A table lookup flux-weakening control method for a brushless motor with delta connection

Abstract

The application provides a table lookup flux-weakening control method for a brushless motor with a delta connection mode, which comprises the following steps: using an existing mathematical model, recording and drawing current diagrams of d-axis and q-axis currents of the motor in different operating regions under MTPA / MTPV algorithm through analysis of motor parameters, and recording current data in the current diagrams to make a lookup table; according to mathematical model analysis of the motor stator delta connection mode, obtaining amplitude and phase of basic voltage vectors under different switching states of the inverter for the delta connection mode, sector division method and basic voltage vector action time; obtaining motor rotor position and speed information, finding given d-axis and q-axis currents via the lookup table, and accurately controlling the brushless motor with the delta connection mode through SVPWM technology control of the existing three-phase inverter circuit output PWM wave. The motor vector control and flux-weakening method of the application can reduce the operation burden of the MCU and accurately and highly control the motor.

Description

Technical Field

[0001] This invention relates to the field of brushless motor control technology, specifically to a lookup table-based field weakening control method for a brushless motor with a delta connection. Background Technology

[0002] Brushless motors have been widely used in various fields. Compared with other motors, brushless DC motors have certain advantages, mainly because they have no moving mechanical parts, thus eliminating wear and tear, resulting in long lifespan and low noise. In use, brushless DC motors offer high efficiency, low power consumption, and convenient maintenance, leading to their widespread application. However, the inventors of this application have discovered that in some applications, a delta-connected brushless motor with a wide speed range is required, necessitating field weakening control. In engineering practice, to improve system real-time performance and reduce the computational burden on the MCU, offline calculation and calibration of the AC and DC axis currents under different torques are often necessary for precise control of the brushless motor and improved system efficiency. Therefore, there is an urgent need for a method that can reduce the computational load on the MCU, quickly and accurately control delta-connected brushless motors, and achieve stable operation through field weakening drive vector control. Summary of the Invention

[0003] To address the technical problem of the need for a field weakening drive vector control method that can reduce the computational load of MCUs and enable rapid and precise control of brushless motors with delta connection, this invention provides a lookup table field weakening control method for brushless motors with delta connection. This method can achieve stable and precise control of brushless motors with delta connection in MCUs with low computing power and high execution speed requirements.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A lookup table-based field weakening control method for a brushless motor with a delta connection includes the following steps:

[0006] S1. Using existing mathematical models, through analysis of motor parameters, the current i of the motor in the rotating coordinate system d-axis and q-axis in different operating regions under the MTPA / MTPV algorithm is compared. d and i q Record and plot the current diagram, and record the current data in the current diagram to make a lookup table and generate a reference current table; the current diagram clearly describes the entire speed range from low speed to high speed, and the stator current needs to meet the current and voltage limits at the same time. Under this premise, the current trajectory of the stator current in the full speed range is studied.

[0007] S2. In the brushless motor control process, based on the mathematical model analysis of the motor stator delta connection, the amplitude and phase of the basic voltage vector, the sector division method, and the action time of the basic voltage vector under different switching states of the inverter for the delta connection are obtained.

[0008] S3. During the control of the brushless motor, the d-axis and q-axis currents are obtained by performing Clark / Park transformation on the three-phase currents of the motor. The rotor position and speed information are obtained by collecting and analyzing the signals fed back from the position sensor. The given i is then retrieved via a lookup table. d and i q The current is calculated by the PI controller and outputs U. d and U q U is calculated after inverse Park transformation. α and U β Finally, the existing space vector pulse width modulation (SVPWM) technology with delta connection is used to control the output PWM wave of the existing three-phase inverter circuit to precisely control the brushless motor with delta connection.

[0009] Furthermore, in step S1, based on the parameters provided by the motor, i is calculated according to different torques and speeds using the MTPA / MTPV algorithm. d and i q The value is used to generate a reference ammeter; using the existing mathematical model, through analysis of motor parameters, the current i of the motor in the rotating coordinate system d-axis and q-axis in different operating regions under the MTPA / MTPV algorithm is calculated. d and i q The current is recorded and plotted into a current diagram, which clearly depicts the entire speed range from low to high. The stator current must simultaneously meet current and voltage limitations. Under this premise, the stator current trajectory across the entire speed range is studied, and the motor operating range is divided into three regions: constant torque region, partial field weakening region, and deep field weakening region. The constant torque region uses MTPA control, while the partial and deep field weakening regions correspond to the constant power region. To use a lookup table method in the program, the current data in the current diagram needs to be recorded and created into a lookup table. This saves calculation steps, simplifies the program, and speeds up execution. Specifically, this includes:

[0010] Establishing a mathematical model in the S11, ABC static coordinate system

[0011] Stator voltage equation:

[0012]

[0013] Magnetic flux linkage equation:

[0014]

[0015] Among them, R s For stator resistance, u a u b u c The voltages of the stator along axes a, b, and c are respectively, i a i b i c For stator current, ψ a ψ b ψ c For three-phase flux linkage, L aa L bb L cc For the self-inductance between phase windings, L ab L ac L ba L bc L ca L cb For the mutual inductance between each phase winding, ψ fa ψ fb ψ fc These are the magnetic flux linkages of the permanent magnets in the stator windings;

[0016] Establish a mathematical model in the S12, α / β stationary coordinate system

[0017] The process of transforming from the stationary coordinate system ABC to the stationary coordinate system α / β is called the Clark transformation. In the α / β stationary coordinate system, the phase difference between the α axis and the β axis is 90 degrees.

[0018] Stator voltage equation:

[0019]

[0020] Magnetic flux linkage equation:

[0021]

[0022] Among them, u α u β The voltages along the α and β axes are respectively, i α i β Let ψ be the current along the α-axis and β-axis, respectively. α ψ β The flux linkages along the α and β axes are respectively, L αα L ββ The self-inductances along the α and β axes are respectively, M αβ M βα The mutual inductances along the α-axis and β-axis are respectively, ψ f It is the permanent magnet flux linkage, and θ is the angle between the permanent magnet flux linkage and the axis α;

[0023] Establish a mathematical model in the S13, d / q rotating coordinate system

[0024] The essence of the Park transformation is to multiply the stationary coordinate system α / β by a rotation matrix to obtain the d / q rotated coordinate system;

[0025] Stator voltage equation:

[0026]

[0027] Magnetic flux linkage equation:

[0028]

[0029] Among them, u d and u q The stator voltages along the d-axis and q-axis are respectively, i d i q Let ψ be the current along the d-axis and q-axis, respectively. d ψ q The flux linkages along the d-axis and q-axis are ω, respectively. e L is the electrical angular velocity of the motor rotor. d L q These are the self-inductances along the d-axis and q-axis, respectively;

[0030] Electromagnetic torque T of permanent magnet synchronous motor e for:

[0031] T e =n p (ψ f i q +(L d -L q )i d i q )

[0032] Where, n p This represents the number of pole pairs of the motor.

[0033] S14, MTPA control, or maximum torque-to-current ratio control, is a set of operating states that maximize the efficiency of permanent magnet synchronous motors at low speeds. It operates under the condition of maximum torque / current, and minimizes the current value when outputting the same torque.

[0034] According to the formula of motion and i d i q Construct the Lagrangian function H from the relation:

[0035]

[0036] Solving for:

[0037]

[0038] Maximum Torque-to-Current Ratio (MTPA) Curve Equation:

[0039]

[0040] MTPA control is used in this range to ensure maximum torque output. The coordinates of the point on the current plane are obtained by combining the MTPA curve and the current limiting circle. Substituting these coordinates into the voltage limiting equation, the rotational speed ω can be obtained. This speed is called the base speed.

[0041]

[0042] Among them, u max This is the limiting voltage;

[0043] S15. In the partial field weakening region, when the rotational speed increases to ω, the voltage just rises to the limit voltage u. max If the speed continues to increase, the voltage limit will not be met. In this case, the magnetic field should be weakened to keep the motor's output power constant and place it in the partially weakened magnetic region. At this time, the motor is simultaneously subjected to the limiting voltage u. max Limiting current i max Given the common constraints, the following current trajectory can be obtained:

[0044]

[0045] S16. During deep field weakening, the motor output power remains at its maximum value, while the speed continues to increase, causing the voltage limiting ellipse to contract. At this point, it is necessary to reduce the current to ensure constant motor power. The trajectory of the current plane follows the MTPV trajectory. Based on the motion formula and voltage limit, construct the constructor H using the Lagrange extremum theorem:

[0046]

[0047] Solving for the maximum torque-voltage ratio curve equation yields:

[0048]

[0049] As the rotational speed continues to increase, the current trajectory should follow the MTPV (Medium-to-Voltage Power Regulator). MTPV control is employed to ensure maximum power output. The corresponding rotational speed ω is called the critical speed. The current coordinates can be obtained by simultaneously solving the current limit equations and the MTPV equations.

[0050] The current coordinates are:

[0051]

[0052] The specific expression for M is as follows:

[0053]

[0054] When using MTPV control, the system operates along the MTPV curve and is only limited by the voltage limit. Therefore, by combining the MTPV expression and the voltage limit equation, the current operating point on the MTPV can be obtained. The specific expression for the current operating point is as follows:

[0055]

[0056] This expression can directly obtain the corresponding dq current component on the MTPV curve by the motor speed, thereby planning the current operating point to run along the MTPV curve.

[0057] Furthermore, in step S2, during the control of the brushless motor with a delta connection, the SVPWM algorithm of the delta connection method is used. The theoretical basis of SVPWM is to combine the basic voltage vectors within one switching cycle so that the average value is equal to the given voltage vector. At a certain moment, the given voltage vector rotates to a certain sector, and the two basic voltage vectors and the zero vector constituting this sector are combined, specifically including:

[0058] S21, Assume U a U b U c If the phase voltage component of a given voltage in a three-phase stationary coordinate system is U, then the phase voltage component of the given voltage in a two-phase stationary coordinate system is U. α U β The transformation equations between the three-phase stationary coordinate system and the two-phase stationary coordinate system are established as follows:

[0059]

[0060] S22. Obtain the given voltage component U from the above. α U β Define the following variables:

[0061]

[0062] Define symbolic functions:

[0063]

[0064] Where x represents a real number as input; sign() represents the sign function;

[0065] Let P = 4sign(A) + 2sign(B) + sign(C), then the relationship between sector number N and P is:

[0066] Sector number N 1 3 2 5 6 4

[0067] S23. After determining the relationship between the given voltage and the sector, it is necessary to determine the duration of the basic voltage vector:

[0068] If T1 + T2 > T, then the following formula should be used for processing:

[0069]

[0070] Where T1 and T2 are the durations of action of two adjacent basic voltage vectors, and T is the total duration of voltage action;

[0071] make

[0072] The relationship between the duration of the basic voltage vector and the sector number N can be obtained as follows:

[0073] <![CDATA[T1]]> Y -Y X -X -Z Z <![CDATA[T2]]> X Z -Z -Y Y -X

[0074] Among them, U dc This is the input bus voltage.

[0075] Seven-segment SVPWM changes the switching state of only one phase each time the switching state changes, and the zero vector's duration is evenly distributed, which makes the resulting PWM waveform symmetrical, thereby reducing the harmonic components of the PWM wave.

[0076] Compared with existing technologies, the lookup table field weakening control method for brushless motors with delta connection provided by this invention calculates and calibrates the AC and DC axis currents under different torques, and analyzes the SVPWM technology of delta connection. By acquiring and calculating rotor position and speed information, and adopting a lookup table method for motor vector control and field weakening control, the controllable speed range is improved, costs are saved, the real-time performance of the system is improved, the computational burden of the MCU is reduced, and precise and high-performance control of the motor is achieved. Attached Figure Description

[0077] Figure 1 This invention provides a method for plotting the MTPA / MTPV current curve of a motor.

[0078] Figure 2 This is a partial motor MTPA / MTPV current data table provided by the present invention.

[0079] Figure 3 This is a schematic diagram of the basic voltage vector and sector division of the delta connection method provided by the present invention.

[0080] Figure 4 This is a block diagram of the field weakening control principle provided by the present invention. Detailed Implementation

[0081] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0082] This invention provides a lookup table-based field weakening control method for a brushless motor with a delta connection, comprising the following steps:

[0083] S1. Using existing mathematical models, through analysis of motor parameters, the current i of the motor in the rotating coordinate system d-axis and q-axis in different operating regions under the MTPA / MTPV algorithm is compared. d and i q Record and plot the current diagram, and create a lookup table from the current data in the diagram. Generate a reference current table, which calculates the current i based on the parameters provided by the motor, using the MTPA / MTPV algorithm, according to different torques and speeds. d and i q The value is used to generate a reference ammeter. Specifically, using existing mathematical models, through analysis of motor parameters, the current i of the motor in the rotating coordinate system d-axis and q-axis in different operating regions under the MTPA / MTPV algorithm is calculated. d and i q Record and draw as Figure 1 The current diagram shown clearly depicts the entire speed range from low to high speed. The stator current must simultaneously meet current and voltage limitations. Under this premise, the stator current trajectory across the entire speed range is studied, and the motor operating range is divided into three regions: constant torque region, partial field weakening region, and deep field weakening region. The constant torque region uses MTPA control, while the partial and deep field weakening regions correspond to the constant power region. To use a lookup table method in the program, the current data in the current diagram needs to be recorded and formatted as follows: Figure 2 The lookup table shown only displays a portion of the table data to save computational steps, making the program simpler and faster. Specifically, it includes:

[0084] Establishing a mathematical model in the S11, ABC static coordinate system

[0085] Stator voltage equation:

[0086]

[0087] Magnetic flux linkage equation:

[0088]

[0089] Among them, R s For stator resistance, u a u b u c The voltages of the stator along axes a, b, and c are respectively, i a i b i c For stator current, ψ a ψ b ψ cFor three-phase flux linkage, L aa L bb L cc For the self-inductance between phase windings, L ab L ac L ba L bc L ca L cb For the mutual inductance between each phase winding, ψ fa ψ fb ψ fc These are the magnetic flux linkages of the permanent magnets in the stator windings;

[0090] Establish a mathematical model in the S12, α / β stationary coordinate system

[0091] The process of transforming from the stationary coordinate system ABC to the stationary coordinate system α / β is called the Clark transformation. In the α / β stationary coordinate system, the phase difference between the α axis and the β axis is 90 degrees.

[0092] Stator voltage equation:

[0093]

[0094] Magnetic flux linkage equation:

[0095]

[0096] Among them, u α u β The voltages along the α and β axes are respectively, i α i β Let ψ be the current along the α-axis and β-axis, respectively. α ψ β The flux linkages along the α and β axes are respectively, L αα L ββ The self-inductances along the α and β axes are respectively, M αβ M βα The mutual inductances along the α-axis and β-axis are respectively, ψ f It is the permanent magnet flux linkage, and θ is the angle between the permanent magnet flux linkage and the axis α;

[0097] Establish a mathematical model in the S13, d / q rotating coordinate system

[0098] The essence of the Park transformation is to multiply the stationary coordinate system α / β by a rotation matrix to obtain the d / q rotated coordinate system;

[0099] Stator voltage equation:

[0100]

[0101] Magnetic flux linkage equation:

[0102]

[0103] Among them, u d and u q The stator voltages along the d-axis and q-axis are respectively, i d i q Let ψ be the current along the d-axis and q-axis, respectively. d ψ q The flux linkages along the d-axis and q-axis are ω, respectively. e L is the electrical angular velocity of the motor rotor. d L q These are the self-inductances along the d-axis and q-axis, respectively;

[0104] Electromagnetic torque T of permanent magnet synchronous motor e for:

[0105] T e =n p (ψ f i q +(L d -L q )i d i q )

[0106] Where, n p This represents the number of pole pairs of the motor.

[0107] S14, MTPA control, or maximum torque-to-current ratio control, is a set of operating states that maximize the efficiency of permanent magnet synchronous motors at low speeds. It operates under the condition of maximum torque / current, and minimizes the current value when outputting the same torque.

[0108] According to the formula of motion and i d i q Construct the Lagrangian function H from the relation:

[0109]

[0110] Solving for:

[0111]

[0112] Maximum Torque-to-Current Ratio (MTPA) Curve Equation:

[0113]

[0114] MTPA control is used in this range to ensure maximum torque output. The coordinates of the point on the current plane are obtained by combining the MTPA curve and the current limiting circle. Substituting these coordinates into the voltage limiting equation, the rotational speed ω can be obtained. This speed is called the base speed.

[0115]

[0116] Among them, u max This is the limiting voltage;

[0117] S15. In the partial field weakening region, when the rotational speed increases to ω, the voltage just rises to the limit voltage u. max If the speed continues to increase, the voltage limit will not be met. In this case, the magnetic field should be weakened to keep the motor's output power constant and place it in the partially weakened magnetic region. At this time, the motor is simultaneously subjected to the limiting voltage u. max Limiting current i max Given the common constraints, the following current trajectory can be obtained:

[0118]

[0119] S16. During deep field weakening, the motor output power remains at its maximum value, while the speed continues to increase, causing the voltage limiting ellipse to contract. At this point, it is necessary to reduce the current to ensure constant motor power. The trajectory of the current plane follows the MTPV trajectory. Based on the motion formula and voltage limit, construct the constructor H using the Lagrange extremum theorem:

[0120]

[0121] Solving for the maximum torque-voltage ratio curve equation yields:

[0122]

[0123] As the rotational speed continues to increase, the current trajectory should follow the MTPV (Medium-to-Voltage Power Regulator). MTPV control is employed to ensure maximum power output. The corresponding rotational speed ω is called the critical speed. The current coordinates can be obtained by simultaneously solving the current limit equations and the MTPV equations.

[0124] The current coordinates are:

[0125]

[0126] The specific expression for M is as follows:

[0127]

[0128] When using MTPV control, the system operates along the MTPV curve and is only limited by the voltage limit. Therefore, by combining the MTPV expression and the voltage limit equation, the current operating point on the MTPV can be obtained. The specific expression for the current operating point is as follows:

[0129]

[0130] This expression can directly obtain the corresponding dq current component on the MTPV curve by the motor speed, thereby planning the current operating point to run along the MTPV curve.

[0131] Specifically, the MTPA (maximum torque current ratio) / MTPV (maximum torque voltage ratio) curve, the current limit circle, and the current i plotted around the horizontal axis. d / i q Sub-images Figure 1 As shown.

[0132] S2. In the brushless motor control process, based on the mathematical model analysis of the delta connection of the motor stator, the amplitude and phase of the basic voltage vector, the sector division method, and the action time of the basic voltage vector are obtained for different switching states of the inverter in the delta connection. Specifically, in the brushless motor control process of the delta connection, the SVPWM algorithm of the delta connection method is used. The theoretical basis of SVPWM is to combine the basic voltage vectors within one switching cycle so that the average value is equal to the given voltage vector; at a certain moment, the given voltage vector rotates to a certain sector, and the two basic voltage vectors and the zero vector constituting this sector are combined. Figure 3 This demonstrates the basic voltage vector and sector division of a delta connection, specifically including:

[0133] S21, Assume U a U b U c If the phase voltage component of a given voltage in a three-phase stationary coordinate system is U, then the phase voltage component of the given voltage in a two-phase stationary coordinate system is U. α U β The transformation equations between the three-phase stationary coordinate system and the two-phase stationary coordinate system are established as follows:

[0134]

[0135] S22. Obtain the given voltage component U from the above. α U β Define the following variables:

[0136]

[0137] Define symbolic functions:

[0138]

[0139] Where x represents a real number as input; sign() represents the sign function;

[0140] Let P = 4sign(A) + 2sign(B) + sign(C), then the relationship between sector number N and P is:

[0141] Sector number N 1 3 2 5 6 4

[0142] S23. After determining the relationship between the given voltage and the sector, it is necessary to determine the duration of the basic voltage vector:

[0143] If T1 + T2 > T, then the following formula should be used for processing:

[0144]

[0145] Where T1 and T2 are the durations of action of two adjacent basic voltage vectors, and T is the total duration of voltage action;

[0146] make

[0147] The relationship between the duration of the basic voltage vector and the sector number N can be obtained as follows:

[0148] <![CDATA[T1]]> Y -Y X -X -Z Z <![CDATA[T2]]> X Z -Z -Y Y -X

[0149] Among them, U dc This is the input bus voltage.

[0150] Seven-segment SVPWM changes the switching state of only one phase each time the switching state changes, and the zero vector's duration is evenly distributed, which makes the resulting PWM waveform symmetrical, thereby reducing the harmonic components of the PWM wave.

[0151] S3. During the control of the brushless motor, the d-axis and q-axis currents are obtained by performing Clark / Park transformation on the three-phase currents of the motor. The rotor position and speed information are obtained by collecting and analyzing the signals fed back from the position sensor. The given i is then retrieved via a lookup table. d and i q The current is calculated by the PI controller and outputs U. d and U q U is calculated after inverse Park transformation. α and U β Finally, the existing space vector pulse width modulation (SVPWM) technology with a delta connection is used to control the output PWM wave of the existing three-phase inverter circuit to precisely control the brushless motor with a delta connection. The specific control flowchart is as follows. Figure 4 As shown.

[0152] Compared with existing technologies, the lookup table field weakening control method for brushless motors with delta connection provided by this invention calculates and calibrates the AC and DC axis currents under different torques, and analyzes the SVPWM technology of delta connection. By acquiring and calculating rotor position and speed information, and adopting a lookup table method for motor vector control and field weakening control, the controllable speed range is improved, costs are saved, the real-time performance of the system is improved, the computational burden of the MCU is reduced, and precise and high-performance control of the motor is achieved.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A lookup table-based field weakening control method for a brushless motor with a delta connection, characterized in that, Includes the following steps: S1. Using existing mathematical models, through analysis of motor parameters, the current i of the motor in the rotating coordinate system d-axis and q-axis in different operating regions under the MTPA / MTPV algorithm is compared. d and i q Record and plot the current diagram, and record the current data in the current diagram to create a lookup table and generate a reference current table; The current diagram clearly describes the entire speed range from low speed to high speed. The stator current must simultaneously meet the current and voltage limits. Under this premise, the current trajectory of the stator current in the full speed range is studied. S2. In the brushless motor control process, based on the mathematical model analysis of the motor stator delta connection, the amplitude and phase of the basic voltage vector, the sector division method, and the action time of the basic voltage vector are obtained for the inverter under different switching states when the delta connection is used. S3. During the control of the brushless motor, the d-axis and q-axis currents are obtained by performing Clark / Park transformation on the three-phase currents of the motor. The rotor position and speed information are obtained by collecting and analyzing the signals fed back from the position sensor. The given i is then retrieved via a lookup table. d and i q The current is calculated by the PI controller and outputs U. d and U q U is calculated after inverse Park transformation. α and U β Finally, the space vector pulse width modulation (SVPWM) technology of the delta connection is used to control the output PWM wave of the existing three-phase inverter circuit to precisely control the brushless motor with the delta connection.

2. The method for lookup table-based field weakening control of a brushless motor with a delta connection as described in claim 1, characterized in that, In step S1, based on the parameters provided by the motor, i is calculated according to different torques and speeds using the MTPA / MTPV algorithm. d and i q The value is used to generate a reference ammeter, and the motor operating range is divided into three regions: constant torque region, partial field weakening region, and deep field weakening region. The constant torque region uses MTPA control, while the partial and deep field weakening regions correspond to the constant power region, specifically including: Establishing a mathematical model in the S11, ABC static coordinate system Stator voltage equation: Magnetic flux linkage equation: Among them, R s For stator resistance, u a u b u c The voltages of the stator along axes a, b, and c are respectively, i a i b i c For stator current, ψ a ψ b ψ c For three-phase flux linkage, L aa L bb L cc For the self-inductance between phase windings, L ab L ac L ba L bc L ca L cb For the mutual inductance between each phase winding, ψ fa ψ fb ψ fc These are the magnetic flux linkages of the permanent magnets in the stator windings; Establish a mathematical model in the S12, α / β stationary coordinate system The process of transforming from the stationary coordinate system ABC to the stationary coordinate system α / β is called the Clark transformation. In the α / β stationary coordinate system, the phase difference between the α axis and the β axis is 90 degrees. Stator voltage equation: Magnetic flux linkage equation: Among them, u α u β The voltages along the α and β axes are respectively, i α i β Let ψ be the current along the α-axis and β-axis, respectively. α ψ β The flux linkages along the α and β axes are respectively, L αα L ββ The self-inductances along the α and β axes are respectively, M αβ M βα The mutual inductances along the α-axis and β-axis are respectively, ψ f It is the permanent magnet flux linkage, and θ is the angle between the permanent magnet flux linkage and the axis α; Establish a mathematical model in the S13, d / q rotating coordinate system The essence of the Park transformation is to multiply the stationary coordinate system α / β by a rotation matrix to obtain the d / q rotated coordinate system; Stator voltage equation: Magnetic flux linkage equation: Among them, u d and u q The stator voltages along the d-axis and q-axis are respectively, i d i q Let ψ be the current along the d-axis and q-axis, respectively. d ψ q The flux linkages along the d-axis and q-axis are ω, respectively. e L is the electrical angular velocity of the motor rotor. d L q These are the self-inductances along the d-axis and q-axis, respectively; Electromagnetic torque T of permanent magnet synchronous motor e for: T e =n p (ψ f i q +(L d -L q )i d i q ) Where, n p This represents the number of pole pairs of the motor. S14, MTPA control, or maximum torque-to-current ratio control, is a set of operating states that maximize the efficiency of permanent magnet synchronous motors at low speeds. It operates under the condition of maximum torque / current, and minimizes the current value when outputting the same torque. According to the formula of motion and i d i q Construct the Lagrangian function H from the relation: Solving for: Maximum Torque-to-Current Ratio (MTPA) Curve Equation: MTPA control is used in this range to ensure maximum torque output. The coordinates of the point on the current plane are obtained by combining the MTPA curve and the current limiting circle. Substituting these coordinates into the voltage limiting equation, the rotational speed ω can be obtained. This speed is called the base speed. Among them, u max This is the limiting voltage; S15. In the partial field weakening region, when the rotational speed increases to ω, the voltage just rises to the limit voltage u. max If the speed continues to increase, the voltage limit will not be met. In this case, the magnetic field should be weakened to keep the motor's output power constant and place it in the partially weakened magnetic region. At this time, the motor is simultaneously subjected to the limiting voltage u. max Limiting current i max Given the common constraints, the following current trajectory can be obtained: S16. During deep field weakening, the motor output power remains at its maximum value, while the speed continues to increase, causing the voltage limiting ellipse to contract. At this point, it is necessary to reduce the current to ensure constant motor power. The trajectory of the current plane follows the MTPV trajectory. Based on the motion formula and voltage limit, construct the constructor H using the Lagrange extremum theorem: Solving for the maximum torque-voltage ratio curve equation yields: As the rotational speed continues to increase, the current trajectory should follow the MTPV (Medium-to-Maintenance Voltage Regulator). MTPV control is employed to ensure maximum power output. The corresponding rotational speed ω is called the critical speed. The current coordinates are obtained by simultaneously solving the current limit equations and the MTPV equations. The current coordinates are: The specific expression for M is as follows: When using MTPV control, the system operates along the MTPV curve and is only limited by the voltage limit. Therefore, by combining the MTPV expression and the voltage limit equation, the current operating point on the MTPV can be obtained. The specific expression for the current operating point is as follows: This expression directly calculates the corresponding dq current component on the MTPV curve based on the motor's rotational speed, thereby planning the current operating point to run along the MTPV curve.

3. The method for lookup table-based field weakening control of a brushless motor with a delta connection as described in claim 1, characterized in that, In step S2, during the brushless motor control process using a delta connection, the SVPWM algorithm based on the delta connection is used. The theoretical basis of SVPWM is to combine the basic voltage vectors within one switching cycle so that the average value is equal to the given voltage vector. At a certain moment, the given voltage vector rotates to a certain sector, and the two basic voltage vectors and the zero vector constituting this sector are combined, specifically including: S21, Assume U a U b U c If the phase voltage component of a given voltage in a three-phase stationary coordinate system is U, then the phase voltage component of the given voltage in a two-phase stationary coordinate system is U. α U β The transformation equations between the three-phase stationary coordinate system and the two-phase stationary coordinate system are established as follows: S22. Obtain the given voltage component U from the above. α U β Define the following variables: Define symbolic functions: Where x represents a real number as input; sign() represents the sign function; Let P = 4sign(A) + 2sign)B) + sign)C), then the relationship between sector number N and P is: S23. After determining the relationship between the given voltage and the sector, it is necessary to determine the duration of the basic voltage vector: If T1 + T2 > T, then the following formula should be used for processing: Where T1 and T2 are the durations of action of two adjacent basic voltage vectors, and T is the total duration of voltage action; make The relationship between the duration of the basic voltage vector and the sector number N is obtained as follows: Among them, U dc This is the input bus voltage.

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