Boost rotor power supply circuit and method for improving pulse motor efficiency

Abstract

Pulsed control of an externally excited synchronous machine (EESM) includes a boost circuit and method for (1) harvesting excitation energy stored in a rotor winding when the EESM transitions to an off-state after a turn-on pulse, (2) storing the harvested excitation energy on a storage device, (3) optionally "augmenting" the harvested excitation energy stored on the storage device, and (4) selectively "augmenting" the excitation energy stored on the storage device. And (4) when the EESM transitions to the on state in the next pulse, the collected and stored excitation energy is supplied as a boost voltage to the rotor, the boost voltage helps the rotor to rapidly overcome its starting inductance and rapidly switch on the rotor, so that the transition time from the off state to the on state is much faster at the beginning of the next pulse.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 404,103, filed on September 6, 2022, and is incorporated herein by reference for all purposes. Background Art

[0003] The present application generally relates to pulsed control of an externally excited synchronous motor (EESM), and more specifically to a boost circuit and method for (1) collecting excitation energy stored in a rotor winding when the EESM transitions to an off state after an on pulse, (2) storing the collected excitation energy in a storage device, (3) "replenishing" the stored energy to compensate for losses caused in power transfer, and (4) supplying the collected and stored excitation energy to the rotor as a "boost voltage" just as the EESM transitions to on in the next pulse, the boost voltage helping the rotor to quickly overcome its starting inductance and quickly turn on the rotor, so that the transition time from the off state to the on state at the beginning of the next pulse is much faster.

[0004] Most EESMs typically include a stator with multiple poles and a rotor that can be operated as a generator or a motor. When operated as a motor, electrical energy is converted into mechanical energy. When operated as a generator, mechanical energy is converted into electrical energy. Therefore, the terms "EESM," "motor," or simply "machine" as used herein are intended to be broadly interpreted to mean both electric motors and generators.

[0005] Electric motors have a relatively high energy conversion efficiency provided they are operated at or close to their optimal operating load. However, when operated below their optimal operating load, their energy conversion efficiency is much lower. Since in many applications electric motors are required to operate below their optimal operating load, the overall operating efficiency of the machine is lower than it could be, which means energy is wasted.

[0006] Pulse control of an electric motor is a known method of improving efficiency. Under operating conditions below the peak efficiency range of a given machine, the motor is intermittently switched from an off state to an on state during pulsed operation. By controlling the magnitude, duty cycle and frequency of the on pulses, the motor can be controlled to generate the desired output while operating only within its peak efficiency range. Thus, overall efficiency is improved compared to conventional continuous operation below the peak efficiency range of the machine.

[0007] A problem with pulsed machine control machines is that a relatively large amount of energy and time is required for each pulse to transition the rotor of a given motor from the off state to the on state.

[0008] Therefore, there is a need to quickly and efficiently transition pulse-controlled motors from an off state to an on state for each pulse, thereby operating such motors at higher efficiency levels. Summary of the invention

[0009] The present application relates to pulsed control of an externally excited synchronous motor (EESM), including a boost circuit and method for (1) collecting excitation energy stored in the inductor of the rotor when the EESM transitions to an off state after a conduction pulse, (2) storing the collected excitation energy in a storage device, (3) "supplementing" the stored energy to compensate for losses caused in power transfer, and (4) supplying the collected and stored excitation energy to the rotor as a "boost voltage" just as the EESM transitions to conduction in the next pulse, the boost voltage helping the rotor to quickly overcome its starting inductance and quickly turn on the rotor, so that the transition time from the off state to the on state at the beginning of the next pulse is much faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention and its advantages may best be understood by referring to the following description in conjunction with the accompanying drawings, in which:

[0011] Figure 1 is a graph illustrating pulsed operation of a machine according to a non-exclusive embodiment of the present invention.

[0012] Figure 2 is a functional block diagram illustrating a machine controller architecture according to a non-exclusive embodiment of the present invention.

[0013] Figure 3 is an operational flow chart illustrating steps implemented by a machine controller according to a non-exclusive embodiment of the present invention.

[0014] Figure 4A is a graph of torque versus efficiency for a machine operating at a fixed speed during the transition from zero to peak efficiency torque.

[0015] Figure 4B is the torque versus work loss relationship for an exemplary machine operating at fixed speed during the transition from zero to peak efficiency torque.

[0016] FIG. 5A to FIG. 5E Various operating modes of an exemplary circuit of an electric machine according to a non-exclusive embodiment of the present invention are respectively shown.

[0017] Figure 6 is a flow chart illustrating steps for operating a motor in pulsed operation according to a non-exclusive embodiment of the present invention.

[0018] In the drawings, like reference numerals are sometimes used to indicate like structural elements. It should also be understood that the depictions in the drawings are diagrammatic and not drawn to scale. DETAILED DESCRIPTION

[0019] 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 motors have relatively high energy conversion efficiencies. However, the energy conversion efficiency of most electric motors can vary greatly based on their operating load. Generally, when operating at or near their peak operating load, the efficiency of the motor is high. However, when operating at lower loads, the efficiency tends to be much lower.

[0020] The present application generally relates to pulsed control of electric machines (e.g., electric motors and generators) to improve their energy conversion efficiency when operating conditions permit. More specifically, under lower load operating conditions, the electric machine is pulsed and intermittently transitions between an off state and an on state during the pulse. By controlling the magnitude, duty cycle, and frequency of the pulses, the electric machine can be controlled to operate only at its higher efficiency level than conventional continuous machine control, thereby delivering a desired average torque output in a more energy efficient manner than before.

[0021] Applicant has filed and received several U.S. patents related to pulsed control of motors, including U.S. Patent 10,742,155 (TULA P200B), U.S. Patent 11,228,272 (TULA P200C), and U.S. Patent 10,944,352 (TULAP201). Each of the above-listed applications is incorporated herein by reference for all purposes.

[0022] Pulse machine control

[0023] refer to Figure 1 , which shows a graph 10 illustrating the basic operation of a pulsed machine control.

[0024] In this example, several assumptions are made, including:

[0025] The electric machine operates as an electric motor.

[0026] • As plotted along the vertical axis, the maximum torque output of the machine is 50 Nm.

[0027] The machine’s peak efficiency range is approximately 95% of its peak output, or approximately 47.5Nm of torque output.

[0028] In this example, the machine is required to generate an output torque of 10 Nm, which is well below its peak efficiency range.

[0029] Using normal operation, the machine is continuously operated to generate the required torque output of 10Nm. Figure 1 denoted by dashed line 12. A disadvantage of operating continuously at a torque output of 10 is that the machine is operating well below its peak efficiency range (eg, 47.5 Nm or more in this example).

[0030] With pulsed operation, on the other hand, the machine is pulsed on and off. Between the on pulses, the machine is off and generates almost no torque output. During the on pulses, the machine:

[0031] (1) is in the on state and operating at or near its peak efficiency (i.e., 50%); and

[0032] (2) The average torque output of the machine over time (during which the machine is intermittently pulsed between the OFF state and the ON state) is sufficient to meet the determined torque request.

[0033] In this example, the frequency of the on pulses occurs once every five (5) time units (as plotted along the horizontal axis). As a result, the machine is pulsed twenty percent (20%) of the time, as represented by pulse 14. By operating the machine at its peak output (e.g., 50) every five time units (i.e., twenty percent (20%) of the time), the required 10 Nm of torque is generated over time. However, because the machine is only operated at or near its peak efficiency during the pulses, the overall operating efficiency of the machine is significantly improved over conventional continuous operation.

[0034] Three-phase wound-field synchronous motor

[0035] In a three-phase wound field synchronous motor, the stator may include three coil windings excited by a three-phase AC input and a field winding on the rotor powered by a DC voltage supply. When the three-phase AC input passes through the three-phase armature windings, a rotating magnetic field (RMF) is generated. The rate of rotation of the RMF is called the synchronous speed (N) of the motor. s ). The interaction between the rotor field winding field and the stator winding field generates an electromotive force (EMF) that causes the rotor to rotate.

[0036] Power Converters

[0037] refer to Figure 2 , which shows a diagram of a power controller 20 for pulsed operation of an electric machine. The power controller 20 includes a power converter 22, a DC power source 24, and an electric machine 26. In this non-exclusive embodiment, the power converter 22 also includes a pulse controller 28.

[0038] Power converter 22 may operate as a power inverter or a power rectifier depending on the direction of energy flow through the system.

[0039] The rotor field is generated by applying a DC current to the rotor field windings.

[0040] When the electric machine 26 is operated as a motor, the power converter 22 is responsible for generating three-phase AC power from the DC power supply 24 to drive the electric machine 26. The three-phase input power, represented as phase A, phase B and phase C, is applied to the windings of the stator of the electric machine 26 for generating RMF as described above. In both cases, the rotor field is generated by supplying current to the rotor windings through an inverter.

[0041] During motor operation, the pulse controller 28 is responsible for selectively pulse-controlling the three-phase stator input power and rotor current provided to the motor 26. During normal (i.e., continuous) operation, the three phases A, B, and C of the stator input power and the rotor current are continuous (i.e., not pulsed). During pulsed operation, the three phases A, B, and C and the rotor current are selectively pulse-controlled.

[0042] When the machine operates as a generator, the power converter 22 operates as a power rectifier and the AC power from the machine 26 is converted to DC power and stored in the DC power source 24. The rotor field required to achieve this power transfer must be supplied by an inverter.

[0043] The line depicting phases A, B, and C is shown with arrows on both ends, indicating that current may flow from power converter 22 to electric machine 26 when the machine is operating as a motor, or in the opposite direction when the machine is acting as a generator.

[0044] The rotor current for motor driving and power generation flows from the inverter into the machine.

[0045] For rotor field energy recovery, current flows from the machine to the inverter.

[0046] Pulse machine control

[0047] refer to Figure 3 , which shows a flow chart 30 showing the steps of the pulse controller 28 in pulse controlling the electric machine 26 when operating as an electric motor.

[0048] In an initial step 32, the current machine output and the current machine speed are determined.

[0049] In decision step 34, a determination is made as to whether the machine should be operated in continuous mode or pulsed mode based on the current machine 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., Figure 1 47.5Nm in the example).

[0050] In step 36 , if the current machine torque request is above the most efficient output torque for the current machine speed, the machine is operated in the continuous mode.

[0051] In an alternative step 38 , if the current machine torque request is below the most efficient output torque for the current machine speed, the machine is operated in the pulse mode.

[0052] In step 40 , the desired pulse magnitude, duty cycle and frequency for operation in the pulse mode are determined so that the average output power or torque over time matches the desired torque output.

[0053] In step 42, the machine is operated in a pulse mode using the determined pulse magnitude, duty cycle and frequency of the pulses.

[0054] The above steps 32-42 are performed continuously while the machine is operating. At any given machine speed, there is a corresponding most efficient output torque at which the machine operates at or near its maximum efficiency. As the instantaneous machine output request and / or current machine speed changes, a decision is made to operate the machine in continuous mode or pulsed mode, as appropriate.

[0055] Conceptually, the more often the desired machine torque is lower than the most efficient output torque for the current machine speed, the more significantly the overall efficiency of the machine can be improved by pulsing the machine.

[0056] Pulse rise time

[0057] Current power converters are typically designed for continuous operation, rather than pulsed operation. Such power converters are typically required to transition from an unpowered state to an energized state relatively infrequently. As a result, to date, little design effort has been made to manage the transition time between when a machine is turned off and when it is turned on. Where any such effort has been made, the emphasis has typically been on achieving a smooth transition, rather than a fast transition. As a result, for most motors, the transition from an unpowered (off) state to an energized state is relatively slow.

[0058] Applicants have discovered that for motor systems that frequently transition from a non-energized state to a peak efficiency state, such as in pulsed operation, further efficiency improvements can be achieved when the transition occurs as quickly as possible. Utilizing fast transitions, such as from zero torque to peak efficiency torque, improves overall average efficiency because the machine spends less time in transitions where efficiency is below peak. This relationship is Figure 4A and Figure 4B Depicted in.

[0059] refer to Figure 4A , which shows a torque versus efficiency graph of an exemplary electric machine operating as a motor at a fixed speed (e.g., 6000 rpm). In the exemplary graph, a torque output range from 0.0 Nm to 250 Nm is plotted along the horizontal axis, while the efficiency of the machine from 0.0% to 100% is plotted along the vertical axis. Curve 46 depicts the transition of the machine from zero to peak efficiency torque. During this transition, as depicted by the shaded area 48, the machine operates at a much lower efficiency before reaching or approaching the peak efficiency of the machine as depicted by reference numeral 50.

[0060] refer to Figure 4B , provides a graph showing torque versus work loss for an exemplary machine operating at a fixed speed during a transition from zero to peak efficiency torque. In the graph, work loss (W) is plotted along the vertical axis, while the torque output of the machine is plotted along the horizontal axis. As shown by curve 52, during the transition from zero to peak efficiency torque, the work loss of the machine increases as the torque output increases. Therefore, the faster the transition time from zero to peak efficiency torque, the less work is done and the less energy is consumed by the motor.

[0061] By substituting time for torque along the horizontal axis and then integrating the area under curve 52, the energy consumed by the motor for a given transition time can be calculated. For example, for the exemplary machine, 7234.5 joules of energy are used in a transition time of 0.5 seconds, while only 723.4 joules of energy are used in a transition time of 0.05 seconds. This comparison shows that the faster the transition time from zero to peak efficiency torque, the lower the energy consumed in losses. It should be noted that for this example, it is assumed that no acceleration of the load occurs, and therefore no energy is added to the load. Just as efficiency is improved by reducing the rise time, efficiency can also be improved by reducing the pulse fall time.

[0062] The transition from zero to peak efficiency torque, peak efficiency torque, and work losses of the machine will vary from machine to machine. Figure 4A and Figure 4B The relationship diagrams should be regarded as exemplary only, and should not be construed as limiting in any respect.

[0063] Applied voltage and rotor current rise time

[0064] Applicants have discovered that by applying a boost voltage to the rotor at the beginning of each pulse, the time it takes for the motor to transition from the off state to the on state can be significantly reduced. By applying the boost voltage, the inherent on time determined by the inductance and resistance of the rotor is reduced, allowing the windings of the rotor to be quickly energized to the target operating current, thereby generating the desired rotor flux more quickly than without the boosted rotor voltage. The overall efficiency of a pulse-controlled motor can be significantly improved by significantly reducing the transition time from the off state to the on state (sometimes referred to as the "rise time") of each pulse.

[0065] The following equation (1) defines the current (i) in the inductor coil of a given rotor of the motor when a voltage V is applied.

[0066] Equation (1): Where R is the resistance of the rotor's coil, L is the inductance of the rotor winding (which is a function of the motor's magnetic flux), and t is time. V is the available voltage, which in the case of the rotor is equal to the applied voltage.

[0067] Equation (1) shows that we can see from this equation that there are at least two ways to improve the desired rotor current I f The rise time it takes. One we can see is by lowering the resistance R, and the second we can see is by raising the voltage V.

[0068] If R is reduced, the time constant L / R remains the same, because for a given winding slot, the resistance is a function of:

[0069] (a) slot area divided by the number of turns (where slot area is the area of ​​the lamination available for inserting copper wire); and

[0070] (b) As the length of the wire changes with the number of turns, the resistance increases with the square of the number of turns.

[0071] However, inductance also increases with the square of the number of turns. Therefore, for a given slot cross-sectional area, the L / R time constant remains constant.

[0072] Therefore, it is evident from equation (1) that by reducing the number of turns but keeping the slot filling (of the slots filled with copper) constant so as to reduce the rotor winding resistance R, the rise time of the rotor current can be reduced, thereby making the rotor turn-on time faster.

[0073] Alternatively, we can keep the same rotor winding and simply increase the applied voltage V by raising the battery voltage, thereby increasing the rise time of the rotor current.

[0074] Rotor excitation energy

[0075] During motor operation, the rotor stores energy in the rotor magnetic field. The rotor is switched on by applying a voltage V to the rotor winding. As the voltage is applied, the current in the rotor winding rises according to equation (1).

[0076] The magnetizing energy stored in the rotor magnetic circuit is defined by Equation 2:

[0077] Equation (2): Among them I f is the rotor current, and L f is the rotor winding inductance.

[0078] As explained in more detail below, the excitation energy E from the rotor is collected and then stored in a storage device (such as a capacitor). The energy storage of a capacitor is defined by the following equation:

[0079] Equation 3: E = V 2 ×C / 2

[0080] Where V is the applied voltage and C is the capacitance of the storage device in Farads.

[0081] It should be noted that the energy E in the rotor and the energy collected and finally stored on the storage device are not necessarily the same. Usually, due to circuit losses, the energy collected and stored is less than the energy in the rotor.

[0082] Boost circuit

[0083] refer to Figure 5A , which shows an exemplary rotor converter 60 of an electric machine having a boost circuit 62 and a rotor boost excitation controller 63. In much of the following explanation, the electric machine is operated as a motor.

[0084] The rotor converter 60 includes a voltage source V1 (such as a battery) coupled 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 coupled to an upper end 68A and a lower end 68B of the rotor winding L1, respectively, and a diode D1. The transistor M1, the rotor winding L1, and the transistor M2 are coupled in series between the positive power rail 64 and the negative power rail 66. The diode D1 is coupled in parallel with the rotor windings L1 and M2 between the upper end 68A of the rotor winding L1 and the transistor M1 and the negative power rail 66.

[0085] D2 is normally connected directly to the positive supply rail 68 , but for the present invention it is used to direct energy to the boost circuit 62 .

[0086] The boost circuit 62 includes the additional components of a diode D3 , a transistor M3 and a capacitor C1 . In addition to the transistors M1 and M2 , the components of the boost circuit 62 are also at least partially controlled by a boost controller 63 .

[0087] In this case, capacitor C1 is shown connected between the positive supply voltage and the boost voltage. In an alternative solution, it can be connected between the negative supply voltage and the boost voltage.

[0088] In a non-exclusive 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 for these components.

[0089] As described above, the boost controller 63 operates in conjunction with the pulse controller 28. Generally, the pulse controller 28 determines whether the machine 60 should be operated in a continuous mode or a pulse mode. If the latter, the pulse controller 28 determines the magnitude, duty cycle and frequency of the on pulses as described above, and directs the power converter 22 to energize the three phases A, B and C of the stator (not shown) of the motor accordingly.

[0090] When the motor switches to the off state, the boost controller 63 cooperates with the pulse controller 28 to operate the various components of the boost circuit 62 to collect energy from the rotor winding L1, store the collected energy, and then apply the collected energy as a "boost" voltage when the rotor is turned on with the start of the next pulse.

[0091] Specifically, the boost controller operates the motor and various components of the boost circuit 62 to:

[0092] (a) storing a boosted voltage derived at least in part from energy harvested from rotor winding L1 on storage device C1 when the motor transitions from an on state at the end of an on pulse to an off state; and

[0093] (b) When the motor transitions from the off state to the on state of the next on pulse, the boost voltage is applied to the rotor winding L1 at the start of the next on pulse.

[0094] When operating in pulse mode, the rotor converter 60 and boost circuit 62 cycle through four (4) different operating modes for each conduction pulse. By cycling through these four modes, boost energy is collected at the end of each pulse and then stored. The boost voltage is then available to be applied to the rotor along with the supply voltage V1 at the beginning of the next pulse. In this way, the transition time for each pulse is greatly reduced.

[0095] The four different modes for each on-pulse include:

[0096] 1. Regulation mode, in which the target operating current through the rotor winding L1 is maintained at a desired level using hysteresis control during the on pulse when the machine is in the on state;

[0097] 2. Field harvesting mode, when the energy E (Equation 2) of the rotor winding L1 is captured and the remaining energy E (Equation 3) after losses is stored on capacitor C1. Field harvesting mode usually occurs at the end of a pulse as the machine 60 transitions from the on state to the off state.

[0098] 3. An optional "topping up" mode, where additional energy from power source V1 is used to provide additional charge to capacitor C1. Since the collected and stored energy is subject to losses, the additional voltage can be optionally used so that capacitor C1 maintains the desired boost level voltage; and

[0099] 4. Boost mode, in which at the beginning of the next on pulse, the boost voltage stored on the capacitor C1 is supplied to the rotor winding L in addition to the voltage V1.

[0100] In addition, the magnitude of the boost voltage can be selected to achieve the desired transition time required for the rotor winding L1 to be energized and the rotor to be turned on. Generally, the larger the boost voltage, the faster the transition. In this case, when the rotor winding L1 is energized, all of the energy stored on C1 may not be transferred to the rotor winding L1.

[0101] refer to FIG. 5A to FIG. 5D , which respectively illustrate the operation of the motor 60, the boost circuit 62 and the boost controller 63 in each of the four modes.

[0102] Adjustment mode

[0103] In regulation, mode hysteresis control of transistors M1 and M2 is used to accurately maintain the target operating current of rotor winding L1 at the desired level during the conduction pulse. Figure 5A Hysteresis control may be better understood as follows.

[0104] As the on pulse begins, transistors M1 and M2 are turned on, while transistor M3 is turned off. Therefore, current flows from power supply V1 through positive power rail 64 and to negative rail 66 through diode D3, transistors M1, M2 and rotor winding L1 (as depicted by arrow 70). With both transistors M1 and M2 turned on, the current increases along the current path defined by arrow 70 at a rate determined by the impedance of the above components. As the current rises, assuming there is sufficient voltage, it will eventually exceed the target operating current. When the current exceeds the target value, transistor M1 is turned off. With M1 turned off, a back electromotive force (BEMF) is generated in the coil of rotor winding L1, causing the upper end 68A of rotor winding L1 to become negative. When this happens, diode D1 is turned on, allowing the current to decay as it flows through rotor winding L1, transistor M2 and diode D1, as depicted by circular arrow 72. Once the current decays below the target operating current, transistor M1 is turned back on, allowing the current to increase. By repeating the above operation, the target operating current through the rotor winding L1 can be accurately maintained within the duration of a given pulse.

[0105] While it is envisaged above that the control will be of the hysteretic type, it may also be of any other digital on / off control type including but not limited to fixed or variable frequency PWM only.

[0106] Collection Mode

[0107] In harvesting mode, when the motor is in the on-state, the energy held in the rotor winding L1 is captured when the transition to the off-state occurs at the end of the on pulse. After unavoidable circuit losses, the remaining energy is stored on capacitor C1. Figure 5B The collection pattern can be best understood as described below.

[0108] At the end of the on pulse, the pulse controller 28 and the boost controller 63 cooperate to turn off transistors M1 and M2. Since the rotor winding L1 is energized, the open circuit induces a BEMF in the rotor winding L1, causing the upper end 68A to become negative and its lower end 68B to become positive. Since the BEMF is greater than the supply voltage V1, current flows through the diode D1, the rotor winding L1, the diode D2 and the capacitor C1, as depicted by the arrow 74. Therefore, when the motor transitions from the on state to the off state at the end of the on pulse, most of the BEMF energy generated by the rotor winding L1 is collected and stored on the capacitor C1 and is subject to circuit losses.

[0109] Supplementary mode

[0110] In an optional boost mode, if capacitor C1 is not sufficiently charged to a suitable or desired level, power from power source V1 can be used to "boost" capacitor C1. The boost voltage stored on capacitor C1 is preferably charged to a desired level to meet the specified rotor off-to-on transition time at the beginning of the next on pulse. If the voltage charge on capacitor C1 is insufficient due to circuit losses or any other reason, voltage source V1 can be used to "boost" the capacitor with additional voltage.

[0111] In reference Figure 5C In one supplemental mode embodiment, pulse width modulation (PWM) is used to selectively turn transistors M1 and M2 on and off. Initially, both transistors M1 and M2 are briefly turned on, allowing rotor winding L1 to be energized by voltage V1 as current flows from positive rail 64 to negative rail 66 (arrow 70). Once energized, both transistors M1 and M2 are turned off, and the additional energy provided to rotor winding L1 induces a BEMF (sometimes referred to as "fly back" energy in this case) that is transferred to capacitor C1 using the current path depicted by arrow 74. As a result, the additional energy is added to the boosted voltage that has been collected and stored on capacitor C1.

[0112] Figure 5D Another method of supplementing the energy stored in capacitor C1 is shown in FIG. 1 . In this embodiment, transistor M1 remains on while transistor M2 is modulated on and off. When both transistor M1 and transistor M2 are on, rotor winding L1 of the rotor is energized. When transistor M2 is off, the BEMF of rotor winding L1 is captured on C1 via diode D2, as depicted by arrow 80. Thus, by modulating transistor M2 on and off, rotor winding L1 can be repeatedly energized and its energy collected and stored on capacitor C1. This process can be repeated until the charge on C1 reaches a desired level.

[0113] It should be noted that the Supplementary Mode can be implemented at any time during the pulsed control operation of the motor. When in the off state, there is no stator current and therefore no torque is generated. When in the on state, we draw more power from the voltage source V1 and instead of following Figure 5A As shown by arrow 72 to circulate current, both M1 and M2 are turned off, allowing some energy to return to C1 before again circulating current in a normal manner.

[0114] Boost Mode

[0115] Finally, in boost mode, if Figure 5EAs best depicted, the boosted voltage stored on capacitor C1 is applied to rotor winding L1 when the motor transitions from the off state to the on state at the beginning of the next pulse. The boosted voltage may consist solely of energy previously harvested from inductor L1, or a combination of harvested energy and the generation of any "supplemental" off voltage as explained above. Either way, the stored energy is returned to rotor winding L1 to help the supply voltage V1 quickly energize the rotor. When the boosted voltage is to be applied to rotor winding L1, transistors M1, M2, and M3 are all turned on, providing a current path (arrow 78) from capacitor C1 through inductor L1 and to negative rail 66 so that the boosted voltage can help quickly energize the rotor.

[0116] When the boost voltage is applied to the rotor, the charge on capacitor C1 is dissipated. Once sufficient or all of the energy has been delivered, voltage V1 continues to energize rotor winding L1 through D3 for the remainder of the on pulse. M3 can then be turned off.

[0117] With the above-described embodiments, most of the existing electrical components of the rotor converter 60, as well as a few additional components described herein, are used to collect, store, and apply the boost voltage. Since many of the existing elements of the rotor converter 60 are used, the benefits of faster transition times are achieved almost "for free," with little expense in additional circuitry or components.

[0118] It is further noted that the specific components mentioned herein are merely exemplary and should not be construed as limiting. Rather, any type of components may be used to implement the functions and operations of the boost circuit 62 and / or boost controller 63 described herein.

[0119] In an alternative embodiment, MOSFETs or similar switches may be used in place of diodes D1, D2, and D3, respectively. One advantage of using MOSFETs or similar switches is that they provide a low voltage drop in the on state, thereby improving efficiency. However, the use of MOSFETs or similar switches may require additional control circuitry and signals. In other embodiments, one or more of diodes D1, D2, and / or D3 may be a Schottky diode, a fast epitaxial diode, or a standard diode, or any combination thereof.

[0120] Pulse Control Operation with Boost

[0121] When the motor is operated in pulse mode, the above four modes can be repeated continuously. With each on-off cycle, the regulation mode, the collection mode and the boost mode (and the optional supplementary mode) are repeated. By repeating this process with each pulse, the overall efficiency of the motor can be significantly improved because the transition time of turning on the rotor from the off state to the on state with each pulse is significantly reduced.

[0122] refer to Figure 6 , which shows a flow chart 90 showing steps for efficiently operating an electric machine.

[0123] In an initial step 92 , the motor 60 is placed in an on state during an on pulse, and the hysteresis described herein is used to accurately regulate a target operating current through the rotor winding L1 .

[0124] In decision step 94, boost controller 93 determines when the current pulse ends.

[0125] In step 96, the boost controller 93 takes steps to harvest the BEMF energy induced in the rotor winding L1 when the motor transitions from the on state to the off state at the end of the pulse. The harvested energy is stored as a boost voltage on the storage device C1.

[0126] In optional step 98 , the boosted voltage stored on storage device C1 may optionally be supplemented.

[0127] In decision step 100 , the boost controller 93 determines whether it is time to begin transitioning from the OFF state to the ON state for the next ON pulse.

[0128] Finally, in step 102, when the motor transitions from the off state to the on state at the beginning of the next pulse, the rotor winding is energized using a combination of the supply voltage V1 and the boost voltage from the storage device C1. With the additional boost voltage, the transition time is reduced relative to the case where no boost voltage is applied.

[0129] If there is insufficient time to replenish the energy stored in C1 during step 98 , this may be done between steps 92 and 94 .

[0130] As the motor cycles between the off state and the on state, steps 92 to 102 are preferably repeated continuously for each pulse. In this way, the boost voltage is collected, stored, and applied to the rotor windings at the end of each pulse at the beginning of the next pulse. Thus, the time to transition between the off state and the on state for each on pulse is significantly reduced, thereby improving the overall operating efficiency of the motor.

[0131] Applicants have found that using the boosted voltage described herein significantly reduces the transition time from the off state to the on state compared to any non-boosted motor equivalent. As a result, the overall efficiency of such motors is significantly improved.

[0132] Generator Operation

[0133] Although the above description is primarily directed to the operation of the electric machine as a motor, this should in no way be construed as limiting. Rather, the boosted voltage to the rotor winding as described herein may also be used as a generator during pulsed control operation.

[0134] Motor Type

[0135] It should be apparent from the above description that the described boost pulse motor control can be used for motors having an external excitation field. The invention should therefore be interpreted broadly to include any such machines, and not just those explicitly mentioned herein.

[0136] Motors and Vehicles

[0137] Electric vehicles are now commonplace and growing in popularity, with some forecasting that they will surpass or completely replace traditional internal combustion engine vehicles within the next decade or two.

[0138] For electric vehicles, one or more on-board motors are provided. When driving the vehicle, the motor acts as a motor to generate torque, which is then used to propel the vehicle. In the case of an electric vehicle, the motor is used exclusively to generate the required torque. The torque can be a positive torque that propels the vehicle, or a negative torque that converts the vehicle's kinetic energy into stored electrical energy. For hybrid vehicles, the on-board motor can be used exclusively, or can be used in conjunction with an internal combustion engine to propel the vehicle. With regenerative braking, the motor is typically used to convert mechanical energy into electrical energy, which is stored in a storage device (such as a battery or capacitor). The stored energy can be used by the motor when the motor is operated as a motor, or alternatively to power other electrical appliances on the vehicle (such as air conditioning, heaters, defrosters, various lighting systems, entertainment systems, etc.).

[0139] Pulsing the onboard motor using the boost voltage described herein is expected to significantly improve efficiency. This increased efficiency can increase the vehicle's range before requiring battery charging and / or refueling, as is the case with hybrid vehicles.

[0140] Additional Embodiments

[0141] Motors used in heating, ventilation, and air conditioning (HVAC) applications are another good example of an application that can benefit from pulsed control. Several factors contribute to pulsed motor control being well suited for HVAC applications. These include the following facts: (a) motors currently used in HVAC applications are primarily induction motors that do not contain permanent magnets; (b) a high percentage of motors used in HVAC applications (particularly including variable speed HVAC condensers and / or air handlers) operate in an operating region below their high efficiency region for a large portion of the time; and (c) the inertia of the fan or pump typically dominates the motor inertia, which tends to further mitigate potential NVH-related effects associated with pulses.

[0142] Although only a few embodiments of the present invention have been described in detail, it should be understood that the present invention may be implemented in many other forms without departing from the spirit or scope of the present invention. In different embodiments, the various pulse controllers and other control elements described may be implemented, grouped, and configured in a variety of different architectures. For example, in some embodiments, the pulse controller may be incorporated into a motor controller or an inverter controller, or it may be provided as a separate component. Similarly, for a generator, the pulse controller may be incorporated into a generator controller or a rectifier controller, and in a combined motor / generator, the pulse controller may be incorporated into a combined motor / generator controller or a combined inverter / rectifier controller. In some embodiments, the control functions described may be implemented in the form of an algorithm in software or firmware executed on a processor, which may take any suitable form, including, for example, a general purpose processor and a microprocessor, a DSP, etc.

[0143] In general, pulsed motor control schemes may be implemented in digital form, in algorithmic form, using analog components, or using a hybrid approach. The pulse generator and / or motor controller may be implemented as code executed on a processor, on programmable logic such as an FPGA (field programmable gate array), in a circuit system such as an ASIC (application specific integrated circuit), on a digital signal processor (DSP), using analog components, or any other suitable hardware. In certain embodiments, the control schemes described may be incorporated into object code for execution on a digital signal processor (DSP) incorporated into an inverter controller (and / or a generator and / or a rectifier controller in the context of a combined inverter / rectifier controller).

[0144] Therefore, 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 and equivalents of the appended claims.

Claims

1. A motor, comprising: a pulse controller configured to pulse-control the motor between an on-state during an on-pulse of the motor and an off-state between the on-pulses; a rotor having a rotor winding configured to be energized during the on-pulses when the motor is in the on-state and to be de-energized when in the off-state between the on-pulses; as well as a boost circuit configured to harvest energy held in the rotor winding when powered in the on-state during an on-pulse, 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 a transition of the motor from the off-state to the on-state at the start of a next on-pulse, respectively, The boost voltage turns the rotor on more quickly by immediately energizing the rotor, thereby reducing the transition time of the motor from the off state to the on state of the next on pulse relative to a situation where the boost voltage is not provided to the rotor during the transition.

2. The electric machine of claim 1 , further configured to operate in a regulation mode, wherein when the machine is in the on-state during the on pulse, 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.

3. The motor according to claim 1 or 2, further configured to operate in a harvesting mode, wherein the energy retained in the rotor winding is harvested and stored on the storage device during a transition of the motor from the on-state during an on-pulse to the off-state between the on-pulses.

4. An electric machine according to any one of claims 1 to 3, further comprising a "boost" mode in which additional energy from a power supply is added to the boosted 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-pulse.

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

7. The electric machine according to any one of claims 1 to 6, further configured to operate in a boost mode, wherein the boost voltage is provided to the rotor during a transition of the electric machine from the off state to the on state at the start of the next on pulse.

8. An electric machine according to any one of claims 1 to 7, wherein the storage device is a capacitor.

9. The electric machine according to any one of claims 1 to 8, 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 off the first transistor and the second transistor to allow the energy held in the rotor winding to flow to the storage device when the storage device is charged 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 the target operating current through the rotor winding to a desired level by selectively turning the first transistor and the second transistor on and off as needed when the motor is in the on state during the on pulse, thereby maintaining the target operating current at the desired level.

12. The electric machine of claim 9, wherein the rotor boost circuit controller is further configured to modulate on and off of the first transistor and the second transistor so that in addition to the boost voltage collected from the rotor winding, additional energy from a power source can be stored on the storage device.

13. The motor of claim 9, wherein the rotor boost circuit controller is further configured to turn on the second transistor and the third transistor so that the boost voltage from the storage device can be applied to the rotor winding during a period when the motor transitions from the off state to the on state at the start of the next on pulse, respectively.

14. The motor according to any one of claims 1 to 13, further comprising a power supply to provide a voltage in addition to the boost voltage to the rotor winding at the start of the next pulse, the voltage from the power supply and the boost voltage acting together to energize the rotor winding during the transition of the motor from the off state to the on state at the start of the next on pulse respectively. 15 . The motor of claim 14 , wherein the boost voltage from the storage device is dissipated as the rotor winding is energized during the transition of the motor from the off state to the on state at the start of the next on pulse, respectively.

16. A method of operating an electric machine, the method comprising: (a) storing a boosted voltage on a storage device when the motor transitions from an on state during an on pulse to an off state, the boosted voltage being derived at least in part from energy harvested from a rotor winding of the motor; as well as (b) When the motor transitions from the off state between on pulses to the on state during a next on pulse, the boost voltage is applied to the rotor winding at the start of the next on pulse.

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

18. The method of claim 16 or 17, wherein storing the boosted voltage on the storage device is further derived at least in part from energy from a power source.

19. The method according to any one of claims 16 to 18, further comprising applying a voltage from a power supply to the rotor winding in addition to the boost voltage when the motor 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 when the motor transitions from the off state to the on state, the boosted voltage on the storage device is dissipated as the rotor winding is energized.

21. The method of any one of claims 16 to 20, further comprising repeating (a) and (b), and during pulsed operation of the motor, for each of the on pulses, the motor transitions from the off state to the on state.

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