A voltage feedback flux weakening control method for permanent magnet synchronous motor based on load characteristics

Abstract

The present invention discloses a method for voltage feedback weakening magnetic field control of a permanent magnet synchronous motor based on load characteristics, including: setting a motor operation mode flag to control the operation mode of the permanent magnet synchronous motor; determining the load characteristics of the permanent magnet synchronous motor based on the instantaneous power of the PMSM speed control system; determining the saturation degree of the current regulator according to the motor terminal voltage; determining the value of the motor operation mode flag according to the saturation degree of the current regulator and the load characteristics of the permanent magnet synchronous motor, thereby determining whether the motor operates in a maximum torque current ratio control mode or a weakening magnetic field control mode; wherein, in the weakening magnetic field control mode, based on the influence of different load conditions and motor speed changes on the load characteristics, corresponding weakening magnetic field control is performed on the permanent magnet synchronous motor under different conditions. The present invention improves and tightens the weakening magnetic field criterion of the existing voltage feedback method, and solves the problem that the existing judgment method may misjudge under heavy load conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a voltage feedback weakening magnetic field control method of a permanent magnet synchronous motor based on load characteristics. Background Art

[0002] In recent years, with the rapid development of power electronics technology and the improvement of the cost-effectiveness of rare earth permanent magnet materials, permanent magnet synchronous motors (PMSM) have been widely used in rail transportation, electric vehicles, indoor air purification, mine tunnel ventilation, wind power generation and other fields due to their simple structure, light weight, small moment of inertia, good control performance and high efficiency.

[0003] During PMSM speed regulation, as the motor speed increases, the motor's back electromotive force will increase linearly, and the motor terminal voltage will also increase accordingly. Since the motor control system is limited by the power supply voltage and the power module is limited by the maximum current output, the operating range of the motor will be constrained. If the PMSM speed regulation system is to be able to operate in the high-speed zone, weak magnetic control is usually required.

[0004] At present, the weak magnetic field control of PMSM speed control system has developed a variety of weak magnetic field control methods such as table lookup method, voltage feedback method, voltage feedforward method and single current regulator method. Among them, the voltage feedback method is easy to implement, has good robustness, is less dependent on motor parameters, and is convenient for achieving a smooth transition between maximum torque current ratio control and weak magnetic field control. It is a more mainstream weak magnetic field control method in engineering. The voltage feedback method determines whether the PMSM enters the weak magnetic field area by comparing the amplitude of the reference voltage vector with the set voltage limit value, and inputs the reference voltage vector amplitude and the set voltage limit value into the proportional integral regulator, which is converted into a negative d-axis current (i.e., weak magnetic field current) to achieve weak magnetic field control.

[0005] The voltage feedback method of weak magnetic field control is to limit the increase of the motor back electromotive force through weak magnetic field, thereby limiting the increase of the motor terminal voltage and increasing the motor speed. However, by analyzing the composition of the motor terminal voltage, it can be seen that in addition to the increase of the motor back electromotive force causing the increase of the motor terminal voltage, the increase of the motor load will also cause the increase of the motor terminal voltage, especially under heavy load conditions, the significant increase of the q-axis current will cause a significant increase in the motor terminal voltage. Therefore, the existing voltage feedback method uses the detection of whether the motor terminal voltage is saturated as the criterion for the PMSM to enter the weak magnetic field area, which may result in misjudgment under heavy load conditions. Entering the weak magnetic field control mode under heavy load conditions often fails to increase the motor speed, but instead causes severe heating of the power module, reduced motor efficiency, and speed jitter. Summary of the invention

[0006] The purpose of the present invention is to provide a permanent magnet synchronous motor voltage feedback weak magnetic control method based on load characteristics, so as to improve and strictly enforce the weak magnetic judgment criterion of the existing voltage feedback method and solve the problem that the existing judgment method may make misjudgment under heavy load conditions.

[0007] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0008] A permanent magnet synchronous motor voltage feedback weakening control method based on load characteristics comprises the following steps:

[0009] Set the motor operation mode flag to control the operation mode of the permanent magnet synchronous motor;

[0010] Determine the load characteristics of the permanent magnet synchronous motor based on the instantaneous power of the PMSM speed control system; determine the saturation level of the current regulator based on the motor terminal voltage;

[0011] The value of the motor operation mode flag is determined according to the saturation degree of the current regulator and the load characteristics of the permanent magnet synchronous motor, thereby determining whether the motor operates in the maximum torque current ratio control mode or the weak magnetic control mode;

[0012] Among them, in the weak magnetic field control mode, based on the influence of different load conditions and motor speed changes on load characteristics, corresponding weak magnetic field control is performed on the permanent magnet synchronous motor under different circumstances.

[0013] Furthermore, the instantaneous power of the PMSM speed control system is used to determine the load characteristics of the permanent magnet synchronous motor, including:

[0014] Real-time calculation of the instantaneous power p of the PMSM speed control system em , the motor rated power P N Multiply by a preset proportional coefficient ζ0 and then subtract p em After that, we get the difference Δp=ζ0P N -p em , Δp is used to determine whether the motor has sufficient output torque to drive the load to a higher speed.

[0015] Further, determining the saturation degree of the current regulator according to the motor terminal voltage includes:

[0016] The d-axis and q-axis voltage u output according to the current adjustment d 、u q Calculate the motor terminal voltage u s , the maximum inverter output voltage U lim Subtract u s After that, we get the difference Δu=U lim -u s, use Δu to build a voltage feedback PI regulator, and judge the saturation degree of the current regulator by the positive or negative value of Δu.

[0017] Further, the value of the motor operation mode flag is determined according to the saturation degree of the current regulator and the load characteristics of the permanent magnet synchronous motor, thereby determining whether the motor operates in the maximum torque current ratio control mode or the weak magnetic control mode, including:

[0018] Case 1: When ModeFLG=0, if both conditions of Δu<0 and Δp>0 are met at the same time, it indicates that the current regulator is saturated and the motor has sufficient output torque to drive the load to increase the speed, then the motor operation mode flag ModeFLG=1; if both conditions of Δu<0 and Δp>0 cannot be met at the same time, the motor is maintained in the maximum torque current ratio control mode;

[0019] Case 2: When ModeFLG=1, if Δu>0, it indicates that the current regulator has exited saturation, and exits the weak magnetic control mode and enters the maximum torque current ratio control mode regardless of the load condition, then ModeFLG=0.

[0020] Furthermore, when the permanent magnet synchronous motor operates in the maximum torque current ratio control mode, the stator current i is output through the motor speed regulator. s , the given value of the d-axis current regulator is calculated according to the maximum torque current ratio algorithm and the given value of the q-axis current regulator

[0021]

[0022] Where ψ f is the permanent magnet flux, L d , L q They are the d-axis and q-axis inductances respectively.

[0023] Furthermore, in the field weakening control mode, based on the influence of different load conditions and motor speed changes on load characteristics, corresponding field weakening control is performed on the permanent magnet synchronous motor under different conditions, including:

[0024] When the motor works in the weak magnetic control mode, two situations may occur: Δp<0 and Δp>0 as the load condition and motor speed change:

[0025] When Δp>0, the traditional voltage feedback method is used for weak magnetic control. The PI regulator is designed according to the difference Δu. The output Δi of the PI regulator d As the DC output current i of the field weakening control dfw , change i dfw and d-axis current given value Superposition, get the weak magnetic control direct axis current idref ; Cross-axis current i of weak magnetic control qref Directly take the given value of the q-axis current regulator According to the direct axis current i dref The calculated limit value is qref Clipping;

[0026] When Δp<0, the DC output current i of the weak magnetic control is dfw Take the maximum value Δi d_max , change i dfw and d-axis current given value Superposition, get the direct axis current i of weak magnetic control dref ; Cross-axis current i of weak magnetic control qref Directly take Similarly, according to the direct axis current i dref The calculated limit value is qref Limiting.

[0027] Furthermore, the maximum DC output current Δi of the weak magnetic control module d_max The value formula is:

[0028]

[0029] Where Δi d (n-1), Δi d_max (n-1) are the DC output current value and maximum value of the weak magnetic control in the n-1th iteration operation, Δi d (n), Δi d_max (n) are the DC output current value and maximum value of the weak magnetic control in the nth iteration operation.

[0030] Compared with the prior art, the present invention has the following technical features:

[0031] The present invention analyzes the load characteristics of the motor by calculating the input power of the system in real time, and further analyzes the main reason for the increase of the motor terminal voltage. If the saturation of the motor terminal voltage is mainly caused by the increase of the motor back electromotive force, the motor enters the weak magnetic field control, and the value of the weak magnetic field current is determined in two cases based on the load characteristics; if the increase of the motor terminal voltage is mainly caused by the increase of the q-axis current under heavy load conditions, the speed regulation system is set not to enter the weak magnetic field control mode to prevent entering the weak magnetic field control mode under heavy load conditions, resulting in the motor speed not being increased, but causing serious heating of the system power module, reduced efficiency, speed jitter and other problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a system block diagram of the permanent magnet synchronous motor weak magnetic control method based on load characteristics of the present invention;

[0033] Figure 2 It is a schematic diagram of the current limit circle and the voltage limit ellipse;

[0034] Figure 3 It is a schematic diagram of the MPSM electromagnetic torque and three load torque curves;

[0035] Figure 4 This is a structural diagram of an improved voltage feedback weak magnetic control module proposed in one embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention provides a permanent magnet synchronous motor voltage feedback weakening magnetic field control method based on load characteristics, which further improves and strictly enforces the weakening magnetic field criterion of the existing voltage feedback method based on the load characteristics of the motor; the method of the present invention comprises:

[0037] Set the motor operation mode flag to control the operation mode of the permanent magnet synchronous motor;

[0038] Determine the load characteristics of the permanent magnet synchronous motor based on the instantaneous power of the PMSM speed control system; determine the saturation level of the current regulator based on the motor terminal voltage;

[0039] The value of the motor operation mode flag is determined according to the saturation degree of the current regulator and the load characteristics of the permanent magnet synchronous motor, thereby determining whether the motor operates in the maximum torque current ratio control mode MPTA or the weak magnetic control mode;

[0040] Among them, in the weak magnetic field control mode, based on the influence of different load conditions and motor speed changes on load characteristics, corresponding weak magnetic field control is performed on the permanent magnet synchronous motor under different circumstances.

[0041] The specific implementation steps of the present invention are further described in detail below with reference to the accompanying drawings.

[0042] Step 1: Set the motor operation mode flag to control the operation mode of the permanent magnet synchronous motor.

[0043] A motor operation mode flag ModeFLG is set. When ModeFLG=0, the motor operates in the maximum torque current ratio (MPTA) control mode. When ModeFLG=1, the motor operates in the weak magnetic control mode. The initial value of ModeFLG is set to 0.

[0044] Step 2: Determine the load characteristics of the permanent magnet synchronous motor based on the instantaneous power of the PMSM speed control system.

[0045] According to the formula p em =u d i d +u q i qCalculate the instantaneous power of the PMSM speed control system in real time and convert the motor rated power P N Multiply by a preset proportionality factor and then subtract p em After that, we get the difference Δp=ζ0P N -p em , (ζ0=0.9), and Δp is used to determine whether the motor has sufficient output torque to drive the load to a higher speed; where u d 、u q is the d-axis and q-axis voltage of the output of the current regulator, i d is the actual feedback value of the d-axis current, i q is the actual feedback value of the q-axis current.

[0046] Step 3: Determine the saturation level of the current regulator based on the motor terminal voltage.

[0047] The d-axis and q-axis voltage u output according to the current adjustment d 、u q , according to the formula Calculate the motor terminal voltage u s , the maximum inverter output voltage U lim Subtract u s After that, we get the difference Δu=U lim -u s , use Δu to build a voltage feedback PI regulator, and use the positive and negative values ​​of Δu to determine the saturation of the current regulator; the maximum output voltage of the inverter is U lim According to the relation Calculate, U dc is the DC bus voltage of the inverter.

[0048] Step 4, determining the value of the motor operation mode flag ModeFLG according to the saturation degree of the current regulator and the load characteristics of the permanent magnet synchronous motor, thereby determining whether the motor operates in the maximum torque current ratio control mode MPTA or the weak magnetic control mode;

[0049] Among them, in the weak magnetic field control mode, based on the influence of different load conditions and motor speed changes on load characteristics, corresponding weak magnetic field control is performed on the permanent magnet synchronous motor under different circumstances.

[0050] There are two situations:

[0051] Case 1: When ModeFLG=0, if both conditions of Δu<0 and Δp>0 are met at the same time, it indicates that the current regulator is saturated and the motor has sufficient output torque to drive the load to increase the speed, then ModeFLG=1; Different from the traditional conditions for entering the weak magnetic control mode, if both conditions of Δu<0 and Δp>0 cannot be met at the same time, the motor does not enter the weak magnetic control mode and maintains operation in the MPTA control mode;

[0052] Case 2: When ModeFLG=1, if Δu>0, it indicates that the current regulator has exited saturation and exits the weak magnetic control mode regardless of the load condition, then ModeFLG=0;

[0053] When ModeFLG=0, go to step 4.1; when ModeFLG=1, go to step 4.2.

[0054] Step 4.1: The motor operates in the maximum torque to current ratio (MPTA) control mode, and the stator current i is output through the motor speed regulator. s , the given value of the d-axis current regulator is calculated according to the maximum torque current ratio algorithm and the given value of the q-axis current regulator The DC output current i of the weak magnetic control module in MPTA mode dfw is zero, according to the given value of d and q axis current regulator And the actual feedback value i d 、i q The d-axis and q-axis currents are controlled by PI, and the output voltages of the d-axis and q-axis current regulators are u d 、u q ; The maximum torque current ratio MPTA algorithm is calculated according to the following formula

[0055]

[0056] Where ψ f is the permanent magnet flux, L d , L q They are the d-axis and q-axis inductances respectively;

[0057] After step 4.1, return to step 2.

[0058] Step 4.2, the motor enters the weak magnetic control mode. Although in step 4, when ModeFLG = 0, the condition of Δp>0 must be met to enter the weak magnetic control mode, but when ModeFLG = 1, two situations will appear: Δp<0 and Δp>0 as the load condition and motor speed change:

[0059] Case 1: When Δp>0, it indicates that the input power p of the system em Less than the motor rated power P N There is a certain margin, the motor has enough output torque to drive the load to a higher speed, and the weak magnetic control is performed according to the traditional voltage feedback method. lim -u s Design a PI regulator. The output of the PI regulator Δi dAs the DC output current i of the weak magnetic control module dfw , change i dfw and d-axis current given value Superposition, get the direct axis current i of weak magnetic control dref ; Cross-axis current i of weak magnetic control qref Directly take According to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows:

[0060]

[0061]

[0062] Case 2: When Δp<0, it indicates that the input power p of the system em Very close to the motor rated power P N , increasing the weak magnetic current to make the motor output greater torque to drive the load and increase the speed, the space is limited. At this time, the DC output current i of the weak magnetic control module dfw Take the maximum value Δi d_max , change i dfw and d-axis current given value Superposition, get the direct axis current i of the weak magnetic algorithm dref ; Weak field algorithm quadrature axis current i qref Directly take Similarly, according to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows:

[0063]

[0064]

[0065] Where i max It is the maximum current that the motor stator winding can sustainably operate.

[0066] Among them, the maximum DC output current Δi of the weak magnetic control module d_max It is obtained in the iterative operation of the first case, and its value formula is:

[0067]

[0068] Where Δi d (n-1), Δi d_max (n-1) are the DC output current value and maximum value of the weak magnetic control module in the n-1th iteration operation, Δi d (n), Δi d_max(n) are respectively the DC output current value and the maximum value of the weak magnetic control module in the nth iteration operation;

[0069] After step 4.2, return to step 2.

[0070] Example

[0071] See also Figures 1 to 4 , which is a schematic diagram of a specific application embodiment of the method of the present invention.

[0072] like Figure 1 This is a block diagram of a permanent magnet synchronous motor weakening control system based on load characteristics of the present invention. In addition to the dual-resistance sampling circuit, Clarke and PARK transformation, maximum torque current ratio control (MTPA), speed loop, dq axis current loop, PARK inverse transformation, rotor position detection and speed calculation, SVPWM calculation and three-phase PWM inverter and other units, the present invention also adds a power real-time calculation module and an improved voltage feedback weakening control module.

[0073] The idea of ​​the present invention is to detect the motor load in real time on the basis of the current limit circle and voltage limit ellipse of the traditional weak magnetic control, and to add the judgment of whether the motor output electromagnetic is greater than the load torque, so as to judge whether the motor can increase the speed.

[0074] The steady-state voltage equation of the permanent magnet synchronous motor in the rotor magnetic field oriented synchronous rotating coordinate system is:

[0075]

[0076] The electromagnetic torque equation of permanent magnet synchronous motor is:

[0077]

[0078] In formulas (1) and (2), u d is the output voltage of the d-axis current regulator, u q is the output voltage of the q-axis current regulator, i d is the actual feedback value of the d-axis current, i q is the actual feedback value of the q-axis current; R is the stator resistance; L d , L q are the d-axis and q-axis inductances respectively; ω is the electrical angular velocity of the motor, ψ f is the permanent magnet flux; p n is the number of motor pole pairs;

[0079] The d and q axis currents are affected by the maximum current i that the motor stator winding can sustainably operate. max The restriction satisfies the relationship:

[0080]

[0081] The d and q axis voltages are affected by the maximum output voltage U lim The restriction satisfies the relationship:

[0082]

[0083] Where U dc is the DC bus voltage of the inverter. In the high-speed region, the voltage drop of the stator resistance can be ignored compared with the voltage drop of the d-axis and q-axis inductances. So we can substitute formula (1) into formula (4) to get the equation:

[0084]

[0085] Formula (3) is the current limit circle equation during motor operation, and formula (5) is the voltage limit ellipse equation. The current limit circle equation, the voltage limit ellipse, and the constant electromagnetic torque curve cluster obtained by formula (2) are plotted in a coordinate system with the q-axis current as the vertical axis and the d-axis current as the horizontal axis, as shown in Figure 2 As shown in the figure, the traditional vector control of permanent magnet synchronous motor is based on Figure 2 Different control methods are adopted for medium and low speed areas and high speed areas respectively.

[0086] But if Figure 2 The figure shown only discusses the problem of limited current and voltage of the control system, and does not discuss the problem of limited electromagnetic torque output by the motor. In fact, the electromagnetic torque output by any motor is limited. Whether the motor can increase its speed depends on the relationship between the electromagnetic torque output by the motor and the load torque, such as Figure 3 Schematic diagram of MPSM electromagnetic torque and three load torque curves. Figure 3 The electromagnetic torque output by the motor is constant when the speed is lower than the weakening magnetic inflection point. At this time, the motor runs in constant torque mode, and the given speed is often achieved by adopting the MTPA control mode. When the motor speed is higher than the weakening magnetic inflection point speed, the motor output torque gradually decreases, and the motor runs in constant power control mode. Traditional weak magnetic control is for Figure 3 The study is based on the medium load and light load conditions shown in the figure. That is, when the motor speed is higher than the weakening magnetic inflection point speed, the motor output torque is less than the load torque. However, the actual load conditions are very complicated, such as the wind turbine running against the wind, electric vehicles running on a slope, etc. Under normal circumstances, the wind turbine load torque curve is as follows Figure 3 The medium load curve, when the fan is in strong headwind, the fan load torque curve is as follows Figure 3 The heavy load curve shows that the motor speed is lower than the weakening magnetic inflection point speed, but the motor output torque is already less than the load torque. If the traditional weakening magnetic control method is still used under heavy load conditions, the motor speed may not be increased, which may cause serious heating of the power module, reduced motor efficiency, and speed jitter.

[0087] Therefore, the present invention Figure 2 A real-time detection curve for motor load torque is added, and its calculation is based on the following formula:

[0088]

[0089] where u d is the output of the d-axis current regulator, u q is the output of the q-axis current regulator, i d is the actual feedback value of the d-axis current, i q is the actual feedback value of the q-axis current, T em The load torque of the motor, ω is the electrical angular velocity of the motor, p em Input power to the system.

[0090] In engineering applications, we cannot simply use the current motor speed increase or decrease to judge Figure 2 The output electromagnetic torque of the motor is less than or greater than the load torque. However, the rated power P of the motor N It is known to the user, so the present invention uses the system input power p em and motor rated power P N The relationship between the output torque and the speed of the load is used to determine whether the motor has sufficient output torque to drive the load to a higher speed.

[0091] from Figure 2 The voltage limit ellipse equation shown in the figure is applied to formula (5), and the motor terminal voltage formula is

[0092]

[0093] The above formula shows that the motor terminal voltage u s In addition to the motor back EMF (ωψ m ) as the main component, |ωL q i q | is also a major component. The traditional voltage feedback weak magnetic control method uses whether the motor terminal voltage reaches the saturation value as the criterion for weak magnetic control. q i q |When the term is relatively large, there may be false disconnection, especially when the motor is under heavy load. The present invention analyzes the load characteristics of the motor by calculating the input power of the PMSM speed control system in real time. If the terminal voltage is saturated when the input power is relatively small, the increase in the motor terminal voltage is mainly caused by the increase in the motor back electromotive force; if the terminal voltage is saturated when the input power is close to the rated power of the motor, it may be caused by the increase in the back electromotive force or the increase in the q-axis current. q i q|term increases, and at this time it is necessary to improve and strictly enforce the weak magnetic field criterion of the existing voltage feedback method.

[0094] like Figure 4 This is the structural diagram of the voltage feedback weak magnetic control module improved by the present invention. Figure 4 Medium current regulator output voltage u d 、u q , according to the formula Get the total voltage vector amplitude u s , the maximum inverter output voltage U lim Subtract u s After that, according to the difference Δu=U lim -u s Design a PI regulator. The output of the PI regulator Δi d , and then determine the DC output current i of the weak magnetic control module in two cases dfw When the system input power p em Less than the motor rated power P N When there is a certain margin, i dfw =Δi d , when the system input power p em Very close to the motor rated power P N When the magnetic field weakening current is increased, the motor cannot output a larger torque to drive the load to a higher speed. dfw Take the maximum value Δi d_max .

[0095] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A voltage feedback weakening magnetic field control method for a permanent magnet synchronous motor based on load characteristics, characterized in that: The following steps are involved: Set the motor operation mode flag to control the operation mode of the permanent magnet synchronous motor; Determine the load characteristics of the permanent magnet synchronous motor based on the instantaneous power of the PMSM speed control system; determine the saturation level of the current regulator based on the motor terminal voltage; The value of the motor operation mode flag is determined according to the saturation degree of the current regulator and the load characteristics of the permanent magnet synchronous motor, thereby determining whether the motor operates in the maximum torque current ratio control mode or the weak magnetic control mode; Among them, in the weak magnetic control mode, based on the influence of different load conditions and motor speed changes on load characteristics, the permanent magnet synchronous motor is subjected to corresponding weak magnetic control under different conditions; The method of determining the load characteristics of the permanent magnet synchronous motor based on the instantaneous power of the PMSM speed control system includes: Real-time calculation of the instantaneous power p of the PMSM speed control system em , the motor rated power P N Multiply by a preset proportional coefficient ζ0 and then subtract p em After that, we get the difference Δp=ζ0P N -p em , using Δp to determine whether the motor has sufficient output torque to drive the load to a higher speed; Determining the saturation degree of the current regulator according to the motor terminal voltage includes: The d-axis and q-axis voltage u output according to the current regulation d 、u q Calculate the motor terminal voltage u s , the maximum output voltage of the inverter U lim Subtract u s After that, we get the difference Δu=U lim -u s , use Δu to build a voltage feedback PI regulator, and judge the saturation degree of the current regulator by the positive or negative value of Δu; In the magnetic field weakening control mode, based on the influence of different load conditions and motor speed changes on load characteristics, corresponding magnetic field weakening control is performed on the permanent magnet synchronous motor under different conditions, including: When the motor works in the weak magnetic control mode, two situations may occur: Δp<0 and Δp>0 as the load condition and motor speed change: When Δp>0, the traditional voltage feedback method is used for weak magnetic control. The PI regulator is designed according to the difference Δu. The output Δi of the PI regulator d As the DC output current i of the field weakening control dfw , change i dfw and d-axis current given value Superposition, get the weak magnetic control direct axis current i dref ; Cross-axis current i of weak magnetic control qref Directly take the given value of the q-axis current regulator According to the direct axis current i dref The calculated limit value is qref Clipping; When Δp<0, the DC output current i of the weak magnetic control is dfw Take the maximum value Δi d_max , change i dfw and d-axis current given value Superposition, get the direct axis current i of weak magnetic control dref ; Cross-axis current i of weak magnetic control qref Directly take Similarly, according to the direct axis current i dref The calculated limit value is qref Limiting.

2. The method for voltage feedback weakening magnetic field control of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: The value of the motor operation mode flag is determined according to the saturation degree of the current regulator and the load characteristics of the permanent magnet synchronous motor, thereby determining whether the motor operates in the maximum torque current ratio control mode or the weak magnetic control mode, including: Case 1: When ModeFLG=0, if both conditions of Δu<0 and Δp>0 are met at the same time, it indicates that the current regulator is saturated and the motor has sufficient output torque to drive the load to increase the speed, then the motor operation mode flag ModeFLG=1; if both conditions of Δu<0 and Δp>0 cannot be met at the same time, the motor maintains the maximum torque current ratio control mode; Case 2: When ModeFLG=1, if Δu>0, it indicates that the current regulator has exited saturation, and exits the weak magnetic control mode and enters the maximum torque current ratio control mode regardless of the load condition, then ModeFLG=0.

3. The method for voltage feedback weakening magnetic field control of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: When the permanent magnet synchronous motor operates in the maximum torque current ratio control mode, the stator current i is output through the motor speed regulator. s , the given value of the d-axis current regulator is calculated according to the maximum torque current ratio algorithm and the given value of the q-axis current regulator Where ψ f is the permanent magnet flux, L d , L q They are the d-axis and q-axis inductances respectively.

4. The method for voltage feedback weakening magnetic field control of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: Maximum DC output current Δi of the weak magnetic control module d_max The formula for the value of is: Where Δi d (n-1), Δi d_max (n-1) are the DC output current value and maximum value of the weak magnetic control in the n-1th iteration operation, Δi d (n), Δi d_max (n) are the DC output current value and maximum value of the weak magnetic control in the nth iteration operation.

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