A method for regulating excitation of a permanent magnet motor in an overload state

Abstract

The application belongs to the technical field of high-efficiency permanent magnet motor control, and discloses a kind of excitation adjustment method of permanent magnet motor overload state, comprising: current, voltage and angular velocity are collected and voltage limit is determined, total flux is calculated according to cross-axis current update inductance and prediction synthesis end voltage;When the predicted value exceeds the limit, calculate the saturation margin, solve the direct-axis field weakening adjustment increment and scale the proportional gain;Update the direct-axis excitation command current and redistribute the cross-axis limit command current;According to the rotor temperature, determine the demagnetization threshold to clamp protection and output control instruction, the application reconstructs the cross-axis cross-saturation flux by cross-axis cross-saturation flux and adaptive proportional gain adjustment, eliminates the demagnetization estimation deviation under deep saturation, and suppresses the voltage overmodulation loss of control risk in dynamic response, to ensure the safety of permanent magnet thermal demagnetization, and improve the motor overload torque output capability.

Description

Technical Field

[0001] This invention relates to the field of high-efficiency permanent magnet motor control technology, and in particular to an excitation regulation method for permanent magnet motors under overload conditions. Background Technology

[0002] In industrial transmission and electric drive systems, permanent magnet synchronous motors are widely used due to their high efficiency. Existing control methods typically employ field-oriented control, calculating the direct-axis and quadrature-axis components of the stator current based on discrete inductance parameters or static mapping tables to achieve motor control. However, under short-term high-rate overload conditions, a large current flows through the stator windings, causing significant cross-saturation of the main magnetic circuit of the iron core. The equivalent inductance of the direct axis and the equivalent inductance of the quadrature axis decrease nonlinearly with increasing saturation. At the same time, the influence of the quadrature-axis current on the direct-axis flux linkage also increases. Existing adjustment methods using fixed parameter models or static mapping tables cannot reflect the changes in inductance under strong saturation conditions and the coupling effects between the direct and quadrature axes in a timely manner, easily leading to deviations in the demagnetizing flux linkage estimation. Therefore, they cannot accurately reflect the actual magnetic field conditions under deep saturation conditions.

[0003] Existing control algorithms still have shortcomings in their excitation regulation mechanisms. For example, Chinese invention patent CN109713960B discloses a field weakening control method and controller for a permanent magnet synchronous motor. This method establishes a target straight line by selecting the intersection of the constant torque curve and the maximum torque-to-current ratio curve, as well as specific voltage characteristic points. It then solves for the intersection of this straight line with the ideal voltage limit ellipse to quickly lock the initial current value. Fine-tuning is then performed using voltage negative feedback. This algorithm is based on the assumption that the direct-axis and quadrature-axis inductances of the motor remain constant throughout the entire operating range, thus enabling the solution of geometric intersections based on ideal algebraic equations. However, under high-rate overload conditions, the motor's main magnetic circuit falls into a deep quadrature-direct-axis cross-saturation state, causing the equivalent inductance to exhibit a drastic and nonlinear sharp drop and drift, resulting in a significant deviation in the actual voltage. When the ellipse undergoes severe deformation and displacement, the initial current value determined based on ideal parameters will deviate significantly from the actual target operating point. This can easily lead to the initial current value deviating from the actual target point, causing current loop oscillation and regulator saturation, and increasing the risk of over-modulation of the terminal voltage. On the other hand, during the overload dynamic response process, if the terminal voltage prediction is inaccurate, the stator terminal voltage may exceed the usable range of the inverter's DC bus, resulting in problems such as over-modulation of voltage and saturation of the current loop. At the same time, motor overload operation will also cause the stator and rotor temperatures to rise. Under the combined effect of high temperature and large demagnetizing current, there is a risk of irreversible thermal demagnetization of the permanent magnet. The fixed demagnetization limit cannot be adjusted with temperature changes, so it is difficult to simultaneously ensure operational safety and overload torque output capability.

[0004] Therefore, under the conditions of deep core saturation and strong coupling between the perpendicular and quadrature axes, how to accurately determine the excitation and demagnetization components during the overload dynamic process, avoid over-modulation of the terminal voltage, and ensure that the permanent magnet is within a safe demagnetization range during temperature changes has become the technical problem to be solved by this invention. Summary of the Invention

[0005] To address the problems in the background art, the present invention provides the following technical solution: a method for excitation adjustment of a permanent magnet motor under overload conditions, the method comprising the following steps:

[0006] Step S1: Collect the stator current, DC bus voltage and rotor electric angular velocity of the permanent magnet motor, obtain the quadrature axis measured current and direct axis measured current through coordinate transformation, and determine the maximum stator voltage amplitude limit based on the DC bus voltage.

[0007] Step S2: Construct a cross-axis and direct-axis saturated flux linkage reconstruction model; update the direct-axis equivalent inductance and cross-axis equivalent inductance based on the measured current of the cross-axis and the measured current of the direct axis; and calculate the total flux linkage of the direct axis and the total flux linkage of the cross-axis.

[0008] Step S3: Calculate the predicted value of the combined amplitude of the stator terminal voltage based on the rotor electric angular velocity, stator phase resistance, direct-axis total flux linkage and quadrature-axis total flux linkage;

[0009] Step S4: When the predicted value of the synthesized amplitude of the stator terminal voltage is greater than the maximum stator voltage amplitude limit, calculate the voltage saturation margin, and solve the direct-axis field weakening excitation regulation current increment based on the voltage saturation margin, rotor electric angular velocity and direct-axis equivalent inductance. The proportional regulation gain is adaptively scaled according to the attenuation ratio of the direct-axis equivalent inductance relative to the initial unsaturated inductance.

[0010] Step S5: Update the direct-axis excitation command current according to the direct-axis field weakening excitation adjustment current increment, and allocate the quadrature-axis limit command current according to the motor overload total current limit;

[0011] Step S6: Obtain the current temperature of the rotor permanent magnet, calculate the limit demagnetizing current constraint threshold based on the intrinsic coercivity temperature coefficient of the permanent magnet material, and when the direct-axis excitation command current touches the limit demagnetizing current constraint threshold, translate the margin exceeding the limit demagnetizing current constraint threshold into an overload derating protection signal, and output the clamped direct-axis command current and quadrature-axis limit command current to the inverter.

[0012] Preferably, in step S2, the direct-axis total flux linkage is determined based on the multiplicative relationship between the direct-axis equivalent inductance, the measured direct-axis current, and the preset intrinsic excitation flux linkage of the rotor permanent magnet, and the quadrature-axis total flux linkage is determined based on the product of the quadrature-axis equivalent inductance and the measured quadrature-axis current; wherein the updating process of the direct-axis equivalent inductance and the quadrature-axis equivalent inductance includes: calculating the cross-saturation correction coefficient based on the measured quadrature-axis current and the measured direct-axis current, and then correcting the preset initial unsaturated direct-axis inductance and the preset initial unsaturated quadrature-axis inductance to obtain the direct-axis equivalent inductance and the quadrature-axis equivalent inductance under the current cross-saturated magnetic field state.

[0013] Preferably, in step S4, the voltage saturation margin is obtained by subtracting the maximum stator voltage amplitude limit from the predicted value of the synthesized amplitude of the stator terminal voltage; when solving the increment of the direct-axis field weakening excitation regulation current, the proportional regulation gain is proportional to the direct-axis equivalent inductance and adaptively scaled, specifically including: calculating the inductance attenuation ratio of the current direct-axis equivalent inductance relative to the preset initial unsaturated inductance, multiplying the inductance attenuation ratio by the proportional regulation gain base value to obtain the scaled proportional regulation gain, so as to offset the open-loop gain drift of the control loop caused by the sharp drop in the direct-axis equivalent inductance.

[0014] Preferably, in step S5, the process of allocating the quadrature axis limit command current includes: calculating the difference between the square of the total overload current limit of the motor and the square of the updated direct axis excitation command current, performing a square root operation on the difference to obtain the upper limit of the quadrature axis amplitude, and determining the quadrature axis limit command current based on the same positive or negative sign as the measured quadrature axis current.

[0015] Preferably, in step S6, the process of calculating the ultimate demagnetizing current constraint threshold includes: obtaining the current temperature of the rotor permanent magnet by estimating the temperature rise of the stator phase resistance or by using a high-frequency injection thermal model; and linearly correcting the initial demagnetizing current threshold at the reference temperature based on the temperature difference between the current temperature and the reference temperature, combined with the intrinsic coercivity temperature coefficient of the permanent magnet material, to obtain the ultimate demagnetizing current constraint threshold corresponding to the current temperature.

[0016] Preferably, in step S6, translating the margin exceeding the limit demagnetizing current constraint threshold into an overload derating protection signal includes: when the calculated direct-axis excitation command current is less than the limit demagnetizing current constraint threshold, forcibly locking the direct-axis excitation command current to the limit demagnetizing current constraint threshold, calculating the current difference between the target direct-axis field weakening current and the limit demagnetizing current constraint threshold, generating a motor power derating ratio command based on the current difference, and sending the motor power derating ratio command to the top-level master control unit of the drive control system to reduce the expected motor load.

[0017] Preferably, the excitation regulation method further includes a maximum torque-voltage ratio trajectory demagnetization compensation process: when redistributing the quadrature axis limit command current, the attenuation rate of the direct axis demagnetizing current increment on the electromagnetic torque is evaluated in real time. When the attenuation rate reaches a predetermined threshold, an orthogonal phase vector compensation component is injected between the updated direct axis excitation command current and the redistributed quadrature axis limit command current. The motor power factor is improved by finely adjusting the phase difference angle between the stator terminal voltage vector and the stator terminal current vector, so that the stator composite terminal voltage is constrained within the maximum stator voltage amplitude limit while improving the overload electromagnetic torque output.

[0018] Preferably, the excitation regulation method further includes a terminal voltage closed-loop verification step: before outputting the clamped direct-axis command current and the redistributed quadrature-axis limit command current to the inverter, the updated direct-axis excitation command current and the redistributed quadrature-axis limit command current are substituted into the quadrature-direct axis cross-saturation flux linkage reconstruction model and voltage prediction equation to recalculate the adjusted stator terminal voltage composite amplitude; when the adjusted stator terminal voltage composite amplitude exceeds the maximum stator voltage amplitude limit, the solution is fine-tuned until the adjusted stator terminal voltage composite amplitude converges to the maximum stator voltage amplitude limit range.

[0019] Preferably, in step S1, the process of determining the maximum stator voltage amplitude limit includes: acquiring the DC bus voltage of the inverter, multiplying the DC bus voltage by the reciprocal of the square root of three according to the DC bus voltage utilization coefficient in the space vector pulse width modulation mode, calculating the maximum stator phase voltage amplitude in the linear modulation zone where the inverter does not overmodulate in the current period, and determining the maximum stator phase voltage amplitude as the maximum stator voltage amplitude limit.

[0020] The beneficial effects of this invention are:

[0021] 1. In the excitation regulation of permanent magnet motors under overload conditions, this invention improves the accuracy of flux linkage estimation and excitation regulation under deep magnetic saturation conditions. Through the cross-axis and direct-axis cross-saturation flux linkage reconstruction model, the equivalent inductance of the direct axis and the equivalent inductance of the quadrature axis can be adjusted according to the overload current and the magnetic circuit saturation state. This reduces the flux linkage estimation deviation caused by fixed inductance parameters under high current conditions. Therefore, when the coupling effect between the direct and quadrature axes is strong, the calculation results of the total flux linkage of the direct axis and the total flux linkage of the quadrature axis can be closer to the actual operating state of the motor, providing a more accurate basis for field weakening regulation and helping to maintain control stability during overload.

[0022] 2. To reduce the risk of voltage overmodulation and control instability during overload dynamic processes, this invention determines the voltage margin based on the predicted value of the synthesized amplitude of the stator terminal voltage and adjusts the proportional gain in conjunction with the change in the direct-axis equivalent inductance. This allows the field weakening regulation to adapt to the changes in inductance parameters during deep magnetic saturation, thereby reducing the change in control loop gain caused by the decrease in inductance. This keeps the stator terminal voltage within the allowable range of the DC bus, reduces problems such as voltage overmodulation, current control instability, and torque fluctuations, and improves the operational stability of the motor during overload dynamic processes.

[0023] 3. Improve the adaptability of permanent magnet demagnetization protection under different temperature conditions. This invention adjusts the limit demagnetization current constraint threshold according to the current temperature of the rotor permanent magnet, so that the demagnetization protection no longer uses a fixed limit value for a long time, but can be adjusted accordingly with the temperature of the permanent magnet. Thus, when the temperature rises, the excessive direct shaft demagnetizing current can be limited in time, reducing the risk of irreversible thermal demagnetization; when the temperature conditions permit, the field weakening capability will not be limited too early due to the overly conservative fixed protection value, thereby balancing the safety of the permanent magnet and the overload torque output of the motor. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0025] Figure 1 This is a flowchart of the dual-constraint excitation adjustment process under overload conditions according to the present invention;

[0026] Figure 2 This is a block diagram illustrating the principle of excitation control signal transmission and interaction in this invention. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0028] A method for excitation regulation of a permanent magnet motor under overload conditions, the method comprising the following steps:

[0029] Step S1: Collect the stator current, DC bus voltage and rotor electric angular velocity of the permanent magnet motor, obtain the quadrature axis measured current and direct axis measured current through coordinate transformation, and determine the maximum stator voltage amplitude limit based on the DC bus voltage.

[0030] Step S2: Construct a cross-axis and direct-axis saturated flux linkage reconstruction model; update the direct-axis equivalent inductance and cross-axis equivalent inductance based on the measured current of the cross-axis and the measured current of the direct axis; and calculate the total flux linkage of the direct axis and the total flux linkage of the cross-axis.

[0031] Step S3: Calculate the predicted value of the combined amplitude of the stator terminal voltage based on the rotor electric angular velocity, stator phase resistance, direct-axis total flux linkage and quadrature-axis total flux linkage;

[0032] Step S4: When the predicted value of the synthesized amplitude of the stator terminal voltage is greater than the maximum stator voltage amplitude limit, calculate the voltage saturation margin, and solve the direct-axis field weakening excitation regulation current increment based on the voltage saturation margin, rotor electric angular velocity and direct-axis equivalent inductance. The proportional regulation gain is adaptively scaled according to the attenuation ratio of the direct-axis equivalent inductance relative to the initial unsaturated inductance.

[0033] Step S5: Update the direct-axis excitation command current according to the direct-axis field weakening excitation adjustment current increment, and allocate the quadrature-axis limit command current according to the motor overload total current limit;

[0034] Step S6: Obtain the current temperature of the rotor permanent magnet, calculate the limit demagnetizing current constraint threshold based on the intrinsic coercivity temperature coefficient of the permanent magnet material, and when the direct-axis excitation command current touches the limit demagnetizing current constraint threshold, translate the margin exceeding the limit demagnetizing current constraint threshold into an overload derating protection signal, and output the clamped direct-axis command current and quadrature-axis limit command current to the inverter.

[0035] Preferably, in step S2, the direct-axis total flux linkage is determined based on the multiplicative relationship between the direct-axis equivalent inductance, the measured direct-axis current, and the preset intrinsic excitation flux linkage of the rotor permanent magnet, and the quadrature-axis total flux linkage is determined based on the product of the quadrature-axis equivalent inductance and the measured quadrature-axis current; wherein the updating process of the direct-axis equivalent inductance and the quadrature-axis equivalent inductance includes: calculating the cross-saturation correction coefficient based on the measured quadrature-axis current and the measured direct-axis current, and then correcting the preset initial unsaturated direct-axis inductance and the preset initial unsaturated quadrature-axis inductance to obtain the direct-axis equivalent inductance and the quadrature-axis equivalent inductance under the current cross-saturated magnetic field state.

[0036] Preferably, in step S4, the voltage saturation margin is obtained by subtracting the maximum stator voltage amplitude limit from the predicted value of the synthesized amplitude of the stator terminal voltage; when solving the increment of the direct-axis field weakening excitation regulation current, the proportional regulation gain is proportional to the direct-axis equivalent inductance and adaptively scaled, specifically including: calculating the inductance attenuation ratio of the current direct-axis equivalent inductance relative to the preset initial unsaturated inductance, multiplying the inductance attenuation ratio by the proportional regulation gain base value to obtain the scaled proportional regulation gain, so as to offset the open-loop gain drift of the control loop caused by the sharp drop in the direct-axis equivalent inductance.

[0037] Preferably, in step S5, the process of allocating the quadrature axis limit command current includes: calculating the difference between the square of the total overload current limit of the motor and the square of the updated direct axis excitation command current, performing a square root operation on the difference to obtain the upper limit of the quadrature axis amplitude, and determining the quadrature axis limit command current based on the same positive or negative sign as the measured quadrature axis current.

[0038] Preferably, in step S6, the process of calculating the ultimate demagnetizing current constraint threshold includes: obtaining the current temperature of the rotor permanent magnet by estimating the temperature rise of the stator phase resistance or by using a high-frequency injection thermal model; and linearly correcting the initial demagnetizing current threshold at the reference temperature based on the temperature difference between the current temperature and the reference temperature, combined with the intrinsic coercivity temperature coefficient of the permanent magnet material, to obtain the ultimate demagnetizing current constraint threshold corresponding to the current temperature.

[0039] Preferably, in step S6, translating the margin exceeding the limit demagnetizing current constraint threshold into an overload derating protection signal includes: when the calculated direct-axis excitation command current is less than the limit demagnetizing current constraint threshold, forcibly locking the direct-axis excitation command current to the limit demagnetizing current constraint threshold, calculating the current difference between the target direct-axis field weakening current and the limit demagnetizing current constraint threshold, generating a motor power derating ratio command based on the current difference, and sending the motor power derating ratio command to the top-level master control unit of the drive control system to reduce the expected motor load.

[0040] Preferably, the excitation regulation method further includes a maximum torque-voltage ratio trajectory demagnetization compensation process: when redistributing the quadrature axis limit command current, the attenuation rate of the direct axis demagnetizing current increment on the electromagnetic torque is evaluated in real time. When the attenuation rate reaches a predetermined threshold, an orthogonal phase vector compensation component is injected between the updated direct axis excitation command current and the redistributed quadrature axis limit command current. The motor power factor is improved by finely adjusting the phase difference angle between the stator terminal voltage vector and the stator terminal current vector, so that the stator composite terminal voltage is constrained within the maximum stator voltage amplitude limit while improving the overload electromagnetic torque output.

[0041] Preferably, the excitation regulation method further includes a terminal voltage closed-loop verification step: before outputting the clamped direct-axis command current and the redistributed quadrature-axis limit command current to the inverter, the updated direct-axis excitation command current and the redistributed quadrature-axis limit command current are substituted into the quadrature-direct axis cross-saturation flux linkage reconstruction model and voltage prediction equation to recalculate the adjusted stator terminal voltage composite amplitude; when the adjusted stator terminal voltage composite amplitude exceeds the maximum stator voltage amplitude limit, the solution is fine-tuned until the adjusted stator terminal voltage composite amplitude converges to the maximum stator voltage amplitude limit range.

[0042] Preferably, in step S1, the process of determining the maximum stator voltage amplitude limit includes: acquiring the DC bus voltage of the inverter, multiplying the DC bus voltage by the reciprocal of the square root of three according to the DC bus voltage utilization coefficient in the space vector pulse width modulation mode, calculating the maximum stator phase voltage amplitude in the linear modulation zone where the inverter does not overmodulate in the current period, and determining the maximum stator phase voltage amplitude as the maximum stator voltage amplitude limit.

[0043] Example 1: In the specific application of the overload excitation regulation method for permanent magnet motors provided in this example, for an integrated permanent magnet synchronous motor with a DC bus voltage of 400V driving an inverter, a stator phase resistance of 0.05Ω, 4 pole pairs, an initial unsaturated direct-axis inductance of 0.0005H, an initial unsaturated quadrature-axis inductance of 0.0010H, and a rotor permanent magnet intrinsic excitation flux linkage of 0.15Wb, when it reaches a speed of 2400rpm and is subjected to a peak overload current of 200A, the three-phase stator current, DC bus voltage, and rotor electric angular velocity are dynamically collected, and the measured direct-axis current is obtained through coordinate transformation. -50A and cross-axis measured current The value is 193.65A; simultaneously, based on the DC bus voltage utilization coefficient in space vector pulse width modulation mode, the maximum stator voltage amplitude limit in the inverter's linear modulation region is calculated by multiplying the DC bus voltage by the reciprocal of the square root of three. It is 230.94V.

[0044] Based on the current cross-axis and direct-axis saturation state of the main magnetic circuit of the iron core, the system constructs a cross-axis and direct-axis cross-axis saturation flux reconstructing model, based on the measured cross-axis current. Measured current along the direct axis Calculate the cross-saturation correction factor and update the current direct-axis equivalent inductance. The equivalent inductance is 0.0005H and the quadrature axis is equal to the cross-axis inductance. The value is 0.0010H. Specifically, the collected cross-axis measured current and direct-axis measured current are input into a preset cross-axis and direct-axis cross-saturation mapping matrix or inductor calibration grid. The cross-saturation correction coefficient under the corresponding current combination is calculated by bilinear interpolation of discrete nodes. This coefficient is configured in the controller's memory as a dimensionless two-dimensional vector data structure containing direct-axis and cross-axis dimensions. When the input direct-axis measured current is -50A and the cross-axis measured current is 193.65A, the interpolation calculation unit outputs numbers in parallel. The direct-axis correction component and quadrature-axis correction component, both with a value of 1.000, are included. This cross-saturation correction coefficient comprises the direct-axis correction component and the quadrature-axis correction component corresponding to the direct-axis equivalent inductance and the quadrature-axis equivalent inductance, respectively. The direct-axis correction component and the quadrature-axis correction component are then multiplied by the initial unsaturated direct-axis inductance and the initial unsaturated quadrature-axis inductance, respectively, to obtain the corrected current direct-axis equivalent inductance and quadrature-axis equivalent inductance. This enables real-time reconstruction of the nonlinear inductance decay under deep core saturation and strong direct-axis-quadrature coupling states, thereby improving the direct-axis equivalent inductance. Cross-axis equivalent inductance Substitute the flux linkage reconstruction model to calculate the total flux linkage along the direct axis. The value of 0.125Wb was obtained, and the total flux linkage along the quadrature axis was calculated simultaneously. The result is 0.19365 Wb, where, The intrinsic excitation flux linkage of the rotor permanent magnet is shown in the flux linkage calculation process, which reflects the cross-coupling relationship between the quadrature axis current and the direct axis flux linkage under magnetic saturation conditions, as well as the inductance change.

[0045] Obtaining the total flux linkage along the direct axis Total magnetic flux linkage And the rotor electric angular velocity obtained from the motor speed. After setting the value to 1005.31 rad / s, the system calculates the predicted value of the combined stator terminal voltage amplitude under the current operating condition based on the stator terminal voltage combined amplitude prediction equation. ,in, Stator phase resistance, The rotor's electric angular velocity; the direct-axis voltage component is calculated by substituting the parameters. -197.18V, quadrature axis voltage component The voltage is 135.34V, from which the predicted amplitude of the synthesized stator terminal voltage is obtained. It is 239.16V; due to the predicted value of the combined amplitude of the stator terminal voltage. The voltage is 239.16V, which is greater than the maximum stator voltage amplitude limit. The voltage is 230.94V, indicating that the system has entered the voltage saturation region. The voltage saturation margin is then calculated. It is 8.22V.

[0046] When solving for the excitation demagnetization compensation, the system relies on the voltage saturation margin. Rotor electric angular velocity and direct-axis equivalent inductance Calculate the increment of direct-axis field weakening excitation regulating current. Among them, proportional adjustment gain Based on the current direct-axis equivalent inductance Relative to the initial unsaturated direct-axis inductance The attenuation ratio is adaptively scaled; the increment of the direct-axis field weakening excitation regulating current is calculated by substituting the base value of the proportional adjustment gain into 1. The current is -16.35A, thus updating the direct-axis excitation command current to... Synchronization is based on the motor's total overload current limit. Redistribute the quadrature axis limit command current to 200A The result is 188.67A, where, This is the motor's total overload current limit. Let be the sign function of the measured current along the quadrature axis, where the equivalent inductance along the direct axis is denoted by . It is used as a parameter to synchronously participate in the prediction of the synthesized amplitude of the stator terminal voltage and the calculation of the increment of the direct-axis field weakening excitation regulation current.

[0047] The system obtains the initial demagnetizing current threshold at a reference temperature of 25°C. The value is -180A, which is used as the limiting demagnetizing current constraint threshold at this temperature to verify the updated direct-axis excitation command current. Greater than the limit demagnetizing current constraint threshold The system determined that the demagnetization constraint boundary had not been reached. The initial demagnetization current threshold of -180A at the reference temperature of 25℃ was calculated based on the magnetic induction intensity at the inflection point of the demagnetization curve of the rotor permanent magnet material at 25℃, combined with the finite element magnetic field simulation model of the motor stator and rotor. Its physical significance is that when the amplitude of the direct-axis reverse demagnetization current reaches 180A, the permanent magnet's operating point just touches the inflection point of the magnetization curve. If this current limit is exceeded, irreversible demagnetization will occur locally in the permanent magnet. Therefore, it is set as the lower limit of the ultimate demagnetization safety protection at 25℃. Subsequently, the updated direct-axis excitation command current... With the redistributed cross-axis limit command current By substituting the cross-axis and direct-axis cross-saturation flux linkage reconstruction model with the stator terminal voltage synthesis amplitude prediction equation for closed-loop verification, the adjusted direct-axis total flux linkage is calculated to be 0.11682 Wb, the cross-axis total flux linkage is 0.18867 Wb, and the direct-axis voltage component... -193.00V and quadrature axis voltage component The calculated predicted value of the combined stator terminal voltage amplitude is 230.97V, which is 126.87V. This ensures that the combined stator terminal voltage is constrained to the maximum stator voltage amplitude limit. Within the range of 230.94V, the system has a voltage limit engineering convergence tolerance band of 5‰. For the maximum stator voltage amplitude limit of 230.94V, the allowable upper limit engineering boundary is 230.94V multiplied by 1.005, which is 232.09V. When the calculated predicted value of the adjusted stator terminal voltage composite amplitude is 230.97V, it falls within the allowable engineering convergence tolerance band. The system then determines that the terminal voltage has converged and is constrained within the linear modulation safety region permitted by the maximum stator voltage amplitude limit.

[0048] In this embodiment, the field weakening regulation is adjusted according to the voltage saturation margin and the inductance attenuation ratio, and the updated direct-axis command current and quadrature-axis command current are output to the inverter to complete the excitation regulation under motor overload conditions.

[0049] Example 2: In this example, a motor drive test bench was constructed consisting of a 150kW built-in permanent magnet synchronous motor and a power dynamometer. The motor stator phase resistance was 0.05Ω, the number of pole pairs was 4, the initial unsaturated direct-axis inductance was 0.0005H, the initial unsaturated quadrature-axis inductance was 0.0010H, and the intrinsic excitation flux linkage of the rotor permanent magnet was 0.15Wb. The inverter DC bus voltage was provided by a regulated DC power supply and set to 400V. This yielded the maximum stator voltage amplitude limit in the linear modulation region. The voltage is 230.94V. The stator current is acquired using a Hall current sensor with a sampling accuracy of ±0.2%. The motor speed and rotor position are acquired using a 1024-line photoelectric encoder with a sampling period of 100μs. This sampling period is determined based on the stator current loop control bandwidth of 1kHz and the inverter switching frequency of 10kHz, and is used to acquire overload dynamic response and control the computational load of the chip. The current temperature of the rotor permanent magnet is obtained by a high-frequency injection thermal model. Infrared temperature sensors embedded in the stator windings and rotor side provide synchronous temperature references. During model calibration, the high-frequency equivalent impedance change corresponding to different temperature points is linearly fitted with the synchronous temperature reference to obtain the linear mapping coefficient between the high-frequency damping characteristics and temperature. During operation, a frequency of 1kHz and an amplitude of 10V are injected into the inverter pulse width modulation signal. A high-frequency small-signal voltage vector is used to collect the high-frequency response current of the stator winding. The high-frequency equivalent impedance and high-frequency inductance are calculated based on the amplitude and phase lag angle. Then, the change in high-frequency equivalent impedance is converted into the current temperature of the rotor permanent magnet using a linear mapping coefficient. During the experiment, Gaussian white noise with a signal-to-noise ratio of 20dB and 50Hz power frequency harmonics are superimposed on the stator current acquisition channel. The rotor permanent magnet temperature is increased from 25℃ to 120℃ during the drag loading process. The experiment includes the present invention sample group, control group A, control group B, and control group C. The present invention sample group uses a cross-axis and direct-axis saturated flux linkage reconstruction model, feedforward voltage prediction, proportional gain adaptive scaling, and temperature adaptive demagnetizing clamping. Control group A uses a constant coefficient inductance model and a fixed magnetic weakening angle. Control group B uses a cross-axis and direct-axis saturated flux linkage reconstruction model but with proportional gain adjustment. Keeping the value at 1.000 and without adaptive scaling, the control group C uses a cross-axis saturated flux linkage reconstruction model and proportional gain scaling, but fixes the demagnetizing current threshold at -180A at 25℃ without temperature correction.

[0050] When the motor is running at 2400 rpm, the rotor electric angular velocity is The dynamometer was set at 1005.31 rad / s, and a sudden overload torque command was applied, injecting a peak overload current of 200 A into the stator. During the initial overload phase at 25°C, the measured direct-axis current in the four sets of tests was... All are -50.0A, measured current across the quadrature axis. Both are 193.65A. The equivalent inductance of the direct axis is updated based on the measured current of the direct and quadrature axes in this invention. 0.0005H quadrature axis equivalent inductance When the value is 0.0010H, expressed in mH units according to experimental records, the direct-axis equivalent inductance is 0.500mH. Substituting these parameters into the cross-axis and direct-axis cross-saturation flux linkage reconstruction model, the total direct-axis flux linkage is obtained. 0.125Wb, cross-axis total flux linkage The value is 0.19365Wb, from which the predicted value of the synthesized amplitude of the stator terminal voltage is obtained. The voltage is 239.16V, providing a voltage saturation margin of 8.22V relative to the maximum stator voltage amplitude limit. Adjust the gain proportionally according to the attenuation ratio of the current direct-axis equivalent inductance relative to the initial unsaturated direct-axis inductance. Adjusted to 1.000, the increment of the direct-axis field weakening excitation regulating current is obtained from the voltage saturation margin, rotor electric angular velocity, and direct-axis equivalent inductance. The direct-axis excitation command current is -16.35A. Updated to -66.35A, and the quadrature axis limit command current is redistributed according to the 200A motor overload total current limit. The input current was 188.67A. After closed-loop verification of the terminal voltage, the adjusted combined amplitude of the stator terminal voltage was 230.97V, the current ripple amplitude was 2.1A, and the irreversible demagnetization rate was 0.0%. Control group A used a fixed direct-axis inductor parameter of 0.500mH under the same input current, with proportionally adjusted gain. The direct-axis command current is adjusted to -50.00A, the flux linkage estimation deviation reaches 18.4%, the predicted and adjusted stator terminal voltage is 248.30V, the low-frequency oscillation amplitude of the stator current and the current ripple amplitude are both 18.5A, and the irreversible demagnetization rate is 0.0%. The direct-axis equivalent inductance of control group B is 0.500mH, the predicted stator terminal voltage is 239.16V, and the proportional adjustment gain... Maintaining a gain of 1.000 without scaling, the adjusted direct-axis command current is -78.30A. The fixed gain causes overcorrection in the demagnetization adjustment after inductance changes. The adjusted stator terminal voltage fluctuates between 225.10V and 236.40V, with a current ripple amplitude of 11.2A, electromagnetic torque ripple of 12.3%, and an irreversible demagnetization rate of 0.0%. The direct-axis equivalent inductance of control group C is 0.500mH, and the proportional gain is adjusted... The value is 1.000. After adjustment, the direct shaft command current is -66.35A, the stator terminal voltage is adjusted from the predicted 239.16V to 230.97V, the current ripple amplitude is 2.1A, and the irreversible demagnetization rate is 0.0%.

[0051] After the dynamometer operated at a high overload rate of 200A for 45 seconds, the temperature of the rotor permanent magnet rose to 120℃. At this time, the measured current of the direct axis of the sample group before readjustment was -66.35A, the measured current of the quadrature axis was 188.67A, and the equivalent inductance of the direct axis was... The predicted amplitude of the composite stator terminal voltage is 0.500mH. Increase to 242.10V, proportionally adjust gain. The value is 1.000, based on the temperature coefficient of the intrinsic coercivity of permanent magnet materials. Temperature correction was applied to the limiting demagnetizing current constraint threshold to -0.003 / ℃ to obtain the limiting demagnetizing current constraint threshold at 120℃. The current direct-axis field weakening target current requirement corresponding to the current voltage saturation state is -140.00A, which is less than the limit demagnetizing current constraint threshold. Therefore, the direct-axis excitation command current is clamped to -128.70A, and the quadrature-axis limit command current is redistributed to 153.09A. At the same time, a motor power derating ratio command is generated based on the difference between the target direct-axis field weakening current and the limit demagnetizing current constraint threshold, and sent to the top-level main control unit of the drive control system to drate the load by 8.5%. After clamping and redistribution, the adjusted stator terminal voltage composite amplitude is 230.94V, the current ripple amplitude is 2.3A, and the irreversible demagnetization rate is 0.0% as detected during shutdown. The measured direct-axis current of control group A under continuous overload at 120℃ is -50.0A, and the measured quadrature-axis current is 193.65A. The direct-axis equivalent inductance is a fixed parameter of 0.500mH, and the gain is proportionally adjusted. With a value of 1.000, the adjusted direct-axis command current remains -50.00A, the predicted and adjusted stator terminal voltages are both 251.20V, the current ripple amplitude increases to 21.0A, and the irreversible demagnetization rate is 0.0%. In control group B, the measured direct-axis current is -66.35A, the measured quadrature-axis current is 188.67A, the equivalent direct-axis inductance is 0.500mH, the predicted stator terminal voltage is 242.10V, and the proportional adjustment gain... Keeping the value at 1.000 and without scaling, the adjusted direct-axis command current is -78.30A, the stator terminal voltage fluctuates between 223.50V and 238.10V, the current ripple amplitude is 13.5A, and the irreversible demagnetization rate is 0.0%. For control group C, the measured direct-axis current is -66.35A, the measured quadrature-axis current is 188.67A, the direct-axis equivalent inductance is 0.500mH, the predicted stator terminal voltage is 242.10V, and the proportional adjustment gain... The value is 1.000. Since the limit demagnetizing current constraint threshold is still fixed at -180A at 25℃, the clamping is not triggered when the direct shaft command current reaches -140.00A. The adjusted stator terminal voltage is 230.94V, the current ripple amplitude is 2.4A, and the irreversible demagnetization rate is 4.8% when the machine is stopped. Irreversible thermal demagnetization occurs in the edge area of ​​the permanent magnet, the local excitation flux permanently decays by 4.8%, and the motor no-load back EMF decreases by 4.6%.

[0052] Based on the response results of each group at the two temperature stages, when the stator overload current exceeds 150A, the main magnetic circuit of the iron core exhibits nonlinear magnetic saturation, and the cross-coupling effect of the quadrature axis current on the direct axis flux linkage increases accordingly. When the temperature of the rotor permanent magnet exceeds 90℃, the intrinsic coercivity of the material decreases, and the limit demagnetizing current constraint threshold shrinks with increasing temperature. The sample group of this invention updates the equivalent inductance and reconstructs the flux linkage based on the measured quadrature and direct axis currents. At the same time, it adjusts the proportional gain according to the attenuation ratio of the direct axis equivalent inductance. When the voltage exceeds the limit, it increases the direct axis weak field excitation regulation current and adjusts the limit demagnetizing current constraint threshold according to the current temperature of the rotor permanent magnet. Thus, the terminal voltage regulation and demagnetizing clamp change with the magnetic saturation state and rotor temperature, respectively.

[0053] Example 3: This example addresses the situation where large-amplitude quadrature-axis and direct-axis currents cause cross-saturation of the main magnetic circuit of the iron core and a nonlinear decrease in inductance under high-rate overload. Based on electromagnetic field finite element analysis and discrete impulse response measurement, a discrete cross-saturation inductance calibration mesh is pre-constructed, and the initial unsaturated direct-axis inductance of the motor is determined. The initial unsaturated quadrature-axis inductance is 0.0005H. The intrinsic excitation flux linkage of the rotor permanent magnet is 0.0010H. The stator phase resistance is 0.15Wb. The current is 0.05Ω, with 4 pole pairs; when the motor is running at 2400rpm and the DC bus voltage is 400V, the sampling module obtains the measured current of the direct shaft. -50A, cross-axis measured current The current is 193.65A. After table lookup and two-dimensional interpolation using the discrete cross-saturated inductance calibration grid, the direct-axis equivalent inductance under the current cross-saturated magnetic field state is updated to obtain the equivalent inductance. 0.0005H quadrature axis equivalent inductance It is 0.0010H, and then according to Solving for direct-axis total flux linkage It is 0.125Wb, according to Solving the total flux linkage along the cross axis It is 0.19365 Wb, of which The intrinsic excitation flux linkage of the rotor permanent magnet is used; the above parameters are then substituted into the stator terminal voltage synthesis amplitude prediction equation. At the rotor electric angular velocity When the value is 1005.31 rad / s, the predicted value of the combined amplitude of the stator terminal voltage is obtained. It is 239.16V, of which Stator phase resistance; the maximum stator voltage amplitude limit obtained from the DC bus voltage in space vector pulse width modulation mode. The current voltage is 230.94V. Greater than ,according to Obtain voltage saturation margin It is 8.22V.

[0054] During the field weakening adjustment process, the current direct-axis equivalent inductance The initial unsaturated direct-axis inductance is 0.0005H. The value is 0.0005H, and the system is based on the attenuation ratio of the two. Proportional adjustment gain Perform adaptive scaling, according to Get the current proportional adjustment gain =1, where Adjust the gain base value proportionally; then according to Calculate the increment of the direct-axis field weakening excitation regulating current. -16.35A, and according to Update the direct-axis excitation command current to -66.35A; motor overload total current limit. For 200A, according to Redistribute quadrature axis limit command current We get 188.67A, where, This is the sign function of the cross-axis measured current.

[0055] After redistributing the quadrature-axis limit command current, the system performs a maximum torque-voltage ratio trajectory demagnetization compensation process. This involves the controller's torque assessment and vector modulation module comparing the electromagnetic torque before and after field weakening. When the torque attenuation rate reaches a preset threshold, it directly applies discrete angle fine-tuning to the phase difference angle between the stator current vector and the stator terminal voltage vector, and evaluates the real-time increment of the direct-axis field weakening excitation regulating current. Attenuation rate of electromagnetic torque ,in, The electromagnetic torque before field weakening. The electromagnetic torque after field weakening; when the attenuation rate When the preset threshold of 0.05 is reached, the deviation of the current electromagnetic torque attenuation rate from exceeding this threshold is calculated. This deviation is then multiplied by a preset orthogonal compensation proportional gain coefficient to obtain the phase fine-tuning angle. Then, this phase fine-tuning angle is used to adjust the updated direct-axis excitation command current. With the redistributed cross-axis limit command current An orthogonal rotation coordinate transformation is performed. After rotation, the orthogonal components formed relative to the original stator current vector are physically solved as direct-axis orthogonal vector compensation current components and quadrature-axis orthogonal vector compensation current components. These orthogonal phase vector compensation components are represented in the data structure as two current increment registers in amperes. The vector decomposition unit calculates the difference between the rotated and unrotated current vectors and projects them onto the direct and quadrature axes respectively. These are then directly injected as orthogonal phase vector compensation components in numerical addition between the direct-axis excitation command current and the quadrature-axis limit command current. While maintaining the stator composite current amplitude unchanged, the phase difference angle between the stator terminal voltage vector and the stator terminal current vector is finely adjusted, causing the stator current vector to deflect in the orthogonal direction of the voltage vector, reducing the reactive current component and improving the motor power factor. After recalculation, the predicted value of the stator terminal voltage composite amplitude converges to 230.97V, which is within the maximum stator voltage amplitude limit. Within the constraint range of 230.94V.

[0056] During continuous high-frequency high-current overload, the system obtains the current temperature of the rotor permanent magnet by using a high-frequency injection thermal model or stator phase resistance temperature rise estimation. When using a high-frequency injection thermal model, the high-frequency equivalent impedance is obtained based on the high-frequency response of the stator winding, and the current temperature of the rotor permanent magnet is obtained based on the calibrated correspondence between the change in high-frequency equivalent impedance and temperature. When using stator phase resistance temperature rise estimation, the stator winding temperature rise is calculated based on the change in stator phase resistance relative to the reference temperature, and the current temperature of the rotor permanent magnet is obtained based on the predetermined correspondence between the stator winding temperature rise and the rotor permanent magnet temperature rise. When continuous overload causes... Temperature coefficient of intrinsic coercivity of permanent magnet materials when the temperature is raised to 120°C The initial demagnetizing current threshold is -0.003 / ℃ at a reference temperature of 25℃. -180A; according to Calculate the limiting demagnetizing current constraint threshold corresponding to the current temperature. It is -128.70A, where, The reference temperature is 25℃. The initial demagnetizing current threshold at the reference temperature. The intrinsic coercivity temperature coefficient.

[0057] When the calculated target direct-axis magnetic weakening current The value is -140.00A, which is less than the limiting demagnetizing current constraint threshold. At that time, the system executes demagnetization clamping, forcibly locking the direct-axis excitation command current to [value missing]. and in accordance with Reallocate the quadrature axis limit command current This yields 153.09A; simultaneously, according to... Calculate the margin of difference between the target direct-axis weakening magnetic current and the limiting demagnetizing current constraint threshold, and then proceed according to... The difference margin is translated into a motor power derating ratio command. The value is 8.07%, and this instruction is sent to the top-level master control unit of the drive control system and written into the target electromagnetic torque upper limit register mapping area of ​​the master control chip in the form of a CAN bus communication frame. The top-level master control unit of the drive will proportionally reduce the original external characteristic torque instruction setpoint input in the next control cycle according to the scaling ratio of 8.07% to reduce the expected motor load.

[0058] After the direct-axis excitation command current is clamped by the limit demagnetizing current constraint threshold, further increasing the direct-axis field weakening current will exceed the demagnetizing constraint boundary corresponding to the current temperature of the rotor permanent magnet. Therefore, the difference between the target direct-axis field weakening current and the limit demagnetizing current constraint threshold represents the current field weakening current margin that cannot be provided. The ratio of this difference to the target direct-axis field weakening current forms the motor power derating ratio command, which reduces the total limit of the stator combined current with the available field weakening capability. Thus, the excitation control maintains the overload state under the joint constraints of the current maximum stator voltage amplitude limit and the limit demagnetizing current constraint threshold.

[0059] Example 4: This example combines Figures 1 to 2 This paper describes a method for excitation regulation under overload conditions of a permanent magnet motor, such as... Figure 1As shown, the stator current, DC bus voltage, and rotor electric angular velocity of the permanent magnet motor are collected. The measured currents of the quadrature axis and direct axis are obtained through coordinate transformation. The maximum stator voltage amplitude limit is determined based on the DC bus voltage, constituting step S1. A cross-axis and direct axis cross-saturation flux linkage reconstruction model is constructed. The equivalent inductances of the direct axis and quadrature axis are updated based on the measured currents of the quadrature axis and direct axis. The total flux linkages of the direct axis and quadrature axis are calculated, constituting step S2. Based on the rotor electric angular velocity, stator phase resistance, total flux linkage of the direct axis, and total flux linkage of the quadrature axis, the predicted value of the composite amplitude of the stator terminal voltage is calculated, constituting step S3. When the predicted value of the composite amplitude of the stator terminal voltage exceeds the maximum stator voltage amplitude limit, the voltage saturation margin is calculated. Based on the voltage saturation margin and rotor electric angular velocity... Step S4 involves calculating the increment of the direct-axis field weakening excitation regulation current using the direct-axis equivalent inductance, where the proportional regulation gain is adaptively scaled according to the attenuation ratio of the direct-axis equivalent inductance relative to the initial unsaturated inductance. Step S5 involves updating the direct-axis excitation command current based on the increment of the direct-axis field weakening excitation regulation current and allocating the quadrature-axis limit command current according to the motor overload total current limit. Step S6 involves obtaining the current temperature of the rotor permanent magnet, calculating the limit demagnetizing current constraint threshold based on the intrinsic coercivity temperature coefficient of the permanent magnet material, and translating the excess of the direct-axis excitation command current beyond the limit demagnetizing current constraint threshold into an overload derating protection signal when the direct-axis excitation command current reaches the limit demagnetizing current constraint threshold. Step S7 involves outputting the clamped direct-axis command current and the quadrature-axis limit command current to the inverter.

[0060] like Figure 2 As shown, the permanent magnet motor transmits the collected current, voltage, and angular velocity to the stator current acquisition and transformation system. The stator current acquisition and transformation system outputs the calculated measured current along the direct and quadrature axes to the cross-saturation flux linkage reconstruction system, outputs the rotor electric angular velocity to the predicted stator terminal voltage, and outputs the voltage amplitude limit to the calculation of the field weakening current increment. The cross-saturation flux linkage reconstruction system feeds back the calculated correction coefficient equivalent inductance based on the measured current along the direct and quadrature axes to the flux linkage and inductance states. The flux linkage and inductance states then input the updated inductance and flux linkage data to the predicted stator terminal voltage. The predicted stator terminal voltage is calculated by combining the rotor electric angular velocity and the inductance and flux linkage data. The system outputs the predicted composite amplitude value to the calculation of the field weakening current increment. The calculated field weakening current increment is used to solve for the field weakening regulation increment based on the predicted composite amplitude value and the voltage amplitude limit, and is output to the update and allocation command. The update and allocation command generates an update command current based on the field weakening regulation increment and sends it to the demagnetizing clamp and derating. The permanent magnet thermal state parameters input the calculated ultimate demagnetizing constraint threshold to the demagnetizing clamp and derating. The demagnetizing clamp and derating, combined with the ultimate demagnetizing constraint threshold, verify the update command current, output the generated clamping control command to the inverter, and send the generated overload derating protection signal to the top-level main control unit.

[0061] Example 5: During the initialization phase of the motor drive control system, when constructing the discrete inductor grid, a high-frequency voltage vector pulse excitation method is used to perform multi-point mapping calibration of the cross-axis and direct-axis saturated magnetic field characteristics of the permanent magnet motor. The test bench is kept at zero speed lock, and the measured current of the direct axis is... Starting from 0A, increase in increments of 10A until the motor's total overload current limit is reached. 200A, and simultaneously the cross-axis measured current. Starting from 0A, the voltage is increased in steps of 10A to 200A. A micro-step voltage signal with an amplitude of 10V and a frequency of 1kHz is injected at each direct-axis current combination node. The transient response waveforms of the stator terminal voltage and stator phase current are acquired. The direct-axis equivalent inductance corresponding to the current node is obtained by integrating the current rise slope and steady-state amplitude. equivalent inductance of cross axis And calculate the total flux linkage along the direct axis. , with cross-axis total magnetic flux The two-dimensional mesh data obtained from solving each quadrature and direct axis current combination node is written into the non-volatile memory of the drive controller to construct a quadrature and direct axis cross saturation flux reconfiguration model covering the full current operating conditions.

[0062] During the on-site deployment and power-on self-test phase of the motor system, the drive controller injects a high-frequency sinusoidal voltage vector into the stator windings without triggering rotor rotation. It then uses the high-frequency response acquisition values ​​of the phase current to calibrate the inductance and resistance references of the motor in its unsaturated state. Based on the amplitude and phase difference of the high-frequency current response, the controller calculates the stator phase resistance at the current ambient temperature. Initial values ​​are determined, and the initial unsaturated direct-axis inductance is calculated based on the high-frequency damping characteristics. 0.0005H, initially unsaturated quadrature-axis inductance The value is 0.0010H; when the deviation of the above measured initial value from the corresponding reference value exceeds the preset 5% threshold, the controller uses this deviation as a calibration coefficient to correct the reference offset of the discrete cross-saturated inductor calibration grid, so that the predicted value of the stator terminal voltage synthesis amplitude during the overload dynamic response is 0.0010H. The calculation benchmark is consistent with the initial state of the physical motor on site, and is a voltage saturation margin. The calculation of the solution and the adjustment of the direct-axis field weakening excitation current increment The solution provides matching initial parameter inputs.

[0063] Example 6: During high-current discharge of the current power battery, a transient drop in the DC bus voltage occurs in the permanent magnet motor during high-rate overload operation. The DC bus voltage drops from 400V to 380V. The sampling module acquires the current DC bus voltage of 380V in real time and, based on the DC bus voltage utilization relationship under space vector pulse width modulation mode, sets the maximum stator voltage amplitude limit. Updated to 219.39V; simultaneously, the measured direct-axis current was obtained through coordinate transformation. -50A, cross-axis measured current The capacitance is 193.65A. The cross-axis and direct-axis cross-saturation flux linkage reconstruction model is based on the direct-axis equivalent inductance. 0.0005H quadrature axis equivalent inductance The total flux linkage along the direct axis is 0.0010H. 0.125Wb, cross-axis total flux linkage The value is 0.19365Wb, at a motor speed of 2400rpm and a rotor electrical angular velocity of When the voltage is 1005.31 rad / s, the predicted value of the combined stator terminal voltage amplitude is obtained according to the prediction equation of the combined stator terminal voltage amplitude. The predicted value is 239.16V; this value exceeds the updated maximum stator voltage amplitude limit of 219.39V, corresponding to a voltage saturation margin. It is 19.77V.

[0064] Based on the current direct-axis equivalent inductance Relative to the initial unsaturated direct-axis inductance The attenuation ratio will be adjusted to control the gain. The value is adjusted to 1, and the increment of the direct-axis field weakening excitation regulating current is obtained based on the voltage saturation margin, rotor electric angular velocity, and direct-axis equivalent inductance. The direct-axis excitation command current is -39.33A. The current rating was updated from -50A to -89.33A; then, according to the motor's total overload current limit... Redistribute the quadrature axis limit command current to 200A The result was 178.94A. Subsequently, a closed-loop verification step for the terminal voltage was performed. The updated direct-axis excitation command current and the redistributed quadrature-axis limit command current were brought back to the quadrature-direct-axis cross-saturation flux linkage reconstruction model, resulting in adjusted direct-axis total flux linkage of 0.10533Wb and quadrature-axis total flux linkage of 0.17894Wb. The adjusted predicted value of the stator terminal voltage composite amplitude was then obtained from the stator terminal voltage composite amplitude prediction equation, which is 217.19V. This value is within the maximum stator voltage amplitude limit of 219.39V. This was achieved through fine-tuning the solution process. During the process, if the recalculated adjusted stator terminal voltage composite amplitude still exceeds the maximum stator voltage amplitude limit, the direct-axis excitation command current is finely adjusted along the field weakening direction with a fixed iteration step size of 0.1A, and the corresponding quadrature-axis limit command current and the predicted value of the stator terminal voltage composite amplitude are recalculated. When the voltage difference obtained from two adjacent iterations is less than 0.1V, or the predicted value of the stator terminal voltage composite amplitude drops below the maximum stator voltage amplitude limit, the iteration is stopped and the finely adjusted converged direct-axis excitation command current and quadrature-axis limit command current are output.

[0065] Before outputting the verified direct-axis excitation command current and quadrature-axis limit command current to the PWM inverter drive module, the system obtains the current temperature of the rotor permanent magnet as 25℃. The limit demagnetization current constraint threshold at this temperature is -180A. The updated direct-axis excitation command current is -89.33A, which is greater than the limit demagnetization current constraint threshold of -180A and does not touch the demagnetization constraint boundary. Therefore, the current direct-axis excitation command current is maintained and output together with the quadrature-axis limit command current. The drive controller modulates the updated direct-axis command current and quadrature-axis command current into a stator voltage vector and outputs the steady-state composite amplitude of the stator terminal voltage. This enables the permanent magnet motor to maintain torque output under the combined effect of transient DC bus voltage drop and strong magnetic saturation, and to operate within the linear modulation region.

[0066] 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 protection scope of the present invention.

Claims

1. A method for excitation adjustment under overload conditions of a permanent magnet motor, characterized in that, The method includes the following steps: Step S1: Collect the stator current, DC bus voltage and rotor electric angular velocity of the permanent magnet motor, obtain the quadrature axis measured current and direct axis measured current through coordinate transformation, and determine the maximum stator voltage amplitude limit based on the DC bus voltage. Step S2: Construct a cross-axis and direct-axis saturated flux linkage reconstruction model; update the direct-axis equivalent inductance and cross-axis equivalent inductance based on the measured current of the cross-axis and the measured current of the direct axis; and calculate the total flux linkage of the direct axis and the total flux linkage of the cross-axis. Step S3: Calculate the predicted value of the combined amplitude of the stator terminal voltage based on the rotor electric angular velocity, stator phase resistance, direct-axis total flux linkage and quadrature-axis total flux linkage; Step S4: When the predicted value of the synthesized amplitude of the stator terminal voltage is greater than the maximum stator voltage amplitude limit, calculate the voltage saturation margin, and solve the direct-axis field weakening excitation regulation current increment based on the voltage saturation margin, rotor electric angular velocity and direct-axis equivalent inductance. The proportional regulation gain is adaptively scaled according to the attenuation ratio of the direct-axis equivalent inductance relative to the initial unsaturated inductance. Step S5: Update the direct-axis excitation command current according to the direct-axis field weakening excitation adjustment current increment, and allocate the quadrature-axis limit command current according to the motor overload total current limit; Step S6: Obtain the current temperature of the rotor permanent magnet, calculate the limit demagnetizing current constraint threshold based on the intrinsic coercivity temperature coefficient of the permanent magnet material, and when the direct-axis excitation command current touches the limit demagnetizing current constraint threshold, translate the margin exceeding the limit demagnetizing current constraint threshold into an overload derating protection signal, and output the clamped direct-axis command current and quadrature-axis limit command current to the inverter.

2. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, In step S2, the direct-axis total flux linkage is determined based on the multiplicative relationship between the direct-axis equivalent inductance, the measured direct-axis current, and the preset intrinsic excitation flux linkage of the rotor permanent magnet. The quadrature-axis total flux linkage is determined based on the product of the quadrature-axis equivalent inductance and the measured quadrature-axis current. The updating process of the direct-axis equivalent inductance and the quadrature-axis equivalent inductance includes: calculating the cross-saturation correction coefficient based on the measured quadrature-axis current and the measured direct-axis current, and then correcting the preset initial unsaturated direct-axis inductance and the preset initial unsaturated quadrature-axis inductance to obtain the direct-axis equivalent inductance and the quadrature-axis equivalent inductance under the current quadrature-direct-axis cross-saturated magnetic field state.

3. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, In step S4, the voltage saturation margin is obtained by subtracting the maximum stator voltage amplitude limit from the predicted value of the synthesized amplitude of the stator terminal voltage. When solving the increment of the direct-axis field weakening excitation regulation current, the proportional regulation gain is proportional to the direct-axis equivalent inductance and adaptively scaled. Specifically, this includes: calculating the inductance attenuation ratio of the current direct-axis equivalent inductance relative to the preset initial unsaturated inductance, multiplying the inductance attenuation ratio by the base value of the proportional regulation gain to obtain the scaled proportional regulation gain, so as to offset the open-loop gain drift of the control loop caused by the sharp drop in the direct-axis equivalent inductance.

4. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, In step S5, the process of allocating the quadrature axis limit command current includes: calculating the difference between the square of the total overload current limit of the motor and the square of the updated direct axis excitation command current, performing a square root operation on the difference to obtain the upper limit of the quadrature axis amplitude, and determining the quadrature axis limit command current based on the same positive or negative sign as the measured quadrature axis current.

5. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, In step S6, the process of calculating the ultimate demagnetizing current constraint threshold includes: obtaining the current temperature of the rotor permanent magnet by estimating the temperature rise of the stator phase resistance or by using a high-frequency injection thermal model; and linearly correcting the initial demagnetizing current threshold at the reference temperature based on the temperature difference between the current temperature and the reference temperature, combined with the intrinsic coercivity temperature coefficient of the permanent magnet material, to obtain the ultimate demagnetizing current constraint threshold corresponding to the current temperature.

6. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, In step S6, translating the margin exceeding the limit demagnetizing current constraint threshold into an overload derating protection signal includes: when the calculated direct-axis excitation command current is less than the limit demagnetizing current constraint threshold, forcibly locking the direct-axis excitation command current to the limit demagnetizing current constraint threshold, calculating the current difference between the target direct-axis field weakening current and the limit demagnetizing current constraint threshold, generating a motor power derating ratio command based on the current difference, and sending the motor power derating ratio command to the top-level master control unit of the drive control system to reduce the expected motor load.

7. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, The excitation regulation method also includes a maximum torque-voltage ratio trajectory demagnetization compensation process: when redistributing the quadrature axis limit command current, the attenuation rate of the direct axis demagnetizing current increment on the electromagnetic torque is evaluated in real time. When the attenuation rate reaches a predetermined threshold, an orthogonal phase vector compensation component is injected between the updated direct axis excitation command current and the redistributed quadrature axis limit command current. By finely adjusting the phase difference angle between the stator terminal voltage vector and the stator terminal current vector, the motor power factor is improved, so that the stator composite terminal voltage is constrained within the maximum stator voltage amplitude limit while improving the overload electromagnetic torque output.

8. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, The excitation regulation method also includes a closed-loop verification step for the terminal voltage: before outputting the clamped direct-axis command current and the redistributed quadrature-axis limit command current to the inverter, the updated direct-axis excitation command current and the redistributed quadrature-axis limit command current are substituted into the quadrature-direct axis cross-saturation flux linkage reconstruction model and voltage prediction equation to recalculate the adjusted stator terminal voltage composite amplitude; when the adjusted stator terminal voltage composite amplitude exceeds the maximum stator voltage amplitude limit, the solution is fine-tuned until the adjusted stator terminal voltage composite amplitude converges to the maximum stator voltage amplitude limit range.

9. The excitation adjustment method for a permanent magnet motor under overload condition according to claim 1, characterized in that, In step S1, the process of determining the maximum stator voltage amplitude limit includes: acquiring the DC bus voltage of the inverter, multiplying the DC bus voltage by the reciprocal of the square root of three according to the DC bus voltage utilization coefficient in the space vector pulse width modulation mode, calculating the maximum stator phase voltage amplitude in the linear modulation zone where the inverter does not overmodulate in the current period, and determining the maximum stator phase voltage amplitude as the maximum stator voltage amplitude limit.

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