WO2021063293A1

WO2021063293A1 - Method for fitting control curve of mtpa of permanent magnet synchronous motor

Info

Publication number: WO2021063293A1
Application number: PCT/CN2020/118216
Authority: WO
Inventors: 尹泉; 罗慧; 黄星迪
Original assignee: 华中科技大学
Priority date: 2019-09-30
Filing date: 2020-09-28
Publication date: 2021-04-08
Also published as: CN110707980A; CN110707980B

Abstract

Disclosed is a method for fitting a control curve of MTPA of a permanent magnet synchronous motor, belonging to the field of motor control. The method comprises: obtaining, in real time, motor parameters ψ_f, L_d and L_q of a permanent magnet synchronous motor, and making the output of a rotation speed regulator be equivalent to I_s; on the basis of ψ_f, L_d and L_q, calculating a switching current I_switch; and determining whether I_s > I_switch, and if so, using an asymptote to fit an i_d, i_q relational expression, otherwise, using a parabola to fit the i_d, i_q relational expression. The present invention proposes switching, according to the magnitude of a stator current amplitude, a fitting curve from a parabola to an asymptote when the current amplitude is I_switch, using a parabola fitting curve when the stator current amplitude is relatively small, and using, when a stator current vector amplitude is relatively large, one of the standard MTPA curve asymptotes as an MTPA fitting curve under a large current amplitude to replace the parabola fitting curve, such that the MTPA control effect is close to the optimal control effect, so as to continue providing a high-output torque.

Description

A Method of Fitting the MTPA Control Curve of Permanent Magnet Synchronous Motor

【Technical Field】

The present invention belongs to the field of motor control, and more specifically, relates to a method for fitting a control curve of a permanent magnet synchronous motor MTPA (Maximum Torque Per Ampere, maximum torque current ratio).

【Background technique】

Since 2010, the scale of the new energy automobile industry using built-in permanent magnet synchronous motors has gradually expanded. In order to meet the new energy vehicle's requirements for output torque during the startup and acceleration process, it is necessary to control the maximum torque-to-current ratio of its motor. Therefore, it is necessary to carry out in-depth research on the realization method of MTPA based on actual working conditions.

To realize MTPA control, its control curve must be solved first. In the process of solving the MTPA curve, not only the accuracy of the curve must be ensured, but also the difficulty of engineering realization must be considered. In order to simplify the MTPA curve while ensuring the output efficiency of the fitted curve as much as possible, Mao Liangliang et al. proposed in 2016 to expand the original MTPA curve by McLaughlin series, simplifying the MTPA curve into a multiplication and addition form. , Thus avoiding the radical and division operations in the calculation, reducing the operation time of the MTPA control strategy.

Since the high-order derivative of the multiplying-adding polynomial will gradually decrease with the decrease of the direct-axis current, when the current amplitude is larger (the direct-axis current is smaller), the polynomial fitting curve is gradually separated from the actual MTPA curve , The fitting effect gradually becomes worse. To ensure that the fitted curve coincides with the actual MTPA under high current amplitude, it is necessary to increase the order reserved by the McLaughlin series expansion. However, this method seriously increases the amount of calculation. Therefore, the polynomial fitting method is only suitable for the case where the stator current amplitude is small. To solve this problem, it is proposed to fit the MTPA curve into a parabola, so as to achieve the purpose of simplifying the calculation. However, in the case of a large current amplitude, the fitted curve deviates from the actual MTPA curve, so that the best MTPA control effect cannot be achieved.

[Summary of the invention]

Aiming at the problem that the parabolic fitting method of the prior art deviates from the actual MTPA curve when the current amplitude is large, the present invention provides a simulation of the MTPA control curve of a permanent magnet synchronous motor. The purpose of the combined method is to achieve the best MTPA control effect when the current amplitude is large.

To achieve the above objective, according to the first aspect of the present invention, a method for fitting a MTPA control curve of a permanent magnet synchronous motor is provided. The method includes the following steps:

S1. Obtain the motor parameters ψ _f , L _d and L _{q of the} permanent magnet synchronous motor in real time, and the output of the speed regulator is equivalent to I _s ;

S2. Calculate the switching current I _switch based on ψ _f , L _d and L _q ;

S3. Judge whether I _s ＞I _switch , if yes, use asymptote to fit the _{relational expression of i d} and i _q , otherwise, use parabola to fit the relational expression of _{i d} and i _q,

Among them, ψ _f represents the permanent magnet flux linkage in the equivalent dq coordinate system, L _d and L _q represent the d-axis and q-axis inductance of the permanent magnet synchronous motor in the dq coordinate system, respectively, I _s represents the motor stator current amplitude, i _d represents the d-axis component of the motor stator current, and i _q represents the q-axis component of the motor stator current.

Specifically, the input variable expression of the MTPA link

Specifically, the calculation formula of the switching current I _{switch is as follows:}

Specifically, the parabola fitting formula is as follows:

The asymptotes fitting formula is as follows:

Specifically, the method further includes:

S4. Combine the input variable expression of the MTPA link with the MTPA fitting curve relational expression, and obtain the values of _{i d} and i _q.

Specifically, when I _s > I _switch , the values of _{i d} and i _q are obtained simultaneously as follows:

When I _s ≤ I _switch , the values of _{i d} and i _q are obtained simultaneously as follows:

In order to achieve the above objective, according to the second aspect of the present invention, a computer-readable storage medium is provided, and a computer program is stored on the computer-readable storage medium. The fitting method of the MTPA control curve of the permanent magnet synchronous motor.

In general, through the above technical solutions conceived in the present invention, the following beneficial effects can be achieved:

The present invention proposes to switch the MTPA fitting strategy according to the magnitude of the stator current amplitude. When the stator current amplitude is small, the parabola fitting curve is adopted, which has a better fitting effect, and the output is closer to the electromagnetic torque of the maximum electromagnetic torque. Moment; when the stator current vector amplitude is large, one of the standard MTPA curve asymptotes is used as the MTPA fitting curve under high current amplitude to replace the parabolic fitting curve, the fitting effect is better and the output is more efficient. _{The present invention switches} the fitting curve from a parabola to an asymptotic curve when the current amplitude is I switch, so that the MTPA control effect is close to the best control effect, and the output torque is continuously high.

【Explanation of the drawings】

FIG. 1 is a flowchart of a method for fitting a MTPA control curve of a permanent magnet synchronous motor according to an embodiment of the present invention;

Fig. 2 is a block diagram of MTPA control provided by an embodiment of the present invention;

3 is a schematic diagram of switching from a parabolic fitting method to an asymptotic fitting method according to an embodiment of the present invention;

4 is a graph of a polynomial fitting curve and an actual MTPA curve provided by an embodiment of the present invention;

FIG. 5 is an asymptotic curve fitting curve and actual MTPA curve diagram provided by an embodiment of the present invention;

Fig. 6 is a graph of torque output efficiency curves of parabola fitting and asymptotic fitting provided by an embodiment of the present invention;

Fig. 7 is a schematic diagram of the simulation results of the maximum torque output of the three curves provided by the embodiment of the present invention when the constant torque is running under different limit values.

【Detailed ways】

In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

As shown in Fig. 1, the present invention provides a method for implementing MTPA control of a permanent magnet synchronous motor. The method includes the following steps:

Step S1. Obtain the motor parameters ψ _f , L _d and L _{q of the} permanent magnet synchronous motor in real time, and the output of the speed regulator is equivalent to I _s , where ψ _f represents the permanent magnet flux linkage in the equivalent dq coordinate system , L _d and L _q respectively represent the d-axis and q-axis inductance of the permanent magnet synchronous motor in the dq coordinate system, and I _s represents the motor stator current amplitude.

The online parameter identification method can be used to obtain the permanent magnet flux linkage ψ _f , the stator d-axis inductance L _d , and the stator q-axis inductance L _q of the permanent magnet synchronous motor in this period. Other methods can also be used to obtain motor parameters.

As shown in Figure 2, let the speed regulator output reference matrix T _ASR equal to the motor stator current amplitude

Among them, i _d represents the d-axis component of the motor stator current, and i _q represents the q-axis component of the motor stator current. The MTPA I _s as part of the input variables. Stator d-axis, q-axis current reference value

As the output variable of the MTPA link.

Step S2. Calculate the switching current I _switch _{based on ψ f} , L _d and L _q .

As shown in Figure 3, since the output efficiency of the parabolic fitting method gradually decreases with the increase of input, the output efficiency of the asymptotic fitting method gradually increases with the increase of input and approaches 100%. In the process of gradually increasing the input from 0, the system needs to switch when the output torque of the two fitting curves is the same in order to achieve continuous high output torque MTPA control. The approximate value of the current is obtained by calculation:

Step S3. Judge whether I _s > I _switch , if yes, use an asymptote to fit the _{relational expressions i d} and i _q ; otherwise, use a parabola to fit the relational expressions _{i d} and i _q.

In order to increase the electromagnetic torque output capacity of the salient-pole permanent magnet synchronous motor under the same current limit value, it is necessary to adopt the maximum torque-to-current ratio control strategy to optimize the distribution of the motor's orthogonal axis current. In the actual implementation process, in order to save the control cycle resources occupied by the MTPA algorithm, it is necessary to perform engineering fitting and simplification of the curve and its current distribution expression on the premise of ensuring its control accuracy as much as possible, so as The reduction of division and radical operation shortens the time consumed by the operation in the CPU. _{The present invention switches} the fitting curve from a parabola to an asymptotic curve when the current amplitude is I switch, so that the MTPA control effect approaches the best control effect.

When I _s ≤I _switch , the parabola fitting formula is as follows:

Output of the electromagnetic torque T _e is determined by the motor stator current vector. Set the sub-current vector amplitude to I _s . For the built-in permanent magnet synchronous motor, due to the salient pole effect, I _s will correspond to a maximum electromagnetic torque value. This torque is defined as T _emax (I _s ).

Suppose that when the stator current amplitude is I _s , the electromagnetic torque that can be generated by the parabolic fitting algorithm theory is T _ef1 (I _s ). As shown in Figure 4, the point (i _d , i _q ) defined on the parabola fitting curve can theoretically generate electromagnetic torque as T _ef1 (i _d , i _q ); A ₁ , A _{2 are} located on the parabola fitting curve Above, B ₁ and B _{2 are} on the actual MTPA curve. When I _s = 10A, A ₁ and B ₁ and the like are on the same basic electromagnetic torque curve, that is _{_{T ef1 (10) ≈T emax (}} 10). It shows that the parabola fitting curve can distribute the current vector, and then obtain the electromagnetic torque T _emax close to the maximum, which is a better substitute for the actual MTPA curve. However, with the increasing of I _s, the calculation is simple parabolic fit curve of higher order terms are omitted generated error became clear, the actual MTPA parabolic curve fitting curve gradually separated. When I _s = 30A, FIG midpoint A ₂ and B, the electromagnetic torque at the point B ₂ in the real theoretical curve MTPA is produced 30N.m _2, and is on the parabolic curve fitting At point A ₂ , the theoretically achievable electromagnetic torque is 28N.m, then T _emax (30)>T _ef1 (30). It can be seen that the electromagnetic torque corresponding to the current vector theory of the point on the parabolic fitting curve is smaller than the output electromagnetic torque of the actual maximum torque-to-current ratio (MTPA) curve.

Therefore, when the stator current amplitude is small, the parabola fitting curve has a better fitting effect. However, when the stator current vector amplitude I _{s is} large, the deviation between the parabolic fitting curve and the actual MTPA curve gradually increases, the output torque gradually decreases, and the fitting effect gradually deteriorates.

Fitting a parabola to solve the problem at the high current output less effective, the present invention proposes a new method of fitting asymptote I _s in the case of large parabolic fitting alternative, i.e. hyperbolic curve fitting MTPA An asymptote of.

When I _s ＞I _switch , the asymptotic curve fitting formula is as follows:

Among them, i _d represents the d-axis component of the motor stator current, and i _q represents the q-axis component of the motor stator current.

As shown in Fig. 5, the electromagnetic torque T _ef2 (i _d , i _q ) that _{can be generated theoretically at a point (i d} , i _{q) on the asymptotic curve fitting curve.} B ₁ and B _{2 are} located on the actual maximum torque current ratio (MTPA) curve, and C ₁ and C _{2 are} located on the asymptotic curve fitting. When I _s = 10A, for B _{_1,} C _1, the actual output torque curve is MTPA 7N.m, the asymptote to a curve fit to the output torque of 6.5Nm, there are T _emax (10)> T _ef2 (10). It can be seen that when the current vector amplitude I _{s is} small, the asymptotic curve fitting curve is equivalent to the i _d =0 control strategy, so the fitting effect is not good. However, with increasing I _s, the actual MTPA curve gradually approaches its asymptote, to a point B _{_2,} C ₂ at _{_2,} C _2, MTPA actual curve fitting curve B asymptote generated The theoretical electromagnetic torque is basically the same, that is, T _emax (30)≈T _ef2 (30).

It can be seen from the above analysis that although the stator current amplitude is small, compared to the asymptotic curve, the parabolic curve has a better fitting effect, and the output is closer to the electromagnetic torque of the maximum electromagnetic torque T _emax . Moment. However, when the stator current vector amplitude I _{s is} large, the actual MTPA curve gradually tends to the asymptotic curve fitting curve. The electromagnetic torque generated by the asymptotic curve fitting theory is larger than the electromagnetic torque produced by the parabolic fitting curve theory. Torque T _ef2 > T _ef1 . At this time, the fitting effect of the asymptotic curve fitting curve is better, and the output is more efficient.

Step S4. Combine the input variable expression of the MTPA link with the MTPA fitting curve relational expression to obtain the values of _{i d} and i _q.

When the maximum torque-to-current ratio (MTPA) is satisfied, the relationship between _{i d} _{and i q is}

Input variable expression of MTPA link

MTPA fitting curve relationship

When I _s ＞I _switch , the values of _{i d} and i _q are obtained simultaneously as follows:

In order to further illustrate the influence of parabolic fitting curve and asymptotic fitting curve on the effect of MTPA, it is necessary to quantitatively analyze the maximum torque of each fitting curve relative to the actual MTPA curve. Under the same current amplitude I _s _{, the electromagnetic torque T emax} (I _s ) that can be generated by the actual MTPA control curve theory is used as a benchmark to measure the torque output of the parabolic fitting curve and the asymptotic fitting curve at different current amplitudes effect.

Defined under the same current vector amplitude I _s , the output efficiency of the approximate fitting curve is η(I _s ).

Among them, T _ef (I _s ) is the electromagnetic torque that can be generated theoretically by a point on the approximate fitting curve.

Simulation results were obtained by fitting a parabolic curve output efficiency curve η ₁ (I _s) and the fitting curve asymptotes output efficiency curve η ₂ (I _s).

It can be seen from Figure 6 that when the stator current amplitude is small, the output efficiency of the parabolic fitting method is greater than the output efficiency of the asymptotic method, so the parabolic fitting curve is used; when the stator current amplitude is greater than I _switch , due to the asymptotic curve The output efficiency of the fitting method is greater than the output efficiency of the parabolic fitting method, so the asymptotic fitting method is used to output the efficiency.

In order to further verify the analysis conclusions of the influence of different given values on the output torque of the parabolic fitting method and the asymptotic curve fitting method, the actual curve is used as a control group, and the three MTPA curves are at the maximum when _{I max = 7A, 16A, and 30A.} Compare the output torque in the torque state. Among them, the three MTPA intervals are respectively given by the speed steps of t=0.04s, 0.06s, and 0.08s. The control strategy is switched from the actual to the parabolic fitting method at t=0.055s, and from the parabolic fitting method at 0.075s. To the asymptomatic fitting method.

As shown in Figure 7, when I _max =7A, since the curve and the parabolic fitting curve basically coincide, the output torque of the two are also consistent. However, since the asymptotic curve fitting is still in the control stage of id=0 at this time, the output torque is significantly smaller than the parabolic fitting method. When I _max _{=12A, the output torque of the parabolic fitting method of I switch} and the asymptotic fitting method is basically the same as the switching point is gradually approaching, but it is obviously slightly lower than the actual method. When I _max =28A, the actual curve is gradually separated from the parabolic fitting curve and approaches the asymptotic fitting curve, so the output torque of the asymptotic fitting curve is obviously greater than the output torque of the parabolic fitting curve. And it is basically consistent with the actual curve output torque.

This verifies the effect that the present invention can achieve: when the current amplitude is small, a parabola is used as the fitting curve of MTPA to output a larger torque; after the current amplitude is _{near I switch} , it is switched by the parabola fitting curve Fitting the curve to the asymptotic curve makes the torque output efficiency of the system gradually rise, thus avoiding the problem of the decrease of the torque output efficiency caused by the continued use of the parabolic curve fitting.

Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present invention, All should be included in the protection scope of the present invention.

Claims

A method for fitting a MTPA control curve of a permanent magnet synchronous motor is characterized in that the method includes the following steps:

S1. Obtain the motor parameters ψ f , L d and L q of the permanent magnet synchronous motor in real time, and the output of the speed regulator is equivalent to I s ;

S2. Calculate the switching current I switch based on ψ f , L d and L q ;

S3. Judge whether I s > I switch , if yes, use an asymptote to fit the relational expressions i d and i q , otherwise, use a parabola to fit the relational expressions i d and i q,

Among them, ψ f represents the permanent magnet flux linkage in the equivalent dq coordinate system, L d and L q represent the d-axis and q-axis inductance of the permanent magnet synchronous motor in the dq coordinate system, respectively, I s represents the motor stator current amplitude, i d represents the d-axis component of the motor stator current, and i q represents the q-axis component of the motor stator current.
The method of claim 1, wherein the input variable expression of the MTPA link
The method according to claim 1, wherein the calculation formula of the switching current I switch is as follows:
The method according to claim 1, wherein the parabola fitting formula is as follows:

The asymptotes fitting formula is as follows:
The method according to any one of claims 1 to 4, wherein the method further comprises:

S4. Combine the input variable expression of the MTPA link with the MTPA fitting curve relational expression, and obtain the values of i d and i q.
The method according to claim 5, wherein when I s > I switch , the values of i d and i q are obtained simultaneously as follows:
When I s ≤ I switch , the values of i d and i q are obtained simultaneously as follows:
A computer-readable storage medium, wherein a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, the permanent magnet synchronization according to any one of claims 1 to 6 is realized. The fitting method of the motor MTPA control curve.