Electric machine system and method of operating electric machine system

Abstract

Various methods, controllers, and motor systems are described that facilitate pulse control of motors (e.g., electric motors and generators) to improve the energy conversion efficiency of the machine. Under selected operating conditions, the motor is intermittently driven (pulsed). The pulsing operation causes an output of the motor to alternate between a first output level and a second output level lower than the first output level. The output levels are selected such that the energy conversion efficiency of at least one of the motor and the system including the motor during the pulsed operation is higher than the energy conversion efficiency of the motor when operating at a third output level required to drive the motor in a continuous manner to deliver a desired output. In some embodiments, the second output level is zero torque.

Description

[0001] This application is a divisional application of a PCT application filed on March 14, 2019, with application number CN 201980020410.3 (international application number PCT / US2019 / 022185), entitled “Pulse Motor Control”, which has entered the Chinese national phase. Background Art

[0002] The present application relates generally to electric motor control and more particularly to control schemes and controller designs that pulse the operation of an electric motor during selected operating conditions to facilitate operating the electric motor in a more energy-efficient manner.

[0003] The phrase "electric machine" as used herein is intended to be broadly understood to refer to both electric motors and generators. Electric motors and generators are very similar in structure. When an electric machine operates as a motor, it converts electrical energy into mechanical energy. When operating as a generator, the electric machine converts mechanical energy into electrical energy.

[0004] Electric motors and generators are used in a wide variety of applications and under a wide variety of operating conditions. In general, many modern electric motors have a relatively high energy conversion efficiency. However, the energy conversion efficiency of most electric motors can vary significantly based on their operating load. Many applications require the motor to operate under a wide variety of different operating load conditions, which means that the motor is often not operating as efficiently as it could. Figure 1 The nature of the problem is demonstrated in the figure which graphically shows the efficiency of a representative motor under different operating conditions. Fig.10 More specifically, the graph plots the energy conversion efficiency of a motor as a function of motor speed (X-axis) and generated torque (Y-axis).

[0005] like Figure 1 It can be seen that when the motor shown is operated within a specific speed range and generates a torque within a limited range, the motor is generally most efficient. For the specific motor shown, the most efficient area within its operating range is the operating area marked as 14, which is generally in the range of 4500RPM to 6000RPM and the torque output is in the range of about 40Nm to 70Nm, wherein the energy conversion efficiency of the motor is about 96%. Region 14 is sometimes referred to herein as the "sweet spot", which is the most efficient operating area of ​​the motor.

[0006] like Figure 1It can be seen that at any particular motor speed there will be a corresponding most efficient output torque, which is graphically illustrated by the maximum efficiency curve 16. For any given motor speed, the efficiency of the motor tends to drop slightly as the load on the motor is above or below the most efficient load. In some regions, the efficiency of the motor tends to drop relatively quickly, for example, when the torque output in the illustrated motor drops below about 30 Nm.

[0007] If the operating conditions can be controlled so that the motor is almost always running at or near its optimal point, the energy conversion efficiency of the motor will be very good. However, many applications require the motor to operate under a wide variety of load conditions, widely varying torque requirements, and widely varying motor speeds. One such application that is easy to imagine is automobiles and other vehicles or mobile applications, where the motor speed may vary from zero when the vehicle is stopped to a relatively high RPM when the vehicle is cruising at highway speeds. The torque requirements may also vary greatly at any of these speeds based on factors such as whether the vehicle is accelerating or decelerating, whether it is going uphill, downhill, whether it is traveling on relatively flat terrain, the weight of the vehicle, and many other factors. Of course, motors used in other applications may also be subject to a wide variety of operating conditions.

[0008] Although the energy conversion efficiency of conventional electric machines is generally good, efforts continue to be made to further improve the energy conversion efficiency over a wider range of operating conditions. Summary of the invention

[0009] Various methods, controllers, and motor systems that facilitate pulse control of motors (e.g., electric motors and generators) to improve the energy conversion efficiency of the motor when operating conditions permit are described. More specifically, under selected operating conditions, the motor is intermittently driven (pulsed). The pulse operation of the motor causes the output of the motor to alternate between a first output level and a second output level that is lower than the first output level. The first output level and the second output level are selected so that the energy conversion efficiency of at least one of the motor and the system including the motor during the pulse operation is higher than the energy conversion efficiency of the motor when the motor is driven in a continuous manner to deliver the desired output at a third output level required for operation. In some embodiments, the second output level is zero torque (or substantially zero torque).

[0010] In some embodiments, the motor is driven in a pulsed manner when the desired output is less than a specified output level at a given motor speed; and the motor 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 motor. 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 pulses can vary widely as required by any particular application.For example, in various embodiments, the motor alternates between the first output level and the second output level at least 10, 100, or 1000 times per second.

[0013] In some embodiments, a Σ-Δ converter is used to control the pulse variation of the motor. A wide variety of different Σ-Δ converter architectures can be used. In some embodiments, the Σ-Δ converter is a first order Σ-Δ converter. In other embodiments, a third order Σ-Δ converter is used. In still other embodiments, a higher order Σ-Δ converter can be used. The Σ-Δ 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 pulse variation of the motor.

[0015] In some embodiments, the first output level varies according to a change in the current operating speed of the motor. In various embodiments, the first output level may correspond to a motor output level that is equal to or close to a maximum system energy conversion efficiency or motor energy conversion efficiency at the current operating speed of the motor. In some embodiments, the duty cycle of the pulse varies according to a change in the desired output.

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

[0017] In various embodiments, the motor can be: an induction motor; a switched reluctance motor; a synchronous AC motor; a synchronous reluctance motor; a permanent magnet synchronous reluctance motor; a hybrid permanent magnet synchronous reluctance motor; an externally excited AC synchronous motor; a permanent magnet synchronous motor; a brushless DC motor; an electrically excited DC motor; a permanent magnet DC motor; a series wound DC motor; a shunt DC motor; a brushed DC motor; a compound DC motor; an eddy current motor; an AC linear motor; an AC mechanically commutated motor or a DC mechanically commutated motor; or an axial flux motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention and its advantages may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 is a representative torque / speed / efficiency graph showing the energy conversion efficiency of a representative electric motor under different operating conditions.

[0020] Figure 2A is a graph showing a pulse drive signal for a motor.

[0021] Figure 2B It is a graphical representation of a continuous three-phase AC drive signal waveform.

[0022] Figure 2C and Figure 2D is a pulsed three-phase AC waveform with a duty cycle of 50%. These pulsed three-phase AC waveforms represent Figure 2B The same average power for consecutive waveforms.

[0023] Figure 3 is a functional block diagram that diagrammatically illustrates a motor control architecture according to one described embodiment.

[0024] Figure 4 is a flow chart illustrating a motor control scheme according to another embodiment.

[0025] Figure 5 is a representative torque / speed / efficiency graph showing the energy conversion efficiency of a representative inverter under different operating conditions.

[0026] Figure 6 is a graph showing the combined energy conversion efficiency of a representative inverter / motor combination.

[0027] Figure 7 is a functional block diagram that diagrammatically illustrates a motor controller architecture including a sigma-delta based pulse generator according to another embodiment.

[0028] Figure 8 is a schematic functional block diagram of a first-order Σ-Δ converter.

[0029] Fig. 9A is a graph graphically showing the expected power rise and fall of pulse power.

[0030] Fig. 9B is a graph that graphically represents the actual power rise and fall that can be seen when a conventional motor is pulsed in the manner described.

[0031] Fig.10 is a torque / speed / efficiency graph showing a drive point distribution representing a simulated output of an automotive electric motor during an FTP 75 drive cycle.

[0032] Fig.11 is a schematic block diagram of a motor / generator having a transient control circuit configured to shorten a rise time and a fall time of turning on / off the motor / generator according to an embodiment.

[0033] In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be understood that the depictions in the drawings are diagrammatic and not to scale. DETAILED DESCRIPTION

[0034] The present disclosure generally relates to pulse control of electric machines (e.g., motors and generators) that would otherwise be operated in a continuous manner to improve the energy conversion efficiency of the electric machine when operating conditions permit. More specifically, under selected operating conditions, the electric machine is intermittently driven (pulsed) at a more efficient energy conversion operating level to deliver a desired average torque more energy efficiently than would be achieved through conventional continuous motor control.

[0035] Traditionally, when many types of electric machines (including mechanically commutated electric machines, electronically commutated electric machines, externally commutated asynchronous electric machines, and externally commutated synchronous electric machines) are used as electric motors to deliver a desired torque output, the machine is driven by a continuous (although possibly varying) drive current. 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 electric motor. In contrast, the power output of many types of generators is controlled by controlling the magnetic field strength, which can be achieved, for example, by controlling the excitation current supplied to the rotor coils by an exciter. (The exciter can be part of a rectifier or other suitable component). Regardless of the type of machine, the drive current of the electric motor, or the current output by the generator, tends to be continuous.

[0036] Pulse control is used to intelligently and intermittently modulate the output of the machine between a "torque on" state and a "zero (no) torque" state in the following manner: (1) meet operating requirements while (2) improving overall efficiency. In other words, under selected operating conditions, the motor is intermittently driven ("torque on" state) at a more efficient energy conversion operating level to deliver the desired output. In the time period between pulses, it is ideal that the machine does not generate or consume any torque ("zero torque" state). Conceptually, this can be considered to be "turning off" the motor. In some embodiments, this can be achieved by effectively "turning off" the motor, such as by cutting off the drive current of the motor or the excitation current of the generator. However, in other embodiments, during the "zero torque" state, the motor can be controlled in a manner that attempts to make the torque generated by the motor zero or close to zero (which may be practical or suitable for a particular machine). In some embodiments, any power converter used in conjunction with the motor can also be effectively turned off in at least a portion of the "zero torque" time period.

[0037] As discussed in the background, Figure 1 The energy conversion efficiency of a representative electric motor is shown. Figure 1The graph shown in is an efficiency graph for an interior permanent magnet synchronous motor used in a 2010 Toyota Prius. It should be understood that this graph is illustrative only. Although the characteristics of the graph will vary with the machine being characterized, a similar efficiency graph can be generated for almost any electric machine.

[0038] like Figure 1 It can be seen that at any particular motor speed, there will be a corresponding most efficient output torque, which is graphically illustrated by the maximum efficiency curve 16. From a conceptual perspective, when the desired motor torque is lower than 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 at or above the maximum efficiency curve 16, the motor can be operated in a conventional (continuous / pulse-free) manner to deliver the desired torque.

[0039] Figure 2A An example of pulsed motor operation is shown. In this particular example, the desired motor torque is 10Nm, but the most efficient torque output for the current operating motor speed is 50Nm. Conceptually, the motor can be driven to deliver a net torque of 10Nm by having the motor deliver 50Nm of torque 20% of the time and then delivering no torque (or zero torque) the remaining 80% of the time. Since the motor operates more efficiently when delivering 50Nm than when delivering 10Nm, the overall efficiency of the motor can be improved by pulsing the operation of the motor in the manner described. Figure 2A In the example shown, the motor produces a motor output (referenced 24) of 50 Nm during a period of 1 time unit out of every 5 time units, and the motor is then controlled to produce zero torque during the intervening 4 time units.

[0040] As long as the desired motor output does not exceed 50Nm, the desired motor output can theoretically be met simply by changing the duty cycle of the motor running at 50Nm. For example, if the desired motor output changes to 20Nm, the duty cycle of the motor running at 50Nm can be increased to 40%; if the desired motor output changes to 40Nm, the duty cycle can be increased to 80%; if the desired motor output changes to 5Nm, the duty cycle can be reduced to 10%, etc. More generally, it may be advantageous to use pulsing the motor any time the desired motor torque drops below the maximum efficiency curve 16.

[0041] The range of time units actually used may vary greatly based on the size, nature, and design requirements of any particular system. In practice, when the motor switches from the "torque on" state to the "zero torque" state relatively quickly to achieve a specified duty cycle, the fact that the motor actually switches back and forth between these states may not materially degrade the performance of the motor from an operational perspective. In some embodiments, the time period of each on / off cycle is expected to range from the order of 100 microseconds to 0.10 seconds (i.e., pulsed at a frequency in the range of 10 Hz to 10,000 Hz), such as in the range of 20 Hz to 1000 Hz, or in the range of 20 Hz to 100 Hz, as discussed in more detail below.

[0042] Conceptually, the zero torque portion of the pulse cycle can be considered to be shut off from the motor - although in many cases the motor may not actually be shut off during these time periods, or may be shut off for only a portion of the "zero torque" interval.

[0043] Many electric motors are designed to run on alternating current. FIG. 2B to FIG. 2D are plots illustrating the difference between continuous and pulsed alternating current that may be input to an electric machine operating as a motor (e.g., a three-phase induction motor). In each plot, current is plotted on the vertical axis and time is plotted on the horizontal axis.

[0044] Figure 2B A conventional sinusoidal three-phase input current 42a, 42b, and 42c delivered to the motor is shown. 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 sine wave period is τ. The three-phase input power 42 is continuous (non-pulsed) and has a specified maximum amplitude of approximately 50 amps. It should be understood that 50 amps is merely a representative maximum current and that the maximum current may have any value.

[0045] Figure 2C and Figure 2D Two examples of different pulsed three-phase currents 44a, 44b and 44c and 46a, 46b and 46c are shown, each having a 50% duty cycle and a peak amplitude of approximately 100 amps. Figure 2B As shown, the period of the base sine wave is τ, however now the sine wave is modulated to be intermittent. Assuming the motor speeds are the same and the torque generated is roughly proportional to the current (which is usually the case), Figure 2C and Figure 2D The delivered current in Figure 2BThe difference between pulse currents 44a-c and 46a-c is the duration of their respective current pulses and the staggered "off" time periods. Figure 2C In , the current pulses 44a-c are interleaved with "off" time periods of equal length. The length of each on time period and off time period is 2τ. Figure 2D In the example shown in Figure 1, the current pulses 46a-c and the interleaved "off" time periods are also of equal duration. In this case, the duration is τ / 2. In both examples, the duty cycle is 50%. However, the duration of the "on" duration and the "off" duration are different, that is, the frequency of the pulse modulation is different. The frequency of the pulse modulation may be different based on the type of motor used, noise and vibration considerations, the speed of the rotor currently running, and other factors.

[0046] Figure 2C to Figure 2D Applications are shown where the "on" motor drive pulses are evenly spaced while the motor is operating at a steady-state desired output level. This approach works well in many situations, but is not a requirement. The duty cycle does not have to be 50%, but can be adjusted to match the desired average output torque. Likewise, the phase of the on / off pulses does not have to be synchronized with the phase of the applied AC power. Thus, the relative size and / or timing of the motor drive pulses can vary, as long as they average out to deliver the desired average torque.

[0047] Power Converters and System Efficiency

[0048] There are a wide variety of different electric machines, and each machine has its own unique efficiency characteristics. Further, at different operating speeds, the motor will have different efficiency curves, which can be seen from the Figure 1 A cursory review of should be apparent. Thus, the operating region over which pulse control can provide efficiency gains will vary significantly based on factors including the specific motor characteristics and the current operating rotor speed.

[0049] When an AC motor is used in conjunction with a battery or other DC power source / sink (storage device), a power converter (e.g., inverter and rectifier) ​​is typically used to convert between DC power and AC power. For example, an inverter is used to convert power received from a DC power supply source (such as a battery or capacitor) to AC input power applied to the motor. Conversely, a rectifier is used to convert AC power received from a motor operating as a generator to DC output power. Depending on whether the motor is used as a motor or a generator, some power converters can be used as inverters or rectifiers.

[0050] The energy conversion efficiency of a power converter will also typically vary over the operating range of the converter. For example, Figure 5 is understood to be a 2010 Toyota Prius inverter (i.e., for Figure 1 ). Although the energy conversion efficiency of the inverter shown is very good, the efficiency of the inverter also drops significantly in certain areas, most notably at lower torque outputs and lower motor speeds. Therefore, when optimizing the control of an electric motor that is part of an inverter / motor combination, it is desirable to consider the energy conversion efficiency of the entire inverter / motor system, rather than the energy conversion efficiency of the individual motors. Similarly, when optimizing the control of a generator that is part of a rectifier / generator system, it is desirable to consider the energy conversion efficiency of the entire rectifier / generator system, rather than the energy conversion efficiency of the individual generators.

[0051] Preferably, the pulse control of the motor will be modeled to take into account the efficiency of any / all components that affect energy conversion during pulse changes. For example, when power for an AC motor is drawn from a battery, the power delivery efficiency of the battery, cabling losses between components, and any other loss factors may be considered in addition to the inverter efficiency and motor efficiency when determining the motor drive signal that delivers the best energy conversion efficiency.

[0052] Typically, the overall energy conversion efficiency of a power converter / motor system is a function of the product of the converter conversion efficiency times the motor conversion efficiency times the delivery efficiency of the other components. Therefore, it should be understood that the parameters of the pulsed drive signal with the maximum system energy conversion efficiency may be different from the parameters that will provide the best energy conversion efficiency for the motor itself.

[0053] Figure 6 is a representative energy conversion efficiency graph of a combined inverter / AC motor. More specifically, Figure 6 The combined efficiency of the Tesla inverter / motor propulsion system is shown. Since the inverter and motor work together, the best overall motor system energy conversion efficiency can be optimized by selecting the pulse voltage and corresponding duty cycle based on the combined system energy conversion efficiency map instead of using only the motor's energy conversion efficiency map.

[0054] Typically, the energy conversion efficiency map for a particular motor system (e.g., combined power converter / motor; battery / power converter / motor, etc.) will be more complex than the efficiency map for the motor itself. As such, there may be local efficiency peaks above the maximum efficiency curve. That is, there may be a region of the energy conversion efficiency map where, at a given motor speed, operation at a particular torque output (above the "maximum" possible efficiency for operation at that motor speed) may be more efficient than a range of intermediate torque outputs that are above the maximum efficiency curve but below that particular torque output. Figure 6 , one such region is designated as 61. It will be appreciated that when the energy conversion efficiency graph has this type of graph, pulsed operation at the local efficiency peaks may be more efficient than continuous operation at these intermediate output levels. In this case, the motor may be pulsed at the local efficiency peak levels to deliver such intermediate torque outputs.

[0055] Pulse system control

[0056] Figure 3 A control architecture suitable for controlling a motor in the manner described is shown. In this embodiment, system 100 includes a machine controller 110, a pulse controller (pulse generator) 120, a power supply source / sink 130, a power controller / converter 140, and a motor 160. Pulse controller 120 is responsible for controlling / directing the timing of pulse changes of motor 160 when pulse operation is required. Figure 3 In the illustrated embodiment, the pulse controller is shown as a separate component from the machine controller 110 to facilitate explanation of the functionality of the pulse controller. However, in various embodiments, the pulse controller may be implemented as part of the machine controller 110, as a separate component, as part of the power controller / converter 140, or in other suitable forms.

[0057] When the machine 160 is operating as a motor, the machine controller functions as a motor controller, and the power controller / converter 140 is responsible for converting the power 132 received from the power supply source 130 into a form suitable for driving the motor 160. Conversely, when the machine 160 is operating 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 supply source / sink can directly supply power in the form required by the motor or directly receive power in the form output by the motor, the power controller 140 can conceptually take the form of a switch or logic multiplier that simply turns the motor on and off to facilitate the desired pulse variation.

[0058] The power supply source / sink 130 can take any suitable form. In some embodiments, the power supply source / sink can take the form of a battery or a capacitor. In other embodiments, the source can be an electrical grid (e.g., "wall power"), a photovoltaic system, or any other available source. Similarly, the sink can be an electrical load (such as an electrically operated machine or appliance, a building, a factory, a home, etc.), an electrical grid, or any other system that uses or stores electricity.

[0059] The power controller / converter 140 may also take a variety of different forms. When the power supply source / sink 130 is a DC power supply source and the motor 160 is an AC motor, the power controller / converter 140 may take the form of an inverter. Conversely, when the power supply source / sink 130 is a DC power sink and the motor 160 is an AC generator, the power controller / converter 140 may take the form of a rectifier. When both the power supply source / sink 130 and the motor are AC components, the power controller / converter 140 may include a bidirectional power converter or a 4-quadrant power converter.

[0060] exist Figure 3 , the requested output is labeled 113, the torque delivered or received by the motor is labeled 161, and the motor / generator speed is labeled 164. In some embodiments, the machine controller 110 includes a data structure 115 (e.g., a lookup table) that serves as a pulse operation map that defines operating regions where pulse motor control is desired and / or appropriate, and specific duty cycles that are appropriate for specific operating conditions.

[0061] Once the desired duty cycle is determined, the duration and nature of the pulses used to drive the motor may 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 .

[0062] exist Figure 3 , a logic multiplier 123 is shown multiplying a pulse control signal 124 by a power level signal 119 output by the machine controller 110 to produce a power converter control signal 128. It should be understood that the logic multiplier 123 is shown for purposes of explanation, and in practice, the functionality of the multiplier 123 may be implemented by the machine controller 110, by the power converter 140, or in other suitable ways. For example, in some embodiments, the machine controller 110 may simply set the output of the power converter 140 to zero during the "off" phase of the duty cycle, and set it to a desired operating output level (e.g., the most efficient output level for the current motor speed) during the "on" phase of the duty cycle.

[0063] Figure 4A control flow that can be executed by the machine controller 110 to efficiently deliver the desired torque to the motor 160 is presented. To simplify the discussion, an embodiment is described in which the motor 160 is used as a motor. In this arrangement, the power supply source / sink 130 is used as a power supply source, and the machine controller 110 is used as a motor controller.

[0064] Initially, the motor controller 110 receives the currently requested motor output 113 and any required motor state information (such as the current motor speed 164 as represented by box 171). The motor controller 110 then determines whether the requested output is within the pulse control range as represented by decision box 172. This decision can be made in any desired manner. For example, in some embodiments, a lookup table 115 or other suitable data structure can be used to determine whether pulse control is appropriate. In some embodiments, a simple lookup table can identify the maximum torque level that is suitable for pulse control at various motor speeds. In such an embodiment, the current motor speed can be used as an index into the lookup table to obtain the maximum torque level that is suitable for pulse control under the current operating conditions. The retrieved maximum torque value can then be compared to the requested torque to determine whether the requested output is within the pulse control range.

[0065] In other embodiments, the lookup table 115 may provide additional information (such as a desired duty cycle for pulsed operation) based on current operating conditions. In one such implementation, the motor speed and torque request may be used as indices into a lookup table, with each entry in the lookup table indicating a desired duty cycle, and interpolation is used to determine the operating duty cycle when the actual torque and / or motor speed is between the index values ​​represented in the table.

[0066] If the requested torque / current operating conditions are outside the pulse control range for any reason, conventional (i.e., continuous / non-pulsed) motor control is used as indicated by the "No" branch flowing out of box 172. Thus, as indicated by box 174, pulses are not used and the power converter 140 is directed to deliver power to the motor 160 in a conventional manner at a level suitable for driving the motor to deliver the requested output 113. Conversely, when the requested torque / current operating conditions are within the pulse control range, pulse control is utilized as indicated by the "Yes" branch flowing out of box 172. In such an embodiment, the motor controller 110 will direct the power converter 140 to deliver power to the motor in a pulsed manner. During the "on" pulse, the power converter 140 is directed to deliver power at a preferred output level - the preferred output level is usually (but not necessarily) equal to or close to the maximum efficiency operating level at the current motor speed. During the "off" pulse, the motor is ideally outputting zero torque. In some embodiments, the timing of the pulses is controlled by the pulse controller 120, as will be discussed in more detail below.

[0067] To facilitate pulse operation, the motor controller 110 determines a desired output level (block 175) and a desired duty cycle (block 176) for pulse operation at the current motor speed (preferably equal to or close to the system's maximum efficiency energy conversion output level at the current motor speed - although other energy efficiency levels may be used as appropriate). The motor controller and pulse controller then direct 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 source on and off at a relatively high frequency so that the fraction of the time that 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 directing the power controller / converter 140 to drive the motor to deliver zero torque.

[0068] The pulse frequency of the power is preferably determined by the machine controller 110 or the pulse controller 120. In some embodiments, the pulse frequency may be fixed for all operations of the motor, while in other embodiments, the pulse frequency may vary based on operating conditions such as motor speed, torque requirements, etc. For example, in some embodiments, the pulse frequency may be determined by using a lookup table. In such embodiments, appropriate indexes such as motor speed, torque requirements, etc. may be used to look up the appropriate pulse frequency for the current motor operating conditions. In other embodiments, the pulse frequency is not necessarily fixed for any given operating condition and may vary as directed by the pulse controller 120. This type of variation is common when Σ-Δ conversion is used in determining the pulse, as discussed below. In some specific embodiments, the pulse frequency may vary proportionally to the motor speed, at least in some operating regions of the motor.

[0069] although Figure 4 Some steps are presented sequentially to facilitate a clear understanding of the functionality provided, but it should be understood that many steps may actually be combined and / or reordered. For example, entries in a multidimensional lookup table 115 using the requested output 113 and the current motor speed 164 as indices may indicate a preferred output level and duty cycle appropriate for the current operation.

[0070] In some embodiments, a value stored in a lookup table, such as a duty cycle of 1 (100%) or other suitable wildcard, may optionally be used to indicate that a pulse is not required. Of course, various other conventions and data structures may be used to provide the same information.

[0071] In some embodiments, the pulse control table can be combined into a larger table that defines operation at all levels so that the operating flow is the same whether conventional control or pulse control is desired (conventional control is defined only by a duty cycle of 1 and an appropriate motor input power level, and pulse control is defined by a smaller duty cycle and using a preferred motor input power level).

[0072] In some embodiments, based on other considerations, it may be desirable to avoid pulses in some operating regions even if this may improve efficiency. As will be discussed in more detail below, these other considerations may be based on factors such as noise and vibration, the actual switching function of the controller, etc.

[0073] The machine controller described herein may be implemented in a variety of different ways, including using software or firmware executed on a processing unit (such as a microprocessor), using programmable logic, using an application specific integrated circuit (ASIC), using discrete logic, etc. and / or using any combination of the foregoing.

[0074] It is noteworthy that in many cases, existing motor and machine controllers can be easily retrofitted to obtain the described benefits. For example, many machine controllers are implemented using software or firmware executed on a processing unit that already has access to control input parameters suitable for the described controls (e.g., requested motor output and current motor speed). In such cases, significant efficiency gains can be obtained by installing a relatively simple software update.

[0075] Pulse Generation

[0076] As described above, once the desired duty cycle is determined, the duration and nature of the pulses used to drive the motor may 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 .

[0077] Note that pulse width modulation is commonly used in certain types of motor control, including AC motor control and DC brushless motor control, but this pulse width modulation is used in very different locations in the control scheme. Specifically, when an AC induction motor is powered by a battery (which provides DC power), an inverter is typically used to facilitate the conversion of DC power to AC power. Typically, 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 motor at a desired frequency and amplitude. A PWM controller is similarly used in a brushless DC motor to control the amplitude of the continuous signal supplied to the motor.

[0078] The pulse power used in this article is very different. Specifically, as mentioned above FIG. 2A to FIG. 2D As discussed, the power converter 140 is controlled to cycle between producing a high efficiency torque output (eg, peak efficiency torque) and producing no torque in the motor 160. In an induction motor, this causes the magnetic flux in the motor windings to effectively drop to zero.

[0079] While conventional pulse width modulation will work in many applications, a potential drawback is that the pulses may generate unwanted vibration or noise when turning the motor and / or power supply on and off. Motors that run in a steady state with the same pulse period for a period of time are particularly susceptible to such vibrations. There are many ways to mitigate this risk, including some that will be described in more detail below. Another approach is to add some jitter to the pulse period of the command.

[0080] As described above, the time period of each cycle during pulse operation (or conversely, the pulse frequency) can vary widely (from microseconds to tenths of a second or longer) based on design needs and the nature of the controlled system. A variety of factors will affect the selection of the cycle time period. These factors include factors such as the capabilities and characteristics of the motor, transient effects associated with switching, potential NVH (noise, vibration and harshness) considerations, expected operating loads, etc. In general, the pulse frequency selected for any particular application will involve a compromise including factors such as NVH considerations, required motor responsiveness, efficiency losses associated with pulses, etc. For example, in some automotive applications, pulse frequencies on the order of 20 Hz to 1000 Hz are considered to perform well.

[0081] Sigma-Delta Control

[0082] Next reference Figure 7 , another embodiment of a pulse generator will be described. The architecture shown is similar to Figure 3 , except that in this embodiment, a sigma-delta converter 190 is used as the pulse generator 120. As will be appreciated by those familiar with sigma-delta control, a characteristic of sigma-delta control is that it facilitates noise shaping and tends to 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, there is less concern as any such noise and / or vibrations will not be annoying to users of the motor. Thus, in the context of automotive motor applications, the use of sigma-delta control tends to reduce the likelihood that noise or vibrations will be perceived by vehicle occupants due to pulsed motor control.

[0083] A variety of different Σ-Δ converters can be used as Σ-Δ converters 190, and the Σ-Δ converters can utilize a variety of different feedback schemes. For example, first-order Σ-Δ conversion performs well. A particularly desirable feature of using a first-order Σ-Δ converter is that the controller is inherently stable. Although the first-order Σ-Δ converter performs well, it should be understood that in other embodiments, a higher-order Σ-Δ converter (e.g., a Σ-Δ converter that utilizes a greater number of integrators than a first-order Σ-Δ converter) can be used. For example, a third-order Σ-Δ converter (e.g., a converter using a Richie architecture) or a higher-order Σ-Δ converter can be used.

[0084] In general, a sigma-delta converter may be implemented algorithmically, digitally, using analog components, and / or using a hybrid approach. For example, in various embodiments, a sigma-delta converter may be implemented on a processor, on programmable logic such as an FPGA, in a circuit system such as an ASIC, on a digital signal processor (DSP), using analog, digital, and / or hybrid components, or any / or other suitable hardware and / or software combination. In various embodiments, a sigma-delta controller may utilize sample data sigma-delta, continuous time sigma-delta, differential sigma-delta, or any other suitable sigma-delta implementation.

[0085] Many representative Σ-Δ converter designs are described in U.S. Patent No. 8,099,224 and U.S. Patent Publication No. 2018-0216551, which are incorporated herein by reference in their entirety. Although the applications described therein are for controlling different types of power plants, similar types of converters can be used in the present application.

[0086] Next reference Figure 8 , a representative first-order Σ-Δ converter 200 will be described. The first-order Σ-Δ 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 differential signal 216, which is fed to the integrator 203. The integrator 203 integrates the differential signal and outputs an integrator output signal 217, which is fed to the comparator 205. The comparator 205 acts as a one-bit quantizer and outputs a pulse (high / low) digital control signal 220 representing 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 actually a string of 1s and 0s, which are output at the frequency of the clock of the Σ-Δ converter. A low signal is regarded as a request for zero power from the power supply source, and a high signal is regarded as a request for the most efficient (or other specified) power level for the current motor speed.

[0087] Typically, to ensure high quality control, it is desirable that the frequency of the Σ-Δ converter clock signal 226 (and therefore the output stream of the comparator 205) 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. Typically, clock frequencies on the order of 100kHz to 1MHz or higher perform well for automotive type applications, in which the input signal (typically based on the driver's torque request - e.g., accelerator pedal) tends to change at a rate of less than 5Hz. That is, the output of the comparator 205 is sampled at a rate of at least 100kHz to 1MHz (although higher and lower sampling rates may be used in various embodiments). 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.

[0088] In various embodiments, comparator 205 can be configured to impose desired constraints on the pulse (sometimes referred to herein as behaving as a functional intelligent comparator). In a simple example, the comparator can be constrained to define minimum and / or maximum "on" time, minimum (and / or maximum) "off" time, etc., which will be understood by technicians familiar with advanced Σ-Δ control. Such constraints may help ensure that the pulse is executed within the desired frequency and "on" pulse length parameters. In other embodiments, the comparator can impose more advanced constraints. For example, if desired, pulse period jitter 223 can be added to the comparator.

[0089] In some embodiments, it may be desirable to perform anti-aliasing filtering on the input signal 209 and the feedback signal 212. The anti-aliasing function may be provided as part of the sigma-delta control circuit, or it may be provided as an anti-aliasing filter before the sigma-delta control circuit, or it may be provided in any other suitable form. In some third-order analog continuous-time sigma-delta control circuits, the first integrator provides the anti-aliasing function. That is, the first integrator effectively acts as a low-pass filter.

[0090] In other embodiments, a variable clock based on the motor speed may be used instead of a fixed clock. Figure 8This arrangement is illustrated in the Σ-Δ converter of , which uses a variable clock based on the motor speed. Specifically, the clock signal is configured to vary proportionally with the motor speed. Using a variable speed clock when the motor is running at a certain speed has the advantage of ensuring that the output of the comparator is better synchronized with the motor speed. This in turn can help 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). The motor speed signal 164 can then be multiplied using a multiplier 231 to obtain the desired sampling rate. The multiple of the motor speed can vary widely based on the needs of any particular system. For example, in some applications, a frequency multiplication of the order of 10 to 1,000,000 times (e.g., 10,000 times) is appropriate. In another example, a Σ-Δ clock rate of the order of 1kHz to several hundred kilohertz is considered suitable for many automotive applications.

[0091] The challenge of using a variable clock approach based on motor speed is that the variable clock may not perform particularly well when the motor is stopped or running at particularly low motor speeds. Several different techniques can be used to mitigate this limitation. For example, a fixed clock can be used when the motor is stopped and / or running at a speed below a specified idle threshold (e.g., below 600 RPM). In other embodiments, a functionally intelligent comparator can be used that has a specified startup routine and stop routine, or switches to a different operating mode during low-speed operation. In still other embodiments, a nonlinear RPM clock can be used for operation at lower speeds.

[0092] There are several ways in which the Σ-Δ converter 200 can be configured. In one embodiment (similar to Figure 8 In the embodiment shown in FIG. 2 , the input signal 209 is the desired motor duty cycle. In this embodiment, the feedback signal 212 is a pulsed digital control signal 220 corresponding to the pulsed digital control signal from Figure 7 The pulse control signal 124. In this embodiment, the pulse control signal 220 represents the desired motor duty cycle.

[0093] In another embodiment (not shown), the input signal 209 may be considered to represent a desired torque or a desired torque fraction, and the feedback signal may be based on the torque output 161 of the motor rather than the pulsed digital control signal 220. In such an embodiment, the feedback is more representative of the actual torque output of the motor than the pulsed control signal 220 because the feedback accounts for any potential torque losses or inefficiencies caused by switching the power supply source and the motor back and forth between a zero state and a most efficient (or other desired) operating state.

[0094] In still other embodiments, the feedback signal 212 may be a proportional combination of the pulsed control signal 220 and the motor's torque output 161. When a higher order sigma-delta converter is used, the pulsed control signal, the motor torque output, or both may be used as feedback sources to provide feedback to different integrators at different scales, as appropriate for the desired adaptive control.

[0095] As mentioned above, first-order sigma-delta converters (like all sigma-delta converters) help push the noise to higher frequencies. However, first-order sigma-delta conversion does not avoid the generation of idle tones - these idle tones 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. This dither can be added in many places in the system. In Figure 8 , an optional pseudo-random jitter generator 223 (shown in dashed lines) may provide an optional jitter signal 224 as an additional input to the differential amplifier 201. In other embodiments, the jitter may instead be injected elsewhere in the sigma-delta converter 200, such as as an additional input to the comparator 205. Higher order sigma-delta converters are less susceptible to idle tones, and therefore, there would be less benefit from adding jitter to such a system. Accordingly, dither would not typically be used in such a system (although it could be used).

[0096] In the embodiments discussed above, pulse width modulation and Σ-Δ conversion are used to generate pulse control signals. Pulse width modulation and Σ-Δ conversion are two types of converters that can be used to represent input signals. Some of the described Σ-Δ converters present oversampling conversion, and in various alternative embodiments, other oversampling converters can be used instead of Σ-Δ conversion. In still other embodiments, other types of converters can also be used. It should be understood that the converter can adopt various modulation schemes, including various pulse height modulation schemes or pulse density modulation schemes, modulation for code division multiple access (CDMA) or other modulation schemes that can be used to represent the input signal, as long as the pulse generator is adjusted accordingly.

[0097] As will be appreciated by those skilled in the art, switched reluctance motors are relatively inexpensive, high-power motors compared to similarly sized induction motors. However, switched reluctance motors tend to be noisy and prone to vibration due to their switching, which makes them unsuitable for use in many applications. A characteristic of sigma-delta conversion is its ability to shape the noise and push the noise to frequencies that are less (or not) annoying to humans. Thus, controlling a switched reluctance motor in a pulsed manner using sigma-delta or other noise shaping conversion techniques has the potential to make it practical to use switched reluctance motors in many applications where they are not currently used.

[0098] Management Transformation

[0099] The inherent inductance of the motor may temporarily delay / slow down the current / power step between the motor on state and the motor off state. During continuous (pulseless) operation, these transient effects tend to have a relatively small impact on overall motor operation. However, when fast pulses are used as contemplated herein, these transient effects can have a larger net impact, and therefore there is more motivation to focus on motor responsiveness. Reference will be made to FIG. 9A to FIG. 9B Describe the nature of the problem.

[0100] As previously described, the overall goal of pulse motor control is to operate (power) the motor at its most efficient level for the current motor speed during the motor "on" time period, and to cut off power (provide zero torque) during the motor "off" time period. Therefore, ideally, the power transition between the motor power "on" state and the motor power "off" state will be a discrete step. This is Fig. 9A This is shown graphically in FIG, which shows the ideal / desired motor drive power for pulse motor control at a duty cycle of 50%. Fig. 9A As shown, the transition between the "on" pulse 302 and the "off" period 304 is an ideal step. In practice, the inductive aspects of the motor and (when used) the inverter will 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. Typically, in response to a step change in the commanded motor drive power, the actual input power to the motor will rise and fall slightly in an exponential manner. The nature of the rise and fall is Fig. 9B As seen therein, there is a rising period of time (rise time) 306 required for the power signal to actually rise from zero to the desired "on" power level, and a falling period of time (fall time) 308 required for the power signal to actually fall from the "on" power level to zero.

[0101] During the power up period and the power down period, the motor continues to be driven. Figure 1 As can be readily appreciated, the motor operates inefficiently during these time periods in varying ways. In general, for most given operating speeds, motor efficiency will decrease as operating power decreases from the maximum efficiency line 16 toward zero, with energy conversion efficiency becoming significantly worse as power levels approach zero. Thus, the pulse distortion represented by the power ramp-up and power ramp-down periods reduces the efficiency gains that may be obtained through the described pulsed operation. In general, the smaller the ratio of the rise / fall time to the pulse length, the less impact the transient switching effects will have on the energy conversion efficiency of the motor during the pulse.

[0102] It should be understood that Fig. 9B The transient effects shown in are shown to illustrate the nature of the problem and do not necessarily reflect the rise / fall times associated with the operation of any particular motor. The relative range of the ratio of rise time to pulse length can vary widely based on the available power supply source voltage and the characteristics of the motor used (primarily referring to rise time and fall time), the pulse frequency (primarily dictated by the control scheme used), and the pulse width (dictated by the control scheme and motor load). If the pulse is slow compared to the motor response, the rise / fall time may be a very small fraction of the pulse width, and the transient switching effects may have minimal impact on motor performance. Conversely, if the pulse changes very quickly and / or the motor response is slow, the ratio of rise / fall time to pulse width may become very large and may even exceed the pulse width. If not properly managed, the transient efficiency losses associated with switching can greatly reduce or even eliminate the theoretical gains that can be obtained through pulse operation. Therefore, it is very important to consider the transient switching effects associated with pulse operation when determining the pulse frequency and control scheme suitable for any particular application.

[0103] A variety of techniques can be used to improve power rise time and power fall time. For example, in some embodiments, a resonant capacitor based on the motor inductance is used. The resonant capacitor can be used to reduce the power rise time and power fall time by a factor of 100 or less (usually substantially less), so the resonant capacitor can significantly reduce the transient switching effects associated with pulse operation. Therefore, it should be understood that compared to existing motors, motors designed with pulse control in mind or motors modified to improve the transient response of the motor to power pulses can gain more benefits from pulse operation.

[0104] In other embodiments, a boost converter and / or a buck-boost converter can be used to significantly reduce the rise time and fall time associated with switching between an "on" motor state and an "off" motor state. In a specific example, the boost converter can charge a boost capacitor (sometimes referred to herein as a kick-start capacitor) to a voltage higher than the input voltage of the motor. Each time the motor is pulsed on, the kick-start capacitor applies this higher voltage to the motor, which can significantly reduce the rise time.

[0105] Similarly, a buck-boost converter can be used to charge the buck-boost capacitor. Each time the motor is pulsed off, the buck-boost capacitor stores energy from the magnetic field of the motor winding, which greatly reduces the transient fall time of the pulse.

[0106] The voltage charge levels and capacitances of the boost capacitor and the buck-boost capacitor, respectively, are appropriately selected for the motor and its inductive and resistive characteristics to shorten the transient rise / fall times associated with the motor being pulsed on and pulsed off, respectively. Preferably, the respective capacitances and charge voltage levels of the boost capacitor and the buck-boost capacitor are also selected to maximize overall motor efficiency during pulse changes, taking into account all aspects, including the inefficiencies associated with the transients themselves and the effects of any overshoot that occurs due to the use of the boost and buck-boost converters. Since the boost and buck-boost capacitors are used to improve transient response, they may each be recharged in a timely manner during the time periods between their respective uses (e.g., during the motor off period).

[0107] Another factor that is particularly relevant to losses during the "off" transient of the motor is related to the dissipation of energy stored in the magnetic field. Generally, any time the motor is running, an electromagnetic field is established inside the motor. The electromagnetic field contains a certain amount of energy stored in the magnets. If the motor is simply turned off, the stored energy will be dissipated, which will result in a loss of energy present in the magnetic field. Any such energy loss will reduce overall system efficiency. By positively controlling the shutdown transient of the motor to deliver zero torque during the "off" period, rather than simply cutting off the current supply to the motor to actually turn off the motor, a portion of this magnetic field energy can be recovered. This causes some "reverse" current to flow back / through the power converter 140 from the windings, so that at least a portion of this energy can be recovered, which means less energy loss, thereby improving system efficiency. In addition, in many applications, managing the power converter 140 to deliver zero torque (rather than simply turning off the power converter) will result in faster transitions.

[0108] Similarly, during the "off" cycle of the generator, the power drawn from the generator may be controlled to efficiently manage the capture of stored energy accumulated in the motor during the "on" cycle.

[0109] Fig.11A power converter / controller is shown incorporating transient control circuitry 343 (which may include resonant circuits, boost circuits, and buck-boost circuits and / or other transient response improvements of the circuits together, individually, or in any suitable combination). In the illustrated embodiment, machine controller 310 directs pulse control of power converter / controller 340, which in turn controls motor 160. Transient control circuitry 343 is incorporated into power converter 340 itself. In other embodiments, transient control circuitry may be provided as an additional unit placed between power converter 340 and the motor / generator, or incorporated into the motor / generator itself to achieve the same functionality (placement not shown).

[0110] Electric Motor Types and Applications

[0111] It should be apparent from the foregoing description that the described pulse machine control can be used in a variety of different applications to improve the energy conversion efficiency of various different types of motors and generators, including AC motor / generators and DC motor / generators.

[0112] Some representative types of motors that can benefit from the described pulses include asynchronous AC motors and synchronous AC motors, including: induction motors (IM); switched reluctance motors (SMR); synchronous reluctance motors (SynRM); permanent magnet synchronous reluctance motors (PMaSynRM); hybrid PMaSynRM; externally excited AC synchronous motors (SyncAC); permanent magnet synchronous motors (PMSM); eddy current machines; AC linear motors; AC mechanically commutated motors and DC mechanically commutated motors; axial flux motors, etc. Representative DC motors include brushless motors, electrically excited motors, permanent magnet motors, series wound motors, shunt motors, brushed motors, compound motors, and others.

[0113] Although the structure, control, and energy conversion efficiency of various types of motors and generators vary greatly, most motors are designed to operate within a certain range of operating conditions, and their energy conversion efficiency will vary (usually greatly) within this operating range. Generally, if the operating range of the motor includes Figure 1 If the area under the equivalent of the maximum efficiency curve shown in , the control principles described in this article can be applied to any type of motor to improve the efficiency of the motor. In some cases, efficiency gains can be obtained by designing the motor with pulse operation in mind.

[0114] Some motor designs utilize windings on the rotor and stator to generate the motor flux, while other motor designs use permanent magnets on the rotor or stator to contribute to the motor flux. A motor incorporating permanent magnets will have flux at zero torque, and therefore will typically have core losses when rotating, and will generate a back electromotive force (BEMF) that exceeds the supply voltage. In such applications, it is often desirable to provide a smaller current to the motor during the "torque off" time period to maintain zero torque. It should be understood that the need to supply current during the "no torque" time period reduces the overall efficiency associated with pulsing, and therefore this need should be considered when determining which operating ranges can benefit from pulsing. In some operating regions, the losses associated with switching and supplying current during the torque off time period may exceed the efficiency gains associated with pulsing, thereby reducing (or completely eliminating) the operating range in which pulsed operation is desired. However, many motors incorporating permanent magnets will have operating regions in which the overall efficiency of the machine can be improved by using pulsing. For example, for an interior permanent magnet synchronous motor (IPMSM), the operating region most suitable for pulse operation is expected to be an operating speed below (or close to) a threshold speed where field weakening is required.

[0115] Currently, there is a great deal of interest in the use of electrical power devices (e.g., electric motors) in vehicle propulsion systems. Electric motors used for vehicle propulsion are generally referred to as traction motors. In the automotive field, great efforts have recently been made to utilize traction motors alone or in combination with internal combustion engines (hybrid power) to drive vehicles. Today, asynchronous motors and three-phase induction motors are most commonly used in automotive applications, both of which are good choices for the above-mentioned pulse motor control. Automotive applications are criticized for expecting the motor to operate under a very wide range of operating conditions, ranging from low speed high torque requirements to high speed low torque requirements and all operating conditions in between. Under most driving conditions (i.e., during most of the time in many driving cycles), the torque required to be produced by the motor is much less than the torque that the motor can produce at the current motor speed, and in fact most of the driving occurs in the area where the requested output of the motor is below (usually much below) the maximum efficiency line 16.

[0116] exist Fig.10 The low-load nature of a typical drive cycle can be seen in the , which plots a series of drive points representing the electric power / torque output of a simulated traction motor / generator when running the Federal Test Procedure for the City Drive Cycle (FTP-75). These drive points are plotted on a torque / speed / efficiency graph. Fig.10It can be seen that a significant portion of the drive cycle requires lower torque than the maximum efficiency curve 16. Thus, a significant portion of a typical drive cycle is in an operating region where benefits (and often significant benefits) can be derived from the described motor control method. Fig.10 Only those portions of the driving cycle where output torque is required are depicted. During some portions of the driving cycle, the motor used as a generator can use regenerative braking. Most of the regenerative braking also occurs at points that can benefit from the pulse control described herein. It is believed that by implementing the described control method in certain automotive applications, an average overall efficiency gain of up to 7% to 12% or more will be obtained. A 7% to 12% increase in efficiency will translate into a 7% to 12% increase in mileage under the same charging conditions, which has significant advantages in the context of automotive applications where range anxiety has severely hindered the widespread adoption of this technology. It can be expected that even greater efficiency improvements will be seen under autonomous driving conditions where the requested motor output has less variation.

[0117] In automotive and other vehicle applications, the operating range of electric motors can be very wide. This is due in part to the fact that in most all-electric vehicle applications, the electric motor is coupled to the driven component(s) at a fixed speed ratio. This is in contrast to internal combustion engine powered vehicles, which typically employ an intermediate transmission with a variable speed ratio between the engine and the driven component(s). Figure 1 It can be clearly seen that the "sweet spot" for motor operation is typically at an intermediate motor speed. When required, a variable speed gear drive can be used to allow the motor to operate in a more efficient region more of the time. Such a gear drive can be readily provided by a transmission, and therefore there are potential advantages to using a transmission in conjunction with the described pulse motor control. The transmission may have a set of gears, or may be continuously variable, or may be of any other suitable form. In such an embodiment, a motor controller or other suitable control component may be arranged to direct the operation of the transmission in a desired manner. Likewise, the use of a transmission may also be beneficially used in a variety of other (non-vehicle) related applications.

[0118] Although automotive applications have been used as examples of vehicle propulsion applications, it should be understood that the control methods described are equally beneficial in other propulsion-related applications, including: electric motors used in other types of vehicles (including trucks, vans, motorcycles, bicycles, drones and other flying devices); robots and other devices that move autonomously in an environment, etc.

[0119] Electric motors used in heating, ventilation and air conditioning (HVAC) applications are another good example of a market that can benefit from pulse control. Several factors exist that contribute to making pulse motor control well suited for HVAC applications. These factors include the following: (a) the motors used in HVAC applications today are primarily induction motors that do not contain permanent magnets; (b) the majority of the operating life of an HVAC motor is spent in an operating region below the high efficiency region of the motor; and (c) the inertia of the fan or pump typically dominates the inertia of the electric motor, which tends to further mitigate potential NVH-related effects associated with pulses.

[0120] Of course, electric motors are also used in a variety of other applications where the motor is operated at less than its optimum efficiency. This may be due to operation over a wide operating range (e.g., at a variety of different loads and / or motor speeds), or due to the use of a motor that is oversized (or not specifically designed) for its application, or any of a variety of other reasons. It should be apparent that the control method described can be beneficial for any of these types of applications.

[0121] High and low torque modulation

[0122] In most of the above examples, pulse variation is achieved by modulating torque between a higher (energy-saving) torque output level and a zero torque output level. Although this is considered to be the preferred method in most pulse control applications, it is expected that there will be situations (e.g., specific machine / machine operating areas): where it may be preferred to modulate between a higher non-zero torque output and a lower non-zero torque output, rather than between high torque and zero torque. For example, in some cases, high / low pulse variation may have better noise, vibration and harshness (NVH) characteristics than on / off pulse variation, and therefore there may be situations where a more desirable compromise between energy conversion efficiency and NVH characteristics can be obtained by high / low pulse variation compared to on / off pulse variation. In another example, for some operating areas of some motors, the high / low pulse variation method can provide better overall energy conversion efficiency than on / off pulse variation. Electric motors that incorporate permanent magnets that require magnetic field weakening to generate zero torque are particularly good choices for using high and low torque modulation.

[0123] Pulse motor overexcitation

[0124] Most electric motors have a specified maximum rated output level. Typically, the maximum rated output level is based on steady-state operation, and the motor can usually be driven at a higher output level for short periods of time without any adverse effects. In some embodiments, in selected operating regions, the output level of the motor can be in the form of pulses where the "on" level is higher than the maximum rated continuous output level under steady-state operation. For some motors within some potential operating ranges, there are several potential advantages to using over-pulses. For example, in some specific operating conditions, the energy conversion efficiency of a motor or system (e.g., a motor and inverter) at a given motor speed may be higher in certain over-pulse regions than in the "normal" operating region, which means that pulse operation at higher torque or power may be more efficient.

[0125] Furthermore, more efficient operation generally results in less heating, which potentially facilitates even higher net torque output. Thus, it is believed that if motors that are traditionally driven with continuous power (such as induction motors and other AC motors, brushless DC motors, switched reluctance motors, etc.) are designed with pulse operation in mind, these motors can sometimes be optimized to use pulse control to achieve higher net torque output than would be possible using more conventional steady / continuous drive power as appropriate.

[0126] Other motor optimization

[0127] There are various factors that contribute to motor inefficiency. One contributing factor involves 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 unity power factor. However, for many types of motors / generators, this ideal situation does not necessarily represent the highest system efficiency point at any given load and speed. When pulse control of a motor as described herein is contemplated and the pulse operating point is taken into account to optimize power factor correction, it is expected that the effective power factor will be improved above the power factor of conventional continuous motor operation.

[0128] Another factor that contributes to motor inefficiency is sometimes called resistive losses or I 2R losses. Resistive losses heat the motor windings, which further increases the resistive losses because the resistivity of the windings generally increases with temperature. Resistive losses are nonlinear—at least increasing with the square of the current. Therefore, at higher motor output levels (such as those used during pulse operation), resistive losses tend to have a greater impact on overall motor efficiency. A rule of thumb for motor design is that magnetic losses should be roughly equal to resistive losses at the target operating set point. Using the pulse motor control method described in this article may affect the design or selection of appropriate motors because motor operating points below the most efficient operating point are generally not used. In other words, the motor is either driven essentially at its most efficient operating point or driven at a higher load. There is no need to consider low-load continuous operation in the design or selection of the motor, which can help further improve the overall efficiency of the system.

[0129] Another factor that contributes to motor inefficiency is sometimes referred to as core loss, which is related to flux orientation losses. One loss mechanism is motor winding leakage reactance, which refers to the flux lines that do not connect between the rotor magnetic elements and the stator magnetic elements. Another core loss mechanism involves hysteresis within the magnetic core and is often represented by a BH curve. Here, B is the flux density and H is the magnetic field strength. They are related to the magnetization of the material through which the field passes, which for some motors is the iron core(s) present in the rotor or stator. Similarly, motors designed specifically for pulse control can be optimized to mitigate core losses during pulse motor operation.

[0130] As discussed above, transient switching losses associated with switching between the motor "on" state and the motor "off" state during pulse changes are another factor that affects the efficiency of the motor during pulse operation. As discussed above, one way to reduce these transient switching losses is to improve (shorten) the motor drive current rise time and fall time associated with the motor pulse on and pulse off. Another way to help manage transient switching losses is to manage the frequency of the pulse. Generally, the lower the switching frequency, the lower the transient switching losses will be. However, there is such a trade-off here that lower frequency switching sometimes causes noise, vibration and harshness (NVH), which may be undesirable or unacceptable in certain applications. Therefore, it is preferred to appropriately select the pulse frequency of any particular motor taking into account motor efficiency and NVH considerations and / or requirements related to the application for which the (multiple) motors are intended. In this way, it is noted that a pulse controller with noise shaping capabilities (such as a pulse controller based on Σ-Δ conversion) can be very helpful in mitigating the NVH effects associated with pulse motor control, and therefore can be helpful in supporting the use of generally lower switching frequencies.

[0131] It should be understood that appropriate pulse frequencies for different motors may be very different based on the motor's construction, operating environment, and operating range. For some motors, a switching frequency on the order of 10kHz to 50kHz may be appropriate - while for other motors, a much lower switching frequency (e.g., a range of 10Hz to 500Hz) may be more appropriate. Still other motors may have a switching frequency between these ranges or above or below one of the stated ranges. For any particular motor, the most appropriate pulse frequency will depend on various factors, including motor size, turn-on / turn-off transient characteristics, NVH considerations, etc.

[0132] The selection of the desired drive point for any particular motor speed can also have an impact on the switching frequency. More specifically, many motors have relatively flat efficiency curves over a relatively wide operating range. Typically, pulse operation at torque levels slightly below the best efficiency point for continuous operation can sometimes facilitate switching at a lower frequency, which—depending on the nature of the switching losses—can result in higher overall motor efficiency during pulse operation. This emphasizes the point that the desired pulse operation drive point associated with any particular motor speed is not necessarily the most efficient torque level for continuous motor operation. Rather, in some cases, the most energy-efficient point for pulse operation may be slightly different from the most energy-efficient point for continuous operation. In addition, NVH considerations and / or other operating considerations or control considerations may influence the decision regarding the drive point that is deemed appropriate for any particular motor speed.

[0133] Additional Embodiments

[0134] Although only a few embodiments of the present invention have been described in detail, it will be appreciated that the present invention may be implemented in many other forms without departing from the spirit or scope of the present invention. In different embodiments, the various described pulse controllers and other control elements may be implemented, grouped, and configured in a variety of different architectures. For example, in some embodiments, the pulse controller may be incorporated into a motor controller or an inverter controller, or may be provided as a separate component. Similarly, for a generator, the pulse controller may be incorporated into a generator controller or a rectifier controller, and in a combined motor / generator, the pulse controller may be incorporated into a combined motor / generator controller or a combined inverter / rectifier controller. In some embodiments, the control functions described may be algorithmically implemented by software or firmware executed on a processor, which may take any suitable form, including, for example, a general purpose processor and a microprocessor, a DSP, and the like.

[0135] The pulse generator or machine controller may be part of a larger control system. For example, in a vehicle application, the control described may be part of a vehicle controller, a powertrain controller, a hybrid powertrain controller, or an ECU (engine control unit), etc., that performs various functions related to vehicle control. In such an application, the vehicle controller or other related controllers, etc. may take the form of a single processor that performs all required controls, or may include multiple processors that are co-located as part of a powertrain or vehicle control module, or distributed in various locations within the vehicle. The specific functions performed by any one of the processors or control units may vary widely.

[0136] 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 methods described are equally applicable to generator and / or generator / rectifier control. 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, descriptions of features of pulse motor control, pulse generator control, or pulse motor / generator control should be understood to be equally applicable to pulse motor control, pulse generator control, and pulse control of a combined motor / generator.

[0137] A variety of different control schemes may be implemented within the pulse controller 120. Typically, these control schemes may be implemented digitally, algorithmically, using analog components or using a hybrid approach. The pulse generator and / or motor controller may be implemented as code executed on a processor, on programmable logic such as an FPGA (field programmable gate array), in a circuit system such as an ASIC (application specific integrated circuit), on a digital signal processor (DSP) using analog components or any other suitable hardware. In some embodiments, the control schemes described may be incorporated into target code to be executed on a digital signal processor (DSP) incorporated into an inverter controller (and / or a rectifier controller in the context of a generator, and / or a combined inverter / rectifier controller).

[0138] In some of the primarily described embodiments, sigma-delta control is used to generate the pulsed control signal. Although sigma-delta control is a particularly good way to generate the pulsed control signal 124, it should be appreciated that in other embodiments, various other control schemes may be used to generate the pulsed control signal.

[0139] Regardless of the nature of the pulses used, torque modulation is preferably managed in a manner so as not to produce NVH that is unacceptable for the intended application.

[0140] The pulse motor control described can be used in a variety of applications. In general, the greatest efficiency gains are often seen in motors and generators that are not continuously driven at anywhere near their best operating efficiency. A good example of this is a motor / generator that has a wide operating range and is intended to be used under widely varying load conditions. Another good example is a motor that is driven on a routine basis. For example, it is not uncommon for a system designer to use a larger motor than is actually required for the application, such as using a 100hp motor when a 50hp motor would be quite sufficient for the specified task. In many cases, the larger motor may operate less efficiently at a reduced load, and in such cases, pulse control can improve the motor efficiency during use.

[0141] Accordingly, the present embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

Claims

1. A motor system, comprising: AC motor; a power converter in the form of or comprising at least one of an inverter and a rectifier; and a controller arranged to direct the power converter to cause pulsed operation of the motor to deliver a desired average output, wherein during pulsed operation of the motor, the controller causes the output of the motor to be alternately turned on and off and turns the power converter off during at least a portion of a time period when the motor is in a zero torque state.

2. The motor system according to claim 1, wherein: The controller turns off the power converter whenever the electric machine is in a zero torque state.

3. The motor system according to claim 2, wherein: The controller alternates the motor on and off at a pulse frequency of at least ten times per second such that the power converter is turned off at least ten times per second.

4. The motor system according to claim 1, wherein: During at least a portion of the time period in which the motor is turned on, the motor outputs at a first output level that is higher than a desired output level, and the first output level is selected so that the overall energy conversion efficiency of the motor system during pulsed operation of the motor system is higher than the overall energy conversion efficiency that the motor would have when the motor is driven in a continuous manner at a third output level to deliver the desired output.

5. The motor system according to claim 4, wherein: The controller changes a first output level according to a change in an operating speed of the motor.

6. The motor system according to claim 1, wherein: The time period between consecutive first output horizontal pulses is a pulse cycle duration, and the controller is configured to direct the pulse cycle duration to vary during operation of the motor.

7. The motor system according to claim 6, wherein: The pulse cycle duration varies according to the rotational speed of the motor.

8. An electric machine system comprising an electric machine, a power converter and a controller arranged to direct the power converter to cause pulsed operation of the electric machine to deliver a desired average output, wherein: During pulse operation of the motor: the controller alternating the output of the electric machine between on and off and shutting down the power converter during at least a portion of a time period when the electric machine is in a zero torque state; During at least a portion of the time period during which the motor is turned on, the motor outputs at a first output level that is higher than a desired output level, and the first output level is selected such that an overall energy conversion efficiency of the motor system during pulsed operation of the motor system is higher than an overall energy conversion efficiency that the motor would have if the motor were driven in a continuous manner at a third output level to deliver the desired output; The controller varies the first output level based on changes in the operating speed of the motor, and the first output level for a given operating speed is selected to optimize energy conversion efficiency of the motor system at the given operating speed.

9. A method of operating an AC motor system, the method comprising directing a power converter to cause pulsed operation of the motor to deliver a desired average output, the power converter being or comprising at least one of an inverter or a rectifier, wherein: During pulsed operation of the motor, a controller alternates the output of the motor between on and off and turns the power converter off during at least a portion of a time period when the motor is in a zero torque state, wherein the output level of the motor varies during the on pulses as a function of the operating speed of the motor, and wherein the output level of the motor is selected such that the energy conversion efficiency of the motor system during the pulsed operation of the motor system is improved over the overall energy conversion efficiency the motor would have if the motor were driven in a continuous manner at a third output level to deliver a desired output.

10. The method according to claim 9, wherein: Whenever the electric machine is in a zero torque state, the power converter is turned off.

11. The method according to claim 9, wherein: The motor alternates between being on and off at a pulse frequency of at least ten times per second such that the power converter is turned off at least ten times per second.

12. The method according to claim 9, wherein: During at least a portion of the time period in which the motor is turned on, the motor outputs at a first output level that is higher than a desired output level, and the first output level is selected so that the overall energy conversion efficiency of the motor system during pulsed operation of the motor system is higher than the overall energy conversion efficiency that the motor would have when the motor is driven in a continuous manner at a third output level to deliver the desired output.

13. A motor system, comprising: Motor; Power converters; and a controller arranged to receive an indication of a desired motor output and to direct the power converter to cause pulsed operation of the motor to deliver a desired average output during at least some operating conditions, the energy conversion efficiency for delivering the desired average output being greater than that which would be achieved when the motor is driven in a continuous manner to deliver the desired output, the controller being configured to vary a pulse frequency of the motor during pulsed operation of the motor based at least in part on one or more selected operating conditions.

14. The motor system according to claim 13, wherein: The pulse frequency varies based at least in part on the motor speed during pulse operation.

15. The motor system according to claim 13, wherein: The pulse frequency varies based at least in part on the requested torque.

16. The motor system according to claim 13, wherein: The pulse frequency varies based at least in part on the motor speed and the requested torque.

17. The electric machine system of claim 13, further comprising a rotor, and wherein: The rotor rotates continuously during pulse operation of the motor.

18. The motor system of claim 13, wherein: During pulse operation, the output of the motor pulses between a first output level and a second output level, and the second output level is selected from: substantially zero torque; and a motor off state.

19. The motor system of claim 13, wherein: In some operating regions of the motor, the pulse frequency varies proportionally to the motor speed.

20. The electric machine system of claim 13, wherein: The pulse frequency is at least 10 Hz.

21. A motor system, comprising: Motor; Power converters; and A controller is arranged to direct the power converter to cause pulsed operation of the motor to deliver a desired average output during at least some operating conditions, the controller being configured to vary the pulse frequency of the motor based at least in part on noise or vibration considerations.

22. A motor system, comprising: Motor; Power converters; a controller arranged to direct the power converter to cause pulsed operation of the electric machine to deliver a desired average output during at least some operating conditions, the controller being configured to vary a pulse frequency of the electric machine based at least in part on one or more selected operating conditions; as well as A pulse frequency lookup table, wherein the controller determines the pulse frequency at least in part by referencing the pulse frequency lookup table.

23. The electric machine system of claim 34, wherein: At least one of the motor speed and the requested torque is used as an index into the pulse frequency lookup table.

24. A motor system comprising: AC motor; a power converter, the power converter comprising at least one of an inverter and a rectifier; and A controller is arranged to direct the power converter to cause pulsed operation of the motor to deliver a desired average output, wherein during pulsed operation of the motor, the controller causes the output of the motor to alternate between a first output level and a zero torque state, and controls current delivered to the motor during a transition period between the first output level and the zero torque state, and shuts down the power converter during at least a portion of the time period when the motor is in the zero torque state.

25. The electric machine system of claim 24, wherein: The controller turns off the power converter whenever the electric machine is in a zero torque state.

26. The electric machine system of claim 2, wherein: The controller alternates the motor on and off at a pulse frequency of at least ten times per second such that the power converter is turned off at least ten times per second.

27. The electric machine system of claim 24, wherein: During at least a portion of the time period in which the motor is turned on, the motor outputs at a first output level that is higher than a desired output level, and the first output level is selected so that the overall energy conversion efficiency of the motor system during pulsed operation of the motor system is higher than the overall energy conversion efficiency that the motor would have when the motor is driven in a continuous manner at a third output level to deliver the desired output.

28. The electric machine system of claim 24, wherein: The controller changes a first output level according to a change in an operating speed of the motor.

29. The electric machine system of claim 24, wherein: The controller causes the electric machine to deliver zero torque during a transition period between the first output level and the zero torque state.

30. The electric machine system of claim 24, wherein: The time period between consecutive first output horizontal pulses is a pulse cycle duration, and the controller is configured to direct the pulse cycle duration to vary during operation of the motor.

31. The motor system of claim 30, wherein: The pulse cycle duration varies according to the rotational speed of the motor.

32. A method of operating an AC motor system, the method comprising directing a power converter to cause pulsed operation of the motor to deliver a desired average output, the power converter being at least one of an inverter or a rectifier or comprising at least one of an inverter and a rectifier, wherein: During pulse operation of the motor: alternating the output of the electric machine between a first output level and a zero torque state; controlling current delivered to or received from the electric machine during a transition period between the first output level and the zero torque state; and The power converter is turned off during at least a portion of a time period when the electric machine is in a zero torque state.

33. The method of claim 32, wherein: Whenever the electric machine is in a zero torque state, the power converter is turned off.

34. The method of claim 32, wherein: The motor alternates between being on and off at a pulse frequency of at least ten times per second such that the power converter is turned off at least ten times per second.

35. The method of claim 32, wherein: The first output level is higher than a desired output level, and the first output level is selected so that the overall energy conversion efficiency of the motor system during pulsed operation of the motor system is higher than the overall energy conversion efficiency that the motor would have when the motor is driven in a continuous manner at a third output level to deliver the desired output.

36. The method of claim 32, wherein: The electric machine is controlled to deliver zero torque during a transition period between the first output level and the zero torque state.

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