.
5 . The electric machine of claim 4 , wherein the additional energy provided to the storage device occurs when the electric machine is in the on state during the on pulses.
6 . The electric machine of claim 4 , wherein the additional energy provided to the storage device occurs when the electric machine is in the off state between the on pulses.
7 . The electric machine of claim 1 , further configured to operate in a boost mode where the boost voltage is provided to the rotor during the transition of the electric machine from the off state to the on state at the start of the next on pulse.
8 . The electric machine of claim 1 , wherein the storage device is a capacitor.
9 . The electric machine of claim 1 , further comprising a rotor boost circuit controller configured to selectively control a first transistor coupled to a first end of the rotor winding and a second transistor coupled to a second end of the rotor winding.
10 . The electric machine of claim 9 , wherein the rotor boost circuit controller is configured to selectively turn the first transistor and the second transistor off to allow the energy maintained in the rotor winding to flow to the storage device when charging the storage device with the boost voltage.
11 . The electric machine of claim 9 , wherein the rotor boost circuit controller is configured to use hysteresis, or any other type of on/off control, to control a target operating current through the rotor winding to a desired level when the electric machine is in the on state during the on pulses by selectively turning the first transistor and the second transistor on and off as needed to maintain the target operating current at the desired level.
12 . The electric machine of claim 9 , wherein the rotor boost circuit controller is further configured modulate the first transistor and the second transistor on and off to enable an additional energy, from a power supply, to be stored on the storage device in addition to the boost voltage harvested from the rotor winding.
13 . The electric machine of claim 9 , wherein the rotor boost circuit controller is further configured turn on the second transistor and a third transistor to enable the boost voltage from the storage device to be applied to the rotor winding during the transitions of the electric machine from the off state to the on state at the start of the next on pulses respectively.
14 . The electric machine of claim 1 , further comprising a power source to provide a voltage, in addition to the boost voltage, to the rotor winding at the start of the next pulses, the voltage from the power supply and the boost voltage acting together to energize the rotor winding during the transitions of the electric machine from the off state to the on state at the start of the next on pulses respectively.
15 . The electric machine of claim 14 , wherein the boost voltage from the storage device dissipates as the rotor winding is energized during the transitions of the electric machine from the off state to the on state at the start of the next on pulses respectively.
16 . A method of operating an electric machine, the method comprising:
(a) storing on a storage device a boost voltage at least partially derived from energy harvested from rotor winding of the electric machine as the electric machine is transitioning from an on state during an on pulse to an off state; and
(b) applying the boost voltage to the rotor winding at a start of a next on pulse as the electric machine transitions from the off state between on pulses to the on state during the next on pulse, wherein the boost voltage causes the rotor to turn on faster, by energizing the rotor sooner, thereby reducing a transition time for the electric machine to transition from the off state to the on state for the next on pulses, relative to if the boost voltage were not provided to the rotor during the transition.
17 . The method of claim 16 , wherein the energy harvested from the rotor winding is derived from a Back Electromagnetic Force (BEMF) generated by the rotor winding.
18 . The method of claim 16 , wherein storing the boost voltage on the storage device is further derived at least partially from energy from a power supply.
19 . The method of claim 16 , further comprises applying a voltage from a power supply, in addition to the boost voltage, to the rotor winding as the electric machine transitions from the off state to the on state during the next pulse, the boost voltage and the voltage from the power supply acting together to energize the rotor winding during the transition.
20 . The method of claim 19 , wherein the boost voltage on the storage device dissipates as the rotor winding is energized as the electric machine transitions from the off state to the on state.
21 . The method of claim 16 , further comprising repeating (a) and (b) and the electric machine transitions from the off state to the on state for each of the on pulses during pulsed operation of the electric machine.