Locked rotor detection method, locked rotor detection device and control system of permanent magnet synchronous motor

文档序号:1415485 发布日期:2020-03-10 浏览:12次 中文

阅读说明:本技术 永磁同步电机的堵转检测方法、堵转检测装置和控制系统 (Locked rotor detection method, locked rotor detection device and control system of permanent magnet synchronous motor ) 是由 程云峰 于 2018-08-31 设计创作,主要内容包括:本发明公开了一种永磁同步电机的堵转检测方法、堵转检测装置和控制系统,所述堵转检测方法包括以下步骤:获取永磁同步电机的相电压和相电流;根据相电压或相电流,计算得到定子的热功率;根据热功率,判断永磁同步电机是否发生堵转。本发明实施例的堵转检测方法,弥补了相关技术的不足,且可以实现转矩电流控制模式或者速度控制模式下的堵转检测,实用性强,并且安全可靠性高。(The invention discloses a locked rotor detection method, a locked rotor detection device and a control system of a permanent magnet synchronous motor, wherein the locked rotor detection method comprises the following steps: acquiring phase voltage and phase current of the permanent magnet synchronous motor; calculating the thermal power of the stator according to the phase voltage or the phase current; and judging whether the PMSM is locked rotor or not according to the thermal power. The locked rotor detection method disclosed by the embodiment of the invention makes up the defects of the related technology, can realize locked rotor detection in a torque current control mode or a speed control mode, and has strong practicability and high safety and reliability.)

1. A locked rotor detection method of a permanent magnet synchronous motor is characterized by comprising the following steps:

obtaining phase voltage and phase current of the permanent magnet synchronous motor;

calculating the thermal power of the stator according to the phase voltage or the phase current;

and judging whether the PMSM is locked rotor or not according to the thermal power.

2. The locked rotor detection method according to claim 1, wherein the determining whether the PMSM is locked rotor according to the thermal power comprises:

calculating to obtain input power according to the phase voltage and the phase current;

and judging whether the PMSM is locked-rotor or not according to the input power and the thermal power.

3. The locked rotor detection method according to claim 2, wherein the determining whether the PMSM is locked rotor according to the input power and the thermal power comprises:

determining a thermal power threshold according to the input power;

and if the thermal power is continuously greater than the thermal power threshold value within a preset time, judging that the permanent magnet synchronous motor is locked.

4. The locked rotor detection method according to claim 3, wherein if the thermal power is continuously greater than the thermal power threshold value within a preset time, determining that the permanent magnet synchronous motor is locked rotor comprises:

when the thermal power is larger than the thermal power threshold, timing is started, and timing data are generated;

if the thermal power is equal to or less than the thermal power threshold, clearing the timing data;

and when the timing data is equal to the preset time, judging that the permanent magnet synchronous motor is locked.

5. The locked rotor detection method according to claim 3, wherein the thermal power threshold is equal to or greater than 80% of the input power.

6. The utility model provides a locked rotor detection device of PMSM which characterized in that includes:

the acquisition module is used for acquiring phase voltage and phase current of the permanent magnet synchronous motor;

the calculation module is used for calculating the thermal power of the stator according to the phase voltage or the phase current;

and the judging module is used for judging whether the PMSM is locked rotor or not according to the thermal power.

7. The locked rotor detection device according to claim 6, wherein the judging module comprises:

the computing unit is used for computing to obtain input power according to the phase voltage and the phase current;

and the judging unit is used for judging whether the permanent magnet synchronous motor is locked according to the input power and the thermal power.

8. The locked-rotor detection device according to claim 7, wherein the determination unit is specifically configured to:

determining a thermal power threshold according to the input power;

and if the thermal power is continuously greater than the thermal power threshold value within a preset time, judging that the permanent magnet synchronous motor is locked.

9. The locked-rotor detection device according to claim 8, wherein the determination unit is configured to:

when the thermal power is larger than the thermal power threshold, timing is started, and timing data are generated;

if the thermal power is equal to or less than the thermal power threshold, clearing the timing data;

and when the timing data is equal to the preset time, judging that the permanent magnet synchronous motor is locked.

10. The stall detection device of claim 8, wherein the thermal power threshold is equal to or greater than 80% of the input power.

11. A control system of a permanent magnet synchronous motor, comprising: a permanent magnet synchronous machine and a stall detection apparatus of a permanent magnet synchronous machine according to any one of claims 6 to 10;

and after the locked rotor detection device judges that the permanent magnet synchronous motor is locked, the permanent magnet synchronous motor is controlled to stop.

12. An electronic device, comprising: memory, processor and computer program stored on the memory and executable on the processor, which when executed by the processor implements the method of stall detection for a permanent magnet synchronous machine according to any of claims 1-5.

13. A non-transitory computer-readable storage medium, on which a computer program is stored, which, when executed by a processor, implements a method of detecting stalling of a permanent magnet synchronous motor according to any one of claims 1-5.

Technical Field

The invention relates to the technical field of permanent magnet synchronous motors, in particular to a locked rotor detection method of a permanent magnet synchronous motor, a locked rotor detection device of the permanent magnet synchronous motor, a control system of the permanent magnet synchronous motor, an electronic device and a non-transitory computer readable storage medium.

Background

When the rotating speed of the motor is zero, the motor still outputs torque, namely, locked rotor occurs. The motor stalling is caused by a plurality of reasons, including mechanical or artificial reasons, for example, the rotor is stuck in contact with the stator, a driven device is stuck, the motor cannot be driven due to too large load of the device, and the like.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the art described above.

Therefore, a first objective of the present invention is to provide a stalling detection method for a permanent magnet synchronous motor, which overcomes the disadvantages of the related art, can implement stalling detection in a torque current control mode or a speed control mode, and has strong practicability and high safety and reliability.

The second purpose of the invention is to provide a locked rotor detection device of a permanent magnet synchronous motor.

A third object of the present invention is to provide a control system of a permanent magnet synchronous motor.

A fourth object of the invention is to propose an electronic device.

A fifth object of the invention is to propose a non-transitory computer-readable storage medium.

In order to achieve the above object, an embodiment of a first aspect of the present invention provides a locked rotor detection method for a permanent magnet synchronous motor, including the following steps: obtaining phase voltage and phase current of the permanent magnet synchronous motor; calculating the thermal power of the stator according to the phase voltage or the phase current; and judging whether the PMSM is locked rotor or not according to the thermal power.

According to the locked rotor detection method of the permanent magnet synchronous motor, the phase voltage and the phase current of the permanent magnet synchronous motor are firstly obtained, then the thermal power of the stator is calculated according to the phase voltage or the phase current, and finally whether the locked rotor occurs to the permanent magnet synchronous motor is judged according to the thermal power. Therefore, the locked rotor detection method makes up the defects of the related technology, can realize locked rotor detection in a torque current control mode or a speed control mode, and has strong practicability and high safety and reliability.

In addition, the locked rotor detection method for the permanent magnet synchronous motor provided by the above embodiment of the present invention may further have the following additional technical features:

in an embodiment of the present invention, the determining whether the pm synchronous motor is locked according to the thermal power includes: calculating to obtain input power according to the phase voltage and the phase current; and judging whether the PMSM is locked-rotor or not according to the input power and the thermal power.

In an embodiment of the present invention, the determining whether the pm synchronous motor is locked according to the input power and the thermal power includes: determining a thermal power threshold according to the input power; and if the thermal power is continuously greater than the thermal power threshold value within a preset time, judging that the permanent magnet synchronous motor is locked.

In an embodiment of the present invention, the determining that the rotation blocking of the permanent magnet synchronous motor occurs if the thermal power is continuously greater than the thermal power threshold within a preset time includes: when the thermal power is larger than the thermal power threshold, timing is started, and timing data are generated; if the thermal power is equal to or less than the thermal power threshold, clearing the timing data; and when the timing data is equal to the preset time, judging that the permanent magnet synchronous motor is locked.

In one embodiment of the invention, the thermal power threshold is equal to or greater than 80% of the input power.

In order to achieve the above object, a second embodiment of the present invention provides a stalling detection device for a permanent magnet synchronous motor, including: the acquisition module is used for acquiring phase voltage and phase current of the permanent magnet synchronous motor; the calculation module is used for calculating the thermal power of the stator according to the phase voltage or the phase current; and the judging module is used for judging whether the PMSM is locked rotor or not according to the thermal power.

According to the locked rotor detection device of the permanent magnet synchronous motor, the phase voltage and the phase current of the permanent magnet synchronous motor are obtained through the obtaining module, the thermal power of the stator is obtained through calculation through the calculating module according to the phase voltage or the phase current, and the judging module is used for judging whether the locked rotor occurs to the permanent magnet synchronous motor or not according to the thermal power. Therefore, the locked rotor detection device makes up the defects of the related technology, can realize locked rotor detection in a torque current control mode or a speed control mode, and is high in practicability, safety and reliability.

In addition, the stalling detection device of the permanent magnet synchronous motor provided by the embodiment of the invention can also have the following additional technical characteristics:

in an embodiment of the present invention, the determining module includes: the computing unit is used for computing to obtain input power according to the phase voltage and the phase current; and the judging unit is used for judging whether the permanent magnet synchronous motor is locked according to the input power and the thermal power.

In an embodiment of the present invention, the determining unit is specifically configured to: determining a thermal power threshold according to the input power; and if the thermal power is continuously greater than the thermal power threshold value within a preset time, judging that the permanent magnet synchronous motor is locked.

In an embodiment of the present invention, the determining unit is configured to: when the thermal power is larger than the thermal power threshold, timing is started, and timing data are generated; if the thermal power is equal to or less than the thermal power threshold, clearing the timing data; and when the timing data is equal to the preset time, judging that the permanent magnet synchronous motor is locked.

In one embodiment of the invention, the thermal power threshold is equal to or greater than 80% of the input power.

In order to achieve the above object, a third embodiment of the present invention provides a control system for a permanent magnet synchronous motor, including: a permanent magnet synchronous motor and a locked rotor detection device of the permanent magnet synchronous motor according to the embodiment of the second aspect of the invention; and after the locked rotor detection device judges that the permanent magnet synchronous motor is locked, the permanent magnet synchronous motor is controlled to stop.

According to the control system of the permanent magnet synchronous motor, the defect of the related technology is overcome through the locked rotor detection device of the permanent magnet synchronous motor, locked rotor detection in a torque current control mode or a speed control mode can be achieved, and the control system is high in practicability and safety and reliability.

To achieve the above object, a fourth aspect of the present invention provides an electronic device, including: the invention further provides a device for detecting stalling of a permanent magnet synchronous motor, which comprises a memory, a processor and a computer program stored on the memory and capable of running on the processor, wherein when the processor executes the program, the method for detecting stalling of a permanent magnet synchronous motor is realized.

According to the electronic equipment provided by the embodiment of the invention, the processor executes the computer program stored on the memory, so that the defects of the related technology are overcome, the locked rotor detection in a torque current control mode or a speed control mode can be realized, the practicability is high, and the safety and the reliability are high.

To achieve the above object, a fifth embodiment of the present invention provides a non-transitory computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the locked rotor detection method for a permanent magnet synchronous motor according to the first embodiment of the present invention.

The non-transitory computer-readable storage medium according to the embodiment of the present invention, by executing the stored computer program, makes up for the deficiencies of the related art, and can implement locked rotor detection in the torque current control mode or the speed control mode, and has high practicability, safety and reliability.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a flowchart of a locked rotor detection method of a permanent magnet synchronous motor according to an embodiment of the present invention;

fig. 2 is a flowchart of a locked rotor detection method of a permanent magnet synchronous motor according to another embodiment of the present invention;

fig. 3 is a flowchart of a locked rotor detection method of a permanent magnet synchronous motor according to yet another embodiment of the present invention;

fig. 4 is a block schematic diagram of a stall detection apparatus of a permanent magnet synchronous machine according to an embodiment of the present invention;

fig. 5 is a block schematic diagram of a stalling detection device of a permanent magnet synchronous machine according to another embodiment of the invention; and

fig. 6 is a block schematic diagram of a control system of a permanent magnet synchronous machine according to one embodiment of the invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

A locked rotor detection method of a permanent magnet synchronous motor, a locked rotor detection device of a permanent magnet synchronous motor, a control system of a permanent magnet synchronous motor, an electronic apparatus, and a non-transitory computer-readable storage medium according to embodiments of the present invention are described below with reference to the accompanying drawings.

Fig. 1 is a flowchart of a locked rotor detection method of a permanent magnet synchronous motor according to an embodiment of the present invention. In an embodiment of the present invention, the permanent magnet synchronous motor may be an alternating current motor.

As shown in fig. 1, the locked rotor detection method of the permanent magnet synchronous motor according to the embodiment of the present invention includes the following steps:

and S1, obtaining phase voltage and phase current of the permanent magnet synchronous motor. The phase voltage of the permanent magnet synchronous motor can be acquired in real time through the voltage sensor, and the phase current of the permanent magnet synchronous motor can be acquired in real time through the current sensor.

And S2, calculating the thermal power of the stator according to the phase voltage or the phase current. Wherein the stator may be a stator resistor.

In the embodiment of the present invention, the thermal power of the stator may be calculated according to the phase current and the stator resistance of the permanent magnet synchronous motor, wherein the thermal power of the stator of the permanent magnet synchronous motor may be calculated by the following formula (1):

PR=I2RS(1)

wherein, PRCan be the thermal power of the stator of the permanent magnet synchronous motor, I can be the phase current of the permanent magnet synchronous motor, RSMay be the resistance of the stator of the permanent magnet synchronous motor.

In other embodiments of the present invention, the thermal power of the stator may also be calculated according to the phase voltage and the stator resistance of the permanent magnet synchronous motor, wherein the thermal power of the stator of the permanent magnet synchronous motor may be calculated by the following formula (1):

Figure BDA0001784433540000041

wherein, PRCan be the thermal power of the stator of the permanent magnet synchronous motor, U can be the phase voltage of the permanent magnet synchronous motor, RSMay be the resistance of the stator of the permanent magnet synchronous motor.

And S3, judging whether the PMSM is locked rotor or not according to the thermal power.

In one embodiment of the present invention, as shown in fig. 2, determining whether the pm synchronous motor is locked according to the thermal power may include the following steps,

and S31, calculating the input power according to the phase voltage and the phase current. The input power can be the input power of the permanent magnet synchronous motor.

The input power of the permanent magnet synchronous motor can be calculated by the following formula (3):

Pin=UI (3)

wherein, PinThe input power of the permanent magnet synchronous motor can be used, U can be the phase voltage of the permanent magnet synchronous motor, and I can be the phase current of the permanent magnet synchronous motor.

And S32, judging whether the PMSM is locked according to the input power and the thermal power.

Further, in an embodiment of the present invention, as shown in fig. 3, the determining whether the pm synchronous motor is locked up according to the input power and the thermal power may include the following steps:

and S321, determining a thermal power threshold according to the input power. Wherein the thermal power threshold may be equal to or greater than 80% of the input power.

And S322, if the thermal power is continuously greater than the thermal power threshold value within the preset time, judging that the permanent magnet synchronous motor is locked. The preset time can be calibrated according to the actual situation.

It should be noted that, considering the influence of the usage environment and other factors, it is determined whether the pm synchronous motor is locked, and it cannot be determined by the instantaneous detection result, that is, it cannot be determined that the motor is locked according to the fact that the thermal power (the thermal power of the stator) at a certain time is greater than the thermal power threshold.

Specifically, if the thermal power is continuously greater than the thermal power threshold within a preset time, it is determined that the rotation blocking of the permanent magnet synchronous motor occurs, which may include: and when the thermal power is greater than the thermal power threshold, timing is started to generate timing data, if the thermal power is equal to or less than the thermal power threshold, the timing data is cleared, and when the timing data is equal to the preset time, the permanent magnet synchronous motor is judged to be locked.

That is to say, after acquiring the thermal power and determining the thermal power threshold, the permanent magnet synchronous motor can determine whether the thermal power is greater than the thermal power threshold, and if the thermal power is greater than the thermal power threshold, start timing and generate corresponding timing data, wherein the timing data includes timing time. And then, the permanent magnet synchronous motor can compare the thermal power obtained in real time with a thermal power threshold value within the period from the timing time to the preset time, if the thermal power obtained in real time is greater than the thermal power threshold value within the period from the timing time to the preset time, the permanent magnet synchronous motor can be judged to be locked, otherwise, the timing data can be cleared, and the step of obtaining the phase voltage and the phase current of the permanent magnet synchronous motor can be returned.

It should be noted that, in this embodiment, after acquiring the thermal power and determining the thermal power threshold, the permanent magnet synchronous motor may determine whether the thermal power is greater than the thermal power threshold, start timing and generate corresponding timing data if it is determined that the thermal power is greater than the thermal power threshold, and otherwise, return to the step of acquiring the phase voltage and the phase current of the permanent magnet synchronous motor.

In the embodiment of the invention, after the permanent magnet synchronous motor is judged to be locked, the permanent magnet synchronous motor can be controlled to stop so as to prevent the permanent magnet synchronous motor from being damaged.

In summary, according to the locked rotor detection method of the permanent magnet synchronous motor in the embodiment of the present invention, the phase voltage and the phase current of the permanent magnet synchronous motor are first obtained, then the thermal power of the stator is calculated according to the phase voltage or the phase current, and finally, whether the locked rotor occurs in the permanent magnet synchronous motor is determined according to the thermal power. Therefore, the locked rotor detection method makes up the defects of the related technology, can realize locked rotor detection in a torque current control mode or a speed control mode, and has strong practicability and high safety and reliability.

Fig. 4 is a block schematic diagram of a stalling detection device of a permanent magnet synchronous machine according to one embodiment of the invention.

As shown in fig. 4, the stalling detection device 1000 of the permanent magnet synchronous motor according to the embodiment of the present invention includes an obtaining module 100, a calculating module 200, and a determining module 300.

The obtaining module 100 is configured to obtain a phase voltage and a phase current of the permanent magnet synchronous motor.

The calculating module 200 is configured to calculate a thermal power of the stator according to the phase voltage or the phase current.

The judging module 300 is configured to judge whether the pmsm has locked rotor according to the thermal power.

In one embodiment of the present invention, as shown in fig. 5, the determining module 300 may include a calculating unit 210 and a determining unit 320.

The calculating unit 210 is configured to calculate an input power according to the phase voltage and the phase current, and the determining unit 320 is configured to determine whether the rotation blocking occurs in the permanent magnet synchronous motor according to the input power and the thermal power.

In an embodiment of the present invention, the determining unit 320 is specifically configured to determine a thermal power threshold according to the input power, and determine that the rotation blockage of the permanent magnet synchronous motor occurs if the thermal power is continuously greater than the thermal power threshold within a preset time.

In an embodiment of the present invention, the determining unit 320 is configured to start timing and generate timing data when the thermal power is greater than the thermal power threshold; and if the thermal power is equal to or less than the thermal power threshold, clearing the timing data, and judging that the permanent magnet synchronous motor is locked when the timing data is equal to the preset time.

In one embodiment of the invention, the thermal power threshold is equal to or greater than 80% of the input power.

It should be noted that details not disclosed in the device for detecting a locked rotor of a permanent magnet synchronous motor according to the embodiment of the present invention refer to details disclosed in the method for detecting a locked rotor of a permanent magnet synchronous motor according to the embodiment of the present invention, and are not described herein again in detail.

To sum up, in the locked rotor detection device of the permanent magnet synchronous motor according to the embodiment of the present invention, the phase voltage and the phase current of the permanent magnet synchronous motor are obtained through the obtaining module, and the thermal power of the stator is calculated and obtained through the calculating module according to the phase voltage or the phase current, so that the determining module determines whether the locked rotor occurs in the permanent magnet synchronous motor according to the thermal power. Therefore, the locked rotor detection device makes up the defects of the related technology, can realize locked rotor detection in a torque current control mode or a speed control mode, and is high in practicability, safety and reliability.

Fig. 6 is a block schematic diagram of a control system of a permanent magnet synchronous machine according to one embodiment of the invention.

As shown in fig. 6, the control system 10 of the permanent magnet synchronous motor according to the embodiment of the present invention includes a permanent magnet synchronous motor 2000 and a locked rotor detection device 1000.

After the stalling detection device 1000 determines that the permanent magnet synchronous motor 2000 stalls, the permanent magnet synchronous motor 200 is controlled to stop.

It should be noted that details not disclosed in the control system of the permanent magnet synchronous motor according to the embodiment of the present invention refer to details disclosed in the stalling detection method of the permanent magnet synchronous motor according to the embodiment of the present invention, and details are not repeated herein.

In summary, the control system of the permanent magnet synchronous motor according to the embodiment of the present invention makes up for the deficiencies of the related art by the above-mentioned stalling detection device of the permanent magnet synchronous motor, and can realize stalling detection in the torque current control mode or the speed control mode, and has strong practicability and high safety and reliability.

In order to implement the foregoing embodiments, the present invention further provides an electronic device, which includes a memory, a processor, and a computer program stored in the memory and running on the processor, and when the processor executes the computer program, the method for detecting a locked rotor of a permanent magnet synchronous motor according to the foregoing embodiments is implemented.

According to the electronic equipment provided by the embodiment of the invention, the processor executes the computer program stored on the memory, so that the defects of the related technology are overcome, the locked rotor detection in a torque current control mode or a speed control mode can be realized, the practicability is high, and the safety and the reliability are high.

In order to implement the above embodiments, the present invention also proposes a non-transitory computer-readable storage medium on which a computer program is stored, which, when executed by a processor, implements the stalling detection method of the permanent magnet synchronous motor of the foregoing embodiments.

The non-transitory computer-readable storage medium according to the embodiment of the present invention, by executing the stored computer program, makes up for the deficiencies of the related art, and can implement locked rotor detection in the torque current control mode or the speed control mode, and has high practicability, safety and reliability.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be considered limiting of the invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

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