LU502778B1

LU502778B1 - Method and system for rapidly detecting demagnetization of permanent magnet synchronous motor of electric automobile

Info

Publication number: LU502778B1
Application number: LU502778A
Authority: LU
Inventors: Fangyuan Qiu; Shiwei Tan; wanyou Huang; Peidong Zhu; Fuzhao Han; Yuanchen Wen; Jiarui Zhao; Ruixia Chu; Hao Chang; Shina Li; Xiang Li; Jun Yang; Zhihua Liu
Original assignee: Univ Shandong Jiaotong
Priority date: 2022-03-21
Filing date: 2022-09-09
Publication date: 2023-03-09
Also published as: CN114487830B; CN114487830A

Abstract

The present invention discloses a method and system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile and relates to the technical field of automobile detection. The method comprises a data acquisition step, an effective working condition determination step, a current change determination step, an efficiency determination step, a critical threshold determination step and a demagnetization aging judgment step. The present invention analyzes a demagnetization aging degree of the motor with a small calculated amount, can perform online real-time detection, and is high in reliability.

Description

a LU502778

METHOD AND SYSTEM FOR RAPIDLY DETECTING DEMAGNETIZATION OF

PERMANENT MAGNET SYNCHRONOUS MOTOR OF ELECTRIC

AUTOMOBILE

TECHNICAL FIELD

The present invention relates to the technical field of automobile detection, particularly to a method and system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile.

BACKGROUND

Permanent magnet synchronous motors featuring simple mechanism, reliable operation, small size, light weight, small loss, high efficiency, high overload capacity, high energy density, wide speed adjustable range and the like are widely adopted in new energy automobiles. However, when high temperature, armature reactions (including overcurrent) and mechanical vibration caused by interturn or interphase short circuit of a stator occur in the permanent magnet synchronous motor, an irreversible demagnetization phenomenon will occur in a permanent magnet, which will affect performance of the permanent magnet so as to further reduce the torque performance of the motor, and even lead to severe consequences such as scrapping of the motor. In particular, with respect to an electric automobile, demagnetization directly affects the driving safety. Research on methods for rapidly detecting accidental, hidden and slowly changed demagnetization of the permanent magnet synchronous motor not only can lower the maintenance cost, but also can reduce the occurrence of accidents, and has critical practical significance for health condition detection and fault diagnosis of the permanent magnet synchronous motor of the electric automobile.

Existing methods for detecting demagnetization of the permanent magnet synchronous motor include a conventional magnetic circuit analysis, a finite element method that establishes a simulation model or analysis combining the two methods. A counter potential signal of a coil is analyzed to detect demagnetization, but the method only can perform detection under a circumstance of power failure of the motor and cannot perform on-site detection in an operating state of the motor. In consideration of influence of temperature on the permanent magnet synchronous motor and measurement of the state of the permanent magnet through an active short circuit current, the method needs to use more instruments for measurement and is relatively complicated. At present, the hidden danger that the permanent magnet synchronous motor is easily subjected to demagnetization has not been solved all the time, most researches only stay in the stage of simulating an ideal model with SIMULINK in laboratory, and existing methods are relatively complicated and cannot perform online rapid detection in real time, so that the operating reliability of the motor is affected.

Therefore, to provide a method and system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile to overcome the problems in the prior art is the problem urgently needed to be solved by those skilled in the art.

SUMMARY

In view of this, the present invention provides a method and system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile, which analyzes a demagnetization aging degree of the motor with a small calculated amount, can perform online real-time detection, and is high in reliability.

In order to achieve the purpose, the present invention adopts a technical solution as follows: a method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile includes the following steps:

S101: a data acquisition step: acquiring output data of the permanent magnet synchronous motor of the electric automobile;

S102: an effective working condition determination step: determining an effective working condition for rapidly detecting demagnetization of the permanent magnet

5a LU502778 synchronous motor when a driving motor is in a power consumption state and a temperature of the driving motor is within a certain range;

S103: a direct current bus current variation determination step: monitoring a direct current bus current variation corresponding to a same output torque in an effective working condition, and determining a reasonable variation range of a direct current bus current of a motor controller along with an electromagnetic torque and an accumulated mileage of the whole vehicle;

S104: a system efficiency determination step: monitoring a system efficiency of the permanent magnet synchronous motor in an operating point according to each mileage range, and determining a reasonable range of the system efficiency of the permanent magnet synchronous motor in each mileage range;

S105: a critical threshold determination step: establishing a real-time database of the direct current bus current of the motor controller and the system efficiency of the motor at the driving motor monitoring operating point, and determining critical thresholds of the direct current bus current of the motor controller and the system efficiency of the motor at the monitoring operating point in each mileage range; and

S106: a demagnetization aging judgment step: extracting and analyzing data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.

Optionally, the output data in the permanent magnet synchronous motor in S101 includes: the accumulated mileage of the whole vehicle, a state of the driving motor, a rotating speed of the driving motor, a torque of the driving motor, the temperature of the driving motor, an input voltage of the motor controller and the direct current bus current of the motor controller.

Optionally, a temperature range of the driving motor in S102 is 20-50°C.

Optionally, the determining the effective operating point in S102 specifically includes: selecting the rotating speed of the driving motor to be 30%, 60% and 90% of a rated rotating speed, where an allowable deviation of the rotating speed is 5% of the rated rotating speed;

and selecting the torque of the driving motor to be 30%, 60% and 90% of a rated torque, wherein an allowable deviation of the torque is 10% of the rated torque.

Optionally, the determining a reasonable variation range of a direct current bus current of a motor controller along with a load power and an accumulated mileage of the whole vehicle according to a torque equation and a kinematic equation of the permanent magnet synchronous motor in S103 has a specific formula as follows:

I= Bln ;

F (D

J he =T, — ue, —T, 2 where Te is an electromagnetic torque with a unit of N.m; np is a number of pole-pairs, and Ln is mutual inductance with a unit of H; L; is self-inductance of a motor rotor with a unit of H; 1s7 is a torque component of a stator current with a unit of A; Wr is a rotor flux with a unit of Wb; om is a rotor mechanical angle frequency with a unit of rad/s; Tm is a load torque with a unit of N.m; u is a rotor loading viscous friction coefficient; and J is rotational inertia with a unit of kg.m?.

Optionally, a calculation formula for the system efficiency of the motor in S103 is as follows:

Tn

Tess ud © where n is the rotating speed of the driving motor with the unit of r/min; T is the torque of the driving motor with the unit of Nm; U is the input voltage of the motor controller with the unit of V; and I is the direct current bus current of the motor controller with the unit of A.

Optionally, the judging the demagnetization aging degree of the permanent magnet synchronous motor in S106 specifically includes: when the direct current bus current and the system efficiency of the motor monitored at any operating point reach alarm thresholds simultaneously for the first time, marking an abnormal demagnetization state of the permanent magnet synchronous motor; when the direct current bus current and the system efficiency of the motor monitored at any operating

5a LU502778 point reach the alarm thresholds simultaneously for successive two times within a set interval period, marking a demagnetization alarming state of the permanent magnet synchronous motor; and when direct current bus current and the system efficiency of the motor monitored at any operating point reach the alarm thresholds simultaneously for successive three times or over within the set interval period, marking a demagnetization fault state of the permanent magnet synchronous motor.

Optionally, the method further includes S107: an early warning step: pushing early warning information to a client side of the electric automobile when judging that the demagnetization aging degree of the permanent magnet synchronous motor is in an alarm state or a fault state.

A system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile includes a data acquisition module, an effective working condition determination module, a current variation determination module, an efficiency determination module, a critical threshold determination module and a demagnetization aging judgment module connected successively, where the data acquisition module is configured to acquire output data of the permanent magnet synchronous motor of the electric automobile; the effective working condition determination module is configured to determine an effective working condition for rapidly detecting demagnetization of the permanent magnet synchronous motor when a driving motor is in a power consumption state and a temperature of the driving motor is within a certain range; the direct current bus current variation determination module is configured to monitor a direct current bus current variation corresponding to a same output torque in an effective working condition, and determine a reasonable variation range of a direct current bus current of a motor controller along with an electromagnetic torque and an accumulated mileage of the whole vehicle; the system efficiency determination module is configured to monitor a system efficiency of the permanent magnet synchronous motor in an operating point in each mileage range, and determine a reasonable range of the system efficiency of the permanent magnet aa LU502778 synchronous motor in each mileage range; the critical threshold determination module is configured to establish a real-time database of the direct current bus current of the motor controller and the system efficiency of the motor at the driving motor monitoring operating point, and determine critical thresholds of the direct current bus current of the motor controller and the system efficiency of the motor at the monitoring operating point in each mileage range; and the demagnetization aging judgment module is configured to extract and analyze data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.

Optionally, the system further includes an early warning module connected to the demagnetization aging judgment module and configured to extract and analyze data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.

It can be known from the above-mentioned technical solution that compared with the prior art, the present invention provides a method and system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile. 1) by acquiring real-time driving motor data, the present invention compares variations of the direct current bus current of the motor controller and the system efficiency of the motor in the real-time operating process of the vehicle at the effective monitoring operating point, thereby judging the demagnetization degree of the permanent magnet synchronous motor; 2) the present invention can judge early warning or fault of the motor system according to the variation values of the direct current bus current of the motor controller and the system efficiency of the motor at the effective monitoring operating point and the number of times to reach the thresholds continuously, has a small calculated amount, can perform online real-time detection, and is high in reliability; and 3) the present invention is simple and feasible in solution without adding extra sensors.

TE LU502778

BRIEF DESCRIPTION OF DRAWINGS

In order to describe the embodiments of the present invention or the technical solution in the prior art more clearly, brief introduction on drawings needed to be used in the embodiment will be made below. It is obvious that the drawings described below are embodiments of the present invention, and those skilled in the technical field further can obtain other drawings according to the drawings without creative efforts.

FIG. 1 is a flowchart of a method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile provided by the present invention.

FIG. 2 is a structural block diagram of a system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile provided by the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the accompanying drawings in the embodiments of the present invention. The described embodiments are merely a part of, rather than all of, the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention. On a basis of the embodiments in the present invention, all other embodiments obtained by those of ordinary in the technical field without creative efforts fall into the scope of protection of the present invention.

Referring to FIG. 1, the present invention discloses a method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile, including the following steps:

S101: a data acquisition step: output data of the permanent magnet synchronous motor of the electric automobile is acquired,

S102: an effective working condition determination step: an effective working condition

Ba LU502778 for rapidly detecting demagnetization of the permanent magnet synchronous motor is determined when a driving motor is in a power consumption state and a temperature of the driving motor is within a certain range;

S103: a direct current bus current variation determination step: a direct current bus current variation corresponding to a same output torque in an effective working condition is monitored, and a reasonable variation range of a direct current bus current of a motor controller along with an electromagnetic torque and an accumulated mileage of the whole vehicle 1s determined;

S104: a system efficiency determination step: a system efficiency of the permanent magnet synchronous motor in an operating point is monitored according to each mileage range, and a reasonable range of the system efficiency of the permanent magnet synchronous motor in each mileage range is determined;

S105: a critical threshold determination step: a real-time database of the direct current bus current of the motor controller and the system efficiency of the motor at the driving motor monitoring operating point is established, and critical thresholds of the direct current bus current of the motor controller and the system efficiency of the motor at the monitoring operating point in each mileage range are determined; and

S106: a demagnetization aging judgment step: data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle are extracted and analyzed, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.

Further, the output data in the permanent magnet synchronous motor in S101 includes: the accumulated mileage of the whole vehicle, a state of the driving motor, a rotating speed of the driving motor, a torque of the driving motor, the temperature of the driving motor, an input voltage of the motor controller and the direct current bus current of the motor controller.

The state of the driving motor includes: a power consumption state, a power generation state, an off state and a preparation state.

Further, a temperature range of the driving motor in S102 is 20-50°C.

9e LU502778

Further, the determining the effective operating point in S102 specifically includes: the rotating speed of the driving motor is selected to be 30%, 60% and 90% of a rated rotating speed, where an allowable deviation of the rotating speed is 5% of the rated rotating speed; and the torque of the driving motor is selected to be 30%, 60% and 90% of a rated torque, where an allowable deviation of the torque is 10% of the rated torque.

Further, the determining a reasonable variation range of a direct current bus current of a motor controller along with a load power and an accumulated mileage of the whole vehicle according to a torque equation and a kinematic equation of the permanent magnet synchronous motor in S103 has a specific formula as follows:

RL.

N (1)

J&P et per -T, à @) where Te is an electromagnetic torque with a unit of N.m; np is a number of pole-pairs, and Lm is mutual inductance with a unit of H; L; is self-inductance of a motor rotor with a unit of H; 1s7 is a torque component of a stator current with a unit of A; Wr is a rotor flux with a unit of Wb; om is a rotor mechanical angle frequency with a unit of rad/s; Tm is a load torque with a unit of N.m; u is a rotor loading viscous friction coefficient; and J is rotational inertia with a unit of kg.m?.

Further, a calculation formula for the system efficiency of the motor in S103 is as follows:

Tn 0 Tassui © where n is the rotating speed of the driving motor with the unit of r/min; T is the torque of the driving motor with the unit of Nm; U is the input voltage of the motor controller with the unit of V; and I is the direct current bus current of the motor controller with the unit of A.

Further, the judging the demagnetization aging degree of the permanent magnet synchronous motor in S106 specifically includes: when the direct current bus current and the system efficiency of the motor monitored at any operating point reach alarm thresholds simultaneously for the first time, marking an abnormal demagnetization state of the permanent magnet synchronous motor, when the direct current bus current and the system efficiency of the motor monitored at any operating point reach the alarm thresholds simultaneously for successive two times within a set interval period, marking a demagnetization alarming state of the permanent magnet synchronous motor; and when direct current bus current and the system efficiency of the motor monitored at any operating point reach the alarm thresholds simultaneously for successive three times or over within the set interval period, marking a demagnetization fault state of the permanent magnet synchronous motor.

Further, the method further includes S107: an early warning step: early warning information is pushed to a client side of the electric automobile when it is judged that the demagnetization aging degree of the permanent magnet synchronous motor is in an alarm state or a fault state.

Referring to FIG. 2, the present invention discloses a system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile includes a data acquisition module, an effective working condition determination module, a current variation determination module, an efficiency determination module, a critical threshold determination module and a demagnetization aging judgment module connected successively, where the data acquisition module is configured to acquire output data of the permanent magnet synchronous motor of the electric automobile; the effective working condition determination module is configured to determine an effective working condition for rapidly detecting demagnetization of the permanent magnet synchronous motor when a driving motor is in a power consumption state and a temperature of the driving motor is within a certain range; the direct current bus current variation determination module is configured to monitor a direct current bus current variation corresponding to a same output torque in an effective working condition, and determine a reasonable variation range of a direct current bus current of a motor controller along with an electromagnetic torque and an accumulated mileage of the whole vehicle; the system efficiency determination module is configured to monitor a system efficiency of the permanent magnet synchronous motor in an operating point in each mileage range, and determine a reasonable range of the system efficiency of the permanent magnet synchronous motor in each mileage range; the critical threshold determination module is configured to establish a real-time database of the direct current bus current of the motor controller and the system efficiency of the motor at the driving motor monitoring operating point, and determine critical thresholds of the direct current bus current of the motor controller and the system efficiency of the motor at the monitoring operating point in each mileage range; and the demagnetization aging judgment module is configured to extract and analyze data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.

Further, the system further includes an early warning module connected to the demagnetization aging judgment module and configured to extract and analyze data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.

Embodiment 1

A method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile specifically includes the following steps:

S101:

A remote service management platform acquires the real-time operating data of each electric automobile. The present invention mainly concerns parameters closely related to the flux weakening degree of the permanent magnet synchronous motor, including the accumulated mileage of the whole vehicle, a state of the driving motor, a rotating speed of the driving motor, a torque of the driving motor, the temperature of the driving motor, an input voltage of the motor controller and the direct current bus current of the motor controller,

and stores the above-mentioned data in a database.

S102:

The effective working condition for rapidly detecting demagnetization of the permanent magnet synchronous motor is determined: the state of the driving motor is in a power consumption state, a temperature range of the motor is selected at 20-50°C, the rotating speed of the driving motor is selected to be 30%, 60% and 90% of a rated rotating speed, where an allowable deviation of the rotating speed is 5% of the rated rotating speed, and the torque of the driving motor is selected to be 30%, 60% and 90% of a rated torque, wherein an allowable deviation of the torque is 10% of the rated torque. There are totally nine operating points monitored. That is, the rotating speed of the motor is 30%+/5% of the rated rotating speed, and the torque of the motor is 30%+/-10% of the rated torque; the rotating speed of the motor is 30%+/5% of the rated rotating speed, and the torque of the motor is 60%+/-10% of the rated torque; the rotating speed of the motor is 30%+/5% of the rated rotating speed, and the torque of the motor is 90%+/-10% of the rated torque; the rotating speed of the motor is 60%+/5% of the rated rotating speed, and the torque of the motor is 30%+/-10% of the rated torque; the rotating speed of the motor is 60%+/5% of the rated rotating speed, and the torque of the motor is 60%+/-10% of the rated torque; the rotating speed of the motor is 60%+/5% of the rated rotating speed, and the torque of the motor is 90%+/-10% of the rated torque; the rotating speed of the motor is 90%+/5% of the rated rotating speed, and the torque of the motor is 30%+/-10% of the rated torque; the rotating speed of the motor is 90%+/5% of the rated rotating speed, and the torque of the motor is 60%+/-10% of the rated torque; the rotating speed of the motor is 90%+/5% of the rated rotating speed, and the torque of the motor is 90%+/-10% of the rated torque.

S103:

A direct current bus current variation with the same output torque is monitored: at the above-mentioned operating point, a reasonable variation range of a direct current bus current of a motor controller along with a load power and an accumulated mileage of the whole vehicle is determined according to a formula (1) and a formula (2) (a torque equation and a kinematic equation of the permanent magnet synchronous motor) For example, the accumulated mileage of the whole vehicle 1s divided at an interval of 30000km, a reasonable range of the electromagnetic torque-varying direct current bus current of the motor controller in each mileage range is determined and represented by a scale factor K1, K1 is a ratio of the direct current bus current of the motor controller at the corresponding monitoring operating point to a theoretical value (the direct current bus current value when the vehicle leaves the factory), and K1 varies along with the operating point and the accumulated mileage of the whole vehicle.

S104:

The system efficiency of the permanent magnet synchronous motor at the monitoring operating point according to each mileage range: at the effective monitoring operating point in each mileage range, after demagnetization of the permanent magnet synchronous motor, the current required by the same electromagnetic torque is increased, resulting in obvious increase of loss of the motor and decrease of the system efficiency of the motor. The reasonable range of the system efficiency of the permanent magnet synchronous motor at the effective monitoring operating point in each mileage range is determined according to a formula (3) (a calculation formula for the system efficiency of the motor) and is represented by a scale factor K2, and K2 1s a ratio of the system efficiency of the permanent magnet synchronous motor at the corresponding monitoring operating point to the efficiency when the vehicle leaves the factory.K2 varies along with the operating point and the accumulated mileage of the whole vehicle.

S105:

A real-time database for monitoring the operating points is established: according to a determined interval period, usually 10 s, the K1 values and K2 values at the monitoring operating points are stored in the database in real time, the real-time database for the direct current bus current of the motor controller and the system efficiency of the motor at the effective monitoring operating point of the driving motor is established, and alarm thresholds of the direct current bus current of the motor controller and the system efficiency of the motor at the corresponding monitoring operating point in each mileage range are determined and stored together in the database.(The K1 value, the K2 value, the bus current, the system efficiency of the motor and the alarm thresholds are in the same database. The alarm thresholds are usually determined according to the direct current bus current and the system efficiency of the motor compared with historical data variation. For example, the direct current bus current is increased by 5% or the system efficiency of the motor 1s decreased by 5% at the same operating point. Specific numerical values are related to the driving millage of the vehicle and the model of the motor, and are not fixed values).

S106:

The demagnetization aging degree of the permanent magnet synchronous motor is judged: according to a determined interval period, usually 10 s, data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle is extracted and analyzed, thereby a demagnetization proportion is calculated to judge the demagnetization aging degree of the motor. If the demagnetization aging degree is within a normal demagnetization aging range, it is considered that the motor is in a good health condition. During data analysis, a center line and two control limits are confirmed by a statistical method, where the center line is usually a data mean value of the monitoring operating point in the database or is obtained by fitting data in the monitoring operating point based on the least square method. The control limits are located on the upper and lower sides of the center line, which are the upper control limit and the lower control limit confirmed to consider the alarm thresholds in Step S5.when the direct current bus current and the system efficiency of the motor monitored at any operating point reach alarm thresholds simultaneously for the first time, marking an abnormal demagnetization state of the permanent magnet synchronous motor; when the direct current bus current and the system efficiency of the motor monitored at any operating point reach the alarm thresholds simultaneously for successive two times within a set interval period, marking a demagnetization alarming state of the permanent magnet synchronous motor; and when direct current bus current and the system efficiency of the motor monitored at any operating point reach the alarm thresholds simultaneously for successive three times or over within the set interval period, marking a demagnetization fault state of the permanent magnet synchronous motor. At the time, the copper loss and the iron loss of the motor will be increased correspondingly, resulting in an obvious temperature rise effect, increase of the temperature of the motor and shortening of the service life. Vehicle driving shall be stopped.

S107:

Farly warning information is pushed: when judging that the demagnetization aging degree of the permanent magnet synchronous motor is in the alarm state or the fault state, the remote service management platform pushes the early warning information to a client side of the electric automobile in case that the warn state is triggered, and pushes parking information to the client side of the electric automobile in case that the fault state is triggered to stop vehicle operating, so as to prevent severe faults of the motor.

The method can also be used for judging the demagnetization aging degree of the permanent magnet synchronous motor in a whole vehicle controller or the motor controller of the electric automobile, so as to perform early warning or fault differentiation, can also be used for acquiring the output data of the permanent magnet synchronous motor of the electric automobile through an onboard diagnostic device so as to judge the demagnetization aging degree of the motor, and can also be used for monitoring other types of driving motors of the electric automobile.

By explaining the disclosed embodiments in a progressive way, those skilled in the art can implement or use the present invention. Various modifications of these embodiments will be obvious for professionals in the art. A general principle defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to these embodiments disclosed herein but is in accordance with the widest scope consistent with principle and novel features of the disclosure.

Claims

I. A method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile, comprising the following steps: S101: a data acquisition step: acquiring output data of the permanent magnet synchronous motor of the electric automobile; S102: an effective working condition determination step: determining an effective working condition for rapidly detecting demagnetization of the permanent magnet synchronous motor when a driving motor is in a power consumption state and a temperature of the driving motor is within a certain range; S103: a direct current bus current variation determination step: monitoring a direct current bus current variation corresponding to a same output torque in an effective working condition, and determining a reasonable variation range of a direct current bus current of a motor controller along with an electromagnetic torque and an accumulated mileage of the whole vehicle; S104: a system efficiency determination step: monitoring a system efficiency of the permanent magnet synchronous motor in an operating point according to each mileage range, and determining a reasonable range of the system efficiency of the permanent magnet synchronous motor in each mileage range; S105: a critical threshold determination step: establishing a real-time database of the direct current bus current of the motor controller and the system efficiency of the motor at the driving motor monitoring operating point, and determining critical thresholds of the direct current bus current of the motor controller and the system efficiency of the motor at the monitoring operating point in each mileage range; and S106: a demagnetization aging judgment step: extracting and analyzing data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.
2. The method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to claim 1, wherein the output data in the permanent magnet synchronous motor in S101 comprises: the accumulated mileage of the whole vehicle, a state of the driving motor, a rotating speed of the driving motor, a torque of the driving motor, the temperature of the driving motor, an input voltage of the motor controller and the direct current bus current of the motor controller.
3. The method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to claim 1, wherein a temperature range of the driving motor in S102 is 20-50°C.
4. The method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to claim 1, wherein the determining the effective operating point in S102 specifically comprises: selecting the rotating speed of the driving motor to be 30%, 60% and 90% of a rated rotating speed, wherein an allowable deviation of the rotating speed is 5% of the rated rotating speed; and selecting the torque of the driving motor to be 30%, 60% and 90% of a rated torque, wherein an allowable deviation of the torque is 10% of the rated torque.
5. The method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to claim 1, wherein the determining a reasonable variation range of a direct current bus current of a motor controller along with a load power and an accumulated mileage of the whole vehicle according to a torque equation and a kinematic equation of the permanent magnet synchronous motor in S103 has a specific formula as follows: nl, 7 = la, N i (4) 789% wf pw, TT dr © (2) wherein Te is an electromagnetic torque with a unit of N.m; np is a number of pole-pairs, and Lm is mutual inductance with a unit of H; L; is self-inductance of a motor rotor with a unit of H; ist is a torque component of a stator current with a unit of A; ris a rotor flux with a unit of Wb; om is a rotor mechanical angle frequency with a unit of rad/s; Tm is a load torque with a unit of N.m; u is a rotor loading viscous friction coefficient; and J is rotational inertia with a unit of kg.m?.
6. The method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to claim 1, wherein a calculation formula for the system efficiency of the motor in S103 1s as follows: ms G)

955.171 wherein n is the rotating speed of the driving motor with the unit of r/min; T is the torque of the driving motor with the unit of Nm; U is the input voltage of the motor controller with the unit of V; and I is the direct current bus current of the motor controller with the unit of A.
7. The method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to claim 1, wherein the judging the demagnetization aging degree of the permanent magnet synchronous motor in S106 specifically comprises: when the direct current bus current and the system efficiency of the motor monitored at any operating point reach alarm thresholds simultaneously for the first time, marking an abnormal demagnetization state of the permanent magnet synchronous motor, when the direct current bus current and the system efficiency of the motor monitored at any operating point reach the alarm thresholds simultaneously for successive two times within a set interval period, marking a demagnetization alarming state of the permanent magnet synchronous motor; and when direct current bus current and the system efficiency of the motor monitored at any operating point reach the alarm thresholds simultaneously for successive three times or over within the set interval period, marking a demagnetization fault state of the permanent magnet synchronous motor.
8. The method for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to any one of claims 1-7, further comprising S107: an early warning step: pushing early warning information to a client side of the electric automobile when judging that the demagnetization aging degree of the permanent magnet synchronous motor is in an alarm state or a fault state.
9. À system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile, comprising a data acquisition module, an effective working condition determination module, a current variation determination module, an efficiency determination module, a critical threshold determination module and a demagnetization aging judgment module connected successively, wherein the data acquisition module is configured to acquire output data of the permanent magnet synchronous motor of the electric automobile; the effective working condition determination module is configured to determine an effective working condition for rapidly detecting demagnetization of the permanent magnet synchronous motor when a driving motor is in a power consumption state and a temperature of the driving motor is within a certain range; the direct current bus current variation determination module is configured to monitor a direct current bus current variation corresponding to a same output torque in an effective working condition, and determine a reasonable variation range of a direct current bus current of a motor controller along with an electromagnetic torque and an accumulated mileage of the whole vehicle; the system efficiency determination module is configured to monitor a system efficiency of the permanent magnet synchronous motor in an operating point in each mileage range, and determine a reasonable range of the system efficiency of the permanent magnet synchronous motor in each mileage range; the critical threshold determination module is configured to establish a real-time database of the direct current bus current of the motor controller and the system efficiency of the motor at the driving motor monitoring operating point, and determine critical thresholds of the direct current bus current of the motor controller and the system efficiency of the motor at the monitoring operating point in each mileage range; and the demagnetization aging judgment module is configured to extract and analyze data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle, thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.
10.The system for rapidly detecting demagnetization of a permanent magnet synchronous motor of an electric automobile according to claim 9, further comprising an early warning module connected to the demagnetization aging judgment module and configured to extract and analyze data of the direct current bus current and the system efficiency of the motor relative to the database in a real-time operating process of the vehicle,

thereby judging a demagnetization aging degree of the permanent magnet synchronous motor.