Slotless synchronous permanent magnet motor
阅读说明:本技术 无槽同步永磁电机 (Slotless synchronous permanent magnet motor ) 是由 J·G·米林格 于 2019-01-29 设计创作,主要内容包括:本发明涉及一种无槽同步永磁电机(1),其包括:转子(5);以及定子(3),其配置成与所述转子进行电磁交互作用;其中,所述转子(5)设置有第一导电金属层(5a),所述第一导电金属层(5a)配置成产生谐波转子凸极性。(The invention relates to a slotless synchronous permanent magnet motor (1), comprising: a rotor (5); and a stator (3) configured to electromagnetically interact with the rotor; wherein the rotor (5) is provided with a first electrically conductive metal layer (5a), the first electrically conductive metal layer (5a) being configured to generate a harmonic rotor saliency.)
1. A slotless synchronous permanent magnet electrical machine (1; 1'; 1 ") comprising:
a rotor (5; 5'); and
a stator (3; 3') configured to interact electromagnetically with the rotor (5; 5');
wherein the rotor (5; 5') is provided with a first conductive metal layer (5 a; 5a '), the first conductive metal layer (5 a; 5a ') being configured to generate a harmonic rotor saliency.
2. The slotless synchronous permanent magnet motor (1; 1 '; 1 ") of any of the preceding claims, wherein the first metal layer (5 a; 5 a'; 5 a") is made of copper or aluminum.
3. A slotless synchronous permanent magnet electrical machine (1; 1') according to any of the preceding claims, wherein the rotor (5; 5'; 5 ") is provided with a second electrically conductive metal layer (5 b; 5b '), the second electrically conductive metal layer (5 b; 5b') being configured to generate a harmonic rotor saliency.
4. A slotless synchronous permanent magnet electrical machine (1; 1 '; 1 ") according to claim 3, wherein the first conductive metal layer (5 a; 5a ') and the second metal layer (5 b; 5b ') are electrically connected.
5. A slotless synchronous permanent magnet electrical machine (1; 1 ") according to any of the preceding claims, wherein, in a cross-section of the rotor (5; 5"), the first metal layer (5 a; 5a ") is circumferentially arranged on the rotor forming an arc of a first sector (7 a; 7 a").
6. The slotless synchronous permanent magnet motor (1) of claim 5 depending on claim 3 or 4, wherein, in a cross-section of the rotor (5), the second metal layer (5b) is circumferentially arranged on the rotor (5) forming an arc of the second sector (7b), the center (9b) of the arc of the second sector (7b) making an angle (α) with the center (9a) of the arc of the first sector (7 a).
7. Slotless synchronous permanent magnet electric machine (1) according to claim 6, wherein the angle (a) is about 180 °.
8. A slotless synchronous permanent magnet electric machine (1') according to claim 3, wherein a first metal layer (5a ') is arranged between the magnet sections (10a-10d) of the rotor (5') to form a first central plane of the rotor (5'), and a second metal layer (5b ') is arranged between the magnet sections (10a-10d) of the rotor (5') to form a second central plane of the rotor (5'), which is perpendicular to the first central plane.
9. A slotless synchronous permanent magnet electrical machine (1; 1 '; 1 ") according to any of the preceding claims, wherein the first metal layer (5 a; 5a '; 5 a") extends along a substantial part of the axial direction length of the rotor (5; 5 '; 5 ").
10. A slotless synchronous permanent magnet motor system (12) comprising:
a slotless synchronous permanent magnet electric machine (1; 1'; 1 ") according to any one of claims 1-9;
a power converter (14) configured to inject a current or voltage into the synchronous permanent magnet electrical machine (1; 1'; 1 ");
a current sensor (16) configured to measure a current generated in the synchronous permanent magnet machine (1; 1') as a result of a current or voltage injected by the power converter (14); and
a control system (18) configured to determine a rotor position based on the current measured by the current sensor (16).
11. The slotless synchronous permanent magnet motor system (12) of claim 10, wherein the power converter (14) is configured to inject current into the synchronous permanent magnet motor (1; 1 '; 1 ") using a switching frequency of switching of the power converter (14) that is sufficiently high for a skin depth in the first metal layer (5 a; 5a '; 5 a") to be smaller than a thickness h of the first metal layer (5 a; 5a '; 5a "), the skin depth being defined by
where ρ is the resistivity of the first metal layer (5 a; 5a '), μ is the permeability of the first metal layer (5 a; 5a'), and f is the switching frequency.
12. The slotless synchronous permanent magnet motor system (12) of claim 10 or 11 wherein the control system (18) is configured to determine an inductance of each electrical phase based on a current ripple of the measured current, wherein the control system (18) is configured to determine a rotor position based on the inductance.
13. The slotless synchronous permanent magnet motor system (12) of claim 12 wherein the rotor position is determined by comparing the inductance to a reference inductance in a look-up table associated with a particular rotor position.
14. The slotless synchronous permanent magnet motor system (12) of any one of claims 10-13 wherein the current sensor (16) is configured to oversample a current ripple of the measured current.
15. A slotless synchronous permanent magnet motor system (12) according to any of claims 10-14 wherein the stator (3) has a plurality of stator phase windings and the control system (18; 18') is configured to compensate for geometric asymmetry of the stator phase windings.
16. The slotless synchronous permanent magnet motor system (12) of claim 15 wherein the control system (18; 18') comprises a first transformation block (23), the first transformation block (23) being configured to perform the compensation by transformation from the rotor reference coordinate system to a three-phase coordinate system with the voltage reference of the power converter (14), the transformation taking into account the displacement of the stator phase windings defining the geometric asymmetry in the circumferential direction of the stator (3).
17. The slotless synchronous permanent magnet motor system (12) of claim 10 or 11 or claim 15 or 16 wherein the control system (18') comprises: a second transformation block (25), the second transformation block (25) being configured to transform the current measured by the current sensor (16) to obtain a d-axis current and a q-axis current; a demodulator block (27), the demodulator block (27) configured to demodulate the q-axis current; and an estimator block (29) comprising a PI observer, the estimator block (29) configured to determine the rotor position using a feed forward of the demodulated q-axis current.
18. A method of determining a rotor position of a rotor of a slotless synchronous permanent magnet electric machine (1; 1'; 1 ") according to any one of claims 1-9, wherein the method comprises:
a) controlling the power converter (14) to inject current or voltage into the slotless synchronous permanent magnet motor (1; 1'; 1 ");
b) obtaining a magnetic field in a slotless synchronous permanent magnet motor (1; 1'; 1 ") the current measured due to the injected current or voltage; and
c) the rotor position is determined from the current.
19. The method of claim 17, wherein the controlling comprises: using a switching frequency of the switches of the power converter (14), the switching frequency being sufficiently high for making a skin depth in the first metal layer (5 a; 5a ') smaller than a thickness h of the first metal layer (5 a; 5a'), the skin depth being defined byDefining;
where ρ is the resistivity of the first metal layer, μ is the permeability of the first metal layer (5 a; 5a') and f is the switching frequency.
20. The method according to claim 17, wherein the stator (3) has a plurality of stator phase windings, wherein step a) comprises compensating for geometric asymmetry of the stator phase windings.
21. The method of claim 19, wherein the compensating comprises: the compensation is performed with a transformation of the voltage reference of the power converter (14) from the rotor reference frame to a three-phase coordinate frame, said transformation taking into account the displacement of the stator phase windings defining the geometric asymmetry in the circumferential direction of the stator (3).
22. The method of claim 17 or any of claims 19-20, wherein said determining comprises: transforming the measured currents to obtain d-axis currents and q-axis currents; demodulating the q-axis current; and using feed forward of the demodulated q-axis current with an estimator block comprising a PI observer.
Technical Field
The present invention generally relates to synchronous machines. And in particular to a slotless synchronous permanent magnet machine.
Background
Slotless permanent magnet motors are often the first choice for applications with high power density requirements, such as industrial assembly and impact tools. This type of application requires advanced motor control, which is typically achieved by a power converter connected to the motor and operating by Pulse Width Modulation (PWM).
For the above applications, commutation sensors or angular encoders are typically used for rotor position detection fed back within the speed control loop of the drive circuit. A disadvantage of using sensors is the increased complexity and size of the motor module.
"sensorless estimation of rotor position for cylindrical brushless dc motors using eddy currents" (Tomita et al, fourth IEEE advanced motion control international seminar-AMC' 96-MIE, 3 months 1996,
Disclosure of Invention
One common method for sensorless rotor position detection for slotted motors involves the use of a salient pole rotor design. By signal processing of the harmonic phase currents, the rotor position can be detected. Salient pole rotor designs for slotless motors require the removal of active permanent magnet material, resulting in reduced motor performance compared to slotted motors.
In view of the above, it is an object of the present invention to provide a slotless synchronous permanent magnet motor which solves or at least alleviates the above mentioned problems.
Thus, according to a first aspect of the present invention, there is provided a slotless synchronous permanent magnet PM machine comprising: a rotor and a stator configured to electromagnetically interact with the rotor, wherein the rotor is provided with a first electrically conductive metal layer configured to generate a harmonic rotor saliency.
From a magnetic perspective, conductive materials (e.g., copper and aluminum) behave like air at low frequencies, but reflect high frequency magnetic flux according to renz's law. For skin depths less than the thickness h of the conductive layer, the reflection becomes significant. Since the rotor is provided with the first metal layer, the high-frequency saliency of the rotor can be obtained. Thus, with the present design, rotor position detection may be achieved based on a salient pole rotor behavior of high switching frequency configured to control the switching of the power converter of the slotless synchronous PM machine. In particular, rotor position detection may be provided with minimal impact on motor performance.
Furthermore, since no sensors are needed to determine the rotor position, the slotless synchronous PM machine can become shorter, cheaper and more reliable.
The structure of providing the first conductive layer on the rotor of a slotless synchronous PM machine is surprisingly much more accurate for rotor position determination than the slotted structure disclosed in the paper by Tomita et al. According to Tomita's paper, the maximum error in rotor position estimation is 26 °, which is not useful for many control schemes, whereas in the case of slotless synchronous PM machines the accuracy can be below ± 5 °, down to ± 2 °. Additionally, for a slotted motor, the rotor position estimate is related to the motor load, whereas for a slotless synchronous PM motor, the rotor position estimate is independent of the motor load. Therefore, the proposed slotless synchronous PM machine structure is more useful for rotor position determination. For example, instead of having to use six-step commutation as is the case with Tomita, motor control involving sinusoidal commutation may be used, so that torque ripple may be eliminated and smooth motion and accurate motor control may be provided.
"rotor position" generally refers to an electric rotor position. For example, the rotor position may be a rotor angle between a stationary coordinate system (e.g., an α β coordinate system) and a rotor reference coordinate system (e.g., a d-q coordinate system).
Harmonic rotor saliency refers to rotor saliency relative to harmonics of the fundamental frequency. The fundamental frequency is the number of revolutions per second of the rotor.
The first metal layer may be a first metal sheet or a first metal coating.
The outer surface of the first metal layer may be flush or substantially flush with the outer surface of the rotor.
The first metal layer may be made of a weakly magnetic material (e.g., a paramagnetic material or a diamagnetic material).
According to one embodiment, the first metal layer is made of copper or aluminum. For example, the first metal layer may be composed of copper or aluminum. Alternatively, the first metal layer may be made of a conductive alloy.
The stator may be provided with a plurality of windings, i.e. stator phase windings, each winding being configured to be connected to a respective electrical phase. In particular, there are two winding portions per winding. The winding portions of the windings are connected to respective terminals of the power converter. The terminals connected to the windings are associated with the same electrical phase.
In examples where the first metal layer is the only metal layer providing harmonic rotor saliency, the first metal layer may be configured to align with both winding portions of the electrical phase winding at the same time at any rotational position of the rotor.
According to one embodiment, the rotor is provided with a second conductive metal layer configured to generate harmonic rotor saliency.
The second metal layer may be a second metal sheet or a second metal coating.
The outer surface of the second metal layer may be flush or substantially flush with the outer surface of the rotor.
The second metal layer may be made of a weakly magnetic material (e.g., a paramagnetic material or a diamagnetic material).
The second metal layer may be made of copper or aluminum. For example, the second metal layer may be composed of copper or aluminum. Alternatively, the second metal layer may be made of a conductive alloy.
In examples including a first metal layer and a second metal layer, the first metal layer and the second metal layer may be configured such that the first metal layer and the second metal layer are simultaneously alignable with respective winding portions of an electrical phase.
According to one embodiment, the first conductive metal layer is electrically connected to the second metal layer. For example, the first conductive metal layer and the second conductive metal layer may be connected to each other at each end portion or end portion of the rotor in the axial direction. Thus, the first and second conductive metal layers can be connected and short-circuited at two locations, one at each end portion or end of the rotor. Thereby, the currents induced in the first and second conductive metal layers will flow in opposite directions with respect to each other, so that the currents will obtain a return path. When a current in the direction of the d-axis is encountered, the induced current level will therefore increase, resulting in a higher rotor saliency. Thus, a stronger saliency indication with a higher signal-to-noise ratio may be obtained. Therefore, the estimation of the rotor position can become more accurate.
According to one embodiment, the first metal layer is circumferentially arranged on the rotor, forming an arc of a first sector, in a cross-section of the rotor.
In embodiments including only the first metal layer, the central angle of the first sector may be at least 120 degrees, such as 120 degrees. Advantageously, this arrangement is used in a synchronous PM machine of the concentrated winding type, which is slotless. In this case, the first metal layer may advantageously be arranged in an inclined manner in the axial direction of the rotor. This improves the detectability of the electrical phase inductance change caused by the harmonic rotor saliency.
According to one embodiment, the second metal layer is circumferentially arranged on the rotor in a cross-section of the rotor forming a second sector of a circle arc, the centre of the second sector of the circle arc being angled with respect to the centre of the circle arc of the first sector.
According to one embodiment, the angle is about 180 °. Having an angle of about 180 ° means a range of 180 ° ± 20 °, for example a range of 180 ° ± 10 °. Alternatively, the angle may be 180 °.
According to one embodiment, the first metal layer is arranged between the magnet sections of the rotor to form a first central plane of the rotor, and the second metal layer is arranged between the magnet sections of the rotor to form a second central plane of the rotor perpendicular to the first central plane.
According to one embodiment, the first metal layer extends along a majority of the axial direction length of the rotor. In particular, the first metal layer may form a continuous structure from a short end portion thereof to an opposite short end portion.
The second metal layer may extend along a majority of the axial length of the rotor. In particular, the second metal layer may form a continuous structure from a short end portion thereof to an opposite short end portion.
According to a second aspect of the present invention, there is provided a slotless synchronous PM machine system comprising: a slotless synchronous PM machine according to the first aspect; a power converter configured to inject a current or voltage to the slotless synchronous PM motor; a current sensor configured to measure a current generated in the slotless synchronous PM motor due to a current or voltage injected by the power converter; and a control system configured to determine a rotor position based on the current measured by the current sensor.
Each current sensor may be configured to measure a current in a respective electrical phase. In particular, the current sensors may be configured to measure the current in the respective windings of the stator. Therefore, the number of measured currents is generally the same as the number of electrical phases of the slotless synchronous PM motor.
In some embodiments, the current measured by the current sensor may be a current ripple. In this case, the control system is configured to determine the rotor position based on the current ripple.
The current ripple may be a commutation-induced current ripple. Commutation occurs when the polarity of the electrical phase changes.
The power converter may include wide bandgap semiconductor switches, e.g., wide bandgap transistors.
According to one embodiment, the power converter is configured to inject current into the slotless synchronous PM machine using a switching frequency of switches of the power converter that is sufficiently high for a skin depth in the first metal layer that is less than the thickness h of the first metal layer
Defining;where ρ is the resistivity of the first metal layer, μ is the permeability of the first metal layer, and f is the switching frequency.
When the rotor is provided with more than one metal layer, the above considerations regarding skin depth and thickness apply to all metal layers, for example the second metal layer.
Slotless synchronous PM machine systems can utilize high switching frequencies, thereby enabling the use of thinner first/second metal layers, thereby minimizing damage to machine performance.
For example, the switching frequency may be about 100 khz.
According to one embodiment, the injected voltage may include a high frequency voltage component, such as a high frequency sinusoidal voltage component. The high frequency components may be injected specifically for rotor position determination purposes. The high frequency component may have an angular frequency higher than the maximum angular frequency of the slotless synchronous PM machine.
According to one embodiment, the control system is configured to determine the inductance of each electrical phase based on the current ripple of the measured current, wherein the control system is configured to determine the rotor position based on the inductance.
For example, the inductance of each phase may be determined by the slope or derivative of the current ripple between commutations
Is determined thereby to passThe inductance L of the electrical phase is obtained, where U is the phase voltage.According to one embodiment, the rotor position is determined by comparing the inductance to a reference inductance in a look-up table associated with a particular rotor position. In particular, the combination of inductances, and in particular the matched reference inductances, provides a single rotor position value in the look-up table.
According to one embodiment, the current sensor is configured to oversample a current ripple of the measured current. Oversampling is understood as a sampling frequency that is higher than the Nyquist frequency.
According to one embodiment, the stator has a plurality of stator phase windings, wherein the control system is configured to compensate for geometric asymmetry of the stator phase windings.
According to studies conducted by the inventors, it has been demonstrated that geometric asymmetry of the stator phase windings (i.e. displacement of one or more stator phase windings in the circumferential direction of the stator such that the symmetry along the radial plane becomes imperfect due to non-ideal manufacturing) can affect the estimation of the rotor position. Specifically, the geometric asymmetry increases the estimation error. By compensating for the geometric asymmetry, the estimation/determination of the rotor position can be made more accurate.
According to one embodiment, the control system comprises a first transformation block configured to perform the compensation by utilizing a transformation of a voltage reference of the power converter from the rotor reference coordinate system to a three-phase coordinate system, the transformation taking into account a displacement of the stator phase winding in a circumferential direction of the stator defining the geometric asymmetry.
In particular, the angular displacement of each stator phase winding may be used to provide a compensated transformation. The transformation may be a linear operator (e.g., a matrix) for transforming between a rotor reference coordinate system and an abc coordinate system or transforming between a stator coordinate system and an abc coordinate system.
According to one embodiment, a control system comprises: a second transformation block configured to transform the current measured by the current sensor to obtain a d-axis current and a q-axis current; a demodulator block configured to demodulate the q-axis current; and an estimator block comprising a PI observer configured to use feed forward of the demodulated q-axis current for determining the rotor position.
Thus, the transient characteristics are improved. In particular, in the case of a transient state, a steady state in which the estimation error is small can be obtained quickly.
According to a third aspect of the present invention, there is provided a method of determining a rotor position of a rotor of a slotless synchronous PM electrical machine according to the first aspect, wherein the method comprises: controlling a power converter to inject current or voltage into a slotless synchronous PM motor; the current resulting from the injected current measured in the slotless synchronous PM machine is obtained and the rotor position is determined from the current.
According to oneEmbodiments, the controlling comprises using a switching frequency of switches of the power converter, the switching frequency being sufficiently high for a skin depth in the first metal layer to be less than a thickness h of the first metal layer, the skin depth being defined by
Defining;where ρ is the resistivity of the first metal layer, μ is the permeability of the first metal layer, and f is the switching frequency.
According to one embodiment, the stator has a plurality of stator phase windings, wherein step a) comprises compensating for geometric asymmetry of the stator phase windings.
According to one embodiment, the compensation comprises a transformation from a rotor reference frame to a three-phase coordinate frame with a voltage reference of the power converter, the transformation taking into account a displacement of the stator phase windings in a circumferential direction of the stator defining the geometric asymmetry.
According to one embodiment, the determining comprises: transforming the measured currents to obtain d-axis currents and q-axis currents; demodulating the q-axis current; and using feed forward of the demodulated q-axis current with an estimator block comprising a PI observer.
According to a fourth aspect of the invention, there is provided a computer program comprising computer code which, when executed by processing circuitry of a slotless synchronous PM motor system, causes the slotless synchronous PM motor system to perform the steps of the method according to the third aspect.
According to a fifth aspect of the invention, there is provided a power tool comprising a slotless synchronous PM motor according to the first aspect.
According to a sixth aspect of the present invention there is provided a power tool comprising a slotless synchronous PM motor system according to the second aspect.
In general, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "an element, device, component, means, etc" are to be interpreted openly as referring to at least one example of the element, device, component, means, etc., unless explicitly stated otherwise.
Drawings
Specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:
fig. 1a schematically shows a cross section of an example of a slotless synchronous PM machine;
fig. 1b schematically shows a cross section of a rotor of the slotless synchronous PM machine in fig. 1 a;
fig. 2 schematically shows a cross-section of another example of a slotless synchronous PM machine;
fig. 3 schematically shows a cross-section of yet another example of a slotless synchronous PM machine;
FIG. 4 schematically illustrates a block diagram of a slotless synchronous PM motor system;
FIG. 5 is a flow chart of a method of determining a rotor position of a rotor of a slotless synchronous PM motor; and
fig. 6 schematically shows an example of an alternative control scheme for controlling a slotless synchronous PM.
Detailed Description
The present inventive concepts will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like reference numerals refer to like elements throughout the specification.
Fig. 1 shows an example of a slotless synchronous PM machine. The slotless
In the case of a geometrically asymmetric stator phase winding, the winding sections do not lie exactly opposite one another. In particular, there may be a small displacement in the circumferential direction of the
The slotless
The
The
According to a variant, the
Fig. 1b depicts the
The first
Fig. 2 shows another example of a slotless synchronous PM machine. The slotless synchronous PM machine 1' is similar to the example described with reference to fig. 1a and 1 b. However, the rotor 5' differs to some extent from the
Also in this case, according to a variant, the
Fig. 3 shows another example of a slotless synchronous PM machine. The slotless
In this case, geometric asymmetry of the stator phase winding may also exist. According to some examples, compensation may be provided for such geometric asymmetry, as described further below.
The slotless
Fig. 4 depicts an example of a slotless synchronous PM machine system 12. The slotless synchronous PM machine system 12 includes a slotless
The power converter 14 is configured to be connected to the windings of the
For example, the switching of the power converter 14 may be controlled by PWM. To this end, for example, the gates of the switches may be controlled to selectively set the switches to an on or off state according to a control signal using PWM.
The power converter 14 and the current sensor 16 form a drive circuit of the slotless
The current sensor 16 is configured to measure the current of the
The
For example, the processing circuitry 18b may utilize any combination of one or more suitable Central Processing Units (CPUs), multiprocessors, microcontrollers, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), or the like, capable of executing any of the operations disclosed herein in connection with motor rotor position determination.
For example, the storage medium 18a may be implemented as a non-volatile storage medium of a device in a memory (e.g., a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM)), and more particularly, in an external memory (e.g., a USB (universal serial bus) memory) or in a flash memory (e.g., a compact flash memory).
In step a), the controller controls the power converter 14 to inject current into the windings of the stator. Such current control typically includes switching control of the switches using PWM as previously described.
Preferably, the switching frequency for controlling the switching of the power converter 14 is sufficiently high for the skin depth in the
In step b), the current sensor 16 measures the current ripple in the windings of the stator. The current ripple measured in each electrical phase is typically a commutation-induced current ripple, which may be derived from the switching control of the switches of the power converter 14. The measured current ripple is obtained by the
Slope or derivative of current ripple between commutations
May be determined based on the current ripple measurement. The phase voltage U of each electrical phase may also be measured.In step c), the rotor position is determined by the
When the inductance L of each electrical phase has been determined, each inductance L may be compared to a reference inductance of the corresponding phase in a look-up table. The reference inductance is associated with a specific rotor position, i.e. the combination of reference inductances matching the determined inductance provides the rotor position (typically the rotor angle).
The rotor angle may then be used to control the power converter by the
FIG. 6 depicts an example of an alternative control scheme for determining rotor position. The control scheme shown in fig. 5 may be implemented as software and/or hardware by the processing circuitry 18 b. For simplicity, power converter 14 and current sensor 16 are not shown.
The exemplary control system 18' includes a high
The exemplary control system 18' also includes a
The exemplary control system 18' includes an
Thus, the method described with reference to fig. 6 is similar to the method described with reference to fig. 5 in the general steps a) -c), but instead of measuring, not using current ripple and not determining the inductance, a high frequency voltage component is injected and the phase currents are measured and processed in an exemplary control scheme.
In some examples, geometric asymmetry of the stator phase windings may be compensated for. Thus, the
The transformation between the rotor reference frame and the abc frame may be configured to take into account the displacement or angular displacement of the stator phase windings in the circumferential direction of the stator that defines the geometric asymmetry. The transformation between different coordinate systems is typically performed by a rotation matrix. The rotation matrix, in particular the parameters of the cosine and sine functions, may comprise respective components related to the angular displacement of the stator phase windings.
In all examples provided herein, the rotor is housed by the stator. However, as an alternative to any of these examples, it is also possible to arrange the rotor around the stator in the opposite configuration, i.e. a so-called outer rotor motor.
The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.
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