Permanent magnet synchronous motor fault-tolerant control method based on series winding topology

Abstract

The invention relates to a permanent magnet synchronous motor fault-tolerant control method based on series winding topology. The invention relates to the field of motor control, and the method comprises the steps: selecting a zero-sequence current reference value according to a fault type; performing zero-sequence current injection according to the selected zero-sequence current reference value; and according to the injected zero-sequence current, performing quasi-proportional resonance control to realize fault-tolerant control of the permanent magnet synchronous motor. Compared with the prior art, the fault-tolerant control method of the series winding permanent magnet synchronous motor is simple and easy to implement, and fault-tolerant control of the series winding permanent magnet synchronous motor driver can be achieved only by updating the zero-sequence current reference value under the condition that a motor model, a modulation strategy and a control framework are not changed. And third harmonics in the zero-sequence current can be suppressed, and the performance of the motor is improved.

Description

Technical Field

[0001] The invention relates to the field of motor control, and is a permanent magnet synchronous motor fault-tolerant control method based on series winding topology. Background Art

[0002] Permanent magnet synchronous motors are used in more and more important occasions, and reliability has become a core indicator for evaluating system performance. However, drive technology that relies on electronic components increases the risk of motor drive failure. Multiphase motors can withstand multiple faults due to their inherent redundant control freedom. In contrast, the traditional star-connected three-phase permanent magnet synchronous motor has no zero-sequence circuit flow path and therefore does not have fault tolerance. The open-winding permanent magnet synchronous motor opens the neutral point and adopts a dual inverter topology to connect each phase winding to the inverter bridge arm to achieve separate control of each phase winding. In terms of performance, this topology can improve the utilization of the DC bus voltage. In terms of reliability, the advantages of multiple switching states of the dual inverter and the ability to control the motor windings individually provide more options for the fault-tolerant operation of the system. However, the dual inverter requires 6 bridge arms, the number of electronic components doubles, and the cost is greatly increased. The series winding topology permanent magnet synchronous motor inherits the advantages of the dual inverter topology, can improve the current DC bus voltage utilization, and has good fault tolerance. At the same time, only 4 bridge arms are required, the number of electronic components does not increase significantly, and the cost is low. There is currently no method to perform fault-tolerant control on permanent magnet synchronous motors based on series winding topology. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a permanent magnet synchronous motor fault-tolerant control method based on a series winding topology. The present invention changes the reference value of zero-sequence current injection to ensure that the motor system can run smoothly after a fault occurs. The fault-tolerant capability of the motor system is increased, making it possible for the motor to achieve safe and reliable operation.

[0004] The present invention provides the following technical solutions:

[0005] A fault-tolerant control method for a permanent magnet synchronous motor based on a series winding topology, the method comprising the following steps:

[0006] Step 1: Select the zero-sequence current reference value according to the fault type;

[0007] Step 2: Perform zero-sequence current injection according to the selected zero-sequence current reference value;

[0008] Step 3: Based on the injected zero-sequence current, quasi-proportional resonant control is performed to achieve fault-tolerant control of the permanent magnet synchronous motor.

[0009] Preferably, the step 1 is specifically:

[0010] According to the fault type, the current of the remaining healthy winding is obtained. According to the A-phase winding short circuit fault, the magnetic motive force before the phase failure is:

[0011]

[0012] The magnetomotive force after phase failure is:

[0013]

[0014] Make the magnetic motive force before and after the phase is cut off equal, MMF F =MMF H , and get the current of the healthy winding:

[0015]

[0016]

[0017] Preferably, the step 2 is specifically as follows: in a healthy state, the fundamental frequency phase current and the current in the αβ coordinate system satisfy the following formula:

[0018]

[0019]

[0020] The injected zero-sequence current is obtained according to Clarke inverse transformation:

[0021]

[0022] Preferably, the step 3 is specifically:

[0023] When phase A fails, in order to ensure that the synthesized magnetic motive force under the fault remains unchanged with the magnetic motive force under the healthy state, it is necessary to ensure that i α and i β unchanged, at this time, i A =0, so the fundamental frequency zero-sequence current injected after the fault can be obtained This current is sent as a given to a quasi-proportional resonant controller whose resonant frequency is the fundamental frequency to obtain the fundamental frequency zero-sequence voltage that needs to be injected.

[0024] Preferably, when phases B and C are faulty, the corresponding fundamental frequency zero-sequence current that needs to be injected is obtained:

[0025]

[0026]

[0027] Preferably, the series winding topology has 4 bridge arms and a total of 16 basic voltage vectors, which are divided into two groups, one group is the basic voltage vectors in the αβ plane, and the other group is the basic voltage vectors on the γ axis; the basic voltage vectors in the αβ plane are used to synthesize the rotating magnetic potential, and the basic voltage vectors on the γ axis are used to complete zero-sequence current control; when the motor has a phase failure or the driver switch tube fails, the idea of ​​virtual health state is used to complete fault-tolerant control.

[0028] Preferably, the injected zero-sequence current can be obtained according to the Clarke inverse transformation. In the case of a phase A circuit breaker fault, after the Clarke inverse transformation, A =i α +i0, when phase A is disconnected A =0, in order to ensure that i α Unchanged, at this time Similarly, when phase B and phase C fail, the zero-sequence currents injected are,

[0029] A permanent magnet synchronous motor fault-tolerant control system based on series winding topology, the system comprising:

[0030] A detection module, wherein the detection module performs zero-sequence current detection according to the type of fault;

[0031] A current injection module, wherein the current injection module injects zero-sequence current according to the detected zero-sequence current;

[0032] A fault-tolerant control module is provided, wherein the fault-tolerant control module performs quasi-proportional resonance control according to the injected zero-sequence current to realize fault-tolerant control of the permanent magnet synchronous motor.

[0033] A computer-readable storage medium stores a computer program, which is executed by a processor to implement a permanent magnet synchronous motor fault-tolerant control method based on a series winding topology.

[0034] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements a permanent magnet synchronous motor fault-tolerant control method based on a series winding topology when executing the computer program.

[0035] The present invention has the following beneficial effects:

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] The present invention proposes a fault-tolerant control method for a permanent magnet synchronous motor based on a series winding topology, and the fault-tolerant control method includes zero-sequence current detection, zero-sequence current injection, quasi-proportional resonant control and 3D-SVPWM and other links. The series winding topology has 4 bridge arms and a total of 16 basic voltage vectors, which can be divided into two groups, one group is the basic voltage vectors in the αβ plane, and the other group is the basic voltage vectors on the γ axis. The basic voltage vectors in the αβ plane are used to synthesize the rotating magnetic potential, and the basic voltage vectors on the γ axis are used to complete zero-sequence current control. When the motor is out of phase or the driver switch fails, the idea of ​​virtual health state is used to complete fault-tolerant control. The idea of ​​the virtual health system is to regard the faulty series winding permanent magnet synchronous motor drive as a healthy drive with additional current constraints. When a phase winding fails, in order to achieve fault-tolerant control and ensure the smooth torque of the motor, it is necessary to ensure that the synthesized magnetic motive force remains unchanged, that is, i α and i β remains unchanged. Therefore, it is necessary to inject zero-sequence current to complete fault-tolerant control, which is implemented according to Clarke inverse transformation. Taking the A-phase open circuit fault as an example, after Clarke inverse transformation, there is i A =i α +i0, when phase A is disconnected A =0, in order to ensure that i α Unchanged, at this time Similarly, when phase B and phase C fail, the zero-sequence currents injected are,

[0038] Compared with the existing methods, the fault-tolerant control method of the series-winding permanent magnet synchronous motor of the present invention is simple and easy to implement. Without changing the motor model, modulation strategy and control framework, it is only necessary to update the zero-sequence current reference value to achieve fault-tolerant control of the series-winding permanent magnet synchronous motor drive. It can also suppress the third harmonic in the zero-sequence current and improve the motor performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 Shown is a topological circuit diagram of a series winding motor system of the present invention;

[0041] Figure 2 Shown is a structural diagram of a series winding motor control system of the present invention;

[0042] Figure 3Shown is a flow chart of the motor operation system of the present invention;

[0043] Figure 4 The current waveform of the B and C windings when the A phase winding of the motor of the present invention has a circuit breaker fault is shown;

[0044] Figure 5 The torque waveform diagram is shown when the A-phase winding of the motor of the present invention has a circuit breaker fault;

[0045] Figure 6 The figure shows the rotation speed waveform when the phase A winding of the motor of the present invention has a circuit breaker fault. DETAILED DESCRIPTION

[0046] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] The present invention is described in detail below in conjunction with specific embodiments. Specific embodiment one:

[0049] according to Figures 1 to 6 As shown, the specific optimization technical solution adopted by the present invention to solve the above technical problems is: the present invention relates to a permanent magnet synchronous motor fault-tolerant control method based on series winding topology.

[0050] A fault-tolerant control method for a permanent magnet synchronous motor based on a series winding topology, the method comprising the following steps:

[0051] Step 1: Select the zero-sequence current reference value according to the fault type;

[0052] Step 2: Perform zero-sequence current injection according to the selected zero-sequence current reference value;

[0053] Step 3: Based on the injected zero-sequence current, quasi-proportional resonant control is performed to achieve fault-tolerant control of the permanent magnet synchronous motor.

[0054] Compared with the existing methods, the fault-tolerant control method of the series-winding permanent magnet synchronous motor of the present invention is simple and easy to implement. Without changing the motor model, modulation strategy and control framework, it is only necessary to update the zero-sequence current reference value to achieve fault-tolerant control of the series-winding permanent magnet synchronous motor drive. It can also suppress the third harmonic in the zero-sequence current and improve the motor performance. Specific embodiment 2:

[0056] The difference between the second embodiment of the present application and the first embodiment is that:

[0057] The step 1 is specifically as follows:

[0058] According to the fault type, the current of the remaining healthy winding is obtained. According to the A-phase winding short circuit fault, the magnetic motive force before the phase failure is:

[0059]

[0060] The magnetomotive force after phase failure is:

[0061]

[0062] Make the magnetic motive force before and after the phase is cut off equal, MMF F =MMF H , and get the current of the healthy winding:

[0063]

[0064] Specific embodiment three:

[0066] The difference between the third embodiment of the present application and the second embodiment is that:

[0067] In a healthy state, the fundamental frequency phase current and the current in the αβ coordinate system satisfy the following equation:

[0068]

[0069]

[0070] The injected zero-sequence current is obtained according to Clarke inverse transformation:

[0071] Specific embodiment four:

[0073] The difference between the fourth embodiment of the present application and the third embodiment is that:

[0074] The step 3 is specifically as follows:

[0075] When phase A fails, in order to ensure that the synthesized magnetic motive force under the fault remains unchanged with the magnetic motive force under the healthy state, it is necessary to ensure that i α and i β unchanged, at this time, i A =0, so the fundamental frequency zero-sequence current injected after the fault can be obtained This current is sent as a given to a quasi-proportional resonant controller whose resonant frequency is the fundamental frequency to obtain the fundamental frequency zero-sequence voltage that needs to be injected. Specific embodiment five:

[0077] The difference between the fifth embodiment of the present invention and the fourth embodiment is that:

[0078] When phases B and C are faulty, the corresponding fundamental frequency zero-sequence current that needs to be injected is obtained:

[0079]

[0080] Specific embodiment six:

[0082] The difference between the sixth embodiment of the present invention and the fifth embodiment is that:

[0083] The series winding topology has 4 bridge arms and a total of 16 basic voltage vectors, which are divided into two groups, one group is the basic voltage vectors in the αβ plane, and the other group is the basic voltage vectors on the γ axis; the basic voltage vectors in the αβ plane are used to synthesize the rotating magnetic potential, and the basic voltage vectors on the γ axis are used to complete zero-sequence current control; when the motor is out of phase or the driver switch tube fails, the idea of ​​virtual health state is used to complete fault-tolerant control. Specific embodiment seven:

[0085] The difference between the seventh embodiment of the present invention and the sixth embodiment is that:

[0086] According to Clarke inverse transformation, the injected zero-sequence current can be obtained. In the case of phase A open circuit fault, after Clarke inverse transformation, i A =i α +i0, when phase A is disconnected A =0, in order to ensure that i α Unchanged, at this time Similarly, when phase B and phase C fail, the zero-sequence currents injected are, Specific embodiment eight:

[0088] The difference between the eighth embodiment of the present invention and the seventh embodiment is that:

[0089] The present invention provides a permanent magnet synchronous motor fault-tolerant control system based on a series winding topology, the system comprising:

[0090] A detection module, wherein the detection module performs zero-sequence current detection according to the type of fault;

[0091] A current injection module, wherein the current injection module injects zero-sequence current according to the detected zero-sequence current;

[0092] A fault-tolerant control module is provided, wherein the fault-tolerant control module performs quasi-proportional resonance control according to the injected zero-sequence current to realize fault-tolerant control of the permanent magnet synchronous motor. Specific embodiment nine:

[0094] The difference between the ninth embodiment of the present invention and the eighth embodiment is that:

[0095] The present invention provides a computer-readable storage medium on which a computer program is stored. The program is executed by a processor to implement a permanent magnet synchronous motor fault-tolerant control method based on a series winding topology.

[0096] The present invention mainly adopts the following technical solutions:

[0097] The present invention proposes a fault-tolerant control method for a permanent magnet synchronous motor based on a series winding topology, and the fault-tolerant control method includes zero-sequence current detection, zero-sequence current injection, quasi-proportional resonant control and 3D-SVPWM and other links. The series winding topology has 4 bridge arms and a total of 16 basic voltage vectors, which can be divided into two groups, one group is the basic voltage vectors in the αβ plane, and the other group is the basic voltage vectors on the γ axis. The basic voltage vectors in the αβ plane are used to synthesize the rotating magnetic potential, and the basic voltage vectors on the γ axis are used to complete zero-sequence current control. When the motor is out of phase or the driver switch fails, the idea of ​​virtual health state is used to complete fault-tolerant control. The idea of ​​the virtual health system is to regard the faulty series winding permanent magnet synchronous motor drive as a healthy drive with additional current constraints. When a certain item fails, in order to achieve fault-tolerant control and ensure the smooth torque of the motor, it is necessary to ensure that the synthesized magnetic motive force remains unchanged, that is, i α and i β remains unchanged. Therefore, it is necessary to inject zero-sequence current to complete fault-tolerant control. The injected zero-sequence current can be obtained according to the Clarke inverse transformation. Taking the A-phase circuit breaker fault as an example, after the Clarke inverse transformation, i A =i α +i0, when phase A is disconnected A =0, in order to ensure that i α Unchanged, at this time Similarly, when phase B and phase C fail, the zero-sequence currents injected are,

[0098] The specific principles and implementation steps are as follows:

[0099] According to the fault type, the current of the remaining healthy winding is obtained:

[0100] Taking the A-phase winding short circuit fault as an example, the magnetic motive force before the phase failure is:

[0101]

[0102] The magnetomotive force after phase failure is:

[0103]

[0104] Make the magnetic motive force before and after the phase is cut off equal, MMF F =MMF H, we can get the current of healthy winding:

[0105]

[0106]

[0107] According to the fault type, the injected fundamental frequency zero-sequence current is obtained. The specific method is as follows:

[0108] In a healthy state, the fundamental frequency phase current and the current in the αβ coordinate system satisfy the following equation:

[0109]

[0110]

[0111] According to Clarke inverse transformation, we get the following formula:

[0112]

[0113] Taking phase A as an example, when phase A fails, in order to ensure that the synthesized magnetic motive force under the fault remains unchanged with the magnetic motive force under the healthy state, it is necessary to ensure that i α and i β remains unchanged. At this time, i A =0, so the fundamental frequency zero-sequence current injected after the fault can be obtained This current is sent as a given to the quasi-proportional resonant controller with the resonant frequency as the fundamental frequency to obtain the fundamental frequency zero-sequence voltage that needs to be injected. Similarly, when phases B and C are faulty, the corresponding fundamental frequency zero-sequence current that needs to be injected can be obtained:

[0114]

[0115] Compared with the existing methods, the fault-tolerant control method of the series-winding permanent magnet synchronous motor of the present invention is simple and easy to implement. Without changing the motor model, modulation strategy and control framework, it is only necessary to update the zero-sequence current reference value to achieve fault-tolerant control of the series-winding permanent magnet synchronous motor drive. It can also suppress the third harmonic in the zero-sequence current and improve the motor performance. Specific embodiment ten:

[0117] The difference between the tenth embodiment of the present invention and the ninth embodiment is that:

[0118] The present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements a permanent magnet synchronous motor fault-tolerant control method based on a series winding topology when executing the computer program. Specific embodiment eleven:

[0120] The difference between the eleventh embodiment of the present invention and the tenth embodiment is that:

[0121] Figure 1 This is the topological circuit diagram of the series winding motor system of the present invention. Four groups of bridge arms are used to connect the windings of the three-phase permanent magnet synchronous motor in series in sequence. This topology has a zero-sequence current flow path, which provides conditions for fault tolerance.

[0122] Figure 2 This is the system control block diagram of the present invention: including zero-sequence current detection, zero-sequence current injection, quasi-proportional resonant control and 3D-SVPWM and other links. The series winding topology has 4 bridge arms and a total of 16 basic voltage vectors, which can be divided into two groups, one group is the basic voltage vectors in the αβ plane, and the other group is the basic voltage vectors on the γ axis. The basic voltage vectors in the αβ plane are used to synthesize the rotating magnetic potential, and the basic voltage vectors on the γ axis are used to complete zero-sequence current control. When the motor is out of phase or the driver switch fails, the idea of ​​virtual health state is used to complete fault-tolerant control. The injected zero-sequence current can be obtained according to the Clarke inverse transform. Taking the A-phase circuit breaker fault as an example, after Clarke inverse transformation, i A =i α +i0, when phase A is disconnected A =0, in order to ensure that i α Unchanged, at this time Similarly, when phase B and phase C fail, the zero-sequence currents injected are,

[0123] The specific principles and implementation steps are as follows:

[0124] According to the fault type, the current of the remaining healthy winding is obtained:

[0125] Taking the A-phase winding short circuit fault as an example, the magnetic motive force before the phase failure is:

[0126]

[0127] The magnetomotive force after phase failure is:

[0128]

[0129] Make the magnetic motive force before and after the phase is cut off equal, MMF F =MMF H , we can get the current of healthy winding:

[0130]

[0131]

[0132] According to the fault type, the injected fundamental frequency zero-sequence current is obtained. The specific method is as follows:

[0133] In a healthy state, the fundamental frequency phase current and the current in the αβ coordinate system satisfy the following equation:

[0134]

[0135]

[0136] According to Clarke inverse transformation, we get the following formula:

[0137]

[0138] Taking phase A as an example, when phase A fails, in order to ensure that the synthesized magnetic motive force under the fault remains unchanged with the magnetic motive force under the healthy state, it is necessary to ensure that i α and i β remains unchanged. At this time, i A =0, so the fundamental frequency zero-sequence current injected after the fault can be obtained This current is sent as a given to the quasi-proportional resonant controller with the resonant frequency as the fundamental frequency to obtain the fundamental frequency zero-sequence voltage that needs to be injected. Similarly, when phases B and C are faulty, the corresponding fundamental frequency zero-sequence current that needs to be injected can be obtained:

[0139]

[0140] Figure 3 The figure is a flow chart of the motor operation. The motor fault is diagnosed, and the zero-sequence current reference value is changed according to the diagnosis result, and the resonant frequency of the quasi-proportional resonant controller is changed at the same time.

[0141] Figure 4 This is the current waveform of the B and C windings when a short circuit fault occurs in the motor phase A winding.

[0142] Figure 5 This is the torque waveform when a short circuit fault occurs in the motor A phase winding.

[0143] Figure 6 This is the speed waveform when a short circuit fault occurs in the motor A phase winding.

[0144] It can be seen from the above simulation waveforms that the permanent magnet synchronous motor fault-tolerant control method based on the series winding topology of the present invention can continue to operate under a three-phase motor phase failure, while the torque is stable and the speed has no obvious fluctuation.

[0145] Compared with the existing methods, the fault-tolerant control method of the series-winding permanent magnet synchronous motor of the present invention is simple and easy to implement. Without changing the motor model, modulation strategy and control framework, it is only necessary to update the zero-sequence current reference value to achieve fault-tolerant control of the series-winding permanent magnet synchronous motor drive. It can also suppress the third harmonic in the zero-sequence current and improve the motor performance.

[0146] The above is only a preferred implementation of a permanent magnet synchronous motor fault-tolerant control method based on a series winding topology. The protection scope of a permanent magnet synchronous motor fault-tolerant control method based on a series winding topology is not limited to the above embodiments. All technical solutions under this idea belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, several improvements and changes without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A fault-tolerant control method for a permanent magnet synchronous motor based on a series winding topology, characterized in that: The method comprises the following steps: Step 1: Select the zero-sequence current reference value according to the fault type; Step 2: Perform zero-sequence current injection according to the selected zero-sequence current reference value; Step 3: Based on the injected zero-sequence current, quasi-proportional resonant control is performed to achieve fault-tolerant control of the permanent magnet synchronous motor.

2. The method according to claim 1, characterized in that: The step 1 is specifically as follows: According to the fault type, the current of the remaining healthy winding is obtained. According to the A-phase winding short circuit fault, the magnetic motive force before the phase failure is: The magnetomotive force after phase failure is: Make the magnetic motive force before and after the phase is cut off equal, MMF F =MMF H , and get the current of the healthy winding:

3. The method according to claim 2, characterized in that: The step 2 is specifically as follows: In a healthy state, the fundamental frequency phase current and the current in the αβ coordinate system satisfy the following equation: The injected zero-sequence current is obtained according to Clarke inverse transformation:

4. The method according to claim 1, characterized in that: The step 3 is specifically as follows: When phase A fails, in order to ensure that the synthesized magnetic motive force under the fault remains unchanged with the magnetic motive force under the healthy state, it is necessary to ensure that i α and i β unchanged, at this time, i A =0, so the fundamental frequency zero-sequence current injected after the fault can be obtained This current is sent as a given to a quasi-proportional resonant controller whose resonant frequency is the fundamental frequency to obtain the fundamental frequency zero-sequence voltage that needs to be injected.

5. The method according to claim 4, characterized in that: When phases B and C are faulty, the corresponding fundamental frequency zero-sequence current that needs to be injected is obtained:

6. The method according to claim 5, characterized in that: The series winding topology has 4 bridge arms and a total of 16 basic voltage vectors, which are divided into two groups, one group is the basic voltage vectors in the αβ plane, and the other group is the basic voltage vectors on the γ axis; the basic voltage vectors in the αβ plane are used to synthesize the rotating magnetic potential, and the basic voltage vectors on the γ axis are used to complete zero-sequence current control; when the motor is out of phase or the driver switch tube fails, the idea of ​​virtual health state is used to complete fault-tolerant control.

7. The method according to claim 6, characterized in that: According to Clarke inverse transformation, the injected zero-sequence current can be obtained. In the case of phase A open circuit fault, after Clarke inverse transformation, i A =i α +i0, when phase A is disconnected A =0, in order to ensure that i α Unchanged, at this time Similarly, when phase B and phase C fail, the zero-sequence currents injected are, 8. A permanent magnet synchronous motor fault-tolerant control system based on series winding topology, characterized by: The system comprises: A detection module, wherein the detection module performs zero-sequence current detection according to the type of fault; A current injection module, wherein the current injection module injects zero-sequence current according to the detected zero-sequence current; A fault-tolerant control module is provided, wherein the fault-tolerant control module performs quasi-proportional resonance control according to the injected zero-sequence current to realize fault-tolerant control of the permanent magnet synchronous motor.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: The program is executed by a processor to implement the method of claims 1-7.

10. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the method of claims 1-7 is implemented.

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