A maximum torque-to-current ratio control method for an asymmetric interior permanent magnet motor

Abstract

The present invention discloses a method for controlling the maximum torque per current ratio (MTPA) of an asymmetric internal permanent magnet motor. The method selects the maximum reluctance axis as the direct axis to establish a mathematical model of the asymmetric internal permanent magnet motor; obtains the MTPA current trajectory equation based on the mathematical model; further determines the intersection of the current trajectory equation with the current limit circle, determines the MTPA current trajectory, and calculates the corresponding positive and negative output torque ranges taking into account the asymmetric operating characteristics to obtain the quadrature and direct axis reference currents. Compared to the nonlinear MTPA current trajectory of a traditional permanent magnet motor, the present invention reduces control complexity, further improves the motor's torque output capacity, and enhances operating efficiency. Furthermore, taking into account the motor's asymmetric operating characteristics, the designed MTPA current trajectory is suitable for operating regions including positive and negative torque outputs.

Description

Technical Field

[0001] The present invention belongs to the field of asymmetric permanent magnet motor operation control, and specifically relates to a maximum torque-to-current ratio control method for an asymmetric internal permanent magnet motor. Background Art

[0002] An asymmetric internal permanent magnet motor is a motor that uses a hybrid rotor structure or auxiliary magnetic barriers to achieve a phase shift between the permanent magnet axis and the maximum reluctance axis based on the traditional internal permanent magnet motor. Its asymmetric rotor structure makes it possible for the permanent magnet torque and reluctance torque to reach their peak values ​​at the same current angle, thereby improving the utilization rate of the torque component.

[0003] Current research on asymmetric interior permanent magnet motors (IPMs) primarily focuses on structural design and optimization to improve motor torque density, while control strategies that consider the asymmetric rotor structure are lacking. Maximum torque per ampere (MTPA) control is commonly used in conventional permanent magnet synchronous motors to optimize the current angle, minimizing stator current while maintaining the same output electromagnetic torque, reducing power losses and improving operating efficiency. However, conventional PMMs require solving nonlinear equations to determine the optimal current angle, which is computationally intensive and complex to control. In contrast, in asymmetric IPMMs, the peak permanent magnet torque and peak reluctance torque can be obtained at the same current angle, thereby reducing the complexity of MTPA control. Furthermore, while the maximum positive torque of an asymmetric IPMM is improved, the opposite directions of the permanent magnet torque and reluctance torque reduce the maximum negative torque of the motor. Existing technologies do not address the design of MTPA control methods for asymmetric IPMMs that consider their asymmetric operating characteristics. Therefore, we propose a maximum torque per ampere control method for an asymmetric IPMM. Summary of the Invention

[0004] The purpose of the present invention is to provide a maximum torque-to-current ratio control method for an asymmetric interior permanent magnet motor. Compared with the nonlinear MTPA current trajectory of a traditional IPM motor, the control complexity and computational complexity are greatly reduced, the torque output capability of the asymmetric interior permanent magnet motor is further improved, and the operating efficiency is improved.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for controlling the maximum torque-to-current ratio of an asymmetric interior permanent magnet motor, comprising the following steps:

[0006] The maximum magnetic resistance axis is selected as the direct axis to establish the mathematical model of the asymmetric interior permanent magnet motor;

[0007] The maximum torque to current ratio control (MTPA) current trajectory equation is obtained based on the established mathematical model of the asymmetric interior permanent magnet motor.

[0008] The intersection of the current trajectory equation and the current limit circle is determined to determine the maximum torque-to-current ratio control (MTPA) current trajectory. Considering the asymmetric operating characteristics, the corresponding positive and negative output torque ranges are calculated to obtain the quadrature and direct axis reference currents.

[0009] Furthermore, the mathematical model of the asymmetric interior permanent magnet motor is established as follows:

[0010] (1) The maximum magnetic resistance axis is selected as the direct axis. The permanent magnet axis of the asymmetric built-in permanent magnet motor is offset by 45° electrical angle from the direct axis. The flux equation and voltage equation in the three-phase coordinate system are established:

[0011]

[0012]

[0013] Where, the rotor position θ r It is expressed as the angle from the quadrature axis to the a-phase axis, ψ PM represents the permanent magnet flux, L abc represents the inductance matrix of each phase, ψ abc represents the stator three-phase flux, i abc Indicates the stator three-phase current, u abc Represents the stator three-phase voltage, R s represents the stator phase resistance;

[0014] (2) Perform Park transformation to obtain the stator voltage equation and torque equation in the corresponding dq coordinate system:

[0015]

[0016]

[0017] Where u d and u q Represent the stator dq axis voltage, i d and i q Represent the stator dq axis current, L d and L q They represent the dq axis inductance, ω represents the rotor electrical angular velocity, T e represents the electromagnetic torque, and p represents the number of motor pole pairs.

[0018] Furthermore, the maximum torque to current ratio control (MTPA) current trajectory equation is obtained according to formula (4), which is as follows:

[0019]

[0020] Where i d and i qRepresent the stator dq axis current, L d and L q They represent the dq axis inductance, ψ PM Represents the permanent magnet flux.

[0021] Furthermore, the method for obtaining the quadrature and direct axis reference currents is as follows:

[0022] (1) Let the straight line l1 in formula (5) be:i d +i q =0, straight line l2: The distance K between l2 and the origin is:

[0023]

[0024] (2) Case 1: I lim ≤|K|,I lim is the maximum stator current, and from formula (5) we can get i d -i q The line segment AB on the plane is the MTPA current trajectory:

[0025] i d +i q =0,T B ≤T * ≤T A (7)

[0026] Where, Points A and B are the intersections of l1 and the current limit circle, T A That is, the maximum positive torque, T B That is, the maximum value of negative torque;

[0027] Substituting equation (7) into torque equation (4), we can obtain the reference value of the quadrature and direct axis current in case 1:

[0028]

[0029] (3) Case 2: I lim >|K|, and we can get i from formula (5) d -i q The broken line ACD on the plane is the MTPA running track:

[0030]

[0031] Where, Point C is the intersection of lines l1 and l2. Considering that line l2 has two intersections with the current limit circle, the point closer to the center of the voltage limit ellipse is selected to achieve high-speed operation through weak magnetic field. Ignoring the resistance voltage drop, the voltage limit ellipse equation is as follows:

[0032]

[0033] Where U lim The maximum phase voltage provided by the bus voltage; the center of the voltage limit ellipse is located in the third quadrant, and the direct-axis current i at point D is qD and i dD for:

[0034]

[0035] Substituting equation (9) into the torque equation (4), we can obtain the reference value of the quadrature and direct axis currents in case 2:

[0036]

[0037]

[0038] The present invention has at least the following beneficial effects:

[0039] 1. The method of the present invention provides a linear MTPA current trajectory, which greatly reduces the control complexity and computational complexity compared to the nonlinear MTPA current trajectory of traditional IPM motors, further improves the torque output capability of asymmetric interior permanent magnet motors, and enhances operating efficiency.

[0040] 2. The method of the present invention takes into account the asymmetric operating characteristics of the motor, and the designed MTPA current trajectory is suitable for the operating area within the calculated positive and negative torque output range.

[0041] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of the method design of the present invention;

[0043] Figure 2 It is a structural block diagram of the overall control system of the present invention;

[0044] Figure 3 The present invention is lim Schematic diagram of MTPA control trajectory when ≤|K|;

[0045] Figure 4 The present invention is lim Schematic diagram of MTPA control trajectory under the condition of >|K|. DETAILED DESCRIPTION

[0046] The following will be combined with the accompanying drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the embodiments described are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present disclosure.

[0047] The present invention discloses a method for controlling the maximum torque current ratio of an asymmetric internal permanent magnet motor. The method design flow chart is as follows: Figure 1 shown.

[0048] like Figure 2 As shown, the working principle of the present invention is: the decoder collects the motor position signal θ and the speed ω in real time, and the speed ω is related to the reference speed ω. ref The difference after comparison is adjusted by the speed PI controller and the reference torque signal T is output. e * ;T e * As the input signal of MTPA control, it outputs the dq axis reference current signal i dMTPA * with i qMTPA * ;i dMTPA * with i qMTPA * After the current PI controller is adjusted, the voltage feedforward decoupling link is added to output the dq axis reference voltage signal u d * with u q * ;u d * with u q * After the Park inverse transform, the αβ axis reference voltage signal u is output α * 、u β * ; According to u α * 、u β * and DC bus voltage U dc The SVPWM module outputs the inverter drive signal; the inverter switch tube acts according to the drive signal to achieve the control effect of the system.

[0049] A method for controlling the maximum torque-to-current ratio of an asymmetric interior permanent magnet motor comprises the following steps:

[0050] S1. Establish a mathematical model of an asymmetric interior permanent magnet motor, as follows:

[0051] (1) The maximum magnetic resistance axis is selected as the direct axis. The permanent magnet axis of the asymmetric built-in permanent magnet motor is offset by 45° electrical angle from the direct axis. The flux equation and voltage equation in the three-phase coordinate system are established:

[0052]

[0053]

[0054] Where, the rotor position θ r It is expressed as the angle from the quadrature axis to the a-phase axis, ψ PM represents the permanent magnet flux, L abc represents the inductance matrix of each phase, ψ abc represents the stator three-phase flux, i abc Indicates the stator three-phase current, u abc Represents the stator three-phase voltage, R s represents the stator phase resistance;

[0055] (2) Perform Park transformation to obtain the stator voltage equation and torque equation in the corresponding dq coordinate system:

[0056]

[0057]

[0058] Where u d and u q Represent the stator dq axis voltage, i d and i q Represent the stator dq axis current, L d and L q They represent the dq axis inductance, ω represents the rotor electrical angular velocity, T e represents the electromagnetic torque, and p represents the number of motor pole pairs.

[0059] S2. Based on the established mathematical model of the asymmetric interior permanent magnet motor, the maximum torque to current ratio control (MTPA) current trajectory equation is obtained, as follows:

[0060] Based on the working principle of MTPA, select i d -i q The working point on the plane where the torque curve is closest to the origin is taken as the MTPA operating point (i d ,i q ), the mathematical expression is as follows:

[0061]

[0062] Eliminate di in formula (5) q / di d , the MTPA current trajectory equation is calculated as follows:

[0063]

[0064] Where i d and i q Represent the stator dq axis current, L d and L q They represent the dq axis inductance, ψ PM Represents the permanent magnet flux.

[0065] S3. Determine the MTPA current trajectory and the positive and negative output torque ranges, and output the quadrature and direct axis reference currents, as follows:

[0066] S3.11, such as Figure 3 As shown, let’s record the straight line l1:i d +i q =0, straight line l2: The distance K between l2 and the origin is:

[0067]

[0068] S3.12, Case 1: I lim ≤|K|, such as Figure 3 As shown, the straight line l1 intersects the current limit circle at points A and B, and the line segment AB is selected as the MTPA current trajectory:

[0069] i d +i q =0,T B ≤T * ≤T A (8)

[0070] Where, T A That is, the maximum positive torque, T B That is, the maximum value of negative torque;

[0071] Substituting equation (8) into torque equation (4), we can calculate the reference value of the quadrature and direct axis current in case 1:

[0072]

[0073] S3.13, Case 2: I lim >|K|, such as Figure 4 As shown, the straight line l2 intersects the current limit circle at points D and D'. Ignoring the resistance voltage drop, the voltage limit ellipse equation is as follows:

[0074]

[0075] Where U lim The maximum phase voltage provided for the bus voltage;

[0076] From formula (10), it can be seen that the center of the voltage limit ellipse of the asymmetric interior permanent magnet motor is located in the third quadrant. Point D can achieve high-speed operation through magnetic weakening. The broken line ACD is selected as the MTPA current trajectory:

[0077]

[0078] Where, where i qD and i dD They are the direct and quadrature axis currents at point D:

[0079]

[0080] Substituting equation (11) into the torque equation (4), we can obtain the quadrature and direct axis current reference values:

[0081]

[0082]

[0083] Considering case 1, substituting the working points A and B on the current limit circle into equation (10), we can obtain the maximum speed ω that the motor can achieve when outputting the maximum positive and negative torque. A and ω B :

[0084]

[0085]

[0086] Compare the maximum positive and negative torques, T A >T B , comparing equations (15) and (16), ω A <ω B It can be seen that the asymmetric interior permanent magnet motor has a larger torque peak when the rotation direction is positive, and a wider speed range when the rotation direction is negative.

[0087] There is coupling between the dq axes of the motor system. Adding a DC-axis feedforward current regulator can play the role of current decoupling control and improve the control performance of the motor control system. The DC-axis voltage feedforward compensation component u fd and u fq for:

[0088]

[0089] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0090] For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on", "installed on", "fixed on" or "set on" another element, it can be directly on the other element or there can be a central element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there can be a central element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only embodiment.

[0091] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0092] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Claims

1. A method for controlling the maximum torque-to-current ratio of an asymmetric interior permanent magnet motor, characterized in that: The following steps are involved: The maximum magnetic resistance axis is selected as the direct axis to establish the mathematical model of the asymmetric interior permanent magnet motor; The maximum torque to current ratio control (MTPA) current trajectory equation is obtained based on the established asymmetric interior permanent magnet motor mathematical model; Determine the intersection of the current trajectory equation with the current limit circle, determine the maximum torque current ratio control (MTPA) current trajectory, calculate the corresponding positive and negative output torque ranges considering the asymmetric operating characteristics, and obtain the quadrature and direct axis reference current.

2. The maximum torque-to-current ratio control method of an asymmetric interior permanent magnet motor according to claim 1, characterized in that: The mathematical model of the asymmetric interior permanent magnet motor is established as follows: (1) The maximum magnetic resistance axis is selected as the direct axis. The permanent magnet axis of the asymmetric built-in permanent magnet motor is offset by 45° electrical angle from the direct axis. The flux equation and voltage equation in the three-phase coordinate system are established: (1) (2) Where, the rotor position θr Use the cross axis to a The angle of the phase axis is expressed as ψPM represents the permanent magnet flux linkage, Labc represents the inductance matrix of each phase, ψabc represents the stator three-phase flux, iabc represents the stator three-phase current, uabc represents the stator three-phase voltage, Rs represents the stator phase resistance; (2) Perform Parker transformation to obtain the corresponding dq Stator voltage equation and torque equation in the coordinate system: (3) (4) In the formula u d and u q Represents stator dq Shaft voltage, i d and i q Represents stator dq Shaft current, L d and L q Respectively dq Shaft inductance, ω represents the rotor electrical angular velocity, T e represents the electromagnetic torque, p Indicates the number of motor pole pairs.

3. The maximum torque-to-current ratio control method of an asymmetric interior permanent magnet motor according to claim 2, characterized in that: According to formula (4), the maximum torque current ratio control (MTPA) current trajectory equation is obtained as follows: (5) In the formula id and iq Represents stator dq Shaft current, Ld and Lq Respectively dq Shaft inductance, ψPM Represents the permanent magnet flux.

4. The maximum torque-to-current ratio control method of an asymmetric interior permanent magnet motor according to claim 3, characterized in that: The method for obtaining the quadrature and direct axis reference current is as follows: (1) Note the straight line in formula (5) l 1: ,straight line l 2: , l 2Distance from origin K for: (6) (2) Case 1: I lim ≤| K |, I lim is the maximum stator current, obtained from formula (5) i d - i q The line segment AB on the plane is the MTPA current trajectory: (7) Where, , ; Points A and B are l 1 intersection with the current limit circle, T A That is, the maximum positive torque, T B That is, the maximum value of negative torque; Substituting equation (7) into torque equation (4), we can obtain the reference value of the quadrature and direct axis current in case 1: (8) (3) Case 2: I lim >| K |, obtained from formula (5) i d - i q The broken line ACD on the plane is the MTPA running track: (9) Where, , ; Point C is a straight line l 1 and l The intersection of 2; Consider a straight line l 2 has two intersection points with the current limit circle. Selecting a point closer to the center of the voltage limit ellipse allows for high-speed operation through magnetic weakening. Ignoring the resistance voltage drop, the voltage limit ellipse equation is as follows: (10) Where, U lim The maximum phase voltage provided for the bus voltage; The center of the voltage limit ellipse is located in the third quadrant, and the direct axis current at point D is i qD and i dD for: (11) Substituting equation (9) into the torque equation (4), we can obtain the reference value of the quadrature and direct axis currents in case 2: (12) (13)。

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