Boost converter for pulsed motor control

Abstract

A vehicle includes: a motor configured to drive the vehicle; a motor controller configured to: operate the motor in a continuous mode if the output required by the motor is higher than a threshold value; or, if the output required by the motor is lower than the threshold value, the motor is operated in a pulse mode; wherein the electric machine is configured to operate in a pulsed mode to: (a) produce a first work output during a conduction pulse; and (b) generating a second power output between the conduction pulses, the second power output being different from the first power output; and a boost circuit coupled to the winding of the electric machine, the boost circuit configured to store energy collected from the winding of the electric machine during a drop of the turn-on pulse and to apply the stored energy to the winding of the electric machine during a rise of a subsequent turn-on pulse. Wherein the stored energy is applied in order to reduce the rise time of the subsequent conduction pulse, relative to the case where the stored energy is not applied.

Description

[0001] Cross-references

[0002] This application is a divisional application of Chinese patent application No. 202080020947.2, filed on September 13, 2021, which is a national phase application of international application No. PCT / US2020 / 022262, filed on March 12, 2020, which claims priority to U.S. Provisional Patent Application No. 62 / 819,097, filed on March 15, 2019. All of the above patent applications are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates to a boost converter for pulse motor control. Background Art

[0004] The present application relates generally to pulsing an electric motor to selectively deliver a desired output in a more energy efficient manner, and more particularly to a boost converter circuit having improved rise and fall times for pulsing the motor.

[0005] As used herein, the term "electrical machine" is intended to be broadly understood to refer to both electric motors and generators. Electric motors and generators are very similar in structure. Both include a rotor and a stator with multiple poles. When an electric motor operates as a motor, it converts electrical energy into mechanical energy. When operating as a generator, the electric motor converts mechanical energy into electrical energy.

[0006] Motors can run on direct current (DC) or alternating current (AC).

[0007] Representative DC motors include brushless motors, electrically excited motors, permanent magnet motors, series wound motors, shunt motors, brushed motors, compound motors, and others.

[0008] There are two general types of AC motors: asynchronous motors and synchronous motors. An example of an asynchronous motor is the three-phase induction motor.

[0009] Modern electric motors have relatively high energy conversion efficiency. However, the energy conversion efficiency of most motors can vary significantly based on their operating load. In many applications, motors are required to operate under a wide range of load conditions. As a result, motors typically operate at or near peak efficiency levels at certain times and at lower efficiency levels at other times.

[0010] Battery-powered electric vehicles provide a good example of motors that operate over a wide range of efficiency levels. During a typical drive 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 its 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 in a high efficiency operating region for a larger proportion of the drive cycle, the vehicle's mileage will increase for a given battery charge level. Since the limited mileage of battery-powered electric vehicles is a major commercial barrier to the use of electric vehicles, extending the vehicle's operating mileage is very advantageous.

[0011] Therefore, there is a need to operate electrical machines, such as motors and generators, at higher efficiency levels. Summary of the Invention

[0012] The present application relates to pulse control of electric machines (such as motors and generators) to improve operating efficiency. In a non-exclusive embodiment, a vehicle includes: an electric machine configured to drive the vehicle; a motor controller configured to: operate the electric machine in a continuous mode if the output required by the electric machine is above a threshold; or operate the electric machine in a pulse mode if the output required by the electric machine is below the threshold; wherein the electric machine is configured to operate in the pulse mode to: (a) generate a first work output during an on-pulse; and (b) generate a second work output between the on-pulses, the second work output being different from the first work output; and a boost circuit coupled to a winding of the electric machine, the boost circuit configured to store energy collected from the winding of the electric machine during the falling period of the on-pulse and apply the stored energy to the winding of the electric machine during the rising period of a subsequent on-pulse. wherein applying the stored energy is used to reduce the rise time of the subsequent on-pulse relative to a situation where the stored energy is not applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention and its advantages may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

[0014] Figure 1 is a representative torque / speed / efficiency graph showing the energy conversion efficiency of a representative electric motor under different operating conditions.

[0015] Figure 2 is a graph showing a pulse current signal applied to the motor.

[0016] Figure 3A is a plot of torque versus efficiency for a motor operating at a fixed speed during the transition from zero to peak efficiency torque.

[0017] Figure 3B are the torque and work losses for an exemplary electric motor operating at a fixed speed during the transition from zero to peak efficiency torque.

[0018] Figure 4 A pulse-controlled electric machine according to a non-exclusive embodiment of the present invention is presented.

[0019] Figure 5A is a graphical representation of a continuous three-phase AC waveform with a peak value of 50 amperes.

[0020] Figure 5B and Figure 5C Is provided with Figure 5A The continuous waveform has the same power output as the pulse waveform with a duty cycle of 50%.

[0021] Figure 6A and Figure 6B is a representative circuit for modeling the current flowing through the three phases A, B, and C of an exemplary electric motor.

[0022] Figure 7A is a circuit diagram showing a prior art power converter.

[0023] Figures 7B to 7F is an exemplary prior art timing diagram showing Figure 5A The switching states and voltages of the power converter are shown.

[0024] Figure 8 A power converter including a boost circuit according to a non-exclusive embodiment of the present invention.

[0025] Figures 9A to 9C is a signal diagram illustrating how a boost circuit improves rise time and fall time during pulse controlled operation of a power converter according to a non-exclusive embodiment of the present invention.

[0026] Figure 10 Exemplary voltages that may be used to drive a motor are shown as a function of time in accordance with a non-exclusive embodiment of the present invention.

[0027] Figure 11 Exemplary voltages that may be used to drive a motor are shown as a function of time in accordance with a non-exclusive embodiment of the present invention.

[0028] Figure 12 is another power converter including a boost circuit according to another non-exclusive embodiment of the present invention.

[0029] Figure 13 is a flow chart illustrating steps of pulse control operation of a motor in a vehicle according to the present invention.

[0030] Figure 14 is a simplified diagram illustrating the modulation of energy supplied to an electric motor according to another embodiment of the present invention.

[0031] 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

[0032] The present application generally relates to pulse control of various electric machines (e.g., motors and generators) that would otherwise operate in a continuous manner. With pulse control, the motor is intelligently and intermittently pulsed on and off to (1) meet operational demands while (2) improving overall efficiency. 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 would be achieved through conventional continuous motor operation. Pulsed operation results in an intentional modulation of the motor torque; however, this modulation is managed in a manner that does not produce unacceptable noise or vibration for the intended application.

[0033] For the sake of brevity, the pulse control of the various motors provided herein is described in the context of a three-phase induction motor in a vehicle. However, this explanation should not be construed as restrictive in any respect. On the contrary, the pulse control described herein can be used for many types of motors - meaning both motors and generators. For example, the motor pulse control described herein can be used for any type of motor, whether it is an AC motor (e.g., an induction motor, a synchronous motor, a motor of any number of poles, etc.) or a DC motor (e.g., a brushless motor, an electrically excited motor, a permanent magnet motor, a series-wound motor, a shunt motor, a brushed motor, a compound motor, etc.). In addition, the pulse control of such motors can be used for any application, not just for electric vehicles. In particular, pulse control can be used for systems requiring lower acceleration and deceleration rates than vehicle applications, such as motors for heating systems, cooling systems, and ventilation systems.

[0034] Pulse engine control is described in U.S. Patent Application No. 16 / 353,159, filed on March 14, 2019, U.S. Provisional Patent Application No. 62 / 644,912, filed on March 19, 2018, U.S. Provisional Patent Application No. 62 / 658,739, filed on April 17, 2018, and U.S. Provisional Patent Application No. 62 / 810,861, filed on February 26, 2019. Each of the above applications is incorporated herein by reference in its entirety.

[0035] Three-phase induction motor

[0036] An induction motor consists of two main components: a stationary stator and a rotating rotor. In a three-phase motor, the stator may include three coil windings excited by a three-phase AC input. When the three-phase AC input passes through the three-phase windings, a rotating magnetic field (RMF) is generated. The rate of rotation of the RMF is called the synchronous speed (N) of the motor. s ). The rotor is typically a "squirrel cage" or "wound-wire" rotor, both of which have multiple conductive elements that are electrically short-circuited at their ends. According to Faraday's law, the RMF induces currents in the rotor's conductive elements. The induced currents create an induced magnetic field that interacts with the magnetic field generated in the stator coils. The interaction of the rotor and stator magnetic fields generates an electromagnetic force (EMF), which causes the rotor to rotate. This type of motor is called an induction motor because the current is induced in the rotor's conductive elements by electromagnetic induction, as opposed to a direct conductive path.

[0037] Three-phase induction motors offer several advantages. First, they are self-starting in nature. Second, the rotor speed is easily controlled. The rotor speed (N r ) is always slightly less than the synchronous speed (N s ). This difference is called slip and can be expressed as a percentage:

[0038] Slip % = (N s -N r ) / N s Equation (1)

[0039] The frequency of the three-phase AC power energizing the stator windings controls the RMF rotation rate, thereby controlling the synchronous frequency. In turn, the speed of the rotor can be controlled based on equation (1) as defined above.

[0040] The frequency supplied to the three-phase winding controls the synchronous speed (N s ), the amplitude of the applied AC controls the output torque of the motor. When the amplitude is higher or lower, the output of the motor is higher or lower respectively.

[0041] Vehicle electric motor efficiency diagram

[0042] refer to Figure 1 , showing exemplary vehicle motor efficiency under different load and speed conditions Figure 10 .Should Figure 10 The torque (N*m) along the vertical axis is plotted as a function of the motor speed (RPM) along the horizontal axis. The maximum steady state output power is given by curve 12 .

[0043] The area under 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 characteristics are apparent:

[0044] The most efficient or "sweet spot" region within the operating range of this particular motor is the operating region labeled 14, which generally falls within the range of 4,500 RPM to 6,000 RPM and has a torque output in the range of approximately 40 Nm to 70 Nm. In region 14, the energy conversion efficiency is approximately 96%, making it the "sweet spot" where the motor operates within its most efficient operating range.

[0045] • As motor speed increases beyond approximately 6,000+ RPM, efficiency decreases regardless of output torque.

[0046] As output torque increases above 70 Nm or below 40 Nm, the efficiency percentage tends to drop from its peak, in some cases quite significantly. For example, when the motor is running at approximately 2,000 RPM and 100 Nm of output torque, the efficiency is approximately 86%. When torque output decreases below approximately 30 Nm, the efficiency drops regardless of motor speed, approaching zero at zero load.

[0047] At any particular motor speed, there will be a corresponding most efficient output torque, which is graphically illustrated by the maximum efficiency curve 16 .

[0048] As shown in the Figure 10 Derived from the electric motor used in the 2010 Toyota Prius. Figure 10 For built-in permanent magnet synchronous motor. It should be understood that Figure 10 It is illustrative only and should not be construed as limiting in any respect. Similar diagrams can be generated for virtually any electric motor, such as a 3-phase induction motor, whether used in a vehicle or in some other application.

[0049] from Figure 10 As can be seen in FIG, a motor generally operates most efficiently 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.

[0050] However, from a practical perspective, many driving situations dictate that the motor be operated outside the speed and torque range of the optimal point 14. Electric vehicles typically lack a transmission, so the ratio of the motor rotation rate to the wheel rotation rate is fixed. In these situations, the motor speed can vary from zero when the vehicle is stopped to relatively high RPMs when cruising at highway speeds. Torque requirements can also vary significantly depending on whether the vehicle is accelerating or decelerating, driving uphill, downhill, on a level surface, braking, and other factors.

[0051] 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 so that the motor operates at or near its optimal point for a certain percentage of the time and at a low or zero torque output level for the remaining time. The average torque thus generated is controlled by controlling the duty cycle of the optimal point operation.

[0052] refer to Figure 2 , shows a graph 20 that plots the total current applied to the motor on the vertical axis and time on the horizontal axis. For a three-phase motor, the applied current can be the sum of the currents of all three phases. For illustrative purposes, it is assumed that each ampere of applied current will produce an output torque of 1 N*m. In this particular example, the desired motor output torque is 10 N*m, which would require a current of 10 amps as shown by the dashed line 22. In this example, the motor's most efficient torque output is 50 N*m, corresponding to an applied current of 50 amps.

[0053] During normal operation, the motor will continuously generate 10 Nm of torque as long as the desired torque remains at that value. In pulse control operation, the motor is pulsed (as represented by pulse 24) to deliver 50 Nm of torque 20% of the time. The motor is off for the remaining 80% of the time. Therefore, the net output of the motor meets the 10 Nm operating demand. Since the motor operates more efficiently when delivering 50 Nm than when delivering 10 Nm, by pulsing the motor with a 20% duty cycle, the overall efficiency of the motor can be improved while still meeting the average torque demand.

[0054] 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 simply changing the duty cycle. For example, if the desired motor output changes to 20N*m, the duty cycle of the motor running at 50N*m can be increased to 40%; if the desired motor output changes to 40N*m, the duty cycle can be increased to 80%; if the desired motor output changes to 5N*m, the duty cycle can be reduced to 10%, and so on. In general, when the desired motor torque drops to Figure 1 Any time below the maximum efficiency curve 16 it is possible to advantageously use pulse motor control.

[0055] 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 / pulseless) manner to deliver the desired torque. Pulsed operation provides an opportunity for efficiency gains only when the average torque the motor needs to deliver is below the average torque corresponding to its maximum operating efficiency point.

[0056] It should be noted that Figure 2 The current and torque values and the time scales provided in are illustrative only and are not intended to be limiting in any way. In actual embodiments where the motor is pulsed, the pulse durations used may vary widely based on the design needs of any particular system. However, typically, the time period for each on / off cycle is expected to range from the order of 10 microseconds to 0.10 seconds (i.e., pulsed at a frequency in the range of 10 Hz to 100,000 Hz), for example, as will be discussed in more detail below, between 0.2 milliseconds to 20 milliseconds (50 Hz to 5000 Hz). Furthermore, there are a wide variety of different motors, and each motor has its own unique efficiency characteristics. Furthermore, a given motor will have different efficiency curves at different motor speeds. The nature of the curves may vary depending on the particular motor. It should also be understood that the current pulses need not be as Figure 2 The top portion is depicted as being flat. Furthermore, the current need not be zero during the off period, but can be some non-zero value. An important characteristic of the current waveform is that a certain percentage of the time the motor is operating at or near its most efficient region for the current motor speed.

[0057] Improved efficiency by increasing the rate of torque rise

[0058] Most 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 devoted to managing these transitions. To the extent that any design effort is devoted to managing these transitions, it is typically aimed at achieving smooth transitions, rather than rapid ones. Consequently, the transition rate of most motors from an energized state to an energized state is typically limited (i.e., relatively slow).

[0059] The applicant has discovered that for motor systems that regularly transition from an unpowered motor state to a peak efficiency state (such as with pulsed operation), efficiency can be even further improved when the transition occurs as quickly as possible. By making rapid transitions (e.g., from zero torque to peak efficiency torque), the overall average efficiency of the motor is improved because the motor spends less time in transitions where efficiency is below peak. This relationship is shown in Figure 1. Figure 3A and Figure 3B shown.

[0060] refer to Figure 3A , shows a torque versus efficiency graph for an exemplary motor operating at a fixed speed (e.g., 6000 rpm). In the exemplary graph, the torque output range from 0.0 Nm to 250 Nm is plotted along the horizontal axis, while the efficiency of the motor is plotted from 0.0% to 100% along the vertical axis. Curve 26 depicts the transition of the motor from zero to peak efficiency torque. During the transition, as shown by the shaded area 27, the peak efficiency torque has a much lower efficiency at peak efficiency torque 28.

[0061] refer to Figure 3B , provides a graph showing torque and work loss for an exemplary motor operating at a fixed speed during a transition from zero to peak efficiency torque. In this graph, work loss (W) is plotted along the vertical axis, while 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, as the torque output increases, the work loss of the motor increases. Therefore, the faster the transition time from zero to peak efficiency torque, the less work is performed and the less energy the motor consumes.

[0062] By replacing torque with time along the horizontal axis and integrating the area under curve 29, the energy consumed by the motor for a given transition time can be calculated. For example, the applicant found that for the exemplary motor, 7234.5 joules of energy were used with a transition time of 0.5 seconds, while only 723.4 joules were used with 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 the load is not accelerating, so no energy is added to the load inertia.

[0063] For different motors, the motor's transition from zero to peak efficiency torque, peak efficiency torque, peak efficiency torque, and work loss will be different. Figure 3A and Figure 3B The drawings should be regarded as merely exemplary and should not be construed as limiting in any respect.

[0064] power converters

[0065] A power converter is a known device used with electric motors to convert a DC power supply, such as that produced by a battery or capacitor, into three-phase AC input power that is applied to the motor's stator windings. In response, the stator windings generate RMF as described above.

[0066] refer to Figure 4, shows a diagram of a power controller 30 for pulsed operation of an electric motor. Power controller 30 includes a power converter 32, a DC power supply 34, an electric motor 36, and a pulse controller 38. Power converter 32 can operate as either a power inverter or a power rectifier, depending on the direction of energy flow through the system. When the electric motor is operating as a motor, power converter 32 is responsible for generating three-phase AC power from DC power supply 34 to drive induction motor 36. Three-phase input power, represented as phase A 37a, phase B 37b, and phase C 37c, is applied to the stator windings of electric motor 36 to generate the RMF as described above. Each phase 37a, phase 37b, and phase 37c is depicted as a line with arrows at both ends, indicating that current can flow from power converter 32 to electric motor 36 when the electric motor is operating as a motor, and that current can flow from electric motor 36 to power converter 32 when the electric motor is operating as a generator. 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 and stored in the DC power supply.

[0067] The pulse controller 38 is responsible for selectively causing the three-phase input power to be pulsed. During normal (i.e., continuous) operation, the three-phase input power is continuous or non-pulsed. On the other hand, during pulse operation, the three-phase input power is pulsed. In non-exclusive embodiments, pulse operation may be achieved using any of the methods described herein, such as, but not limited to, the pulsed operation described herein. Figure 5B 、 Figure 5C and Figures 8 to 14 Described method.

[0068] refer to Figures 5A to 5C , provides plots for illustrating the difference between continuous three-phase input power and pulsed three-phase input power provided to the induction motor 36. In each plot, current is plotted on the vertical axis and time is plotted on the horizontal axis.

[0069] Figure 5A Conventional sinusoidal three-phase input current 42a, 42b, and 42c is shown delivered to an induction motor 36. Phase B, represented by curve 42b, lags phase A, represented by curve 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 current 42a, 42b, and 42c is continuous (not 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 can have any value.

[0070] Figure 5B and Figure 5CTwo examples of different pulsed three-phase current waveforms 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 5A As shown, the period of the reference sine wave is τ, but now the sine wave is modulated to be intermittent. Figure 5B and Figure 5C The current delivered in Figure 5A The same average torque is achieved with the three-phase input current applied continuously in the same manner (assuming torque is proportional to current, which is generally the case). The difference between the pulsed currents 44a-c and 46a-c lies in the duration of their respective current pulses and the staggered "off" periods. Figure 5B In , the current pulses 44a-c are interleaved with "off" periods of equal length. The length of each on period and off period is 2τ. Figure 5C In the example, current pulses 46a-c and the interleaved "off" 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" and "off" periods differs, i.e., the frequency of the pulse modulation is different. The frequency of the pulse modulation may vary based on the type of motor used, noise and vibration considerations, the current operating rotor speed, and other factors.

[0071] Figures 5B to 5C An application is shown where the "on" motor drive pulses are evenly spaced while the motor is operating at the steady state desired output level. This approach works well in many cases 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. Figure 5B and Figure 5C In some embodiments, the phase of the on / off pulses is synchronized with the applied AC power; however, in some embodiments, the phase of the on / off pulses need not 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.

[0072] Electric Motor Physics and Constraints

[0073] For any given motor, physics ultimately limits the possible speed of transition from zero to peak efficiency torque. Typically, the transition speed is based on the physics of how fast the electric field in the motor can build up, which in turn is limited by the applied voltage, the motor's back electromotive force ("BEMF"), and the inductance of the motor windings.

[0074] If we assume that the set point of power converter 32 is increased at time zero and the feedback is zero, the control of the output stage of each phase will saturate. As a result, the low or high output power device of each motor phase will be hard-on. This leads to six possible combinations, including:

[0075] 1. Phase A and phase B are positive, phase C is negative,

[0076] 2. Phase A is the positive pole, phase B and phase C are the negative poles,

[0077] 3. Phase B and phase C are positive, phase A is negative,

[0078] 4. Phase B is the positive pole, phase A and phase C are the negative poles,

[0079] 5. Phase C and phase A are positive, phase B is negative, and

[0080] 6. Phase C is the positive pole, and phases A and B are the negative poles.

[0081] For each of these six possible combinations, the current in motor 36 at time zero will be (a) full current in one phase and (b) split current in the other two phases. As further described below, the ratio of these currents will depend on the rotor position at time zero.

[0082] refer to Figure 6A , shows a representative circuit for modeling the current flowing through the three phases A, B and C.

[0083] Each phase A, B, and C is represented by its self-inductance ("LS"), mutual inductance ("LM"), resistance ("R"), and BEMF.

[0084] In the case shown, Ic = Ia + Ib. The sum of the currents flowing into the mutual inductance is zero, and therefore the mutual inductance has no effect on the current flow. Assuming that the BEMF of the motor is zero, the simplified equivalent circuit obtained is Figure 6B As shown. This circuit requires time for the current to accumulate to a given value:

[0085]

[0086] If the BEMF is not zero, the voltage applied to each phase will be different. Because the phase impedance and phase current are balanced, the neutral point of the winding in this case = V 总线 *2 / 3. If winding B is connected to the negative rail, then the neutral voltage will be = V 总线 / 3. This defines the currents Ia, Ib, and Ic for phases A, B, and C as:

[0087]

[0088] Since all of the above values are instantaneous, the value at time zero depends on the instantaneous value of the BEMF for each phase, which in turn depends on the position of the rotor within one electrical cycle or pole-pair spacing. It is also important to note that the instantaneous BEMF voltage for each phase, the voltage applied to the motor inductance, and the rate of rise of the motor phase current also vary over time.

[0089] The goal is to bring the currents to their desired values and phases to provide the required torque. Currents are typically controlled using field-oriented control, or "FOC," so the phase currents are transformed into rotating coordinate system values of "iq" (quadrature current) and "id" (DC current), where the vector sum of id and iq equals the peak magnitude of the phase current, and ArcTan id / iq is its angle. The cosine of this angle is the power factor. Therefore, deriving the values of id and iq using direct quadrature zero transformation yields:

[0090]

[0091] When examining the above equations, the BEMF waveform Vpk affects only iq (quadrature current), while both currents are affected by the bus voltage V 总线 and the rotor angular position θ. Neither the angle nor the motor BEMF can be changed without changing the motor, so the only parameter that can be controlled to affect the rate of rise of the phase current and therefore the motor torque is the applied bus voltage V 总线 Therefore, one aspect of the present invention provides for reducing the transition time from zero to peak efficiency torque during pulse application by temporarily increasing or "boosting" the bus voltage to a higher value than the normal operating bus voltage.

[0092] It should be noted that when the converter is off, energy stored in the motor windings returns to the bus voltage supply. If the supply is unable to absorb this energy, the bus voltage will rise as the bus capacitance absorbs this energy. Due to the capacitance of the bus supply, this normal process typically only increases the bus voltage by a small amount, which is usually not enough to be considered a boosted bus voltage. However, if this energy is captured separately, such as by being captured and stored in a storage device such as a capacitor or battery, it can be recycled back to the motor in the form of a boosted voltage.

[0093] Alternatively, during the "off" period, the bus voltage can be increased by a separate boost voltage source using a charge pump, or a separate voltage source. This boost supply should not be designed to charge the main bus capacitance, but rather a separate capacitor that can discharge to the motor during the transition time from zero to the required torque.

[0094] Conventional power converter circuit

[0095] Therefore, the inherent inductance of the motor may temporarily delay / slow down the voltage / power step between the motor-on state and the motor-off state. During continuous (pulse-free) 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 an incentive to reduce leading and trailing edge pulse transition times.

[0096] refer to Figure 7A , shows a circuit diagram of a representative prior art power converter 32. The power converter circuit 32 includes three pairs of switches, denoted as S1 to S6. Each pair of switches S1 to S2, S3 to S4, and S5 to S6 is connected in series between two voltage buses (+V 总线 ) and (-V 总线 ). Two voltage buses (+V 总线 ) and (-V 总线 ) is a usable potential for operating the motor 36. Each of the switches S1 to S6 may have a bypass diode (D1 to D6) electrically connected in parallel with the switch. These diodes help prevent switch-damaging voltage spikes that may be generated during switching operations.

[0097] The diodes also provide a path for recirculating current that might be blocked by the switches. This is particularly important when the motor 36 is used as a generator. Switches S1 to S6 can each be a MOSFET (metal oxide semiconductor field effect transistor) switch with an integrated diode. Alternatively, other types of transistors, such as, but not limited to, insulated gate bipolar transistors (IGBTs), can be used.

[0098] The connections to the stator coil windings of the motor 36 are made between each switch pair. For phase A, the connections are made between switch pairs S1 and S2 and are designated as 37a. For phase B, the connections are made between switch pairs S3 and S4 and are designated as 37b. For phase C, the connections are made between switch pairs S5 and S6 and are designated as 37c.

[0099] Within the motor 36, each phase stator winding can be modeled as an inductor 31, a resistor 33, and a mutual inductance 35. Figure 7A These components are labeled only for phase C, but similar components exist in the phase A winding and the phase B winding.

[0100] Switches S1 through S6 may be collectively referred to as a switch network that controls power to and from the motor 36 .

[0101] When the motor 36 is operated as a motor, the switches S1 to S6 operate in a conventional manner to apply current to each stator winding. For example, the switches can operate as a six-step inverter that provides AC power to the motor 36.

[0102] Figure 7B The switching sequence for obtaining a sixth-order output from power converter 32 is shown. Each switch is turned on for a 1 / 2 cycle period in an interleaved manner. For each winding, current can flow through one switch in the top row and one or two switches in the bottom row. Switch pairs S1-S2, S3-S4, and S5-S6 are never turned on simultaneously because this would short-circuit DC power supply 34.

[0103] Figure 7C The voltage between points A and B is shown as voltage V ab .

[0104] Similarly, Figure 7D and Figure 7E The voltages are shown separately between points B and C and between points C and A. Adding these voltages allows the voltage between each phase and neutral to be determined.

[0105] Figure 7F The resulting phase voltage of phase A is shown. The resulting 6th order waveform approximates a sine wave with a frequency of ω and is often referred to as a modulating signal. The phase voltages of phases B and C are phase-shifted by 120° and 240°, respectively, relative to the phase A voltage.

[0106] It should be understood that the electric machine 36 can operate as a generator as well as a motor. When operating as a generator, energy flows from the electric machine 36 to the DC supply 34. The power converter 32 acts as a 3-phase rectifier rather than an inverter.

[0107] In a typical prior art system, a switching network is used to control power flow to the motor using pulse width modulation (PWM) control. PWM control reduces the time the switching network is in the active configuration of switches S1 through S6 (in which power can flow to the motor). That is, the portion of time switches S1 through S6 are in the inactive configuration (either S1, S3, and S5 or S2, S4, and S6 are all off) increases as the desired motor torque output decreases.

[0108] Power converter with boost

[0109] Figure 8 FIG. 1 shows a power converter circuit 132 including a boost circuit according to a non-exclusive embodiment of the present invention. Figure 7A Compared to the prior art power converter circuit 32 shown in FIG, the power converter circuit 132 further includes additional switches SA and SB, both of which are controlled by the pulse controller 38. The two switches can be connected to a common signal line 41 (eg, Figure 8 shown) control or may have independent control lines ( Figure 8 When the switch SA is turned on, the positive power supply voltage (+V DC ) coupled to (+V 总线 When the switch SB is turned on, the negative power supply voltage (-V DC ) coupled to (-V 总线 ).

[0110] During operation, the pulse controller 38 operates to selectively turn on and off the switch SA or SB by applying a pulse waveform to the signal line 41, which electrically connects the pulse controller 38 to the switches SA and SB. When the switches SA and SB are turned on, current can be delivered to the motor 36. Conversely, when SA and / or SB are turned off, no current or only a transient current is delivered to the motor 36.

[0111] The power converter circuit 132 also includes a capacitor C1 having a voltage coupled to (+V 总线 ) of a conductive plate and coupled to (-V 总线 ) of the other conductive plate. Switches SA and SB and capacitor C1 can be collectively referred to as a boost circuit because their purpose is to increase +V at the beginning of the "on" pulse. 总线 and -V 总线 The initial voltage on the bus is described below. In various embodiments, the boost circuit may be incorporated into the switching network or may include components distinct from the switching network.

[0112] As previously noted, the goal of pulsed motor control is to operate the motor 36 at substantially the most efficient level of the motor at the current motor speed during the motor "on" time period, and to cut power (provide zero or negligible power) during the "off" time period. For example, the power supplied during the off time period may be less than 10%, 5%, 1%, 0.5% or 0.1% of the power supplied during the "on" time period. The operating point when operating during the "on" time period may have an efficiency within 5%, 2% or 1% of the maximum operating efficiency point of the motor at the current motor speed. The transition through the low efficiency operating region between the "off" and "on" time periods should be as fast as possible to maximize efficiency. Therefore, the managed transition between the motor power "on" and "off" states ideally has a leading edge for the vertically upward transition and a falling edge for the vertically downward transition. Such a "perfect" pulse 60 in Figure 9A This is shown diagrammatically in FIG, which shows an ideal motor drive current versus time for pulse control with a 50% duty cycle. In this figure, the current pulse represents the sum of the currents in all phases. Although the current pulse is shown as being flat on top, this is not necessarily the case.

[0113] In the real world, many practical limitations make it difficult to generate such perfect pulses. For example, the inductance of the circuitry of both the motor 36 and the power converter 32 slows 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 motor's speed, and the available bus voltage. Typically, the actual rise and fall of the pulses occurs more slowly, meaning that there is a shift over time. The nature of the rise and fall in the real world is Figure 9B As seen therein, there is a rising period of time (rise time) 62 required for the current to actually rise from zero to the desired "on" power level, and a falling period of time (fall time) 64 required for the current to actually fall from the "on" power level to zero.

[0114] During the power ramp-up and ramp-down periods, the motor 36 continues to consume or generate power. However, during these transition periods, the motor operates at a lower efficiency. Typically, when the operating current is reduced from its maximum efficiency condition ( Figure 1 As the current level (curve 16) decreases toward zero, motor efficiency decreases, with energy conversion efficiency significantly deteriorating as the current level approaches zero. Consequently, pulse distortion, represented by the current rise and fall periods, reduces the efficiency gains achieved through pulse operation. Generally, the smaller the ratio of rise / fall time to pulse length, the less impact transient switching effects have on the motor's energy conversion efficiency during pulse application.

[0115] It should be understood that Figure 9B The transient effects shown in Figure 1 are illustrative and do not necessarily reflect the actual 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 characteristics of the motor used (primarily referring to rise and fall times), the pulse frequency (primarily dictated by the control scheme used), and the pulse width (dictated by the control scheme and motor load). The voltage available to power the motor and the motor speed also affect the pulse rise and fall times. If the pulse is slow compared to the motor response, the rise / fall time may be a small fraction of the pulse width, and transient switching effects may have minimal impact on motor performance. Conversely, if the pulse is very fast and / or the motor response is slow, the rise / fall time may be a significant fraction of the pulse width, and in some cases may even exceed the pulse width. If not properly managed, the transient efficiency losses associated with switching can significantly reduce or even eliminate any theoretical gains that can be achieved through pulse operation. Therefore, it is important to consider the transient switching effects associated with pulse operation when determining the pulse frequency and control scheme appropriate for any particular application.

[0116] Included in Figure 8Capacitor C1 in the power converter circuit 132 is provided to improve current rise and fall times. Capacitor C1 can store energy from the motor 36 during the fall period and supply energy to the motor 36 during the rise period. This results in faster turn-on and turn-off transitions than without capacitor C1.

[0117] To better understand the operation of power converter 132, assume that power converter 132 is initially in the "on" state and motor 36 is operating as a motor. This means that switches SA and SB are conducting, allowing current to flow from the positive terminal of DC supply 34 through power converter 132 to motor 36 and back to the negative terminal of DC supply 34. Switches S1 to S6 will be in the Figure 7B The configuration shown oscillates to apply AC power to the motor 36 .

[0118] To terminate the motor operation, switches SA and SB can be turned off, allowing +V 总线 and -V 总线 The bus has a different potential than the corresponding terminals of the DC power supply 34. Since the circuit is now open, current must cease to flow through the circuit; however, there may be a significant amount of energy in the motor 36 associated with the magnetic field generated by the current. At least some of this energy can be extracted from the motor 36 and captured in capacitor C1 and stored there. This will increase the potential difference between the positive voltage bus and the negative voltage bus. For example, line +V 总线 The potential on the positive terminal of the DC power supply may be increased to a value higher than the potential of the positive terminal of the DC power supply +V DC , while line-V 总线 The potential on the DC power supply may drop below the potential of the negative terminal of the DC power supply -V DC Note that switches S1 through S6 all have bypass diodes that allow unidirectional current flow from the motor 36 to line +V 总线 and from line-V 总线 Flow to the motor 36 regardless of the switch position. Coincidently or almost coincidentally with the turning off of switches SA and SB, any of the switches S1 to S6 that may have been turned on will be turned off when switches SA and SB are turned off, so current will not flow from line +V 总线 with -V 总线 Any of these switches between them flows to the motor 36.

[0119] When the motor is required to run again, switches S1 to S6 can be switched Figure 7B The switching pattern must correspond to the rotor rotation angle so that the phase of the applied current matches the correct phase to supply power to the motor 36 again. 总线 The voltage on the DC And -V总线 Rising to -V DC The circuit configuration and control method are arranged to provide a higher initial voltage to be applied to the motor 36 at the beginning of the "on" phase, which advantageously reduces the pulse rise time.

[0120] Figure 10 Shows the Figure 8 An exemplary +V 总线 and -V 总线 Waveform vs. Time. The pulse generator 38 generates a digital waveform 43 consisting of a series of digital "0"s and "1"s. A 1 may correspond to turning the motor 36 "on" and a 0 may correspond to turning the motor "off." Figure 10 In FIG. 1 , pulses are applied to the motor 36 at a 40% duty cycle; however, this is exemplary only and any duty cycle may be used. +V 总线 The voltage on the rail 45 increases to +V during the falling period. 升压 And -V 总线 The voltage on the rail 47 drops to -V during the falling period. 升压 +V 总线 and -V 总线 The voltage changes on the bus can be equal or different. 总线 Voltage 45 and -V 总线 Voltage 47 remains relatively constant during the motor off time because energy from the motor ramp down is stored in capacitor C1. When the pulse generator waveform 43 returns to digital "1", the energy stored in capacitor C1 is supplied to the motor 36 through the switch array S1 to S6. This causes +V 总线 The voltage on rail 45 is returned to +V DC , and -V 总线 The voltage on rail 47 returns to -V DC , because the charge in capacitor C1 has dissipated and the energy stored in capacitor C1 is used to drive the motor. Motor operation during the "on" period is maintained by turning on switches SA and SB so that energy from DC power supply 34 can be used to drive the motor. The boost circuit effectively increases the available potential between the positive voltage bus and the negative voltage bus for driving the motor at the beginning of at least one pulse in the series of pulses. It should be understood that the positive voltage bus and the negative voltage bus are relative terms, and the potential on each of these buses can be positive or negative relative to ground potential. The boost circuit can be used to increase the available potential for driving the motor during all pulses in the series of pulses.

[0121] Although the exemplary power converter with a boost circuit Figure 81 is shown as having a switch adjacent to the positive and negative terminals of the DC power supply source, but this is not required. In some embodiments, only a single switch may be required.

[0122] Switches SA and SB, in conjunction with capacitor C1, can be used to reduce power ramp-up and ramp-down times, in some cases by a factor of two, five, ten, or even less. By storing energy recovered from the motor during ramp-down, the voltage across capacitor C1 can be raised above the voltage of the power supply. The magnitude of this voltage increases with the amount of magnetic energy that can be extracted and captured. This can significantly reduce potentially harmful transient switching effects associated with pulsed operation.

[0123] Figure 9C An example of improved rise and fall times is shown schematically in FIG. As is evident from the figure, Figure 9B The rise time 66 on the leading edge of the pulse is faster / shorter than the corresponding rise time 62 shown in FIG. Figure 9B , the fall time 68 of the trailing edge of the pulse is faster / shorter than the corresponding fall time 64 shown in FIG. It will be appreciated, therefore, that motors designed with pulse control in mind or modified to improve the motor's transient response to power pulses can benefit more from pulse operation than existing motors.

[0124] It will be appreciated that the appropriate pulse frequency implemented by the pulse controller 38 for different motors may vary significantly based on the motor's configuration, operating environment, and operating range. For some motors, a switching frequency on the order of 10 kHz to 50 kHz may be appropriate—while for other motors, a much lower switching frequency (e.g., in the range of 10 Hz to 500 Hz) may be more appropriate. The most appropriate pulse application frequency for any particular motor will depend on a variety of circumstances, such as the type of motor, the load on the motor, and / or the application of the motor.

[0125] It should be understood that the details of the boost circuit used to shorten the rise and fall times of power to or from the motor can vary depending on the type of motor and its operating conditions. For example, in some cases, one of the switches SA or SB can be eliminated from the power converter circuit 132. Other types of power converter circuits and control strategies can be used. For example, in some cases, a Z-source inverter can be used, in which a diode, two inductors, and two capacitors are located between the power supply source and the switching network.

[0126] The voltage boost level and size of capacitor C1 can be 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. Preferably, the capacitance and voltage boost level are also selected to maximize the overall motor efficiency during the pulse application, including the effects of the inefficiencies associated with the transients themselves and any overshoot that may occur due to the use of capacitor C1. Since capacitor C1 is used to improve transient response, the capacitor can be recharged in a timely manner during periods when the motor is not being supplied with power (e.g., during motor off periods). In the following description of Figure 11 This mode of operation is explained in more detail in the description of .

[0127] Depending on motor speed and load, the energy stored in the motor field may not be sufficient to fully increase +V 总线 and -V 总线 The voltage is increased to achieve fast rise and fall times. In this case, it may be desirable to increase the potential difference across the motor during the off period between pulses. Example voltage waveforms showing two boost cycles 73a and 73b are shown as Figure 11 As shown. It should be understood that more or less than two boost cycles may be used depending on the operating conditions of the motor. An appropriate switching network and control strategy are required to implement this type of control.

[0128] refer to Figure 12 , shows another power converter 200 including a boost circuit 202 according to another embodiment of the present invention. The power converter 200 includes switches S1 and S2 for phase A, switches S3 and S4 for phase B, and switches S5 and S6 for phase C. Each pair of switches S1 to S2, S3 to S4, and S5 to S6 is connected in series between two voltage buses (+V 总线 ) and (-V 总线 ). Two voltage buses (+V 总线 ) and (-V 总线 ) is the available potential for operating the motor 36. Switches S1 through S6 are collectively referred to as a switching network, which controls the flow of power to and from the motor 36. When operating as a motor, power from a DC supply source is provided through the switching network of switches S1 through S6. Furthermore, as previously described, the switching network provides phased energy to the three phases of the stator windings of the motor 36. Similarly, when operating as a generator, energy flows from the motor 36 to a storage device, such as a battery.

[0129] The boost circuit 202 includes a boost supply source 204, a switch 206, a capacitor C1, a battery, and a control signal 208 generated by a pulse controller 38. Since the pulse controller 38 has been previously described, its detailed description is omitted for brevity.

[0130] In various embodiments, the boost supply 204 can be a dedicated circuit capable of generating a boosted voltage (e.g., a charge pump or a separate voltage source) and / or a storage device such as another capacitor and / or a battery. In the latter embodiment, at least some of the energy stored by the storage device can come from the motor 38 itself. For example, when the motor 36 is operating as a generator, or when the motor 36 is acting as a motor and transitioning from an on state to an off state, such as during a pulse application, the energy generated can be transferred to certain components in the boost circuit 202 (such as capacitor C1 and / or a battery) and stored. The stored energy can then be used to "boost" the positive rail (+V 总线 ).

[0131] The switch 206 can be any type of switch capable of switching between the positive (+) and negative (-) electrodes of the boost supply 204. It is contemplated that the switch will be constructed using semiconductor devices. In a specific but non-exclusive embodiment, the switch 206 is a single-pole double-throw switch.

[0132] During continuous motor operation, as is well known in the art, phased power is provided to the stator windings of the motor 36 through switches S1 and S2 for phase A, switches S3 and S4 for phase B, and switches S5 and S6 for phase C. The net result is a continuous torque output from the motor as previously described.

[0133] During pulse operation, the pulse controller 38 controls the switch 206 to control the boost circuit 202 via the control signal 208. In the case of a positive pulse transition, the switch 206 is activated to switch the positive rail (+V 总线 ) is connected to the positive (+) terminal of the boost supply 204. As a result, the boost supply 204, operating in conjunction with capacitor C1 and the battery, is used to supply power to the positive rail (+V 总线 As the voltage on the positive rail increases or is boosted, the transition time decreases. Once the energy stored in the boost circuit decreases or the peak torque level has been reached, the control signal 208 instructs the switch to switch the positive rail (+V 总线 ) is connected to the negative (-) terminal of the boost supply 204. As a result, the boost voltage is effectively taken from the positive rail (+V 总线 ) removed.

[0134] The effect of the boost circuit 202 is also Figures 9A to 9C In particular, Figure 9A shows an ideal pulse with no transition time, Figure 9B A "real world" pulse is shown having a transition time designated by reference numeral 62. As previously noted, the inductive aspects of the circuitry of the motor 36 and power converter 200 slow down the current rise and fall times. Figure 9C 2 shows the transition assisted by the boost circuit 202. By comparison, it can be easily understood that Figure 9C The "boosted" transition time 66 shown is significantly less (i.e., faster) than the Figure 9B The transition time 62 is shown.

[0135] exist Figure 12 In the embodiment of FIG. 5 , capacitor C1 is arranged in parallel with each switch pair S1 - S2 , S3 - S4 and S5 - S6 at the positive rail (+V 总线 ) and the negative rail (-V 总线 ). In a non-exclusive embodiment, the size of C1 is derived from the ripple current when the power converter 200 acts as an inverter. With this arrangement, the ability of the boost circuit 202 to reduce the pulse rise time and fall time is improved.

[0136] Operation flow chart

[0137] Figure 13 It shows that Figure 1 The steps of the pulse control operation of the motor are depicted in the flowchart 70 , which are of those characteristics.

[0138] In an initial step 72 , the current motor output and the current motor speed are determined.

[0139] In decision step 74, a determination is made as to whether the motor should be operated in continuous mode or pulsed mode based on the current motor output and the current motor speed. In other words, a determination is made as to whether the desired motor torque is higher or lower than the most efficient output torque for the current motor speed (i.e., Figure 1 If the maximum efficiency curve of the motor shown in FIG16 is higher, the motor is operated in continuous mode. ... lower, the motor can advantageously be operated in pulsed mode.

[0140] In step 76 , if the current motor torque is higher than the most efficient output torque for the current motor speed, the motor is operated in continuous mode 76 .

[0141] In step 78, the power output or magnitude of the "on" pulses that provides substantially maximum efficiency operation at the current motor speed is determined.

[0142] In step 80 , the desired pulse duty cycle for operation in the pulse mode is determined so that the average output power or torque matches the desired output.

[0143] The motor is operated in pulse mode using the determined pulse duty cycle and pulse power output in step 82. Using the power controller 30 with the boost power converter circuit 132 or some other power converter circuit capable of storing and releasing magnetic energy from the motor typically significantly reduces the rise and fall times of the pulses, further improving motor efficiency.

[0144] The above steps 72 to 82 are continuously executed while the motor is running. At any specific motor speed, there will be a corresponding most efficient output torque, which is determined by Figure 1 The maximum efficiency curve 16 in FIG. As the instantaneous motor output request and / or current motor speed change, a decision is made to operate the motor in the appropriate continuous or pulsed mode. 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. As a result, for motor-powered vehicles, the overall vehicle efficiency is improved, which means that the vehicle range between battery recharges is extended.

[0145] Figure 14 is a simplified diagram illustrating a system 300 for modulating energy supplied to an electric machine 36 according to another non-exclusive embodiment of the present invention. The system 300 includes the electric machine 36, the power converter 32, a torque control decision module 302, a feedback sensor 304 for generating a feedback signal 306 indicative of the angular position of the rotor of the electric machine 36, and a torque and speed estimator 308.

[0146] During operation of the system 300, the torque modulation decision module 302 receives a torque request. In response, the torque modulation decision module 302 determines whether the requested torque is less than the peak efficiency torque of the electric machine 36 when operating as a motor.

[0147] If not, meaning the torque demand is greater than the peak efficiency torque, then the electric machine 36 operates in continuous mode as a motor. In this case, the torque demand waveform 310 provided to the power converter 32 indicates continuous operation of the electric machine 36 operating as a motor.

[0148] On the other hand, if the torque demand is less than the peak efficiency torque of the motor 36, the motor 36 is operated in pulse mode as a motor. In this case, the torque modulation decision module 302 generates a modulation waveform 310 for the power converter 32 to cause the motor 36 to switch or pulse between the peak efficiency torque of the motor and a lower torque (the average of which is substantially equal to the desired torque) when operating as a motor. In various embodiments, the lower torque can be zero, but it does not need to be zero. The lower torque can be some other torque value greater than zero, provided that the average of the lower torque and the peak efficiency torque is substantially equal to the desired torque.

[0149] The power converter 32 includes a switching network including switch pairs S1-S2 for phase A, switch pairs S3-S4 for phase B, and switch pairs S5-S6 for phase C, all of which are not shown in the figure for simplicity. As previously noted, switches S1 through S6 are controlled by the power converter 32 to cause the motor 36 to (1) operate continuously as a motor when the torque demand is greater than the peak efficiency torque, thereby generating a continuous torque output, or (2) operate in a pulsed mode when the torque demand is less than the peak efficiency torque. The power converter 32 can control the energy supplied to the motor 36 using any of a number of different protocols, such as pulse width modulation (PWM), direct torque control (DTC), hysteresis, or "deadbeat" control, as a form of current modulation.

[0150] In an alternative embodiment, a method such as Figure 8 132 or Figure 12 Boost power converter of 200. Where the boost version of power converter 32 is used, the efficiency and performance of the motor operation of electric machine 36 is improved due to faster rise and / or fall times of the pulses during pulse operation.

[0151] Feedback sensor 304 generates feedback signal 306, which indicates the angular position of the rotor of motor 36. The feedback signal is provided to each of power converter 32 and torque and speed estimator 308. Knowing the angular position of the rotor, torque and speed estimator 308 can provide accurate estimates of the torque and speed of the motor to torque modulation decision module 302. In response, waveform 310 can be adjusted as needed, so that the timing of the switching network within power converter 32 (i.e., the timing of the on / off switching of switches S1 to S6) can be precisely controlled so that the energy of each of phases A, B, and C is timed to coincide with the current position of the rotor. As a result, the operation of motor 36 as a motor is both smooth and efficient. It should be noted that the use of feedback sensor 304 is not mandatory, and other techniques can be used to measure or estimate the angular position of the rotor of motor 36. For example, any of a variety of sensorless methods can also be used.

[0152] Other motor and generator types

[0153] There are a variety of known and commercially available electric machines (both motors and generators), including DC and AC motor / generators. Although the structure, control, and energy conversion efficiency of various types of motors and generators vary greatly, most motors and generators are designed to operate within a certain range of operating conditions, and their energy conversion efficiency will vary (usually significantly) within this operating range. Generally, if the operating range includes Figure 1 If the area under the equivalent of the maximum efficiency curve 16 shown in FIG, the control principles described herein can be applied to any type of motor to improve efficiency.

[0154] Some prior art electric motors currently operate using pulse width modulation (PWM) control. However, such motors are not driven at their most efficient energy conversion levels. Therefore, the described method can also be used to improve the energy conversion efficiency of such motors.

[0155] Traditionally, many types of electric motors (including brushless DC motors, induction motors, synchronous AC motors, switched reluctance motors, etc.) are driven by a continuous (although possibly varying) drive current to deliver the desired torque output. The drive current is often controlled by controlling the output voltage of an inverter and / or converter (which serves as the voltage input to the motor). Typically, an electric motor can be operated as a generator by changing the relative phase between the rotor and stator magnetic fields. Therefore, the circuits and control methods described in terms of electric motors are equally applicable to situations where the motor is used as a generator. The pulse control described is particularly beneficial when such electric motors and generators operate in a region below their respective maximum energy conversion efficiency points.

[0156] 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.

[0157] The embodiments of the present application also provide the following technical solutions.

[0158] 1. A device comprising:

[0159] power supply source;

[0160] An electric machine having windings in which magnetic energy is stored;

[0161] a motor controller configured to selectively operate the motor in a pulse mode; and

[0162] a power converter coupled between the power supply and the motor, the power converter arranged to deliver pulsed power to or receive pulsed power from windings of the motor in response to the motor controller;

[0163] wherein the power converter includes a boost circuit arranged to extract at least some of the magnetic energy present in the motor at the end of a pulse to reduce the pulse fall time, store at least some of the energy, and apply at least some of the energy at the beginning of a subsequent pulse, thereby reducing the rise time and fall time of the pulse power relative to the rise time and fall time of the pulse power in the absence of the boost circuit.

[0164] 2. An apparatus as described in claim 1, wherein during the pulses of the pulsed operation, the motor operates substantially at its maximum efficiency operating point.

[0165] 3. The device as described in Option 1 or 2, wherein the power supply source is a DC power supply source.

[0166] 4. An apparatus as described in any one of options 1 to 3, wherein the power converter operates as a power inverter to convert DC power generated by the DC power supply source into AC power to drive the motor.

[0167] 5. An apparatus as described in any one of options 1 to 3, wherein the power converter operates as a power rectifier to convert the AC power generated by the motor into DC power stored in the DC power supply source.

[0168] 6. An apparatus as described in any of options 3 to 5, wherein the boost circuit includes a switch electrically connected between terminals of the DC power supply source and a switching network that controls power to and from the motor.

[0169] 7. The apparatus of claim 6, wherein the boost circuit comprises a capacitor selectively electrically connected to the switch network via the switch.

[0170] 8. An apparatus as described in any one of schemes 1 to 7, wherein the boost circuit uses the magnetic energy stored in the stator windings to temporarily boost the available electrical potential for driving the motor.

[0171] 9. An apparatus as described in any one of embodiments 1 to 8, wherein during the off time period of the motor, the boost circuit uses a series of one or more boost steps to increase the available potential for driving the motor.

[0172] 10. An apparatus as described in any of embodiments 3 to 9, wherein the boost circuit includes a diode located between the power supply source and a switching network that controls power to and from the motor.

[0173] 11. A method of operating a motor, comprising:

[0174] operating the motor in a pulsed manner such that power applied to or drawn from the motor consists of a series of pulses separated by periods of reduced power, wherein a duty cycle of the series of pulses is determined so as to deliver a desired torque magnitude;

[0175] extracting at least some of the magnetic energy present in the motor at the end of the pulse to reduce the pulse fall time;

[0176] storing at least some of the energy; and

[0177] At least some of this energy is applied at the beginning of a subsequent pulse, thereby reducing the rise time and fall time of the pulse power.

[0178] 12. A method as described in claim 11, wherein the power applied to or obtained from the motor during the pulses in the series of pulses causes the motor to operate substantially at the most efficient operating point of the motor.

[0179] 13. A method as described in embodiment 11 or 12, wherein the series of pulses is generated by a power converter including a boost circuit, and the boost circuit is arranged to reduce the rise time and fall time of the pulses in the series of pulses relative to the rise time and fall time of these pulses in the absence of the boost circuit.

[0180] 14. The method of claim 13, wherein the power converter operates as a power inverter to convert DC power generated by a DC power supply source into AC power to drive the motor.

[0181] 15. The method of claim 13, wherein the power converter operates as a power rectifier to convert AC power generated by the motor into DC power that is stored in the DC power supply source.

[0182] 16. A method as described in any of embodiments 11 to 15, wherein the electric machine is operated as a motor or a generator.

[0183] 17. A method as described in any of options 11 to 16, wherein the motor operates as a motor and the series of pulses is generated by a power converter including a boost circuit that increases the available potential for driving the motor at the beginning of at least one pulse in the series of pulses.

[0184] 18. A method as described in claim 17, wherein the boost circuit increases the available potential for driving the motor at the end of the pulse preceding the at least one pulse in the series of pulses.

[0185] 19. A method as described in any of options 17 to 18, wherein the boost circuit increases the available potential for driving the motor during an off time period preceding the at least one pulse in the series of pulses.

[0186] 20. The method of claim 19, wherein the boost circuit increases the available electrical potential for driving the motor using a series of one or more steps.

[0187] 21. A method of operating a motor, comprising:

[0188] operating the motor in a pulsed manner such that power applied to or drawn from the motor consists of a series of pulses separated by periods of reduced power, wherein a duty cycle of the series of pulses is determined so as to deliver a desired torque magnitude; and

[0189] The potential difference between the positive voltage bus and the negative voltage bus is increased to respectively reduce the transition time of the series of pulses.

[0190] 22. A method as described in claim 21, wherein during the time period between the series of pulses, the potential used to drive the motor is increased in a series of one or more steps.

[0191] 23. A method as described in claim 21 or 22, wherein the potential difference exceeds the potential difference of a power supply source used to store or deliver energy to the motor.

[0192] 24. A method as described in any of embodiments 21 to 23, wherein the power applied to or obtained from the motor during the time period of negligible power is selected from the group consisting of: less than 10%, 5%, 1%, 0.5% and 0.1% of the power supplied to or obtained from the motor during the series of pulses.

[0193] 25. A system comprising:

[0194] electric motor;

[0195] A torque modulation module, the torque modulation module being arranged to:

[0196] (a) receiving torque demand;

[0197] (b) determining whether the received torque demand is less than the peak efficiency torque of the motor; and

[0198] (c) if the torque demand is less than the peak efficiency of the motor, generating a modulated waveform;

[0199] a power converter arranged to receive the modulated waveform, the power converter arranged to generate a series of energy pulses in response to the modulated waveform, the series of energy pulses driving the electric motor to generate a torque at peak efficiency of the electric motor and a lower torque, respectively, the average of which is substantially equal to the received torque demand; and

[0200] A voltage boost circuit is coupled to the power converter, the voltage boost circuit reducing a transition time of the series of energy pulses relative to a transition time in the absence of the voltage boost circuit.

[0201] 26. The system of claim 25, wherein the lower torque is zero.

[0202] 27. A system as described in Option 25 or 26, wherein the lower torque is greater than zero but less than the torque at the peak efficiency of the motor.

[0203] 28. A system as described in any of embodiments 25 to 27, wherein the power converter includes a switching network coupled between a first power rail maintained at a first potential and a second power rail maintained at a second potential, and the boost circuit is arranged to boost the potential difference between the first power rail and the second power rail to a potential difference greater than the potential difference between the first potential and the second potential in the absence of the boost circuit.

[0204] 29. A system as described in Option 28, wherein the switching network includes a pair of switches for driving each of the three-phase energy of the motor, and each switch in the pair of switches is coupled in series between the first power rail and the second power rail.

[0205] 30. The system of claim 28, further comprising a switch for selectively coupling the boost circuit to at least the first power rail of the power converter.

[0206] 31. The system of any one of schemes 25 to 30, wherein the boost circuit comprises one of the following:

[0207] (a) Charge pump;

[0208] (b) voltage source;

[0209] (c) capacitors;

[0210] (d) batteries; or

[0211] (e) Any combination of (a) to (d).

[0212] 32. The system of any one of schemes 25 to 31, wherein the modulation waveform is modulated by the torque modulation module using one of the following:

[0213] (a) Pulse width modulation (PWM);

[0214] (b) Direct torque control (DTC);

[0215] (c) hysteresis; or

[0216] (d) Deadbeat control.

[0217] 33. A system as described in any of options 25 to 32, further comprising a speed estimator module, which is arranged to generate an estimated speed of the motor based on a signal indicative of the angular position of the rotor of the motor.

[0218] 34. A system as described in any of options 25 to 33, further comprising a torque estimator module, which is arranged to generate an estimated torque of the motor based on a signal indicating the angular position of the rotor of the motor.

[0219] 35. A system as described in any of options 25 to 34, wherein the torque modulation module is further configured to adjust the modulation waveform in response to a signal obtained from the sensed angular position of the rotor of the electric motor.

[0220] 36. A system as described in any of options 25 to 35, wherein the torque modulation module is further configured to cooperate with the power converter to operate the motor in a continuous mode when the received torque demand is greater than the peak efficiency torque of the motor.

[0221] 37. A system as described in any of options 25 to 36, wherein the electric motor is an electric machine capable of operating as a generator capable of operating in a continuous mode or a pulsed mode.

[0222] 38. A system as described in any of embodiments 25 to 37, wherein the power converter includes a switching network, the switching network includes a plurality of switches coupled between a first power rail and a second power rail, and the boost circuit includes a capacitor coupled in parallel with the plurality of switches in the switching network between the first power rail and the second power rail.

Claims

1. A vehicle comprising: a motor configured to drive the vehicle; a motor controller configured to: operate the motor in a continuous mode if the output required by the motor is above a threshold; or operate the motor in a pulsed mode if the output required by the motor is below the threshold; wherein the motor is configured to operate in the pulse mode to: (a) generating a first work output during a conduction pulse; and (b) generating a second work output between the conduction pulses, the second work output being different from the first work output; and a boost circuit coupled to the winding of the motor, the boost circuit being configured to store energy collected from the winding of the motor during a falling period of the conduction pulse and to apply the stored energy to the winding of the motor during a rising period of a subsequent conduction pulse; Wherein, compared with a situation where the stored energy is not applied, applying the stored energy is used to reduce a rise time of the subsequent conduction pulse.

2. The vehicle according to claim 1, wherein The boost circuit is further configured to selectively apply the harvested and stored energy to a power rail coupled to the motor during a rising period of the subsequent conduction pulse, and to apply the harvested energy to “boost” the voltage of the power rail to a level higher than the power rail voltage during a rising period of the subsequent conduction pulse.

3. The vehicle according to claim 1, wherein: The boost circuit includes a capacitor coupled to a power rail of a power converter for the electric machine, and a switch that selectively decouples the capacitor from a power supply used to energize the power rail.

4. The vehicle according to claim 1, wherein The boost circuit further includes a switch configured to selectively decouple a storage device from a power supply source during a falling period of the conduction pulse, such that energy collected from the windings of the motor is stored in the storage device instead of the power supply source.

5. The vehicle according to claim 1, wherein The energy collected, stored and applied is electromagnetic energy.

6. The vehicle according to claim 1, wherein The motor includes a stator and a rotor, and the winding is a rotor winding.

7. The vehicle according to claim 1, wherein: The motor controller is further configured to select a frequency, an amplitude, and a duty cycle of the on-pulses when operating the motor in the pulse mode, the frequency, the amplitude, and the duty cycle being selected so that the first work output generated during the on-pulses meets a desired output of the motor.

8. The vehicle according to claim 1, wherein The threshold value is a peak efficiency threshold value of the electric machine at a given speed of the vehicle or the electric machine.

9. The vehicle of claim 1 , further comprising a power converter coupled between a direct current (DC) power supply and the electric machine, the power converter being arranged to deliver pulsed power from the DC power supply to the electric machine, or vice versa.

10. The vehicle according to claim 9, wherein When the electric machine operates as a motor, the power converter operates as a power inverter that converts the DC power generated by the DC power supply source into alternating current (AC) power for the electric machine.

11. The vehicle according to claim 9, wherein: When the motor operates as a generator, the power converter operates as a power rectifier that converts alternating current (AC) power generated by the motor into DC power that is stored in the DC power supply source.

12. The vehicle of claim 1, wherein: The first work output is greater than the second work output.

13. The vehicle of claim 1, wherein: The second work output is substantially zero.

14. A method of operating a vehicle, comprising: receiving a torque request; If the torque demand is below a threshold, the electric motor for driving the vehicle is operated in a pulse mode, wherein the electric motor: (a) generating a first work output during the on-pulse period; as well as (b) generating a second work output between the conduction pulses, the second work output being different from the first work output; collecting energy from the windings of the motor during the falling periods of the conduction pulses; respectively storing the energy collected during the falling period of the conduction pulse; as well as applying the harvested energy from the storage to the winding during the rising period of each subsequent conduction pulse; Wherein, compared with the case where the stored energy is not applied, applying the stored energy is used to respectively reduce the rise time of the subsequent conduction pulse.

15. The method according to claim 14, further comprising: A storage device is selectively decoupled from a power supply during the falling period of the conduction pulse, so that energy harvested from the windings of the motor is stored in the storage device instead of the power supply.

16. The method according to claim 14, further comprising: During the rising period of the subsequent on-pulse, the harvested and stored energy is selectively applied to a power rail coupled to the motor, the harvested energy being applied to “boost” the voltage of the power rail to a level above the power rail voltage.

17. The method according to claim 14, further comprising: The harvested energy is stored by charging a capacitor, and the stored energy is applied to the winding by discharging the capacitor.

18. The method according to claim 14, wherein The winding is the rotor winding of the motor.

19. The method according to claim 14, further comprising: A frequency, an amplitude, and a duty cycle of the on-pulses are selected when operating the electric machine in the pulse mode, the frequency, the amplitude, and the duty cycle being selected such that the first work output generated during the on-pulses meets the torque demand.

20. The method of claim 14, further comprising: Whether to operate the motor in the pulse mode is determined based on one of the following: (i) Received torque request; (ii) the speed of the motor; (iii) the speed of the vehicle; or (iv) Any combination of (i) to (iii).

21. The method of claim 14, further comprising: If the torque demand is less than a threshold value at a given speed of the electric machine or the vehicle, the electric machine is operated in the pulse mode.

22. The method of claim 14, further comprising: If the torque demand is greater than a threshold at a given speed of the electric machine or the vehicle, the electric machine is operated in a continuous mode.

23. The method of claim 14, further comprising: A power converter coupled between a DC power supply and the motor is operated to deliver pulsed power from the DC power supply to the windings of the motor in the pulse mode, or vice versa.

24. The method of claim 14, further comprising: When the electric machine operates as a motor, the power converter operates as a power inverter, and the power inverter converts DC power generated by a DC power supply source into AC power for the electric machine.

25. The method of claim 14, further comprising: When the motor operates as a generator, the power converter operates as a power rectifier, which converts the alternating current (AC) power generated by the motor into direct current (DC) power that is stored in a direct current (DC) power supply source.

26. The method according to claim 14, wherein The energy collected, stored and applied is electromagnetic energy.

27. The method according to claim 14, wherein The first work output is greater than the second work output.

28. The method according to claim 14, wherein The second work output is substantially zero.

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