Pulsed electric machine control

Abstract

To improve the energy conversion efficiency of an electric machine.SOLUTION: A variety of methods, controllers, and electric machine systems are described that facilitate pulsed control of electric machines (e.g., electric motors and generators) to improve the machines' energy conversion efficiency. Under selected operating conditions, an electric machine is intermittently driven (pulsed). A pulsed operation causes the output of the electric machine to alternate between a first output level and a second output level that is lower than the first output level. The output levels are selected such that at least one of the electric machine and a system that includes the electric machine has a higher energy conversion efficiency during the pulsed operation than the electric machine would have when operated at a third output level that would be required to drive the electric machine in a continuous manner to deliver a desired output. In some embodiments, the second output level is zero torque.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 62 / 644,912, filed on Mar. 19, 2018; No. 62 / 658,739, filed on Apr. 17, 2018; and No. 62 / 810,861, filed on Feb. 26, 2019. Each of these is hereby incorporated by reference in its entirety.

Background Art

[0002] Background This application generally relates to electromechanical control. More particularly, control methods and controller designs are described for pulsing the operation of an electromechanical device between selected operating conditions to promote operation of the electromechanical device in a more energy - efficient manner.

[0003] The term "electromechanical device" as used herein is intended to be construed broadly to mean both electric motors and generators. Electric motors and generators are structurally very similar. When an electromechanical device operates as a motor, it converts electrical energy into mechanical energy. When operating as a generator, the electromechanical device converts mechanical energy into electrical energy.

[0004] Electric motors and generators are used in a very wide variety of applications and under a wide variety of operating conditions. Generally, many of the latest electrical machines have a relatively high energy conversion efficiency. However, the energy conversion efficiency of most electrical machines can vary significantly based on their operating load. Many applications require that the electrical machine operate under a wide variety of different operating load conditions, which means that the electrical machine often does not operate as efficiently as its capabilities would allow. The nature of this problem is shown in FIG. 1. FIG. 1 is a motor efficiency map 10 that schematically shows the efficiency of a representative motor under different operating conditions. More specifically, this figure plots the energy conversion efficiency of the motor as a function of motor speed (X-axis) and the torque generated (Y-axis).

[0005] As can be seen in FIG. 1, the illustrated motor is generally most efficient when it is operating within a particular speed range and generating torque within a defined range. For the particular motor shown, the most efficient region of its operating range is in the range of approximately 4500 - 6000 RPM and has a torque output in the range of approximately 40 - 70 Nm, with an energy conversion efficiency of approximately 96%, the operating region labeled 14. Region 14 is sometimes referred to herein simply as the "sweet spot", which is the most efficient operating region of the motor.

[0006] As can be seen in FIG. 1, at any given motor speed, there will be a corresponding most efficient output torque, approximately indicated by the maximum efficiency curve 16. For any given motor speed, when the load on the motor is higher or lower than the most efficient load, the efficiency of the motor tends to drop somewhat. In some regions, for example, when the torque output drops below approximately 30 Nm in the illustrated motor, the efficiency of the motor tends to drop relatively rapidly.

[0007] If the operating conditions can be controlled so that the motor can be operated almost constantly at or near its sweet spot, the energy conversion efficiency of the motor can be extremely excellent. However, many applications require the motor to operate over a wide variety of load conditions with widely varying torque requirements and widely varying motor speeds. One such application that comes to mind is automobiles and other vehicles or mobility applications where the motor speed can vary between 0 when the vehicle is stopped and a relatively high RPM when driving around at highway speeds. The torque requirements can also vary widely at any of those speeds depending on whether the vehicle is accelerating or decelerating, going uphill or downhill, driving on relatively flat ground, etc., the weight of the vehicle, and many other factors. Of course, motors used in other applications can also be exposed to a wide variety of operating conditions.

[0008] The energy conversion efficiency of conventional electromechanical devices is generally good, but efforts continue to further improve the energy conversion efficiency over a wider range of operating conditions. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0009] SUMMARY Various methods, controllers, and electromechanical systems for facilitating pulsed control of an electromechanical device (e.g., an electric motor and a generator) to improve the energy conversion efficiency of the electromechanical device when operating conditions are guaranteed are described. More specifically, under selected operating conditions, the electromechanical device is driven intermittently (pulsed). The pulsed operation of the electromechanical device alternates the output of the electromechanical device between a first output level and a second output level lower than the first output level. The first and second output levels are such that at least one of the electromechanical device and the system including the electromechanical device has a higher energy conversion efficiency than it may have when the electromechanical device is operated at a third output level required to drive the electromechanical device in a continuous manner to deliver a desired output during the pulsed operation. In some embodiments, the second output level is zero torque (or substantially zero torque).

[0010] In some embodiments, the electromechanical device is driven in a pulsed manner when the desired output is less than a specified output level for a given motor speed, and is driven in a continuous manner when the desired motor output is greater than or equal to the specified output level.

[0011] In some embodiments, a power converter is used to control the output of the electromechanical device. Depending on the application, the power converter can take the form of an inverter, a rectifier, or other suitable power converter.

[0012] The frequency of the pulsing can vary widely with the requirements of any particular application. By way of example, in various embodiments, the electromechanical device alternates between the first and second output levels at least 10, 100, or 1000 times per second.

[0013] In some embodiments, a sigma-delta converter is used to control the pulsing of an electromechanical device. A wide variety of different sigma-delta converter architectures can be used. In some embodiments, the sigma-delta converter is a first-order sigma-delta converter. In others, a third-order sigma-delta converter is used. In still others, higher-order sigma-delta converters can be used. The sigma-delta converter can be implemented algorithmically, digitally, using analog components, and / or using a hybrid approach.

[0014] In other embodiments, a pulse-width modulation controller is used to control the pulsing of an electromechanical device.

[0015] In some embodiments, the first output level changes in accordance with a change in the current operating speed of the electromechanical device. In various embodiments, the first output level can correspond to the highest system or electromechanical energy conversion efficiency at the current operating speed of the electromechanical device, or an electromechanical output level close thereto. In some embodiments, the duty cycle of the pulsing changes in accordance with a change in the desired output.

[0016] A mechanical controller and an electromechanical system have been described for implementing all of the functionality described above. In various embodiments, the system can be configured to operate as a motor, a generator, or a motor / generator.

[0017] In various embodiments, the electromechanical device can be an induction machine, a switched reluctance electromechanical device, a synchronous AC electromechanical device, a synchronous reluctance machine, a permanent magnet synchronous reluctance machine, a hybrid permanent magnet synchronous reluctance machine, an externally excited AC synchronous machine, a permanent magnet synchronous machine, a brushless DC electromechanical device, an electrically excited DC electromechanical device, a permanent magnet DC electromechanical device, a lap-wound DC electromechanical device, a shunt-wound DC electromechanical device, a brushed DC electromechanical device, a compound-wound DC electromechanical device, an eddy current machine, an AC linear machine, an AC or DC machine flow-through machine, or an axial flux machine.

[0018] Brief Description of the Drawings The present invention and its advantages can be most deeply understood by referring to the following description in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0019]

Figure 1

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Figure 2D

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Figure 11

[0020] In the drawings, like reference numerals are sometimes used to designate like structural elements. Also, it is to be understood that the depictions in the figures are schematic and not drawn to scale. It should also be understood that the depictions in the figures are schematic and not drawn to scale.

[0021] DETAILED DESCRIPTION The present disclosure generally relates to pulsed control of electromechanical devices (e.g., electric motors and generators) that can be operated in a continuous manner otherwise, for improving the energy conversion efficiency of the electromechanical device when operating conditions warrant. More specifically, under selected operating conditions, the electromechanical device is driven (pulsed) at a more efficient energy conversion operating level to deliver a desired average torque at a higher energy efficiency than can be achieved by traditional continuous motor control.

[0022] Many types of electrical machines, including mechanical commutation machines, electronic commutation machines, externally commutated asynchronous machines, and externally commutated synchronous machines, are traditionally driven by a continuous, but in some cases varying, drive current when the machine is used as a motor to deliver a desired torque output. The drive current is often controlled by controlling the output voltage of a power converter (e.g., an inverter) that serves as the voltage input to the motor. Conversely, the power output of many types of generators is controlled by controlling the strength of the magnetic field - this can be achieved, for example, by controlling the excitation current supplied to the rotor coil by an exciter. (The exciter can be part of a rectifier or other suitable component.) Regardless of the type of machine, the drive current for a motor, or the current output by a generator, tends to be continuous.

[0023] By using pulsed control, the output of the machine is intelligently and intermittently modulated between a "torque-on" state and a "0 (no) torque" state in a way that (1) meets the operating requirements while, on the other hand, (2) improving the overall efficiency. In other words, under selected operating conditions, the electrical machine is intermittently driven at a more efficient energy conversion operating level ("torque-on" state) to deliver the desired output. During the period between pulses, the machine ideally generates or consumes no torque at all ("0 torque" state). Conceptually, this can be thought of as turning the electrical machine "off". Depending on the implementation, this can be achieved by effectively turning the electrical machine "off", for example, by interrupting the drive current to the motor or the excitation current for the generator. However, in other implementations, the electrical machine can be controlled in a way that attempts to make the torque generated by the electrical machine zero, or nearly zero, as may be practical or appropriate for a particular machine, during the "0 torque" state. Depending on the implementation, any power converter used in conjunction with the electrical machine can similarly be effectively turned off for at least part of the "0 torque" period.

[0024] As explained in the background, FIG. 1 shows the energy conversion efficiency of a representative motor. The map shown in FIG. 1 is an efficiency map for an interior permanent magnet synchronous motor used in the 2010 Toyota Prius. It should be understood that this map is merely illustrative. Similar efficiency maps can be generated for almost any electromechanical device. However, the characteristics of the map will vary with the machine being characterized.

[0025] As can be seen in FIG. 1, at any given motor speed, there will be a corresponding most efficient output torque, schematically indicated by the maximum efficiency curve 16. From a conceptual perspective, when the desired motor torque is below the most efficient output torque for the current motor speed, the overall efficiency of the motor can be improved by pulsing the motor. Conversely, when the desired motor torque is above the maximum efficiency curve 16, the motor can be operated in a conventional (continuous / non-pulsed) manner to deliver the desired torque.

[0026] FIG. 2A shows an example of pulsed motor operation. In this particular example, the desired motor torque is 10 Nm, but the most efficient torque output for the current operating motor speed is 50 Nm. Conceptually, the motor can be driven to deliver a net torque of 10 Nm by causing the motor to deliver 50 Nm of torque for 20% of the time and then 0 torque for the remaining 80% of the time. Since the motor operates at a higher efficiency when it is delivering 50 Nm than when it is delivering 10 Nm, the overall efficiency of the motor can be improved by pulsing the motor's operation in the manner described above. In the example shown in FIG. 2A, the motor generates a motor output of 50 Nm (labeled 24) for a period of 1 hour out of every 5-hour period, and then the motor is controlled to generate 0 torque during the intervening 4-hour period.

[0027] As long as the desired motor output does not exceed 50 Nm, theoretically, the desired motor output can be satisfied simply by changing the duty cycle of a motor operating at 50 Nm. For example, when the desired motor output changes to 20 Nm, the duty cycle of the motor operating at 50 Nm can be increased to 40%, when the desired motor output changes to 40 Nm, the duty cycle can be increased to 80%, and when the desired motor output changes to 5 Nm, the duty cycle can be decreased to 10%, and so on. More generally, pulsing the motor can potentially be advantageously used whenever the desired motor torque drops below the maximum efficiency curve 16.

[0028] The scale of the time unit actually used can vary widely based on the size, nature, and design requirements of any particular system. In practice, when the motor is switched relatively rapidly from the "torque on" to the "0 torque" state to achieve a specified duty cycle, the fact that the motor is actually switching back and forth between these states may not significantly degrade the performance of the motor from an operational perspective. In some embodiments, the scale of the period for each on / off cycle is expected to be on the order of 100 μsec to 0.10 seconds, for example, within the range of 20 - 1000 Hz, or 20 - 100 Hz (i.e., pulsing at frequencies within the range of 10 - 10,000 Hz), as will be described in more detail below.

[0029] The 0 torque portion of the pulse cycle could conceptually be considered to be shutting off the motor - however, in many cases, the motor may not actually be shut off during those periods, or may only be shut off for portions of the "0 torque" period.

[0030] Many electrical machines are designed to operate using alternating current. FIGS. 2B - 2D are plots showing the difference between a continuous alternating current and a pulsed alternating current that can be input into an electrical machine operating as a motor - for example, as a three - phase induction motor. In each plot, current is plotted on the vertical axis and time is plotted along the horizontal axis.

[0031] FIG. 2B shows the conventional sinusoidal three - phase input currents 42a, 42b, and 42c sent to the electrical machine. Phase B, represented by curve 42b, leads phase A, represented by 42a, by 120 degrees. Phase C, represented by curve 42c, leads phase B by 120 degrees. The sinusoidal period is τ. The three - phase input power 42 is continuous (not pulsed) and has a specified maximum amplitude of approximately 50 amperes. It should be understood that 50 amperes is merely a representative maximum current and the maximum current can have any value.

[0032] FIGS. 2C and 2D show different pulsed three - phase currents 44a, 44b, and 44c, and 46a, each having a 50% duty cycle and a peak amplitude of approximately 100 amperes Examples of two of 46b and 46c are shown. As seen in FIG. 2B, the period of the base sine wave is τ. However, this time, the sine wave is modulated on and off. Assuming, as is common, that the motor speed is the same and the torque generated is substantially proportional to the current, the output current in FIGS. 2C and 2D produces the same average torque as the continuously applied three-phase input current in FIG. 2B. The differences between the pulsed currents 44a-c and 46a-c are the respective durations of their current pulses and the alternately arranged "off" periods. In FIG. 2C, the current pulses 44a-c have alternately arranged "off" periods of equal length. The length of each on and off period is 2τ. In FIG. 2D, the current pulses 46a-c and the alternately arranged "off" periods also have equal durations in this case. In this case, the duration is τ / 2. In both examples, the duty cycle is 50%. However, the durations for the "on" and "off" times are different. That is, the frequencies of the pulse modulation are different. The frequency of the pulse modulation can vary based on the type of electromechanical device used, considerations of noise and vibration, the current operating rotor speed, and other factors.

[0033] FIGS. 2C-2D show applications where the "on" motor drive pulses are evenly spaced and the motor is operated at the desired output level in a steady state. Such an approach works well in many situations but is not a requirement. The duty cycle does not have to be 50% and can be adjusted to match the desired average output torque. Also, the phase of the on / off pulses does not have to be synchronized with the phase of the applied AC power. Therefore, the relative size and / or timing of the motor drive pulses can be changed as long as they average out to deliver the desired average torque.

[0034] Power Converter and System Efficiency There are a wide variety of different electric machines, and each machine has its own efficiency characteristics. Further, at different operating speeds, the electric machines will have different efficiency curves, as should be apparent from the general review of FIG. 1. Thus, the operating regions in which pulse-width control can bring about efficiency improvements will vary significantly based on factors including the characteristics of a particular electric machine and the current operating rotor speed.

[0035] When an AC electric machine is used in conjunction with a battery or other DC power source / sink (storage device), a power converter (e.g., an inverter and a rectifier) will typically be used to convert between DC and AC power. For example, an inverter is used to convert power received from a DC power source such as a battery or a capacitor into AC input power applied to a motor. Conversely, a rectifier is used to convert AC power received from an electric machine operating as a generator into DC output power. Some power converters can function as either an inverter or a rectifier, depending on whether the electric machine is functioning as a motor or as a generator.

[0036] The energy conversion efficiency of a power converter will also typically vary over the operating range of the converter. For example, FIG. 5 is to be understood as an inverter energy conversion efficiency map for the inverter of the 2010 Toyota Prius (i.e., the inverter for the motor shown in FIG. 1). The illustrated inverter has very good energy conversion efficiency, but its efficiency also drops significantly, most notably in a particular region - at lower torque outputs and at lower motor speeds. Therefore, when optimizing the control of a motor, which is a composite part of an inverter / electric motor, it is desirable to consider the energy conversion efficiency of the entire inverter / electric motor system, as opposed to the energy conversion efficiency of the motor alone. Similarly, when optimizing the control of a generator, which is part of a rectifier / generator system, it is desirable to consider the energy conversion efficiency of the entire rectifier / generator system, as opposed to the energy conversion efficiency of the generator alone.

[0037] Preferably, the pulsed control of the electromechanical device will be modeled to account for the efficiency of any / all of the components that affect energy conversion during pulsing. For example, when power for an AC electric motor is drawn from a battery, in determining the motor drive signal that delivers the best energy conversion efficiency, in addition to the inverter and motor efficiency, the battery power delivery efficiency, wiring losses between components, and any other loss factors can be considered.

[0038] Generally, the overall energy conversion efficiency of a power converter / electromechanical system is a function of the product of the converter conversion efficiency · times · the electromechanical conversion efficiency · times · the delivery efficiency of the other components. Therefore, it should be understood that the parameters of the pulsed drive signal having the maximum system energy conversion efficiency may be different from the parameters that can provide the best energy conversion efficiency for the motor itself.

[0039] FIG. 6 is a representative energy conversion efficiency map for a composite inverter / AC electric motor. More specifically, FIG. 6 shows the combined efficiency of a Tesla inverter / motor propulsion system. Since the inverter and the electric motor cooperate, the best overall electric motor system energy conversion efficiency can be optimized by selecting the pulse voltage and the corresponding duty cycle based on the combined system energy conversion efficiency map, rather than using the energy conversion efficiency map of the electric motor alone.

[0040] Often, the energy conversion efficiency map for a particular electromechanical system (e.g., a hybrid power converter / electromechanical, battery / power converter / electromechanical, etc.) can be more complex than the efficiency map for the electromechanical itself. Therefore, there can be local efficiency peaks above the maximum efficiency curve. That is, at a given motor speed, an operation at a particular torque output above the "maximum" possible efficiency for operation at that motor speed, although above the maximum efficiency curve, can be more efficient than the range of intermediate torque outputs below that particular torque output. There can be a region of the energy conversion efficiency map where this occurs. One such region is designated 61 in FIG. 6. When the energy conversion efficiency map has this kind of topography, it should be understood that a pulsed operation at the local efficiency peak can be more efficient than a continuous operation at those intermediate output levels. In such a situation, the motor can be pulsed at the level of the local efficiency peak to deliver such an intermediate torque output.

[0041] Pulsation System Control FIG. 3 shows a control architecture suitable for controlling an electromechanical in the manner described above. In this embodiment, system 100 includes a machine controller 110, a pulse controller (pulse generator) 120, a power source / sink 130, a power controller / converter 140, and an electromechanical 160. Pulse controller 120 is tasked with controlling / instructing the timing of the pulsation of electromechanical 160 when a pulsation operation is required. In the embodiment shown in FIG. 3, the pulse controller is shown as a separate component from machine controller 110 to facilitate the description of its function. However, in various embodiments, the pulse controller can be implemented as part of machine controller 110, as a separate component, as part of power controller / converter 140, or in other suitable forms.

[0042] When the electromechanical device 160 is operated as a motor, the machine controller functions as a motor controller, and the power controller / converter 140 is tasked with converting the power 132 received from the power source 130 into a form suitable for driving the motor 160. Conversely, when the machine 160 is operated as a generator, the machine controller 110 functions as a generator controller, and the power controller / converter 140 converts the power received from the generator into a form suitable for delivery to the power sink 130. In embodiments where the power source / sink can directly supply or receive power in the form required by or output by the electromechanical device, the power controller 140 can conceptually take the form of a switch or logical AND gate that simply turns the motor on and off to facilitate the desired pulsing.

[0043] The power source / sink 130 can take any suitable form. In some implementations, the power source / sink can take the form of a battery or capacitor. In other implementations, the supply source can be a power grid (e.g., "wall power"), a solar power system, or any other available supply source. Similarly, the sink can be an electrical load (a mechanically or electrically operated machine or device, a building, a factory, a residence, etc.), a power grid, or any other system that uses or stores power.

[0044] The power controller / converter 140 can also take a wide variety of different forms. When the power source / sink 130 is a DC power source and the electromechanical device 160 is an AC motor, the power controller / converter 140 can take the form of an inverter. Conversely, when the power source / sink 130 is a DC power sink and the electromechanical device 160 is an AC generator, the power controller / converter 140 can take the form of a rectifier. When both the power source / sink 130 and the electromechanical device are AC components, the power controller / converter 140 can include a bidirectional or four-quadrant power converter.

[0045] In FIG. 3, the required output is labeled 113, the torque sent or received by the electromechanical device is labeled 161, and the motor / generator speed is labeled 164. In some embodiments, the machine controller 110 serves as a (e.g., in the form of a look-up table) data structure 115 that defines a pulsed operation map for the operating regions where pulsed motor control is desired and / or appropriate, and for specific duty cycles suitable for specific operating conditions.

[0046] Once the desired duty cycle is determined, the duration and nature of the pulses used to drive the motor can be determined / generated in a variety of ways. As will be described in more detail below, one relatively simple approach is to use a pulse width modulation (PWM) controller as the pulse controller 120.

[0047] In FIG. 3, the logical multiplier 123 is shown as multiplying the pulsed control signal 124 by the power level signal 119 output by the machine controller 110 to create the power converter control signal 128. The logical multiplier 123 is shown for illustrative purposes; it should be understood that in practice, the function of the multiplier 123 can be achieved by the machine controller 110, by the power converter 140, or in other suitable ways. For example, in some embodiments, the machine controller 110 can set the output of the power converter 140 to simply 0 during the "off" phase of the duty cycle and to the desired operating output level (e.g., the most efficient output level for the current machine speed) during the "on" phase of the duty cycle.

[0048] FIG. 4 shows a control flow that can be performed by the machine controller 110 to efficiently deliver the desired torque to the electromechanical device 160. For simplicity of explanation, one embodiment where the electromechanical device 160 functions as a motor is described. In this configuration, the power source / sink 130 serves as a power source and the machine controller 110 functions as a motor controller.

[0049] First, the motor controller 110 receives any required motor state information such as the currently requested motor output 113 and the current motor speed 164, as represented by block 171. Next, the motor controller 110 determines, as represented by decision block 172, whether the requested output is within the pulse control range. This determination can be made in any desired manner. As an example, in some embodiments, a look-up table 115 or other suitable data structure can be used to determine whether pulse control is appropriate. In some implementations, a simple look-up table can identify the maximum torque level at which pulse control may be suitable for various motor speeds. In such an implementation, the current motor speed can be used as an index into the look-up table to obtain the maximum torque level at which pulse control is appropriate for the current operating conditions. Next, the obtained maximum torque value can be compared to the requested torque to determine whether the requested output is within the pulse control range.

[0050] In other embodiments, the look-up table 115 can provide additional information such as a desired duty cycle for pulse operation based on the current operating conditions. In one such implementation, the motor speed and torque request can be used as indices for the look-up table, each entry in the look-up table indicating a desired duty cycle, and interpolation being used to determine the operating duty cycle when the actual torque and / or motor speed is between the index values shown in the table.

[0051] If the required torque / current operating conditions are outside the pulse control range for any reason, then traditional (i.e., continuous / non-pulsed) motor control is used, as represented by the "No" branch flowing from block 172. Therefore, pulsing is not used, and the power converter 140 is instructed to send power to the motor 160 at a level suitable for driving the motor to deliver the required output 113 in a conventional manner, as represented by block 174. Conversely, if the required torque / current operating conditions are within the pulse control range, then pulse control is utilized, as represented by the "Yes" branch flowing from block 172. In such an embodiment, the motor controller 110 will instruct the power converter 140 to send power to the motor in a pulsed manner. During the "on" pulse, the power converter 140 is instructed to send power - typically, (although not necessarily) at a preferred output level that may be at or near the maximum efficiency operating level for the current motor speed - During the "off" pulse, the motor ideally outputs zero torque. In some embodiments, the timing of the pulsing is controlled by the pulse controller 120, as will be described in more detail below.

[0052] To facilitate the pulsing operation, the motor controller 110 determines a desired output level (block 175) and a desired duty cycle (block 176) for the pulsing operation at the current motor speed (this is preferably at or near the maximum efficiency energy conversion output level of the system at the current motor speed - however, other highly energy-efficient levels can also be used as required). Next, the motor controller and the pulse controller instruct the power converter to implement the desired duty cycle at the specified power level (block 178). Conceptually, this can be achieved by effectively turning the power supply on and off at a relatively high frequency such that the proportion of time during which power is supplied to the motor corresponds to the desired duty cycle and the power level corresponds to the preferred output level. In some embodiments, the "off" portion of the duty cycle can be implemented by instructing the power controller / converter 140 to drive the motor to deliver zero torque.

[0053] The frequency at which the power is pulsed is preferably determined by the machine controller 110 or the pulse controller 120. In some embodiments, the pulsing frequency can be fixed for all operations of the motor, while in others it can vary based on operating conditions such as motor speed, torque requirements, etc. For example, in some embodiments, the pulsing frequency can be determined through the use of a look-up table. In such embodiments, appropriate indices such as motor speed, torque requirements, etc. can be used to look up the appropriate pulsing frequency for the current motor operating conditions. In other embodiments, the pulsing frequency is not necessarily fixed for any given operating condition and can vary as defined by the pulse controller 120. This type of variation is common when using sigma-delta conversion in the determination of the pulses as described later. In some specific embodiments, the pulsing frequency can vary proportionally as a function of the motor speed, at least within some operating regions of the motor.

[0054] ​FIG. 4 sequentially shows some of the steps to facilitate a clear understanding of the functionality provided, but it should be understood that many of the steps can actually be combined and / or the order changed. For example, the entries in the multidimensional look-up table 115 that use the required output 113 and the current electric motor speed 164 as indices can indicate both a preferred output level and a duty cycle suitable for the current operation.

[0055] In some embodiments, a value stored in the look-up table (such as a 1 (100%) duty cycle or other suitable wild card) can optionally be used to indicate that pulsing is not desired. Of course, a wide variety of other conventions and data structures can be used to provide the same information.

[0056] In some embodiments, the pulsing control table can be incorporated into a larger table that defines the operation at all levels, so that the operation flow is the same regardless of whether conventional control or pulsing control is desired. Conventional control is simply defined by a duty cycle of 1 and an appropriate motor input power level, and it is desired that pulsing control be defined by the use of a smaller duty cycle and a preferred motor input power level.

[0057] In some embodiments, in some operating regions, it may be desirable to avoid the use of pulsing, even when an efficiency improvement is possible, based on other considerations. As will be explained in more detail below, these other considerations can be based on factors such as noise and vibration, the actual switching ability of the controller, etc.

[0058] The machine controller described herein can use software or firmware executed on a processing unit such as a microprocessor, use programmable logic, application specific integrated circuit It can be implemented in a variety of different ways, including using an ASIC, using individual logic, etc., and / or using any combination of the above.

[0059] It is worth noting that in many situations, existing electromechanical and mechanical controllers can be easily retrofitted to obtain the above benefits. For example, many mechanical controllers are implemented using software or firmware executed on a processing unit that originally has access to control input parameters (such as required motor output and current motor speed) suitable for use in the above control. In such cases, it may be possible to obtain significant efficiency improvements by installing a relatively simple software update.

[0060] Pulse generation As suggested above, once the desired duty cycle is determined, the duration and nature of the pulses used to drive the motor can be determined / generated in a variety of ways. One relatively simple approach is to use a pulse width modulation (PWM) controller as the pulse controller 120.

[0061] Pulse width modulation is generally used in certain types of motor control, including AC electric motor control and DC brushless motor control, but it should be noted that such pulse width modulation is used in very different places in the control scheme. Specifically, when an AC induction motor is powered by a battery (providing DC power), an inverter is typically used to facilitate the conversion of DC power to AC power. Generally, a PWM controller (not shown) is used as part of the inverter controller to control the amplitude of the AC signal generated by the inverter. The continuous AC power generated by the inverter is then supplied to the electric motor at the desired frequency and amplitude. The PWM controller is similarly used in a brushless DC motor to control the amplitude of the continuous signal supplied to the motor.

[0062] The pulsed power utilized herein is very different. Specifically, the power converter 140 is controlled to periodically switch between generating high-efficiency torque output (e.g., peak efficiency torque) and zero torque in the electromechanical device 160 as described above with reference to FIGS. 2A-2D. In an induction motor, as a result, the magnetic flux in the motor windings effectively drops to zero.

[0063] Traditional pulse width modulation will function in many applications, but a potential drawback is that the pulsing can generate undesirable vibrations or noise when the motor and / or power supply is turned on and off. The steady-state operation of the motor in the same pulse cycle over a period is particularly prone to such vibrations. There are numerous methods for reducing such risks, including some that will be described in more detail below. Another approach is to add some dither to the commanded pulse cycle.

[0064] As suggested above, the per-cycle period (or conversely the pulsing frequency) during the pulsing operation can vary widely in the range from a few microseconds to several tens of seconds or more, based on the design requirements and the nature of the system being controlled. Various factors will influence the selection of the cycle period. These include factors such as the motor's capabilities and characteristics, the transient effects associated with switching, concerns about potential NVH (noise, vibration, and harshness), the expected operating load, etc. Generally, the pulsing frequency selected for any particular application will involve trade-offs including factors such as NVH considerations, the required responsiveness of the electromechanical device, and the efficiency losses associated with pulsing. For example, in some automotive applications, pulsing frequencies on the order of 20 Hz to 1000 Hz are thought to function well.

[0065] Sigma-delta control Next, referring to FIG. 7, another embodiment of the pulse generator is described. The illustrated architecture is similar to the architecture shown in FIG. 3, except that in this embodiment, the sigma-delta converter 190 is used as the pulse generator 120. As can be understood by those skilled in sigma-delta control, the characteristics of sigma-delta control are such that it tends to facilitate noise shaping, reduce / eliminate idle tones, and push noise to higher frequencies. When the noise is randomized and / or spread to frequencies above the limits of human perception, such noise and / or vibration are no longer bothersome to the user of the motor, so the noise is less of a concern. Thus, in the context of automotive electric motor applications, the use of sigma-delta control tends to reduce the likelihood that vehicle occupants will perceive noise or vibration due to the pulsed motor control. Noise or vibration.

[0066] A wide variety of different sigma-delta converters can be used as the sigma-delta converter 190, and the sigma-delta converter can utilize various different feedback schemes. As an example, first-order sigma-delta conversion works well. One particularly desirable feature of using a first-order sigma-delta converter is that the controller is inherently stable. Although the first-order sigma-delta converter works well, it should be understood that in other embodiments, higher-order sigma-delta converters (e.g., sigma-delta converters that utilize more integrators than a first-order sigma-delta converter) can be used. For example, a third-order sigma-delta converter (e.g., as a converter using the Ritchie architecture), or a higher-order sigma-delta converter can be used.

[0067] Generally, a sigma-delta converter can be implemented algorithmically, digitally, using analog components, and / or using a hybrid approach. For example, in various embodiments, a sigma-delta converter can be implemented on a processor, on programmable logic such as an FPGA, within circuitry such as an ASIC, on a digital signal processor (DSP), using analog, digital, and / or hybrid components, or using any other suitable combination of hardware and / or software. In various embodiments, a sigma-delta controller can utilize sample-data sigma-delta, continuous-time sigma-delta, differential sigma-delta, or any other suitable sigma-delta implementation.

[0068] U.S. Patent No. 8,099,224 and U.S. Patent Application Publication No. 2018-0216551, which are hereby incorporated by reference in their entirety, describe a number of representative sigma-delta converter designs. The applications described therein are for controlling different types of power plants, but similar types of converters can be used for the present application.

[0069] Next, referring to FIG. 8, a representative first-order sigma-delta converter 200 will be described. The first-order sigma-delta converter 200 includes a differential amplifier 201, an integrator 203, and a comparator 205. The differential amplifier 201 amplifies the difference between the input signal 209 and the feedback signal 212, and outputs a difference signal 216 that is supplied to the integrator 203. The integrator 203 integrates the difference signal and outputs an integrator output signal 217 that is supplied to the comparator 205. The comparator 205 serves as a one-bit quantizer and outputs a pulsed (high / low) digital control signal 220 that represents the input signal 209. The one-bit control signal 220 output from the comparator 216 is generated by comparing the output of the integrator 203 with a reference voltage. The output is effectively a stream of 1s and 0s that is output at the frequency of the clock of the sigma-delta converter. The low signal is treated as a request for zero power from the power supply, and the high signal is treated as a request for the most efficient (or other specified) power level for the current motor speed.

[0070] Generally, to ensure high-quality control, the clock signal 226 for the sigma-delta converter (and hence the output stream of the comparator 205) desirably has a frequency that is many times the expected frequency of the rate of change of the input signal 209 to provide good resolution and oversampling of the input signal. Generally, for automotive-type applications where the input signal (generally based on the driver's torque demand - e.g., the accelerator pedal) tends to change at a rate of less than 5 Hz, clock frequencies on the order of 100 kHz to 1 MHz or higher work well. That is, the output of the comparator 205 is sampled at a rate of at least 100 kHz to 1 MHz (although in various embodiments, both higher and lower sampling rates may be used). The clock signal 226 provided to the comparator 216 can come from any suitable source. For example, in some embodiments, the clock signal 226 is provided by a crystal oscillator.

[0071] In various embodiments, the comparator 205 may be configured to enforce the desired constraints on the pulsing (which is sometimes referred to herein as functionally acting as an intelligent comparator). In a simple example, as may be understood by those skilled in high - degree sigma - delta control, the comparator may be constrained to define minimum and / or maximum “on” times, minimum (and / or maximum) “off” times, etc. Such constraints can help ensure that the pulsing is performed within the parameters of the desired frequency and “on” pulse length. In other embodiments, more advanced constraints may be imposed by the comparator. For example, if desired, a pulse cycle dither 223 can be added to the comparator.

[0072] In some embodiments, it may be desirable to anti - alias filter the input signal 209 and the feedback signal 212. The anti - alias functionality can be provided as part of the sigma - delta control circuit, or it can be provided as an anti - alias filter preceding the sigma - delta control circuit, or it can be provided in any other suitable form. In some third - order analog continuous - time sigma - delta control circuits, the first integrator provides the anti - alias functionality. That is, it effectively acts as a low - pass filter.

[0073] In other embodiments, a variable clock based on the motor speed may be used instead of the fixed clock. Such a configuration is schematically shown in the sigma-delta converter of FIG. 8 that uses a variable clock based on the motor speed. Specifically, the clock signal is configured to vary proportionally with the motor speed. The use of a variable speed clock when the motor is operating at high speed has the advantage of ensuring that the output of the comparator is more favorably synchronized with the motor speed. This can, in turn, help to simplify the overall design of the converter. The clock can be easily synchronized with the motor speed by utilizing a phase-locked loop 229 driven by an indication of the motor speed (e.g., a tachometer signal). Next, a multiplier 231 may be used to multiply the motor speed signal 164 to achieve the desired sampling speed. The multiplication of the motor speed can vary widely based on the requirements of any particular system. As an example, for some applications, a frequency multiplication on the order of 10 to 1,000,000 times, such as 10,000 times, may be appropriate. In another example, a sigma-delta clock speed on the order of 1 kHz to several hundred kilohertz is considered suitable for many automotive applications.

[0074] The problem with using a motor speed-based variable clock approach is that it does not work very well when the motor is stopped or operating at a particular low motor speed. Several different techniques can be used to mitigate such limitations. As an example, a fixed clock can be used when the motor is stopped and / or operating at a speed below a specified idle threshold (e.g., less than 600 RPM). In other embodiments, a functionally intelligent comparator having specified start and stop routines or switching to a different operating mode during low-speed operation may be used. In yet other embodiments, a non-linear RPM clock may be used for operation at lower speeds.

[0075] There are several ways to configure the sigma-delta converter 200. In one embodiment (similar to the embodiment shown in FIG. 8), the input signal 209 is the desired motor duty cycle. In this embodiment, the feedback signal 212 is the pulsed digital control signal 220 corresponding to the pulsed control signal 124 from FIG. 7. In this embodiment, the pulsed control signal 220 represents the desired motor duty cycle.

[0076] In another embodiment (not shown), the input signal 209 can be considered to represent the desired torque or desired torque ratio, and the feedback signal can be based on the torque output of the motor 161 instead of the pulsed digital control signal 220. In such an embodiment, the feedback better represents the actual torque output of the motor than the pulsed control signal 220 in order to account for any potential torque losses or inefficiencies resulting from the feedback causing the power supply and motor to switch back and forth between the zero and most efficient (or other desired) operating states. In still other embodiments, the feedback signal 212 can be a scaled combination of the pulsed control signal 220 and the torque output of the motor 161. When higher-order sigma-delta converters are used, the pulsed control signal, the motor torque output, or both can be used as feedback sources to provide differently scaled feedback to different integrators as needed for the desired adaptive control.

[0077]

[0078] As suggested above, a first-order sigma-delta converter (like all sigma-delta converters) helps push noise to higher frequencies. However, first-order sigma-delta conversion is not immune to the generation of - idle tones that can be a source of unwanted noise or vibration. One way to help minimize or eliminate idle tones is to add dither to the system. Such dither can be added at many places within the system. In the embodiment shown in FIG. 8, an optional pseudo-random dither generator 223 (shown in dashed lines) may provide an optional dither signal 224 as an additional input to differential amplifier 201. In other embodiments, the dither may instead be introduced at other places within the sigma-delta converter 200, for example, as an additional input to comparator 205. Higher-order sigma-delta converters are less susceptible to the effects of idle tones and thus there is less benefit to adding dither to such systems. Thus, typically, dither will not be used in such systems (although it is possible to do so).

[0079] In the embodiments described above, pulse-width modulation and sigma-delta conversion are used to generate a pulsed control signal. Pulse-width modulation and sigma-delta conversion are two types of converters that can be used to represent an input signal. Some of the sigma-delta converters described above exhibit oversampled conversion and in various alternative embodiments, other oversampled converters can be used in place of sigma-delta conversion. In still other embodiments, other types of converters can likewise be used. The converter can employ a wide variety of modulation schemes, including various pulse-height or pulse-density modulation schemes, code division multiple access (CDMA)-oriented modulation, or it is to be understood that other modulation schemes can be used to represent the input signal as long as the pulse generator is appropriately adjusted.

[0080] As can be appreciated by those skilled in the art, switched reluctance motors are powerful motors that are relatively inexpensive when compared to similarly sized induction motors. However, switched reluctance motors tend to be noisy and susceptible to vibration due to their switching, which makes them unsuitable for use in many applications. A feature of sigma-delta conversion is its ability to shape noise and push it to frequencies that are less annoying (or annoying) to humans. Therefore, controlling switched reluctance motors in a pulsed manner using sigma-delta or other noise shaping conversion techniques has the potential to make the use of switched reluctance motors practical in many applications where they are not currently used.

[0081] Transition Control The inherent inductance of the motor temporarily reduces the current / power step between the on and off motor states. The transient effects can be delayed / slowed down incrementally. During continuous (non-pulsed) operation, these transient effects tend to have a relatively minimal impact on overall motor operation. However, when high speed pulsing is used as contemplated herein, the transient effects can have a larger net impact, and therefore there is a stronger motivation to focus on motor responsiveness. The nature of this challenge is explained with reference to Figures 9A-9B.

[0082] As described above, the general goal of pulsed motor control is to operate (feed power to) the motor at its most efficient level for the current motor speed during the motor "on" period, and to cut off power (provide zero torque) during the motor "off" period. Therefore, ideally, the power transition between the "on" and "off" states of the motor power can be a discrete step. This is schematically shown in FIG. 9A, which shows the ideal / desired motor drive power for pulsed motor control at a 50% duty cycle. As can be seen in FIG. 9A, the transition between the "on" pulse 302 and the "off" period 304 is ideally a step. In reality, there are inductive aspects of both the motor and the inverter (when used) that slow down the rise and fall of the power signal. The actual response of a particular motor will vary widely with the electrical characteristics of the motor. Generally, the actual input power to the motor will rise and fall somewhat exponentially in response to the step changes in the commanded motor drive power. FIG. 9B schematically shows the nature of the rise and fall. As can be seen in the figure, there is a ramp-up period (rise time) 306 required for the power signal to actually rise from 0 to the desired "on" power level, and a ramp-down period (fall time) 308 required for the power signal to actually fall from the "on" power level to 0.

[0083] During the power lamp-up and lamp-down periods, the motor continues to be driven. However, during those periods, as can be readily understood with reference to FIG. 1, the operation of the motor decreases in efficiency in a changing manner. Generally, for most given operating speeds, the motor efficiency will decrease as the operating power drops from the maximum efficiency line 16 towards 0, and the energy conversion efficiency deteriorates significantly as the power level approaches 0. Therefore, the pulse distortion represented by the power lamp-up and lamp-down periods impairs the efficiency improvement that can be obtained by the above-described pulsed operation. Generally, the smaller the ratio of the rise / fall time to the pulse length, the smaller the impact of the transient switching effect on the energy conversion efficiency of the motor during pulsing.

[0084] It should be understood that the transient effect shown in FIG. 9B is shown for the purpose of exemplifying the nature of the problem and does not necessarily reflect the rise / fall times associated with the operation of any particular motor. The relative scale of the ratio of the rise time to the pulse length can vary widely based on the available supply voltage, and the characteristics of the motor being used (which primarily define the rise and fall times), the frequency of pulsing (which is primarily defined by the control method being used), and the pulse width (which is defined by the control method and the motor load). When the pulsing is slow compared to the motor response, the rise / fall times can be a small fraction of the pulse width, and the impact of the transient switching effect on the motor performance can be minimized. Conversely, when the pulsing is very fast and / or the motor response is slow, the ratio of the rise / fall time to the pulse width can be extremely large and can even exceed the pulse width. If not carefully controlled, the transient efficiency losses associated with switching can significantly reduce or even eliminate the theoretical improvement achievable by the pulsed operation. Therefore, it is important to consider the transient switching effects associated with the pulsed operation when determining the appropriate pulsing frequency and control method for any particular application.

[0085] To improve the power rise and fall times, a number of techniques can be used. For example, in some embodiments, a resonant capacitor based on the motor inductance is employed. The resonant capacitor can be used to reduce the power rise and fall times by a factor of 100 or more (and in many cases substantially more), and thus they can significantly reduce the transient switching effects associated with the pulsed operation. Therefore, it should be understood that motors designed with pulsed control in mind or modified to improve the motor's transient response to power pulses can benefit even more from pulsed operation than existing motors.

[0086] In other embodiments, a boost converter and / or a buck - boost converter can be used to significantly reduce the rise and fall times associated with switching between the "on" and "off" motor states. In a particular example, the boost converter can charge a boost capacitor (sometimes referred to herein as a kick - start capacitor) to a voltage higher than the motor's input voltage. Each time the motor is pulsed on, the kick - start capacitor applies a higher voltage to the motor, which can significantly shorten the rise time.

[0087] Similarly, a buck - boost converter can be used to charge a buck - boost capacitor. Each time the motor is pulsed off, the buck - boost capacitor can store energy from the magnetic field of the motor windings, which can significantly shorten the transient fall time of the pulse.

[0088] The voltage charge levels and capacitances of the boost and buck-boost capacitors are each appropriately selected for the motor and its inductive and resistive characteristics so as to shorten the transient rise / fall times respectively associated with pulsing the motor on and off. Preferably, the respective capacitances and charge voltage levels of the boost and buck-boost capacitors are also selected to maximize the overall motor efficiency during pulsing, taking into account all aspects including the inefficiencies associated with the transient events themselves, as well as any overshoot effects that may occur due to the use of the boost and buck-boost converters. Since the boost and buck-boost capacitors are used to improve the transient response, they can each be recharged looking at the machine during the period between their respective uses - for example, during the motor off period.

[0089] Another factor particularly relevant to losses during the motor "off" transient event is associated with the dissipation of energy stored in the magnetic field. Generally, whenever the motor is operating, there will be an electromagnetic field established within the motor. The electromagnetic field encompasses a certain amount of energy stored in the magnetics. When the motor is simply turned off, the stored energy will dissipate, resulting in a loss of energy present in the magnetic field. Any such energy loss decreases the overall system efficiency. Some of the energy in the field can be recovered by actively controlling the motor's off transient event to deliver zero torque during the "off" cycle, rather than simply cutting off the supply of current to the motor to effectively turn it off. This causes some "reverse" current flow back from / to the windings to the power converter 140, thereby allowing at least some of that energy to be recovered. This means that the lost energy is reduced, thereby improving the efficiency of the system. Further, in many applications, controlling the power converter 140 to deliver zero torque (as opposed to simply turning off the power converter) will result in a faster transition.

[0090] Similarly, during the "off" cycle of the generator, the power drawn from the generator can be controlled to efficiently manage the capture of the stored energy accumulated in the motor during the "on" cycle. It can be controlled to.

[0091] FIG. 11 shows a power converter / controller incorporating a transient control circuitry mechanism 343 (which may include a resonant circuit, boost and buck-boost circuits, and / or other transient response improvement circuits, together, alone, or in any suitable combination). In the illustrated embodiment, the mechanical controller 310 instructs the pulsed control of the power converter / controller 340 - which in turn controls the electromechanical 160. The transient control circuitry mechanism 343 is incorporated within the power converter 340 itself. In other embodiments, the transient control circuitry mechanism may be provided as an additional unit disposed between the power converter 340 and the motor / generator, or incorporated within the motor / generator itself (not shown) to achieve the same functionality.

[0092] Motor Types and Applications From the above description, it should be apparent that the pulsed mechanical control described above can be utilized in a variety of different applications to improve the energy conversion efficiency of a variety of different types of electric motors and generators. These include both AC and DC motors / generators.

[0093] Some representative types of electric machines that can benefit from the pulsed control described above include induction machines (IM), switched reluctance machines (SMR), synchronous reluctance machines (SynRM), permanent magnet synchronous reluctance machines (PMa Both asynchronous and synchronous AC electrical machines are included, such as interior permanent magnet synchronous reluctance machines (SynRM), hybrid PMaSynRM, externally excited AC synchronous machines (SyncAC), permanent magnet synchronous machines (PMSM), eddy current machines, AC linear machines, AC and DC machine axial flow machines, axial flux motors, etc. Representative DC electrical machines include brushless types, electrically excited types, permanent magnet types, lap-wound types, shunt-wound types, brushed types, compound-wound types, and others.

[0094] The structures, controls, and energy conversion efficiencies of various types of electric motors and generators vary significantly, but most electrical machines are designed to operate over a range of operating conditions, and their energy conversion efficiencies will - often significantly - vary over that operating range. Generally, the control principles described herein can be applied to any type of electrical machine to improve the efficiency of the electrical machine when the operating range of the electrical machine includes a region below the equivalent of the maximum efficiency curve shown in FIG. 1. In some situations, efficiency improvements can be achieved by designing the electrical machine with pulsed operation in mind.

[0095] Some motor designs utilize windings on both the rotor and the stator to generate motor flux, while others use permanent magnets on either the rotor or the stator to contribute to the motor flux. Motors incorporating permanent magnets will have flux at zero torque and, thus, will typically have core losses when rotating and generate a back electromotive force (back EMF, BEMF) that exceeds the supply voltage. In such applications, it is often desirable to provide a small current to the motor during the "torque off" period to maintain zero torque. The need to supply current during the "zero torque" period reduces the overall efficiency associated with pulsing and, thus, it should be understood that this must be considered when determining which operating ranges can benefit from pulsing. Depending on the operating region, the losses associated with switching and current supply during the torque off period can exceed the efficiency improvement associated with pulsing, thereby reducing (or even eliminating entirely) the operating ranges for which pulsed operation is desirable. However, many electromechanical devices incorporating permanent magnets will have an operating region where the overall efficiency of the machine can be improved through the use of pulsing. For example, for an Internal Permanent Magnet Synchronous Motor (IPMSM), the most suitable operating region for pulsed operation is expected to be the operating speed below (or near) the threshold speed at which field weakening is required. and will have an operating region where this can be achieved. For example, for an Internal Permanent Magnet Synchronous Motor (IPMSM), for pulsed operation the most suitable operating region is expected to be the operating speed below (or near) the threshold speed at which field weakening is required.

[0096] There is a growing interest in using electric power devices (e.g., electric motors) in vehicle propulsion systems nowadays. Electric motors used for vehicle propulsion are generally called traction motors. In the automotive space, in recent years, a great deal of effort has been made to utilize traction motors alone or in combination with an internal combustion engine (hybrid) to drive vehicles. Today, asynchronous motors and three-phase induction motors are most commonly used in automotive applications - both of which are good candidates for the above-mentioned pulsed motor control. Automotive applications are well-known for a very wide range of operating conditions in which the motor is expected to operate - from low-speed high-torque requirements to high-speed low-torque requirements and everything in between. Under most driving conditions (i.e., for most of many driving cycles), the motor is required to produce a torque much smaller than the ability it has at the current motor speed - in fact, most driving occurs in a region where the motor's required output is below (often well below) the maximum efficiency line 16.

[0097] In FIG. 10, the nature of a typical drive cycle at low load can be seen. The figure plots a series of drive points representing the power / torque output of a simulated traction motor / generator that executes the Federal Test Procedure (FTP-75) for an urban driving cycle. The drive points are plotted on a torque / speed / efficiency graph. As can be seen in FIG. 10, a significant portion of the drive cycle requires lower torque compared to the maximum efficiency curve 16. Therefore, a significant portion of a typical drive cycle is within the operating region where it can benefit (and in many cases, greatly benefit) from the motor control approach described above. FIG. 10 shows only those portions of the drive cycle where output torque is required. During some portions of the drive cycle, regenerative braking can be used where the electromechanical device functions as a generator. Much of the regenerative braking is also performed in that it can benefit from the pulsed control described herein. Depending on the automotive application, it is believed that by implementing the control approach described above, an average overall efficiency improvement of 7% to 12% or more can be achieved. The fact that the efficiency is 7 to 12 percent better leads to a 7% to 12% longer driving range with the same charge, which has a significant advantage in the context of automotive applications where range anxiety is a major hindrance to the widespread adoption of the technology. It is expected that even greater efficiency improvements can be seen under autonomous driving conditions where the variability of the required motor output is less.

[0098] In automotive and other vehicle applications, the operating range of an electric motor can be quite broad. This is due in part to the fact that in most all-electric vehicle applications, the electric motor is coupled to a driven component with a fixed speed ratio. This is in contrast to internal combustion engine-powered vehicles, which typically employ an intermediate transmission device with a variable speed ratio between the engine and the driven component. As can be seen rather clearly in Figure 1, the "sweet spot" of electric motor operation is often at an intermediate motor speed. When desired, a variable gear mechanism can be used to operate the motor in a more efficient region for more of the time. Such a gear mechanism can be readily provided by a transmission device, and thus there are potential advantages to using the transmission device in conjunction with the pulsed motor control described above. The transmission device can have a set of gears, or can be continuously variable, or can have any other suitable form. In such embodiments, a motor controller or other suitable control component can be configured to direct the operation of the transmission device in a desired manner. Again, as in the previous case, the use of the transmission device is beneficial in a wide variety of other (non-vehicle) related applications as well.

[0099] Although automotive applications were used as an example of vehicle propulsion applications, it should be understood that the control approach described above is equally beneficial in other types of vehicles, including trucks, carts, motorcycles, bicycles, drones, and other flying devices, in robots and other devices that autonomously move within an environment, and in other propulsion-related applications that include electric motors used elsewhere.

[0100] Motors used in heating, ventilation, and air conditioning (HVAC) applications are another good example of a market that can benefit from pulse-width modulation control. There are several factors that contribute to the suitability of pulse-width motor control for HVAC applications. These include the following facts: (a) motors used in HVAC applications today are mainly induction motors that do not contain permanent magnets, (b) a high percentage of the operating life of HVAC motors is spent in operating regions below their high-efficiency regions, and (c) the inertia of the fan or pump typically dominates the motor inertia. - This has a tendency to further reduce the potential NVH-related effects associated with pulsing.

[0101] Of course, motors are used in a wide variety of other applications where they are operated below their optimum efficiency. This can be due to operating over a wide range of operating conditions (e.g., at a variety of different loads and / or motor speeds), or it can be due to the motor being oversized for the application (or otherwise not being specifically designed), or any of a variety of other reasons. It should be clear that the control approach described above can be beneficial for any of these types of applications.

[0102] High-low torque modulation In most of the examples described above, pulsing is achieved by modulating torque between a higher (more energy-efficient) torque output level and a zero torque output level. While this is considered the preferred approach in most pulsing control applications, there may be situations (e.g., certain machines / machine operating regions) where it may be preferable to modulate between a higher torque output and a lower non-zero torque output rather than between high torque and zero torque. For example, depending on the situation, high / low pulsing may have better noise, vibration, and harshness (NVH) characteristics than on / off pulsing, and thus there may be situations where high / low pulsing achieves a more desirable trade-off between energy conversion efficiency and NVH characteristics than on / off pulsing. In another example, for some operating regions of some motors, the high / low pulsing approach may result in better overall energy conversion efficiency than on / off pulsing. Motors incorporating permanent magnets that require field weakening to generate zero torque are particularly good candidates for the use of high-low torque modulation.

[0103] Pulsed Motor Overdrive Most motors have a specified maximum rated output level. Generally, the maximum rated output level is based on steady-state operation, and often a motor can be driven at a higher output level for a short period of time without any ill effects. Depending on the embodiment, within a selected operating region, the output level of the motor can be pulsed by setting the "on" level higher than the maximum rated continuous output level for steady-state operation. For some motors, there are some potential advantages to using overdrive pulses within some of their potential operating ranges. For example, in some specific operating situations, the energy conversion efficiency of a motor or system (e.g., a motor and an inverter) at a given motor speed may be higher within a certain overdrive region than within the "normal" operating region. This means that pulsed operation at higher torque or power can be even more efficient. This means that pulsed operation at higher torque or power can be even more efficient.

[0104] Furthermore, more efficient operation typically results in less heating, which potentially promotes an even higher net torque output. Therefore, when motors that are traditionally driven using continuous power (such as induction and other AC motors, brushless DC motors, switched reluctance motors, etc.) are designed with pulsed operation in mind, they can sometimes be optimized to achieve a higher net torque output using pulsed control than would be appropriate using more conventional steady / continuous drive power.

[0105] Other motor optimizations There are various factors that contribute to motor inefficiency. One contributing factor is related to the power factor, which is the cosine of the angle between the rotating voltage and current vectors. Ideally, the voltage and current should be in phase, or have a power factor of 1. However, for many types of electric motors / generators, this ideal does not necessarily represent the highest system efficiency point for any given load and speed. When pulsed control of the motor as described herein is contemplated and the power factor correction is optimized considering the pulsed operating point, it is expected that the effective power factor will be improved to exceed that of traditional continuous motor operation.

[0106] Another factor that contributes to motor inefficiency is sometimes referred to as resistance or I 2 2R losses. The resistive losses heat the motor windings, which in turn results in further increased resistive losses, since the resistivity of the windings generally increases with temperature. The resistive losses are non-linear - increasing at least with the square of the current. Thus, resistive losses tend to have a greater impact on overall motor efficiency at higher motor output levels, such as the levels used during pulsed operation. A rule of thumb for the design of electric motors is that the magnetic losses should approximately equal the resistive losses at the target operating set point. Since motor operating points below the most efficient operating point generally are not used, using the pulsed motor control method described herein can affect the proper design or selection of the motor. In other words, the motor is driven substantially either at its most efficient operating point or at a higher load. Low load continuous operation need not be considered in the design or selection of the electric motor - this can also help to further improve the overall efficiency of the system, as was the case previously.

[0107] Another factor contributing to motor inefficiency is sometimes what is referred to as core loss, which is associated with losses in the magnetic flux system. One loss mechanism is the motor winding leakage reactance, which refers to flux lines that do not link between the rotor and stator magnetic elements. Another core loss mechanism is associated with hysteresis in the magnetic core and is often represented in the B-H curve, where B is the magnetic flux density and H is the magnetic field strength. They are related by the magnetization of the material through which the field passes, which in some motors is the core present in the rotor or stator. Again, motors specifically designed for pulsed control can be optimized to reduce core losses during pulsed motor operation.

[0108] As described above, the transient switching losses associated with the switching between the motor "on" state and the motor "off" state during pulsed drive are another factor that affects the efficiency of the motor during the pulsed operation. As described above, one way to reduce these transient switching losses is to improve (shorten) the rise and fall times of the motor drive current associated with turning the motor on and off. Another way to help control the transient switching losses is to control the pulse frequency. Generally, the lower the switching frequency, the lower the transient switching losses. However, there is a trade-off here in that lower frequency switching can sometimes cause noise, vibration, and harshness (NVH) that may be undesirable or unacceptable in certain applications. Therefore, the pulse frequency for any given motor is preferably appropriately selected taking into account both motor efficiency and NVH concerns, and / or requirements related to the intended application of the motor. Along these lines, it should be noted that a pulsed controller having noise shaping capabilities, such as a sigma-delta conversion based pulsed controller, can be very helpful in reducing the impact of NVH associated with pulsed motor control and thus can help support the use of generally lower switching frequencies.

[0109] It should be understood that the appropriate pulse frequency for different motors can vary widely based on the motor's structure, operating environment, and operating range. For some motors, a switching frequency on the order of 10 - 50 kHz may be appropriate - whereas for other motors, a much lower switching frequency, for example, in the range of 10 - 500 Hz, may be more appropriate. Still other electromechanicals can have switching frequencies between these ranges, or above or below either of the ranges described above. The most appropriate pulse frequency for any given motor will depend on a variety of factors including motor size, on / off transient characteristics, NVH considerations, etc.

[0110] The selection of the desired operating point for any particular motor speed can also affect the switching frequency. More specifically, many motors have a relatively flat efficiency curve over a relatively wide operating range. Generally, pulsating operation at a torque level slightly lower than the optimal efficiency point for continuous operation can sometimes - depending on the nature of the switching losses - promote switching at a slightly lower frequency that can result in a higher overall motor efficiency during pulsating operation. This emphasizes the point that the desired pulsating operation drive point associated with any particular motor speed is not necessarily the torque level at which continuous motor operation can be most efficient. Rather, depending on the situation, the maximum energy efficiency point for pulsating operation can be somewhat different from the maximum energy efficiency point for continuous operation. Additionally, NVH considerations and / or other operating control considerations can affect the determination of the drive point that is deemed appropriate for any particular motor speed.

[0111] Additional Embodiments Although only a few embodiments of the present invention have been described in detail, it should be understood that the present invention can be implemented in many other forms without departing from the spirit and scope of the present invention. The various pulse controllers and other control elements described above can be implemented, grouped, and configured in a wide variety of different architectures in different embodiments. For example, in some embodiments, the pulse controller can be incorporated within a motor controller or an inverter controller, or it can be provided as a separate component. Similarly, for a generator, the pulse controller can be incorporated within a generator controller or a rectifier controller, and in a combined motor / generator, the pulse controller can be incorporated within a combined motor / generator controller or a combined inverter / rectifier controller. In some embodiments, the control functionality described above can be implemented algorithmically in software or firmware - which can take any suitable form, for example, including general-purpose processors and microprocessors, DSPs, etc. - executed on a processor.

[0112] The pulse generator or machine controller can be part of a larger control system. For example, in a vehicle application, the above-described control is performed by a vehicle controller, a power train controller, a hybrid power train controller, roller, or a component such as an ECU (engine control unit), etc. can be. In such an application, the vehicle or other related controller, etc. can take the form of a single processor that executes all of the required control, or it can be co-located as part of a power train or vehicle control module, or it can include multiple processors distributed at various locations within the vehicle. The specific functionality performed by any of the processors or control units can be widely diverse.

[0113] The present invention has been described primarily in the context of motor control and / or inverter / motor control. However, it should be understood that the above approach is equally applicable to the control of generators and / or generator / rectifiers. Therefore, whenever motor control is described, it should be understood that similar techniques can be applied to generator control. Therefore, unless the context requires a different interpretation, the description of the features of pulsed motor control, pulsed generator control, or pulsed motor / generator control should be understood to apply equally to pulsed motor control, pulsed generator control, and pulsed control of a combined motor / generator.

[0114] Various different control methods can be implemented within the pulse controller 120. Generally, the control method can be implemented digitally, algorithmically, using analog components, or using a hybrid approach. The pulse generator and / or motor controller can be on a processor, an FPGA (field programmable gate array On programmable logic such as a mable gate array)) or within a circuit mechanism such as an ASIC (application specific integrated circuit), a digital signal It may be implemented as code executed on a processor (DSP) using analog components or part of any other suitable hardware. Depending on the implementation form, the above control method may be incorporated into the object code to be executed on a digital signal processor (DSP) incorporated within an inverter controller (and / or, in the context of a generator and / or a composite inverter / rectifier controller, a rectifier controller).

[0115] In some of the first-mentioned embodiments, sigma-delta control is used to create a pulsed control signal. Sigma-delta control is one particularly excellent way to create the pulsed control signal 124, but it should be understood that in other embodiments, various other control methods may be used to create the pulsed control signal.

[0116] Regardless of the nature of the pulsing used, the torque modulation is preferably controlled in such a way that unacceptable NVH for the intended application is not produced.

[0117] The above-described pulsed motor control can be used in a wide variety of applications. The greatest efficiency improvements will typically be seen in motors and generators that are not consistently driven near their optimum operating efficiency. A good example of this is a motor / generator that has a wide operating range and is intended for use under widely varying load conditions. Another good example is a motor that is routinely in an under-driven state. For example, it is not uncommon for a system designer to use a larger motor than is actually required for an application - for example, using a 100 hp motor when a 50 hp motor would be more than adequate for a given task. Often, the larger the motor, the lower its operating efficiency can be at reduced loads, and in such situations, pulsed control can improve the efficiency of the motor in use.

[0118] Accordingly, the embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not limited to the details given herein but may be modified within the scope of the appended claims and equivalents thereof.

Claims

1. 1. A method of controlling an electric machine, the method including directing a pulsed operation of the electric machine to deliver a desired output, the pulsed operation of the electric machine alternating the output of the electric machine between a first power level and a second power level lower than the first power level, the first and second power levels being selected such that at least one of the electric machine and a system including the electric machine has a higher energy conversion efficiency during the pulsed operation than the electric machine may have when operated at a third power level that may be required to drive the electric machine in a continuous manner to deliver the desired output.

2. 2. The method of claim 1, wherein a power converter is used to control the output of the electric machine, the method further comprising controlling the power converter to alternate the output of the electric machine between the first output level and the second output level.

3. The method of claim 1 , wherein the second power level is substantially zero torque.

4. The method of claim 1 , wherein the electric machine is pulsed at a frequency of at least 10 times per second.

5. The method of claim 1 , wherein the electric machine alternates between the first and second power levels at least 100 times per second.

6. The method of claim 1 , wherein a sigma-delta converter is used to control the pulsing of the electric machine.

7. The method of claim 6 , wherein the sigma-delta converter is a first order sigma-delta converter.

8. The method of claim 6 , wherein the sigma-delta converter is at least a third order sigma-delta converter.

9. The method of claim 1 , wherein the electric machine has a current operating speed, the method further comprising: varying the first power level according to changes in the current operating speed of the electric machine.

10. The method of claim 1 , wherein a pulse width modulation controller is used to control the pulsing of the electric machine.

11. The method of claim 1 , wherein the first power level corresponds to an electric machine power level having substantially the highest system or electromechanical energy conversion efficiency at a current operating speed of the electric machine.

12. The method of claim 1 , wherein the system is configured to operate as a motor / generator.

13. The method of claim 1 further comprising varying a duty cycle of the pulsing in accordance with changes in the desired output.

14. A method according to any one of the preceding claims, wherein the electric machine is an induction machine.

15. The method of claim 14 , wherein the induction machine has at least three phases.

16. A method according to any one of claims 1 to 13, wherein the electric machine is a switched reluctance electric machine.

17. The method according to any one of claims 1 to 13, wherein the electric machine is a synchronous AC electric machine.

18. The electric machine comprises: Synchronous Reluctance Machine, Permanent Magnet Synchronous Reluctance Machine, Hybrid permanent magnet synchronous reluctance machine, Externally excited AC synchronous machine, and Permanent magnet synchronous machine 20. The method of claim 17, selected from the group consisting of:

19. A method according to any one of claims 1 to 13, wherein the electric machine is a brushless DC electric machine.

20. The electric machine comprises: Electrically excited DC electric machine, Permanent magnet DC electric machines, Series-wound DC electric machines, Shunt-wound DC electric machine, Brushed DC electric machines, and Compound-wound DC electric machine The method according to any one of claims 1 to 13, wherein the compound is selected from the group consisting of:

21. The electric machine comprises: Eddy current machines, AC Linear Machine, AC and DC mechanically commutated machines, and Axial Flux Machine The method according to any one of claims 1 to 13, wherein the compound is selected from the group consisting of:

22. 1. A method of controlling a motor to deliver a desired torque, the method comprising: determining whether a desired motor power is less than a designated power level, the designated power level being a power level with high energy conversion efficiency; driving the motor with a pulsed power signal to cause the motor to deliver the desired power when the desired motor output is less than the designated power level, the pulsed power signal alternating between a first power level corresponding to the designated power level and a second power level that is substantially zero, the motor having a higher energy conversion efficiency when driven by the pulsed power signal than when operating at a third power level that may be required to drive the motor in a continuous manner to deliver the desired power, the third power level being less than the first power level; driving the motor to deliver the desired motor power when the desired motor power is equal to or greater than the designated power level; The method includes:

23. 23. A method according to any preceding claim, wherein a power converter is used to control the output of the electric machine, the method further comprising controlling the power converter to alternate the output of the electric machine between the first output level and the second output level.

24. A method as claimed in any preceding claim, wherein the second power level is substantially zero torque.

25. A method as claimed in any preceding claim, wherein the electric machine alternates between the first and second power levels at least 100 times per second.

26. A method according to any one of claims 1 to 5 and 11 to 25, wherein a sigma-delta converter is used to control the pulsing of the electric machine.

27. 27. The method of claim 26, wherein the sigma-delta converter is a first order sigma-delta converter.

28. 27. The method of claim 26, wherein the sigma-delta converter is at least a third order sigma-delta converter.

29. A method according to any one of claims 1 to 5 and 11 to 25, wherein a pulse width modulated controller is used to control the pulsing of the electric machine.

30. 30. The method of any one of claims 1 to 29, wherein the first power output level is selected based at least in part on energy conversion efficiency and at least in part on noise, vibration, and harshness (NVH) considerations.

31. A method according to any preceding claim, wherein the first power level corresponds to an electric machine power level having substantially the highest system or electromechanical energy conversion efficiency at a current operating speed of the electric machine.

32. 32. The method of any one of claims 1 to 31, wherein the electric machine has a current operating speed, the method further comprising varying the first power level in accordance with changes in the current operating speed of the electric machine.

33. A method according to any preceding claim, wherein the electric machine is operated as at least one of a motor and a generator.

34. The method of any one of claims 1 to 33, wherein the power converter includes at least one of an inverter and a rectifier.

35. 1. A method of controlling an AC motor to deliver a desired torque, the method comprising providing an alternating power signal to the AC motor for driving the AC motor to deliver a desired torque, the alternating power signal being pulsed between a first power level and a second power level that is substantially zero, the AC motor having a higher energy conversion efficiency when operating at the first power level than when operating at a third power level required to drive the AC motor in a continuous manner to deliver the desired torque, the third power level being lower than the first power level.

36. 36. The method of claim 35, wherein the speed of the AC motor is controlled by adjusting the frequency of the alternating power signal.

37. 36. The method of claim 35, wherein a phase of switching between the first power level and the second power level is synchronized with a phase of the alternating power signal.

38. 36. The method of claim 35, wherein the phase of switching between the first power level and the second power level is not synchronized with the phase of the alternating power signal.

39. A machine controller configured to perform a method according to any preceding claim.

40. 1. A system, comprising: Electrical machinery and A power converter; and a machine controller configured to direct the power converter to cause pulsed operation of the electric machine within a selected operating range to deliver a desired output, wherein the pulsed operation of the electric machine alternates the output of the electric machine between a first output level and a second output level lower than the first output level, the first and second output levels being selected such that the system has a higher energy conversion efficiency during the pulsed operation of the electric machine than it would have when the system was operated at a third output level that may be required to drive the electric machine in a continuous manner to deliver the desired output.

41. 41. The system of claim 40, wherein the second power level is substantially zero torque.

42. 41. The system of claim 40, wherein the machine controller includes a pulse controller that directs the timing of the pulsing of the electric machine.

43. 43. The system of claim 42, wherein the pulse controller utilizes a sigma-delta converter to dynamically determine at least one of a duration, timing, or frequency of the pulses of the first power level.

44. An electro-machine controller comprising a sigma-delta converter configured to direct pulsing operation of the machine controller.

45. 44. The system of claim 43, wherein the sigma-delta converter is a first order sigma-delta converter.

46. 44. The system of claim 43, wherein the sigma-delta converter is at least a third order sigma-delta converter.

47. 44. The system of claim 43, wherein the period between a series of first power level pulses is a pulse cycle duration, said pulse cycle duration varying during operation of the electric machine.

48. 48. The system of claim 47, wherein the pulse cycle duration varies with rotational speed of the electric machine.

49. 44. The system of claim 43, wherein the sigma-delta converter utilizes a variable clock that varies with the operating speed of the electric machine.

50. 43. The system of claim 42, wherein the pulse controller utilizes a pulse width modulator to determine the duration of the pulses of the first power level.

51. 43. The system of claim 42, wherein the pulse controller is configured to cause the electric machine to be pulsed at a frequency of at least 10 times per second.

52. The system of claim 40, wherein the electric machine is configured to operate as a motor / generator.

53. 41. The system of claim 40, wherein the machine controller is configured to vary the first power level in accordance with changes in an operating speed of the electric machine.

54. A system according to any one of claims 40 to 53, wherein the electric machine is an induction machine.

55. 55. The system of claim 54, wherein the induction machine has at least three phases.

56. A system according to any one of claims 40 to 53, wherein the electric machine is a switched reluctance electric machine.

57. A system according to any one of claims 40 to 53, wherein the electric machine is a synchronous AC electric machine.

58. The electric machine comprises: Synchronous Reluctance Machine, Permanent Magnet Synchronous Reluctance Machine, Hybrid permanent magnet synchronous reluctance machine, Externally excited AC synchronous machine, and Permanent magnet synchronous machine 58. The system of claim 57, selected from the group consisting of:

59. A system according to any one of claims 40 to 53, wherein the electric machine is a brushless DC electric machine.

60. The electric machine comprises: Electrically excited DC electric machine, Permanent magnet DC electric machines, Series-wound DC electric machines, Shunt-wound DC electric machine, Brushed DC electric machines, and Compound-wound DC electric machine The system of any one of claims 40 to 53, selected from the group consisting of:

61. The electric machine comprises: Eddy current machines, AC Linear Machine, AC and DC mechanically commutated machines, and Axial Flux Machine The system of any one of claims 40 to 53, selected from the group consisting of:

62. The machine controller controls a pulse generator that dictates the timing of the pulsing of the electric machine. A system according to any one of claims 40 to 61, comprising a controller.

63. A system as claimed in any one of claims 40 to 62, wherein the second power level is substantially zero torque.

64. 64. The system of any one of claims 40-49 and 51-63, wherein the pulse controller utilises a sigma-delta converter to dynamically determine at least one of the duration, timing or frequency of the pulses of the first power level.

65. 65. A system or electromachine controller as claimed in claim 44 or 64, wherein the sigma-delta converter is a first order sigma-delta converter.

66. 65. A system or electromachine controller as claimed in claim 44 or 64, wherein the sigma-delta converter is at least a third order sigma-delta converter.

67. A system or electric machine controller as claimed in any one of claims 44 and 64 to 66, wherein the period between successive pulses of the first power level is a pulse cycle duration, said pulse cycle duration varying during operation of the electric machine.

68. 68. A system or electric machine controller as claimed in claim 67, wherein the pulse cycle duration varies depending on the rotational speed of the electric machine.

69. A system or electromachine controller as claimed in any one of claims 44 and 64 to 68, wherein the sigma-delta converter utilises a variable clock which varies with the operating speed of the electric machine.

70. A system as claimed in any one of claims 40 to 69, wherein the electric machine functions at least at times as a motor and the power converter includes an inverter.

71. A system as claimed in any one of claims 40 to 70, wherein the electric machine functions at least sometimes as a generator and the power converter includes a rectifier.

72. A system according to any one of claims 40 to 71, wherein the system is configured to operate as a motor / generator.

73. A system as claimed in any one of claims 40 to 72, wherein the pulse controller is configured to cause the electric machine to switch between the first and second power levels at least 100 times per second.

74. A system as claimed in any one of claims 40 to 73, wherein the machine controller is configured to vary the first power level in accordance with changes in the operating speed of the electric machine.

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