Method for increasing rise rate of torque in electric machine using stator current bias

Abstract

A method of controlling an electric machine having independently excitable rotors and stators includes pulse-controlling the electric machine and controlling the electric machine to an OFF state. Pulse control of the electric machine includes simultaneously exciting the rotor with a direct current and exciting the stator with a stator bias current to produce magnetic flux in the rotor via two independent paths. Pulse control of the electric machine may also include terminating the stator bias current when a desired magnetic flux is generated in the rotor. Pulse control of the electric machine may include providing a stator flux to the stator such that the electric machine provides a pulsed torque.

Description

Technical Field

[0001] The present disclosure relates to pulse control of a motor, and more particularly to a method of improving the torque rise rate of an externally excited synchronous motor by using a stator current bias. Background Art

[0002] Winding field synchronous machines can be winding field synchronous electric motors (WFSM) and winding field synchronous generators (WFSG). Winding field synchronous machines can also be called externally excited synchronous machines, which have an independently excited rotor and an independently excited stator. The rotor can be fed via slip rings, rotating magnets or capacitively coupled rotating power transformers. A DC current can be provided to the rotor to excite the rotor, thereby generating a magnetic flux of the rotor.

[0003] A multiphase inverter can be used to generate magnetic flux or stator flux in the stator. For example, a multiphase inverter can be a three-phase inverter that generates stator flux in the stator. The magnetic flux of the rotor interacts with the stator flux in the air gap between the stator and the rotor, causing the rotor to rotate and generate electricity in the form of electromotive force (EMF).

[0004] The current EESM is designed to only need to provide a small amount of current to the rotor compared to the current provided to the stator. For example, a current in the range of 10-90 amps may be provided to the rotor, and a current in the range of 100-1000 amps and sometimes greater than 1000 amps may be provided to the stator. Therefore, the rotor has a large number of turns and therefore has a high resistance and high inductance resulting in a high time constant, which is not conducive to turning on and off at a frequency in the range of 5 to 100 Hz.

[0005] When the EESM is delivering a constant level of power, high resistance and high inductance are not a problem because once the magnetic flux of the rotor flux is established, the current supplied to the rotor is not turned on and off, but is controlled at a constant level based on the maximum efficiency operating point of the EESM. However, when the EESM is pulsed on and off, such as during dynamic motor drive (DMD) control, the rotor current needs to be turned on and off as quickly and efficiently as possible. Summary of the invention

[0006] The present disclosure generally relates to a method of controlling a motor to increase the rate of rise of the magnetic flux in the EESM rotor, thereby increasing the rate of rise of the torque provided by the EESM. For example, the method disclosed herein can reduce the time for the motor to transition from zero or near-zero torque to a desired pulsed torque when the motor is pulsed on (ON) and off (OFF). The method detailed herein can be used to increase the rate of decrease of the magnetic flux in the EESM rotor. In some embodiments, the method detailed herein can be performed on a conventional EESM that is configured to operate in a continuous control mode without considering pulsed control. In certain embodiments, the method detailed herein can be performed on an EESM that has been modified to operate in a pulsed mode.

[0007] Furthermore, any embodiment or aspect described herein may be used in combination with any or all other embodiments or aspects described herein, within the scope of consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various aspects of the present disclosure are described below with reference to the accompanying drawings, which are incorporated into and constitute a part of this specification, in which:

[0009] Figure 1 is a representative torque / speed / efficiency graph showing the energy conversion efficiency of a representative electric motor under different operating conditions;

[0010] Figure 2 is a graph showing a pulsed torque signal applied to an electric motor;

[0011] Figure 3A is a torque versus efficiency graph for a motor running at a fixed speed during the transition from zero to peak efficiency torque;

[0012] Figure 3B is a graph of torque versus work loss for an example motor operating at a fixed speed during the transition from zero to peak efficiency torque;

[0013] Figure 4 A pulse controlled motor according to a non-exclusive embodiment is shown;

[0014] Figure 5A is a schematic diagram of a continuous three-phase AC waveform having a peak value of 50 amperes for an armature winding;

[0015] Figure 5B is a schematic diagram of a continuous DC signal at 5 amperes for the field winding;

[0016] Figure 5C and Figure 5E is a pulsed waveform with a 50% duty cycle, which provides Figure 5A The same power output of continuous waveform;

[0017] Figure 5D and Fig. 5F is a pulsed DC signal with a 50% duty cycle, which provides Figure 5B The same power output as the continuous DC signal;

[0018] Figure 6A-6C is a signal diagram illustrating benefits of a non-exclusive embodiment; and

[0019] Figure 7 is a graph of a model provided according to an embodiment of the present disclosure, which shows the current rise time of the rotor as the stator current bias changes;

[0020] Figure 8 is a flow chart of a method for improving the torque rise rate in a motor provided by the present disclosure; and

[0021] Fig. 9 is a block diagram of an example controller that can perform one or more operations described herein. DETAILED DESCRIPTION

[0022] The present disclosure will now be described more fully below with reference to the accompanying drawings and with reference to example embodiments thereof, wherein in each of the several views, the same reference numerals represent the same or corresponding elements. These example embodiments are described to make the present disclosure more thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Features from one embodiment or aspect may be combined with features from any other embodiment or aspect in any appropriate combination. For example, any individual or collective feature of the method aspect or embodiment may be applied to the device, product or component aspect or embodiment, and vice versa. The present disclosure may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; on the contrary, these embodiments are provided to enable the present disclosure to meet applicable legal requirements. As used in the specification and the appended claims, the singular forms "one", "an" and "the" include plural referents unless the context clearly dictates otherwise. In addition, although reference may be made herein to quantitative measurements, numerical values, geometric relationships, etc., unless otherwise specified, any one or more (if not all) of these may be absolute or approximate to take into account acceptable variations that may occur, such as variations due to manufacturing or engineering tolerances, etc.

[0023] As used herein, the term "machine" is intended to be broadly interpreted as an electric motor and a generator. Electric motors and generators are very similar in structure, both including a stator and a rotor with multiple poles. When the electric machine operates as a motor, it converts electrical energy into mechanical energy, and when it operates as a generator, the electric machine converts mechanical energy into electrical energy.

[0024] Modern electric motors have relatively high energy conversion efficiencies. However, the energy conversion efficiency of most electric motors can vary significantly based on their operating load. In many applications, electric motors are required to operate under a variety of different operating load conditions. Therefore, electric motors typically operate at or near their highest efficiency levels at certain times, while at other times, they operate at lower efficiency levels.

[0025] Battery-powered electric vehicles provide a good example of motors that operate at various efficiency levels. In a typical driving cycle, the electric vehicle will accelerate, cruise, decelerate, brake, turn, etc. Within certain rotor speed and / or torque ranges, the motor operates at or near the most efficient operating point (i.e., its "sweet spot"). Outside these ranges, the motor operates at a lower efficiency. As driving conditions change, the motor transitions between a high operating efficiency level and a low operating efficiency level as the rotor speed and / or torque changes. If the motor can be made to operate a greater proportion of the driving cycle in the efficient operating area, then the vehicle's range will increase at a given battery charge level. Since the limited range of battery-powered electric vehicles is a major commercial barrier to their use, it is very advantageous to extend the vehicle's operating range. Therefore, there is a need to operate motors (such as motors and generators) at higher efficiency levels.

[0026] The present application generally relates to pulsed control of an externally excited synchronous motor (EESM) capable of operating in either a continuous or pulsed manner. With pulsed control, the motor can be intelligently intermittently pulsed on and off to (1) meet operating demands while (2) improving overall efficiency compared to continuous control. More specifically, under selected operating conditions, the motor is intermittently pulsed at a more efficient energy conversion operating level to deliver a desired average output more efficiently than continuous control. Pulsed control results in careful modulation of the motor torque; however, the modulation is managed in such a manner that, for the intended application, noise or vibration levels are minimized.

[0027] For the sake of brevity, the pulsed control of the EESM provided herein is described in the context of a three-phase electric winding excitation synchronous motor in a vehicle. However, this explanation should not be interpreted as being restrictive in any respect. On the contrary, the pulsed control described herein can be used for many types of electric winding excitation synchronous motors, namely electric motors and generators. In addition, the pulsed control of such electric winding excitation synchronous motors can be used for any application, not just electric vehicles. In particular, pulsed control can be used for systems that require lower acceleration and deceleration rates than vehicle applications, such as electric motors for heating, cooling, and ventilation systems. Pulse engine control is described in U.S. Patent Publication No. 2019 / 0288629, the entire contents of which are incorporated herein by reference.

[0028] Winding-excited synchronous motor

[0029] A winding-field synchronous motor is a motor or generator that can convert electricity into mechanical motion or mechanical motion into electricity without permanent magnets. A winding-field synchronous motor can be a winding-field synchronous motor (WFSM) and a winding-field synchronous generator (WFSG). A winding-field synchronous motor may also be referred to as an externally excited synchronous motor (EESM). A WFSM may include a winding-field synchronous rotor, wherein the field coils (also referred to as field windings) are located in the rotor and the armature phase windings are located in the stator. In a WFSM, the field coils are powered by a DC power supply. In most WFSMs, the armature windings are powered by an AC power supply. In a WFSM, slip rings may be used to provide electrical contact between the DC power supply and the field coils on the rotor. In some embodiments, an air gap may be used to provide electrical contact with the field coils. A DC motor places the field coils on the stator and converts DC power into AC power using a commutator connected to the rotor.

[0030] Three-phase externally excited synchronous motor

[0031] In a three-phase EESM, the stator may include three coil windings excited by the three-phase AC input and the field coils on the rotor powered by the DC input. When the three-phase AC input passes through the three-phase armature windings, a rotating magnetic field (RMF) is generated. The speed of the RMF is called the synchronous speed of the motor (N s ). The interaction of the rotor's field coils and armature windings produces an electromagnetic force (EMF) that causes the rotor to rotate.

[0032] Vehicle Motor Efficiency Diagram

[0033] refer to Figure 1 , which shows an example vehicle motor efficiency graph 10 under different load and speed conditions. Graph 10 plots torque (N*m) along the vertical axis as a function of motor speed (RPM) along the horizontal axis. The maximum steady state output power is given by curve 12. The example vehicle motor efficiency graph is shown to help illustrate the improvement in efficiency of the EESM, which can be provided by the pulsed control of the EESM.

[0034] The area below the peak torque / speed curve 12 is mapped into a number of regions, each labeled by a percentage of operating efficiency. For the particular motor shown, the following features are apparent:

[0035] The most efficient or "sweet spot" region within its operating range is the operating region labeled 14, which is typically in the range of 4500-6000 RPM, with torque output in the range of about 40-70 N*m. In region 14, the energy conversion efficiency is about 96%, making it the "sweet spot" where the motor operates within its most efficient operating range.

[0036] • As motor speed increases beyond about 6000+RPM, efficiency tends to decrease regardless of output torque.

[0037] As output torque increases above 70 Nm or drops below 40 Nm, the efficiency percentage tends to drop from its peak, quite significantly in some cases. For example, when the motor is running at about 2000 RPM and 100 Nm of output torque, the efficiency is about 86%. When the torque output drops below about 30 Nm, the efficiency drops regardless of motor speed, approaching zero at zero load.

[0038] At any particular motor speed, there is a corresponding most efficient output torque, which is schematically illustrated by the maximum efficiency curve 16 .

[0039] The graph 10 shown is derived from an electric motor used in a 2010 Toyota Prius, which utilizes an interior permanent magnet synchronous motor. It should be understood that the graph 10 is merely illustrative and should not be construed as limiting in any respect. A similar graph can be generated for virtually any electric motor, such as a three-phase induction motor, whether used in a vehicle or in some other application.

[0040] As can be seen from graph 10, a motor is generally most efficient when operating within the speed and torque range of an optimal point 14. If operating conditions can be controlled so that the motor operates at or near its optimal point 14 for a greater proportion of the time, the overall energy conversion efficiency of the motor can be significantly improved.

[0041] However, from a practical standpoint, many driving situations require the motor to operate outside the speed and torque range of the optimal point 14. In electric vehicles, there is typically no transmission and therefore a fixed ratio of electric motor speed to wheel speed. In such situations, the motor speed may vary from zero speed when the vehicle is stopped to relatively high RPMs when cruising at highway speeds. The torque requirements may also vary widely based on whether the vehicle is accelerating or decelerating, going uphill, downhill, on a level surface, braking, etc.

[0042] As from Figure 1It can be seen that at any particular motor speed, there is a corresponding most efficient output torque, which is schematically 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 pulse controlling the motor so that the motor is operated at or near its optimal point for a certain proportion of the time, and the rest of the time is operated at a low torque output level or zero torque output level. The resulting average torque is controlled by controlling the duty cycle of the optimal point operation.

[0043] refer to Figure 2 , which shows a graph 20 with torque plotted on the vertical axis and time plotted on the horizontal axis. During normal operation, the motor will continuously produce 10N*m, as shown by the dashed line 22, as long as the desired torque is maintained at this value. With pulsed control operation, the motor is pulsed with a current pulse signal (as shown by pulse 24) to deliver 50N*m of torque 20% of the time. The motor is off the remaining 80% of the time. Therefore, the net output of the motor meets the operating requirements for an average torque level of 10N*m. Since the motor operates more efficiently when delivering 50N*m than when delivering a continuous torque of 10N*m, the overall efficiency of the motor can be improved by pulse controlling the motor using a 20% duty cycle while still meeting the average torque requirement. Therefore, pulsed operation provides higher energy efficiency than continuous operation.

[0044] In the above example, the duty cycle is not necessarily limited to 20%. As long as the desired motor output does not exceed 50N*m, the desired motor output can be met by changing the duty cycle. For example, if the desired motor output becomes 20N*m, the duty cycle of the motor running at 50N*m can be increased to 40%; if the desired motor output becomes 40N*m, the duty cycle can be increased to 80%; if the desired motor output becomes 5N*m, the duty cycle can be reduced to 10%, and so on. In general, it is possible to potentially change the duty cycle when the desired motor torque drops to Figure 1 Pulse motor control is advantageously used at any time below the maximum efficiency curve 16.

[0045] On the other hand, when the desired motor torque is at or above the maximum efficiency curve 16, the motor can be operated in a conventional (continuous or non-pulsed) manner to deliver the desired torque. Pulsed operation provides an opportunity for efficiency gains when the motor is required to deliver an average torque below the torque corresponding to its maximum operating efficiency point.

[0046] It should be noted that Figure 2The torque values ​​and time scales provided in are illustrative only and are not intended to be limiting in any way. In actual motor pulse control embodiments, the pulse durations used may vary widely based on the design requirements of any particular system. However, in general, the scale of the period of each on / off cycle is expected to be on the order of 10 milliseconds (ms) to 0.10 seconds (i.e., pulse control at a frequency in the range of 10 to 100 Hz). In addition, there are many different EESMs, and each EESM has its own unique efficiency characteristics. In addition, a given motor will have different efficiency curves at different motor speeds. The nature of the curve may vary depending on the specific winding-excited synchronous motor or the specific application. For example, the torque output need not be as Figure 2 A flat top is shown, and / or the torque need not be zeroed during shutdown, but may be some non-zero value. However, regardless of the particular curve used, at some time during which the EESM operates, for a given EESM, the EESM preferably operates at or near its highest efficiency region. Efficiency improvement for improving the rate of rise and fall of rotor current Enter

[0047] The vast majority of current motor converters are typically designed for continuous operation, rather than pulsed operation. Such motors typically transition from an unpowered state to an energized state relatively infrequently. As a result, little design effort is put into managing the rate of rise of the rotor current during such transitions. Any design effort that is done in managing the transition is typically to achieve a smooth transition, rather than a fast transition. As a result, the transition of most motors from an unpowered state to an energized state is typically rate limited.

[0048] It has been found that for electric motors that periodically transition from an unpowered motor state (such as by pulsed operation) to a peak efficiency state, further efficiency improvements can be achieved when the transition occurs as quickly as possible, for example by increasing the rotor current rise rate. By making rapid transitions, such as from zero torque to peak efficiency torque, the overall average motor efficiency is improved because the motor spends less time in the transition where the efficiency is below peak. This relationship is shown in Figure 3A and Figure 3B shown.

[0049] refer to Figure 3A , which shows a torque and efficiency graph of an example electric motor running at a fixed speed (e.g., 6000 rpm). In the example graph, a torque output range of 0.0 Nm to 250 Nm is plotted along the horizontal axis, while motor efficiency of 0.0% to 100% is plotted along the vertical axis. Curve 26 depicts the transition of the motor from zero to peak efficiency torque. During this transition, as shown by the shaded area 27, the peak efficiency torque has a much lower efficiency at the peak efficiency torque 28.

[0050] refer to Figure 3B , provides a graph showing the relationship between torque and work loss for an example motor running at a fixed speed during the transition from zero to peak efficiency torque. In the graph, work loss (W) is plotted along the vertical axis and the torque output of the motor is plotted along the horizontal axis. As shown by curve 29, during the transition from zero to peak efficiency torque, the work loss of the motor increases as the torque output increases. Therefore, the faster the transition time from zero to peak efficiency torque, the less work is done and the less energy is consumed by the electric motor.

[0051] By replacing torque with time along the horizontal axis and integrating the area under curve 29, the energy consumed by the electric motor for a given transition time can be calculated. For example, for the example motor, 7234.5 joules of energy are used in a transition time of 0.5 seconds, while only 723.4 joules of energy are used in a transition time of 0.05 seconds. This comparison shows that the faster the transition time from zero to peak efficiency torque, the lower the energy consumed in losses. It should be noted that in this example, it is assumed that acceleration of the load has not yet occurred, so no energy is added to the load inertia. Just as efficiency is improved by reducing the rise time, reducing the fall time will also improve efficiency.

[0052] The transition from zero to peak efficiency torque, peak efficiency torque, and power loss of the motor will vary from motor to motor. Figure 3A and Figure 3B The diagrams should be regarded as examples only and should not be construed as limiting in any respect.

[0053] Power Converters

[0054] A power inverter is a known device used with electric motors to convert a DC power source (such as that produced by a battery or capacitor) into a multi-phase AC input power (such as a three-phase AC input power) that is applied to the stator windings of the motor. In response, the stator windings generate RMF as described above.

[0055] refer to Figure 4, which shows a schematic diagram of a power controller 30 for pulsed operation of an electric machine. The power controller 30 includes a power converter 32, a DC power supply 34, and an electric machine 36. In this non-exclusive embodiment, the power converter 32 includes a pulse controller 38. Depending on the direction of energy flow through the system, the power converter 32 can operate as a power inverter or a power rectifier. When the electric machine is operated as a motor, the power converter 32 is responsible for generating three-phase AC power from the DC power supply 34 to drive the electric machine 36. The three-phase input power represented as phase A 37a, phase B 37b, and phase C 37c is applied to the windings of the stator of the electric machine 36 to generate RMF as described above. The lines depicting each phase 37a, 37b, and 37c are depicted with arrows at both ends, indicating that when the electric machine is used as a motor, current can flow from the power converter 32 to the electric machine 36, and when the electric machine is used as a generator, current can flow from the electric machine 36 to the power converter 32. When the motor operates as a generator, the power converter 32 operates as a power rectifier and the AC power from the motor 36 is converted to DC power for storage in the DC power supply. Line 37d depicting the field current carries the DC field current which is generally unidirectional for both motor and generator operating modes.

[0056] The pulse controller 38 is responsible for selectively pulse-controlling the three-phase input power. During normal (i.e., continuous) operation, the three-phase and field coil input power is continuous or not pulsed. On the other hand, during pulsed operation, the three-phase and field coil input power is pulsed. In a non-exclusive embodiment, pulsed operation may be achieved using any of the methods described herein, such as, but not limited to, the methods described below.

[0057] refer to Figure 5A-5F , which provide graphs for illustrating the difference between continuous and pulsed three-phase and field current input power provided to the motor 36. In each graph, phase and field current are plotted on the vertical axis, while time is plotted along the horizontal axis.

[0058] Figure 5A Conventional sinusoidal three-phase input currents 42a, 42b, and 42c are shown delivered to the armature windings of the motor 36. Phase B, represented by curve 42b, lags phase A, represented by 42a, by 120 degrees. Phase C, represented by curve 42c, lags phase B by 120 degrees. The sine wave period is τ. The three-phase input currents 42a, 42b, and 42c are continuous (not pulsed) and have a specified maximum amplitude of approximately 50 amperes. Figure 5BA conventional DC field current 42d is shown delivered to the field coil. The field current is continuous (not pulsed) and has an amplitude of 5 amps. It should be understood that 50 amps (for the phase current delivered to the armature winding) and 5 amps (for the field current delivered to the field coil) are merely representative maximum currents, and the maximum current may have any value.

[0059] Figure 5C and Figure 5D Example pulsed three-phase current waveforms 44a, 44b and 44c are shown (eg Figure 5C ) and a pulsed DC excitation current 44d having a 50% duty cycle (as shown Figure 5D As shown in FIG. 4 , the three-phase waveforms 44a, 44b and 44c have a peak amplitude of about 100 amperes, while the field current 44d has a peak amplitude of about 10 amperes. Figure 5A As shown, the period of the basic sine wave is τ, and now the sine wave is modulated on and off. Figure 5C and Figure 5D The average torque delivered by the delivered current is Figure 5A and Figure 5B The three-phase input current is applied continuously in the same way (assuming that torque is proportional to current, which is usually the case). Figure 5C and Figure 5D In the example, the current pulses 44a-d are interleaved with "off" periods of equal length. The length of each on and off period is 2τ. In this example, the duty cycle is 50%. The frequency of the pulse modulation may vary depending on the type of motor used, noise and vibration factors, the rotor speed currently being operated, and other factors.

[0060] Figure 5C and Figure 5D This example in illustrates an application where the "on" motor drive pulses are evenly spaced when the motor is operating at a steady state desired output level. This approach works well in many situations, but is not required. The duty cycle does not need to be 50%, but can be adjusted to match the desired average output torque. Figure 5C and Figure 5D In some embodiments, the phase of the on / off pulses is synchronized with the applied power; however, in some embodiments, the phase of the on / off pulses need not be synchronized with the phase of the applied 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.

[0061] This example shows how the armature winding AC current and DC field coil current can be pulse controlled. Pulse control is designed to allow the EESM to operate at efficient torque levels while reducing the amount of power required to provide the desired torque level.

[0062] Figure 5E and Fig. 5F Pulsed three-phase current waveforms 46a, 46b and 46c are shown (eg Figure 5E As shown) and a pulsed DC excitation current 46d having a 50% duty cycle (as shown Fig. 5F As another example shown in FIG. 4 , the three-phase waveforms 46a, 46b, and 46c have a peak amplitude of about 100 amperes, while the field current 46d has a peak amplitude of about 10 amperes. Figure 5A As shown, the period of the basic sine wave is τ, and now the sine wave is modulated on and off. Figure 5E and Fig. 5F The average torque delivered by the delivered current is Figure 5A and Figure 5B The three-phase input current is applied continuously in the same way (assuming that torque is proportional to current, which is usually the case). Figure 5E and Fig. 5F In the example, the current pulses 46a-d are interleaved with "off" periods of equal length. The length of each on and off period is τ / 2. In this example, the duty cycle is 50%. The frequency of the pulse modulation may vary depending on the type of motor used, noise and vibration factors, the rotor speed currently being operated, and other factors.

[0063] Power Converter Circuit

[0064] The inherent inductance of the motor can temporarily delay / slow down the voltage / power step between the motor's on and off states. During continuous (non-pulsed) operation, these transient effects tend to have a relatively small impact on the overall motor operation. However, when fast pulse control is used as contemplated herein, the transient effects can have a larger net impact, so there is an incentive to reduce the leading and trailing edge pulse transition times. This is particularly important for the excitation current, which can take much longer to establish magnetic flux in the rotor than it takes for the stator to establish stator flux when current is applied to the armature windings.

[0065] As previously described, the goal of pulsed motor control is to operate the motor 36 at substantially the most efficient level for the current motor speed during the "on" period, and to cut off power (provide zero or negligible power) during the "off" period. For example, the power supplied during the off period may be less than 10%, 5%, 1%, 0.5%, or 0.1% of the power supplied during the "on" period. When operating during the "on" period, the efficiency of the operating point may be within 5%, 2%, or 1% of the maximum operating efficiency point of the motor at the current motor speed. The transition through the inefficient operating region during the "off" and "on" periods should be as fast as possible to maximize efficiency. Therefore, the power transition between the motor power "on" and "off" states ideally has a leading edge that transitions vertically upward and a trailing edge that transitions vertically downward. Fig. 6A Such a "perfect" pulse 60 is schematically shown in FIG, which shows the relationship between the ideal motor drive current and time for pulsed control with a 50% duty cycle. In this figure, the current pulse represents the excitation winding current. Although the current pulse is shown as flat-topped, this is not necessarily the case in reality.

[0066] In the real world, many practical limitations make it difficult to achieve such perfect pulse generation. For example, the inductive aspects of the motor 36 and the power converter 32 wiring slow down the current rise and fall times. The actual response of a particular motor will vary with the electrical characteristics of the motor 36, the speed of the motor, and the available bus voltage. In general, the actual rise and fall of the pulse occurs more slowly, which means that the transition occurs over time. Figure 6B The nature of the rise and fall in the real world is schematically illustrated in FIG. As shown, there is a ramp-up period (rise time) 62 required for the current to actually rise from zero to the desired "on" power level, and a ramp-down period (fall time) 64 required for the current to actually fall from the "on" power level to zero.

[0067] During the power ramp-up and ramp-down periods, the winding-excited synchronous motor 36 continues to consume or generate power. However, during these transition periods, the winding-excited synchronous motor operates at a lower efficiency. Generally speaking, as the operating current decreases from its maximum efficiency condition ( Figure 1 As the curve 16 in Fig. 1 decreases towards zero, the efficiency of the winding-excited synchronous motor will decrease, and the energy conversion efficiency will deteriorate significantly as the current level approaches zero. Therefore, the pulse distortion represented by the current ramp-up and ramp-down periods will reduce the efficiency gain brought by the pulsed control operation. In general, the smaller the ratio of the rise / fall time to the pulse length, the smaller the impact of transient switching effects on the energy conversion efficiency of the motor during pulse control.

[0068] It should be understood that Figure 6BThe transient effects shown in are illustrative in nature and do not necessarily reflect the actual rise / fall times associated with the operation of any particular winding-excited synchronous motor. The relative scale of the rise time to pulse length ratio can vary widely based on the characteristics of the winding-excited synchronous motor used (which primarily determines the rise and fall times), the frequency of the pulse control (which is primarily determined by the control scheme used), and the pulse width (which is determined by the control scheme and the motor load). The voltage supplying the winding-excited synchronous motor and the motor speed will also affect the pulse rise and fall times. If the pulse is very slow compared to the winding-excited synchronous motor response, the rise / fall time may be only a small fraction of the pulse width, and the transient switching effects may have little effect on the motor performance. Conversely, if the pulse is very fast and / or the winding-excited synchronous motor response is slow, the rise / fall time may be a large fraction of the pulse width, and in some cases may even exceed the pulse width. If not carefully managed, the transient efficiency losses associated with the switching can significantly reduce or even eliminate any theoretical gains that can be obtained from pulsed operation. Therefore, it is very important to consider the transient switching effects associated with pulsed operation when determining the pulse control frequency and control scheme appropriate for any particular application.

[0069] As described above, for continuous control of the motor, it is not necessary to increase the torque accumulation rate in the motor. In contrast, for pulsed control of the motor (such as DMD), it is necessary to increase the torque accumulation rate in the motor.

[0070] One way to increase the torque accumulation rate in a motor is to increase the torque accumulation rate by continuously supplying current to the rotor and modulating or pulsing the stator current to maintain the magnetic flux in the rotor. However, supplying continuous current to the rotor reduces the efficiency of the motor and may cause pulsed control to be less efficient than continuous control in some cases. Therefore, it is necessary to increase the accumulation of the magnetizing flux of the rotor when the rotor current is pulsed on and off.

[0071] Analyzing how the magnetizing flux of the EESM generates torque in the EESM has been shown to provide a method to improve the torque accumulation rate in the EESM. The torque of the EESM can be expressed by the following torque equation:

[0072]

[0073] where k r is a constant. Based on this torque equation, the magnetizing flux can be directly derived from the rotor as k r i r , or from the stator However, through the stator The magnetizing flux cannot be generated by directly energizing the rotor (e.g. k r ir ) to produce the same torque as efficiently. Therefore, during normal continuous torque operation, the stator DC current (i d ) is controlled to zero so that the magnetizing flux is entirely generated by the current supplied to the rotor.

[0074] As described below, simultaneous excitation of the rotor and stator can be used to rapidly generate magnetizing flux, thereby increasing the torque accumulation rate in the motor. For example, by providing a current i re To utilize the first path of magnetic flux generation and to provide a bias current i to the stator d By utilizing the second path for generating magnetic flux, the rise of magnetic flux in the motor can be improved, and thus the torque rise rate in the motor can be increased. Increasing the torque rise rate in the motor can reduce the transition time between the ON and OFF states of the motor.

[0075] refer to Figure 7 , which shows a model of rotor current versus time for different stator bias currents according to an embodiment of the present disclosure. The rotor current represents the torque produced by the motor. As shown in the model, the stator bias current is provided at 1 ms. For the model shown, the maximum torque of the motor is provided at a rotor current of 20 amps, while normal pulsed torque is provided in the rotor current range of 7-10 amps.

[0076] As shown in the model, the rotor is excited as a single path only, i.e., the stator bias current is zero (i d =0), the motor requires 8.5ms to deliver 10 amps of rotor current, and requires 10ms to deliver 20 amps of rotor current. The improved rate of rise by providing a DC current to the stator to excite the second path of the stator is shown. For example, providing a 100 amp DC stator bias current reduces the time the motor delivers 10 amps to 5.5ms, and reduces the time to deliver 20 amps to 6.75ms. It further shows that by providing a 700 amp DC stator bias current, the time the motor delivers 10 amps can be reduced to 0.5ms, and the time to deliver 20 amps can be reduced to 0.75ms.

[0077] It has been found that the stator bias current can be provided to the EESM simultaneously with the rotor current without modifying the existing EESM. For example, the power controller 30 can be configured to simultaneously excite the first path of the rotor and the second path of the stator during the transition of the motor from the off state to the on state, thereby providing a stator bias current to the stator to improve the rise of the magnetic flux in the rotor. In some embodiments, the power controller 30 can provide all available voltages to the stator and the rotor, and adjust the phase angle of the applied stator voltage by saturating the stator current controller so that each path is excited at the same time to increase the maximum rise rate of the magnetic flux and accumulate the motive flux of the motor. The power controller 30 can exit the voltage saturation to control the magnitude and phase of the stator bias current and the magnitude of the rotor current, so as to achieve the desired pulse torque in the shortest time. The power controller 30 can control the voltage saturation so that the magnetic flux accumulates in the effective path for pulsed control (e.g., DMD) applications. In some embodiments, the symmetry of the control of the stator current in parallel with the rotor current can be used to shorten the time required to extract the magnetizing field so that the pulses of the motor can be turned off quickly and efficiently.

[0078] Once the magnetic flux accumulates in the rotor so that the motor produces the desired torque (e.g., pulsed torque), the power controller 30 terminates the stator bias current and maintains the rotor current until the pulse ends. In some embodiments, when the motor transitions from the ON state to the OFF state or from the OFF state to the ON state, the power controller 30 can smooth the transition between these states to reduce the sharpness of the transition. This transition can improve the noise, vibration, or harshness characteristics of the motor.

[0079] The improvement in rotor current rise described in detail above has been demonstrated on a motor that achieved magnetic flux at a rotor current of 8 amps. When rotor current was applied without stator bias current, the motor required 15.4 ms to reach a rotor current of 8 amps. In contrast, when rotor current was applied with a stator bias current of 300 amps, the motor achieved a rotor current of 8 amps in 1 ms.

[0080] Reference now Figure 8 According to an embodiment of the present disclosure, a method for increasing the torque rise rate in a motor is provided, generally referred to as method 800. Figure 4 Method 800 is described with reference to an example motor 36 and power controller 30. The example motor 36 may be an EESM. As described below, method 800 is used during pulsed control of a motor (e.g., an EESM) to increase the torque ramp rate of each pulse of the motor. However, method 800 may be used to transition between an initial off state of the motor and a continuous on (ON) torque of the motor.

[0081] As described above, when it is determined that the motor 36 is more efficient when operating under pulsed control than under continuous control, the power controller 30 may initiate pulsed control of the motor 36 (step 810). The decision to enter pulsed control may be made within the power controller 30 or another controller in signal communication with the power controller 30. In pulsed control, the power controller 30 may determine the pulsed torque and duty cycle of the motor 36, or the pulsed torque and duty cycle may be provided by another controller in signal communication with the power controller 30.

[0082] When the power controller 30 enters the pulsed control of the motor 36, the power controller 30 may transition from the continuous control to the pulsed control (step 815). In order to transition the motor 36 from the continuous control to the pulsed control, the power controller 30 terminates the rotor current in the form of direct current to the rotor and the stator flux in the form of multi-phase alternating current to the stator, so that the motor 36 is in the OFF state (step 820).

[0083] With the motor in the OFF state, the power controller 30 performs pulse control on the motor 36 (step 830). In order to perform pulse control on the motor 36, the power controller 30 excites the rotor by providing a DC current to the rotor of the motor 36 via the excitation line or path 37d (step 832). While exciting the rotor, the power controller 30 also excites the stator via the phase lines 37a, 37b and 37c with a stator bias current as a DC current (step 834). The power controller 30 can provide the stator bias current by saturating each phase line 37a, 37b and 37c. As described above, by simultaneously exciting the rotor and the stator, the rise of the magnetic flux of the motor 36 is increased. When the motor 36 reaches the magnetic flux of the pulse torque, the power controller 30 terminates the stator bias current (step 836) and provides the stator flux to the stator in the form of a multi-phase AC current (step 838). The power controller 30 can terminate or transition from the stator bias current to the stator flux by controlling the magnitude and phase of the current provided to each phase line 37a, 37b, and 37c, so that the motor 36 provides a pulse torque. When the pulse is completed, the power controller 30 controls the motor 36 to return to the off state (step 820), and repeats the pulse control of the motor (step 830) until the motor 36 is switched back to continuous control or the motor 36 is controlled to an extended off state. During the pulse control of the motor 36, each pulse (step 830) can have a different magnitude and / or duty cycle so that the motor 36 provides the desired torque. In some embodiments, controlling the motor 36 from the continuous control mode or after the pulse to the off state can include using the stator bias current to reduce the time for the magnetizing flux of the rotor to reach zero. For example, the power controller 30 can modify the magnitude and / or phase of the stator flux to the stator bias current to reduce the time for the magnetizing flux of the rotor to reach zero. Reducing the time for the rotor's magnetizing flux to reach zero may improve the ramp-down of torque in the electric machine 36 .

[0084] The above method 800 can be used without modifying the motor 36 (the motor 36 was previously constructed or configured to operate in a continuous control mode, such as an EESM). In some embodiments, the above method 800 can be combined with a modified motor. For example, in combination with the above method, the number of turns of the rotor can be modified to increase the torque rise rate of the EESM. For more information on modifying the number of turns of the rotor to increase the torque rise rate of the EESM, reference can be made to U.S. Provisional Patent Application No. 63 / 322,376, entitled “DELAY REDUCTION FOR PULSED WOUND FIELD SYNCHRONOUS MACHINES,” filed on March 22, 2022, the entire contents of which are incorporated herein by reference.

[0085] Fig. 9 is a block diagram of an example controller 900 that can perform one or more operations described herein according to some embodiments. For example, the controller 900 can be used as the power controller 30 or the pulse controller 32 described in detail above. The controller 900 can communicate signals with other computing devices or controllers by being integrated therein or connected via a LAN, an intranet, an extranet, and / or the Internet. In some embodiments, although only a single controller is shown, the term "controller" can be taken to include any collection of controllers that individually or jointly execute a set (or multiple sets) of instructions to perform the methods discussed herein.

[0086] The example controller 900 may include a processing device (e.g., a general purpose processor, a PLD, etc.) 902, a main memory 904 (e.g., synchronous dynamic random access memory (DRAM), read-only memory (ROM)), a static memory 906 (e.g., flash memory and a data storage device 918), which may communicate with each other via a bus 930.

[0087] The processing device 902 may be provided by one or more general-purpose processing devices, such as a microprocessor, a central processing unit, etc. In an illustrative example, the processing device 902 may include a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or a processor that implements other instruction sets or a processor that implements a combination of instruction sets. The processing device 902 may include one or more special-purpose processing devices, such as an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a network processor, etc. According to one or more aspects of the present disclosure, the processing device 902 may be configured to perform the operations described herein, for performing the operations and steps discussed herein.

[0088] The computing device 900 may include a network interface device 908 that can communicate with the communication network 920. The computing device 900 may include a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device (e.g., a keyboard), a cursor control device (e.g., a mouse), and an acoustic signal generating device (e.g., a speaker). In one embodiment, the video display unit, the alphanumeric input device, and the cursor control device may be combined into a single component or device (e.g., an LCD touch screen).

[0089] According to one or more aspects of the present disclosure, the data storage device 918 may include a computer-readable storage medium 928 on which one or more sets of instructions 925 may be stored, which may include instructions for one or more components (e.g., motor 36) for implementing the operations described herein. During execution of the instructions 925 by the computing device 900, the main memory 904, and the processing device 902 constituting the computer-readable medium, the instructions 925 may reside completely or at least partially within the main memory 904 and / or within the processing device 902. The instructions 925 may be sent or received through the communication interface 920 via the interface device 908.

[0090] Although the computer-readable storage medium 928 is shown as a single medium in the illustrative example, the term "computer-readable storage medium" should be taken to include a single medium or multiple media (e.g., a centralized or distributed database and / or associated caches and servers) that store one or more sets of instructions. The term "computer-readable storage medium" can be taken to include any medium that is capable of storing, encoding, or carrying a set of instructions for a motor to execute and cause the motor to perform the methods described herein. Thus, the term "computer-readable storage medium" should be taken to include, but is not limited to, solid-state memories, optical media, and magnetic media.

[0091] The examples described herein may involve an apparatus for performing the operations described herein. The apparatus may be constructed specifically for the desired purpose, or it may include a general-purpose computing device selectively programmed by a computer program stored in a computing device. Such a computer program may be stored in a computer-readable non-transitory storage medium.

[0092] The methods and illustrative examples described herein are not inherently related to any particular computer or other device. Various general purpose systems may be used in accordance with the teachings described herein, or it may prove convenient to construct more specialized devices to perform the required method steps. The structures required for various such systems will be described in the above description.

[0093] The above description is intended to be illustrative rather than restrictive. Although the present disclosure has been described with reference to specific illustrative examples, it should be appreciated that the present disclosure is not limited to the described examples. The scope of the present disclosure should be determined with reference to the attached claims and the full scope of equivalents to which the claims are entitled.

[0094] As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", and / or "including" when used herein may specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Therefore, the terms used herein are only used to describe particular embodiments and are not intended to be limiting.

[0095] In some embodiments, the functions / actions may not occur in the order shown in the figures. For example, two figures shown in succession may actually be executed substantially simultaneously, or may sometimes be executed in the reverse order, depending on the functions / actions involved.

[0096] Although method operations are described in a particular order, it should be understood that other operations may be performed between the described operations, that the described operations may be adjusted to occur at slightly different times, or that the described operations may be distributed in a system that allows processing operations to occur at various intervals associated with the processing.

[0097] Various units, circuits, or other components may be described or claimed as being "configured to" or "configurable to" perform one or more tasks. In such contexts, the phrases "configured to" or "configurable to" are used to refer to structures, indicating that the unit / circuit / component includes structures (e.g., circuits) that perform one or more tasks during operation. Thus, even when the specified unit / circuit / component is not currently operating (e.g., not turned on), it can be said that the unit / circuit / component is configured to perform the task, or is configurable to perform the task. Units / circuits / components used with the "configured to" or "configurable to" language include hardware, such as circuits, memory storing program instructions executable to implement operations, and the like. Stating that a unit / circuit / component is "configured to" perform one or more tasks or "configurable to" perform one or more tasks expressly does not invoke 35 U.S.C. § 112, sixth paragraph, with respect to the unit / circuit / component. Furthermore, "configured to" or "configurable to" may include general structures (e.g., general circuitry) that are manipulated by software and / or firmware (e.g., an FPGA or a general purpose processor executing software) to operate in a manner capable of performing one or more of the tasks discussed. "Configured to" may include adjusting a manufacturing process (e.g., a semiconductor manufacturing facility) to manufacture a device (e.g., an integrated circuit) suitable for implementing or performing one or more of the tasks. "Configurable to" is expressly not applicable to blank media, an unprogrammed processor or an unprogrammed general purpose computer, or an unprogrammed programmable logic device, programmable gate array, or other unprogrammed device, unless accompanied by a programming medium that enables the unprogrammed device to be configured to perform one or more of the functions disclosed.

[0098] For the purpose of illustration, the foregoing description has been described with reference to specific embodiments. However, the above illustrative discussion is not intended to be exhaustive or to limit the present embodiments to the precise form disclosed. In view of the above teachings, many modifications and variations are possible. The embodiments are selected and described in order to best explain the principles of the embodiments and their practical application, so that others skilled in the art can best utilize the embodiments and various modifications that may be suitable for the intended specific use. Therefore, the present embodiments should be regarded as illustrative and not restrictive, and the present embodiments are not limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

[0099] Although several embodiments of the present disclosure are shown in the accompanying drawings, the present disclosure is not intended to be limited thereto, as the scope of the present disclosure should be as broad as the art allows, and the specification should be interpreted similarly. Any combination of the above embodiments is also conceivable and within the scope of the appended claims. Therefore, the above description should not be interpreted as limiting, but only as an example of a specific embodiment. Those skilled in the art will envision other modifications within the scope of the appended claims.

Claims

1. A method of controlling an electric machine having an independently energizable rotor and stator, the method comprising: Energizing the motor, comprising: simultaneously exciting the rotor with a direct current and exciting the stator with a stator bias current to generate magnetic flux in the rotor via two independent paths; and providing a stator flux to the stator so that the electric machine provides torque; and The motor is controlled to be in the OFF state. 2 . The method of claim 1 , wherein energizing the motor comprises terminating the stator bias current when a desired magnetic flux is generated in the rotor.

3. The method of claim 2, wherein the desired magnetic flux is generated in the rotor when the rotor current reaches 8 amperes.

4. The method of claim 3, wherein energizing the rotor with the stator bias current comprises the stator bias current being at least 300 amps. The method of claim 4 , wherein the rotor current reaches 8 amps within 1 ms.

6. The method of claim 2, wherein providing the stator flux occurs in response to generating the desired magnetic flux in the rotor.

7. The method of claim 1, wherein energizing the motor produces a pulse torque.

8. The method of claim 1, wherein simultaneously exciting the rotor with the DC current and exciting the stator with the stator bias current is configured to increase a rate of rise of magnetic flux in the rotor compared to exciting only the rotor.

9. The method of claim 1, wherein energizing the stator with the stator bias current comprises energizing the stator with a direct current.

10. The method of claim 1, wherein terminating the stator bias current comprises controlling an amplitude or a phase of a current provided as the stator bias current to provide the stator flux. 11 . The method of claim 1 , wherein energizing the electric machine comprises the electric machine being an externally excited synchronous machine (EESM) configured to operate in a continuous control mode.

12. The method of claim 11, wherein energizing the electric machine comprises pulse controlling the EESM, the EESM being unmodified to operate in a pulsed control mode.

13. The method of claim 1 wherein terminating the DC current to the rotor and the stator flux comprises transitioning the stator flux to a stator bias current before terminating the DC current to the rotor to reduce the time for the magnetic flux of the rotor to reach zero.

14. The method of claim 1, wherein simultaneously exciting the rotor with the DC current and exciting the stator with the stator bias current produces a desired magnetic flux within 1 ms.

15. A controller for controlling an electric machine having an independently energizable rotor and stator, the controller comprising: Memory; as well as A processing device operably coupled to the memory to perform the following operations: simultaneously exciting the rotor with a direct current and exciting the stator with a stator bias current to generate magnetic flux in the rotor via two independent paths; providing a stator flux to the stator so that the motor provides torque; and The motor is controlled to an OFF state by terminating the DC current to the rotor and the stator flux.

16. A controller as claimed in claim 15, wherein providing pulses of the stator flux to the stator causes the motor to provide torque.

17. The controller of claim 15, wherein a processing device further terminates the stator bias current when a desired magnetic flux is generated in the rotor.

18. A non-transitory computer readable medium storing instructions that, when executed by a processing device, cause the processing device to control an electric machine having an independently energizable rotor and stator by: simultaneously exciting the rotor with a direct current and exciting the stator with a stator bias current to generate magnetic flux in the rotor via two independent paths; providing a stator flux to the stator so that the motor provides torque; and The motor is controlled to an OFF state by terminating the DC current to the rotor and the stator flux.

19. The non-transitory computer readable medium of claim 18, wherein providing pulses of the stator flux to the stator causes the motor to provide torque.

20. The non-transitory computer readable medium of claim 18, wherein when a desired magnetic flux is generated in the rotor, a processing device is further caused to terminate the stator bias current.

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