Boost rotor supply circuit and method for improving efficiency of pulsed electric machines - Patents.com

Abstract

Pulse control of an externally excited synchronous machine (EESM) includes a boost circuit and method for: (1) recovering magnetic energy stored in a rotor winding when the EESM transitions to an off-state after an on-pulse, (2) storing the recovered magnetic energy in a storage device, (3) optionally replenishing the recovered energy stored in the storage device, and (4) supplying the recovered and stored magnetic energy as a "boosted voltage" to the rotor when the EESM transitions to on at the start of the next pulse. The boosted voltage helps quickly overcome the rotor's starting inductance, quickly turning on the rotor and significantly shortening the transition time from the off-state to the on-state at the start of the next pulse.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 404,103, filed September 6, 2022, which is incorporated herein by reference for all purposes.

[0002] This application relates generally to pulsating control of Externally Excited Synchronous Machines (EESMs), and more particularly to a boost circuit and method for (1) harvesting magnetic energy stored in a rotor inductor when the EESM is transitioning to an off-state following an on-pulse, (2) storing the harvested magnetic energy in an electrical storage device, (3) "topping up" the stored energy to compensate for losses incurred in power transfer, and (4) supplying the harvested and stored magnetic energy as a "boost voltage" to the rotor as the EESM transitions on for the next pulse, which helps the rotor quickly overcome its starting inductance and rapidly turn on the rotor, resulting in a significantly faster transition time from the off-state to the on-state at the beginning of the next pulse. [Background technology]

[0003] Most EESMs typically include a stator with multiple poles and a rotor, and operate as either a generator or a motor. When operating as a motor, electrical energy is converted into mechanical energy. When operating as a generator, mechanical energy is converted into electrical energy. Therefore, as used herein, the terms "EESM," "electric machine," or simply "machine" are intended to be broadly interpreted to mean both electric motors and generators.

[0004] Electric machines have a relatively high energy conversion efficiency when operating at or near their optimum operating load. However, when they operate below their optimum operating load, their energy conversion efficiency is significantly lower. In many applications, electric machines must operate below their optimum operating load, resulting in a lower overall operating efficiency of the machine than possible and wasted energy.

[0005] Pulse control of electric machines is a known approach to improving efficiency. Under operating conditions below a given machine's peak efficiency range, the electric machine intermittently transitions from an off state to an on state during pulsed operation. By controlling the magnitude, duty cycle, and frequency of the on-pulses, the electric machine can be controlled to generate the required power while operating only within its peak efficiency range. This results in improved overall efficiency compared to traditional continuous operation below the machine's peak efficiency range. Summary of the Invention

[0006] A problem with pulsed machine controlled machines is that it takes a relatively large amount of energy and time to transition the rotor of an electric machine from an off state to an on state with each pulse.

[0007] Therefore, a need exists to quickly and efficiently transition pulsed controlled electric machines from an off state to an on state with each pulse, thereby allowing such electric machines to operate at even higher efficiency levels.

[0008] This application relates to pulsating control of an externally excited synchronous machine (EESM) and includes a boost circuit and method that (1) recovers magnetic energy stored in a rotor inductor when the EESM is transitioning to an off-state following an on-pulse, (2) stores the recovered magnetic energy in a storage device, (3) "tops up" the stored energy to compensate for losses incurred in power transfer, and (4) supplies the recovered and stored magnetic energy as a "boost voltage" to the rotor as the EESM transitions on for the next pulse, which helps the rotor quickly overcome its starting inductance and rapidly turn on the rotor, resulting in a significantly faster transition time from the off-state to the on-state at the beginning of the next pulse. [Brief explanation of the drawings]

[0009] The invention and its advantages are best understood by referring to the following description taken in conjunction with the accompanying drawings.

[0010] FIG. 1 is a graph illustrating the pulsing operation of a machine in accordance with a non-limiting embodiment of the present invention.

[0011] FIG. 2 is a functional block diagram illustrating the architecture of a machine controller in accordance with a non-limiting embodiment of the present invention.

[0012] FIG. 3 is an operational flow diagram illustrating steps implemented by a machine controller in accordance with a non-limiting embodiment of the present invention.

[0013] FIG. 4A is a torque versus efficiency map for a machine operating at a fixed speed during the transition from zero to peak efficiency torque.

[0014] FIG. 4B is torque versus lost work for an exemplary machine operating at a fixed speed during the transition from zero to peak efficiency torque.

[0015] 5A-5E respectively illustrate various modes of operation of an exemplary circuit of an electric machine according to non-limiting embodiments of the present invention.

[0016] FIG. 6 is a flow diagram illustrating a procedure for pulsing operation of an electric machine in accordance with a non-limiting embodiment of the present invention.

[0017] In the drawings, like reference numerals may be used to designate like structural elements, and it should be understood that the depictions in the figures are schematic and not to scale. DETAILED DESCRIPTION OF THE INVENTION

[0018] Electric motors and generators are used in a wide variety of applications and under a wide variety of operating conditions. In general, many modern electric machines have relatively high energy conversion efficiencies. However, the energy conversion efficiency of most electric machines varies significantly with operating load. In general, electric machines have high efficiency when operating at or near their peak operating load. However, when operating at lower loads, efficiency tends to be significantly lower.

[0019] This application relates generally to pulsed control of electric machines (e.g., electric motors and generators) to improve energy conversion efficiency when operating conditions permit. More specifically, under lower load operating conditions, the electric machine is pulsed, transitioning intermittently between off and on states during pulses. By controlling the magnitude, duty cycle, and frequency of the pulses, the electric machine can be controlled to operate exclusively at its higher efficiency level compared to traditional continuous motor control, thereby providing a desired average torque output in a more energy-efficient manner than previously possible.

[0020] Applicant has filed and been granted several U.S. patents covering pulsed motor control of electric machines, including U.S. Patent 10,742,155 (TULA P200B), U.S. Patent 11,228,272 (TULA P200C), and U.S. Patent 10,944,352 (TULA P201), each of which is incorporated herein by reference for all purposes.

[0021] Pulsed Machine Control Referring to Figure 1, a graph 10 illustrating the basic operation of pulsed machine control is shown. In this example, several assumptions are made: The electric machine operates as an electric motor. The maximum torque output of the machine is 50 Nm, as plotted on the vertical axis. The peak efficiency range of the machine is approximately 95% of peak power output, or a torque output of approximately 47.5 Nm. In this example, the machine is being called upon to produce an output torque of 10 Nm, which is well below its peak efficiency range.

[0022] In conventional operation, the machine runs continuously to produce the required torque output of 10 Nm, which is represented in Figure 1 by dashed line 12. The drawback of running continuously at a torque output of 10 is that the machine operates well below its peak efficiency range (e.g., above 47.5 Nm in this example).

[0023] In pulsed operation, on the other hand, the machine is pulsed on and off. Between on-pulses, the machine is in an off state and produces little or no torque output. During the on-pulses, the machine: (1) It is in the on state and is operating at or near peak efficiency (i.e., 50). (2) The time-average torque output of the machine while it is intermittently pulsing between off and on states is sufficient to meet the perceived torque demand.

[0024] In this example, the on-pulse frequency occurs once every five time units, as plotted on the horizontal axis. As a result, the machine is pulsed on twenty percent (20%) of the time, as represented by pulse 14. By operating the machine at its peak power (e.g., 50) every five time units (i.e., 20 percent of the time), the requested 10 Nm of torque is produced over time. However, because the machine is only operating at or near peak efficiency during the pulses, the overall operating efficiency of the machine is significantly improved over traditional continuous operation.

[0025] Three-phase winding field synchronous machine In a three-phase wound field synchronous machine, the stator may include a three-coil winding that is excited by a three-phase AC input and a field winding on the rotor that is powered by a DC voltage source. When the three-phase AC input is passed through the three-phase armature windings, a rotating magnetic field (RMF) is generated. The rotational speed of the RMF is equal to the synchronous speed (N s The interaction of the rotor field winding magnetic field with the stator winding magnetic field generates an electromagnetic force (EMF) that causes the rotor to rotate.

[0026] Power Converter 2, a diagram of a power controller 20 for pulsed operation of an electric machine is shown. Power controller 20 includes a power converter 22, a DC power source 24, and an electric machine 26. In this non-limiting embodiment, power converter 22 also includes a pulse controller 28.

[0027] The power converter 22 can be operated as a power inverter or a power rectifier depending on the direction of energy flow in the system.

[0028] The rotor magnetic field is generated by passing a DC current through the rotor field winding.

[0029] When operating electric machine 26 as a motor, power converter 22 serves to generate three-phase AC power from DC power source 24 to drive electric machine 26. Three-phase input power, designated as Phases A, B, and C, is applied to the stator windings of electric machine 26 to generate RMF as described above. In either case, the rotor magnetic field is generated by an inverter supplying current to the rotor windings.

[0030] During motor operation, the pulse controller 28 is responsible for selectively pulsing the three-phase stator input power and rotor current supplied to the electric machine 26. In conventional (i.e., continuous) operation, the three phases A, B, and C of the stator input power and rotor current are continuous (i.e., not pulsed). During pulsed operation, the three phases A, B, and C and the rotor current are selectively pulsed.

[0031] When the electric machine is operating as a generator, the power converter 22 acts as a power rectifier, and the AC power coming from the electric machine 26 is converted to DC power and stored in the DC power supply 24. The rotor magnetic field required to enable this power transfer must be supplied by the inverter.

[0032] The lines representing phases A, B, and C have arrows at both ends, indicating that current can flow from the power converter 32 to the electric machine 36 when the machine is being used as a motor, and in the opposite direction when the machine is being used as a generator.

[0033] The rotor current for driving the motor and generating electricity flows from the inverter to the machine.

[0034] When recovering rotor magnetic energy, current flows from the machine to the inverter.

[0035] Pulsed Machine Control Referring to FIG. 3, a flow diagram 30 is shown illustrating the steps implemented by pulse controller 28 to provide pulsed controlled operation of electric machine 26 while operating as an electric motor.

[0036] The first step 32 is to determine the current machine power and current machine speed.

[0037] In decision step 34, a determination is made as to whether the machine should be operated in continuous or pulsed mode based on the current machine power output and the current machine speed. In other words, a determination is made as to whether the desired machine torque is above or below the most efficient output torque range for the current machine speed (e.g., 47.5 Nm in the example of FIG. 1).

[0038] In step 36, if the current machine torque demand exceeds the most efficient output torque for the current machine speed, the machine is operated in continuous mode.

[0039] In an alternative step 38, if the current machine torque demand is below the most efficient output torque for the current machine speed, the machine is operated in a pulsed mode.

[0040] In step 40, the desired pulse magnitude, duty cycle and frequency for operation in pulsed mode are determined so that the average output power or torque over time matches the desired torque output.

[0041] In step 42, the machine is operated in a pulsed mode using the determined pulse magnitude, duty cycle and frequency of the pulses.

[0042] Steps 32-42 above are performed continuously during machine operation. At any machine speed, there is a corresponding most efficient output torque at which the machine operates at or near maximum efficiency. As instantaneous machine output demand and / or current machine speed change, a determination is made as to whether to operate the machine in either continuous mode or pulsed mode, as appropriate.

[0043] From a conceptual standpoint, the more often the required machine torque is below the most efficient output torque for the current machine speed, the more the overall efficiency of the machine can be improved by pulsing the machine.

[0044] Pulse Rise Time Current power converters are typically designed for continuous operation, rather than pulsed operation. Such power converters typically transition from an unenergized state to an energized state relatively infrequently. As a result, to date, little design effort has been devoted to managing the machine's off-to-on transition time. When such effort is made, the emphasis is typically on achieving a smooth transition, as opposed to a fast transition. Thus, in most electric machines, the transition from the unenergized (off) state to the energized state is not very fast.

[0045] Applicants have discovered that for electromechanical systems that frequently transition from a non-powered state to a peak efficiency state, such as in pulsed operation, further efficiency gains can be realized if the transition occurs as quickly as possible. For example, a fast transition from zero torque to peak efficiency torque improves overall average efficiency because the machine spends less time in a transition below peak efficiency. This relationship is illustrated in Figures 4A and 4B.

[0046] Referring to FIG. 4A, a torque versus efficiency map is shown for an exemplary electric machine operating as a motor at a fixed speed (e.g., 6000 rpm). In the exemplary map, the range of torque output from 0.0 Nm to 250 Nm is plotted along the horizontal axis, and the efficiency of the machine from 0.0 percent to 100 percent is plotted along the vertical axis. Curve 46 shows the machine's transition from zero to peak efficiency torque. During this transition, as depicted by the shaded region 48, the machine operates at a much lower efficiency before reaching or near the machine's peak efficiency, as indicated by reference numeral 50.

[0047] 4B, a map is provided illustrating torque versus work loss for an exemplary machine operating at a fixed speed during a transition from zero to peak efficiency torque. In this map, work loss (W) is plotted along the vertical axis, and torque output of the machine is plotted along the horizontal axis. As shown by curve 52, the work loss of the machine increases as torque output increases during the transition from zero to peak efficiency torque. Thus, the faster the transition time from zero to peak efficiency torque, the less work is performed and the less energy is consumed by the electric machine.

[0048] By substituting time for torque on the horizontal axis and integrating the area under curve 52, the energy consumed by the electric machine for a given transition time can be calculated. For example, for the exemplary machine, a 0.5-second transition time dissipates 7234.5 joules of energy, while a 0.05-second transition time dissipates only 723.4 joules. This comparison shows that the faster the transition time from zero to peak efficiency torque, the less energy is consumed in losses. Note that this example assumes no load inertia acceleration occurs, so no energy is added to the load. Just as faster rise times increase efficiency, faster pulse fall times can also increase efficiency.

[0049] For different machines, the machine's zero to peak efficiency torque transition, peak efficiency torque, and work loss will all be different. Therefore, the maps of Figures 4A and 4B should be considered merely illustrative and should not be construed as limiting in any way.

[0050] Applied voltage vs. rotor current rise time Applicant has discovered that the OFF-to-ON transition time of a pulsed electric machine can be significantly reduced by applying a boosted rotor voltage at the beginning of each pulse. The application of the boosted voltage reduces the inherent turn-on time, determined by the rotor's inductance and resistance, allowing the rotor windings to be rapidly energized to the target operating current and develop the desired rotor flux sooner than would be possible without the boosted rotor voltage. By significantly reducing the OFF-to-ON transition time of each pulse (sometimes referred to as the "rise time"), the overall efficiency of a pulsed electric machine can be significantly improved.

[0051] Equation (1) below defines the current (i) when a voltage V is applied to the inductor coil of a given rotor of an electric machine.

number

[0052] Equation (1) expresses the given rotor current I f This shows that there are at least two ways to improve the rise time to reach . One is to reduce the resistance R, and the other is to increase the voltage V.

[0053] The time constant L / R remains constant even when R is reduced because, for a particular winding slot, the resistance is determined by the following function: (a) Slot area divided by the number of turns (where slot area is the area of ​​the laminate into which copper wire can be inserted). (b) Because the length of the wire varies as a function of the number of turns, the resistance increases as the square of the number of turns.

[0054] However, the inductance also increases with the square of the number of turns, so the time constant L / R remains constant for a given slot cross-sectional area.

[0055] Therefore, as is clear from equation (1), by reducing the number of turns while keeping the slot fill (the percentage of slots filled with copper) constant, the rotor current rise time can be reduced, resulting in a faster rotor turn-on time.

[0056] Alternatively, the rotor current rise time can be lengthened by simply increasing the applied voltage V by boosting the battery voltage while leaving the rotor winding as is.

[0057] Rotor Magnetic Energy During operation of an electric machine, the rotor stores energy in the rotor magnetic field. The rotor is turned on by applying a voltage V to the rotor winding. When voltage is applied, the current through the rotor winding rises as shown in equation (1).

[0058] The magnetic energy stored in the rotor magnetic circuit is defined by Equation 2:

number

[0059] As will be explained in more detail below, the magnetic energy E from the rotor is collected and stored in a storage device such as a capacitor. The stored energy of a capacitor is defined as:

number

[0060] Note that the energy E in the rotor and the energy recovered and ultimately stored in the power storage device are not necessarily the same. Typically, due to circuit losses, the recovered and stored energy is smaller than the energy in the rotor.

[0061] Boost circuit 5A, there is shown an exemplary rotor converter 60 for an electric machine with a boost circuit 62 and a rotor boost excitation controller 63. In much of the following description, the electric machine will be operated as a motor.

[0062] Rotor converter 60 includes a voltage source V1, such as a battery, connected between a positive power rail 64 and a negative power rail 66, an inductor L1 representing a rotor winding (not shown), transistors M1 and M2 connected to an upper end 68A and a lower end 68B of rotor winding L1, respectively, and a diode D1. Transistor M1, rotor winding L1, and transistor M2 are connected in series between positive power rail 64 and negative power rail 66. Diode D1 is connected in parallel with rotor winding L1 and transistor M2, between upper end 68A of rotor winding L1 and transistor M1 and the negative power rail 66.

[0063] D2 is normally connected directly to the positive power rail 68, but in the present invention is used to direct energy to the boost circuit 62.

[0064] The boost circuit 62 includes the following additional components: a diode D3, a transistor M3, and a capacitor C1. In addition to transistors M1 and M2, the components of the boost circuit 62 are at least partially controlled by a boost controller 63.

[0065] Capacitor C1 in this example is shown as being connected between the positive side of the supply voltage and the boost voltage, although in an alternative solution it may be connected between the negative side of the supply voltage and the boost voltage.

[0066] In one non-limiting embodiment, transistors M1, M2, and M3 are MOSFET transistors. In other embodiments, other types of transistors, or any type of electronic switch, may be used as these components.

[0067] The boost controller 63 operates in cooperation with the pulse controller 28 described above. Generally, the pulse controller 28 determines whether the machine 60 should operate in continuous or pulsed mode. In the latter case, the pulse controller 28 determines the magnitude, duty cycle, and frequency of the on-pulses as described above, and responsively directs the power converter 22 to energize the three phases A, B, and C of the electric machine's stator (not shown).

[0068] Boost controller 63, in cooperation with pulse controller 28, operates the components of boost circuit 62 to recover energy from rotor winding L1 when the electric machine transitions to an off state, store the recovered energy, and apply it as a "boost" voltage when the rotor turns on with the start of the next pulse. Specifically, the boost controller operates the electric machine and the components of boost circuit 62 as follows: (a) storing in electrical storage device C1 a boosted voltage derived at least in part from energy recovered from rotor winding L1 when the electric machine transitions from an on-state to an off-state at the end of an on-pulse; (b) When the electric machine transitions from the off state to the on state for the next on-pulse, a boost voltage is applied to the rotor winding L1 at the start of the next on-pulse.

[0069] When operating in pulse mode, the rotor converter 60 and boost circuit 62 cycle through four different operating modes with each on-pulse. By cycling through these four modes, boost energy is recovered and stored at the end of each pulse. This allows the boost voltage to be applied to the rotor along with the supply voltage V1 at the start of the next pulse. In this way, the transition time of each pulse is significantly reduced.

[0070] The four modes per on-pulse include: 1. Regulation mode: When the machine is in the on state, hysteretic control is used to maintain the target operating current through the rotor winding L1 at the desired level during the on pulse. 2. Field harvesting mode: This is the mode when the energy E (Equation 2) in the rotor winding L1 is captured and the remaining energy E (Equation 3) after losses is stored in capacitor C1. Field harvesting mode typically occurs at the end of a pulse when machine 60 transitions from an on-state to an off-state. 3. An optional "topping up" mode, where additional energy from power supply V1 is used to provide additional charge to capacitor C1. Because there are losses in the recovered and stored energy, additional voltage can optionally be used to maintain capacitor C1 at the desired boosted level voltage. 4. Boost mode: Here, at the start of the next on-pulse, the rotor winding L is supplied with the boost voltage stored in the capacitor C1 in addition to the voltage V1.

[0071] Additionally, the magnitude of the boost voltage can be selected to achieve the desired transition time required for the rotor winding L1 to energize and turn on the rotor. Generally, the larger the boost voltage, the faster the transition. In this case, all of the energy stored in C1 may not be transferred to the rotor winding L1 when it is energized.

[0072] 5A to 5D, the operation of the electric machine 60, the boost circuit 62, and the boost controller 63 in each of the four modes will be described.

[0073] Regulation Mode In regulation mode, mode hysteretic control of transistors M1 and M2 is used to precisely maintain the target operating current in rotor winding L1 at the desired level during the on-pulse. The hysteretic control described below is best understood with reference to Figure 5A.

[0074] When an on-pulse begins, transistors M1 and M2 turn on and transistor M3 turns off. As a result, current flows from power supply V1 through positive power rail 64, diode D3, transistors M1 and M2, rotor winding L1, and then to negative power rail 66 (illustrated by arrow 70). When both transistors M1 and M2 are on, the current increases at a rate determined by the impedance of the components along the current path indicated by arrow 70. As the current increases, it eventually exceeds the target operating current, provided sufficient voltage is applied. Once the current exceeds the target value, transistor M1 turns off. When M1 turns off, a back electromagnetic force (BEMF) is generated in the coil of rotor winding L1, causing the top end 68A of rotor winding L1 to go negative. At this point, diode D1 turns on, and current decays as it flows through rotor winding L1, transistor M2, and diode D1, as depicted by circular arrow 72. When the current decays below the target operating current, transistor M1 turns on again, allowing the current to increase. By repeating the above, the target operating current through rotor winding L1 can be precisely maintained for the duration of a given pulse.

[0075] Although the above assumes hysteretic control, other digital on / off control types are also possible, including but not limited to fixed or variable frequency PWM. Harvesting Mode

[0076] In recovery mode, the energy stored in the rotor winding L1 while the electric machine was in the on-state is captured as it transitions to the off-state at the end of the on-pulse. Any remaining energy after unavoidable circuit losses is stored in capacitor C1. The recovery mode described below is best understood with reference to Figure 5B.

[0077] When the on-pulse ends, the pulse controller 28 and boost controller 63 cooperate to turn off transistors M1 and M2. Because energy is stored in the rotor winding L1, a BEMF is induced in the open circuit, with the upper end 68A of the rotor winding L1 negative and the lower end 68B positive. Because the BEMF is greater than the supply voltage V1, current flows through diode D1, rotor winding L1, diode D2, and capacitor C1, as shown by arrow 74. Thus, most of the BEMF energy generated by the rotor winding L1 is stored in capacitor C1, although it incurs circuit losses when the electric machine transitions from an on-state to an off-state at the end of the on-pulse.

[0078] Topping Up Mode In an optional top-up mode, if capacitor C1 is not sufficiently charged to the appropriate or desired level, it can be "topped up" using power from power supply V1. The boost voltage stored in capacitor C1 is desirably charged to the desired level to meet the specified rotor off-to-on transition time for the initiation of the next on-pulse. If the charge on capacitor C1 is insufficient due to circuit losses or other reasons, voltage source V1 can be used to "top-up" the capacitor with additional voltage.

[0079] In one embodiment of the replenishment mode, shown in Figure 5C, transistors M1 and M2 are selectively turned on and off using pulse-width modulation (PWM). Initially, both transistors M1 and M2 are turned on briefly, causing current to flow from the positive rail 64 to the negative rail 66, energizing rotor winding L1 with voltage V1 (arrow 70). Once energized, both transistors M1 and M2 are turned off, and the excess energy provided to rotor winding L1 induces a BEMF (sometimes referred to in this context as "flyback" energy) that is transferred to capacitor C1 using the current path indicated by arrow 74. This results in additional energy being added to the boost voltage already recovered and stored in capacitor C1.

[0080] Another method for replenishing the energy stored in capacitor C1 is shown in FIG. 5D. In this embodiment, transistor M1 remains on while transistor M2 is toggled on and off. When both transistors M1 and M2 are on, the rotor winding L1 of the rotor is energized. When transistor M2 is turned off, the BEMF of rotor winding L1 is coupled to C1 through diode D2, as indicated by arrow 80. In this manner, by switching transistor M2 on and off, rotor winding L1 can be repeatedly energized, and its energy can be recovered and stored in capacitor C1. This process can be repeated until the charge on C1 reaches the desired level.

[0081] Note that topping mode can be implemented at any time during pulsed control operation of the electric machine. In the off state, there is no stator current, so no torque is generated. In the on state, instead of drawing a little more power from voltage source V1 and circulating current as shown by arrow 72 in Figure 5A, both M1 and M2 can be turned off, returning energy to C1, and then circulating current again in the normal manner.

[0082] Boost Mode Finally, in boost mode, as best shown in FIG. 5E, when the electric machine begins its transition from an off-state to an on-state at the beginning of the next pulse, the boost voltage stored in capacitor C1 is applied to rotor winding L1. This boost voltage may include only the energy previously recovered from inductor L1, or it may include a combination of recovered energy and any "top-up" off-voltage generation as described above. Either way, the stored energy is returned to rotor winding L1, helping supply voltage V1 rapidly energize the rotor. When the boost voltage is applied to rotor winding L1, transistors M1, M2, and M3 all turn on, providing a current path (arrow 78) from capacitor C1 through inductor L1 to the negative rail 66, allowing the boost voltage to rapidly energize the rotor.

[0083] As the boost voltage is applied to the rotor, the charge on capacitor C1 dissipates. When sufficient or all of the energy has been transferred, voltage V1 continues to energize rotor winding L1 through D3 for the remainder of the on-pulse. M3 can then be turned off.

[0084] In the above-described embodiment, many of the existing electrical components of rotor converter 60 are used to recover, store, and apply the boosted voltage, along with some additional components as described herein. Because many existing elements of rotor converter 60 are used, there is little overhead in terms of additional circuitry or components, and the benefit of faster transition times is achieved almost "for free."

[0085] It should also be noted that the particular components referenced herein are merely exemplary and should not be construed as limiting in any way. Rather, any type of component may be used to implement the functionality and operation of boost circuit 62 and / or boost controller 63 as described herein.

[0086] In an alternative embodiment, each of the diodes D1, D2, and D3 may be replaced with a MOSFET or similar switch. One advantage of using a MOSFET or similar switch is that it has a lower voltage drop when on, thereby improving efficiency. However, using a MOSFET or similar switch may require additional control circuitry and signals. In yet other embodiments, one or more of the diodes D1, D2, and / or D3 may be a Schottky diode, a high-speed epitaxial diode, or a standard diode, or any combination thereof.

[0087] Pulsed control operation with boost While the electric machine is operating in pulsed mode, the four modes described above can be cycled continuously. Each on-off cycle cycles through regulation, recovery, and boost (and optionally top-up) modes. By repeating this process with each pulse, the transition time for the rotor to go from the off state to the on state with each pulse is significantly reduced, thereby significantly improving the overall efficiency of the electric machine.

[0088] Referring to FIG. 6, a flow diagram 90 illustrating steps for efficiently operating an electric machine is shown.

[0089] In a first step 92, the electric machine 60 is in an on-state for one on-pulse and the target operating current through the rotor winding L1 is precisely adjusted using hysteresis as described herein.

[0090] At decision step 94, boost controller 93 determines when the current pulse has ended.

[0091] In step 96, boost controller 93 takes steps to recover the BEMF energy induced in rotor winding L1 when the electric machine transitions from an on-state to an off-state at the end of the pulse. The recovered energy is stored in storage device C1 as a boost voltage.

[0092] In optional step 98, the boosted voltage stored in power storage device C1 may optionally be topped off.

[0093] At decision step 100, boost controller 93 determines if it is time to initiate a transition from the OFF state to the ON state for the next ON pulse.

[0094] Finally, in step 102, the rotor winding is energized with a combination of both the source voltage V1 and the boost voltage from the power storage device C1 when the electric machine transitions from the off state to the on state at the beginning of the next pulse. The additional boost voltage reduces the transition time beyond what would occur if no boost voltage were applied.

[0095] If there is not enough time during step 98 to replenish the energy stored in C1, replenishment may occur between steps 92 and 94.

[0096] Steps 92 through 102 are preferably repeated continuously as the electric machine cycles between the off and on states for each pulse. In this manner, the boosted voltage is recovered and stored at the end of each pulse and applied to the rotor winding at the beginning of the next pulse. As a result, the transition time between the off and on states for each on-pulse is significantly reduced, improving the overall operating efficiency of the electric machine.

[0097] Applicants have found that by using a boosted voltage as described herein, the transition time from the OFF state to the ON state is significantly reduced compared to a comparable electric machine that is not boosted, resulting in a significant improvement in the overall efficiency of such an electric machine.

[0098] Generator operation Although the above description has primarily described operation of the electric machine as a motor, this should not be construed as limiting in any way. Rather, the boost voltage to the rotor winding as described herein can be used during pulsed control operation as a generator as well.

[0099] Types of Electrical Machines As is apparent from the foregoing, the described boost pulse machine control can be utilized with electric machines having external excitation fields, and the present invention should therefore be construed broadly to include any such machines, not just those expressly mentioned herein.

[0100] Electrical Machinery and Vehicles Electric vehicles are now commonplace and growing in popularity, with predictions that they will surpass or completely replace traditional internal combustion engine vehicles within the next 10 to 20 years.

[0101] An electric vehicle is equipped with one or more onboard machines. When driving the vehicle, the machine acts as a motor, generating torque that propels the vehicle. In an electric vehicle, the electric machine(s) are used alone to generate the required torque. The torque may be positive to propel the vehicle or negative to convert the vehicle's kinetic energy into stored electrical energy. In a hybrid vehicle, the onboard electric machine is used alone or in conjunction with the internal combustion engine to propel the vehicle. In regenerative braking, the machine is typically used to convert mechanical energy into electrical energy that is stored in a storage device such as a battery or capacitor. The stored energy can be used when the electric machine operates as a motor or to power other electrical devices in the vehicle, such as the air conditioner, heater, defroster, various lighting systems, and entertainment systems.

[0102] Pulsing on-board electric machines in vehicles with boosted voltages as described herein promises significant efficiency benefits that can extend the vehicle's range before needing to charge the battery or refuel, as in hybrid vehicles.

[0103] Further embodiments Motors used in heating, ventilation, and air conditioning (HVAC) applications are another good example of an application that can benefit from pulsing control. Several factors contribute to pulsed motor control being well-suited for HVAC applications. These include: (a) the motors used in HVAC applications today are dominated by induction motors that do not contain permanent magnets; (b) a high percentage of motors used in HVAC applications (especially those containing variable-speed HVAC capacitors and / or air handlers) spend significant amounts of time operating below their high-efficiency region; and (c) the inertia of the fan or pump typically dominates the inertia of the motor, which tends to further mitigate potential NVH-related effects associated with pulsing.

[0104] Although only a few embodiments of the present invention have been described in detail, it should be understood that the present invention may be embodied in many other forms without departing from the spirit or scope of the present invention. The variously described pulse controllers and other control elements may be implemented, grouped, and configured in a wide variety of different architectures in different embodiments. For example, in some embodiments, the pulse controller may be incorporated into a motor controller or inverter controller, or may be provided as a separate component. Similarly, in a generator, the pulse controller may be incorporated into a generator controller or rectifier controller, and in a combined motor / generator, the pulse controller may be incorporated into a combined motor / generator controller or combined inverter / rectifier controller. In some embodiments, the described control functions may be implemented algorithmically in software or firmware running on a processor. The processor may take any suitable form, including, for example, a general-purpose processor, a microprocessor, a DSP, or the like.

[0105] In general, schemes for pulsed motor control can be implemented digitally, algorithmically, with analog components, or using a hybrid approach. The pulse generator and / or motor controller can be implemented as code running on a processor, programmable logic such as an FPGA (field programmable gate array), circuitry such as an ASIC (application specific integrated circuit), a digital signal processor (DSP), analog components, or other suitable hardware. In certain aspects, the described control schemes can be incorporated into object code running on a digital signal processor (DSP) incorporated into the inverter controller (and / or the rectifier controller in the context of a generator and / or combined inverter / rectifier controller).

[0106] Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims and their equivalents.

Claims

1. a pulse controller configured to pulse the electric machine between an on state during on-pulses and an off state between the on-pulses; a rotor having a rotor winding configured to be energized when the electric machine is in an on state during the on-pulses and de-energized when the electric machine is in an off state between the on-pulses; a boost circuit configured to recover energy retained in the rotor winding when energized in an on-state during the on-pulse, the boost circuit being further configured to store the recovered energy in an electrical storage device as a "boosted" voltage and to supply the boosted voltage to the rotor while the electric machine transitions from an off-state to an on-state at the beginning of the next on-pulse; Equipped with the boosted voltage energizes the rotor sooner, thereby turning the rotor on faster, thereby reducing the transition time for the electric machine to transition from an off state to an on state for the next on-pulse compared to if the boosted voltage were not supplied to the rotor during the transition; Electrical machinery.

2. 10. The electric machine of claim 1, further configured to operate in a regulated mode in which hysteresis or other type of on / off control is used to maintain a target operating current through the rotor winding at a desired level when the electric machine is in an on state during the on-pulse.

3. 3. The electric machine of claim 1, further configured to operate in a recovery mode in which energy held in the rotor winding is recovered and stored in the storage device while the electric machine transitions from an on state during the on-pulses to an off state between the on-pulses.

4. 4. An electric machine according to any preceding claim, further comprising a "topping" up mode in which additional energy from a power source is added to the boosted voltage stored in the power 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 an on-state during the on-pulse.

6. The electric machine of claim 4 , wherein the additional energy provided to the storage device occurs when the electric machine is in an off state between the on-pulses.

7. 7. The electric machine of claim 1, further configured to operate in a boost mode in which the boosted voltage is supplied to the rotor while the electric machine transitions from an off state to an on state at the beginning of a next on-pulse.

8. An electric machine according to any preceding claim, wherein the electrical storage device is a capacitor.

9. 9. The electric machine of claim 1, further comprising a rotor boost circuit controller configured to selectively control a first transistor connected to a first end of the rotor winding and a second transistor connected to a second end of the rotor winding.

10. 10. The electric machine of claim 9, wherein the rotor boost circuit controller is configured to selectively turn off the first transistor and the second transistor when charging the power storage device with the boosted voltage so that energy stored in the rotor winding flows to the power storage device.

11. 10. The electric machine of claim 9, wherein the rotor boost circuit controller is configured to use hysteretic control or other type of on / off control as needed to control a target operating current through the rotor winding at a desired level when the electric machine is in an on state during the on-pulse, by selectively turning the first transistor and the second transistor on and off to maintain the target operating current at the desired level.

12. 10. The electric machine of claim 9, wherein the rotor boost circuit controller is further configured to switch the first transistor and the second transistor on and off to enable the storage device to store additional energy from a power source in addition to the boosted voltage recovered from the rotor winding.

13. 10. The electric machine of claim 9, wherein the rotor boost circuit controller is further configured to turn on the second transistor and the third transistor to apply the boosted voltage from the storage device to the rotor winding while the electric machine transitions from an off state to an on state at the beginning of a next on-pulse.

14. 14. The electric machine of claim 1, further comprising a power supply that supplies a voltage to the rotor winding in addition to the boosted voltage at the start of a next pulse, wherein the voltage from the power supply and the boosted voltage cooperate to energize the rotor winding, respectively, while the electric machine transitions from an off state to an on state at the start of a next on-pulse.

15. 15. The electric machine of claim 14, wherein the boosted voltage from the storage device is dissipated by energizing the rotor winding while the electric machine transitions from an off state to an on state at the beginning of a next on-pulse.

16. 1. A method of operating an electric machine, comprising: (a) storing in an electrical storage device a boosted voltage derived at least in part from energy recovered from a rotor winding of the electric machine when the electric machine transitions from an on-state to an off-state during an on-pulse; (b) applying the boosted voltage to the rotor winding at the beginning of the next on-pulse when the electric machine transitions from an off state between the on-pulses to an on state during the next on-pulse; A method comprising:

17. 17. The method of claim 16, wherein the energy recovered from the rotor winding is derived from back electromotive force (BEMF) generated by the rotor winding.

18. 18. The method of claim 16 or 17, wherein the storage of the boosted voltage in the power storage device also derives at least in part from energy from a power source.

19. 19. The method of any of claims 16 to 18, further comprising applying a voltage from a power supply in addition to the boost voltage to the rotor winding when the electric machine transitions from an off state to an on state during the next pulse, the boost voltage and the voltage from the power supply acting in combination to energize the rotor winding during the transition.

20. 20. The method of claim 19, wherein the rotor winding is energized when the electric machine transitions from an off state to an on state, thereby dissipating the boosted voltage of the electrical storage device.

21. 21. The method of claim 16, further comprising repeating (a) and (b), wherein during pulsed operation of the electric machine, the electric machine transitions from an off state to an on state during each on-pulse.

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