An automatic calibration method for permanent magnet synchronous motor full speed domain lookup table

Abstract

The application relates to the technical field of motor control, and particularly discloses an automatic calibration method for a full-speed-domain lookup table of a permanent magnet synchronous motor, which comprises the following steps: MTPA automatic calibration, d-axis limit current search, MTPA automatic calibration-based d-axis limit current search, and maximum q-axis current boundary line-based acquisition of a field-weakening region current lookup table. In the method, the MTPA and the field-weakening region calibration are both based on rotor flux orientation current loop control, without additional voltage control and lookup table conversion, so that the lookup table calibration for full-speed-domain control of the motor is efficiently realized, and meanwhile, the d-axis limit current search fully considers the voltage limit ellipse under a higher rotating speed, thereby achieving the efficiency that cannot be achieved by traditional offline calibration and avoiding the possible instability problem of the existing calibration technology.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, specifically to an automatic calibration method for a full-speed-domain lookup table for a permanent magnet synchronous motor. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) are widely used in the power sector due to their high power density and efficiency, becoming a core component of electric vehicle drive systems. To achieve excellent drive performance under various operating conditions, the motor's drive control strategy is crucial. While electric motors at rated speed and torque are sufficient for industrial applications, electric vehicles place far more stringent demands on their drive motors. Depending on actual road conditions, such as climbing hills and frequent start-stop cycles, the motor needs to provide greater torque at low speeds and higher power output at high speeds. Furthermore, certain specific operating conditions require even higher performance levels from the motor. Therefore, achieving efficient control of PMSMs is of paramount importance.

[0003] In permanent magnet synchronous motors (PMSMs), performance is good in the low-speed operating range. For operation below the reference speed, the MTPA method is a commonly used strategy to minimize copper losses while meeting the given load torque requirements. However, when the motor speed reaches the rated speed, it is difficult to increase the speed further due to the limitation of DC voltage. For electric vehicles, achieving high-speed operation is crucial, so field weakening control strategies for motors have always been a research focus in the field of high-performance control. Field weakening control of PMSMs is similar to speed control of excitation DC motors. When the terminal voltage of an excitation DC motor reaches its limit, higher speed operation is achieved by reducing the excitation current. However, the excitation magnetic field of a PMSM is generated by permanent magnets, and the magnetic field remains constant. Since it is difficult to directly adjust the flux linkage inside the permanent magnets, if it is necessary to continue to increase the speed, it is necessary to increase the reverse component of the direct-axis current to offset part of the permanent magnet magnetic field, thereby accelerating the motor operation. However, if the motor's current operating point is already close to the current limit circle, it is impossible to continue operating at constant torque to further increase the speed. It is necessary to increase the direct-axis demagnetizing current component while ensuring that the phase current does not exceed the current limit value, which will lead to a reduction in the quadrature-axis current component.

[0004] To ensure the accuracy of the given current, the establishment of the current lookup table for the experimental method of permanent magnet synchronous motor requires a lot of time, and the calibration process requires additional manual labor costs. In addition, due to the inherent defects of manual operation, the current given in the field weakening region may not be the optimal value.

[0005] Patent document 1 (CN109617486A) describes a method for automatically calibrating a permanent magnet synchronous motor, applied to the calibration testing of pure electric vehicles. The method includes the following steps: Step 1: Using a dynamometer to drive the permanent magnet synchronous motor to be calibrated at a set speed; Step 2: Recording the maximum torque current point at a set current vector amplitude, i.e., the optimal operating point; Step 3: Gradually increasing the current vector amplitude according to a preset current gradient; Step 4: This invention rationally plans the change process of the current vector angle, i.e. Figure 1 The current vector angle β on the left gradually decreases from 90° to 0°, avoiding the motor runaway that may occur when the current vector angle β gradually increases from 0° to 90° during the calibration process of the traditional method. When the base speed is above, the initial current vector angle is directly set to 0°. However, when the amplitude of the initial calibration current vector is large and exceeds the range of the voltage limit ellipse, the voltage will be insufficient to adjust the current magnitude, thus causing the motor to run away.

[0006] Patent document 2 (CN115225002A) relates to the field of permanent magnet synchronous motor calibration technology. It obtains a target current command by decoupling the motor torque command; based on feedback quantities such as the motor's rotor position and three-phase current, the target current command and target torque value are achieved. Constant torque zone calibration involves torque estimation under low motor speed conditions by providing different current amplitudes and angles, covering a torque estimation table across the entire operating current range, thus achieving automated calibration. After constant torque zone calibration, the voltage amplitude reaches its maximum. When the motor speed is further increased, constant power zone calibration is introduced using the same method. The constant power zone calibration is achieved by controlling the battery simulator, measurement and control machine, and motor controller via CAN communication using a benchtop host computer. With a fixed voltage amplitude, the maximum torque under the corresponding conditions is obtained by adjusting the voltage angle.

[0007] Existing automatic calibration technologies all propose automatic calibration methods based on a benchtop host computer that automatically outputs given commands to control the motor via CAN communication. This solves the inherent problem of excessively long manual calibration time in traditional offline calibration. However, existing calibration technologies still have certain problems. For example, Patent 1 does not consider the possibility of motor runaway and efficiency reduction when the current command is still given incrementally from zero at higher speeds; while Patent 2 uses voltage commands for calibration, but the calculation of voltage lookup table to current lookup table is cumbersome and complex, and open-loop control still has the risk of voltage instability.

[0008] To improve computational speed, reduce computational load, and avoid excessive pressure on the controller MCU, a lookup table method is proposed. This method utilizes extensive current calibration experiments to generate torque-current lookup tables for the motor in the MTPA and field-weakening regions. During motor operation, a two-dimensional lookup table (LUT) is used to query the relationship between the current command and the given torque and speed in real time, based on the given torque and speed, thereby obtaining the optimal current vector. This method is applicable to almost all speed ranges and achieves optimization through current control of the motor. This control method effectively avoids the burden of real-time calculations and improves computational speed.

[0009] The MTPA current curve was obtained using an exhaustive current calibration method. This method controls the motor stator current amplitude to be constant and gradually decreases the actual value of the d-axis current starting from 0A, recording the actual output torque of the motor under different current vectors until the output torque begins to decrease. This method records the current angle at which the motor output torque is at its maximum for each current amplitude, thus obtaining the relationship between the motor's MTPA current and the given torque.

[0010] The lookup table method exhibits high reliability and excellent dynamic performance in field weakening control. Therefore, improving and optimizing the offline calibration of the lookup table method is of great significance for the stable operation of electric vehicles and the manufacture of high-quality electric vehicles. The process of obtaining the current setpoint lookup table through bench calibration is also known as motor current calibration. Motor current calibration typically involves two main aspects: MTPA calibration and field weakening zone calibration. MTPA calibration is performed under low-speed conditions, estimating torque data tables across the entire operating current range of the motor by setting different combinations of current amplitude and angle. Since the motor speed and voltage input are fixed during calibration in the MTPA region, automated calibration is relatively easy to achieve. Field weakening zone calibration is performed after the inverter input voltage saturates, obtaining the maximum torque under corresponding conditions by adjusting the current angle. The corresponding conditions here mainly refer to different motor setpoint speeds under a fixed DC bus voltage.

[0011] To obtain the current reference table for the field weakening region, the motor must first be operated under the calibrated MTPA current condition. Then, by inputting corresponding commands, the dynamometer slowly increases the speed of the motor under test, observing the line voltage amplitude. The speed at which the line voltage first reaches its maximum value is recorded; this speed is defined as the transition speed between the MTPA and field weakening regions. Next, the motor speed is adjusted to slightly above the transition speed using the dynamometer, while maintaining a constant current amplitude. Then, the current angle is changed, and the current vector angle value at which the bus voltage reaches its maximum value and the current follows is recorded. Finally, at the same speed, the current amplitude corresponding to the maximum torque is selected, and data with larger current amplitudes at that speed are discarded. Compared to the MTPA region current calibration method, the complexity and operational difficulty of the field weakening region current calibration are significantly increased, and manual judgment is required to determine whether the given voltage is close to the system's limiting voltage.

[0012] As can be seen from the above, the disadvantages of traditional manual calibration techniques include: 1) The calibration of the current in the MTPA and the weak magnetic region mainly relies on manual labor, which takes a lot of time, is labor-intensive and inefficient; 2) Due to the inherent defects of manual operation, current control instability is prone to occur, or the current calibration value in the weak magnetic region is not the optimal value. The disadvantages of existing automatic calibration technologies are as follows: 1) The calibration method of Patent 1 requires repeated execution of steps 3 and 4 in the calibration process at each set speed. The continuous step-by-step iteration of the current vector amplitude and angle requires a lot of program calculation time, and the current command value occupies more storage space. At the same time, this scheme does not consider current runaway at higher speeds. At this time, the voltage limit ellipse no longer includes the origin of the current vector. That is, if the current vector amplitude is still increased step by step from zero, the operating point will exceed the voltage constraint, causing the motor to run away from control. 2) The calibration method of Patent 2 is based on the voltage control framework. The current vector control is used when the motor is running normally. Therefore, it is necessary to decouple the optimal torque point represented by voltage at each operating point into the current operating point. This will lead to additional workload and consume a certain amount of memory. At the same time, the open-loop voltage is directly given in the constant power area calibration process without the introduction of closed-loop control, which may lead to operational instability, unnecessary fault diagnosis and bench restart time.

[0013] Based on this technical background, this invention studies an automatic calibration method for a full-speed domain lookup table of a permanent magnet synchronous motor. Summary of the Invention

[0014] To address the shortcomings of existing technologies, this invention proposes an automatic calibration method for a full-speed-domain lookup table for permanent magnet synchronous motors. Both the MTPA (Metal-to-Pole Aspect Ratio) and field-weakening zone calibrations are based on rotor flux-oriented current loop control, eliminating the need for additional voltage control and lookup table conversion. This achieves highly efficient lookup table calibration for full-speed-domain motor control. Furthermore, the d-axis limiting current search fully considers the voltage limiting ellipse at higher speeds, achieving an efficiency unmatched by traditional offline calibration while avoiding potential instability issues in existing calibration techniques.

[0015] To achieve the above objectives, the present invention provides an automatic calibration method for a full-speed domain lookup table of a permanent magnet synchronous motor, comprising:

[0016] MTPA Automatic Calibration: When the motor under test is running below the rated speed, the current vector trajectory that traverses the current limit circle region is used to obtain the MTPA current lookup table;

[0017] d-axis limiting current search: When the motor under test is running at high speed and deep field weakening speed, obtain the speed-d-axis limiting current table under zero q-axis current;

[0018] Automatic calibration of the weak magnetic field zone: Based on the MTPA current lookup table, the speed-d axis limit current table, and the maximum q axis current boundary line, a weak magnetic field zone current lookup table is obtained.

[0019] The technical effects of this invention include:

[0020] (1) The automatic calibration method of the full-speed domain lookup table of permanent magnet synchronous motor proposed in this invention is based on the current loop control of rotor flux orientation for both MTPA and field weakening zone calibration. No additional voltage control and lookup table conversion are required, which can realize the lookup table calibration of the full-speed domain control of the motor with high efficiency. At the same time, the d-axis limit current search fully considers the voltage limit ellipse at higher speeds, which not only achieves the efficiency that traditional offline calibration does not have, but also avoids the possible instability problems of existing calibration technology.

[0021] (2) The automatic calibration method of the full-speed domain lookup table of permanent magnet synchronous motor proposed in this invention ensures that the low torque current vector point falls on the voltage limit in the d-axis limit current search, thus guaranteeing motor efficiency. At the same time, the automatic calibration in the field weakening zone draws on the field weakening control method of single current regulator and proposes q-axis voltage constraint limit control to maintain d-axis voltage. This achieves constant d-axis command current vector and q-axis vertical stabilization in the field weakening zone, automatically satisfying the voltage vector not exceeding the voltage limit, improving calibration stability and reducing the probability of runaway phenomena.

[0022] (3) The automatic calibration method for the full-speed domain lookup table of permanent magnet synchronous motor proposed in this invention, the three-step calibration method of "MTPA automatic calibration - d-axis limit current search - weak field zone automatic calibration", can send the pre-set calibration current command through the host computer software at intervals of T1, and control the motor by transmitting the command through CAN communication. This overcomes the tedious operation of the traditional method that requires manual traversal of current commands and inputting them one by one into the host computer before controlling the motor, and greatly reduces manual labor time.

[0023] (4) The automatic calibration method of the full-speed domain lookup table of permanent magnet synchronous motor proposed in this invention automatically gives the current command set by the motor controller through the host computer on the test bench, and then transmits the actual torque and current information back through CAN communication. The data post-processing constructs the full-speed domain current lookup table, which has a high degree of automation, greatly reduces manual labor hours, and reduces labor costs.

[0024] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0025] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0026] Figure 1 This is a schematic flowchart of the automatic calibration method for the full-speed domain lookup table of permanent magnet synchronous motors proposed in this invention.

[0027] Figure 2 This is a schematic diagram of the field weakening current trajectory and MTPA calibration in a specific embodiment of the automatic calibration method for the full-speed domain lookup table of permanent magnet synchronous motors proposed in this invention.

[0028] Figure 3 This is a schematic diagram of the automatic search control structure for the d-axis limit current in a specific embodiment of the automatic calibration method for the full-speed domain lookup table of a permanent magnet synchronous motor proposed in this invention.

[0029] Figure 4 This is a schematic diagram of the d-axis limit current search trajectory in a specific embodiment of the automatic calibration method for the full-speed domain lookup table of a permanent magnet synchronous motor proposed in this invention.

[0030] Figure 5 This is a schematic diagram of the calibration of the weak magnetic region when the d-axis limiting current does not occur, in a specific embodiment of the automatic calibration method for the full-speed domain lookup table of the permanent magnet synchronous motor proposed in this invention.

[0031] Figure 6This is a schematic diagram illustrating the calibration of the field weakening region when the d-axis limiting current occurs, in a specific embodiment of the automatic calibration method for the full-speed domain lookup table of a permanent magnet synchronous motor proposed in this invention.

[0032] Figure 7 This is a schematic diagram of the automatic stabilization control structure for the calibration voltage in the weak magnetic field zone, as described in a specific embodiment of the automatic calibration method for the full-speed domain lookup table of a permanent magnet synchronous motor proposed in this invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] SA - A-phase bridge arm switch signal of the frequency converter; SC - C-phase bridge arm switch signal of the frequency converter; iA - A-phase current; iC - C-phase current; θ C - Electrical angle of the motor, id - d-axis current of the motor, iq - q-axis current of the motor Direct-axis given voltage, Transformed quadrature-axis reference voltage Shaft given voltage, Shaft given voltage, SVPWM - Space Vector Pulse Width Modulation, PMSM - Permanent Magnet Synchronous Motor, MTPA - Maximum Torque Current Ratio, MTPV - Maximum Torque Voltage Ratio, EVM - Error Vector Amplitude. Detailed Implementation

[0035] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0036] In this invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its normal operating state, for example, as shown in the reference. Figure 1 In the drawing orientation, "inner" and "outer" refer to those relative to the outline of the device. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0037] This invention provides an automatic calibration method for a full-speed domain lookup table of a permanent magnet synchronous motor, such as... Figure 1 As shown, it includes:

[0038] MTPA Automatic Calibration: When the motor under test is running below the rated speed, the current vector trajectory that traverses the current limit circle region is used to obtain the MTPA current lookup table;

[0039] d-axis limiting current search: When the motor under test is running at high speed and deep field weakening speed, obtain the speed-d-axis limiting current table under zero q-axis current;

[0040] Automatic calibration of the field weakening zone: Based on the MTPA current lookup table, the speed-d axis limit current table, and the maximum q axis current boundary line, the field weakening zone current lookup table is obtained.

[0041] In this invention, both MTPA and field weakening zone calibration are based on rotor flux-oriented current loop control, eliminating the need for additional voltage control and lookup table conversion. This achieves highly efficient lookup table calibration for full-speed-domain motor control. Meanwhile, the d-axis limiting current search fully considers the voltage limiting ellipse at higher speeds, achieving an efficiency unmatched by traditional offline calibration while avoiding potential instability issues in existing calibration techniques.

[0042] According to the present invention, when the tested motor is operating below its rated speed, the current vector trajectory traversing the current limit circle region is used to obtain the MTPA current lookup table, which includes:

[0043] When the motor under test is running below the rated speed and maintaining a constant speed, the amplitude of the current vector is ranged from zero to the current limit amplitude, and the angle range of the current vector is ranged from 0° to 90°. The current vector trajectory is traced, and the maximum torque of the motor under test and its corresponding current point information are recorded as the MTPA current lookup table.

[0044] According to the present invention, the amplitude range and angle range of the current vector are both sent by the host computer on the test bench to the motor controller via the CAN bus to control the operation of the motor under test.

[0045] The maximum torque and its corresponding current point information are recorded in real time by the power analyzer and transmitted back to the host computer on the test bench via the CAN bus.

[0046] In this invention, the host computer on the test bench automatically gives the current command set by the motor controller, and then the actual torque and current information are transmitted back via CAN communication. The data post-processing constructs a full-speed domain current lookup table, which has a high degree of automation, greatly reduces manual labor hours, and lowers labor costs.

[0047] According to the present invention, when the tested motor is operating under high-speed, deep field-weakening conditions, the speed-d-axis limiting current meter at zero q-axis current includes:

[0048] The test bench, controlled by a host computer, adjusts the motor under test from a set high speed in incremental increments. A zero q-axis current and a negative d-axis current are given, and the d-axis current is adjusted. When the current oscillation of the tested motor just disappears, the corresponding d-axis current is recorded; this is the d-axis limit current at that speed. All speeds and their corresponding d-axis current data are compiled into a speed-d-axis limit current table.

[0049] By setting both the d-axis and q-axis currents to zero using the host computer on the test bench, the voltage constraint relationship of the voltage limit ellipse is used to calculate the difference between the actual current and the voltage limit. This difference is then processed by the voltage outer loop PI regulator and limiter to obtain the d-axis current compensation value. The difference between the d-axis current compensation value and the zero d-axis current is then calculated to obtain the speed-d-axis limit current meter.

[0050] In this invention, the low torque current vector point in the d-axis limit current search falls on the voltage limit, ensuring motor efficiency. At the same time, the automatic calibration in the field weakening region draws on the field weakening control method of a single current regulator and proposes a q-axis voltage constraint limiting control to maintain the d-axis voltage. This achieves a constant d-axis command current vector and a vertical stabilization of the q-axis in the field weakening region, automatically satisfying the voltage vector not exceeding the voltage limit, improving calibration stability and reducing the probability of runaway phenomena.

[0051] In this invention, the three-step calibration method of "MTPA automatic calibration - d-axis limit current search - automatic calibration of weak magnetic region" can send a pre-set calibration current command at intervals of T1 through the host computer software, and control the motor by transmitting the command through CAN communication. This overcomes the tedious operation of the traditional method, which requires manually traversing the current command one by one and inputting it into the host computer before controlling the motor, and greatly reduces manual labor time.

[0052] Preferably, the expression for the voltage constraint relationship of the voltage limit ellipse is:

[0053]

[0054] Among them, U smax To test the motor's limiting voltage, i d i q These are the d-axis and q-axis currents of the motor, respectively, L d L q These are the d-axis and q-axis inductances of the test motor, respectively, and ψ f For permanent magnet flux linkage, ω r To test the angular velocity of the motor.

[0055] According to the present invention, based on the MTPA current lookup table, the speed-d-axis limiting current table, and the maximum q-axis current boundary line, a current lookup table for the weak magnetic region is obtained, including:

[0056] When the speed of the motor under test is within the shallow field weakening zone range where the d-axis limit current does not occur, the host computer on the test bench gives different speeds, and the current vector traverses the curve of the MTPA current lookup table and the boundary line of the maximum q-axis current from the intersection of the d-axis and q-axis each time. When the host computer on the test bench detects the maximum torque, it stops the current traversal at that speed. All speeds and their corresponding maximum torques form a field weakening zone current lookup table.

[0057] According to the present invention, it further includes:

[0058] When the speed of the motor under test is within the deep field weakening region where the d-axis limit current appears, the intersection of the curves of the d-axis current compensation value and the MTPA current lookup table is obtained based on the speed-d-axis limit current table. The host computer on the test bench gives different speeds, and the current vector traverses from the intersection of the curves along the curve of the MTPA current lookup table and the boundary line of the maximum q-axis current corresponding to the highest speed of the motor under test. When the host computer on the test bench detects the maximum torque, the current traversal at that speed is stopped. All speeds and their corresponding maximum torques form a field weakening region current lookup table.

[0059] Preferably, when the current vector exceeds the voltage constraint relationship of the voltage limit ellipse during the process of traversing the curve of the MTPA current lookup table and the maximum q-axis current boundary line corresponding to the highest speed of the motor under test from the intersection of the curves, the corresponding current vector directly corresponds to the voltage constraint relationship boundary of the voltage limit ellipse.

[0060] According to the present invention, in the expression for the voltage constraint relationship of the voltage limiting ellipse, the point (-ψ) is used. f / L d An ellipse with center (0, 0);

[0061] The corresponding current vector directly corresponds to the voltage constraint boundary of the voltage limit ellipse, which includes:

[0062] When the magnitudes of the d-axis and q-axis current vectors exceed the voltage limit constraint, the transformed quadrature axis given voltage is selected as the final given voltage.

[0063] When the magnitudes of the d-axis and q-axis current vectors do not exceed the voltage limit constraint, the quadrature axis reference voltage is selected as the final given voltage.

[0064] According to the present invention, the quadrature-axis reference voltage is obtained by a PI regulator from the current vector;

[0065] The current vector is also used to obtain the direct-axis given voltage through a PI regulator;

[0066] The expression for the transformed quadrature-axis given voltage is:

[0067]

[0068] in, Provide a voltage for the direct axis. Given a voltage u to the transformed quadrature axis lim To test the output limiting voltage of the motor.

[0069] The present invention will now be described in more detail through specific embodiments.

[0070] Example 1

[0071] This embodiment provides an automatic calibration method for a lookup table in the full speed domain of a permanent magnet synchronous motor. The specific implementation process includes:

[0072] The automatic calibration hardware and software system for the full-speed domain current set is composed of a host computer on the test bench, a control motor, the motor under test, a motor controller, and a DC voltage source. In the current calibration process of the full-speed domain lookup table, the functions of each part can be summarized as follows: the host computer on the test bench pre-controls the DC voltage source to stabilize the DC bus voltage at a certain fixed voltage, and controls the control motor to make the motor under test run at a given speed. Then, the host computer software on the test bench automatically gives the calibration current command set in the program, which is transmitted to the motor controller via CAN communication. The motor under test runs at different operating points. Finally, the real-time current and its corresponding torque information are transmitted back to the host computer on the test bench via CAN communication, and the maximum torque value and its current vector value are recorded.

[0073] In this embodiment, some constraints in the field weakening control of the permanent magnet synchronous motor are explained as follows:

[0074] In the vector control system of a permanent magnet synchronous motor, the inverter's operating current and voltage cannot exceed the maximum current and voltage that the inverter can withstand, which are usually defined as the limiting current I. smax and limiting voltage U smax The stator current i of the motor s The following conditions must be met:

[0075] i s ≤I smax ;

[0076] Therefore, the trajectory of the current vector is centered at the origin (0,0) and revolves around I. smax A circle with radius is defined as the current-limiting circle;

[0077] stator voltage u of the motor s The conditions to be met are:

[0078] u s ≤U smax ;

[0079] In the synchronously rotating dq coordinate system, the dq-axis voltage equation is:

[0080]

[0081] In the formula, u d u q These are the d-axis and q-axis voltages of the motor, respectively; i d i q These are the d-axis and q-axis currents of the motor, respectively; L d L q These are the d-axis and q-axis inductances of the motor, respectively; ψf For permanent magnet flux linkage; R s ω is the motor resistance. r The electric angular velocity of the motor;

[0082] The magnitude of the stator voltage vector is:

[0083]

[0084] Neglecting the stator resistance voltage drop, the voltage equation for the permanent magnet synchronous motor during steady-state operation can be simplified to:

[0085]

[0086] Substituting the voltage equation into the voltage limit constraints, we get...

[0087]

[0088] For the built-in permanent magnet synchronous motor involved in this invention, the limiting voltage equation is based on the point (-ψ). f / L d An ellipse centered at (ω, 0) is also called a voltage limit ellipse; as the motor speed ω increases... r As the voltage limit ellipse increases, the voltage limit ellipse will gradually decrease;

[0089] When the motor is running stably at a certain speed, the stator current vector should be located in the overlapping area of ​​the voltage limit ellipse and the current limit circle corresponding to that speed.

[0090] In this embodiment, to achieve optimal performance of the motor at different speeds and torques, the operating states of the current vector can be divided into: Figure 2 The three areas shown on the left:

[0091] 1) MTPA Trajectory (OGEDA Curve): In this region, the motor operates along the trajectory of the maximum torque-to-current ratio. This region is entirely below the rated speed, allowing for precise torque control by adjusting the current while maintaining a constant speed. As the speed increases, the motor's output torque can remain constant while reducing energy loss, enabling the motor to achieve optimal performance at low speeds.

[0092] 2) Weak field zone (region OAB): In this region, the motor operates above the rated speed and works along the curve between the maximum torque-to-current ratio and the current limit circle; this region includes the constant torque curve and the curve on the current limit circle; when the motor runs along the current limit circle, the torque will gradually decrease as the speed increases, but the output power of the motor will remain constant.

[0093] 3) MTPV trajectory (curve BFH): In this region, the motor operates along the trajectory of maximum torque-voltage ratio. It should be noted that not all types of permanent magnet motors possess an MTPV operating trajectory; it only occurs when specific conditions ψ are met. f / L d <I smax Only certain types of motors can achieve this; motors running along the MTPV trajectory can increase their speed without limit, but in this region, the motor's torque capability gradually becomes limited; the MTPV trajectory is known as the field weakening high-speed operating region, suitable for certain types of permanent magnet motors, which achieve higher speeds while providing moderate torque control;

[0094] Figure 2 The right side clearly illustrates the first step of the full-speed-domain automatic calibration of this invention: MTPA automatic calibration;

[0095] Set a speed ω lower than the rated speed using the benchtop host computer. N The test motor operates at a relatively low speed, and the control unit is used to keep it running stably at this constant speed, thus ensuring that the current operating point does not touch the terminal voltage limit boundary; the current command trajectory is pre-set in the host computer of the test bench, that is, the current amplitude I is given in variable step size starting from zero. s Until the current limit amplitude I smax Simultaneously, with a fixed current vector amplitude, the angle β gradually increases from 0° to 90° in fixed steps, thus forming a current command trajectory that traverses the current limit circle region of the second quadrant. The host computer on the test bench sends the set current command interval T1 to the motor controller via CAN communication to control the motor. Then, the torque and current values ​​recorded in real time by the power analyzer are transmitted back to the host computer on the test bench via CAN communication. The test bench records the maximum torque and its corresponding current point information, and finally, an MTPA current lookup table is created.

[0096] Figure 3 and Figure 4 The second step of the full-speed domain automatic calibration of this invention is described: d-axis limit current search;

[0097] The d-axis limiting current needs to be defined beforehand as the current at the first intersection of the voltage limiting ellipse and the negative d-axis, such as... Figure 4 Point P in the middle;

[0098] like Figure 3 The control structure combining various hardware and software is shown. When the rotation speed increases to the deep field weakening rotation speed ω3, the voltage limit ellipse and the current vector origin (0,0) intersect for the first time. If the rotation speed continues to increase, as shown by rotation speed ω4 in the figure, the general calibration method usually does not take this situation into account or the d-axis current does not fall on the boundary of the voltage limit ellipse during calibration, which will lead to instability or reduced efficiency. To address this, the present invention proposes a current command preprocessing stage for calibration in the field weakening region, namely, d-axis limit current search.

[0099] Two methods were studied for searching the d-axis limiting current under high-speed, deep magnetic weakening conditions. The first method was a manual search, in which the test motor was gradually increased from speed ω3 by a test bench-controlled measuring and control computer. The host computer was manually operated to provide a zero q-axis current and a negative d-axis current, and the magnitude of the d-axis current was gradually adjusted. When the motor current oscillation was just eliminated, the d-axis current was recorded, which is the d-axis limiting current at that speed. This method is simple, convenient, and easy to operate, but the current point found may only be near point P, not at the optimal point P. The second method was an automatic search based on voltage outer loop feedback to automatically adjust the d-axis current. First, the host computer on the test bench provided both the d- and q-axis currents to be zero. Using the voltage constraint relationship of the voltage limit ellipse, the difference between the actual current and the voltage limit was calculated. This difference was passed through the voltage outer loop PI regulator and limiting circuit to output the d-axis current compensation value. The difference with the zero d-axis current was then used to obtain the given value of the d-axis limiting current. Both proposed d-axis limiting current search methods are feasible, and the second method was selected in this embodiment.

[0100] Figure 4 This is a schematic diagram of the current vector trajectory after the d-axis limit current search control method. The d-axis limit current is independently searched by the d-axis limit current search algorithm under deep field weakening. The host computer records the given speed and its corresponding feedback d-axis current value transmitted back by CAN communication, and forms a speed-d-axis limit current table. This table, combined with the MTPA lookup table, obtains the host computer's given current vector command table for automatic calibration of the field weakening zone.

[0101] Figures 5 to 7 Together, they demonstrate the third step of the full-speed-domain automatic calibration of this invention: automatic calibration in the weak magnetic region;

[0102] First, some current trajectory curves need to be defined; define Figure 5 and Figure 6 The AS line in the middle is the maximum i q Boundary line, i where point S is located d The current value at this time is the maximum current amplitude I. smax ;

[0103] After the first and second steps of the full-speed-domain automatic calibration method of this invention, the rated speed ω was obtained respectively. N The following MTPA torque-current lookup table and the speed-d-axis limit current lookup table for depth field weakening speeds above ω3 are used to combine these two tables with the maximum i q The boundary lines are combined to obtain the rated speed ω N The above field weakening zone calibration - host computer current command setting table is used as the current command input from the host computer to the motor controller;

[0104] Weak field zone calibration - the host computer current command setpoint table can be divided into two stages according to different rotational speeds: rotational speed ω N A shallow magnetic weakening region between rotational speed ω3 and speed ω3 where no d-axis limiting current occurs; a deep magnetic weakening region where the d-axis limiting current occurs above rotational speed ω3.

[0105] like Figure 5 The figure shows the trajectory of the given current command in a shallow magnetic field weakening region; at a rotational speed ω N Between the rotational speed ω3 and the given rotational speed ω3, the current vector always originates from point O along the MTPA curve and the maximum i at different test bench rotational speeds. q Boundary line traversal, that is, traversal along the OAS curve, when the host computer detects the maximum torque point N, the current command traversal at that speed is stopped;

[0106] like Figure 6 The image shows the trajectory of the given current command in the deep magnetic weakening region; above the rotational speed ω3, using the rotational speed-d-axis limit current lookup table obtained in the second step, the trajectory of the given current command in the shallow magnetic weakening region passes through the d-axis limit current Δi. d After compensation, the trajectory table of the given current command for the deep magnetic weakening region is obtained and stored in the host computer, such as... Figure 6 The torque is recorded by traversing the QAN curve at a speed of ω4, which is higher than the rotational speed ω3.

[0107] Along such Figure 5 and Figure 6 The field weakening zone calibration shown is performed by scanning the voltage limit ellipse boundary using the current command trajectory given by the host computer. Without a specific voltage stabilization control algorithm, the motor may experience voltage runaway; for example: Figure 5 Given a point M, it can only actually run at point M'. Figure 6 Given a point Q, it can only actually run at point P;

[0108] To achieve the control requirement of automatic stabilization when the given current command vector exceeds the voltage constraint, this embodiment draws on the single-current field weakening control method in the classic field weakening control scheme and creatively proposes a method that can achieve i d unchanged, i q A single d-axis current calibration control method for vertical descent; the essence of the classic single current regulator method is voltage angle control, the current loop only retains the direct axis current regulator, and the field weakening control is completed with only a single current loop, which also improves the field weakening depth; the single current regulator method mainly utilizes the cross-coupling effect between the d and q axes at high speed, and completes the purpose of field weakening control and speed adaptation simultaneously through a single current regulator, which is relatively simpler in structure and has a faster dynamic response;

[0109] like Figure 7As shown, the single d-axis current calibration control method proposed in this invention does not need to consider the cross-coupling effect between the d and q axes. This method does not have a quadrature-axis current regulator, and the quadrature-axis voltage reference value is not obtained from the current regulator output. When the motor operating point touches the voltage limit ellipse, to ensure the motor operates stably at the optimal operating point and fully utilizes the inverter output voltage, the quadrature-direct axis voltage must satisfy the voltage limit ellipse formula. Therefore, the quadrature-axis voltage setting formula is:

[0110]

[0111] in, The current is given by the direct-axis current regulator. At this time, the motor is rotating forward, which is the electric mode. According to the formula, the stator current vector of the motor is always on the boundary of the voltage limit ellipse. At the same time, since the voltage output controlled by the PI of the d-axis current is not subject to additional restrictions, the d-axis current given by the host computer will remain unchanged due to the zero steady-state error characteristic of the DC quantity controlled by the PI. However, due to the voltage ellipse constraint, the q-axis voltage will converge to another stable value to ensure that the voltage falls on the boundary of the voltage ellipse. This is reflected in the change of the current command, that is, the d-axis current remains unchanged, while the q-axis current will drop vertically to the dq-axis current ellipse represented by the voltage limit. Since the motor needs to meet the voltage and current constraints at the same time, its steady-state operating point is located in the common area of ​​the voltage limit ellipse and the current limit circle.

[0112] Figure 7 The overall calibration control system includes two current loops for the d and q axes. The host computer on the test bench provides the pre-set calibration current command for the field weakening zone, and the voltage reference value is obtained through the corresponding regulator. When the motor enters the field weakening zone, the direct axis given voltage is obtained through the PI regulator. and quadrature axis reference voltage The final input quadrature-axis voltage to the motor Need to pass Figure 7 The control switching module is used for selection: when the current operating point exceeds the voltage limit ellipse. otherwise This is the reference voltage output by the quadrature-axis PI regulator. After that, u d u q Perform a coordinate transformation to obtain u α u β Input SVPWM module;

[0113] When the current command vector given by the host computer is inside the voltage limiting ellipse, it is necessary to add... Figure 7 The q-axis setpoint voltage control switching module in the middle;

[0114] Control switching mode: When the magnitude of the dq-axis voltage vector exceeds the voltage limit constraint, select the quadrature axis setpoint voltage. As the final given voltage; when the magnitude of the dq-axis voltage vector does not exceed the voltage limit constraint, the quadrature axis reference voltage is selected. As the final given voltage;

[0115] like Figure 5 and Figure 6 In the process, the host computer's given current command points M and N, which are outside the voltage limit ellipse, descend vertically to the current points M' and N' on the boundary of the voltage limit ellipse, respectively. Meanwhile, the host computer's given current command points E and G inside the voltage limit ellipse remain unchanged, meaning the control switching module does not operate. The current points after descent and their corresponding torque information are transmitted back to the host computer on the test bench via CAN communication, thereby creating a current lookup table for the weak magnetic field zone.

[0116] In this embodiment, the automatic calibration method for the full-speed domain lookup table of the permanent magnet synchronous motor is based on the MTPA and field weakening zone calibration, which are both based on rotor flux orientation current loop control. No additional voltage control and lookup table conversion are required, which can efficiently realize the lookup table calibration of the full-speed domain control of the motor. At the same time, the d-axis limit current search fully considers the voltage limit ellipse at higher speeds, which not only achieves the efficiency that traditional offline calibration does not have, but also avoids the instability problems that may occur in existing calibration techniques.

[0117] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An automatic calibration method for a full-speed domain lookup table of a permanent magnet synchronous motor, characterized in that, include: MTPA Automatic Calibration: When the motor under test is running below the rated speed, the current vector trajectory that traverses the current limit circle region is used to obtain the MTPA current lookup table; d-axis limiting current search: When the motor under test is running at high speed and deep field weakening speed, obtain the speed-d-axis limiting current table under zero q-axis current; Automatic calibration of the field weakening zone: Based on the MTPA current lookup table, the speed-d axis limit current table, and the maximum q axis current boundary line, a field weakening zone current lookup table is obtained; Based on the MTPA current lookup table, the speed-d-axis limiting current table, and the maximum q-axis current boundary line, the current lookup table for the weak magnetic region is obtained as follows: When the speed of the motor under test does not appear d When the shallow field weakening region of the axis limiting current is within the range, the host computer on the test bench gives different speeds, and the current vector traverses the curve of the MTPA current lookup table and the boundary line of the maximum q-axis current from the intersection of the d-axis and q-axis each time. When the host computer on the test bench detects the maximum torque, it stops the current traversal at that speed. All speeds and their corresponding maximum torques form a field weakening region current lookup table. When the speed of the motor under test is within the deep field weakening region where the d-axis limiting current occurs, based on the speed- d The d-axis limit current meter obtains the intersection point of the curve between the d-axis current compensation value and the MTPA current lookup table. The host computer on the test bench gives different speeds, and the current vector traverses from the intersection point of the curve along the curve of the MTPA current lookup table and the boundary line of the maximum q-axis current corresponding to the highest speed of the motor under test. When the host computer on the test bench detects the maximum torque, it stops the current traversal at that speed. All speeds and their corresponding maximum torques form a current lookup table for the field weakening region. When the current vector exceeds the voltage constraint relationship of the voltage limit ellipse during each traversal of the curve from the intersection point of the curves along the curve of the MTPA current lookup table and the boundary line of the maximum q-axis current corresponding to the highest speed of the motor under test, the corresponding current vector directly corresponds to the voltage constraint relationship boundary of the voltage limit ellipse.

2. The method according to claim 1, characterized in that, When the tested motor is operating below its rated speed, the current vector trajectory traversing the current limit circle region yields the MTPA current lookup table, which includes: When the motor under test is running below the rated speed and maintaining a constant speed, the amplitude of the current vector is ranged from zero to the current limit amplitude, and the angle range of the current vector is ranged from 0° to 90°. The current vector trajectory is traversed, and the maximum torque of the motor under test and its corresponding current point information are recorded as the MTPA current lookup table.

3. The method according to claim 2, characterized in that, The amplitude and angle range of the current vector are both sent to the motor controller by the host computer on the test bench via the CAN bus, thereby controlling the operation of the motor under test. The maximum torque and its corresponding current point information are recorded in real time by the power analyzer and transmitted back to the host computer on the test bench via the CAN bus.

4. The method according to claim 3, characterized in that, When the tested motor operates under high-speed, deep field-weakening conditions, the speed-d-axis limiting current table at zero q-axis current includes: The test bench, controlled by a host computer, adjusts the motor under test from a set high speed in incremental increments. A zero q-axis current and a negative d-axis current are given, and the d-axis current is adjusted. When the current oscillation of the tested motor just disappears, the corresponding d-axis current is recorded; this is the d-axis limit current at that speed. All speeds and their corresponding d-axis current data are compiled into a speed-d-axis limit current table. By setting both the d-axis and q-axis currents to zero using the host computer on the test bench, the voltage constraint relationship of the voltage limit ellipse is used to calculate the difference between the actual current and the voltage limit. This difference is then processed by the voltage outer loop PI regulator and limiter to obtain the d-axis current compensation value. The difference between the d-axis current compensation value and the zero d-axis current is then calculated to obtain the speed-d-axis limit current meter.

5. The method according to claim 4, characterized in that, The expression for the voltage constraint relationship of the voltage limit ellipse is: ； Among them, U smax To test the motor's limiting voltage, i d i q These are the d-axis and q-axis currents of the motor, respectively, L d L q These are tests for the d-axis and q-axis inductance of the motor, respectively. ψ f It is a permanent magnet flux chain. ω r To test the angular velocity of the motor.

6. The method according to claim 1, characterized in that, The voltage limit ellipse is the expression for the voltage constraint relationship of the voltage limit ellipse, with point (- ψ f / L d An ellipse with center 0; The corresponding current vector directly corresponds to the voltage constraint boundary of the voltage limit ellipse, which includes: When the magnitudes of the d-axis and q-axis current vectors exceed the voltage limit constraint, the transformed quadrature axis given voltage is selected as the final given voltage. When the magnitudes of the d-axis and q-axis current vectors do not exceed the voltage limit constraint, the quadrature axis reference voltage is selected as the final given voltage.

7. The method according to claim 6, characterized in that, The quadrature-axis reference voltage is obtained from the current vector via a PI regulator; The current vector is also used to obtain the direct-axis given voltage through a PI regulator; The expression for the transformed quadrature-axis given voltage is: ； in, Provide a voltage for the direct axis. Apply a voltage to the transformed quadrature axis. To test the output limiting voltage of the motor.

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