Boost Converter for Pulse Motor Control

Abstract

The boost circuit is arranged to reduce the rise time and fall time of the pulse power for the pulse control operation of the motor. The boost circuit extracts the magnetic energy present in the motor at the end of the pulse to reduce the pulse fall time. The energy is stored by the boost circuit and then applied at the start of the subsequent pulse to reduce the rise time. By reducing the rise time and fall time compared to not using such a boost circuit, the motor efficiency is improved.

Description

Technical Field

[0001] The present disclosure relates to a boost converter for pulse motor control.

[0002] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 819,097, filed on Mar. 15, 2019, which is hereby incorporated by reference in its entirety. Background Art

[0003] This application generally relates to pulse control of 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 applying pulses to the motor.

[0004] As used herein, the term "electric motor" is intended to be broadly understood to refer to both electric motors and electric generators. Electric motors and electric generators are very similar in structure. Both include a rotor and a stator having a plurality of poles. When the 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.

[0005] Electric motors can operate using direct current (DC) or alternating current (AC).

[0006] Representative DC motors include brushless motors, electrically excited motors, permanent magnet motors, series wound motors, shunt motors, brushed motors, compound motors, and other motors.

[0007] There are two general types of AC motors: asynchronous motors and synchronous motors. An example of an asynchronous motor is a three-phase induction motor.

[0008] Modern electric motors have a relatively high energy conversion efficiency. However, the energy conversion efficiency of most electric motors can vary significantly based on their operating load. In many applications, electric motors need to operate under a variety of different operating load conditions. As a result, electric motors typically operate at the highest efficiency level or near the highest efficiency level at certain times, while at other times, these electric motors operate at a lower efficiency level.

[0009] Battery-powered electric vehicles provide a good example of motors operating over a wide range of efficiency levels. During a typical drive cycle, an 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 of these ranges, the motor operates less efficiently. As the driving conditions change, the motor transitions between high and low operating efficiency levels as the rotor speed and / or torque changes. If the motor can be made to operate in the high-efficiency operating region for a greater proportion of the drive cycle, the vehicle's range will increase for a given battery charge level. Since the limited range of battery-powered electric vehicles is a major commercial obstacle to the use of electric vehicles, it is highly advantageous to extend the vehicle's operating range.

[0010] Accordingly, there is a need to operate motors, such as electric motors and generators, at higher efficiency levels. SUMMARY OF THE INVENTION

[0011] This application relates to pulse control of a motor (such as an electric motor and a generator) to improve operating efficiency. In a non-exclusive embodiment, such a pulse-controlled motor includes: a power supply source, a stator having windings, a rotor whose design depends on the motor topology, a motor controller configured to selectively operate the motor in a pulse mode, and a power converter coupled between the power supply source and the motor. The power converter is arranged to provide pulsed input power to the windings of the stator of the motor in response to the motor controller. Additionally, the power converter may include a boost circuit. The boost circuit is arranged to reduce the rise time and fall time of the pulsed power relative to the rise time and fall time of the pulsed power in the absence of the boost circuit. The boost circuit extracts at least some of the magnetic energy present in the motor at the end of the pulse to reduce the pulse fall time, stores at least some of this energy, and applies at least some of this energy at the start of a subsequent pulse in order to reduce the rise time. By reducing the rise time and fall time of the pulsed power, the efficiency of the motor and the overall electrical system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention and its advantages may be best understood by reference to the following description in conjunction with the accompanying drawings, in which:

[0013] Figure 1 is a representative torque / speed / efficiency curve graph showing the energy conversion efficiency of a representative electric motor under different operating conditions.

[0014] Figure 2 is a curve graph showing the pulsed current signal applied to the electric motor.

[0015] Figure 3AIt is a torque - efficiency graph of a motor operating at a fixed speed during the transition from zero to peak - efficiency torque.

[0016] Figure 3B It is the torque - power loss of an exemplary motor operating at a fixed speed during the transition from zero to peak - efficiency torque.

[0017] Figure 4 It shows a pulse - controlled electric motor according to a non - exclusive embodiment of the present invention.

[0018] Figure 5A It is a graphical representation of a continuous three - phase AC waveform with a peak of 50 amperes.

[0019] Figure 5B and Figure 5C is a pulse waveform with a 50% duty cycle that provides the same power output as the continuous waveform of Figure 5A

[0020] Figure 6A and Figure 6B is a representative circuit that models the currents flowing through phases A, B, and C of an exemplary motor.

[0021] Figure 7A It is a circuit diagram showing a prior - art power converter.

[0022] Figures 7B to 7F is an exemplary prior - art timing diagram showing the switching states and voltages of the power converter shown in Figure 5A

[0023] Figure 8 It is a power converter including a boost circuit according to a non - exclusive embodiment of the present invention.

[0024] Figures 9A to 9C It is a signal diagram showing how the boost circuit improves the rise time and fall time during the pulse - control operation of the power converter according to a non - exclusive embodiment of the present invention.

[0025] Figure 10 It shows an exemplary voltage available for driving a motor as a function of time according to a non - exclusive embodiment of the present invention.

[0026] Figure 11 It shows an exemplary voltage available for driving a motor as a function of time according to a non - exclusive embodiment of the present invention.

[0027] Figure 12 It is another power converter including a boost circuit according to another non - exclusive embodiment of the present invention.

[0028] Figure 13It is a flowchart showing the steps of the pulse control operation of an electric motor in a vehicle according to the present invention.

[0029] Figure 14 It is a schematic diagram showing the modulation of the energy supplied to an electric motor according to another embodiment of the present invention.

[0030] In the drawings, the same reference numerals are sometimes used to designate the same structural elements. It should also be understood that the depictions in the drawings are diagrammatic and not to scale. Detailed Description

[0031] This application generally relates to the pulse control of various electric motors (e.g., electric motors and generators) that would otherwise operate in a continuous manner. Through pulse control, the electric motor is intelligently and intermittently pulsed on and off to (1) meet the operating demands while (2) improving the overall efficiency. More specifically, under selected operating conditions, the electric motor is driven by intermittently applying pulses at a more efficient energy conversion operating level to deliver the desired average output more efficiently compared to the effects obtained through conventional continuous electric motor operation. The pulsed operation results in an intentional modulation of the motor torque; however, the manner in which this modulation is managed does not produce unacceptable noise or vibration for the intended application.

[0032] For the sake of brevity, the pulse control of the various electric 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 limiting in any way. Instead, the pulse control described herein can be used for a variety of types of electric motors - meaning both electric motors and generators. For example, the electric motor pulse control described herein can be used for any type of electric motor, whether an AC motor (e.g., induction motor, synchronous motor, motor of any number of poles, etc.) or a DC motor (e.g., brushless motor, electrically excited motor, permanent magnet motor, series wound motor, shunt motor, brushed motor, compound motor, etc.). In addition, the pulse control of such electric motors can be used for any application, not limited to electric vehicles. In particular, the pulse control can be used for systems with lower acceleration and deceleration rates required compared to vehicle applications, such as electric motors for heating systems, cooling systems, and ventilation systems.

[0033] 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 hereby incorporated by reference in its entirety.

[0034] Three-phase induction motor

[0035] An induction motor includes two main components: a stationary stator and a rotating rotor. In a three-phase motor, the stator may include a three-coil winding excited by a three-phase AC input. When the three-phase AC input passes through the three-phase winding, a rotating magnetic field (RMF) is generated. The rotational speed of the RMF is called the synchronous speed (N s ). The rotor is typically a "squirrel cage" or "wound" rotor, both of which have multiple conductive elements that are electrically short-circuited at their ends. According to Faraday's law, the RMF induces a current in the conductive elements of the rotor. The induced current establishes an induced magnetic field that interacts with the magnetic field generated in the stator coils. The interaction between the rotor and stator magnetic fields generates an electromagnetic force (EMF), which causes the rotor to rotate. This type of electric motor is called an induction motor because, as opposed to a direct conduction path, a current is induced in the rotor conductive elements by electromagnetic induction.

[0036] Three-phase induction motors offer several advantages. First, three-phase induction motors are inherently self-starting. Second, the speed of the rotor is easily controllable. The speed of the rotor (N r ) is always slightly less than the synchronous speed (N s ). This difference is called slip and can be expressed as a percentage:

[0037] Slip % = (N s - N r ) / N s Equation (1)

[0038] The frequency of the three-phase AC power that energizes the stator winding controls the RMF rotation rate and thus the synchronous frequency. Further, the speed of the rotor can be controlled based on Equation (1) as defined above.

[0039] While providing a frequency-controlled synchronous speed (N s ) to the three-phase winding, 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 respectively higher or lower.

[0040] Vehicle motor efficiency map

[0041] Reference Figure 1 shows the exemplary vehicle motor efficiency at different load and speed conditions Figure 10 . This Figure 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.

[0042] The area under the peak torque / speed curve 12 is mapped into a number of regions, each marked by a percentage of operating efficiency. For the particular motor shown, the following characteristics are evident:

[0043] • The most efficient or "sweet spot" region within the operating range of this particular motor is the operating region marked 14, which is typically in the range of 4,500 RPM to 6,000 RPM and has a torque output in the range of approximately 40 N*m to 70 N*m. 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.

[0044] • As the motor speed increases beyond approximately 6,000+ RPM, the efficiency decreases regardless of the output torque.

[0045] • As the output torque increases beyond 70 N*m or decreases below 40 N*m, the percentage efficiency tends to drop from its peak, in some cases quite significantly. For example, when the motor is operating at approximately 2,000 RPM and an output torque of 100 N*m, the efficiency is approximately 86%. When the torque output is reduced below approximately 30 N*m, the efficiency decreases regardless of the motor speed and approaches zero at no load.

[0046] • At any given motor speed, there will be a corresponding most efficient output torque, which is graphically shown by the maximum efficiency curve 16.

[0047] As shown this Figure 10 is derived from the motor used in the 2010 Toyota Prius. Figure 10 For an interior permanent magnet synchronous motor. It should be understood that this Figure 10 is merely illustrative and should not be construed as restrictive in any way. Similar plots can be generated for almost any motor (such as a three-phase induction motor) whether used in a vehicle or in some other application.

[0048] As can be seen from Figure 10 it, generally, the motor is most efficient when operating within the speed and torque range of the sweet spot 14. If the operating conditions can be controlled such that the motor operates at or near its sweet spot 14 for a greater percentage of the time, the overall energy conversion efficiency of the motor can be significantly improved.

[0049] However, from a practical perspective, many driving situations specify that the electric motor operates outside the speed and torque range of the optimal point 14. There is usually no transmission in an electric vehicle, so the ratio of the electric motor rotation rate to the wheel rotation rate is fixed. In this case, the electric motor speed can vary from zero when the vehicle is stopped to a relatively high RPM when cruising at highway speeds. The torque requirements can also vary significantly depending on factors such as whether the vehicle is accelerating or decelerating, going uphill, downhill, driving on a level road surface, braking, etc.

[0050] As Figure 1 can be seen, at any particular electric motor speed, there will be a corresponding most efficient output torque, which is graphically shown by the maximum efficiency curve 16. From a conceptual perspective, when the desired electric motor torque is lower than the most efficient output torque at the current electric motor speed, the overall efficiency of the electric motor can be increased by applying pulses to the electric motor, so that the electric 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.

[0051] Referring Figure 2 , graph 20 is shown, which plots the total current applied to the electric motor on the vertical axis and time on the horizontal axis. For a three-phase electric 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 1 N*m of output torque. In this particular example, the desired electric motor output torque is 10 N*m, which will require 10 amps of current as shown by the dashed line 22. In this example, the most efficient torque output of the electric motor is 50 N*m, corresponding to an applied current of 50 amps.

[0052] During normal operation, the electric motor will continuously generate 10 N*m of torque as long as the desired torque remains at that value. In pulse control operation, the electric motor is pulsed (as represented by pulse 24) to deliver 50 N*m of torque for 20% of the time. For the remaining 80% of the time, the electric motor is turned off. Thus, the net output of the electric motor meets the operating requirement of 10 N*m. Since the electric motor operates more efficiently when delivering 50 N*m than when delivering 10 N*m, the overall efficiency of the electric motor can be increased by pulsing the electric motor with a 20% duty cycle while still meeting the average torque requirement.

[0053] In the above example, the duty cycle is not necessarily limited to 20%. As long as the desired motor output does not exceed 50 N*m, the desired motor output can be satisfied by changing only the duty cycle. For example, if the desired motor output changes to 20 N*m, the duty cycle of the motor operating at 50 N*m can be increased to 40%; if the desired motor output changes to 40 N*m, the duty cycle can be increased to 80%; if the desired motor output changes to 5 N*m, the duty cycle can be decreased to 10%, and so on. Generally, it is possible to advantageously use pulse motor control at any time when the desired motor torque drops below Figure 1 the maximum efficiency curve 16.

[0054] On the other hand, when the desired motor torque is at or above the maximum efficiency curve 16, the motor can operate in a conventional (continuous / non-pulsed) manner to deliver the desired torque. Pulse operation can provide an opportunity for increased efficiency gain only when the average torque that the motor needs to deliver is lower than the average torque corresponding to its maximum operating efficiency point.

[0055] It should be noted that Figure 2 the current values, torque values, and time scales provided in Figure 2 are merely illustrative and are not intended to be limiting in any way. In actual embodiments of applying pulses to the motor, the pulse duration used can vary widely based on the design requirements of any particular system. However, generally, the range of the period of each on / off cycle is expected to be on the order of 10 microseconds to 0.10 seconds (i.e., pulses are applied at a frequency in the range of 10 Hz to 100,000 Hz), for example, between 0.2 milliseconds and 20 milliseconds (50 Hz to 5000 Hz) as will be discussed in more detail below. In addition, there are a wide variety of different motors, and each motor has its own unique efficiency characteristics. Moreover, at different motor speeds, a given motor will have different efficiency curves. The nature of the curves can vary depending on the particular motor. It should also be understood that the current pulses do not need to have a flat top as Figure 2 depicts. Also, the current does not have to go to zero during the off period and can be some non-zero value. An important characteristic of the current waveform is that the motor operates at or near the maximum efficiency region of its current motor speed for a certain percentage of the time.

[0056] Improving efficiency by increasing the torque rise rate

[0057] Most current motor converters are typically designed for continuous operation rather than pulsed operation. Such motors generally do not transition frequently from an unpowered state to a powered state. As a result, little design work has been done in managing such transitions. To the extent any design work has been done in managing transitions, it has generally been aimed at achieving smooth transitions rather than rapid transitions. Accordingly, the rate of transition of most motors from a powered state to a powered state is typically limited (i.e., relatively not fast).

[0058] The present applicant has discovered that for a motor system that transitions regularly from an unpowered motor state to a peak efficiency state (such as with pulsed operation), efficiency can even be further improved when the transition occurs as quickly as possible. By rapidly transitioning (e.g., from zero torque to peak efficiency torque), the overall average efficiency of the motor is increased because the motor spends less time in a transition where the efficiency is below peak. This relationship is as Figure 3A and Figure 3B shown.

[0059] Refer to Figure 3A , which shows a torque versus efficiency plot of an exemplary motor operating at a fixed speed (e.g., 6000 rpms). In the exemplary plot, a torque output range from 0.0 N*m to 250 N*m is plotted along the horizontal axis, while the efficiency of the motor from 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 the transition as shown in the shaded region 27, the peak efficiency torque has a much lower efficiency at peak efficiency torque 28.

[0060] Refer to Figure 3B , which provides a plot showing the torque versus power loss of an exemplary motor operating at a fixed speed during a transition from zero to peak efficiency torque. In this plot, the power 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 power loss of the motor increases. Accordingly, the faster the transition time from zero to peak efficiency torque, the less work is performed and the less energy the motor consumes.

[0061] By replacing torque with time along the horizontal axis and then integrating the area under curve 29, the energy consumed by the motor during a given transition time can be calculated. For example, the present applicant has found that for an exemplary motor, 7234.5 joules of energy were used in the case of a transition time of 0.5 seconds, while only 723.4 joules of energy were used in the case of 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 the loss. It should be noted that in this example, it is assumed that the load does not accelerate, and thus no energy is added to the load inertia.

[0062] For different motors, the transition of the motor from zero to peak efficiency torque, the peak efficiency torque, the peak efficiency torque and the power loss will all be different. Therefore, Figure 3A and Figure 3B the figures of

[0063] Power converter

[0064] should be regarded as merely exemplary and should not be construed as restrictive in any way.

[0065] Reference Figure 4 , shows a diagram of a power controller 30 for pulse operation of an electric machine. The power controller 30 includes a power converter 32, a DC power supply 34, an electric machine 36, and a pulse controller 38. The power converter 32 can operate as a power inverter or a power rectifier depending on the direction of energy flow through the system. When the electric machine operates as a motor, the power converter 32 is responsible for generating three-phase AC power from the DC power supply 34 to drive the induction motor 36. The three-phase input power represented as phase A 37a, phase B 37b, and phase C 37c is applied to the stator windings of the electric machine 36 to generate the RMF as described above. The individual phases 37a, 37b, and 37c are depicted by lines with arrows at both ends, thus 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 electric machine operates as a generator, the power converter 32 operates as a power rectifier, and the AC power from the electric machine 36 is converted into DC power and stored in the DC power supply.

[0066] The pulse controller 38 is responsible for selectively making the three-phase input power 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, any method described herein can be used to implement pulse operation, such as but not limited to the methods described with respect to Figure 5B , Figure 5C and Figures 8 to 14 .

[0067] Reference Figures 5A to 5C , provides a plot for showing the difference between the continuous three-phase input power and the pulsed three-phase input power supplied to the induction motor 36. In each plot, current is plotted on the vertical axis and time is plotted on the horizontal axis.

[0068] Figure 5A shows the conventional sinusoidal three-phase input currents 42a, 42b, and 42c delivered to the induction 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 sinusoidal wave period is τ. The three-phase input currents 42a, 42b, and 42c are continuous (non-pulsed) and have a specified maximum magnitude of approximately 50 amperes. It should be understood that 50 amperes is merely a representative maximum current, and the maximum current can have any value.

[0069] Figure 5B and Figure 5C shows two examples of different pulsed three-phase current waveforms 44a, 44b, and 44c and 46a, 46b, and 46c, where each current waveform has a 50% duty cycle and a peak magnitude of approximately 100 amperes. As Figure 5A shown, the period of the reference sinusoidal wave is τ, however now the sinusoidal wave is modulated to be intermittent. Figure 5B and Figure 5C the current delivery in Figure 5A delivers the same average torque as the continuously applied three-phase input current in Figure 5B assuming that torque is proportional to current, which is usually the case. The difference between the pulsed currents 44a-c and 46a-c lies in the duration of their respective current pulses and the interleaved "off" time periods. In Figure 5C the current pulses 44a-c are interleaved with "off" time periods of equal length. The length of each on-time period and off-time period is 2τ. In

[0070] Figures 5B to 5C shows 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 cases, but it is not a requirement. The duty cycle does not have to be 50%, but can be adjusted to match the desired average output torque. In Figure 5B and Figure 5CIn [the above], the phase of the turn-on / turn-off pulse is synchronized with the applied AC power; however, in some embodiments, the phase of the turn-on / turn-off pulse need not be synchronized with that of the applied AC power. Accordingly, the relative magnitude and / or timing of the motor drive pulses can vary as long as they average out to deliver the desired average torque.

[0071] Motor physics and constraints

[0072] For any given motor, physics ultimately limits the possible speed of transitioning from zero to peak efficiency torque. Generally, the transition speed is based on the physics of the electric field build-up speed in the motor, which in turn is limited by the applied voltage, the motor back electromotive force (“BEMF”), and the inductance of the motor windings.

[0073] If it is assumed that the setpoint of the power converter 32 increases at time zero and the feedback is zero, the control of the output stage for each phase will saturate. As a result, the low or high output power devices for each motor phase will be hard-conducted. This results in six possible combinations, including:

[0074] 1. Phase A and Phase B are positive, and Phase C is negative,

[0075] 2. Phase A is positive, and Phase B and Phase C are negative,

[0076] 3. Phase B and Phase C are positive, and Phase A is negative,

[0077] 4. Phase B is positive, and Phase A and Phase C are negative,

[0078] 5. Phase C and Phase A are positive, and Phase B is negative, and

[0079] 6. Phase C is positive, and Phase A and Phase B are negative.

[0080] For each of these six possible combinations, the current in the motor 36 at time zero will be (a) full current in one phase and (b) shunt current in the other two phases. As further described below, the ratio of these currents will depend on the rotor position at time zero.

[0081] Reference Figure 6A , shows a representative circuit for modeling the currents flowing through the three phases A, B, and C.

[0082] Each of the phases A, B, and C is represented by its self-inductance (“LS”), mutual inductance (“LM”), resistance (“R”), and BEMF.

[0083] In the case shown, Ic = Ia + Ib. The sum of the currents flowing into the mutual inductance is zero, and thus the mutual inductance has no effect on the current flow. Assuming the BEMF of the motor is zero, the resulting simplified equivalent circuit is as Figure 6BAs shown. The circuit takes time to accumulate the current to a given value:

[0084]

[0085] If the BEMF is not zero, the voltage applied to each phase will be different. Since 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, the neutral voltage will = V 总线 / 3. This defines the currents Ia, Ib, and Ic of phases A, B, and C as:

[0086]

[0087]

[0088]

[0089] Since all the above values are instantaneous values, the value at time zero depends on the instantaneous value of the BEMF of each phase, which in turn depends on the position of the rotor within one electrical cycle or pole-pair pitch. It must also be noted that over time, the rate of rise of the instantaneous BEMF voltage of each phase, the voltage applied to the motor inductance, and the motor phase current also change.

[0090] The aim is to make the current reach its desired value and phase to provide the required torque. The current is usually controlled using field-oriented control or "FOC". Therefore, the phase currents are transformed into the rotating coordinate system values of "iq" (quadrature current) and "id" (direct current), where the vector sum of id and iq is equal to the peak magnitude of the phase current, and ArcTan id / iq is its angle. The cosine of this angle is the power factor. Therefore, the values of id and iq are derived using the direct orthogonal zero transformation as follows:

[0091]

[0092]

[0093] When examining the above formula, the BEMF waveform Vpk only affects iq (quadrature current), while both currents are affected by the bus voltage V 总线 and the angular position of the rotor The angle and the motor BEMF cannot be changed without modifying the motor. Therefore, the only parameter that can be controlled to affect the rate of rise of the phase current and thus the motor torque is the applied bus voltage V 总线Accordingly, one aspect of the present invention proposes to temporarily increase or "boost" the bus voltage to a value higher than the normal operating bus voltage during the transition time from zero to peak efficiency torque during the application of a pulse, thereby reducing this transition time.

[0094] It should be noted that when the converter is turned off, the energy stored in the motor windings returns to the bus voltage supply source. If this supply source is unable to absorb this energy, the bus voltage will rise as the bus capacitance absorbs this energy. Due to the capacitance on the bus supply source, this normal process typically only raises the bus voltage by a small fraction, which is usually not sufficient to be considered a boosted bus voltage. However, if this energy is captured independently, such as being captured and stored in a storage device such as a capacitor or a battery, it can be recycled back to the motor in the form of a boosted voltage.

[0095] Alternatively, during the "off" period, the bus voltage can be increased by using a separate boosted voltage source using a charge pump, or a separate voltage source. This boosted supply source should not be designed to charge the main bus capacitance, but rather as an independent capacitor that can discharge to the motor during the transition time from zero to the required torque.

[0096] Conventional power converter circuit

[0097] Thus, 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 the overall motor operation. However, when using fast pulses as envisioned herein, these transient effects can have a large net impact, and thus there is motivation to reduce the leading and trailing edge pulse transition times.

[0098] Reference 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 ). The potential between the two voltage buses (+V 总线 ) and (-V 总线 ) is the available potential for operating the motor 36. Each of the switches S1 to S6 can have a bypass diode (D1 to D6) electrically connected in parallel with the switch. These diodes help prevent switch damage voltage spikes that may be generated during switch operation.

[0099] The diode also provides a path for recycling current that may be blocked by the switches. This is particularly important when the motor 36 is used as a generator. The 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 can be used, such as but not limited to insulated gate bipolar transistors (IGBTs).

[0100] Connections to the stator coil windings of the motor 36 are made between each pair of switches. For phase A, the connection is between the switch pair S1 to S2 and is designated 37a. For phase B, the connection is between the switch pair S3 to S4 and is designated 37b. For phase C, the connection is between the switch pair S5 to S6 and is designated 37c.

[0101] Within the motor 36, each phase stator winding can be modeled as an inductor 31, a resistor 33, and a mutual inductance 35. In Figure 7A these elements are only labeled for phase C, but similar elements exist in the phase A winding and the phase B winding.

[0102] The switches S1 to S6 can be collectively referred to as a switch network that controls the power to and from the motor 36.

[0103] When the motor 36 operates 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.

[0104] Figure 7B A switching sequence for obtaining a six-step output from the power converter 32 is shown. Each switch is turned on for a 1 / 2 cycle time period in a staggered manner. For each winding, current can flow through one switch in the top row and one or two switches in the bottom row. The switch pairs S1 - S2, S3 - S4, and S5 - S6 never conduct simultaneously because this would short-circuit the DC power supply source 34.

[0105] Figure 7C The voltage between points A and B is shown as voltage V ab .

[0106] Similarly, Figure 7D and Figure 7E the voltages between points B and C and between points C and A are shown respectively. Summing these voltages allows determination of the voltage between each phase and the neutral point.

[0107] Figure 7F The resulting phase voltage for phase A is shown. The resulting six-step waveform approximates a sine wave with a frequency of ω and is commonly referred to as a modulation signal. The phase voltages of phases B and C are phase-shifted 120° and 240° respectively with respect to the phase A voltage.

[0108] It should be understood that the electric machine 36 can operate as both a generator and a motor. When operating as a generator, the energy flow is from the electric machine 36 to the DC supply source 34. The power converter 32 acts as a three-phase rectifier instead of an inverter.

[0109] In a typical prior art system, a switching network is used to control the power flowing to the electric motor through pulse width modulation (PWM) control. The PWM control reduces the time that the switching network is in the active configuration of switches S1 to S6, where power can flow to the electric motor. That is, the time portion during which switches S1 to S6 are in the non-active configuration (S1, S3, and S5 or S2, S4, and S6 are all off) increases as the desired motor torque output decreases.

[0110] Power converter with boost

[0111] Figure 8 A power converter circuit 132 including a boost circuit is shown according to a non-exclusive embodiment of the present invention. Compared with the prior art power converter circuit 32 shown in Figure 7A , the power converter circuit 132 further includes additional switches SA and SB, both of which are controlled by the pulse controller 38. These two switches can be controlled by a common signal line 41 as shown in Figure 8 or can have independent control lines (not shown in Figure 8 ). When switch SA is turned on, the positive power supply source voltage (+V DC ) is coupled to (+V 总线 ). When switch SB is turned on, the negative power supply source voltage (-V DC ) is coupled to (-V 总线 ).

[0112] During operation, the pulse controller 38 operates to selectively turn on and off switch SA or SB by applying a pulse waveform to the signal line 41, which electrically connects the pulse controller 38 to switches SA and SB. When switches SA and SB are turned on, current can be delivered to the electric machine 36. Conversely, when SA and / or SB are turned off, no current or only transient current is delivered to the electric machine 36.

[0113] The power converter circuit 132 further includes a capacitor C1 having one conductive plate coupled to (+V 总线 ) and another conductive plate coupled to (-V 总线 ). Switches SA and SB and capacitor C1 can be collectively referred to as a boost circuit because their purpose is to increase +V 总线 and -V 总线 at the start of the "on" pulse.The initial voltage on the bus is as described below. In various embodiments, the boost circuit may be incorporated into the switching network or may include elements different from the switching network.

[0114] As previously noted, the goal of pulse 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 off 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" period. The operating point 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. Thus, the managed transition between the motor power "on" and "off" states ideally has a leading edge that transitions straight up and a falling edge that transitions straight down. Such a "perfect" pulse 60 is Figure 9A illustrated graphically in the figure, which shows the ideal motor drive current versus time for pulse control with a 50% duty cycle. In the figure, the current pulse represents the sum of the currents in all phases. Although the current pulse is shown as having a flat top, this is not necessarily the case.

[0115] In the real world, many practical limitations make it difficult to generate such a perfect pulse. For example, the inductance aspects of the circuitry of both the motor 36 and the power converter 32 slow down the current rise time and fall time. 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. Generally, the actual rise and fall of the pulse occur more slowly, meaning that the transition occurs over time. The nature of the rise and fall in the real world is Figure 9B illustrated graphically in the figure. As can be seen therein, there is a rise time period (rise time) 62 during which the current actually rises from zero to the desired "on" power level, and a fall time period (fall time) 64 during which the current actually falls from the "on" power level to zero.

[0116] During the power rise and fall time periods, the motor 36 continues to consume or generate power. However, during these transition time periods, the motor operates at a lower efficiency. Generally, when the operating current is away from its maximum efficiency condition ( Figure 1When the curve 16) of approaches zero, the motor efficiency will decrease. Among them, when the current level approaches zero, the energy conversion efficiency will deteriorate significantly. Therefore, the pulse distortion represented by the current rise period and the current fall period will reduce the efficiency gain obtained through pulse operation. Generally, the smaller the ratio of the rise / fall time to the pulse length, the smaller the impact of the transient switching effect on the energy conversion efficiency of the motor during pulse application.

[0117] It should be understood that Figure 9B the transient effects shown in are illustrative in nature and do not necessarily reflect the actual rise / fall times associated with the operation of any specific motor. The relative range of the ratio of the rise time to the pulse length can vary widely based on the characteristics of the motor used (mainly referring to the rise time and the fall time), the pulse frequency (mainly indicated by the control scheme used), and the pulse width (indicated by the control scheme and the motor load). The voltage available to power the motor and the motor speed will also affect the pulse rise time and fall time. If the pulse is slow compared to the motor response, the rise / fall time may be a small fraction of the pulse width, and the transient switching effect may have a minimal impact on the motor performance. On the contrary, if the pulse is very fast and / or the motor response is low, the rise / fall time may account for a large portion of the pulse width and may even exceed the pulse width in some cases. If not properly managed, the transient efficiency losses associated with switching will greatly reduce or even eliminate any theoretical gain that can be obtained through pulse operation. Therefore, it is very important to consider the transient switching effects associated with pulse operation when determining the pulse frequency and control scheme applicable to any specific application.

[0118] Included in Figure 8 the power converter circuit 132 of, the capacitor C1 is provided to improve the current rise time and fall time. The 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 compared to the case without the capacitor C1.

[0119] To better understand the operation of the power converter 132, assume that the power converter 132 is initially in the "on" state and the motor 36 is operating as a motor. This means that the switches SA and SB are conducting, allowing current to flow from the positive terminal of the DC supply source 34 through the power converter 132 to the motor 36 and back to the negative terminal of the DC supply source 34. The switches S1 to S6 will oscillate in the Figure 7B configuration shown to apply AC power to the motor 36.

[0120] To terminate the motor operation, the switches SA and SB can be turned off, allowing +V 总线 and -V 总线The bus has a different electrical potential from the corresponding terminals of the DC power supply 34. Since the circuit is now open, the current must stop flowing through the circuit; however, there may be a large amount of energy associated with the magnetic field generated by the current in the motor 36. At least some of this energy can be extracted from the motor 36 and captured and stored in the capacitor C1. This will increase the potential difference between the positive voltage bus and the negative voltage bus. For example, the electrical potential on the line +V 总线 may be increased to a potential higher than the positive terminal of the DC power supply +V DC , while the electrical potential on the line -V 总线 may be decreased to a potential lower than the negative terminal of the DC power supply -V DC . Note that switches S1 to S6 all have bypass diodes that allow unidirectional current to flow from the motor 36 to the line +V 总线 and from the line -V 总线 to the motor 36, regardless of the switch positions. Consistent with or almost consistent with the turn-off of switches SA and SB, any one of the switches S1 to S6 that may have been conducting will be turned off when switches SA and SB are opened, so that current will not flow from the line +V 总线 to the motor 36 through any of these switches between -V 总线 .

[0121] When motor operation is required again, switches S1 to S6 can be turned on in one of the Figure 7B shown patterns. The switching pattern must correspond to the rotor rotation angle such that the phase of the applied current matches the correct phase to supply power to the motor 36 again. When the voltage on +V 总线 drops to +V DC and -V 总线 rises to -V DC , switches SA and SB are closed. This circuit configuration and control method are arranged to provide a higher initial voltage to be applied to the motor 36 at the start of the "on" phase, which advantageously reduces the pulse rise time.

[0122] Figure 10 Shows the exemplary +V Figure 8 and -V 总线 waveforms and time for the circuit shown in 总线 . The pulse generator 38 generates a digital waveform 43 consisting of a string of digits "0" and "1". 1 can correspond to "turning on" the motor 36, and 0 can correspond to "turning off" the motor. In Figure 10 , pulses are applied to the motor 36 with a duty cycle of 40%; however, this is only exemplary, and any duty cycle can be used. The voltage 45 on the +V 总线 rail is increased to +V 升压 during the falling period and -V 总线The voltage 47 on the rail drops to -V during the falling period 升压 +V 总线 and -V 总线 The magnitudes of the voltage changes on the bus can be equal or different. +V 总线 Voltages 45 and -V 总线 The voltage 47 remains relatively constant during the motor-off time because the energy dropping from the motor is stored in the capacitor C1. When the pulse generator waveform 43 returns to the digital "1", the energy stored in the capacitor C1 is supplied to the motor 36 through the switch array S1 to S6. This causes +V 总线 The voltage 45 on the rail returns to +V DC and -V 总线 The voltage 47 on the rail returns to -V DC because the charge in the capacitor C1 has dissipated and the energy stored in the capacitor C1 is used to drive the motor. The operation of the motor during the "on" period is maintained by turning on switches SA and SB so that energy from the 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 start of at least one of a 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 the ground potential. The boost circuit can be used to increase the available potential for driving the motor during all of the pulses in the series.

[0123] Although the exemplary power converter with a boost circuit is shown in Figure 8 as having switches adjacent to the positive and negative terminals of the DC power supply, this is not necessary. In some embodiments, only a single switch may be required.

[0124] Switches SA and SB in combination with capacitor C1 can be used to reduce the power rise and fall times, in some cases reducing them to one-half, one-fifth, one-tenth or less. By storing the energy recovered from the motor during the motor-down period, the voltage across the capacitor C1 can be raised above the voltage of the power supply. The magnitude of the voltage increases with the amount of magnetic energy that can be extracted and captured. This can significantly reduce the potentially harmful transient switching effects associated with pulsed operation.

[0125] Figure 9C Examples of improved rise and fall times are schematically shown in Figure 9B As is apparent in the figure, the rise time 66 on the pulse front is faster / shorter compared to the corresponding rise time 62 shown in Figure 9BCompared with the corresponding fall time 64 shown in [Fig.], the fall time 68 of the trailing edge of the pulse is faster / shorter. Therefore, it should be understood that, compared with existing motors, motors designed with pulse control in mind or modified to improve the transient response of the motor to power pulses can obtain more benefits from pulse operation.

[0126] It should be understood that, depending on the construction, operating environment, and operating range of the motor, the appropriate pulse frequency implemented by the pulse controller 38 for different motors can vary significantly. For some motors, switching frequencies on the order of 10 kHz to 50 kHz may be appropriate - while for other motors, much lower switching frequencies (e.g., in the range of 10 Hz to 500 Hz) may be more appropriate. The most suitable 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.

[0127] It should be understood that the details of the boost circuit used to shorten the rise and fall times of the power going 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 removed from the power converter circuit 132. Other types of power converter circuits and control strategies can be used. For example, in certain cases, a Z-source inverter can be used, where diodes, two inductors, and two capacitors are located between the power supply source and the switch network.

[0128] The voltage boost level and magnitude of the capacitor C1 can be appropriately selected for the motor and its inductive and resistive characteristics to shorten the transient rise / fall times associated with pulse-on and pulse-off of the motor. Preferably, including the inefficiencies associated with the transient itself and any overshoot that may occur due to the use of the capacitor C1, the corresponding capacitance and voltage boost level are also selected to maximize the overall motor efficiency during pulse application. Since the capacitor C1 is used to improve the transient response, this capacitor can be recharged in a timely manner during periods when the motor is not being supplied with power (e.g., during the motor-off time period). This mode of operation is explained in more detail in the following description of Figure 11 This mode of operation is explained in more detail in the following description of

[0129] Depending on the motor speed and load, the energy stored in the motor magnetic field may not be sufficient to adequately boost the +V 总线 and -V 总线 voltages to achieve fast rise and fall times. In such cases, it may be desirable to increase the potential difference across the motor during the off periods between pulses. An exemplary voltage waveform showing two boost cycles 73a and 73b is as Figure 11 shown. It should be understood that depending on the operating conditions of the motor, more or fewer than two boost cycles can be used. Appropriate switch networks and control strategies are required to implement this type of control.

[0130] Reference 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 ). The potential difference between the two voltage buses (+V 总线 ), and (-V 总线 ) is the available potential for operating the motor 36. The switches S1 to S6 are collectively referred to as a switch network, which controls the power going to and coming from the motor 36. When operating as a motor, power from a DC supply source is provided through the switch network of switches S1 to S6. Further, as described above, the switch network provides phased energy to the three phases of the stator windings of the motor 36. Similarly, when operating as a generator, the energy flow is from the motor 36 to a storage device, such as a battery.

[0131] 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 described previously, for the sake of brevity, it will not be described in detail again here.

[0132] In various embodiments, the boost supply source 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 a later 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 acts as a motor and transitions from an on state to an off state, such as during a pulse application, the generated energy can be transferred to and stored in certain components (such as capacitor C1 and / or the battery) in the boost circuit 202. Then the stored energy can be used to "boost" the normal rail (+V 总线 ) during the positive transition as described below.

[0133] The switch 206 can be any type of switch capable of switching between the positive (+) and negative (-) electrodes of the boost supply source 204. It is expected that the switch will be constructed using semiconductor devices. In a particular but non-exclusive embodiment, the switch 206 is a single-pole double-throw switch.

[0134] During continuous motor operation, as is well known in the art, phased power is supplied to the stator windings of motor 36 by switches S1 and S2 for phase A, switches S3 and S4 for phase B, and switches S5 and S6 for phase C. The end result is the continuous torque output of the motor as previously described.

[0135] During pulse operation, pulse controller 38 controls switch 206 via control signal 208 to control boost circuit 202. In the case of a positive pulse transition, switch 206 is activated to connect the positive rail (+V 总线 ) to the positive (+) terminal of boost supply source 204. As a result, boost supply source 204 operating in cooperation with capacitor C1 and the battery is used to boost the voltage on 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 has decreased or the peak torque level has been reached, control signal 208 instructs the switch to connect the positive rail (+V 总线 ) to the negative (-) terminal of boost supply source 204. As a result, the boost voltage is effectively removed from the positive rail (+V 总线 ).

[0136] The effect of boost circuit 202 is also shown in Figures 9A to 9C In particular, Figure 9A shows an ideal pulse with no transition time, Figure 9B shows a "real-world" pulse with a transition time designated by reference numeral 62. As previously noted, the inductive aspects of the circuitry of motor 36 and power converter 200 slow down the current rise time and fall time. Figure 9C shows the transition assisted by boost circuit 202. It can be readily understood by comparison that the "boosted" transition time 66 as shown in Figure 9C is significantly less than (i.e., faster than) the transition time 62 as shown in Figure 9B

[0137] In the Figure 12 embodiment, capacitor C1 is arranged to be in parallel with each switch pair S1 - S2, S3 - S4, and S5 - S6 between 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 power converter 200 acts as an inverter. With this arrangement, the ability of boost circuit 202 to reduce the pulse rise time and fall time is enhanced.

[0138] Operation flow chart

[0139] Figure 13 shows having, for example, Figure 1Flowchart 70 of the steps of the pulse control operation of the motor with the characteristics depicted in

[0140] In an initial step 72, the current motor output and the current motor speed are determined.

[0141] In a decision step 74, based on the current motor output and the current motor speed, it is determined whether the motor should operate in a continuous mode or a pulse mode. In other words, it is determined whether the desired motor torque is higher or lower than the most efficient output torque at the current motor speed (i.e., Figure 1 the maximum efficiency curve 16 of the motor diagram shown in ). If it is higher, the motor operates in a continuous mode. If it is lower, the motor can advantageously operate in a pulse mode.

[0142] In step 76, if the current motor torque is higher than the most efficient output torque at the current motor speed, the motor is operated in a continuous mode 76.

[0143] In step 78, the power output or magnitude of the "on" pulse that provides substantially maximum efficiency operation at the current motor speed is determined.

[0144] In step 80, the desired pulse duty cycle for operating in a pulse mode is determined such that the average output power or torque matches the desired output.

[0145] In step 82, the motor is operated in a pulse mode using the determined pulse duty cycle and pulse power output. Using the power controller 30 together with a 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 time and fall time of the pulses, thereby further improving the motor efficiency.

[0146] The above steps 72 to 82 are continuously executed while the motor is running. At any particular motor speed, there will be a corresponding most efficient output torque, which is graphically shown by Figure 1 the maximum efficiency curve 16 in . As the instantaneous motor output request and / or the current motor speed change, a decision is made to operate the motor in an appropriate continuous or pulse mode. From a conceptual perspective, when the desired motor torque is lower than the most efficient output torque at the current motor speed, the overall efficiency of the motor can be increased by applying pulses to the motor. As a result, for a vehicle powered by the motor, the overall efficiency of the vehicle is increased, which means that the vehicle mileage between battery recharges is extended.

[0147] Figure 14FIG. 0 is a schematic diagram of a system 300 for modulating the energy supplied to an electric machine 36 in accordance with another non-exclusive embodiment of the present invention. System 300 includes an electric machine 36, a 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.

[0148] During operation of system 300, the torque modulation decision module 302 receives a torque demand. 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.

[0149] If not, meaning the torque demand is greater than the peak efficiency torque, the electric machine 36 operates as a motor in a continuous mode. 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.

[0150] On the other hand, if the torque demand is less than the peak efficiency torque of the electric machine 36, the electric machine 36 operates as a motor in a pulse mode. In this case, the torque modulation decision module 302 generates a modulation waveform 310 for the power converter 32 that causes the electric machine 36 operating as a motor to switch or pulse between the peak efficiency torque of the motor and a lower torque (the average of the two being substantially equal to the required torque). In various embodiments, the lower torque can be zero, but it does not have to be zero. The lower torque can be some other torque value above zero, provided that the average of the lower torque and the peak efficiency torque is substantially equal to the required torque.

[0151] The power converter 32 includes a switch network that includes 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 electric machine 36 (1) to operate continuously as a motor when the torque demand is greater than the peak efficiency torque, thereby generating a continuous torque output, or (2) to operate in a pulse mode when the torque demand is less than the peak efficiency torque. The power converter 32 can control the energy supplied to the electric machine 36 using any one of a variety of different protocols in the form of current modulation, such as pulse width modulation (PWM), direct torque control (DTC), hysteresis, or "deadbeat" control.

[0152] In an alternative embodiment, it is possible to use, for example Figure 8 132 or Figure 12A boost power converter of 200. In the case of using the boost version of the power converter 32, due to the faster rise and / or fall time of the pulses during pulse operation, the efficiency and performance of the motor operation of the motor 36 are improved.

[0153] The feedback sensor 304 generates a feedback signal 306 that indicates the angular position of the rotor of the motor 36. The feedback signal is provided to each of the power converter 32 and the torque and speed estimator 308. Given the angular position of the rotor, the torque and speed estimator 308 can provide an accurate estimate of the torque and speed of the motor to the torque modulation decision module 302. In response, the waveform 310 can be adjusted as needed, so that the timing of the switching network within the power converter 32 (i.e., the timing of the conduction / turn-off of the switches S1 to S6) can be precisely controlled, such that the energy of each of the phases A, B, and C is timed to coincide with the current position of the rotor. As a result, the operation of the motor 36 as a motor is both smooth and efficient. It should be noted that the use of the feedback sensor 304 is not mandatory, and other techniques can be used to measure or estimate the angular position of the rotor of the motor 36. For example, any of a variety of sensorless methods can also be used.

[0154] Other types of motors and generators

[0155] There are various known and commercially available motors (both motors and generators), including DC and AC motor / generators. Although the structures, controls, and energy conversion efficiencies 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 efficiencies will vary (usually significantly) within that operating range. Generally, if the operating range includes the area below the equivalent of the maximum efficiency curve 16 shown in Figure 1 then the control principles described herein can be applied to any type of motor to improve efficiency.

[0156] Some prior art motors currently use pulse width modulation (PWM) control to operate. However, the driving of such motors does not consider their most efficient energy conversion levels. Therefore, the described method can also be used to improve the energy conversion efficiency of such motors.

[0157] 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 a desired torque output. The drive current is often controlled by controlling the output voltage of a control inverter and / or converter, which serves as the voltage input to the motor. Typically, by varying the relative phase between the rotor and the stator magnetic field, the electric motor can operate as a generator. Thus, the circuits and control methods described in terms of an electric motor are equally applicable when the electric machine is operating as a generator. The described pulse control is particularly beneficial when such electric motors and generators are operating in regions below their respective maximum energy conversion efficiency points.

[0158] Accordingly, this embodiment should be considered illustrative rather than restrictive and the invention is not limited to the details given herein, but may be modified within the scope of the appended claims and their equivalents.

Claims

1. An apparatus for pulse control of an electric motor, comprising: a power supply source; an electric motor having windings in which energy is stored; a motor controller configured to selectively operate the motor in a pulse mode, wherein the motor produces an output during an on-pulse and no output between on-pulses; and a power converter coupled between the power supply source and the motor, the power converter arranged to deliver pulsed power to or receive pulsed power from the windings of the motor in response to the motor controller; wherein the power converter includes a boost circuit arranged to extract at least some of the energy present in the motor at the end of an on-pulse to reduce the on-pulse fall time, store at least some of the energy present in the motor, and apply at least some of the energy present in the motor at the start of a subsequent on-pulse, thereby reducing the rise time and fall time of the pulsed power relative to the rise time and fall time of the pulsed power in the absence of the boost circuit.

2. The apparatus according to claim 1, wherein, during pulse operation during the on-pulse, the motor operates near its maximum operating efficiency point.

3. The apparatus according to claim 1, wherein, the power supply source is a DC power supply source.

4. The apparatus according to claim 3, wherein, the power converter operates as a power inverter to convert the DC power generated by the DC power supply source into AC power to drive the motor.

5. The apparatus according to claim 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.

6. The apparatus according to claim 3, wherein, the boost circuit includes a switch electrically connected between a terminal of the DC power supply source and a switching network that controls power to and from the motor.

7. The apparatus according to claim 6, wherein, the boost circuit includes a capacitor selectively electrically connected to the switching network through the switch.

8. The apparatus according to claim 1, wherein, the boost circuit uses the energy stored in the stator windings to temporarily boost the available potential for driving the motor.

9. The apparatus according to any one of claims 1 to 8, wherein, during a shut-down period of the motor, the boost circuit increases the available potential for driving the motor with a series of one or more boost steps.

10. The apparatus according to any one of claims 3 to 8, wherein, the boost circuit includes a diode located between the power supply source and the switching network that controls power to and from the motor.

11. A method of operating an electric motor, comprising: operating the motor in a pulsed manner such that the power applied to or obtained from the motor consists of a series of on-pulses separated by periods of no power between on-pulses, wherein the duty cycle of the series of on-pulses is determined to deliver a desired torque magnitude; Extract at least some of the energy present in the motor at the end of the conduction pulse to reduce the conduction pulse fall time; Store at least some of the energy present in the motor; and Apply at least some of the energy present in the motor at the start of a subsequent conduction pulse, thereby reducing the rise time and fall time of the pulse power.

12. The method according to claim 11, wherein, The power applied to or obtained from the motor during the conduction pulses in the series of conduction pulses causes the motor to operate at a point close to the maximum operating efficiency point of the motor.

13. The method according to claim 11, wherein, The series of conduction 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 conduction pulses in the series of conduction pulses relative to the rise time and fall time of these conduction pulses in the absence of the boost circuit.

14. The method according to claim 13, wherein, The power converter operates as a power inverter, converting DC power generated by a DC power supply source into AC power to drive the motor.

15. The method according to claim 13, wherein, The power converter operates as a power rectifier, converting the AC power generated by the motor into DC power stored in a DC power supply source.

16. The method according to claim 11, wherein, The motor operates as a motor or a generator.

17. The method according to claim 16, wherein, The motor operates as a motor and the series of conduction pulses is generated by a power converter including a boost circuit, and the boost circuit increases the available potential for driving the motor at the start of at least one conduction pulse in the series of conduction pulses.

18. The method according to claim 17, wherein, The boost circuit increases the available potential for driving the motor at the end of the conduction pulse before the at least one conduction pulse in the series of conduction pulses.

19. The method according to any one of claims 17 to 18, wherein, The boost circuit increases the available potential for driving the motor during the off period before the at least one conduction pulse in the series of conduction pulses.

20. The method according to claim 19, wherein, The boost circuit increases the available potential for driving the motor in a series of one or more steps.

21. A method of operating a motor, comprising: Operating the motor in a pulsed manner such that the power applied to or obtained from the motor consists of a series of conduction pulses separated by periods of no power between the conduction pulses, wherein the duty cycle of the series of conduction pulses is determined to deliver a desired torque magnitude; Extract at least some of the energy present in the motor at the end of the conduction pulse to reduce the conduction pulse fall time; Store at least some of the energy present in the motor; Use at least some of the stored energy to increase the potential difference between the positive voltage bus and the negative voltage bus and Apply at least some of the energy present in the motor at the start of subsequent conduction pulses, thereby reducing the rise time and fall time of the pulse power to reduce the transition time of the series of conduction pulses respectively.

22. The method according to claim 21, wherein, During the time period between the series of conduction pulses, a series of one or more steps are used to increase the electrical potential for driving the motor.

23. The method according to claim 21, wherein, The potential difference exceeds the potential difference of the power supply source for storing or delivering energy to the motor.

24. The method according to any one of claims 21 to 23, wherein, The power applied to or obtained from the motor during a 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 conduction pulses.

25. A system for pulse control of an electric motor, comprising: The electric motor; A torque modulation module arranged to: a) Receive a torque demand; b) Determine whether the received torque demand is within or outside the pulse control range of the motor; and c) If the torque demand is within the pulse control range of the motor, generate a modulation waveform; A power converter arranged to receive the modulation waveform, the power converter being arranged to generate a series of energy pulses in response to the modulation waveform for operating the motor in a pulse mode, the series of energy pulses driving the motor in the pulse mode to generate a first torque respectively during the series of energy pulses, and a second torque lower than the first torque or equal to zero between the series of energy pulses, the average value of the first torque and the second torque being equal to the received torque demand; and A boost circuit coupled to the power converter, the boost circuit reducing the transition time of the series of energy pulses relative to the transition time without the boost circuit.

26. The system according to claim 25, wherein, The second torque is greater than zero.

27. The system according to claim 25, wherein, The power converter includes a switch network coupled between a first power rail maintained at a first electrical potential and a second power rail maintained at a second electrical potential, and the boost circuit is arranged to boost the potential difference between the first power rail and the second power rail to be greater than the potential difference between the first electrical potential and the second electrical potential without the boost circuit.

28. The system according to claim 27, wherein, The switch network includes a pair of switches for each of the three-phase energies for driving the motor, and each switch in the pair of switches is coupled in series between the first power rail and the second power rail respectively.

29. The system according to claim 27, further comprising a switch for selectively coupling the boost circuit to at least the first power rail of the power converter.

30. The system according to claim 25, wherein, The boost circuit includes one of the following: a) A charge pump; b) A voltage source; c) A capacitor; d) a battery; or e) any combination of a) to d).

31. The system according to claim 25, wherein, the modulation waveform is modulated by the torque modulation module using one of the following: a) Pulse Width Modulation (PWM); b) Direct Torque Control (DTC); c) Hysteresis; or d) Deadbeat control.

32. The system according to claim 25, further comprising a speed estimator module arranged to generate an estimated speed of the motor based on a signal indicative of the angular position of the rotor of the motor.

33. The system according to claim 25, further comprising a torque estimator module arranged to generate an estimated torque of the motor based on a signal indicative of the angular position of the rotor of the motor.

34. The system according to claim 25, 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 motor.

35. The system according to claim 25, 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 outside the pulse control range of the motor.

36. The system according to claim 25, wherein, the motor is an electric machine capable of operating as a generator that can operate in a continuous mode or the pulse mode.

37. The system according to any one of claims 25 to 36, wherein, the power converter includes a switch network including 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 switch network between the first power rail and the second power rail.

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