An optimal torque control method for a permanent magnet synchronous motor with variable flux leakage based on variable operating conditions

Abstract

The present invention discloses an optimal torque control method for a variable-magnetic-leakage permanent-magnet synchronous motor based on variable operating conditions. The method derives the relationship between electromagnetic torque and stator current based on the mathematical model of the permanent-magnet synchronous motor. The optimal torque control formula is solved by assuming that the derivative of the electromagnetic torque with respect to the stator current vector angle is zero, and by assuming that the quadrature-axis and direct-axis currents are related to the stator current. The flux linkage, quadrature-axis inductance, and direct-axis inductance values ​​measured by a static experimental method are used as initial values, and a single parameter is used to replace the flux linkage, quadrature-axis inductance, and direct-axis inductance in the current relationship to further simplify the formula. The range of the replacement parameter and the step size of the iterative calculation are selected based on the motor operating conditions. Finally, based on the principle of optimal torque control that minimizes the stator current under constant torque, the parameters are corrected in real time to minimize the stator current. The present invention improves the efficiency of optimal torque control for a variable-magnetic-leakage permanent-magnet synchronous motor by correcting the parameters in real time.

Description

Technical Field

[0001] The present invention belongs to the field of permanent magnet synchronous motor control, and specifically relates to an optimal torque control method for a variable flux leakage permanent magnet synchronous motor with multiple motor parameters changing. The method is applicable to high-efficiency drive control scenarios of variable flux leakage permanent magnet synchronous motors. Background Art

[0002] As countries around the world pay more and more attention to environmental protection, technological progress and energy security, internal combustion engines that consume fossil energy are gradually being replaced by power systems based on other energy sources in the field of road transportation, and the new energy vehicle industry has ushered in a good opportunity for development.

[0003] To meet the complex operating conditions of new energy vehicles, variable-leakage permanent magnet synchronous motors (PMSMs) have attracted widespread attention due to their advantages such as wide speed regulation and high efficiency. However, in these PMSMs, the flux linkage and quadrature-axis and direct-axis inductances change with increasing current, posing several challenges to motor control. Since the quadrature-axis and direct-axis inductances are unequal, a maximum torque-current ratio control method can be used to exploit their reluctance torque, thereby improving the motor's torque utilization and operating efficiency. However, constant-parameter maximum torque-current ratio control involves the motor's flux linkage, quadrature-axis inductance, and direct-axis inductance. In PMSMs, these parameters vary with the motor's operating conditions, making them unattainable under maximum torque-current ratio control. Conventional control methods, while relying on parameter identification and estimation, can simultaneously estimate two motor parameters in real time. However, the flux linkage, quadrature-axis inductance, and direct-axis inductance of PMSMs with variable-leakage current all vary with the motor's current. Furthermore, offline lookup tables require extensive experimental data, and the resulting errors significantly impact the motor's control effectiveness. Therefore, the changes in multiple parameters of the variable flux leakage permanent magnet synchronous motor lead to the problem that the motor cannot achieve optimal torque-current ratio control. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of maximum torque-to-current ratio control under variable operating conditions of a variable flux leakage permanent magnet synchronous motor, thereby improving the motor's operating efficiency and adaptability to variable operating conditions.

[0005] The technical solution adopted by the present invention is: an optimal torque control method for a variable flux leakage permanent magnet synchronous motor considering variable operating conditions, specifically comprising:

[0006] In the dq axis synchronous rotating coordinate system, the relationship between the stator current and the quadrature and direct axis current is obtained:

[0007]

[0008] Where i q is the quadrature axis current, id is the direct axis current, i s is the stator current, and β is the stator current vector angle.

[0009] Electromagnetic torque formula of variable flux leakage permanent magnet synchronous motor

[0010]

[0011] Where, T e is the electromagnetic torque, P is the number of motor pole pairs, ψ f is the permanent magnet flux, L q is the quadrature-axis inductance, L d is the direct-axis inductance.

[0012] The relationship between electromagnetic torque and stator current vector angle is further derived;

[0013]

[0014] According to the relationship between the electromagnetic torque and the stator current vector angle, the derivative of the electromagnetic torque with respect to the stator current vector angle is obtained:

[0015]

[0016] When the motor operates at the MTPA control point, that is, the optimal current angle, the derivative of the electromagnetic torque with respect to the stator current vector angle is zero, that is,

[0017]

[0018] According to the value of the derivative of the electromagnetic torque with respect to the stator current vector angle being zero, and the relationship between the stator current and the quadrature and direct axis currents, the relationship is solved as follows:

[0019]

[0020] Replace the flux linkage, quadrature-axis inductance, and direct-axis inductance with the parameter λ, and use the flux linkage, quadrature-axis inductance, and direct-axis inductance measured by static experiments as the initial values ​​of the calculated parameter λ, that is,

[0021]

[0022] The relationship between the quadrature axis and direct axis currents and the stator current is further simplified to

[0023]

[0024] Based on the relationship between the quadrature-axis and direct-axis currents and the stator current, the parameter λ is adjusted to achieve the minimum current value under constant torque.

[0025] The change relationship of parameter λ is expressed as:

[0026] λ(k+1)=λ(k)+μΔλ

[0027] Among them, μ represents the iterative calculation direction, and Δλ represents the step size of the iterative calculation.

[0028] The judgment logic for the increase or decrease of parameter λ, i.e., the value of μ, is:

[0029] If λ(k+1)>λ(k), i s (k+1)>i s (k), then k=k+1, μ=-1;

[0030] If λ(k+1)>λ(k), i s (k+1)≤i s (k), then k=k+1, μ=1;

[0031] If λ(k+1)≤λ(k), i s (k+1)>i s (k), then k=k+1, μ=1;

[0032] If λ(k+1)≤λ(k), i s (k+1)≤i s (k), then k=k+1, μ=-1.

[0033] The corresponding permanent magnet torque T is measured by controlling id=0 PM The corresponding quadrature-axis current i q , and then according to the permanent magnet torque T PM and the quadrature axis current i q The ratio of the working condition is divided into low torque parameter area, medium torque parameter area and high torque parameter area, and the quadrature axis current i q As the basis for judging the working condition, the variation range of the parameter λ of each partition is determined according to the parameter λ of each partition boundary point, and the step size Δλ of the iterative calculation of the corresponding partition is determined according to the size of the variation range of the parameter λ of each partition.

[0034] According to the above description, it can be expressed as:

[0035] (1) Low torque parameter area: η∈[η0,η1], i q ∈[i q0 ,i q1 ],

[0036] (2) Middle torque parameter area: η∈(η1,η2], i q ∈(i q1 ,i q2 ],

[0037] (3) High torque parameter area: η∈(η2,η3], i q ∈(i q2 ,i q3 ],

[0038] Where η represents the permanent magnet torque T PM and the quadrature axis current i q The ratio of η = T PM / i q , η0, η1, η2, η3 correspond to the quadrature axis current i q for i q0 、i q1 、i q2 、i q3 The value at time i q0 、i q1 、i q2 、i q3 The quadrature axis current i corresponding to the beginning of the low torque parameter area, the end of the low torque parameter area (the beginning of the medium torque parameter area), the end of the medium torque parameter area (the beginning of the high torque parameter area), and the end of the high torque parameter area is q The value of λ0, λ1, λ2, and λ3 correspond to the quadrature axis current i q for i q0 、i q1 、i q2 、i q3 ; Δλ1, Δλ2, and Δλ3 represent the values ​​of Δλ in different partitions.

[0039] Based on the above content, the expressions of the given values ​​of the quadrature-axis and direct-axis currents can be obtained:

[0040]

[0041] Optimal torque control can be achieved by inputting the DC axis current given value into the PI current loop.

[0042] The beneficial effects of the present invention are:

[0043] 1. The present invention replaces multiple motor parameters in the formula with one parameter, thereby eliminating the need for real-time estimation of multiple parameters and reducing the model complexity.

[0044] 2. The present invention reduces the error of optimal torque control by correcting parameters in real time, without the need to measure a large amount of experimental data and also avoids the need to store a large amount of data.

[0045] 3. The control method proposed in the present invention can meet the high-precision and high-power requirements of drive control in the electric vehicle field. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1Block diagram of the optimal torque control system of a variable flux leakage permanent magnet synchronous motor considering variable operating conditions provided by an embodiment of the present invention

[0047] Figure 2 Parameter real-time correction control logic diagram provided by the embodiment of the present invention

[0048] Figure 3 Comparison of stator current amplitudes at a speed of 600 r / min based on the constant parameter method and the real-time parameter correction method provided by the embodiment of the present invention DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention clearer, the control method proposed in the present invention is further explained below with reference to the accompanying drawings and implementation cases. It should be pointed out that the implementation cases described are only intended to facilitate the understanding of the present invention and do not have any limiting effect on it.

[0050] like Figure 1 As shown in FIG, the optimal torque control system of a variable flux leakage permanent magnet synchronous motor considering variable operating conditions includes a speed loop and a current loop dual closed-loop vector control system and an optimal torque control module.

[0051] The optimal torque control method of a variable flux leakage permanent magnet synchronous motor considering variable operating conditions includes the following steps:

[0052] In the dq axis synchronous rotating coordinate system, the relationship between the stator current and the quadrature and direct axis current is obtained:

[0053]

[0054] Where i q is the quadrature axis current, i d is the direct axis current, i s is the stator current, and β is the stator current vector angle.

[0055] The relationship between electromagnetic torque and stator current vector angle is derived based on the mathematical model of permanent magnet synchronous motor in dq axis synchronous rotating coordinate system;

[0056]

[0057] Where, T e is the electromagnetic torque, P is the number of motor pole pairs, ψ f is the permanent magnet flux, L q is the quadrature-axis inductance, L d is the direct-axis inductance;

[0058] According to the relationship between the electromagnetic torque and the stator current vector angle, the derivative of the electromagnetic torque with respect to the stator current vector angle is obtained:

[0059]

[0060] When the motor operates at the optimal torque control point, the derivative of the torque with respect to the stator current vector angle is zero, that is,

[0061]

[0062] According to the value of the derivative of the electromagnetic torque with respect to the stator current vector angle being zero, and the relationship between the stator current and the quadrature and direct axis currents, the relationship is solved as follows:

[0063]

[0064] Replace the flux linkage and dq-axis inductance with the parameter λ, and use the flux linkage value and dq-axis inductance value measured by static experiment as the initial value of the calculation parameter λ, that is,

[0065]

[0066] The relationship between the quadrature axis and direct axis currents and the stator current is further simplified to

[0067]

[0068] According to the above current relationship, the parameter λ is used as a variable. When the motor is in a steady state, the parameter λ is corrected in real time to achieve the minimum current value under constant torque.

[0069] As shown in Figure (2), the strategy for real-time parameter correction is:

[0070] First, the iterative calculation formula of parameter λ is:

[0071] λ(k+1)=λ(k)+μΔλ

[0072] Among them, μ represents the iterative calculation direction, and Δλ represents the step size of the iterative calculation.

[0073] The judgment logic of the increase or decrease of parameter λ, i.e. the value of μ, is

[0074] If λ(k+1)>λ(k), i s (k+1)>i s (k), then k=k+1, μ=-1;

[0075] If λ(k+1)>λ(k), i s (k+1)≤i s (k), then k=k+1, μ=1;

[0076] If λ(k+1)≤λ(k), i s (k+1)>i s (k), then k=k+1, μ=1;

[0077] If λ(k+1)≤λ(k), i s (k+1)≤i s (k), then k=k+1, μ=-1.

[0078] The corresponding permanent magnet torque T is measured by controlling id=0 PM The corresponding quadrature-axis current i q , and then according to the permanent magnet torque T PM and the quadrature axis current i q The ratio of the working condition is divided into low torque parameter area, medium torque parameter area and high torque parameter area, and the quadrature axis current i q As the basis for judging the working condition, the variation range of the parameter λ of each partition is determined according to the parameter λ of each partition boundary point, and the step size Δλ of the iterative calculation of the corresponding partition is determined according to the size of the variation range of the parameter λ of each partition.

[0079] According to the above description, it can be expressed as:

[0080] (1) Low torque parameter area: η∈[η0,η1], i q ∈[i q0 ,i q1 ],

[0081] (2) Middle torque parameter area: η∈(η1,η2], i q ∈(i q1 ,i q2 ],

[0082] (3) High torque parameter area: η∈(η2,η3], i q ∈(i q2 ,i q3 ],

[0083] Where η represents the permanent magnet torque T PM and the quadrature axis current i q The ratio of η = T PM / i q , η0, η1, η2, η3 correspond to the quadrature axis current i q for i q0 、i q1 、i q2 、i q3 The value at time i q0 、i q1 、i q2 、i q3The quadrature axis current i corresponding to the beginning of the low torque parameter area, the end of the low torque parameter area (the beginning of the medium torque parameter area), the end of the medium torque parameter area (the beginning of the high torque parameter area), and the end of the high torque parameter area is q The value of λ0, λ1, λ2, and λ3 correspond to the quadrature axis current i q for i q0 、i q1 、i q2 、i q3 ; Δλ1, Δλ2, and Δλ3 represent the values ​​of Δλ in different partitions.

[0084] Therefore, the given values ​​of the quadrature-axis and direct-axis currents are expressed as:

[0085]

[0086] like Figure 3 Figure 2 shows a comparison of the stator current amplitudes for a variable-leakage permanent magnet synchronous motor using a constant parameter method and a real-time parameter correction method, respectively, at a motor speed of 600 r / min. Using the constant parameter method, the stator current amplitudes are 12.5A and 18.4A for load torques of 10 N·m and 15 N·m, respectively. Using the real-time parameter correction method, the stator current amplitudes are 12.4A and 18A for load torques of 10 N·m and 15 N·m, respectively. The simulation waveforms show that the optimal torque control method for a variable-leakage permanent magnet synchronous motor using the real-time parameter correction method achieves higher accuracy.

[0087] The above content is a description of a specific implementation scheme of the present invention, but the scope of protection of the present invention is not limited to the above-mentioned specific implementation scheme. Any modifications made by any technician familiar with the field according to the technical solution of the present invention within the scope of the claims are covered by the scope of protection of the present invention.

Claims

1. A method for controlling the optimal torque of a variable flux leakage permanent magnet synchronous motor based on variable operating conditions, characterized in that: The steps include: Step 1: derive the relationship between the electromagnetic torque and the stator current vector angle based on the mathematical model of the variable flux leakage permanent magnet synchronous motor in the dq axis synchronous rotating coordinate system; Step 2: According to the relationship between the electromagnetic torque and the stator current vector angle, the derivative of the electromagnetic torque with respect to the stator current vector angle is obtained. When the motor runs at the optimal torque control point, the derivative of the electromagnetic torque with respect to the stator current vector angle is zero, and the quadrature axis current i is obtained. q , direct axis current i d and stator current i s The relationship between Step 3: Measure the initial values ​​of the motor's flux, quadrature-axis inductance, and direct-axis inductance through static experiments. Use the parameter λ to replace the flux, quadrature-axis inductance, and direct-axis inductance in the current relationship. q , direct axis current i d and stator current i s Simplify the relationship; Step 4: Divide the range of parameter λ into segments according to the operating conditions of the motor, and set the step size Δλ of the parameter iterative calculation according to the parameter variation range; Step 5: Under the steady-state condition of the motor, according to the principle of minimum stator current under constant torque of optimal torque control, the parameter λ is adjusted in real time through the corresponding control logic, so that the stator current i s smallest; In the step 2, the quadrature axis current i q , direct axis current i d and stator current i s The relationship is: Where, ψ f is the permanent magnet flux, L q is the quadrature-axis inductance, L d is the direct-axis inductance, i q is the quadrature axis current, i d is the direct axis current, i s is the stator current; In the step 3, the quadrature axis current i q , direct axis current i d and stator current i s The simplified relationship is: Where i q is the quadrature axis current; i d is the direct axis current; i s is the stator current; the parameter λ represents the ratio of the permanent magnet flux value to the difference between the quadrature and direct axis inductances, that is, The specific process of step 4 is as follows: The corresponding permanent magnet torque T is measured by controlling id=0 PM The corresponding quadrature-axis current i q , and then according to the permanent magnet torque T PM and the quadrature axis current i q The ratio of the working condition is divided into low torque parameter area, medium torque parameter area and high torque parameter area, and the quadrature axis current i q As the basis for judging the working condition; determine the variation range of the parameter λ of each partition according to the parameter λ of each partition boundary point, and determine the step size Δλ of the iterative calculation of the corresponding partition according to the size of the variation range of the parameter λ of each partition; According to the above description, it can be expressed as: (1) Low torque parameter area: η∈[η0,η1], i q ∈[i q0 ,i q1 ], (2) Middle torque parameter area: η∈(η1,η2], i q ∈(i q1 ,i q2 ], (3) High torque parameter area: η∈(η2,η3], i q ∈(i q2 ,i q3 ], Where η represents the permanent magnet torque T PM and the quadrature axis current i q The ratio of η = T PM / i q , η0, η1, η2, η3 correspond to the quadrature axis current i q for i q0 、i q1 、i q2 、i q3 The value at time i q0 、i q1 、i q2 、i q3 The quadrature axis current i corresponding to the beginning of the low torque parameter area, the end of the low torque parameter area (the beginning of the medium torque parameter area), the end of the medium torque parameter area (the beginning of the high torque parameter area), and the end of the high torque parameter area is q The value of λ0, λ1, λ2, and λ3 correspond to the quadrature axis current i q for i q0 、i q1 、i q2 、i q3 Δλ1, Δλ2, and Δλ3 represent the values ​​of Δλ in different partitions; In step 5, according to the principle of minimum stator current under constant torque in optimal torque control, the parameter λ is adjusted in real time through the corresponding control logic, so that the stator current i s Minimum: The change of parameter λ is expressed in discrete form as: λ(k+1)=λ(k)+μΔλ Among them, μ represents the iterative calculation direction, Δλ represents the step size of the iterative calculation; The judgment logic for the increase or decrease of parameter λ, i.e., the value of μ, is: If λ(k+1)>λ(k), i s (k+1)>i s (k), then k=k+1, μ=-1; If λ(k+1)>λ(k), i s (k+1)≤i s (k), then k=k+1, μ=1; If λ(k+1)≤λ(k), i s (k+1)>i s (k), then k=k+1, μ=1; If λ(k+1)≤λ(k), i s (k+1)≤i s (k), then k=k+1, μ=-1.

2. The optimal torque control method for a variable flux leakage permanent magnet synchronous motor based on variable operating conditions according to claim 1 is characterized in that: In the step 1, the mathematical model of the variable flux leakage permanent magnet synchronous motor in the dq axis synchronous rotating coordinate system derives the relationship between the electromagnetic torque and the stator current vector angle as follows: Where, T e is the electromagnetic torque, P is the number of motor pole pairs, ψ f is the permanent magnet flux, L q is the quadrature-axis inductance, L d is the direct-axis inductance, i s is the stator current, and β is the stator current vector angle.

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