Surface-mounted permanent magnet synchronous motor minimum loss control method based on curve fitting

Abstract

The invention provides a surface-mounted permanent magnet synchronous motor minimum loss control method based on curve fitting. The method comprises the steps that S1, an SPMSM mathematical model considering the iron loss influence is constructed; based on an LMC method, establishing an extreme value solving equation under conditional constraints; s2, obtaining a loss expression based on an extreme value solving equation under conditional constraints and an SPMSM mathematical model considering the iron loss influence; s3, performing approximation fitting analysis according to the loss expression, and performing approximation fitting on the loss expression according to an approximation fitting analysis result to obtain an approximation fitting expression; and S4, obtaining a d-axis current reference value setting formula according to the approximation fitting expression. According to the method, the influence of motor parameters can be reduced while the calculation process is simplified, and the robustness of the method and the motor efficiency are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet synchronous motor control, and in particular to a minimum loss control method for a surface mounted permanent magnet synchronous motor. Background Art

[0002] Surface-mounted permanent magnet synchronous motors (SPMSMs) have the characteristics of high power factor, small size, and high reliability, and are widely used in aerospace, CNC machine tools, robotics and other fields. In mobile power systems or places where motors need to run for a long time, efficiency is an important indicator to measure motor performance. How to improve motor efficiency through control means is one of the hot topics of current research.

[0003] In order to optimize the efficiency of PMSM, the minimum loss control (LMC) method based on the iron loss model has attracted extensive attention. According to different implementation methods, LMC can be divided into: model method and search method.

[0004] Among them, since it is difficult to solve the d-axis and q-axis current reference values ​​that meet the minimum loss, the model method is to establish a mathematical model that includes the motor iron loss and derive the d-axis and q-axis current reference values ​​with the minimum loss through approximation. The literature (G. Feng, C. Lai, X. Tan, W. Peng and NCKar, "Multi-parameter estimation of PMSM using differential model with core loss compensation," IEEE Trans. Transp. Electrific., vol. 8, no. 1, pp. 1105–1115, Mar. 2022.) simplifies the process of obtaining the minimum loss by approximating the motor equivalent circuit. The literature (S. Zhu, J. Dong, Y. Li, W. Hua, “Fast calculation of carrier harmonic iron losses caused by pulse width modulation in interior permanent magnet synchronous motors,” IET Electr. Power Appl., vol. 14, no. 7, pp. 1163-1176, 2020.) performed a polynomial fitting on the analytical expression of current that satisfies the minimum loss, and used the polynomial calculation to obtain the current reference value that satisfies the minimum loss. The literature (MNUddin, MMRahman, B.Patel, and B.Venkatesh, "Performance of a loss model based nonlinear controller for IPMSM drive incorporating parameter uncertainties," IEEE Trans. Power Electron., vol. 34, no. 6, pp. 5684-5696 June 2019.) simplifies the solution process of the current reference value by using the backstepping adaptive control method. Although the model method has good speed, it is highly dependent on the motor parameters. The uncertainty of the parameters becomes a difficulty in the implementation of such control methods.

[0005] The search method uses various forms of gradient descent algorithms to calculate DC power and loss in real time, and achieves online search of the current vector angle under the constraint of minimum loss. The advantage of the search method is that it avoids the influence of motor parameters to the greatest extent, has high robustness, and avoids the analytical solution of complex models. However, the implementation of such methods usually requires additional hardware circuits to detect the input power. Summary of the invention

[0006] In view of the technical problems that the existing technology is highly dependent on motor parameters and requires hardware circuit support, the present invention proposes a minimum loss control method for a surface-mounted permanent magnet synchronous motor based on curve fitting. The method based on curve fitting simplifies the solution of the d-axis reference current and is suitable for the surface-mounted synchronous motor operating in the speed working mode. It can simplify the calculation process while reducing the influence of motor parameters, effectively improving the robustness of the method and the motor efficiency.

[0007] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A method for controlling minimum loss of a surface-mounted permanent magnet synchronous motor based on curve fitting comprises the following steps:

[0009] S1: Construct the SPMSM mathematical model considering the influence of iron loss and obtain the relationship A between the d-axis and q-axis current torque components and the d-axis and q-axis currents; based on the LMC method, establish the extreme value solution equation under conditional constraints;

[0010] S2: Obtain the loss expression based on the extreme value solution equation under conditional constraints and the relationship A between the d-axis and q-axis current torque components and the d-axis and q-axis currents;

[0011] S3: performing approximate fitting analysis on the loss expression, and performing approximate fitting on the loss expression according to the approximate fitting analysis result to obtain an approximate fitting expression;

[0012] S4: Obtain a d-axis current reference value setting formula according to the approximate fitting expression.

[0013] Furthermore, the method for obtaining the relationship A is: based on the SPMSM mathematical model that considers the influence of iron loss, the iron loss component formula I of the d and q axis currents and the current relationship equation between the d and q axis currents and the iron loss component and the torque component are obtained, and simplified to obtain the relationship A between the d and q axis current torque components and the d and q axis currents.

[0014] Further, the method for establishing the extreme value solution equation under conditional constraints described in step S1 is: define the total loss equation according to the motor copper loss and the motor iron loss, establish the extreme value solution equation according to the total loss equation, introduce the constraint conditions, and obtain the extreme value solution equation under conditional constraints:

[0015] The total loss equation is:

[0016]

[0017] Among them, R s is the stator resistance, i d is the d-axis current, i q is the q-axis current, i dt and i qt are the d-axis and q-axis current torque components that actually generate torque in the d-axis and q-axis currents, respectively. s is the motor inductance, λ f is the permanent magnet flux amplitude, ω e is the electrical angular velocity, P Cu is the motor copper loss, P Fe is the motor iron loss;

[0018] The extreme value solution equation is:

[0019]

[0020] Where η is the motor efficiency, P in is the input power, P loss is the total motor loss;

[0021] The constraints are:

[0022]

[0023] Among them, I s is the stator phase current amplitude.

[0024] Further, the method for obtaining the loss expression in step S2 is: according to the relationship A, the d-axis current torque component i dt and the q-axis current torque component i qt They are represented as d-axis current i d and q-axis current i q The function of d-axis current torque component and d-axis current torque component is obtained. The iron loss component formula of d-axis current and q-axis current torque component is obtained according to the relational equation I and the current relation equation of d-axis current and iron loss component and torque component.

[0025] According to the relational expression A, the relational expression II between the q-axis current and the d-axis current is obtained;

[0026] Combining the total loss equation, the iron loss component formula Ⅱ of the d and q axis currents and the relation Ⅱ, the iron loss expression is obtained; combining the total loss equation and the relation Ⅱ, the copper loss expression is obtained.

[0027] Further, the iron loss expression is:

[0028] PFe =A(a1i d 2 +b1i d +c1);

[0029] Among them, A, a1, b1, c1 are parameters related to the iron loss expression determined by the motor parameters;

[0030] The copper loss expression is:

[0031] P Cu =D(a2i d 2 +b2i d +c2);

[0032] Among them, D, a2, b2, and c2 are parameters related to the copper loss expression determined by the motor parameters.

[0033] Further, the parameters related to the iron loss expression are:

[0034]

[0035] The relevant parameters of the copper loss expression are:

[0036]

[0037] Furthermore, the process of the approximate fitting analysis described in step S3 is: according to the iron loss expression and the copper loss expression, the copper loss, the total loss and the curves of the motor efficiency changing with the d-axis current are respectively drawn in the simulation software; according to the characteristics of the curve of the copper loss changing with the d-axis current and the characteristics of the curve of the iron loss changing with the d-axis current, combined with the verification of the second-order derivative of the iron loss with respect to the d-axis current, the feasibility of the approximate fitting of the iron loss curve is determined.

[0038] Further, the method of performing approximate fitting on the loss expression according to the approximate fitting analysis result in step S3 to obtain the approximate fitting expression is: considering the iron loss as the value of the d-axis current i d The linear function, combined with the total loss equation, obtains the total loss P loss About d-axis current i d The quadratic parabola of , as an approximate fitting expression:

[0039]

[0040] Further, the method for obtaining the setting formula of the d-axis current reference value in step S4 is: according to the characteristics of the parabola, the minimum value of the total motor loss is obtained at the extreme point, and the setting formula of the d-axis current reference value is:

[0041]

[0042] Furthermore, the permanent magnet flux λ in the iron loss expression related parameters and the copper loss expression related parameters used in the setting formula of the d-axis current reference value is f and inductor L s The way to obtain is:

[0043]

[0044] The beneficial effects of the present invention are:

[0045] By using curve fitting to approximate the iron loss to a linear function, the complex problem of solving the extreme value of a quadratic function is simplified to the solution of a linear function, which greatly reduces the computational complexity. This makes this method more suitable for the application of real-time control systems.

[0046] It has high robustness to changes in motor parameters and can maintain good control effects even when parameter uncertainties are large. It is suitable for SPMSM under different speeds and load torques and has a wide range of applications.

[0047] No additional hardware circuit is required to detect input power, reducing system complexity and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0049] Figure 1 Flow chart of the method of the present invention.

[0050] Figure 2 It is a waveform diagram of the copper loss and iron loss changing with the d-axis current in the present invention.

[0051] Figure 3 It is the overall control block diagram based on curve fitting of the present invention.

[0052] Figure 4 It is the d-axis current reference value and the motor total loss change curve in the present invention.

[0053] Figure 5 The actual output values ​​of the d and q axes, the current reference values ​​of the d and q axes, and the motor phase current variation diagram are when the reference speed of the SPMSM in the present invention is 1000r / min and the load torques are 2Nm, 4Nm, 6Nm, and 8Nm respectively, and three steps are performed.

[0054] Figure 6 In the figure, (a), (b), (c), and (d) are the curves of the motor efficiency changing with the d-axis current when the reference speed of the SPMSM is 1000r / min and the load torque is 2N, 4N, 6N, and 8N respectively.

[0055] Figure 7 This is the steady-state SPMSM model of the present invention that takes into account the influence of iron loss. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] A minimum loss control method for surface mounted permanent magnet synchronous motor based on curve fitting, such as Figure 1 As shown, the steps include:

[0058] S1: Construct a mathematical model of SPMSM considering the influence of iron loss and obtain the relationship A between the d-axis and q-axis current torque components and the d-axis and q-axis currents; based on the LMC method, establish the extreme value solution equation under conditional constraints.

[0059] The steady-state SPMSM model considering the influence of iron loss is constructed as follows: Figure 7 As shown, the steady-state voltage equation and torque equation are obtained according to the SPMSM mathematical model considering the influence of iron loss, where:

[0060] The steady-state voltage equation is:

[0061]

[0062] Among them, R s is the stator resistance; R Fe is the iron loss resistance, u d and u q are d and q axis voltages respectively; i dt and i qt are the d-axis and q-axis current torque components that actually generate torque in the d-axis and q-axis currents respectively; L s is the motor inductance, λ f is the permanent magnet flux amplitude, ω e is the electrical angular velocity, Figure 7 in i d 、i q are d-axis and q-axis currents respectively.

[0063] The torque equation is:

[0064]

[0065] Among them, n p is the pole pair number, T e is the electromagnetic torque.

[0066] Further, according to Figure 7 , the iron loss component formula of d and q axis current is:

[0067]

[0068] Among them, R Fe is the iron loss resistance.

[0069] Further, according to Figure 7 , the current relationship equation between the d-axis and q-axis currents and the iron loss component and torque component can be obtained:

[0070]

[0071] Furthermore, by substituting formula (3) into the iron loss component formula I of the d-axis and q-axis currents, the relationship between the d-axis and q-axis current torque components and the d-axis and q-axis currents is obtained:

[0072]

[0073] Among them, i d is the d-axis current, i q is the q-axis current.

[0074] Furthermore, according to the minimum loss control (LMC) method based on the iron loss model, an extreme value solution equation under conditional constraints is established. Specifically, the total loss equation is defined according to the motor copper loss and the motor iron loss, and the extreme value solution equation is established according to the total loss equation. Constraints are introduced to obtain the extreme value solution equation under conditional constraints:

[0075]

[0076] Where η is the motor efficiency, P in is the input power, I s is the stator phase current amplitude, st represents the constraint condition; in formula (5) Solve the equation for the extreme value, P loss is the total loss of the motor. For surface-mount motors, the total loss equation is:

[0077]

[0078] Among them, P Cu is the motor copper loss, P Fe is the motor iron loss.

[0079] S2: Obtain the loss expression based on the extreme value solving equation under conditional constraints and the relationship A between the d-axis and q-axis current torque components and the d-axis and q-axis currents.

[0080] In order to analyze the changing trend of copper loss and iron loss with the change of d-axis current, the total loss equation needs to be transformed to obtain the loss expression, which includes the iron loss expression and the copper loss expression.

[0081] Specifically, according to formula (4), the d-axis current torque component i dt and the q-axis current torque component i qt They are represented as d-axis current i d and q-axis current i q Function, we get relation I:

[0082]

[0083] Further, according to formula (4), the q-axis current i is obtained q and the d-axis current i d Relationship II:

[0084]

[0085] Furthermore, substituting equation (7) into equation (3) yields the iron loss component equation II of the d and q axis currents:

[0086]

[0087] Furthermore, according to the torque equation (2), when the load is constant, the q-axis current torque component i qt Certain, iron loss P Fe It can be expressed as about the d-axis current i d The function of the d-axis current i is obtained by substituting the iron loss component formula II and formula (8) of the d-axis current into the iron loss expression in formula (6). d , q-axis current torque component i qt The iron loss expression of SPMSM under given speed and torque conditions is:

[0088] P Fe =A(a1i d 2 +b1i d +c1) (9)

[0089] The relevant parameters of the iron loss expression determined by the motor parameters are:

[0090]

[0091] Further, substituting equation II into the copper loss expression in equation (6), we can obtain the copper loss with respect to the d-axis current i d , q-axis current torque component i qt expression.

[0092] Under given speed and torque conditions, the copper loss expression of SPMSM is:

[0093] P Cu =D(a2i d 2 +b2i d +c2) (11)

[0094] The relevant parameters of the copper loss expression determined by the motor parameters are:

[0095]

[0096] S3: Perform an approximate fitting analysis on the loss expression, and perform an approximate fitting on the loss expression according to the approximate fitting analysis result to obtain an approximate fitting expression.

[0097] From equations (8) and (10), it can be seen that the copper loss and iron loss are expressed as d However, it is still too complicated to directly solve the d-axis current reference value under the minimum loss.

[0098] In the simulation, the curves of copper loss and iron loss changing with d-axis current are plotted respectively, as shown in Figure 2 shown.

[0099] According to the copper loss and iron loss, the d-axis current i d The simulation of the curve, (a) is copper loss, (b) is iron loss, the extreme point of iron loss deviates from the maximum range of the motor range, and shows a linear function characteristic within a given interval; the iron loss is fitted as the d-axis current i d The linear function of the fitting is combined with the iron loss and copper loss, and the total loss is expressed as about the d-axis current i d The quadratic function is used to quickly solve the d-axis current reference value corresponding to the minimum motor loss point by using the extreme value characteristics of the quadratic function.

[0100] The purpose of minimum loss control is to minimize the sum of copper loss and iron loss, but the extreme points of the quadratic function of copper loss and iron loss about id are not at the same point. The iron loss is fitted as a linear function, and the sum of iron loss and copper loss can be approximated as a quadratic function about id, thereby avoiding the solution of high-order nonlinear equations in the process of solving the current reference value. Therefore, the present invention simplifies the solution process of the d-axis current reference value by introducing the approximate fitting of the iron loss curve.

[0101] In order to verify the feasibility of the iron loss curve approximation, the slope of the iron loss curve is analyzed and the second-order derivative verification is performed.

[0102] Furthermore, within the rated current range of the motor, at low and medium speeds, due to R Fe >>ω e L s In order to obtain the variation trend of iron loss with respect to d-axis current, the equation (8) with respect to d-axis current i d Find the second-order derivative:

[0103]

[0104] Therefore, it can be verified that the change trend of iron loss with respect to d-axis current is approximately 0, and the iron loss curve can be approximated as a linear curve.

[0105] Furthermore, the iron loss expression is approximated: the iron loss is considered to be the value of the d-axis current i within a given range. d The copper loss and iron loss under the fitting curve are expressed as follows:

[0106]

[0107] Furthermore, according to the loss equation (5), the total loss P loss is the d-axis current i d The quadratic parabola of , which is used as the approximate fitting expression:

[0108]

[0109] S4: Obtain a d-axis current reference value setting formula according to the approximate fitting expression.

[0110] Furthermore, according to the characteristics of the parabola, the minimum value of the total motor loss is obtained at the extreme point. At this time, the setting formula of the d-axis current reference value is:

[0111]

[0112] Furthermore, in order to reduce the influence of motor parameters, when setting the d-axis current reference value, the permanent magnet flux and inductance of the iron loss expression related parameters (A, b1) and the copper loss expression related parameters (D, a2, b2) used in the setting formula of the d-axis current reference value are obtained by the following formula:

[0113]

[0114] At the same time, the stator resistance can be obtained through the built-in thermistor of the motor and the relationship between the thermistor resistance and temperature. The specific relationship is as follows:

[0115] R s =Rs0 (1+k(T-T0)) (18)

[0117] Where k is the temperature coefficient, R s0 is the stator winding resistance when the temperature is T0, and T is the current temperature value.

[0118] In order to simply explain how to achieve minimum loss control of the surface-mounted permanent magnet synchronous motor by setting the d-axis current reference value, the overall control process is briefly described as follows: Figure 3 shown.

[0119] 1. Sample the three-phase current i of abc at the motor end a 、i b 、i c Electrical angular velocity ω e , and then the d and q axis voltages and currents are obtained through Clark, Park transformation and PI controller. The d and q axis voltages used need to consider the influence of digital control delay and inverter nonlinear voltage and need to be compensated.

[0120] 2. Substitute the d-axis and q-axis voltage and current, stator resistance and iron loss resistance into formula (16) to realize the setting of the d-axis current reference value. The q-axis current is obtained by the speed loop through the PI controller, thereby realizing the setting of the d-axis current reference value under the minimum loss of the surface-mounted permanent magnet synchronous motor.

[0121] 3. The d and q current reference values ​​are converted into d and q axis voltages by PI controller, which are then input into space vector pulse width modulation (SVPWM) after inverse park transformation to generate a control signal acting on the inverter. The modulation signal controls the motor by controlling the three-phase voltage generated by the inverter.

[0122] In order to verify the accuracy of the d-axis current reference value setting obtained by the method proposed in the present invention, the present invention built an SPMSM simulation model through MATLAB according to the motor parameters shown in Table 1 and the measured iron loss resistance value. When the motor speed is 1000r / min and the load torque is 2Nm, the d-axis current is controlled to change from 0A to -3A, and the d-axis current reference value calculated by the method proposed in the present invention and the motor total loss change curve are recorded, as shown in FIG. Figure 4 As shown in the figure, it can be seen that when the d-axis current reference value obtained by the method proposed in the present invention approaches the d-axis current corresponding to the minimum total loss point.

[0123] In order to further verify the effectiveness of the proposed method, an experimental system was built. The parameters of the surface-mounted permanent magnet synchronous motor are shown in Table 1. In the experimental system, the control unit uses TMS320F28335. The sampling frequency of the control system is 10kHz, the control cycle is 100μs, the load is provided by the torque generator, the motor input power is measured by the MDA805A electric drive analyzer with integrated high-sensitivity voltage probe and high-precision current clamp meter, and the output power is measured by the torque sensor.

[0124] Table 1 SPMSM motor parameters

[0125]

[0126] In order to verify the efficiency optimization effect of the proposed method, the d-axis current value corresponding to the minimum loss point when the SPMSM speed is 1000r / min and the load torque is 2Nm, 4Nm, 6Nm, and 8Nm is first measured by MDA805A electric drive analyzer and Yokogawa oscilloscope, as shown in Table 2. Figure 5 shown.

[0127] From top to bottom, the SPMSM speed is 1000r / min and the load torque is in steps of 2N, 4N, 6N, and 8N.

[0128] 1)q-axis current current reference value i qref , the actual output value of the q-axis current i q .

[0129] 2) d-axis current, current reference value i dref , the actual output value of the d-axis current i d .

[0130] 3) Motor phase current I s .

[0131] The middle is the whole, and the Zooms on both sides are the magnified parts. The main parts are the d-axis current, q-axis current and phase current waveforms for three steps corresponding to 2N, 4N, 6N and 8N torques.

[0132] Among them, -2.0A is the d-axis current corresponding to the optimal efficiency measured by the offline test method at a SPMSM speed of 1000r / min, such as Figure 6 (a), (b), (c), and (d) are surface-mount motors with 1000r / min, 2N, 4N, 6N, and 8N, respectively, and the d-axis current varies from 0 to -6A at 0.2A intervals. The motor efficiency changes with the d-axis current. This set of data is used to obtain the d-axis current corresponding to the maximum efficiency point under different working conditions, and is used to compare whether the proposed method can track the d-axis current of the maximum efficiency point online.

[0133] It can be seen from the above results that the method proposed in the present invention can better track the d-axis current when the efficiency is optimal.

[0134] Table 2

[0135]

[0136] In summary, the method proposed in the present invention firstly theoretically analyzes the analytical expression of iron loss with respect to d-axis current under the mathematical model of iron loss, and then focuses on analyzing the changing trend of iron loss with d-axis current, and proposes that within the rated current range of the motor, the iron loss can be considered to be approximately a linear function of the d-axis current, thereby simplifying the complex solution process of the d-axis current reference value that satisfies the minimum loss to a quadratic function extreme value solution problem, which provides a new method for setting the current reference value of the surface-mounted permanent magnet synchronous motor.

[0137] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A minimum loss control method for a surface-mounted permanent magnet synchronous motor based on curve fitting, characterized in that: Includes steps: S1: Construct the SPMSM mathematical model considering the influence of iron loss and obtain the relationship A between the d-axis and q-axis current torque components and the d-axis and q-axis currents; based on the LMC method, establish the extreme value solution equation under conditional constraints; S2: Obtain the loss expression based on the extreme value solution equation under conditional constraints and the relationship A between the d-axis and q-axis current torque components and the d-axis and q-axis currents; S3: performing approximate fitting analysis on the loss expression, and performing approximate fitting on the loss expression according to the approximate fitting analysis result to obtain an approximate fitting expression; S4: Obtain a d-axis current reference value setting formula according to the approximate fitting expression.

2. The method for controlling minimum loss of a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 1, characterized in that: The method for obtaining the relationship A is: based on the SPMSM mathematical model that considers the influence of iron loss, the iron loss component formula I of the d and q axis currents and the current relationship equation between the d and q axis currents and the iron loss component and the torque component are obtained, and simplified to obtain the relationship A between the d and q axis current torque components and the d and q axis currents.

3. The minimum loss control method for a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 2 is characterized in that: The method for establishing the extreme value solution equation under conditional constraints described in step S1 is: define the total loss equation according to the motor copper loss and the motor iron loss, establish the extreme value solution equation according to the total loss equation, introduce the constraint conditions, and obtain the extreme value solution equation under conditional constraints: The total loss equation is: Among them, R s is the stator resistance, i d is the d-axis current, i q is the q-axis current, i dt and i qt are the d-axis and q-axis current torque components that actually generate torque in the d-axis and q-axis currents, respectively. s is the motor inductance, λ f is the permanent magnet flux amplitude, ω e is the electrical angular velocity, P Cu is the motor copper loss, P Fe is the motor iron loss; The extreme value solution equation is: Where η is the motor efficiency, P in is the input power, P loss is the total motor loss; The constraints are: Among them, I s is the stator phase current amplitude.

4. The method for controlling minimum loss of a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 3 is characterized in that: The method for obtaining the loss expression in step S2 is: according to the relationship A, the d-axis current torque component i dt and the q-axis current torque component i qt They are represented as d-axis current i d and q-axis current i q The function of d-axis current torque component and d-axis current torque component is obtained. The iron loss component formula of d-axis current and q-axis current torque component is obtained according to the relational equation I and the current relation equation of d-axis current and iron loss component and torque component. According to the relational expression A, the relational expression II between the q-axis current and the d-axis current is obtained; Combining the total loss equation, the iron loss component formula Ⅱ of the d and q axis currents and the relation Ⅱ, the iron loss expression is obtained; combining the total loss equation and the relation Ⅱ, the copper loss expression is obtained.

5. The method for controlling minimum loss of a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 4, characterized in that: The iron loss expression is: P Fe =A(a1i d 2 +b1i d +c1); Among them, A, a1, b1, c1 are parameters related to the iron loss expression determined by the motor parameters; The copper loss expression is: P Cu =D(a2i d 2 +b2i d +c2); Among them, D, a2, b2, and c2 are parameters related to the copper loss expression determined by the motor parameters.

6. The method for controlling minimum loss of a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 5, characterized in that: The parameters related to the iron loss expression are: The relevant parameters of the copper loss expression are:

7. The method for minimum loss control of a surface-mounted permanent magnet synchronous motor based on curve fitting according to any one of claims 4 to 6, characterized in that: The process of approximate fitting analysis described in step S3 is: according to the iron loss expression and the copper loss expression, the copper loss, the total loss and the curve of the motor efficiency changing with the d-axis current are respectively drawn in the simulation software; according to the characteristics of the curve of copper loss changing with the d-axis current and the characteristics of the curve of iron loss changing with the d-axis current, combined with the verification of the second-order derivative of iron loss with respect to the d-axis current, the feasibility of the approximate fitting of the iron loss curve is determined.

8. The method for controlling minimum loss of a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 7, characterized in that: The method for performing approximate fitting on the loss expression according to the approximate fitting analysis result in step S3 to obtain the approximate fitting expression is: the iron loss is regarded as the d-axis current i d The linear function, combined with the total loss equation, obtains the total loss P loss About d-axis current i d The quadratic parabola of , as an approximate fitting expression:

9. The method for controlling minimum loss of a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 8, characterized in that: The method for obtaining the setting formula of the d-axis current reference value in step S4 is: according to the characteristics of the parabola, the minimum value of the total motor loss is obtained at the extreme point, and the setting formula of the d-axis current reference value is:

10. The method for minimum loss control of a surface-mounted permanent magnet synchronous motor based on curve fitting according to claim 9, characterized in that: The permanent magnet flux λ in the iron loss expression related parameters and the copper loss expression related parameters used in the setting formula of the d-axis current reference value f and inductor L s The way to obtain is:

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