Self-adaptive field weakening control method of permanent magnet synchronous motor

Abstract

The invention discloses a self-adaptive field weakening control method for a permanent magnet synchronous motor, and the method comprises the following steps: 1, obtaining a difference value between a reference rotating speed and an actual rotating speed, and carrying out the PI operation of the difference value to obtain a reference current vector amplitude; 2, obtaining a difference value between the maximum reference torque angle and the current torque angle, carrying out PI operation on the difference value, and multiplying a PI operation result by the adaptive gain to obtain a compensation value of a reference current vector amplitude; 3, compensating the reference current vector amplitude through the compensation value to obtain an optimal reference current vector amplitude; obtaining a reference quadrature-axis current and a reference direct-axis current through the optimal reference current vector amplitude; 4, obtaining a reference quadrature-axis voltage and a reference direct-axis voltage, and carrying out amplitude limiting on the reference quadrature-axis voltage and the reference direct-axis voltage; and step 5, performing field weakening control on the permanent magnet synchronous motor according to the reference quadrature-axis voltage and the reference direct-axis voltage after amplitude limiting. According to the invention, low-development and high-reliability field weakening control can be realized.

Description

Technical Field

[0001] The design of the present invention relates to the technical field of permanent magnet synchronous motor control, and particularly to an adaptive field-weakening control method for a permanent magnet synchronous motor. Background Art

[0002] Permanent magnet synchronous motors have the advantages of high power density, small volume, low price, etc., and are widely used in fields such as new energy vehicles and household appliances.

[0003] The power supply of a permanent magnet synchronous motor drive system is often provided by a lithium battery, a lead-acid battery, etc. As the battery capacity decreases, the battery voltage also decreases, which often makes it impossible for the permanent magnet synchronous motor to maintain the highest speed. The field-weakening control of a permanent magnet synchronous motor is a commonly used technology to increase the speed under low voltage conditions. Traditional field-weakening control is based on calibration technology, and a large amount of test data is relied on during the development process to support the calibration of a single motor. The traditional method not only has a large development workload; at the same time, because the parameters of the motor body will change non-linearly during operation, the calibration data cannot adapt to this change, resulting in a decrease in system efficiency. Especially in the deep field-weakening state, it will cause current fluctuations and reduce the system reliability. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides an adaptive field-weakening control method for a permanent magnet synchronous motor to solve the technical problems of large workload and poor reliability in the calibration of the field-weakening method in the prior art.

[0005] The present invention provides an adaptive field-weakening control method for a permanent magnet synchronous motor, including the following steps:

[0006] Step 1: Obtain the difference between the reference speed and the actual speed, and obtain the reference current vector amplitude through PI operation on the difference;

[0007] Step 2: Obtain the maximum reference torque angle in real time and construct an adaptive gain;

[0008] Obtain the difference between the maximum reference torque angle and the current torque angle, perform PI operation on the difference, and multiply the result of the PI operation by the adaptive gain to obtain the compensation value of the reference current vector amplitude;

[0009] Step 3: Compensate the reference current vector amplitude with the compensation value of the reference current vector amplitude to obtain the optimal reference current vector amplitude; obtain the reference quadrature-axis current and the reference direct-axis current through the optimal reference current vector amplitude;

[0010] Step 4: Obtain the reference quadrature-axis voltage and the reference direct-axis voltage through the actual quadrature-axis current, the actual direct-axis current, the reference quadrature-axis current, and the reference direct-axis current, and limit the reference quadrature-axis voltage and the reference direct-axis voltage;

[0011] Step 5: Perform field-weakening control on the permanent magnet synchronous motor according to the limited reference quadrature-axis voltage and reference direct-axis voltage.

[0012] Further, in the said Step 2, the formula for obtaining the maximum reference torque angle is:

[0013]

[0014] In the formula, ψ m , L q , L d are respectively the permanent magnet flux linkage, quadrature-axis inductance, and direct-axis inductance of the permanent magnet synchronous motor; ψ s , ψ d , ψ q are respectively the synthesized flux linkage, direct-axis flux linkage, and quadrature-axis flux linkage; i q , i d are respectively the actual quadrature-axis current and actual direct-axis current.

[0015] Further, in the said Step 2, the method for obtaining the adaptive gain is:

[0016] Perform partial differentiation on the current vector through the absolute value of the current torque angle, and the specific formula is:

[0017]

[0018] In the formula, δ is the current torque angle; i s is the current vector.

[0019] Further, the calculation formula for the current torque angle is:

[0020]

[0021] In the formula, γ is the current vector angle; i s is the current vector; ψ m is the permanent magnet flux linkage; L d is the direct-axis inductance.

[0022] Further, in the said Step 2, the formula for obtaining the compensation value of the reference current vector amplitude is:

[0023]

[0024] In the formula, G adj is the adaptive gain; k pδ , T iδ are respectively the proportional coefficient and integral constant in the PI operation; δ is the current torque angle; δ max is the maximum reference torque angle; represents integration.

[0025] Further, in the step 3, the specific formulas for obtaining the reference quadrature-axis current and the reference direct-axis current through the amplitude of the optimal reference current vector are as follows:

[0026]

[0027] In the formula, is the amplitude of the optimal reference current vector; γ * is the angle of the reference current vector; ψ m , L q , L d are the permanent magnet flux linkage, the quadrature-axis inductance, and the direct-axis inductance of the permanent magnet synchronous motor respectively; i q , i d are the actual quadrature-axis current and the actual direct-axis current respectively.

[0028] Further, in the step 4, the method for limiting the reference quadrature-axis voltage and the reference direct-axis voltage is as follows:

[0029] Limit the reference quadrature-axis voltage and the reference direct-axis voltage according to the battery discharge current limit and the current battery bus voltage.

[0030] Further, the specific method for limiting the reference quadrature-axis voltage and the reference direct-axis voltage is as follows:

[0031] When the sum of the squares of the reference quadrature-axis voltage and the reference direct-axis voltage is greater than , adjust the reference quadrature-axis voltage and the reference direct-axis voltage through the limiting coefficient until the condition is satisfied.

[0032] Among them, R s is the phase resistance of the permanent magnet synchronous motor; i lim is the battery discharge current limit; U dc is the current battery bus voltage.

[0033] Advantages of the present invention:

[0034] To solve the problems of large workload for weak magnetic calibration and poor reliability of traditional weak magnetic methods, the present invention realizes low-development and high-reliability weak magnetic control by means of a method of closed-loop controlling the torque angle and observing the current change rate to adaptively adjust the gain of the torque angle control loop.

[0035] The present invention adopts an online adaptive current vector adjustment method, adjusts the current vector in real time to meet the requirements of the motor under different operating states, and improves the dynamic performance and operating efficiency of the motor, especially in the deep weak magnetic region.

[0036] The present invention designs an adaptive gain by using the small signal analysis method to overcome the nonlinear effect in the deep weak magnetic region, improves the dynamic performance of the motor at high speeds, and realizes smooth torque control.

[0037] In the weak magnetic field region of the present invention, the optimal reference current vector amplitude is determined through analytical calculation rather than a voltage control loop, which improves the response speed and control accuracy of the system and reduces the calculation burden. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings. The drawings are schematic and should not be construed as imposing any limitation on the present invention. In the drawings:

[0039] Figure 1 is a flowchart of a specific embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0041] The present invention will be further illustrated below with reference to specific embodiments. Those skilled in the art should understand that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Modifications of various equivalent forms of the present invention fall within the scope defined by the appended claims of this application.

[0042] As Figure 1 shown, the present invention provides an adaptive field-weakening control method for a permanent magnet synchronous motor, including the following steps:

[0043] Step S1: Set the reference speed of the permanent magnet synchronous motor, obtain the actual speed of the permanent magnet synchronous motor, subtract the actual speed from the reference speed, and obtain the reference current vector amplitude through PI operation on the difference value;

[0044] Step S2: Obtain the maximum reference torque angle in real time and construct an adaptive gain;

[0045] Among them, the calculation method of the maximum reference torque angle is:

[0046]

[0047] In the formula, ψ m , L q , L d are the permanent magnet flux linkage, quadrature-axis inductance, and direct-axis inductance of the permanent magnet synchronous motor respectively; ψ s , ψ d , ψ q are the synthetic flux linkage, direct-axis flux linkage, and quadrature-axis flux linkage respectively; iq and i d are the actual quadrature-axis current and the actual direct-axis current, respectively;

[0048] An adaptive gain is constructed using the partial derivative of the current vector with respect to the absolute value of the current torque angle. The specific formula is as follows:

[0049]

[0050] In the formula, δ is the current torque angle; i s is the current vector;

[0051] Using the small-signal model of the torque angle control loop to analyze the sensitivity of the torque angle δ to the current amplitude i s The adaptive gain is inversely proportional to the static gain In this way, the nonlinear effect at high speeds can be eliminated, and the stability and dynamic performance of the system can be maintained.

[0052] Obtain the maximum reference torque angle and the current torque angle, subtract the current torque angle from the maximum reference torque angle, perform PI operation on the difference, and multiply the result of the PI operation by the adaptive gain to obtain the compensation value of the reference current vector amplitude;

[0053] Among them, the calculation method of the current torque angle is:

[0054]

[0055] In the formula, γ is the current vector angle;

[0056] The specific calculation method of the compensation value of the reference current vector amplitude is:

[0057]

[0058] In the formula, k pδ , T iδ are the proportional coefficient and the integral constant in the PI operation of the compensation value of the reference current vector amplitude respectively; The selection of PI parameters can refer to the parameters of the current loop PI; δ is the current torque angle; δ max The maximum reference torque angle; represents integration.

[0059] Step S3: Compensate the reference current vector amplitude through the compensation value of the reference current vector amplitude to obtain the optimal reference current vector amplitude. The calculation formula is:

[0060]

[0061] In the formula, i s_ref is the reference current vector amplitude;

[0062] The reference quadrature-axis current and the reference direct-axis current are obtained through the amplitude of the optimal reference current vector and the angle of the reference current vector. The specific formulas are as follows:

[0063]

[0064] In the formulas, is the amplitude of the optimal reference current vector; γ * is the angle of the reference current vector; ψ m , L q , L d are the permanent magnet flux linkage, the quadrature-axis inductance, and the direct-axis inductance of the permanent magnet synchronous motor respectively; i q , i d are the actual quadrature-axis current and the actual direct-axis current respectively;

[0065] Step S4: The reference quadrature-axis voltage and the reference direct-axis voltage are obtained through the actual quadrature-axis current, the actual direct-axis current, the reference quadrature-axis current, and the reference direct-axis current, and the reference quadrature-axis voltage and the reference direct-axis voltage are limited. The specific method of limiting is as follows:

[0066] According to the battery discharge current limit i lim and the current battery bus voltage U dc , the reference quadrature-axis voltage u q and the reference direct-axis voltage u d are limited,

[0067] When the reference quadrature-axis voltage u q and the reference direct-axis voltage u d meet , there is no need to limit the reference quadrature-axis voltage u q and the reference direct-axis voltage u d ;

[0068] When the reference quadrature-axis voltage u q and the reference direct-axis voltage u d do not meet , it is necessary to limit the reference quadrature-axis voltage u q and the reference direct-axis voltage u d through the limiting coefficient k. The limiting coefficient k meets:

[0069] Step S5: According to the limited reference quadrature-axis voltage and the reference direct-axis voltage, the duty ratios of the three-phase drive voltages are obtained, and field-weakening control is performed on the permanent magnet synchronous motor.

[0070] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. An adaptive field-weakening control method for a permanent magnet synchronous motor, characterized in that, It includes the following steps: Step 1: Obtain the difference between the reference speed and the actual speed, and obtain the amplitude of the reference current vector through PI operation on the difference; Step 2: Obtain the maximum reference torque angle in real time and construct an adaptive gain; Obtain the difference between the maximum reference torque angle and the current torque angle, perform PI operation on the difference, and multiply the result of the PI operation by the adaptive gain to obtain the compensation value of the reference current vector amplitude; Step 3: Compensate the reference current vector amplitude with the compensation value of the reference current vector amplitude to obtain the optimal reference current vector amplitude; obtain the reference quadrature-axis current and the reference direct-axis current through the optimal reference current vector amplitude; Step 4: Obtain the reference quadrature-axis voltage and the reference direct-axis voltage through the actual quadrature-axis current, the actual direct-axis current, the reference quadrature-axis current and the reference direct-axis current, and limit the reference quadrature-axis voltage and the reference direct-axis voltage; Step 5: Perform field-weakening control on the permanent magnet synchronous motor according to the limited reference quadrature-axis voltage and the reference direct-axis voltage.

2. The adaptive field-weakening control method for a permanent magnet synchronous motor according to claim 1, characterized in that, In the said Step 2, the formula for obtaining the maximum reference torque angle is: where ψ m , L q , L d are the permanent magnet flux linkage, quadrature-axis inductance, and direct-axis inductance of the permanent magnet synchronous motor, respectively; ψ s , ψ d , ψ q are the resultant flux linkage, direct-axis flux linkage, and quadrature-axis flux linkage, respectively; i q , i d are the actual quadrature-axis current and actual direct-axis current, respectively.

3. The adaptive field-weakening control method for the permanent magnet synchronous motor according to claim 1, characterized in that, In the said Step 2, the method for obtaining the adaptive gain is: Perform partial differentiation on the current vector by the absolute value of the current torque angle, and the specific formula is: where δ is the current torque angle; i s is the current current vector.

4. The adaptive field-weakening control method for a permanent magnet synchronous motor according to claim 1 or 3, characterized in that The calculation formula for the said current torque angle is: where γ is the current vector angle; i s is the current vector; ψ m is the permanent magnet flux linkage; L d is the direct-axis inductance.

5. The adaptive field-weakening control method for the permanent magnet synchronous motor according to claim 4, wherein, In the said Step 2, the formula for obtaining the compensation value of the reference current vector amplitude is: where G adj is the adaptive gain; k pδ , T iδ are the proportional coefficient and integral constant in the PI operation respectively; δ is the current torque angle; δ max is the maximum reference torque angle; represents integration.

6. The adaptive field-weakening control method for a permanent magnet synchronous motor according to claim 1, characterized in that In the said Step 3, the specific formula for obtaining the reference quadrature-axis current and the reference direct-axis current through the optimal reference current vector amplitude is: Wherein, is the amplitude of the optimal reference current vector; γ * is the angle of the reference current vector; ψ m , L q , L d are the permanent magnet flux linkage, the quadrature-axis inductance, and the direct-axis inductance of the permanent magnet synchronous motor respectively; i q , i d are the actual quadrature-axis current and the actual direct-axis current respectively.

7. The adaptive field-weakening control method for a permanent magnet synchronous motor according to claim 1, wherein In the said Step 4, the method for limiting the reference quadrature-axis voltage and the reference direct-axis voltage is: Limit the reference quadrature-axis voltage and the reference direct-axis voltage according to the battery discharge current limit and the current battery bus voltage.

8. The adaptive field-weakening control method for a permanent magnet synchronous motor according to claim 7, wherein The specific method for limiting the reference quadrature-axis voltage and the reference direct-axis voltage is: When the sum of the squares of the reference quadrature-axis voltage and the reference direct-axis voltage is greater than the reference quadrature-axis voltage and the reference direct-axis voltage are adjusted by the limiting factor until the condition is satisfied. Among them, R s is the phase resistance of the permanent magnet synchronous motor; i lim is the battery discharge current limit; U dc is the current battery bus voltage.

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