A method for increasing the speed of permanent magnet synchronous motor based on load characteristics

Abstract

The invention discloses a speed expansion method of a permanent magnet synchronous motor based on load characteristics, comprising: during the operation of the permanent magnet synchronous motor system according to the actual working load, the load characteristics of the motor are analyzed by calculating the motor terminal voltage in real time to determine whether the d and q current loops of the motor are saturated; if the d and q current loops are not saturated, the motor is controlled by the maximum torque current ratio control mode; if the current loop is saturated, it is further determined whether the motor terminal voltage saturation is mainly caused by the increase of the q axis current under heavy load conditions, or by the increase of the motor back electromotive force; if it is the former, the PMSM speed control system adopts magnetization control to increase the motor speed; if it is the latter, the PMSM speed control system adopts weak magnetic control to increase the motor speed. The present invention can effectively avoid entering the weak magnetic control mode under heavy load conditions, resulting in the motor speed not being improved, but causing the system power module to heat up seriously, reduce efficiency, and jitter the speed.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a speed expansion 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] When PMSM is used for speed regulation, the back electromotive force of the motor will increase linearly as the motor speed increases, 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 needs to expand its speed, that 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 to achieve 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 compares the amplitude of the reference voltage vector with the set voltage limit value to determine whether the PMSM enters the weak magnetic field area, inputs the reference voltage vector amplitude and the set voltage limit value into the proportional integral regulator, and converts it into a negative d-axis current (i.e., weak magnetic field current) to achieve weak magnetic field control. However, it is shown in engineering practice that when the motor load characteristics are complex, the speed expansion of the motor through the weak magnetic field control method may not increase the speed of the motor, but instead cause serious heating of the power module, reduced motor efficiency and speed jitter. The following is an explanation of the weak magnetic field control of the voltage feedback method.

[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 present invention provides a permanent magnet synchronous motor speed expansion method based on load characteristics, further improves and strictly enforces the weak magnetic field criterion of the existing voltage feedback method, and performs magnetization or weak magnetic field control on the motor according to different situations to achieve the purpose of speed expansion of the permanent magnet synchronous motor.

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

[0008] A method for increasing the speed of a permanent magnet synchronous motor based on load characteristics, comprising:

[0009] During the operation of the permanent magnet synchronous motor system according to the actual working load, the motor terminal voltage is calculated in real time to analyze the load characteristics of the motor and determine whether the d and q current loops of the motor are saturated;

[0010] If the d and q current loops are not saturated, the PMSM speed control system uses the maximum torque current ratio control mode to control the motor;

[0011] If the d and q current loops are saturated, it is further determined whether the motor terminal voltage saturation is mainly caused by the increase of q-axis current under heavy load conditions or the increase of motor back electromotive force; if it is the former, the PMSM speed control system adopts magnetization control to increase the motor speed; if it is the latter, the PMSM speed control system adopts weak magnetic control to increase the motor speed.

[0012] Furthermore, the real-time calculation of the motor terminal voltage to analyze the load characteristics of the motor and determine whether the d and q current loops of the motor are saturated includes:

[0013] According to the d-axis and q-axis voltage u output by the current regulator 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=Ulim -u s , use Δu to construct a voltage feedback PI regulator, and use the positive and negative values ​​of Δu to determine whether the d and q current loops are saturated; when Δu is positive, the d and q current loops are saturated, and when Δu is negative, the d and q current loops are not saturated.

[0014] Furthermore, the maximum output voltage of the inverter is lim According to the relation Calculate, U dc is the DC bus voltage of the inverter.

[0015] Furthermore, if the d and q current loops are not saturated, the PMSM speed control system uses a maximum torque current ratio control mode to control the motor, including:

[0016] The PMSM speed regulation system adopts the maximum torque current ratio control mode. The speed regulator outputs the stator current i 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 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 respectively.

[0017] Furthermore, if the d and q current loops are saturated, further determining whether the motor terminal voltage saturation is mainly caused by an increase in the q-axis current under heavy load conditions or an increase in the motor back electromotive force includes:

[0018] Determine the current speed n of the motor act Is it close to the weak magnetic base speed n? fw , if n act <ζ0n fw , it indicates that the motor terminal voltage saturation is mainly caused by the increase of q-axis current under heavy load conditions; if n act ≥ζ0n fw , it indicates that the motor terminal voltage saturation is mainly caused by the increase of the motor back electromotive force; where ζ0 is the preset proportional coefficient.

[0019] Furthermore, the weak magnetic base speed n fw , which is obtained by testing the permanent magnet synchronous motor system with no-load operation through the traditional voltage feedback method.

[0020] Furthermore, if the former is the case, the PMSM speed control system adopts magnetization control to increase the motor speed, including:

[0021] The PMSM speed control system enters the magnetization control mode to increase the motor speed, and the output Δi of the voltage feedback PI regulator d Take a negative value as the DC output current i for magnetization control dfe , change i dfe and d-axis current given value Superposition, get the direct axis current i of the magnetization algorithm dref ; Magnetization algorithm quadrature axis current i qref Directly take According to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows:

[0022]

[0023]

[0024] Where i max It is the maximum current that the motor stator winding can sustainably operate.

[0025] Furthermore, when the system enters the magnetization control mode, the output Δi of the voltage feedback PI regulator d A negative value is taken as the magnetizing current. At this time, the maximum magnetizing current of the system is determined by whether the motor speed continues to increase. When the magnetizing current increases to a certain value, the speed no longer increases. The magnetizing current at this time is taken as the maximum magnetizing current.

[0026] Furthermore, if the latter is the case, the PMSM speed control system adopts weak magnetic control to increase the motor speed, including:

[0027] The instantaneous power of the system p em With motor rated power P N Compare and analyze the load conditions of the motor to further determine whether the speed control system should use weak magnetic control to increase the motor speed:

[0028] If p em >ζ1P N , indicating the input power p of the system em Very close to the motor rated power P N , the motor does not have enough output torque to drive the load to continue to increase the speed, and the system maintains the maximum torque current ratio control mode; where ζ1 is the preset proportional coefficient;

[0029] If p em <ζ1P N , indicating the instantaneous power p of the system em Less than the motor rated power P NThere 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. The output Δi of the voltage feedback 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 direct axis current i of the weak magnetic algorithm dref ; Weak field algorithm quadrature axis current i qref Directly take According to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows:

[0030]

[0031]

[0032] Where i max It is the maximum current that the motor stator winding can sustainably operate.

[0033] Furthermore, according to the formula p em =u d i d +u q i q Real-time calculation of the instantaneous power of the system, where 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.

[0034] Compared with the prior art, the present invention has the following technical features:

[0035] 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 motor terminal voltage saturation is mainly caused by the increase of the motor back electromotive force, the motor enters the weak magnetic mode to achieve the motor speed increase; if the increase of the motor terminal voltage is mainly caused by the increase of the cross-axis current under heavy load conditions, the motor enters the magnetization mode to achieve the motor speed increase. The present invention can effectively avoid entering the weak magnetic 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

[0036] 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;

[0037] Figure 2 It is a schematic diagram of the current limit circle and the voltage limit ellipse;

[0038] Figure 3 It is a schematic diagram of the MPSM electromagnetic torque and three load torque curves;

[0039] Figure 4 This is a structural diagram of the improved magnetization or weak magnetic speed expansion module of the present invention;

[0040] Figure 5 The figure is a flow chart of speed expansion of a permanent magnet synchronous motor in a specific application example of the present invention. DETAILED DESCRIPTION

[0041] The existing method of increasing the speed of permanent magnet synchronous motors is to limit the increase of the motor back electromotive force through weak magnetic field so as to increase the motor speed. However, in addition to the motor back electromotive force, the increase of motor load will also lead to an increase in the motor terminal voltage, especially under heavy load conditions, the significant increase of the quadrature axis current will lead to a significant increase in the motor terminal voltage. Under heavy load conditions, entering the weak magnetic field control mode often cannot increase the motor speed, but instead causes severe heating of the power module, reduced motor efficiency and speed jitter.

[0042] The present invention provides a method for increasing the speed of a permanent magnet synchronous motor based on load characteristics, the method comprising:

[0043] During the operation of the permanent magnet synchronous motor system according to the actual working load, the motor terminal voltage is calculated in real time to analyze the load characteristics of the motor and determine whether the d and q current loops of the motor are saturated;

[0044] If the d and q current loops are not saturated, the PMSM speed control system uses the maximum torque current ratio control mode to control the motor;

[0045] If the d and q current loops are saturated, it is further determined whether the motor terminal voltage saturation is mainly caused by the increase of q-axis current under heavy load conditions or the increase of motor back electromotive force; if it is the former, the PMSM speed control system adopts magnetization control to increase the motor speed; if it is the latter, the PMSM speed control system adopts weak magnetic control to increase the motor speed.

[0046] The specific contents of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0047] Step 1: During the operation of the permanent magnet synchronous motor system according to the actual working load, the motor terminal voltage is calculated in real time to analyze the load characteristics of the motor and determine whether the d and q current loops of the motor are saturated.

[0048] According to the d-axis and q-axis voltage u output by the current regulator 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 whether the d and q current loops are saturated; 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.

[0049] Step 2: If the d and q current loops are not saturated, the PMSM speed control system uses the maximum torque current ratio control mode to control the motor.

[0050] If the difference Δu=U lim -u s >0, indicating that the d and q current loops are not saturated, the system adopts the maximum torque current ratio (MPTA) control mode, and the speed regulator outputs the stator current i 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 ;

[0051] The maximum torque current ratio MPTA algorithm is calculated according to the following formula

[0052]

[0053] Where ψ f is the permanent magnet flux, L d , L q They are the d-axis and q-axis inductances respectively.

[0054] Step 3, if the d and q current loops are saturated, further determine whether the motor terminal voltage saturation is mainly caused by the increase of q-axis current under heavy load conditions or the increase of motor back electromotive force; if it is the former, the PMSM speed control system adopts magnetization control to increase the motor speed; if it is the latter, the PMSM speed control system adopts weak magnetic control to increase the motor speed.

[0055] If the difference Δu=U lim -u s ≤0, indicating that the d and q current loops are saturated and further determination of the motor's current speed n is required act Is it close to the weak magnetic base speed n? fw , the motor is magnetized or weakened according to the situation to achieve the speed increase of the permanent magnet synchronous motor:

[0056] Case 1: n act <ζ0n fw ,(ζ0=0.8~0.9), the current speed of the motor n act The weak magnetic base speed n is not reached or approached fw , indicating that the motor terminal voltage saturation is mainly caused by the increase of q-axis current under heavy load conditions. The speed control system enters the magnetization control mode to increase the motor speed. The output Δi of the voltage feedback PI regulator d Take a negative value as the DC output current i of the magnetization control module dfe , change i dfe and d-axis current given value Superposition, get the direct axis current i of the magnetization algorithm dref ; Magnetization algorithm quadrature axis current i qref Directly take According to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows:

[0057]

[0058]

[0059] Where i max is the maximum current that the motor stator winding can sustainably operate. fw , which is obtained by testing the permanent magnet synchronous motor system with no-load operation through the traditional voltage feedback method.

[0060] When the system enters the magnetization control mode, the output Δi of the voltage feedback PI regulator d A negative value is taken as the magnetizing current. At this time, the maximum magnetizing current of the system is determined by whether the motor speed continues to increase. When the magnetizing current increases to a certain value, the speed no longer increases. The magnetizing current at this time is taken as the maximum magnetizing current.

[0061] Case 2: n act ≥ζ0n fw ,(ζ0=0.8~0.9), the current speed of the motor n act Close to weak magnetic base speed n fw, indicating that the motor terminal voltage saturation is mainly caused by the increase of the motor back electromotive force. Then the system instantaneous power p em With motor rated power P N Compare and analyze the load conditions of the motor to further determine whether the speed control system should use weak magnetic control to increase the motor speed. em =u d i d +u q i q Real-time calculation of the instantaneous power of the system, where 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.

[0062] If p em >ζ1P N , (ζ1=0.9), indicating that the input power p of the system em Very close to the motor rated power P N , the motor does not have enough output torque to drive the load to continue to increase the speed, and the system maintains operation in MTPA mode;

[0063] If p em <ζ1P N , (ζ1=0.9), indicating that the instantaneous 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. The output Δi of the voltage feedback PI regulator d As 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 the weak magnetic algorithm dref ; Weak field algorithm quadrature axis current i qref Directly take According to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows:

[0064]

[0065]

[0066] Where i max It is the maximum current that the motor stator winding can sustainably operate.

[0067] Example

[0068] like Figures 1 to 5 It is an accompanying drawing during the specific implementation process of a permanent magnet synchronous motor speed expansion method based on load characteristics disclosed by the present invention.

[0069] like Figure 1 The present invention is a block diagram of a permanent magnet synchronous motor weakening control system based on load characteristics. In addition to units such as a dual-resistance sampling circuit, Clarke and PARK transformation, maximum torque current ratio control (MTPA), a speed loop, a dq-axis current loop, a PARK inverse transformation, a rotor position detection and speed calculation, a SVPWM calculation, and a three-phase PWM inverter, the present invention also adds a power real-time calculation module and an improved magnetization or weakening speed expansion module.

[0070] 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.

[0071] The steady-state voltage equation of the permanent magnet synchronous motor in the rotor magnetic field oriented synchronous rotating coordinate system is:

[0072]

[0073] The electromagnetic torque equation of permanent magnet synchronous motor is:

[0074]

[0075] 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;

[0076] 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:

[0077]

[0078] The d and q axis voltages are affected by the maximum output voltage U lim The restriction satisfies the relationship:

[0079]

[0080] 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 relative to the voltage drop of the d-axis and q-axis inductances. So formula (1) can be substituted into formula (4) to obtain the equation:

[0081]

[0082] 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.

[0083] 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.

[0084] 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:

[0085]

[0086] 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.

[0087] 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.

[0088] from Figure 2 The voltage limit ellipse equation shown in the figure is applied to formula (5), and the motor terminal voltage formula is

[0089]

[0090] 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 speed expansion 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.

[0091] like Figure 4 This is the structure diagram of the improved system magnetization or weak magnetic speed expansion module of 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 output voltage of the inverter 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 , when the system is running with magnetization, i dfw =0,i dfe =-Δi d ; When the system is running with weak magnetic field, i dfw =Δi d ,i dfe =0.

[0092] like Figure 5 This is a flow chart of the speed expansion of the permanent magnet synchronous motor of the present invention. The specific steps have been explained in detail in the content of the invention.

[0093] 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 method for increasing the speed of a permanent magnet synchronous motor based on load characteristics, characterized in that: include: During the operation of the permanent magnet synchronous motor system according to the actual working load, the motor terminal voltage is calculated in real time to analyze the load characteristics of the motor and determine whether the d and q current loops of the motor are saturated; If the d and q current loops are not saturated, the PMSM speed control system uses the maximum torque current ratio control mode to control the motor; If the d and q current loops are saturated, it is further determined whether the motor terminal voltage saturation is mainly caused by the increase of the q axis current under heavy load conditions or the increase of the motor back electromotive force; if it is the former, the PMSM speed control system adopts magnetization control to increase the motor speed; if it is the latter, the PMSM speed control system adopts weak magnetic control to increase the motor speed; If the former is the case, the PMSM speed control system adopts magnetization control to increase the motor speed, including: The PMSM speed control system enters the magnetization control mode to increase the motor speed, and the output Δi of the voltage feedback PI regulator d Take a negative value as the DC output current i for magnetization control dfe , change i dfe and d-axis current given value Superposition, get the direct axis current i of the magnetization algorithm dref ; Magnetization algorithm quadrature axis current i qref Directly take According to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows: Where i max It is the maximum current that the motor stator winding can sustainably operate; If the latter is the case, the PMSM speed control system uses weak magnetic control to increase the motor speed, including: The instantaneous power of the system p em With motor rated power P N Compare and analyze the load conditions of the motor to further determine whether the speed control system should use weak magnetic control to increase the motor speed: If p em >ζ1P N , indicating the input power p of the system em Very close to the motor rated power P N , the motor does not have enough output torque to drive the load to continue to increase the speed, and the system maintains the maximum torque current ratio control mode; where ζ1 is the preset proportional coefficient; If p em <ζ1P N , indicating the instantaneous 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. The output Δi of the voltage feedback 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 direct axis current i of the weak magnetic algorithm dref ; Weak field algorithm quadrature axis current i qref Directly take According to the direct axis current i dref The calculated limit value is qref Limiting, the algorithm formula is as follows: Where i max It is the maximum current that the motor stator winding can sustainably operate.

2. The method for increasing the speed of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: The real-time calculation of the motor terminal voltage to analyze the load characteristics of the motor and determine whether the d and q current loops of the motor are saturated includes: According to the d-axis and q-axis voltage u output by the current regulator d 、u q , according to the formula 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 construct a voltage feedback PI regulator, and use the positive and negative values ​​of Δu to determine whether the d and q current loops are saturated; when Δu is positive, the d and q current loops are saturated, and when Δu is negative, the d and q current loops are not saturated.

3. The method for increasing the speed of a permanent magnet synchronous motor based on load characteristics according to claim 2, characterized in that: 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.

4. The method for increasing the speed of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: If the d and q current loops are not saturated, the PMSM speed control system uses the maximum torque current ratio control mode to control the motor, including: The PMSM speed regulation system adopts the maximum torque current ratio control mode. The speed regulator outputs the stator current i 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 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 respectively.

5. The method for increasing the speed of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: If the d and q current loops are saturated, it is further determined whether the motor terminal voltage saturation is mainly caused by the increase of the q axis current under heavy load conditions or the increase of the motor back electromotive force, including: Determine the current speed n of the motor act Is it close to the weak magnetic base speed n? fw , if n act <ζ0n fw , it indicates that the motor terminal voltage saturation is mainly caused by the increase of q-axis current under heavy load conditions; if n act ≥ζ0n fw , it indicates that the motor terminal voltage saturation is mainly caused by the increase of the motor back electromotive force; where ζ0 is the preset proportional coefficient.

6. The method for increasing the speed of a permanent magnet synchronous motor based on load characteristics according to claim 5, characterized in that: The weak magnetic base speed n fw , which is obtained by testing the permanent magnet synchronous motor system with no-load operation by the traditional voltage feedback method.

7. The method for increasing the speed of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: When the system enters the magnetization control mode, the output Δi of the voltage feedback PI regulator d A negative value is taken as the magnetizing current. At this time, the maximum magnetizing current of the system is determined by whether the motor speed continues to increase. When the magnetizing current increases to a certain value, the speed no longer increases. The magnetizing current at this time is taken as the maximum magnetizing current.

8. The method for increasing the speed of a permanent magnet synchronous motor based on load characteristics according to claim 1, characterized in that: According to the formula p em =u d i d +u q i q Real-time calculation of the instantaneous power of the system, where 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.

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