Method for remanufacturing asynchronous motor rotor into high-efficiency energy-saving synchronous motor rotor

Abstract

The invention discloses a method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor, relates to the technical field of motor remanufacturing, and systematically solves the application bottleneck of remanufacturing the asynchronous motor into the synchronous motor rotor, and a gradient observer is fused with flux linkage on-line identification, so that the improved motor is in an ultra-low rotating speed region, and the reliability of the motor is improved. Wind speed fluctuation is automatically adapted, the risk of out-of-control power generation caused by parameter mismatch is thoroughly eliminated, and an external unloading circuit is not needed; a self-adaptive derivative updating mechanism based on voltage difference is introduced, the power tracking precision is still kept under the rotating speed fluctuation working condition, and compensation lag caused by model misalignment in a traditional scheme is avoided; the rotor grooves are filled with the soft magnetic composite material layers, air-gap magnetic field distortion is directly weakened, interference of harmonic waves on a control algorithm is reduced from the source, and the requirement for follow-up filtering computing power is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of motor remanufacturing, and in particular to a method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor. Background Art

[0002] In the wave of wind power equipment renewal, transforming asynchronous generator rotors into direct-drive permanent magnet synchronous rotors has become the mainstream technical transformation direction; this type of transformation can save gearbox losses and is especially suitable for old wind farms in low-wind areas with an average annual wind speed of less than 6m / s.

[0003] After the modification, the motor's efficiency increased by 8%-12% under rated operating conditions. However, the synchronized rotor's sudden flux changes and low inertia characteristics meant that when wind speed pulsations caused the wind turbine speed to fluctuate continuously, such as in the 150-200 rpm range, the traditional maximum power point tracking (MPPT) algorithm, which relies on the steady-state speed-power curve, could not adapt to the dynamic response of the modified motor.

[0004] Some existing solutions bypass the unloading circuit and force the connection of a braking resistor when the DC bus is overvoltage. However, frequent operation accelerates the aging of the IGBT. Alternatively, a speed compensation algorithm is used to estimate the wind speed through Kalman filtering. However, the change in rotor inertia after the modification makes the model inaccurate and the compensation lags significantly. The root cause is that current modification technologies focus too much on hardware permanent magnetization, such as the embedded magnetic steel process of patent CN110098679B, but ignore the electromagnetic-control coupling variation brought about by synchronization. This also significantly increases the cost. Therefore, there is an urgent need to find a method to remanufacture the asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor to solve this problem. Summary of the Invention

[0005] In view of the above existing problems, the present invention is proposed.

[0006] The present invention provides a method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor to solve the problems of low-speed power generation instability, surge in harmonic losses, and high hardware remediation costs in converting old wind turbine asynchronous rotors into synchronous rotors.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] An embodiment of the present invention provides a method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor, which comprises:

[0009] Step S1, turning the surface of the asynchronous motor rotor to form a reduced-diameter rotor base;

[0010] Step S2, forming an axially extending permanent magnet slot on the surface of the reduced diameter rotor base;

[0011] Step S3, embedding the permanent magnet into the permanent magnet slot, and filling a soft magnetic composite material layer between the slot wall and the permanent magnet;

[0012] Step S4: injecting a high-frequency pulse voltage signal into the motor control system and identifying equivalent flux parameters based on the stator current response;

[0013] Step S5, initializing a gradient observer based on the equivalent flux parameters;

[0014] Step S6: Dynamically correct the voltage reference value of maximum power point tracking through the gradient observer.

[0015] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to the present invention, the high-frequency pulse voltage signal in step S4 is:

[0016] The frequency range is 5 to 10 times the fundamental frequency;

[0017] The upper limit of the amplitude is 5% of the rated voltage;

[0018] The injection direction forms an angle of 90 degrees with the positive direction of the rotor d-axis.

[0019] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to the present invention, the initialization of the gradient observer in step S5 includes:

[0020] Establish a first-order derivative observation module of power to voltage, and its observation value update condition is that the voltage change exceeds the set threshold;

[0021] The first-order derivative calculation adopts a differential approximation model;

[0022] Write the identified equivalent flux parameters into the observer flux initial value register.

[0023] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to the present invention, in the process of calculating the first-order derivative in step S5, when the k-th voltage-power pair (V k ,P k ), the voltage difference between adjacent sampling points is calculated and the decision value is formed:

[0024] |ΔV k |=|V k -V k-1 |,

[0025] Where, ΔV k Indicates the voltage difference between point k and point k-1, in V, V k Represents the stator phase voltage at point k, V k-1 represents the stator phase voltage at point k-1, only when |ΔV k |≥V thOnly when D k =D k-1 ;

[0026] To set the adaptive threshold:

[0027]

[0028] Among them, V th represents the derivative update threshold, with units of V, γ represents the threshold configuration constant, with units of V·√W, P rated Indicates the rated power of the motor, in W;

[0029] Perform differential calculation to obtain instantaneous power change:

[0030] ΔP k =P k -P k-1 ,

[0031] Where ΔP k Represents the power difference between point k and point k-1, P k represents the stator input power at point k, P k-1 represents the stator input power at point k-1;

[0032] Calculate the unfiltered derivative using the formula:

[0033]

[0034] in, Indicates the approximate value of the instantaneous power voltage derivative, in W·V -1 , ΔP k Represents the power difference, ΔV k Indicates voltage difference;

[0035] Construct adaptive smoothing coefficients:

[0036]

[0037] Among them, α k represents the smoothing coefficient, ΔV k Represents the voltage difference, V n Indicates the rated line voltage of the motor;

[0038] Recursively update the smoothed derivative,

[0039] Among them, D k Represents the smoothed derivative estimate of the kth point, in units of W·V -1 , α k represents the smoothing coefficient, D k-1 Represents the smooth derivative of the k-1th point, in units of W·V -1, Represents the approximate value of the instantaneous derivative, in W·V -1 ; After the calculation is completed, D k Write the gradient observer power voltage channel register to correct the voltage reference value of the maximum power point in real time.

[0040] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to the present invention, the dynamic correction of step S6 includes:

[0041] Set the step adjustment coefficient that is negatively correlated with the DC bus voltage;

[0042] generating a voltage reference value increment based on a gradient direction identification signal;

[0043] When the DC bus voltage exceeds 105% of the inverter rated voltage, the incremental negative locking mechanism is triggered.

[0044] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to the present invention, in step S6, the step of generating a voltage reference value increment based on the gradient direction identification signal includes:

[0045] Extract the gradient direction identification signal:

[0046] s k =sgn(D k ),

[0047] Among them, s k is the gradient direction identification signal of the kth point, D k is the smoothed power voltage derivative at point k, in W·V -1 ;

[0048] Construct the step size adjustment coefficient slope:

[0049]

[0050] Where μ is the step voltage slope coefficient, in V -1 , β max The upper limit of the step coefficient is 0.1, β min The lower limit of the step coefficient is 0.01, V lim is the DC bus voltage limit, V dc,nom is the rated DC voltage of the inverter;

[0051] Piecewise linear mapping step size adjustment coefficient, including:

[0052]

[0053] Among them, β kis the step adjustment coefficient of the kth point, V dc,k is the DC bus voltage at point k, in V;

[0054] Generates voltage reference increment ΔV with negative lock ref,k :

[0055]

[0056] Where, ΔV ref,k is the voltage reference increment at point k;

[0057] Recursively update the voltage reference value:

[0058] V ref,k =V ref,k-1 +ΔV ref,k ,

[0059] Among them, V ref,k is the voltage reference value of point k, in V, V ref,k-1 is the voltage reference value at point k-1.

[0060] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor described in the present invention, the set threshold is dynamically configured according to the rated power of the motor, and the configuration relationship is that the threshold is inversely proportional to the square root of the rated power.

[0061] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor described in the present invention, the value range of the step adjustment coefficient is 0.01 to 0.1, and the mapping relationship with the DC bus voltage is a piecewise linear decreasing function.

[0062] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to the present invention, the soft magnetic composite material layer in step S3:

[0063] Contains iron-silicon alloy powder and silicone resin;

[0064] The filling thickness is 5% to 8% of the permanent magnet thickness;

[0065] The particle size distribution of the iron-silicon alloy powder satisfies D50=20-50 μm, and the particle size standard deviation is less than 15 μm.

[0066] As a preferred solution of the method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to the present invention, the permanent magnet slots in step S2 are:

[0067] An eccentric inverted trapezoidal cross section is used, with the ratio of the groove bottom width to the groove opening width ranging from 1.2:1 to 1.5:1;

[0068] The inclination angle of the slot wall is 3 to 5 degrees relative to the radial direction of the rotor.

[0069] The beneficial effects of the present invention are as follows: the present invention systematically resolves the application bottleneck of remanufacturing asynchronous motors into synchronous motor rotors. The gradient observer integrates online identification of magnetic flux, allowing the modified motor to automatically adapt to wind speed pulsations in the ultra-low speed range of 150-200rpm, completely eliminating the risk of power generation out of control caused by parameter mismatch, without the need for an external unloading circuit; the introduction of an adaptive derivative update mechanism based on voltage difference maintains power tracking accuracy under speed fluctuations of ±30%, avoiding compensation lag caused by model inaccuracy in traditional solutions; the rotor slots are filled with a layer of soft magnetic composite material to directly weaken the air gap magnetic field distortion, reduce the interference of 5th / 7th harmonics on the control algorithm from the source, and reduce the demand for subsequent filtering computing power;

[0070] The present invention adopts an eccentric inverted trapezoidal slot structure with a slot bottom / mouth ratio of 1.2-1.5 to ensure the anti-centrifugal ability of the permanent magnet. Combined with the soft magnetic layer with optimized particle size D50=20-50μm, it supports repeated modification within the wind turbine's 20-year design life. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0072] Figure 1 Schematic diagram of the process of remanufacturing the asynchronous motor rotor in Example 1 into a high-efficiency and energy-saving synchronous motor rotor. DETAILED DESCRIPTION

[0073] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0074] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0075] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0076] Example 1, with reference to Figure 1 This embodiment provides a method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor, comprising:

[0077] Step S1, turning the surface of the asynchronous motor rotor to form a reduced-diameter rotor base;

[0078] Step S2, forming an axially extending permanent magnet slot on the surface of the reduced diameter rotor base;

[0079] Permanent magnet slot of step S2:

[0080] An eccentric inverted trapezoidal cross section is used, with the ratio of the groove bottom width to the groove opening width ranging from 1.2:1 to 1.5:1;

[0081] The inclination angle of the slot wall is 3 to 5 degrees relative to the radial direction of the rotor;

[0082] Step S3, embedding the permanent magnet into the permanent magnet slot, and filling the space between the slot wall and the permanent magnet with a soft magnetic composite material layer;

[0083] Soft magnetic composite material layer in step S3:

[0084] Contains iron-silicon alloy powder and silicone resin;

[0085] The filling thickness is 5% to 8% of the permanent magnet thickness;

[0086] The particle size distribution of the iron-silicon alloy powder satisfies D50=20-50 μm, and the particle size standard deviation is less than 15 μm;

[0087] Step S4, injecting a high-frequency pulse voltage signal into the motor control system, and identifying equivalent flux parameters based on the stator current response;

[0088] In step S4, the high-frequency pulse voltage signal:

[0089] The frequency range is 5 to 10 times the fundamental frequency;

[0090] The upper limit of the amplitude is 5% of the rated voltage;

[0091] The injection direction forms an angle of 90 degrees with the positive direction of the rotor d-axis;

[0092] Step S5, initializing the gradient observer based on the equivalent flux parameters;

[0093] The initialization of the gradient observer in step S5 includes:

[0094] Establish a first-order derivative observation module of power to voltage, and its observation value update condition is that the voltage change exceeds the set threshold;

[0095] The first-order derivative calculation uses a difference approximation model;

[0096] Write the identified equivalent flux parameters into the observer flux initial value register;

[0097] In the first-order derivative calculation process of step S5, when the kth voltage-power pair (V k ,P k ), the voltage difference between adjacent sampling points is calculated and the decision value is formed:

[0098] |ΔV k |=|V k -V k-1 |,

[0099] Where, ΔV k Indicates the voltage difference between point k and point k-1, in V, V k Represents the stator phase voltage at point k, V k-1 represents the stator phase voltage at point k-1, only when |ΔV k |≥V th Only when D k =D k-1 ;

[0100] To set the adaptive threshold:

[0101]

[0102] Among them, V th represents the derivative update threshold, with units of V, γ represents the threshold configuration constant, with units of V·√W, P rated Indicates the rated power of the motor, in W;

[0103] Perform differential calculation to obtain instantaneous power change:

[0104] ΔP k =P k -P k-1 ,

[0105] Where ΔP k Represents the power difference between point k and point k-1, P k represents the stator input power at point k, P k-1 represents the stator input power at point k-1;

[0106] Calculate the unfiltered derivative using the formula:

[0107]

[0108] in, Indicates the approximate value of the instantaneous power voltage derivative, in W·V -1 , ΔP k Represents the power difference, ΔV kIndicates voltage difference;

[0109] Construct adaptive smoothing coefficients:

[0110]

[0111] Among them, α k represents the smoothing coefficient, ΔV k Represents the voltage difference, V n Indicates the rated line voltage of the motor;

[0112] Recursively update the smoothed derivative,

[0113] Among them, D k Represents the smoothed derivative estimate of the kth point, in units of W·V -1 , α k represents the smoothing coefficient, D k-1 Represents the smooth derivative of the k-1th point, in units of W·V -1 , Represents the approximate value of the instantaneous derivative, in W·V -1 ; After the calculation is completed, D k Write the gradient observer power voltage channel register to correct the voltage reference value of the maximum power point in real time;

[0114] Specifically, the piecewise difference model switches between static hold and dynamic update using a threshold determination method. Exponential decay smoothing suppresses noise while retaining a sensitive response to voltage mutations, avoiding the phase lag caused by fixed window filtering. The threshold scales with the rated power, allowing high-power motors to still enter derivative updates during small voltage drifts, while reducing false touches for low-power devices. The recursive formula integrates historical derivatives with current disturbances, weakening the impact of single-point anomalies on the results. The real-time derivative provides a continuous gradient direction for maximum power point tracking, guiding the voltage reference value to converge toward the energy efficiency optimal zone, significantly improving tracking speed and system robustness.

[0115] The threshold is set dynamically according to the rated power of the motor, and the configuration relationship is that the threshold is inversely proportional to the square root of the rated power;

[0116] Step S6, dynamically correcting the voltage reference value for maximum power point tracking through a gradient observer;

[0117] The dynamic correction of step S6 includes:

[0118] Set the step adjustment coefficient that is negatively correlated with the DC bus voltage;

[0119] generating a voltage reference value increment based on a gradient direction identification signal;

[0120] When the DC bus voltage exceeds 105% of the inverter rated voltage, the incremental negative locking mechanism is triggered;

[0121] In step S6, the step of generating a voltage reference value increment based on the gradient direction identification signal includes:

[0122] Extract the gradient direction identification signal:

[0123] s k =sgn(D k ),

[0124] Among them, s k is the gradient direction identification signal of the kth point, D k is the smoothed power voltage derivative at point k, in W·V -1 ;

[0125] Construct the step size adjustment coefficient slope:

[0126]

[0127] Where μ is the step voltage slope coefficient, in V -1 , β max The upper limit of the step coefficient is 0.1, β min The lower limit of the step coefficient is 0.01, V lim is the DC bus voltage limit, V dc,nom is the rated DC voltage of the inverter;

[0128] Piecewise linear mapping step size adjustment coefficient, including:

[0129]

[0130] Among them, β k is the step adjustment coefficient of the kth point, V dc,k is the DC bus voltage at point k, in V;

[0131] Generates voltage reference increment ΔV with negative lock ref,k :

[0132]

[0133] Where, ΔV ref,k is the voltage reference increment at point k;

[0134] Recursively update the voltage reference value:

[0135] V ref,k =V ref,k-1 +ΔV ref,k ,

[0136] Among them, V ref,k is the voltage reference value of point k, in V, V ref,k-1 is the voltage reference value of point k-1;

[0137] Specifically, the step adjustment coefficient decreases in sections with the DC bus voltage. When the bus voltage approaches the limit, the increment is automatically reduced to prevent overvoltage caused by large adjustments. The gradient direction identification signal only takes the sign information to ensure that the algorithm is insensitive to derivative amplitude noise. The negative locking mechanism forcibly prohibits positive increments when the DC voltage exceeds the limit, quickly pulling the operating point back to the safe zone. The linear slope μ is uniquely determined by the boundary conditions, so that β k Continuously differentiable over the entire range, it facilitates implementation of digital controllers. The overall closed loop allows the voltage reference value to converge rapidly along the power voltage gradient, while taking into account bus voltage safety and step size adaptation, improving maximum power point tracking efficiency and system steady-state robustness.

[0138] The value range of the step size adjustment coefficient is 0.01 to 0.1, and the mapping relationship with the DC bus voltage is a piecewise linear decreasing function.

[0139] 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 the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor, characterized in that: include, Step S1, turning the surface of the asynchronous motor rotor to form a reduced-diameter rotor base; Step S2, forming an axially extending permanent magnet slot on the surface of the reduced diameter rotor base; Step S3, embedding the permanent magnet into the permanent magnet slot, and filling a soft magnetic composite material layer between the slot wall and the permanent magnet; Step S4, injecting a high-frequency pulse voltage signal into the motor control system, and identifying equivalent flux parameters based on the stator current response; Step S5, initializing a gradient observer based on the equivalent flux parameters; Step S6: Dynamically correct the voltage reference value of maximum power point tracking through the gradient observer.

2. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 1, characterized in that: In step S4, the high-frequency pulse voltage signal: The frequency range is 5 to 10 times the fundamental frequency; The upper limit of the amplitude is 5% of the rated voltage; The injection direction forms an angle of 90 degrees with the positive direction of the rotor d-axis.

3. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 1, characterized in that: The initialization of the gradient observer in step S5 includes: Establish a first-order derivative observation module of power to voltage, and its observation value update condition is that the voltage change exceeds the set threshold; The first-order derivative calculation adopts a differential approximation model; Write the identified equivalent flux parameters into the observer flux initial value register.

4. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 3, characterized in that: In the first-order derivative calculation process of step S5, when the kth voltage-power pair (V k ,P k ), the voltage difference between adjacent sampling points is calculated and the decision value is formed: |ΔV k |=|V k -V k-1 |, Where, ΔV k Indicates the voltage difference between point k and point k-1, in V, V k Represents the stator phase voltage at point k, V k-1 represents the stator phase voltage at point k-1, only when |ΔV k |≥V th Only when D k =D k-1 ; To set the adaptive threshold: Among them, V th represents the derivative update threshold, with units of V, γ represents the threshold configuration constant, with units of V·√W, P rated Indicates the rated power of the motor, in W; Perform differential calculation to obtain instantaneous power change: ΔP k =P k -P k-1 , Where ΔP k Represents the power difference between point k and point k-1, P k represents the stator input power at point k, P k-1 represents the stator input power at point k-1; Calculate the unfiltered derivative using the formula: in, Indicates the approximate value of the instantaneous power voltage derivative, in W·V -1 , ΔP k Represents the power difference, ΔV k Indicates voltage difference; Construct adaptive smoothing coefficients: Among them, α k represents the smoothing coefficient, ΔV k Represents the voltage difference, V n Indicates the rated line voltage of the motor; Recursively update the smoothed derivative, Among them, D k Represents the smoothed derivative estimate of the kth point, in units of W·V -1 , α k represents the smoothing coefficient, D k-1 Represents the smooth derivative of the k-1th point, in units of W·V -1 , Represents the approximate value of the instantaneous derivative, in W·V -1 ; After the calculation is completed, D k Write the gradient observer power voltage channel register to correct the voltage reference value of the maximum power point in real time.

5. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 1, characterized in that: The dynamic correction of step S6 includes: Set the step adjustment coefficient that is negatively correlated with the DC bus voltage; generating a voltage reference value increment based on a gradient direction identification signal; When the DC bus voltage exceeds 105% of the inverter rated voltage, the incremental negative locking mechanism is triggered.

6. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 5, characterized in that: In step S6, the step of generating a voltage reference value increment based on the gradient direction identification signal includes: Extract the gradient direction identification signal: s k =sgn(D k ), Among them, s k is the gradient direction identification signal of the kth point, D k is the smoothed power voltage derivative at point k, in W·V -1 ; Construct the step size adjustment coefficient slope: Where μ is the step voltage slope coefficient, in V -1 , β max The upper limit of the step coefficient is 0.1, β min The lower limit of the step coefficient is 0.01, V lim is the DC bus voltage limit, V dc,nom is the rated DC voltage of the inverter; Piecewise linear mapping step size adjustment coefficient, including: Among them, β k is the step adjustment coefficient of the kth point, V dc,k is the DC bus voltage at point k, in V; Generates voltage reference increment ΔV with negative lock ref,k : Where, ΔV ref,k is the voltage reference increment at point k; Recursively update the voltage reference value: V ref,k =V ref,k-1 +ΔV ref,k , Among them, V ref,k is the voltage reference value of point k, in V, V ref,k-1 is the voltage reference value at point k-1.

7. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 3, characterized in that: The set threshold is dynamically configured according to the rated power of the motor, and the configuration relationship is that the threshold is inversely proportional to the square root of the rated power.

8. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 5, characterized in that: The step size adjustment coefficient has a value range of 0.01 to 0.1, and its mapping relationship with the DC bus voltage is a piecewise linear decreasing function.

9. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 1, characterized in that: Soft magnetic composite material layer in step S3: Contains iron-silicon alloy powder and silicone resin; The filling thickness is 5% to 8% of the permanent magnet thickness; The particle size distribution of the iron-silicon alloy powder satisfies D50=20-50 μm, and the particle size standard deviation is less than 15 μm.

10. The method for remanufacturing an asynchronous motor rotor into a high-efficiency and energy-saving synchronous motor rotor according to claim 1, characterized in that: Permanent magnet slot of step S2: An eccentric inverted trapezoidal cross section is used, with the ratio of the groove bottom width to the groove opening width ranging from 1.2:1 to 1.5:1; The inclination angle of the slot wall is 3 to 5 degrees relative to the radial direction of the rotor.

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