Motor system

Abstract

A motor system (100) comprises: a motor unit (110) comprising: a first portion (120); a second portion (130) movable relative to the first portion (120); a plurality of spaced apart activatable motor elements (140) disposed on the first portion (120), each activatable motor element (140) being operable to generate relative motion between the first and second portions (120, 130) when activated by applying a current thereto; and a plurality of power electronic drive modules (150), each power electronic drive module (150) being operable to generate relative motion between the first and second portions (120, 130) when activated by applying a current thereto. The drive modules (150) are operably associated with different subsets of the plurality of activatable motor elements (140) and include a power converter operable to convert direct current into a periodic current for powering the activatable motor elements; a power supply device (170) comprising: at least one direct current power supply (180); and a plurality of parallel direct current power lines (190), each parallel direct current power line (190) being used to transmit direct current from the at least one direct current power supply (180) to different subsets of the plurality of power electronic drive modules (150).

Description

Technical Field

[0001] The present invention relates to an electric motor system and, in particular but not exclusively, to an electric motor system for providing propulsion to electric vehicles and other forms of electric transportation. Background Art

[0002] Figure 1 A conventional motor power control system 10 for an electric vehicle is shown, which includes a battery power source 20 that supplies power to a three-phase inverter 30 , which in turn supplies power to a three-phase rotating electric machine 50 via a power supply line 40 .

[0003] The battery power supply 20 includes rechargeable battery cells 22, with a plurality of battery cells 24 (e.g., 200x100Ahr cells) arranged in series to generate 800V DC power for a three-phase inverter 30. A battery management system (BMS) 26 is provided in conjunction with the battery power supply 20 to monitor and regulate the state of the rechargeable battery cells 22.

[0004] As shown, a three-phase inverter 30 is operable to convert DC power into three-phase AC power (800V and 1000A peak per phase) for transmission along AC power lines 40 to three separate phases of a rotating electric machine 50 provided with activatable electromagnetic coils.

[0005] In a typical vehicle, the speed and torque range required for normal operation is wide - high speeds for highway use, high torque for steep grades and heavy loads in a road vehicle. Historically, this operating range has been facilitated by a selection of transmissions. However, for optimal efficiency, reduced wear and maintenance, it is desirable to avoid (or at least minimize) the use of transmissions in electric vehicles.

[0006] In order to provide sufficient headroom in terms of voltage and current in an electric vehicle (i.e., voltage to achieve the desired maximum motor speed and current to achieve the maximum force / torque), the battery unit 22 must have sufficient voltage and current capacity to handle the maximum speed and torque specified for the vehicle. In addition, in order to provide a speed and torque range, the battery and power electronics must be able to provide and handle the full range of voltage and current. To achieve the maximum speed of a three-phase motor, 400V to 800V is typically required.

[0007] Typically, motors are wound with multiple electromagnetic coils connected in series, which allows a single or small number of inverters to power the entire machine, but the consequence is that high voltages are required to overcome the sum of the back EMFs of the series coils. Higher voltages have many consequences. First, the power electronics must be rated for voltages significantly higher than the supply voltage to ensure fail-safe switching. Higher voltage switches introduce more conduction losses and switching losses. Higher voltages require stronger insulation for all motor coils, leaving less space for conductor copper. Higher voltages result in high capacitive coupling to ground, which in turn causes more losses and EMI issues. This is particularly acute when the semiconductor switches are set to switch faster for efficiency purposes, resulting in larger dV / dt, which both strengthens the insulation by increasing ionization and increases capacitive coupling to ground, increasing EMI and losses. Higher voltages also require larger DC link capacitors, increasing the size and mass of the inverter.

[0008] Typically the higher voltage devices are IGBT or Sic switches. These have a relatively constant voltage drop of about 2V per device. Conversely, the lower voltage switches (200V or less) are typically Mosfet devices. These devices have resistive losses, so the higher current devices have lower resistance and therefore lower losses. However, these devices cannot handle the voltages required to allow the series coil to operate at high speeds, unless the series coil is wound with a much lower number of turns, i.e. to limit the total back EMF. This option would require the use of very high current devices and would be subject to large coil conductors, large cables and large resistance I 2 The influence of R loss.

[0009] Because of the high voltages / currents involved, great care must be taken to ensure safe installation and occupant safety during any incident (e.g., vehicle collision). Summary of the invention

[0010] The applicants have identified an improved motor system design that provides higher efficiency and safer performance than the prior art.

[0011] According to the present invention, there is provided a motor system, comprising: a motor unit, comprising: a first part; a second part, which is movable relative to the first part; a plurality of spaced-apart activatable motor elements, which are arranged on the first part, each activatable motor element is operable when activated by applying current thereto to produce relative movement between the first and second parts; and a plurality of power electronic drive modules, each power electronic drive module is operably associated with a different subset of the plurality of activatable motor elements and comprises a power converter operable to convert direct current into a periodic current (e.g., pulsed direct current or alternating current) to power the activatable motor elements; and a power supply device, comprising: at least one direct current power supply; and a plurality of parallel direct current power lines, each parallel direct current power line being used to transmit direct current from at least one direct current power supply to a different subset of the plurality of power electronic drive modules.

[0012] In this way, a motor system can be provided in which activatable motor elements and associated power electronics are connected in parallel to multiple (e.g., low voltage) power sources and lines providing enhanced redundancy and reduced power handling. In particular, the activatable motor elements and power electronics can be configured for low voltage operation that can provide higher efficiency than high voltage equivalents (e.g., where the low voltage power switches are more efficient than the equivalent high voltage devices). Thus, through optimal selection of voltage, winding, and connection type, a parallel low voltage system can be achieved while significantly reducing losses, e.g., losses may be reduced by a factor of 5 or more.

[0013] In one embodiment, the plurality of activatable motor elements are divided into p plurality of phase groups, wherein each phase group receives current (eg, from a power electronic drive module) at a different time than the other phase groups.

[0014] In one embodiment, p ≥ 2 (eg, p ≥ 3).

[0015] In one embodiment, n>p (eg, n>2p).

[0016] In one embodiment, there are q multiple power electronic drive modules.

[0017] In one embodiment, q>p (eg, q>2p).

[0018] In one embodiment, q≥n (eg, q≥2n).

[0019] In one embodiment, a plurality of power electronic drive modules are arranged on the first part.

[0020] In one embodiment, each power electronic drive module is operably associated with a separate activatable motor element or subgroup of motor elements.

[0021] In one embodiment, each power electronic drive module is operably associated with a plurality of m activatable electric machine elements (eg, wherein each of the m activatable electric machine elements is local to the respective power electronic drive module).

[0022] In one embodiment, m=p.

[0023] In one embodiment, the plurality of parallel DC power lines extend substantially from the at least one DC power source to the motor unit.

[0024] In one embodiment, the at least one DC power source comprises a power source derived directly from a generator (eg from a distributed power grid or from a local (eg on-board) generator).

[0025] In one embodiment, at least one DC power source includes at least one dischargeable power storage device (eg, a dischargeable battery or a dischargeable fuel cell).

[0026] In one embodiment, at least one of the dischargeable power storage devices is rechargeable (eg, a rechargeable battery or a rechargeable fuel cell, or a rechargeable capacitor or capacitors).

[0027] In one embodiment, the at least one DC power source includes a plurality of DC power sources (eg, k plurality of DC power sources).

[0028] In one embodiment, at least one DC power source includes a plurality of dischargeable power storage devices (eg, k plurality of dischargeable power storage devices).

[0029] In one embodiment, the at least one DC power source includes a plurality of rechargeable power storage devices (eg, k plurality of rechargeable power storage devices).

[0030] In one embodiment, each of a plurality of DC sources (eg, k DC power sources) is associated with (eg, electrically connected to) a different one of the n parallel DC power lines.

[0031] In one embodiment, n≥k (eg, n>k or n=k).

[0032] In one embodiment, k>p (eg, k>2p).

[0033] In one embodiment, q≥k (eg, q≥2k).

[0034] Typically, each of the n plurality of parallel DC power supply lines includes a supply line and a return line.

[0035] In one embodiment, each of the n plurality of parallel DC power lines is operable to transmit a low voltage (e.g., approximately 200 volts or less, e.g., approximately 150 volts or less, e.g., approximately 100 volts or less, e.g., approximately 50 volts or less) to the motor unit (e.g., to a corresponding subset of its plurality of power electronic drive modules).

[0036] Typically, each of the n plurality of parallel DC power lines is electrically insulated from (eg, and separated from) another of the n plurality of parallel DC power lines (eg, the power lines are disposed within an electrically insulating sheath or the like).

[0037] In one embodiment, the plurality of dischargeable power storage devices are each a low voltage device (eg, operable to provide a voltage of approximately 200 volts or less, such as approximately 150 volts or less, such as approximately 100 volts or less, such as approximately 50 volts or less).

[0038] In one embodiment, each dischargeable power device (eg, each battery) has its own integrated (eg, substantially low voltage) management system (eg, integrated battery management system) for monitoring (eg, monitoring and adjusting) the state of the dischargeable power device.

[0039] In one embodiment, the activatable electromechanical element is an activatable electromagnetic element (eg, an element comprising at least one conductive coil operable to generate a magnetic field when activated).

[0040] In one embodiment, the activatable electromechanical element is an activatable electrostatic element (eg, an element including at least one conductive element that operates to generate an electric field when activated).

[0041] In one embodiment, the power converter is an AC converter (eg, an inverter) that operates to convert direct current to alternating current.

[0042] In another embodiment, the power converter is a pulsed DC converter (eg, a switching or modulator device) operable to convert DC power into pulsed DC power.

[0043] In one embodiment, the power converter of each power electronic drive module is a single-phase power converter (e.g., an H-bridge power converter), for example, for connecting one or more active motor elements associated with a single-phase group. For example, in the case of an AC converter, the AC converter can be a single-phase AC converter (e.g., an H-bridge inverter).

[0044] In one embodiment, the power converter is a multiphase power converter (e.g., a three-phase power converter or higher phase power converter), for example, for connection to a plurality of activatable motor elements, each activatable motor element being associated with a different phase group. For example, in the case of an AC converter, the AC converter may be a three-phase or higher phase inverter.

[0045] In one embodiment, the motor unit is a rotary motor unit.

[0046] In one embodiment, the motor unit is a linear motor unit.

[0047] In one embodiment, the first part is a movable (eg rotor) part and the second part is a stator part.

[0048] In one embodiment, the first part is a stator part and the second part is a movable (eg rotor) part.

[0049] In one embodiment, each power electronic drive module comprises a local control circuit operable to control the supply of current to the activatable motor elements under its control.

[0050] In one embodiment, each local control circuit is operable to sense the relative position of the first portion with respect to the second portion and (e.g., independently) determine the optimal current timing and magnitude delivered to the activatable motor elements under its control. In this way, each power electronics module is operable to independently synchronize its operation to maximize force and minimize losses while providing full independence / redundancy.

[0051] In one embodiment, the motor system is an electric vehicle propulsion motor system, an electric aircraft propulsion motor system, or an electric marine propulsion motor system. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0053] Figure 1 is a schematic diagram of a prior art electric vehicle motor system;

[0054] Figure 2A is a schematic diagram of a motor system according to an embodiment of the present invention;

[0055] Figure 2B yes Figure 2A a schematic diagram of a motor of the motor system; and

[0056] Figure 3 is used for Figure 2A Schematic diagram of an alternative motor for the motor system. Specific embodiments

[0057] Figure 2A and 2B Details of the motor system 100 are shown together, and the motor system 100 includes a P-phase rotating motor unit 110 and a DC power supply device 170 .

[0058] The rotating electric machine unit 110 includes a radially outer stator 120 and a radially inner rotor 130, which is separated from the stator 120 by an effective air gap 115 and can rotate relative to the stator 120 about a rotation axis "A", and the rotor 130 is operable to drive an output shaft 132 to rotate along the rotation axis "A". The stator 120 supports a plurality of circumferentially spaced, independently activatable motor coil elements 140, a plurality of integrally circumferentially spaced, segmented power electronic drive modules 150, and a low current distribution ring 160, which is operable to distribute power to each power electronic drive module 150.

[0059] Each segmented power electronic drive module 150 is operably associated with a different subset m of the plurality of activatable motor coil elements 140 and includes power converter electronics in the form of a three-phase inverter module 155 operable to convert direct current into three-phase alternating current for powering the activatable motor coil elements 140. Each activatable motor coil element 140 is operable to apply magnetic flux across the effective air gap 115 to produce relative motion between the rotor 130 and the stator 120 when activated by applying current thereto. In this embodiment, the activatable motor elements are activatable electromagnetic elements (e.g., elements including at least one conductive coil operable to produce a magnetic field when activated), but in the case of an electrostatic motor, the activatable motor elements would be activatable electrostatic elements (e.g., elements including at least one conductive element operable to produce an electric field when activated).

[0060] Return to Figure 2A , the DC power supply device 170 includes k multiple rechargeable low voltage (50V, 130AHr) batteries 180; and n parallel DC power lines 190, each of the n parallel DC power lines 190 substantially extending from its corresponding rechargeable battery 180 connected to the motor unit 110. In this specific example, p=m=3, k=n=12 (for simplicity, only 8 of the 12 rechargeable batteries 180 and 8 of the 12 DC power lines 190 are depicted) and q=24.

[0061] Each of the plurality of parallel DC power lines 190 includes a power line 192 and a return line 194 and is operable to transmit DC current from its respective rechargeable battery 180 to a different subset of the plurality of power electronic drive modules 150. Each DC power line 190 may be carried in a separate insulated cable or conduit to enhance redundancy. As shown, each rechargeable battery 180 is equipped with its own independent integrated battery management system 182 that is operable to monitor the status of the battery 180.

[0062] Each of the q three-phase inverter modules 155 is operable (at 50V, 120A) to convert DC power to AC power and is integrated into the stator 120. However, for applications where the direction of the current used to activate the motor elements is not important, each inverter module can also take the form of a pulsed DC converter (e.g. a switch or modulator device) for converting DC power to pulsed DC power. Each battery 180 provides power to a different pair of three-phase inverter modules (i.e., 2 inverter modules per 50V battery block), and each three-phase inverter module 155 is in turn directly connected to a set of three locally activatable motor coil elements 140 (one for each of the 3 motor phases).

[0063] Although k multiple rechargeable batteries are shown (as would be required for common transportation applications), depending on the application, the DC power source may include a single power source, such as a single DC generator derived power source (e.g., from a distributed power grid or from a local (e.g., on-board) generator) or a single battery source with n multiple parallel DC power lines 190 connected to the single power source. However, since the activatable motor coil elements 140 and the power converter electronics 160 are configured for low voltage operation, it is desirable to use separate low voltage DC power sources (here, k low voltage batteries 172) for redundancy purposes. Thus, the entire system becomes parallel from the power source through the cables, through the electronics to the motor coils, and allows each individual low voltage DC power source to be independently managed by a corresponding simple low voltage battery management system 182 that can be easily integrated with the battery. In the event of any failure, each battery / battery management system combination can be easily replaced (and even carry spares for extreme situations). In contrast, the battery power source for the high voltage system used to power the vehicle must usually be integrated into the vehicle architecture, so that removing it is a major overhaul and requires a properly isolated battery management system to handle hundreds of battery packs.

[0064] Since the current control of the power stage needs to be synchronized with the rotor 130, each power electronic drive module 150 may include a local control circuit that is operable to control the current supply to the activatable motor elements under its control. Each local control circuit is operable to sense the relative position of the rotor 130 with respect to the stator 120 and independently determine the optimal timing and amplitude of the current to be delivered to the activatable motor coil elements 140 under its control to produce the optimal force / torque.

[0065] Advantageously, since the parallel connection to the power electronics drive module 150 is implemented locally on the motor unit 110 (i.e., the power electronics drive module is integrated into the motor unit), there is no need to carry high currents through cables to the motor unit. Furthermore, when providing the motor unit 110 with a plurality of discrete activatable motor coil elements 140, the number of turns arranged for each coil can be optimized. Instead of connecting the coils in series as in conventional systems, the coils can be connected individually or only in short series groups of 2 or 3 coils, or connected in parallel with their respective inverter modules 155.

[0066] Since low voltage power switches (such as Mosfets) have an inherent resistance drop and are therefore more efficient at handling current in parallel than high voltage devices with a fixed voltage drop, very large loss reductions can be achieved by paralleling low voltage systems through an optimal choice of voltage, windings and connection method. In typical cases, this will reduce losses by at least a factor of 2 to 20.

[0067] For example, Figure 1 The inverter losses of the prior art motor system 10 are compared to the motor system 100 having a motor with 72 coils, with each machine running at the same speed and producing the same force.

[0068] In the first case (motor system 10), each leg of the star connected three phase system will have 24 coils in series. This effectively provides 48 coils on the supply simultaneously. If each coil has 1 turn, this will provide 48 turns of coil, equivalent to the indicated 800v supply.

[0069] In the second case (motor system 100), the 72 coils are again divided into 3 phase groups of 24 coils, but each low voltage supply is star-connected to 2 coils in series instead of 48 coils. This will allow the voltage to be 1 / 24 of the motor system 10 voltage (e.g. 33v) without a change in current. Thus there will be 24x33v groups of devices in parallel.

[0070] However, Mosfet devices can easily be operated at voltages up to 100V or 200V. So an optimum voltage of 150V for example would allow 4 coil turns instead of 1, and reduce the current rating of a device to 250A instead of 1000A.

[0071] Furthermore, low voltage MOSFETs are able to switch faster - both because they have to swing over a smaller voltage range (even though the switching speed is proportional to the high voltage device, in this case there will be 3 times less losses) and because they are inherently faster due to manufacturing factors. Thus achieving a double gain in switching losses.

[0072] The following calculation can be used to evaluate the comparison of potential losses in more detail:

[0073] Existing motor system 10:

[0074] The loss of a traditional 800V inverter is usually 4V voltage drop (2V x 2 switches) x 1000A current = 4000W

[0075] PWM switching loss = about 4000W

[0076] Total = 8000W

[0077] Parallel low voltage motor system 100:

[0078] Mosfet resistance - about 500 microohms per 250A device, which equals (in a star connected 3 coil set) 500 + (500 + 500) (total resistance is one series coil plus two parallel coils) = 750 microohms x 250A 2 Current = 47W x 24 inverters = 750W (assuming 2 / 3 are active at any time)

[0079] PWM switching loss = about 250W

[0080] Total = 1000W

[0081] Therefore, compared with the motor system 10 of the prior art, the motor system 100 can reduce the loss of the inverter by up to 8 times at the same motor torque.

[0082] In this way, an electric drive system with improved efficiency, reliability and safety is provided, which includes a multi-stage motor powered by multiple power electronic drive modules, whose power is in turn provided through multiple power supply cables and multiple power supply sources (such as battery modules or DC power supplies derived from mains).

[0083] In one embodiment of the present invention, the electric motor system 100 is configured as an electric vehicle propulsion motor system (e.g., operable to drive one or more wheels of a wheel-driven vehicle). In another embodiment, the electric motor system 100 may be configured as an electric aircraft propulsion motor system, operable to drive propulsion of an electric aircraft (e.g., drive a propeller or a rotor that generates lift of an electric aircraft) or an electric watercraft propulsion motor system, operable to drive propulsion of an electric watercraft (e.g., drive a propeller or a propeller).

[0084] Figure 3 One example of an alternative / phase rotating motor unit 110' for the motor system 100 is shown, an alternative to the motor unit 110 of the motor system 100 (common features are labeled accordingly). Whereas the motor unit 110 has an inner rotor 130 and a segmented power electronic drive module 150 is located axially adjacent to the activatable motor coil elements 140, in the motor unit 110', the rotor 130' is an outer rotor and the segmented power electronic drive module 150' is located radially inwardly of the stator 120'.

Claims

1. A motor system, include: Motor unit, comprising: Part I; a second portion movable relative to the first portion; a plurality of spaced apart activatable motor elements disposed on the first portion, each of the activatable motor elements being operable when activated by application of an electric current thereto to produce relative motion between the first portion and the second portion; and a plurality of power electronic drive modules, each of the power electronic drive modules being operatively associated with a different subset of the plurality of activatable motor elements and including a power converter operable to convert direct current into a periodic current for powering the activatable motor elements; and A power supply unit, comprising: at least one DC power source; and a plurality of parallel DC power lines, each of the parallel DC power lines being operable to transmit DC power from the at least one DC power source to a different subset of the plurality of power electronic drive modules, wherein each power electronic drive module comprises a local control circuit operable to control the supply of current to the activatable motor element under its control, wherein each of the local control circuits is operable to sense the relative position of the first portion with respect to the second portion and determine the optimal timing and amplitude of the current to be delivered to the activatable motor element under its control.

2. The motor system according to claim 1, in, The plurality of activatable motor elements are divided into p multi-phase groups, wherein each phase group receives current at a different time than the other phase groups. The electric machine system according to claim 2 , wherein n>p.

4. The motor system according to claim 2 or 3, in, There are q power electronic drive modules and q>p.

5. The motor system according to any one of claims 1 to 3, in, The at least one DC power source includes at least one dischargeable power storage device.

6. The motor system according to any one of claims 1 to 3, in, The at least one DC power source includes a plurality of dischargeable power storage devices.

7. The motor system according to claim 6, in, Each of the plurality of dischargeable power storage devices is associated with a different one of the plurality of n parallel DC power lines.

8. The motor system according to claim 6, in, Each of the plurality of dischargeable power storage devices is a low voltage device operable to provide a voltage of 200 volts or less.

9. The motor system according to claim 6, in, Each dischargeable power source device has its own integrated management system operable to monitor and adjust the status of the dischargeable power source device.

10. The motor system according to any one of claims 1 to 3, in, The power converter is an AC converter operable to convert direct current power into alternating current power.

11. The motor system according to any one of claims 1 to 3, in, The power converter is a pulsed DC converter operable to convert DC power into pulsed DC power.

12. The motor system according to any one of claims 1 to 3, in, The electric machine system is an electric vehicle propulsion electric machine system.

13. The motor system according to any one of claims 1 to 3, in, The motor system is an electric aircraft propulsion motor system.

14. The motor system according to any one of claims 1 to 3, in, The motor system is an electric marine propulsion motor system.

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