Controller and method for axial flux machines

Abstract

A method and controller for controlling an axial flux machine are described, wherein alternating current supplied to multiple coils is injected as a compensating current to reduce the mechanical resonance components of the rotor. This compensating current is added to an orthogonal current (IA) as the rotor rotates within one or more speed ranges. q ) component and DC (I d The modulated current component is a modulation current component of at least one of the following components (when the alternating current is represented as a vectorized DC component). This modulated current component has: an electrical frequency that varies with the rotor speed within a frequency range between a first frequency and a second frequency, including a frequency substantially the same as the rotor's fundamental mechanical resonant frequency; and a phase that is different from the rotor's fundamental mechanical resonant frequency.

Description

Technical Field

[0001] This invention relates to a method for controlling an axial flux machine, an axial flux machine controller, and an axial flux machine, and more particularly to a method, controller, and machine with lower mechanical resonance. Background Technology

[0002] All structures have a natural vibration frequency, at which the excitation force is amplified. This amplification occurs under the so-called resonance condition where the excitation frequency coincides with the natural frequency.

[0003] Rotating machines are extremely prone to mechanical vibrations due to resonance when their natural frequency is at or near, for example, the excitation frequency corresponding to the rotor speed. For machines such as pumps, turbines, electric motors, and generators, resonance can amplify the minute vibrational forces generated during machine operation and can sometimes lead to severe and destructive vibrations.

[0004] For variable speed drives, the excitation frequency varies with the motor speed, thus resonance occurs whenever the excitation harmonic frequency intersects with the natural resonant frequency. The resonance intensity varies not only with the excitation amplitude and its proximity to the natural frequency, but also with the damping, mass, and stiffness of the machine components related to the natural frequency.

[0005] The natural resonant frequency of a rotating machine is a factor to consider in machine design and can be adjusted according to the material properties and design of key components (usually the stator, rotor, and housing) to either reduce the frequency to the maximum extent possible or, sometimes, shift it.

[0006] However, even with efforts to shift or minimize the resonant frequency through material selection and mechanical design, the noise, vibration, and acoustic harshness (NVH) caused by resonance often remain a challenge to be addressed in finished machines.

[0007] Once the design of the machine is determined, its fundamental resonant frequency will become a constant. At this point, the resonance effect can only be reduced by changing the excitation frequency and intensity.

[0008] For variable speed axial flux machines, the rotor is often the component with the greatest risk of resonance problems because its rotor is a planar disk shape that has a variety of common vibration modes.

[0009] Since the fundamental (0,1) mode (i.e., the f0 and f01 modes, sometimes also called the zeroth-order mode) is most prone to excitation, this mode becomes the primary focus of this invention. Although this invention can be equally applied to higher-order intrinsic resonance modes, the following description and emphasis will focus on its impact on the fundamental resonance mode. It should be understood that these techniques can also be applied to higher-order modes.

[0010] Since axial flux machines often employ a stator-rotor air gap of approximately 1 mm to optimize power and torque, the aforementioned basic resonance and vibration modes are of additional importance for such machines. Even at small amplitudes, the noise generated by resonance-induced vibrations can be a source of disturbance.

[0011] The principle of suppressing resonance / noise by applying a canceling current is well known and has been applied in permanent magnet machines where the rotor position alternates between high-energy and low-energy states to reduce vibration and noise generated by the interaction between the permanent magnet rotor and the relative stator poles. Some examples in this regard include AU2015396604, which relates to reducing cogging forces by weakening magnetic flux, thereby reducing resonant excitation. US2005 / 0231143 discloses methods for reducing stator vibration in radial machines. US2008315818 discloses methods for applying a pair of harmonic currents whose order differs from the fundamental sinusoidal current by two. US2015108938 discloses methods for canceling oscillations caused by asymmetry within a machine by applying a compensating current.

[0012] The inventors have recognized the need for further suppression of planar resonance in the rotor of axial flux motors. Summary of the Invention

[0013] Therefore, the present invention provides a method for controlling an axial flux machine, an axial flux machine controller, and an axial flux machine according to the appended independent claims. Furthermore, the appended dependent claims provide more advantageous embodiments.

[0014] Specifically, this document describes a method for controlling an axial flux machine, the axial flux machine comprising: a stator including a stator housing enclosing a plurality of stator pole pieces circumferentially spaced around an axis of the machine, each stator pole piece having a coil assembly wound thereon to generate a magnetic field; and a rotor including a permanent magnet assembly and mounted for rotation about the axis of the machine, the rotor being spaced from the stator along the axis of the machine to define a gap between the stator and the rotor, the magnetic flux of the machine being generally axial within the gap, the method comprising: controlling an alternating current supplied to the plurality of coils to inject a compensating current for reducing the mechanical resonance component of the rotor, the compensating current being injected as the rotor rotates in one or more speed ranges, each of the one or more speed ranges of the rotor including a corresponding predetermined speed of the rotor, wherein the alternating current flowing through each coil is represented as including mutually orthogonal direct currents (I0). d ) components and orthogonal currents (I qThe vectorized DC component of the component; and wherein the compensation current includes the current added to the quadrature current (I) q ) and the DC (I d The modulated current component of at least one of the components has: an electrical frequency that varies with the rotational speed of the rotor in a frequency range between a first frequency and a second frequency, the frequency range including a frequency substantially the same as the fundamental mechanical resonance frequency of the rotor; and a phase that is different from the fundamental mechanical resonance frequency of the rotor.

[0015] By applying the above method, a reduction in rotor internal resonance can be observed.

[0016] The one or more corresponding predetermined speeds of the rotor may depend on one or more corresponding mechanical resonant excitation orders of the rotor, such as one or more excitation orders among 12, 18, 36, and 72. These orders are of interest for certain machine topologies (such as 18 / 12 topologies). Other topologies may have other excitation orders of interest. For example, for a 12 / 8 machine, the excitation orders of interest may be 8, 12, 24, and 48. For a 24 / 16 topology, the excitation orders of interest may be 16, 24, 48, and 96.

[0017] The one or more corresponding predetermined speeds of the rotor can be defined by the following relationship:

[0018]

[0019] Each speed range within the rotor's speed range can be based on a percentage change in the rotor's fundamental mechanical resonant frequency for a given mechanical resonant excitation order. The percentage change in the rotor's fundamental mechanical resonant frequency can be ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonant frequency.

[0020] In each of the one or more speed ranges of the rotor, the amplitude of the compensation current may vary between a lower amplitude and a peak amplitude in at least a portion of the speed range of the rotor, wherein the peak amplitude of the compensation current substantially coincides with the corresponding predetermined speed of the rotor.

[0021] The method may further include: receiving vibration data from a vibration sensor that detects mechanical vibration within the rotor; identifying a mechanical resonance component of the rotor from the vibration data; and injecting a compensation current in response to the identified mechanical resonance component of the rotor. This type of method is a closed-loop method, wherein the compensation current is injected when data from the vibration sensor indicates the presence of resonance.

[0022] In this closed-loop method, the compensation current can be injected only when the identified mechanical resonance component is greater than a threshold. The amplitude of the compensation current can be proportional to the amplitude of the identified mechanical resonance component.

[0023] In this closed-loop method, the vibration sensor can be an accelerometer.

[0024] In any of the above methods, in each of the one or more speed ranges of the rotor, the modulation current component may have a frequency at the first frequency when the rotor rotates at a speed corresponding to the lowest speed in the corresponding speed range of the rotor, wherein the modulation current component may have a frequency at the second frequency when the rotor rotates at a speed corresponding to the highest speed in the corresponding speed range of the rotor.

[0025] In each of the one or more speed ranges of the rotor, the modulated current component may have a frequency substantially the same as the fundamental mechanical resonant frequency that the rotor has when it is at a speed corresponding to the respective predetermined speed.

[0026] The first frequency may be lower than the second frequency. Furthermore, the modulation current component may be based on a percentage change in the rotor's fundamental mechanical resonant frequency within the frequency range between the first and second frequencies, wherein the percentage change in the rotor's fundamental mechanical resonant frequency is ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonant frequency.

[0027] The alternating current supplied to the plurality of coils can be a three-phase alternating current, wherein I d and I q This represents the vectorized DC component of the combined result of all three phases.

[0028] The axial flux machine can be an electric motor or a generator.

[0029] The present invention also provides a controller for controlling an axial flux machine, the axial flux machine comprising: a stator including a stator housing enclosing a plurality of stator pole pieces circumferentially spaced around the axis of the machine, each stator pole piece having a coil assembly wound thereon to generate a magnetic field; and a rotor including a permanent magnet assembly and mounted for rotation about the axis of the machine, the rotor being spaced from the stator along the axis of the machine to define a gap between the stator and the rotor, the magnetic flux of the machine being generally axial within this gap, the controller comprising: for The controller includes one or more electrical input terminals for receiving one or more currents; and one or more electrical output terminals for supplying one or more alternating currents to the axial flux machine coils, wherein the controller is configured to: control the alternating currents supplied to the plurality of coils to inject a compensating current for reducing the mechanical resonance component of the rotor, the compensating current being injected as the rotor rotates within one or more speed ranges, each of the one or more speed ranges of the rotor including a corresponding predetermined speed of the rotor, wherein the alternating current flowing through each coil is represented as including mutually orthogonal direct currents (I0). d ) components and orthogonal currents (I q The vectorized DC component of the component; and wherein the compensation current includes the current added to the quadrature current (I) q ) and the DC (I d The modulated current component of at least one of the components has: an electrical frequency that varies with the rotational speed of the rotor in a frequency range between a first frequency and a second frequency, the frequency range including a frequency substantially the same as the fundamental mechanical resonance frequency of the rotor; and a phase that is different from the fundamental mechanical resonance frequency of the rotor.

[0030] The one or more corresponding predetermined speeds of the rotor may depend on one or more corresponding mechanical resonant excitation orders of the rotor, such as one or more excitation orders among 12, 18, 36, and 72. These orders are of interest for certain machine topologies (such as 18 / 12 topologies). Other topologies may have other excitation orders of interest. For example, for a 12 / 8 machine, the excitation orders of interest may be 8, 12, 24, and 48. For a 24 / 16 topology, the excitation orders of interest may be 16, 24, 48, and 96.

[0031] The one or more corresponding predetermined speeds of the rotor can be defined by the following relationship:

[0032]

[0033] Each speed range within the rotor's speed range may be based on a percentage change in the rotor's fundamental mechanical resonant frequency for a given mechanical resonant excitation order. For example, the percentage change in the rotor's fundamental mechanical resonant frequency may be ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonant frequency.

[0034] The controller can be used to cause the amplitude of the compensation current to vary between a lower amplitude and a peak amplitude in at least a portion of the rotor's rotational speed range, wherein the peak amplitude of the compensation current substantially coincides with the corresponding predetermined rotational speed of the rotor.

[0035] The controller may include: a vibration sensor input for receiving vibration data from a vibration sensor that detects mechanical vibration within the rotor, wherein the controller is configured to: identify a mechanical resonance component of the rotor from the vibration data; and inject a compensation current in response to the identified mechanical resonance component of the rotor.

[0036] The controller can be used to inject the compensation current only when the identified mechanical resonance component is greater than a threshold. The amplitude of the compensation current can be proportional to the amplitude of the identified mechanical resonance component.

[0037] The vibration sensor can be an accelerometer.

[0038] In each of the one or more speed ranges of the rotor, the controller can control the modulation current component to have a frequency at the first frequency when the rotor rotates at a speed corresponding to the lowest speed in the corresponding speed range of the rotor; wherein the controller can control the modulation current component to have a frequency at the second frequency when the rotor rotates at a speed corresponding to the highest speed in the corresponding speed range of the rotor.

[0039] In each of the one or more speed ranges of the rotor, the controller can control the modulated current component to have a frequency substantially the same as the fundamental mechanical resonant frequency of the rotor at the speed corresponding to the respective predetermined speed.

[0040] The first frequency may be lower than the second frequency. The modulation current component may be based on a percentage change in the rotor's fundamental mechanical resonance frequency within the frequency range between the first and second frequencies, wherein the percentage change in the rotor's fundamental mechanical resonance frequency is ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonance frequency.

[0041] The one or more alternating currents supplied to the plurality of coils can be three-phase alternating currents, wherein I d and I q This represents the vectorized DC component of the combined result of all three phases.

[0042] The axial flux machine can be an electric motor or a generator.

[0043] The present invention also provides an axial flux machine, comprising: a stator including a stator housing enclosing a plurality of stator pole pieces circumferentially spaced around an axis of the machine, each stator pole piece having a coil assembly wound thereon to generate a magnetic field; and a rotor including a permanent magnet assembly and mounted for rotation about the axis of the machine, the rotor being spaced from the stator along the axis of the machine to define a gap between the stator and the rotor, the magnetic flux of the machine being generally axial within the gap, wherein the axial flux machine is connected to the aforementioned controller, the controller supplying alternating current to the plurality of coils.

[0044] The axial flux machine may include a vibration sensor mounted on the machine to sense vibrations within the rotor. The vibration sensor may be an accelerometer.

[0045] The stator housing may have an annular shape that forms a hollow region around the axis of the machine, wherein the rotor may be formed of an annular object and have a hollow central region around the axis of the machine.

[0046] The axial flux machine may include a second rotor located on the side of the stator opposite to the first rotor, the second rotor including a group of permanent magnets on a first side of the second rotor facing the stator, the second rotor being mounted for rotation about the axis of the machine relative to the stator, the second rotor being spaced apart from the stator along the axis of the machine to define an axial gap between the stator and the second rotor, within which the flux of the machine is generally axial.

[0047] The machine can be an electric motor or a generator. Attached Figure Description

[0048] The invention will now be described by way of example only and with reference to the accompanying drawings. In the drawings:

[0049] Figure 1a Figures 1 to 1c show the overall structure of the dual-rotor axial flux machine, an illustrative topology of the axial flux permanent magnet machine, and a side view of the yokeless segmented armature (YASA) machine.

[0050] Figure 2 is a perspective view of the YASA machine shown in Figure 1c;

[0051] Figure 3 is an exploded perspective view of the stator and stator housing in a YASA machine;

[0052] Figure 4 A waterfall plot illustrating the relationship between the rotational speed (rpm) of an axial flux machine rotor and electrical frequency and resonance.

[0053] Figure 5 The image shows the direction of I. d The decrease in resonant force when a modulating component is applied to a DC component;

[0054] Figure 6 The graph shows the relationship between noise level (dB) and rotor speed before and after using the method of the present invention. Detailed Implementation

[0055] In short, this document describes a method and controller for controlling an axial flux machine, wherein a compensating current for reducing the mechanical resonance components of the rotor is injected by applying alternating current to multiple coils. This compensating current is added to the quadrature current (IA) as the rotor rotates within one or more speed ranges. q ) component and DC (I d The modulated current component is a modulation current component of at least one of the following components (when the alternating current is represented as a vectorized DC component). This modulated current component has an electrical frequency that varies with rotor speed within a frequency range between a first frequency and a second frequency, including frequencies substantially the same as the rotor's fundamental mechanical resonant frequency. The phase of the modulated current component is out of phase with the frequency of the rotor's fundamental mechanical resonant component. For example, if the rotor of an axial flux machine has a fundamental mechanical resonant frequency of approximately 1 kHz, then depending on the rotor speed, the frequency of the modulation current component varies with the rotor speed. q and / or I d A modulated current component with an electrical frequency range between approximately 1 kHz and approximately 1 kHz is added to the current component to reduce mechanical vibration of the rotor during use.

[0056] The following description first outlines the background of an axial flux mechanism structure as an illustrative application of the method and controller of the present invention. First, reference is made to Figures 1c, 2, and 3, cited in PCT application WO2012 / 022974. Figure 1c is a schematic diagram of a yokeless segmented armature mechanism 10.

[0057] Machine 10 includes a stator 12 and two rotors 14a, 14b. The stator 12 consists of a series of individual stator bars (or pole pieces) 16 circumferentially spaced about the rotation axis 20 of the rotors 14a, 14b. Each bar 16 has its own axis (not shown), which is preferably, but not necessarily, parallel to the rotation axis 20. Each end of each stator bar is provided with pole shoes 18a, 18b, which serve to limit the physical purpose of coil stacks 22, which are preferably made of insulated square / rectangular cross-section wire to achieve a high fill factor. The coils 22 are connected to a circuit (not shown) that, in the case of an electric motor, energizes the coils so that the magnetic poles of the resulting magnetic fields generated by the currents flowing in adjacent stator coils 22 are opposite.

[0058] Two rotors 14a and 14b carry permanent magnets 24a and 24b that are opposite each other to the stator coils 22 (the permanent magnets are similar when the stator bars are inclined bars different from those shown in the figure). In each of the two pole shoe / magnet pairs 18a / 24a and 18b / 24b, a corresponding air gap 26a and 26b is provided between the pole shoe and the magnet. A number of coils and magnets are arranged around the rotation axis 20, and preferably, the number of coils is different from the number of magnets to avoid the coils always being aligned with the corresponding magnet pair at the same time and in the same rotational position of the rotor relative to the stator. This reduces cogging effect. Each rotor is generally a disc-shaped rotor with the mounting point located near its center, and the circumferential edge is a free edge floating above the stator (or, in the case of an annular disc with a central hole, each rotor is located outside the stator along its central rotation axis).

[0059] In the electric motor, when coil 22 is energized, its polarity alternates, causing the coil to align with different magnet pairs at different times, thereby applying torque between the rotor and stator. The rotors 14a, 14b are generally connected together (e.g., via a connecting shaft (not shown)) and rotate together about axis 20 relative to stator 12. Two adjacent stator bars 16 and two magnet pairs 24a, 24b provide a magnetic circuit 30, and the guards 32a, 32b of each rotor communicate the magnetic flux between the back sides of each magnet 24a, 24b away from the corresponding coil 22. The stator coils 16 are enclosed within a housing that extends through air gaps 26a, 26b and defines a chamber for supplying cooling medium.

[0060] Referring to Figure 3, in stator 12a, stator coils are disposed between clamshell-shaped half-shells 42a and 42b made of plastic material, which together form the stator outer shell. These clamshell-shaped half-shells have a cylindrical outer wall 44, a cylindrical inner wall 46, and a radial annular wall 48. Figure 3 Existing TechnologyIn the example, the radial wall 48 includes pole shoes 18a, 18b that accommodate the stator bar 16 when the two clamshell halves 42a, 42b of the stator 12a are assembled together, and serves to house the internal cavity 50 of the stator coil assembly 16, 22, 18a, 18b. The stator housings 42a, 42b define an inner coil space 52 and an outer coil space 54 along the outer surface of the coil 22, and an inter-coil space 56 also exists between the coils. The spaces 52, 54, 56 are interconnected, thereby defining a cooling chamber. Although not shown in Figure 3, in the assembled state, the stator housings 42a, 42b are provided with openings to allow a cooling medium such as oil to be pumped into the spaces 52, 54, 56 and circulate around the coils to cool them.

[0061] While the single-stator dual-rotor implementation has been described above, an axial flux segmented armature design containing a single-stator single-rotor type structure can also be employed. In such devices, to achieve a complete magnetic return path, it is generally necessary to remove the rotor and replace it with a yoke. The rest of the structure remains the same as the dual-rotor type structure.

[0062] Axial flux machines typically achieve a short axial length by employing a short stator. This stator's armature is usually combined with clockwise-distributed ferromagnetic pole pieces, whose magnetic field is typically axial, and a disk-shaped permanent magnet rotor. The magnets on this rotor are distributed clockwise and oriented towards the axis opposite to the armature's magnetic field. By using a short stator and a disk-shaped rotor, high-torque machines with short (axial) lengths can be developed.

[0063] As mentioned above, all solid structures exhibit mechanical resonance, which can typically be excited by relatively small disturbances. For disk-shaped rotors, the distortion caused by resonance is essentially precisely dependent on the material and physical structure such as thickness, ribs, and laminations, and a particular rotor design will produce mechanical resonance at a specific frequency.

[0064] In axial flux motors, efforts are being made to develop rigid rotors with high flexural modulus to overcome the bending attraction between the rotor permanent magnets and the stator. The rotor's stiffness allows for a smaller air gap between the rotor and stator. A smaller air gap results in greater torque and higher magnetic efficiency, but simultaneously increases the risk of catastrophic failure due to rotor contact with the stator during operation.

[0065] For axial flux motors, low-order resonant modes are of particular interest because they can cause the rotor to bend a considerable distance (relative to the rotor size). The more bending nodes there are, the easier it is for the rotor stiffness to confine larger distortions to a smaller distance, thus avoiding the adverse mechanical effects of resonance. Acoustic noise in the human hearing range remains a concern for both low- and high-order resonant modes.

[0066] Among the various low-order resonance modes, the zero-order resonance mode (0, 1), or the fundamental resonance mode, is particularly noteworthy. This is because this mode involves the entire rotor disk, has no segmented bending axis, and is one reason for the up-and-down pulsation of the outer periphery of the disk due to bending when the center of the rotor disk is fixed. The zero-order mode is easily excited, thus generating disturbing noise through vibration. Moreover, since this mode involves the entire rotor, it is most likely to cause bending distortion and may also cause significant air disturbance, leading to vibration of the motor cover.

[0067] For axial flux machines, the zero-order resonant mode of the rotor disk can be measured. Parameters of interest include the fundamental resonant frequency, excitation amplitude and force, the resonant amplitude generated by the rotor, and the rotor temperature. For axial flux machines containing a rotor, one excitation method is finite element modeling. Alternatively, similar to determining the resonant characteristics of cymbals, tuning forks, or bells, the fundamental resonant mode and resonant frequency can be determined by gently tapping the rotor to induce vibration.

[0068] In addition, rotor resonance modes can be evaluated within the internal environment of an axial flux machine, where the rotor is typically located. This involves increasing the machine's operating speed from zero revolutions per minute (rpm) to its maximum operating speed, and then using appropriate sensors such as acoustic sensors, vibration sensors, or accelerometers to measure resonance.

[0069] Figure 4 A waterfall plot illustrating the relationship between the rotational speed (rpm) of an axial flux machine rotor and electrical frequency and resonance. Figure 4 The vertical axis represents the electrical excitation frequency, and the horizontal axis represents the rotor speed (rpm). Resonance is measured by an acoustic sensor, and this information is also plotted in this graph.

[0070] In the figure, the horizontal line starting from a point on the vertical axis corresponds to the zero-order (basic) resonant frequency of the rotor, while the other lines starting from the origin (i.e., the point where the rotational speed and frequency are both zero) correspond to the harmonics of the zero-order resonant mode.

[0071] Furthermore, the intersection point where the zero-order resonant frequency line intersects with higher-order harmonic lines of the zero-order resonance can correspond to the excitation region that produces the resonance. Not all resonances lead to noise, vibration, and acoustic harshness (NVH) problems, and the rpm values ​​of some resonant vibrations may not be significant for the use of the machine. However, when the harmonics of the zero-order resonant mode correspond to the normal operating mode of the machine, the resulting resonance can cause problems.

[0072] for Figure 4 For example, the 72nd, 36th, 18th, and 12th harmonics, which are of significant importance, correspond to RPM values ​​of 900 rpm, 1600 rpm, 3300 rpm, and 5000 rpm, respectively. Since these RPM values ​​fall within the machine's operating range, the machine will experience corresponding vibrations when accelerating from zero RPM to its maximum operating RPM. The purpose of this invention is to reduce such vibrations.

[0073] The basic idea of ​​this invention is to reduce the mechanical resonance of the rotor (and / or other parts of the system) by introducing an additional current component into the supply current of the coil. This will be described in further detail below.

[0074] During operation, the current supplied to the coil to generate the magnetic field (or, in the case of a generator, the current generated by the coil) is an alternating current supplied to the controller (such as an inverter with a controllable output current). For simplicity, this explanation uses an electric motor (i.e., a machine that generates a magnetic field by supplying current to the coil, rather than a machine that generates current in the coil by rotating a rotor) as an example, but it will be apparent to those skilled in the art that the following method is equally applicable to machines that operate as generators.

[0075] For the machine described herein, the alternating current is generally a three-phase alternating current, but it can also be a single-phase or multi-phase alternating current. Adjacent coils are supplied with currents of different phases, and the alternating current supplied to each coil is (nearly) sinusoidal, thereby generating a rotating magnetic field that interacts with the permanent magnets of the rotor and exerts a circumferential pulling effect on the permanent magnets.

[0076] In the field of axial flux machine control, the single-phase or multi-phase alternating current input to the coil is usually represented as two vectorized DC components that are orthogonal to each other, namely the well-known orthogonal current components (I0). q ) and DC component (I d Thus, the combined three-phase input currents U, V, W can be expressed as having a DC quadrature component I. q and orthogonal DC component I dA single vectorized DC current. This can be achieved using methods known in the art, such as the Park transform. q This represents the useful torque-generating current, while I... d This refers to the current that is in the same direction as the magnetic field induced by the permanent magnet.

[0077] Normally, when the machine is operating normally as an electric motor, I d Current value less than I q 10%. For example, in some cases, I q =200A, and I d It can be in the range of 10A to 25A.

[0078] As described above, the method described below is applicable not only to single-rotor and dual-rotor structures, but also to two types of axial flux machinery structures: electric motors and generators, regardless of whether the supply current (or the current generated) is single-phase or multi-phase alternating current.

[0079] Methods for reducing mechanical vibrations within a rotor and / or machine include controlling alternating current supplied to multiple coils to inject compensating current for reducing the mechanical resonance components of the rotor.

[0080] In the method used in this invention, the controller is configured to control the supply of alternating current to the coil, so as to supply I... q and / or I d A modulated current component is added. This is achieved by controlling the supply of alternating current via a controller, so that the current added to I... q and / or I d The electrical frequency range of the modulated current component includes electrical frequencies that are substantially the same as, but out of phase with, the fundamental mechanical resonant frequency of the rotor. As described above, by injecting modulated I... q and I d The components are such that these two components have different magnitudes relative to each other. Although it is possible to direct I q and / or I d The current component is added with a modulation current, but in a preferred embodiment of the invention, the modulation current component is only injected into I. d The current component, because this reduces the amount added to I. q The probability that the modulated current component will manifest as ripple in the machine's output torque. The following description only addresses the addition of the modulated current component to I. d However, it should be noted that this should be interpreted as referring to the situation where I... q and / or I d A modulated current component is added to the current component.

[0081] Assuming the fundamental mechanical resonant frequency is, for example, 1kHz, then add to Id The DC component of the modulation current has an electrical frequency range around 1 kHz. Similarly, if the fundamental mechanical frequency is 2 kHz, then it is added to I. d The DC component of the modulating current has an electrical frequency range around 2kHz. In practical applications, the resonant mechanical frequency of the rotor of the machine of interest is approximately 877Hz; therefore, in practical applications, an additional current is added to I... d The DC component of the modulating current should have an electrical frequency range of approximately 877 Hz. However, for simplicity, an example with a rotor mechanical resonant frequency of 1 kHz is used here, but it should be understood that the invention is not limited to this frequency. The injected electrical frequency range, which depends on the rotor speed, will be described below.

[0082] Figure 5 The figure shown is based on the invention in the direction of I d The decrease in resonant force when the DC component is modulated by the DC component. During the time interval between t=0 and t=5 (I... q =200A), I d The nominal value is zero, indicating that no compensation current has been injected. During this time period, as shown in the figure, the peak-to-peak value of the axial force is 42N, indicating the presence of a mechanical resonance component.

[0083] At t=5, send to I d A modulated current component (with the same electrical frequency as the rotor's fundamental mechanical resonant frequency) is added to the DC component. The axial force ripple decreases to a more acceptable level of 4N peak-to-peak value, indicating a significant reduction in the peak-to-peak value of the resonant force.

[0084] Figure 6 The graph shows the relationship between noise level (dB) and rotor speed under two conditions: no compensation current (dark line) and compensation current (gray line).

[0085] As can be seen, the dark lines include amplitude peaks that coincide with the 72nd, 36th, 18th, and 12th resonance modes of the rotor (the 12th mode is around 5000 rpm, the 18th mode is around 3400 rpm, the 36th mode is around 1800 rpm, and the 72nd mode is around 850 rpm). This situation occurs when the axial flux machine is not operating using the present invention.

[0086] The situation after applying the compensation current is shown by the gray line. It can be seen that the peak noise amplitude in the same corresponding resonance mode is significantly reduced. Clearly, this invention provides an axial flux mechanism that significantly reduces mechanical resonance.

[0087] Although this method can be used across the entire target rotor speed range of the machine, meaning that compensating current can be injected into I at all rotor speeds. dA DC component is possible, but this is impractical because it would increase the power requirements of the machine across the entire operating range. As mentioned above, mechanical resonance is only noticeable at certain rotor speeds, therefore it is not necessary to apply a compensating current across the entire operating range of the rotor.

[0088] Accordingly, the controller can be used to apply a compensating current when the rotor's rotational speed is equal to or approximately equal to one or more predetermined rotor speeds. This is because the additional current injected into the machine will increase the machine's power requirements (due to the current applied to I). d DC component, not I q The orthogonal current components (therefore they do not produce a significant gain on the power output) are used to reduce the power requirements while still retaining the advantage of reducing rotor mechanical resonance.

[0089] The aforementioned one or more predetermined rotor speeds may depend on one or more corresponding resonant excitation orders of the rotor, such as one or more of 12th, 18th, 36th, and 72nd excitation orders. Of course, it will be apparent to those skilled in the art that other excitation orders of the rotor may also be used. In this application, it has been found that these orders are the most common in machine operation.

[0090] It should be noted that the above rotational speed (in rpm) can be determined by the following formula:

[0091]

[0092] For example, taking the aforementioned rotor's fundamental mechanical resonance frequency of 1kHz as an example, the predetermined speed (the speed at which the compensation current is applied) is equal to 60000 divided by the excitation order. Therefore, the predetermined speeds for excitation orders 72, 36, 18, and 12 are 833 rpm, 1666 rpm, 3333 rpm, and 5000 rpm, respectively.

[0093] Accordingly, when the rotor reaches one or more of the aforementioned speeds (which can be physically measured by a sensor located on the rotor or the rotor output terminal, or electrically measured by the frequency of the power supply current in the variable frequency machine), a compensation current can be applied to reduce the mechanical resonance component of the rotor.

[0094] Furthermore, for each of the aforementioned one or more predetermined speeds of the rotor, a compensating current can be injected within a rotor speed range extending above and below the corresponding rotor speed. This is because mechanical resonance does not have a narrow peak precisely centered at the expected speed. Instead, within the rotor speed range, the amplitude of the mechanical resonance component first gradually climbs to a peak value coinciding with the corresponding rotor speed of the expected resonance order, and then gradually tails down as the rotor speed moves away from this resonance peak.

[0095] One method for determining the appropriate range of compensation current application for a given rotor resonant excitation order is to consider the range of rotor speeds based on the percentage change of the rotor's fundamental mechanical resonant frequency.

[0096] Referring again to equation (1), it can be seen that the predetermined speed is proportional to the result of dividing the rotor's fundamental resonant frequency by the excitation order. When considering the fundamental mechanical resonant frequency that is within the range of the resonant peak, the required rotor speed range can be determined using the resonant range for which the compensation current is to be applied for a given excitation order.

[0097] The percentage variation of the rotor's fundamental mechanical resonant frequency can be, for example, ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonant frequency. Alternatively, this percentage variation can be greater than or within these ranges. In practical applications, ±10% is a suitable range for the rotor speed to which the compensation current is applied. That is, the predetermined rotor speed is calculated to be between 900 Hz and 1.1 kHz (±10% of 1 kHz).

[0098] Based on equation (1) and the above data, the following rotor speed range (rpm) can be obtained:

[0099] resonance order Rotor speed lower limit Peak resonant rotor speed upper limit of rotor speed 12th order 4500 5000 5500 18th level 3000 3333 3666 36 levels 1500 1666 1833 72nd step 750 833 916

[0100] Although the above describes the application of compensating current over several relatively narrow rotor speed ranges, it is also possible to apply compensating current over one or more different ranges.

[0101] For example, a specific resonance order can be selected (the resonance order that is of most concern for reducing NVH for the machine topology). For this resonance order, a compensating current can be added over a relatively narrow range of rotor speeds (consistent with the above, but here we only focus on, for example, order 36). Alternatively, a compensating current can be added over a very wide range of rotor speeds (e.g., between 0 rpm and the maximum rotor speed).

[0102] As another example, compensation currents can be applied over a wider range (compared to the above). That is, the upper and lower ranges for each of the above-mentioned one or more resonance orders can be greater than the ±20% mentioned above.

[0103] As mentioned above, add to I dThe frequency of the modulated current component of the DC component varies within each of the one or more speed ranges. That is, a first electrical frequency is selected corresponding to the lowest rotor speed in each range; a second electrical frequency is selected corresponding to the highest rotor speed in each range; and an electrical frequency substantially the same as the rotor's mechanical resonant frequency is selected corresponding to the target peak resonant rotor speed. The first and second electrical frequencies represent the lowest and highest frequencies of the frequency range, respectively.

[0104] This frequency range can be, for example, ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonant frequency. Alternatively, the frequency range can be greater than or between these ranges. In practical applications, ±10% is a suitable electrical frequency range value. That is, depending on the rotor speed and based on the fundamental mechanical resonant component of 1 kHz, the aforementioned electrical frequency range can be between 900 Hz and 1.1 kHz (±10% of 1 kHz).

[0105] Based on the above example data table and rotational speed data, it can be seen that the frequency of the modulation current component at the lowest rotational speed in each rotational speed range is 900Hz, the frequency at the highest rotational speed in each rotational speed range is 1.1kHz, and the frequency at the target peak resonant speed is 1kHz. Within each range, this frequency varies from 900Hz to 1.1kHz with the change of rotor speed.

[0106] In addition to applying a compensating current within the rotor speed range, adding current to I within that speed range d The amplitude of the DC component of the modulating current can also vary within this range. This amplitude can gradually increase from a lower amplitude to a peak amplitude within at least a portion of the rotor speed range. Preferably, the current amplitude varies with the resonant amplitude within this range, rising from a low value at low speeds to a peak value coinciding with the peak of the resonant amplitude, and then tailing down to a low value as the speed gradually approaches the upper limit of the rotor speed range.

[0107] In the open-loop control scheme where the rotor speed value is stored in memory and invoked by the controller, a simple approach can be implemented: first, the compensation current amplitude increases from a low value at low rotor speeds; then, the compensation current reaches its peak amplitude at the resonant rotor speed; and finally, the compensation current amplitude decreases to the upper limit of the rotor speed. The amplitude can increase and decrease linearly, or it can increase and decrease in a suitable shape. Furthermore, the modulation current component is preferably out of phase with the rotor's mechanical resonance component (to prevent the control scheme from increasing resonance rather than reducing it). Preferably, the modulation component is completely out of phase with the rotor's mechanical resonance component. However, the control scheme can function as long as the modulation component is at least partially out of phase with the rotor's mechanical resonance component.

[0108] In the open-loop scheme, the phase value is characterized during the manufacturing process and stored in memory, enabling the controller to process I... d The DC component is correctly modulated. While the response of the injected modulated current component is preferably completely out of phase with the rotor's mechanical resonance component (to minimize rotor resonance), it should be understood that in an open-loop control scheme, this effect may not be achieved throughout the machine's entire lifespan. Over time, the mechanical characteristics of components may change, causing a drift in the phase characteristics of the resonance. As long as the injected modulated current component is at least partially out of phase with the rotor's mechanical resonance component, rotor resonance can be reduced to some extent when the modulated current component is injected.

[0109] In an open-loop control scheme, the controller can calculate the appropriate rotor speed for applying the compensation current based on manufacturer-stored values ​​such as the fundamental mechanical resonant frequency components (based on the machine's characterization at the time of manufacturing) and the desired excitation mode. These values ​​can be calculated during machine operation. Alternatively, these rotational speed values ​​can be provided in the form of a lookup table at the time of manufacturing, which the controller can then access during the operation of the control scheme.

[0110] An alternative to open-loop control is closed-loop control. In this type of control, the machine is equipped with vibration sensors such as accelerometers. The vibration sensors are preferably mechanically mounted relative to the rotor (e.g., on a cover near or adjacent to the rotor, or on other mechanical components near or adjacent to the rotor) so that they can sense the mechanical vibrations of the rotor, especially rotor resonances.

[0111] This closed-loop scheme uses data from vibration sensors to detect the rotor's mechanical resonance peak as the rotor speed changes. The controller can then inject compensating current based on the detected rotor mechanical resonance components. Furthermore, in the closed-loop scheme, because the controller knows the timing of the resonance, it can also maintain the resonance phase value. Thus, it can inject compensation current into I... d A suitable modulation current component with an appropriate frequency and a phase that is out of phase (preferably opposite to) the mechanical resonance component is injected into the DC component. Consistent with the open-loop scheme described above, resonance can be reduced to some extent as long as the phase is at least partially out of phase with the rotor's mechanical resonance component. As mentioned above, the frequency of the modulation current component varies with the rotor speed within a frequency range that includes the rotor's fundamental mechanical resonance frequency.

[0112] The compensation current can be injected only when the amplitude of the detected mechanical resonance component exceeds a threshold. Thus, since the compensation current is injected only when compensation for the mechanical resonance component is needed, the power requirements of the machine can also be improved.

[0113] Since the resonance occurring in the rotor is directly measured at various speeds, the controller can apply a compensation current whose amplitude is proportional to the amplitude of the detected mechanical resonance component.

[0114] Using a closed-loop approach is advantageous because machine performance can vary throughout its lifespan. Therefore, the resonant peak may shift as components age. However, this approach increases cost due to the addition of extra components (vibration sensors) and requires additional computing power to monitor vibration sensor data, determine the resonant peak, and apply appropriate compensation current.

[0115] While the above discussion pertains to 18 / 12 topologies (18 pole pieces and 12 poles) with 12th, 18th, 36th, and 72nd orders being the most desirable excitation orders, the aforementioned techniques can also be applied to other topologies, such as 12 / 8 topologies (12 pole pieces and 8 poles) with 8th, 12th, 24th, and 48th orders being the most desirable excitation orders, and 24 / 16 topologies (24 pole pieces and 16 poles) with 16th, 24th, 48th, and 96th orders being the most desirable excitation orders. Other topologies are known to those skilled in the art. The techniques described above can also reduce the mechanical resonance of rotors in machines employing these other topologies.

[0116] Undoubtedly, those skilled in the art will conceive of many other effective alternatives. It should be understood that the present invention is not limited to the embodiments described above, but includes modifications that are obvious to those skilled in the art and fall within the scope of the appended claims.

Claims

1. A method of controlling an axial flux machine, characterized by, The axial flux machine includes: a stator including a stator housing enclosing a plurality of stator pole pieces circumferentially spaced around an axis of the machine, each stator pole piece having a coil assembly wound thereon to generate a magnetic field; and a rotor including a permanent magnet assembly and mounted for rotation about the axis of the machine, the rotor being spaced from the stator along the axis of the machine to define a gap between the stator and the rotor, the magnetic flux of the machine being generally axial within this gap, the method comprising: The alternating current supplied to the plurality of coils is controlled to inject a compensating current for reducing the mechanical resonance component of the rotor. This compensating current is injected as the rotor rotates within one or more speed ranges, each of the one or more speed ranges comprising a corresponding predetermined speed of the rotor. The alternating current flowing through each coil is represented as a vectorized DC component comprising mutually orthogonal DC components and orthogonal current components. The compensation current includes a modulation current component added to at least one of the quadrature current component and the DC component. The modulation current component has: an electrical frequency that varies with the rotational speed of the rotor within a frequency range between a first frequency and a second frequency, the frequency range including a frequency substantially the same as the fundamental mechanical resonance frequency of the rotor; and a phase that is different from the fundamental mechanical resonance frequency of the rotor.

2. The method of claim 1, wherein, One or more of the corresponding predetermined speeds of the rotor depend on one or more corresponding mechanical resonant excitation orders of the rotor.

3. The method of claim 2, wherein, The one or more corresponding mechanical resonance excitation orders are one or more of the 12th, 18th, 36th and 72nd excitation orders.

4. The method of claim 2, wherein, One or more of the corresponding predetermined speeds of the rotor are defined by the following relationship: 。 5. The method of claim 1, wherein, Each of the rotor's speed ranges is based on a percentage change in the rotor's fundamental mechanical resonant frequency for a given mechanical resonant excitation order.

6. The method of claim 5, wherein, The percentage change in the rotor's basic mechanical resonance frequency is ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's basic mechanical resonance frequency.

7. The method of claim 1, wherein, In each of the one or more speed ranges of the rotor, the amplitude of the compensation current varies obliquely between a lower amplitude and a peak amplitude in at least a portion of the speed range of the rotor, the peak amplitude of the compensation current substantially coinciding with the corresponding predetermined speed of the rotor.

8. The method of claim 1, wherein, include: Vibration data is received from a vibration sensor, which detects mechanical vibrations within the rotor. Identify the mechanical resonance components of the rotor from the vibration data; as well as The compensation current is injected in response to the identified mechanical resonance component of the rotor.

9. The method of claim 8, wherein, The compensation current is injected only when the identified mechanical resonance component is greater than the threshold.

10. The method of claim 8, wherein, The amplitude of the compensation current is proportional to the amplitude of the identified mechanical resonance component.

11. The method of claim 8, wherein, The vibration sensor is an accelerometer.

12. The method of claim 1, wherein, In each of the one or more speed ranges of the rotor, the modulated current component has a frequency at the first frequency when the rotor rotates at a speed corresponding to the lowest speed in the corresponding speed range of the rotor; The modulated current component has a frequency at the second frequency when the rotor rotates at a speed corresponding to the highest speed within the corresponding speed range of the rotor.

13. The method of claim 1, wherein, In each of the one or more speed ranges of the rotor, the modulated current component has a frequency substantially the same as the fundamental mechanical resonant frequency of the rotor when it is at a speed corresponding to the respective predetermined speed.

14. The method of claim 12, wherein, The first frequency is lower than the second frequency.

15. The method of claim 12, wherein, The percentage change of the modulation current component within the frequency range between the first frequency and the second frequency based on the rotor's fundamental mechanical resonance frequency, wherein the percentage change of the rotor's fundamental mechanical resonance frequency is ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonance frequency.

16. The method of claim 1, wherein, The alternating current supplied to the plurality of coils is a three-phase alternating current, wherein the DC component and the quadrature current component represent the vectorized DC component of the combination result of all three phases.

17. The method of claim 1, wherein, The axial flux machine is an electric motor or a generator.

18. A controller for controlling an axial flux machine, characterized in that, The axial flux machine includes: a stator including a stator housing enclosing a plurality of stator pole pieces circumferentially spaced around an axis of the machine, each stator pole piece having a coil assembly wound thereon to generate a magnetic field; and a rotor including a permanent magnet assembly and mounted for rotation about the axis of the machine, the rotor being spaced from the stator along the axis of the machine to define a gap between the stator and the rotor, the magnetic flux of the machine being generally axial within this gap, and the controller including: One or more electrical input terminals for receiving one or more currents; One or more electrical output terminals for supplying one or more alternating currents to the plurality of coils of the axial flux machine. The controller is used for: The alternating current supplied to the plurality of coils is controlled to inject a compensating current for reducing the mechanical resonance component of the rotor. This compensating current is injected as the rotor rotates within one or more speed ranges, each of the one or more speed ranges comprising a corresponding predetermined speed of the rotor. The alternating current flowing through each coil is represented as a vectorized DC component comprising mutually orthogonal DC components and orthogonal current components. The compensation current includes a modulation current component added to at least one of the quadrature current component and the DC component. The modulation current component has: an electrical frequency that varies with the rotational speed of the rotor within a frequency range between a first frequency and a second frequency, the frequency range including a frequency substantially the same as the fundamental mechanical resonance frequency of the rotor; and a phase that is different from the fundamental mechanical resonance frequency of the rotor.

19. The controller according to claim 18, characterized in that, One or more of the corresponding predetermined speeds of the rotor depend on one or more corresponding mechanical resonant excitation orders of the rotor.

20. The controller according to claim 19, characterized in that, The one or more corresponding mechanical resonance excitation orders are one or more of the 12th, 18th, 36th and 72nd excitation orders.

21. The controller according to claim 19, characterized in that, One or more of the corresponding predetermined speeds of the rotor are defined by the following relationship: 。 22. The controller according to claim 18, characterized in that, Each of the rotor's speed ranges is based on a percentage change in the rotor's fundamental mechanical resonant frequency for a given resonant excitation order.

23. The controller according to claim 22, characterized in that, The percentage change in the rotor's basic mechanical resonance frequency is ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's basic mechanical resonance frequency.

24. The controller according to claim 18, characterized in that, The controller is configured to cause the amplitude of the compensation current to vary obliquely between a lower amplitude and a peak amplitude in at least a portion of the rotor's rotational speed range, wherein the peak amplitude of the compensation current substantially coincides with the corresponding predetermined rotational speed of the rotor.

25. The controller according to claim 18, characterized in that, include: The vibration sensor input terminal is used to receive vibration data from a vibration sensor, which detects mechanical vibrations within the rotor. The controller is used for: Identify the mechanical resonance components of the rotor from the vibration data; and The compensation current is injected in response to the identified mechanical resonance component of the rotor.

26. The controller according to claim 25, characterized in that, The controller is used to inject the compensation current only when the identified mechanical resonance component is greater than a threshold.

27. The controller according to claim 25, characterized in that, The amplitude of the compensation current is proportional to the amplitude of the identified mechanical resonance component.

28. The controller according to claim 25, characterized in that, The vibration sensor is an accelerometer.

29. The controller according to claim 18, characterized in that, In each of the one or more speed ranges of the rotor, the controller controls the modulated current component to have a frequency at the first frequency when the rotor rotates at a speed corresponding to the lowest speed in the respective speed range of the rotor; The controller controls the modulated current component to have a frequency at the second frequency when the rotor rotates at a speed corresponding to the highest speed within the corresponding speed range of the rotor.

30. The controller according to claim 18, characterized in that, In each of the one or more speed ranges of the rotor, the controller controls the modulated current component to have a frequency substantially the same as the fundamental mechanical resonant frequency that the rotor has when it is at a speed corresponding to the respective predetermined speed.

31. The controller according to claim 29, characterized in that, The first frequency is lower than the second frequency.

32. The controller according to claim 29, characterized in that, The percentage change of the modulation current component within the frequency range between the first frequency and the second frequency based on the rotor's fundamental mechanical resonance frequency, wherein the percentage change of the rotor's fundamental mechanical resonance frequency is ±1%, ±5%, ±10%, ±15%, or ±20% of the rotor's fundamental mechanical resonance frequency.

33. The controller according to claim 18, characterized in that, The one or more alternating currents supplied to the plurality of coils are three-phase alternating currents, wherein the DC component and the quadrature current component represent the vectorized DC component of the combined result of all three phases.

34. The controller according to claim 18, characterized in that, The axial flux machine is an electric motor or a generator.

35. An axial flux machine, characterized in that, include: The stator includes a stator housing containing a plurality of stator pole pieces circumferentially spaced around the axis of the machine, each stator pole piece having a coil group wound thereon to generate a magnetic field; and A rotor, comprising an assembly of permanent magnets and mounted for rotation about the axis of the machine, is spaced apart from the stator along the axis of the machine to define a gap between the stator and the rotor, within which the magnetic flux of the machine is generally axial. The axial flux machine is connected to a controller according to claim 18, which supplies alternating current to the plurality of coils.

36. The axial flux machine according to claim 35, characterized in that, It includes a vibration sensor, which is mounted on the machine to sense vibrations within the rotor.

37. The axial flux machine according to claim 36, characterized in that, The vibration sensor is an accelerometer.

38. The axial flux machine according to claim 35, characterized in that, The stator housing has an annular shape that forms a hollow region around the axis of the machine, and the rotor is formed of an annular structure and has a hollow central region around the axis of the machine.

39. The axial flux machine according to claim 35, characterized in that, The machine includes a second rotor located on the side of the stator opposite to the rotor, the second rotor including a group of permanent magnets on a first side of the second rotor facing the stator, the second rotor being mounted for rotation relative to the stator about the axis of the machine, the second rotor being spaced apart from the stator along the axis of the machine to define an axial gap between the stator and the second rotor, within which the magnetic flux of the machine is generally axial.

40. The axial flux machine according to claim 35, characterized in that, The machine is either an electric motor or a generator.

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