CN115411997A - Torque calibration method for permanent magnet synchronous motor - Google Patents

Abstract

The invention discloses a torque calibration method for a permanent magnet synchronous motor. The process is as follows: controlling the rotating speed to change from the initial rotating speed to the final calibration rotating speed in sequence according to the first step length; at each rotating speed, controlling the current to change from the initial current to the final calibration current in turn according to the second step length; continuously adjusting the control angle when a current is given until the output torque of the motor reaches the maximum, and obtaining a modulation coefficient under the corresponding rotating speed-current and a current ratio of a d axis and a q axis of the motor; comparing the modulation coefficient with a threshold value, and recording and storing data at the moment if the modulation coefficient is smaller than a first threshold value; if the modulation factor is larger than or equal to the first threshold value, the control angle is adjusted again until the modulation factor is equal to the second threshold value, and the data at the moment is recorded and stored. The invention judges the modulation coefficient in the calibration process, adjusts the control angle to ensure that the modulation coefficient is near 0.95, and further determines the weak magnetic curve.

Description

Torque calibration method for permanent magnet synchronous motor

Technical Field

The invention belongs to the technical field of automobiles, and particularly relates to a torque calibration method for a permanent magnet synchronous motor.

Background

The torque calibration of the permanent magnet synchronous motor is mainly divided into two sections, before a weak magnetic region, the motor outputs the maximum torque as much as possible under the same current for the purpose of optimal efficiency, and the curve is called as a maximum torque current ratio curve (MTPA curve); after the weak magnetic region, the output voltage is insufficient, the motor is ensured not to enter an overmodulation region through weak magnetism, and the curve is called a weak magnetic curve. The torque calibration means to mark the two curves under all conditions. At present, many manufacturers determine the two curves by traversing different combinations of currents of the DQ shaft under different torques and different rotating speeds, and the calibration process is complex.

Meanwhile, in the prior art, different voltage levels need to be considered, and as the field weakening curve of the motor changes along with the change of the voltage, the calibration of a plurality of voltage levels is often required during the calibration, which takes long time.

Disclosure of Invention

The invention aims to solve the defects existing in the background technology and provide a permanent magnet synchronous motor torque calibration method which is simple to operate.

The technical scheme adopted by the invention is as follows: a torque calibration method of a permanent magnet synchronous motor is characterized in that under calibrated bus voltage, the rotating speed is controlled to change from the initial rotating speed to the final calibrated rotating speed in sequence according to a first step length;

at each rotating speed, controlling the current to change from the initial current to the final calibration current in turn according to the second step length;

continuously adjusting the control angle when a current is given until the output torque of the motor reaches the maximum, and obtaining a modulation coefficient under the corresponding rotating speed-current and a current ratio of a d axis and a q axis of the motor;

comparing the modulation coefficient with a threshold value, and recording and storing the rotating speed, the torque, the given current and the control angle if the modulation coefficient is smaller than a first threshold value;

if the modulation factor is larger than or equal to the first threshold value, the control angle is adjusted again until the modulation factor is equal to the second threshold value, and the rotating speed, the torque, the given current and the control angle at the moment are recorded and stored.

Further, after calibration under all rotation speeds and currents is completed, a two-dimensional table is manufactured according to the recorded and stored data.

Further, the two-dimensional table is a two-dimensional table with torque as an abscissa, rotation speed as an ordinate, and contents of d-axis current and q-axis current.

Further, the method also comprises the step of determining calibration data under different bus voltages, and the process is as follows: and converting the feedback rotating speed under the current bus voltage, and searching the two-dimensional table through the converted rotating speed to obtain calibration data under the current bus voltage.

Further, the speed is fed back for conversion by the following formula:

INs＝Un*Ns/Udc

wherein INs is the converted rotation speed; un is a calibrated bus voltage; ns is the feedback rotation speed; udc is the current bus voltage.

Further, in the calibration process, the temperatures of the motor and the controller are monitored in real time, if the temperature is greater than or equal to the temperature threshold, the calibration is suspended, and the calibration is continued until the temperature is less than the temperature threshold.

Further, the first step size is 100rpm to 300rpm.

Further, the second step size is 10A-30A.

Further, the first threshold is 1.0

Further, the second threshold is 0.95 ± 0.03.

The invention has the beneficial effects that:

1) The invention judges the modulation coefficient in the calibration process, adjusts the control angle to ensure that the modulation coefficient is near 0.95, and further determines the weak magnetic curve.

2) The invention carries out normalization processing on the rotating speed during table look-up, and processes the ordinate of the table into the reciprocal of the current magnetic flux, thereby considering the influence of the bus voltage on the weak magnetic curve and avoiding repeated calibration under different voltage platforms.

Drawings

FIG. 1 is a flow chart of the present invention.

Fig. 2 is a trace diagram of a voltage limit circle and a current limit circle on a d-q coordinate plane.

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

In general, a driving motor for an electric car is torque-controlled, and in the control, not only an accurate torque needs to be output, but also the influence of a voltage limit circle and a current limit circle on the control needs to be considered. The optimal control is realized by realizing the maximum torque current ratio control, namely, the maximum torque is output under the same current.

In a steady state situation, the voltage vector equation of the motor in d-q coordinates is:

u _q ＝R _s i _q +ω _r L _d i _d +ω _r ψ _f (1)

u _d ＝R _s i _d -ω _r L _q i _q (2)

in the formula: u. u _q Equal q-axis voltage; u. of _d Equal d-axis voltage; r _s Is a stator resistor; i.e. i _q Is the q-axis current; i.e. i _d Is the d-axis current; omega _r The motor rotating speed; psi _f Is a magnetic linkage; l is a radical of an alcohol _q Is a q-axis inductance; l is _d Is the d-axis inductance.

In the formula: u. u _s Is a voltage vector.

When the motor runs at high speed, the resistance voltage drop in the formula (1) can be ignored, and the formula (3) can be written as follows:

|u _s |＝(ω _r ψ _f +ω _r L _d i _d ) ² +(ω _r L _q i _q ) ² (4)

namely:

the trajectories of the voltage limit circle and the current limit circle on the d-q coordinate plane, which can be obtained from the voltage limit equation (4) and the current limit equation (5), are shown as a curve s and a curve w in fig. 2.

The torque equation of the permanent magnet synchronous motor is as follows:

in the formula: t is _e Is the torque; p is the number of pole pairs of the motor.

According to Lagrange's extremum method, when minimum stator current is achieved

The relationship between the direct current component id and the quadrature current component iq can be found as:

the maximum torque to current ratio (MTPA) curve obtained according to equation (7) is shown as curve L in fig. 2.

In fig. 2: w1, w2, w3, w4 represent 4 different rotation speeds, w1< w2< w3< w4; t1, T2, T3, T4 represent 4 different torques T1> T2> T3> T4. The current trajectory was analyzed from two conditions:

(1) The current speed is 0 and the torque is 0, and the current is at point O. The speed is increased to w2 while the current is still at point O. The output torque of the motor is continuously increased to T1. At which point the current trajectory has reached the boundary of the voltage limit circle w2 after moving from point O along the MTPA curve L to point C, at which time the torque is T2. If torque is to be increased further at this time, the current trajectory moves along the voltage limit circle from point C to point E. Point E is the tangent point of the voltage limit circle w2 and the iso-torque curve T1, which indicates that the point has reached the peak torque of the motor at the rotation speed, and the torque of the motor is T1.

(2) The current speed is 0 and the torque is 0, and the current is at point O. The speed is increased to w1, while the current is still at point O. Increasing the torque to T3, and after the current track is sent from the point O and moves to the point B along the MTPA curve L, the torque is T3; the rotating speed is continuously increased to w2, at the moment, the point B is still within the voltage limit circle w2, and the current track is still at the point B; the speed continues to increase to w3, at which point B is not within the voltage limit circle w3, and the current trajectory moves from point B along the iso-torque curve T3 to point G, at which the speed is w3 and the torque is T3.

The summary is summarized as follows: when the current track is within the voltage limit circle, an MTPA curve is followed; after the current track exceeds the voltage limit circle, the current track runs along the voltage limit circle; after the current trajectory runs to the tangent point of the constant torque curve and the voltage limit circle (as shown by the MTPV curve in the single arc line in fig. 2), the motor limit is reached and the current does not increase any more.

Based on the principle, the invention provides a torque calibration method for a permanent magnet synchronous motor, wherein when a current track is within a voltage limit circle, an MTPA curve is followed.

When the relationship between id and iq is as shown in the formula (7), the maximum torque can be output at the same current. According to the calibration method. In the non-flux weakening region, a fixed current is output, and by adjusting a current phase angle (control angle), when the output maximum torque is found, the current value and the current phase angle are recorded.

After the current trajectory exceeds the voltage limit circle, the current trajectory runs along the voltage limit circle:

see equation (5), where u _s Has a maximum value of

That is, when the bus voltage is determined, the area of the voltage limit circle is continuously reduced along with the increase of the rotating speed. For calibration convenience, modulation factors are defined.

And during calibration, the modulation coefficient is ensured to be equal to 0.95 all the time under different rotating speeds of the weak magnetic area. The current value and current phase angle are recorded.

After the tangent point of the torque curve and the voltage limit circle reaches the limit of the motor, the current is not increased any more.

Physical quantities to be adjusted in calibration:

(1) Magnitude of input current

The input current increases according to a certain rule, and 20A is currently planned as an interval calibration point. Starting at 0A and ending at a torque at which the output torque reaches an off-peak characteristic.

(2) Phase angle of current

The current optimal phase angle can be derived from the optimal phase angle corresponding to the current obtained by simulation in the design of the motor, and the point of outputting the maximum torque is found by modifying the phase angle in the calibration process.

(3) Rotational speed

The rotating speed of the motor is increased progressively according to a certain rule, and the current planned interval is 150rpm as an interval calibration point. Starting at 0rpm and ending at the peak speed.

As can be seen from equation (5), the elliptical area is smaller as the rotation speed is higher; when the voltage is smaller, the voltage area is also smaller. In the weak magnetic region, we are actually at the boundary of the calibration ellipse. This boundary is understood to be a magnetic flux. The flux is determined by the quotient of the bus voltage and the motor speed.

As shown in fig. 1, the specific calibration process is as follows: under the calibrated bus voltage, controlling the rotating speed to sequentially increase from the initial rotating speed according to the first step length until the final calibrated rotating speed (namely the peak rotating speed); the initial rotation speed is 150rpm and the first step is between 100rpm and 300rpm, preferably 150rpm.

At each rotating speed, the control current is changed from the initial current to the final calibration current (namely the peak current) in turn according to the second step length; the initial current is 20A and the second step size is 10A-30A, preferably 20A.

Continuously adjusting the control angle theta when a current is given until the output torque of the motor reaches the maximum, and obtaining a modulation coefficient under the corresponding rotating speed-current and a current ratio of a d axis and a q axis of the motor;

comparing the modulation coefficient with the threshold value, namely judging whether the current modulation coefficient is in a non-weak magnetic region or a weak magnetic region, wherein the current modulation coefficient is in the non-weak magnetic region when the rotating speed is small (such as less than about 1700 rpm), and when the rotating speed is increased to about 1700rpm, the current modulation coefficient enters the weak magnetic region, so that the modulation coefficient is used as the reference for judging in order to accurately determine the located region.

If the modulation coefficient is smaller than a first threshold value which is 1.0, indicating that the magnetic field is in a non-weak magnetic area, recording and storing the rotating speed, the torque, the given current and the control angle at the moment;

if the modulation factor is greater than or equal to the first threshold value, which indicates that the magnetic flux density zone is entered, the control angle is adjusted again until the modulation factor is equal to a second threshold value, wherein the second threshold value is 0.95 +/-0.03, preferably 0.95, and the rotating speed, the torque, the given current and the control angle at the moment are recorded and stored.

And after the calibration under all rotating speeds and currents is finished, a two-dimensional table is manufactured according to the recorded and stored data. The two-dimensional table is a two-dimensional table with torque as an abscissa, rotating speed as an ordinate, and contents of d-axis current and q-axis current.

In the above scheme, the method further comprises determining calibration data under different bus voltages, and the process is as follows: and converting the feedback rotating speed under the current bus voltage, and searching the two-dimensional table through the converted rotating speed to obtain calibration data under the current bus voltage. The conversion is carried out by feeding back the rotation speed through the following formula:

INs＝Un*Ns/Udc

wherein INs is the converted rotation speed; un is a calibrated bus voltage; ns is the feedback rotation speed; udc is the current bus voltage.

In the scheme, the temperatures of the motor and the controller are monitored in real time in the calibration process, and if the temperature of the motor is greater than or equal to the first temperature threshold and/or the temperature of the controller is greater than or equal to the second temperature threshold, the calibration is suspended until the temperatures of the motor and the controller are less than the corresponding temperature thresholds, and then the calibration is continued.

Examples

The voltage platform of the motor is set to be 576V, the peak power is 150KW, the peak rotating speed is 3000rpm, and the peak current is 420A.

The calibration process is as follows:

1. calibration voltage platform determination

The bus voltage is regulated to 576V, and the value is subsequently used as the bus voltage value during table lookup processing, namely: un =576V

2. MTPA curve determination at the same speed

The dynamometer firstly gives a rotation speed of 150rpm, a current of a motor to be measured is 20A, a control angle is adjusted to enable the output torque to be maximum, and data (the rotation speed, the torque, the current and the control angle) are stored after a system is stabilized. Keeping the dynamometer machine speed constant at 150rpm, the motor current was increased to 40A, the previous operation was repeated and the saved data recorded. The motor current is then increased to 60A and the operation is repeated. One point every 20A until the motor current is increased to 420A.

3. MTPA curve determination at different rotational speeds

The dynamometer speed is increased to 300rpm and the operation of step 2 is repeated, with a given current of the motor from 20A to 420A, one point every 20A. Care was taken in these processes to monitor the temperature of the motor and controller, with the motor not exceeding 150 ℃ maximum and the controller not exceeding 90 ℃ maximum. The MTPA curve can be obtained under different rotating speeds by continuously increasing the rotating speed.

4. Flux weakening curve determination at the same rotational speed

When the rotation speed of the dynamometer is increased to be about 1700rpm, the peak torque of the motor should enter weak magnetism, and the modulation factor is ensured to be close to 0.95 at this time. If the modulation factor exceeds it, the control angle is adjusted so that the modulation factor is around 0.95. After the system is stabilized, the data (rotational speed, torque, current, control angle) are saved. The above operation is repeated. One point every 20A until the motor output power increases to 150KW.

5. Flux weakening curve determination at different rotational speeds

Along with the increase of the rotating speed of the dynamometer, more and more points enter weak magnetism, the control angle is adjusted, and the modulation coefficient is ensured to be near 0.95. After the system is stabilized, the data (rotational speed, torque, current, control angle) is saved.

6. Form processing

After all the calibrations are completed, two-dimensional tables with the torque as the abscissa and the rotating speed as the ordinate in the full power range and the table contents of Id and Iq can be obtained. And (4) importing the two tables into a model, and looking up the table by the model according to the current rotating speed, the bus voltage and the target torque to obtain the target DQ axis current.

Id＝Is*sinθ (9)

Iq＝Is*cosθ (10)

Wherein Id is D-axis current; IQ is Q axis current; is the calibration current; θ: and controlling the angle.

It should be understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy presented.

The foregoing description of the embodiments and specific examples of the invention have been presented for purposes of illustration and description; it is not intended to be the only form in which the embodiments of the invention may be practiced or utilized. The embodiments are intended to cover the features of the various embodiments as well as the method steps and sequences for constructing and operating the embodiments. However, other embodiments may be utilized to achieve the same or equivalent functions and step sequences.

In the foregoing detailed description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, invention lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. To those skilled in the art; various modifications to these embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the embodiments described herein are intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when employed as a transitional word in a claim. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or".

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Those not described in detail in this specification are within the skill of the art.

Claims (10)

1. A permanent magnet synchronous motor torque calibration method is characterized in that:

under the calibrated bus voltage, controlling the rotation speed to change from the initial rotation speed to the final calibrated rotation speed in sequence according to the first step length;

at each rotating speed, controlling the current to change from the initial current to the final calibration current in turn according to the second step length;

continuously adjusting the control angle when a current is given until the output torque of the motor reaches the maximum, and obtaining a modulation coefficient under the corresponding rotating speed-current and a current ratio of a d axis and a q axis of the motor;

comparing the modulation factor with a threshold value, and recording and storing the rotating speed, the torque, the given current and the control angle at the moment if the modulation factor is smaller than a first threshold value;

if the modulation factor is larger than or equal to the first threshold value, the control angle is adjusted again until the modulation factor is equal to the second threshold value, and the rotating speed, the torque, the given current and the control angle at the moment are recorded and stored.

2. The permanent magnet synchronous motor torque calibration method according to claim 1, characterized in that: and after the calibration under all the rotating speeds and currents is completed, a two-dimensional table is manufactured according to the recorded and stored data.

3. The permanent magnet synchronous motor torque calibration method according to claim 2, characterized in that: the two-dimensional table is a two-dimensional table with torque as an abscissa, rotating speed as an ordinate, and contents of d-axis current and q-axis current.

4. The permanent magnet synchronous motor torque calibration method according to claim 2, characterized in that: the method further comprises the following steps of determining calibration data under different bus voltages, and the process is as follows: and converting the feedback rotating speed under the current bus voltage, and searching the two-dimensional table through the converted rotating speed to obtain calibration data under the current bus voltage.

5. The permanent magnet synchronous motor torque calibration method according to claim 4, characterized in that: the conversion is carried out by feeding back the rotation speed through the following formula:

INs＝Un*Ns/Udc

wherein INs is the converted rotational speed; un is a calibrated bus voltage; ns is the feedback rotation speed; udc is the current bus voltage.

6. The permanent magnet synchronous motor torque calibration method according to claim 1, characterized in that: and in the calibration process, the temperatures of the motor and the controller are monitored in real time, if the temperature is greater than or equal to the temperature threshold, the calibration is suspended, and the calibration is continued until the temperature is less than the temperature threshold.

7. The permanent magnet synchronous motor torque calibration method according to claim 1, characterized in that: the first step size is 100rpm to 300rpm.

8. The permanent magnet synchronous motor torque calibration method according to claim 1, characterized in that: the second step size is 10A-30A.

9. The permanent magnet synchronous motor torque calibration method according to claim 1, characterized in that: the first threshold is 1.0.

10. The permanent magnet synchronous motor torque calibration method according to claim 1, characterized in that: the second threshold is 0.95 ± 0.03.

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