Electric vehicle permanent magnet synchronous motor single current field weakening trajectory control method

Abstract

The application relates to a single-current field-weakening trajectory control method for a permanent magnet synchronous motor of an electric vehicle, and belongs to the field of field-weakening control technology of the permanent magnet synchronous motor of the electric vehicle. The method solves the problems of the complicated double-current field-weakening control method and the incapability of deep field weakening in the prior art. The method comprises the following steps: collecting the mechanical angular velocity and the load torque of the permanent magnet synchronous motor in real time; when the mechanical angular velocity is within the base speed range, controlling the direct and quadrature axis currents of the permanent magnet synchronous motor to run on a first trajectory; when the mechanical angular velocity exceeds the base speed range, controlling the permanent magnet synchronous motor through single-current control; when the load torque is not increased, controlling the direct and quadrature axis currents to run on a second trajectory; when the direct and quadrature axis currents of the permanent magnet synchronous motor run on the second trajectory and the load torque is increased, controlling the direct and quadrature axis currents to run on a third trajectory; and when the load torque of the motor is stable, controlling the direct and quadrature axis currents to run on a fourth trajectory. The single-current field-weakening trajectory control of the permanent magnet synchronous motor of the electric vehicle is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of permanent magnet synchronous motor weak magnetic control of electric vehicles, and particularly relates to a single-current weak magnetic trajectory control method for a permanent magnet synchronous motor of an electric vehicle. BACKGROUND

[0002] At present, the existing permanent magnet synchronous motor control of electric vehicles generally selects a double-current weak magnetic control technology, wherein for negative i ds The compensation method cannot achieve deep weak magnetism, and cannot make the electric vehicle motor run at a higher speed: for the lookup table method, a large number of electric vehicle motor tables need to be obtained, which is time-consuming and has poor portability; the gradient increment method is complex and requires accurate electric vehicle motor parameters; and the current angle method cannot run in three zones. The double-current weak magnetic control technology in the prior art is difficult to overcome the actual working conditions of the electric vehicle in the high-speed running state, the poor road conditions, and the sudden load torque.

[0003] For the traditional fixed-interaxis voltage single-current weak magnetic control, although the cross-coupling effect problem is solved, it only falls into the fixed-interaxis single-current weak magnetic control, and the load capacity is not high; and for the variable-interaxis voltage weak magnetic control running in the voltage limiting circle, although the voltage utilization rate is improved, and the current trajectory runs on the voltage limiting circle, it is difficult to directly switch from the base speed state to the voltage limiting circle, and the problem of loss of control easily exists.

[0004] Therefore, the prior art lacks a single-current weak magnetic trajectory control method for a permanent magnet synchronous motor of an electric vehicle. SUMMARY

[0005] In view of the above analysis, the embodiments of the present application aim to provide a single-current weak magnetic trajectory control method for a permanent magnet synchronous motor of an electric vehicle, to solve the problems of poor robustness, complex control method, and inability to achieve deep weak magnetism of the existing traditional double-current weak magnetic control method.

[0006] In one aspect, the embodiments of the present application provide a single-current weak magnetic trajectory control method for a permanent magnet synchronous motor of an electric vehicle, comprising:

[0007] real-time collection of mechanical angular velocity and load torque of the permanent magnet synchronous motor;

[0008] when the mechanical angular velocity is within the base speed range, controlling the fixed-interaxis current of the permanent magnet synchronous motor to run on a first trajectory;

[0009] When the mechanical angular velocity exceeds the base speed range, the permanent magnet synchronous motor is controlled by single current; when the load torque does not increase, the direct and quadrature axis current is controlled to run on the second track; when the direct and quadrature axis current of the permanent magnet synchronous motor runs on the second track and the load torque increases, the direct and quadrature axis current is controlled to run to the third track; when the motor load torque is stable, the direct and quadrature axis current is controlled to run on the fourth track.

[0010] Further, the third track is a line segment from the position of the load torque switching point S1 along the symmetry axis of the voltage limiting circle to the speed maximum torque point B1.

[0011] Further, the voltage limiting circle model is expressed as:

[0012]

[0013] Wherein, i d is the direct axis current, ω is the mechanical angular velocity, L s is the stator inductance, ψ m is the back EMF coefficient, R s is the stator winding resistance, i q is the quadrature axis current, U smax is the maximum phase voltage.

[0014] Further, the symmetry axis of the voltage limiting circle is expressed as:

[0015]

[0016] Wherein, i d is the direct axis current, ω is the mechanical angular velocity, L s is the stator winding inductance value, ψ m is the back EMF coefficient, R s is the stator winding resistance.

[0017] Further,

[0018] The speed maximum torque point B1 is the intersection of the voltage limiting circle and the symmetry axis of the voltage limiting circle.

[0019] Further, when the mechanical angular velocity exceeds the base speed range, the field weakening control voltage is set, the direct and quadrature axis current of the permanent magnet synchronous motor runs along the second track, and the second track is a curve running along the direct and quadrature axis voltage track ES with E point as the starting point; the E point is the base speed and the starting torque overcoming point;

[0020] The direct and quadrature axis voltage track ES is limited by the following constraint conditions:

[0021]

[0022]

[0023]

[0024] wherein i q is the quadrature axis current, ω r = Pω is the electrical angular velocity of the motor, L s is the stator winding inductance, R s is the stator winding resistance, i d is the direct axis current, V FWC is the flux-weakening control voltage, ψ m is the back EMF coefficient, T e is the electromagnetic torque, P is the number of poles of the motor, T L is the load torque, ω is the mechanical angular velocity, J is the moment of inertia, and B is the viscous coefficient.

[0025] Further, the load torque switching point S1 is the intersection of the axis of symmetry of the voltage limit circle and the direct-quadrature axis voltage trajectory ES.

[0026] Further, when the mechanical angular velocity is in the base speed range, the control algorithm of i d = 0 is used to determine the first trajectory, which is a line segment running from the direct-quadrature axis origin to the base speed and overcoming the starting torque E point.

[0027] The E point is the base speed and overcoming the starting torque point, and the E point quadrature axis current is expressed as:

[0028]

[0029] T e = T L + Bω1+ kJ

[0030] i q is the quadrature axis current, T e is the electromagnetic torque, P is the number of poles of the motor, ψ m is the back EMF coefficient, T L is the load torque, B is the viscous coefficient, ω1 is the base speed value of the motor mechanical angular velocity, k is the acceleration of the motor mechanical angular velocity, and J is the moment of inertia.

[0031] Further,

[0032] When the permanent magnet synchronous motor runs on the second trajectory, the load torque increases, and the permanent magnet synchronous motor first runs to the S1 point and then runs along the third trajectory.

[0033] Further, when the load torque is stable, a variable quadrature axis voltage flux-weakening control algorithm is used to set the fourth trajectory, so that the motor runs on the voltage limit circle.

[0034] Compared with the prior art, the application can achieve at least one of the following beneficial effects:

[0035] 1. The permanent magnet synchronous motor single current field weakening trajectory operation planning method improves the controllable ability of the permanent magnet synchronous motor field weakening control;

[0036] 2. The method of adopting the fixed-axis single current field weakening control, making the current trajectory run on the fixed-axis single current field weakening curve, and then transitioning to the voltage limiting circle solves the problems of poor robustness, complex control method and inability to deep field weakening of the traditional double current field weakening control method;

[0037] 3. The single current field weakening trajectory operation planning method adopted by the application solves the problem of poor load capacity of the traditional fixed-axis voltage single current field weakening control, and also solves the problem of easy loss of control in the switching process of variable-axis voltage field weakening control.

[0038] The above technical solutions can be combined with each other to achieve more preferred combination solutions. Other features and advantages of the application will be described in the subsequent specification, and some advantages will become apparent from the specification or will be understood by implementing the application. The purpose and other advantages of the application can be achieved and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0039] The accompanying drawings are only for the purpose of illustrating specific embodiments and are not considered as limiting the application, and in the entire drawings, the same reference signs represent the same parts.

[0040] Figure 1 The flow chart of the electric vehicle permanent magnet synchronous motor single current field weakening trajectory control method shown in an embodiment of the application;

[0041] Figure 2 The single current field weakening control schematic diagram shown in an embodiment of the application;

[0042] Figure 3 The electric vehicle permanent magnet synchronous motor single current field weakening trajectory control trajectory schematic diagram shown in an embodiment of the application;

[0043] Figure 4 The voltage limiting circle model schematic diagram shown in an embodiment of the application;

[0044] Figure 5 The structure diagram of the electric vehicle permanent magnet synchronous motor single current field weakening trajectory control method shown in an embodiment of the application. DETAILED DESCRIPTION

[0045] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0046] like Figure 1 As shown, a specific embodiment of the present invention discloses a single current magnetic weakening trajectory control method for a permanent magnet synchronous motor of an electric vehicle, comprising:

[0047] S10, collecting the mechanical angular velocity and load torque of the permanent magnet synchronous motor in real time;

[0048] Specifically, the fixed and quadrature axis currents of the permanent magnet synchronous motor are controlled according to the different values ​​of the mechanical angular velocity of the permanent magnet synchronous motor and the change of the load torque.

[0049] Specifically, for a current-controlled AC motor, the direct-axis current i d and the quadrature axis current i q There is a linear relationship, which can be expressed as:

[0050]

[0051] From formula (1), we can see that: First, when the motor runs below the base speed, due to the quadrature axis voltage v q The amplitude of is not limited, so i d and i q can be controlled independently; secondly, when the motor runs above the base speed, due to the quadrature axis voltage v q Limited by the DC bus voltage, i d and i q There is a strong cross-coupling relationship between them; Figure 2 This is a schematic diagram of single current weakening magnetic control. Figure 2 It can be seen that the current command generated by the speed regulator contains not only torque current information but also demagnetization current information. Compared with the two current regulators of the traditional dual current weakening magnetic field, only one controller is used to actively control i d Current; quadrature axis voltage v q is a fixed value V FWC , then i q Will be automatically generated.

[0052] When the PMSM of an electric vehicle runs below the base speed, the motor adopts the zero current (i d * =0) control, the speed regulator outputs the quadrature axis current i q * , through the direct axis current regulator PI regulator output quadrature axis voltage v q * ,i d* = 0 is regulated by the PI regulator of the cross-axis current regulator to output a voltage v d * .

[0053] Specifically, when the electric vehicle needs to run at a higher speed, the PMSM needs to run above the base speed, the flux-weakening condition is reached, and a switching command is given, and the output of the speed regulator is given as the given i d * The i d is regulated by the PI regulator of the direct-axis current loop, so that the flux-weakening is achieved, and the change in the direct-axis current causes a change in the cross-axis current according to the cross-coupling relationship.

[0054] S20, when the mechanical angular velocity is in the base speed range, controlling the direct-axis and cross-axis currents of the permanent magnet synchronous motor to run on a first trajectory;

[0055] Specifically, as Figure 3 shown, when the mechanical angular velocity is in the base speed range, the control algorithm of is used to determine the first trajectory, and the first trajectory is a line segment running from the origin of the direct-axis and cross-axis to the point of base speed and overcoming the starting torque E. The motor runs in the base speed range, and the traditional control is used. For electric vehicles, the starting torque is relatively large, and as the load torque increases, the electromagnetic torque also increases to T e1 For a labeled permanent magnet synchronous motor, the electromagnetic torque is directly proportional to the cross-axis current i q Therefore, the actual current running trajectory runs from the origin to E.

[0056] The E point is the base speed and the point of overcoming the starting torque, that is, when the mechanical angular velocity ω reaches the base speed value ω1 of the motor mechanical angular velocity, the corresponding cross-axis current of the E point is expressed as:

[0057]

[0058]

[0059] i q is the cross-axis current, ω1 is the base speed value of the motor mechanical angular velocity, T e is the electromagnetic torque, P is the number of poles of the motor, ψ m is the back EMF coefficient, T L is the load torque, B is the viscous coefficient, is the acceleration of the motor mechanical angular velocity, and J is the moment of inertia.

[0060] S30, when the mechanical angular velocity exceeds the base speed range, the permanent magnet synchronous motor is controlled by single current; when the load torque does not increase, the permanent magnet synchronous motor stator-interaxis current is controlled to run on the second track; when the permanent magnet synchronous motor stator-interaxis current runs on the second track and the load torque increases, the permanent magnet synchronous motor stator-interaxis current is controlled to run to the third track; when the motor load torque is stable, the permanent magnet synchronous motor stator-interaxis current is controlled to run on the fourth track.

[0061] Specifically, as shown in Figure 3 when the mechanical angular velocity exceeds the base speed range, the weak magnetic control voltage is set, the permanent magnet synchronous motor stator-interaxis current runs along the second track, and the second track is a curve starting from point E and running along the stator-interaxis voltage track ES; more specifically, when the motor needs to run beyond the base speed range, the motor needs to run at a higher speed in the weak magnetic mode, and the stator-interaxis voltage single current weak magnetic control method is used, that is, the interaxis voltage is given a constant value as the weak magnetic control voltage V FWC , with the continuous increase of the speed, the current track in the weak magnetic region runs on the ES curve along the second track of the stator-interaxis voltage.

[0062] The ES curve is limited by the following constraint conditions:

[0063]

[0064]

[0065]

[0066] wherein i q is the interaxis current, ω r =Pω is the motor electrical angular velocity, L s is the stator winding inductance value, R s is the stator winding resistance, i d is the direct-axis current, V FWC is the weak magnetic control voltage, ψ m is the back electromotive force coefficient, T e is the electromagnetic torque, P is the motor pole number, T L is the load torque, ω is the mechanical angular velocity, J is the moment of inertia, and B is the viscous coefficient.

[0067] Specifically, the intersection of the stator-interaxis voltage track ES line segment and the symmetry axis of the voltage limiting circle is the load torque switching S1 point;

[0068] Specifically, the intersection of the voltage limiting circle and the symmetry axis of the voltage limiting circle is the maximum speed torque point B1.

[0069] More specifically, as shown in Figure 3 the third trajectory is a line segment from the position of the load torque switching point S1 along the symmetry axis of the voltage limit circle to the position of the speed maximum torque point B1;

[0070] More specifically, when the permanent magnet synchronous motor operates on the second trajectory, the load torque increases, and the permanent magnet synchronous motor first operates to the S1 point and then operates along the third trajectory.

[0071] Specifically, as shown in Figure 4 the voltage limit circle model is expressed as:

[0072]

[0073] where i d is the direct-axis current, ω is the mechanical angular velocity, L s is the stator inductance, ψ m is the back EMF coefficient, R s is the stator winding resistance, i q is the quadrature-axis current, U smax is the phase voltage maximum. As shown in Figure 4 the voltage limit circle changes with .

[0074] Specifically, the symmetry axis of the voltage limit circle is expressed as:

[0075]

[0076] where i d is the direct-axis current, ω is the mechanical angular velocity, L s is the stator inductance value, ψ m is the back EMF coefficient, R s is the stator winding resistance.

[0077] Specifically, when the electric vehicle changes from a flat road to a poor road, it needs to overcome greater friction, so the load torque of the motor increases, at this time the motor needs to have the ability to reach the maximum torque at the corresponding speed, and the point where the motor is selected to operate to have the opportunity to reach the maximum torque output is the symmetry axis of the voltage limit circle, and then to the third trajectory, along to cope with the increase in load torque, and the symmetry axis is the intersection between the direct-axis voltage trajectory and the quadrature-axis voltage trajectory, which is defined as the load torque switching S1 point, when the load torque increases again, it switches to the third trajectory, that is, the motor current will first return to the S1 point, and then along When the motor is pushed from the S1 point to the B1 point, that is, the corresponding speed maximum torque point, specifically, the B1 point is defined as the intersection between the voltage limit circle and the symmetry axis At the intersection of the two axes, the motor switches from fixed quadrature axis voltage single current control to variable quadrature axis voltage flux weakening control. This means that the motor is able to operate at its maximum output capacity.

[0078] Specifically, when the load torque is stable, a variable quadrature axis voltage flux weakening control algorithm is used to set the fourth trajectory so that the motor runs on the voltage limit circle.

[0079] More specifically, the current trajectory operates on the voltage limit circle of the fourth trajectory variable quadrature-axis voltage control, i.e., at the point of maximum voltage utilization. At this point, the electric vehicle is capable of achieving maximum torque output at the corresponding speed, to cope with the actual operating conditions of high-speed operation, deteriorating road conditions, and sudden load torque increases.

[0080] Specifically, Figure 5 As shown in FIG, a single current flux weakening trajectory control method for a permanent magnet synchronous motor of an electric vehicle is described in detail.

[0081] First, we need to detect the three-phase current. We collect the i of the permanent magnet synchronous motor in the three-phase stationary coordinate system. a ,i b ,i c The three-phase current is used as the input of Clarke transformation, which transforms the detected three-phase current into i in the two-phase stationary coordinate system. α and i β , i in the two-phase stationary coordinate system α and i β As the input of Park transform, Park transform output is i in two-phase rotating coordinate system d and i q .

[0082] Direct axis voltage v d and quadrature axis voltage v q As the input of the space vector pulse width modulation (SVPWM), the output three-phase voltage v a , v b , v c .

[0083] Specifically, under the base speed of PMSM of electric vehicles, PMSM adopts i d * =0 control mode; when the electric vehicle PMSM needs to run at a higher speed, we let the motor enter the weak magnetic region. First, let the motor adopt the single current weak magnetic control mode. The output of the speed PI controller is current, The current output is the quadrature axis voltage v d * , and v d * By the fixed value V FWCto determine; then use The current trajectory is moved to the voltage limit circle by using a method of variable alternating-axis voltage flux weakening control to make the motor run on the voltage limit circle.

[0084] (1) First trajectory

[0085] When the motor speed is within the base speed range (the motor parameters can be used to find the maximum speed of the motor), we use i d =0 control algorithm: consists of a first outer loop speed controller, a first inner loop current controller and a second inner loop current controller.

[0086] Specifically, the reference speed ω set in the first outer loop speed controller * Same as actual speed The speed difference Δω is obtained by performing the difference, and the speed difference Δω is used as the input of the first PI regulator in the first outer ring speed controller. The output of the first outer ring speed loop is the first quadrature axis reference current. Specifically, the actual rotational speed may be detected by a position sensor and then subjected to differentiation processing, or may be observed by an observer controlled without a speed sensor.

[0087] The first inner loop current controller is i d Axis current controller, the second inner loop current controller is i q Axis current controller:

[0088] set up As the first inner loop current controller (i.e. d The input of the axis current controller) is then transformed with Park to output the fixed axis current i d Do the difference and get the first fixed axis current difference Δi d1 , the first fixed axis current difference Δi d1 As the first inner loop current controller (i.e. d The input of the second PI regulator in the axis current controller); the first inner loop current controller (i.e. d Axis current controller) outputs the first fixed axis output voltage

[0089] First quadrature-axis reference current As the second inner loop current controller (i.e. q The input of the quadrature axis current controller) is then converted with the Park transform output. q Do the difference and get the first quadrature axis current difference Δi q1 , the first quadrature-axis current difference Δi q1 As the input of the third PI regulator in the second inner loop current controller; the second inner loop current controller (i.e., i qthe output first quadrature axis output voltage

[0090] Specifically, when the permanent magnet synchronous motor operates in the base speed range, the conventional i d =0 control is adopted, and for an electric vehicle, the starting torque is relatively large, and as the load torque increases, the electromagnetic torque also increases to a first electromagnetic torque T e1 For a labeled permanent magnet synchronous motor, the electromagnetic torque is directly proportional to the quadrature axis current i q Therefore, the actual current operating trajectory runs from the origin to the E point.

[0091] More specifically, i d =0 control is equivalent to only the quadrature axis current i q is output to provide energy to the motor, and as the motor speed ω and the load torque T L increase, the electromagnetic torque T e is also constantly increasing, and the quadrature axis current i q also increases, so as shown in FIG. 1, in the i d -i q trajectory analysis diagram, it can be seen that the current trajectory is this curve OE; Figure 4

[0092] (2) Second trajectory

[0093] When the current speed is above the base speed (i.e., the motor given speed is greater than the motor maximum speed), the motor is first operated in the constant quadrature axis single current flux weakening control algorithm, which is composed of a second outer loop speed controller and a third inner loop current controller (i d current controller), the set reference speed ω * is subtracted from the actual speed ω to obtain Δω, and Δω is input into the fourth PI regulator in the second outer loop speed controller, and the output of the second outer loop speed controller is the first constant axis reference current

[0094] The first constant axis reference current is again subtracted from i d to obtain the second constant axis current difference Δi d2 , and the second constant axis current difference Δi d2 is input into the fifth PI regulator in the third inner loop current controller, and the output of the third inner loop current controller is the second constant axis output voltage

[0095] The second quadrature axis output voltage V FWC is the flux weakening control voltage, which is a fixed value, and is the final value of the first constant axis output voltage output in the first trajectory.​

[0096] Specifically, when the electric vehicle load torque is constant, the electromagnetic torque T e is constant, the speed increases, the second trajectory is approximately a straight line, as shown in Figure 4 the middle straight line ES.

[0097] (3) the third trajectory

[0098] When the permanent magnet synchronous motor operates on the second trajectory, the electric vehicle speed operates above the base speed, the actual road condition is poor, and the load torque T L increases, so that the motor operates on the symmetric axis of the voltage limit circle, that is at this time, the fourth inner loop current controller (i d current controller) is composed of;

[0099] The current is input to the fourth inner loop current controller (i d current controller), and the stator current i d output by the Park transformation is subtracted to obtain the third stator current difference Δi d3 , the third stator current difference Δi d3 is input to the sixth PI regulator, and the fourth inner loop current controller outputs the third stator output voltage

[0100] The third quadrature axis output voltage V FWC is the flux-weaken control voltage, which is a fixed value, and is the final value of the first stator output voltage in the first trajectory.

[0101] As the load torque increases, the electromagnetic torque T e also increases, i q , and therefore also increases, as shown in Figure 4 , at this time the current trajectory operates on the S1B1 curve;

[0102] (4) the fourth trajectory

[0103] Faster, the load torque is stable, and the motor load torque T L is stable, so we use a variable quadrature axis voltage flux-weakening control algorithm to make the motor operate on the voltage limit circle, which is composed of a third outer loop speed controller and a fifth inner loop current controller (i d current controller).

[0104] The given speed ω * is subtracted from the actual speed ω to obtain the speed difference Δω, and the speed difference Δω is input to the seventh PI regulator in the third outer loop speed controller, and the third outer loop speed controller outputs the second stator reference current

[0105] Second constant-axis reference current Same constant-axis current i d Subtracting, fourth constant-axis current difference Δi d4 , fourth constant-axis current difference Δi d4 As the input of the eighth PI regulator in the fifth inner loop current controller (i d Current controller), the fifth inner loop current controller outputs the fourth constant-axis output voltage

[0106] Fourth quadrature-axis output voltage Expressed as:

[0107]

[0108] Wherein, U smax is the maximum phase voltage value, is the quadrature-axis voltage given value.

[0109] As Figure 4 shown, at this time the motor operates on the voltage limit circle.

[0110] The single current field-weakening trajectory control method of the permanent magnet synchronous motor of the electric vehicle uses the single current field-weakening trajectory control method to improve the controllable ability of the field-weakening control of the permanent magnet synchronous motor; adopts the constant quadrature-axis single current field-weakening control, so that the current trajectory runs on the constant quadrature-axis single current field-weakening curve, and then transits to the method of operating on the voltage limit circle, solves the problems of poor robustness, complex control method and inability to deep field-weakening of the traditional double current field-weakening control method; the single current field-weakening trajectory running planning method adopted by the application solves the problem of poor load capacity of the traditional constant quadrature-axis voltage single current field-weakening control, and also solves the problem of easy loss of control in the switching process of the variable quadrature-axis voltage field-weakening control.

[0111] Those skilled in the art can understand that all or part of the processes of the above-mentioned embodiments can be completed by a computer program instructing related hardware, and the program can be stored in a computer readable storage medium. The computer readable storage medium is a disk, an optical disk, a read-only memory or a random access memory, etc.

[0112] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered within the protection scope of the application.

Claims

1. A method for flux trajectory control of a permanent magnet synchronous motor for an electric vehicle, characterized by, The method comprises: real-time acquisition of mechanical angular velocity and load torque of the permanent magnet synchronous motor; when the mechanical angular velocity is within the base speed range, controlling the permanent magnet synchronous motor direct-quadrature axis current to run on a first track; when the mechanical angular velocity exceeds the base speed range, the permanent magnet synchronous motor is controlled by a single current; when the load torque does not increase, controlling the direct-quadrature axis current to run on a second track; when the permanent magnet synchronous motor direct-quadrature axis current runs on the second track and the load torque increases, controlling the direct-quadrature axis current to run to a third track, the third track being a line segment from a load torque switching point S1 to a maximum torque point B1 along an axis of symmetry of a voltage limit circle, wherein the load torque switching point S1 is an intersection of the axis of symmetry of the voltage limit circle and a direct-quadrature axis voltage track ES, and the maximum torque point B1 is an intersection of the voltage limit circle and the axis of symmetry of the voltage limit circle; when the motor load torque is stable, controlling the direct-quadrature axis current to run on a fourth track.

2. The single current field weakening track control method for the permanent magnet synchronous motor of the electric vehicle according to claim 1, wherein the voltage limit circle model is expressed as:

3. The single current field weakening track control method for the permanent magnet synchronous motor of the electric vehicle according to claim 1, wherein the axis of symmetry of the voltage limit circle is expressed as: where i d is the direct axis current, ω is the mechanical angular speed, L s is the stator inductance, ψ m is the back EMF coefficient, R s is the stator winding resistance, i q is the quadrature axis current, U smax is the phase voltage maximum.

4. The single current field weakening track control method for the permanent magnet synchronous motor of the electric vehicle according to claim 1, wherein when the mechanical angular velocity exceeds the base speed range, a field weakening control voltage is set, and the permanent magnet synchronous motor direct-quadrature axis current runs along a second track, the second track being a curve starting from an E point and running along the direct-quadrature axis voltage track ES; the E point being a base speed and overcoming a starting torque point; the direct-quadrature axis voltage track ES is limited by the following constraint conditions: where i d is the direct axis current, ω is the mechanical angular speed, L s is the stator winding inductance value, ψ m is the back EMF coefficient, R s is the stator winding resistance.

5. The single current field weakening track control method for the permanent magnet synchronous motor of the electric vehicle according to claim 4, wherein the E point is a base speed and overcoming a starting torque point, and an E point direct-quadrature axis current is expressed as:

6. The single current field weakening track control method for the permanent magnet synchronous motor of the electric vehicle according to claim 1 or 5, wherein when the permanent magnet synchronous motor runs on the second track and the load torque increases, the permanent magnet synchronous motor first runs to the S1 point and then runs along the third track.

7. The single current field weakening track control method for the permanent magnet synchronous motor of the electric vehicle according to claim 1, wherein when the load torque is stable, a fourth track is set by using a variable quadrature axis voltage field weakening control algorithm to make the motor run on the voltage limit circle. where i q is the quadrature-axis current, ω r = Pω is the electrical angular velocity of the motor, L s is the stator winding inductance, R s is the stator winding resistance, i d is the direct-axis current, V FWC is the field-weakening control voltage, ψ m is the back-emf coefficient, T e is the electromagnetic torque, P is the number of poles of the motor, T L is the load torque, ω is the mechanical angular velocity, J is the moment of inertia, and B is the viscous coefficient. ​ when the mechanical angular speed is in the base speed range, the control algorithm with i d = 0 determines the first trajectory, which is a line segment running from the origin of the direct-quadrature axis to the base speed and overcoming the starting torque E point; ​ T e = T L + Bω1+ kJ i q is the quadrature axis current, T e is the electromagnetic torque, P is the number of motor poles, ψ m is the back EMF coefficient, T L is the load torque, B is the viscous coefficient, ω1 is the motor mechanical angular speed base value, k is the motor mechanical angular speed acceleration, J is the moment of inertia. ​ ​ ​ ​

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