Method and system for adjusting speed of motor by adjusting flux weakening

Abstract

The invention relates to the technical field of motor speed regulation, in particular to a method and system for regulating the speed of a motor by adjusting flux weakening, and the method comprises the following steps: detecting the operation state of the motor, and obtaining the operation state data; calculating a voltage limit ellipse and a current limit circle according to the operation state data; calculating a current vector trajectory which simultaneously meets the constraints of the voltage limit ellipse and the current limit circle; calculating a motor target rotating speed according to the motor operation state data and the motor parameters; and by adjusting the direct-axis current component and the quadrature-axis current component of the motor stator and combining the target rotating speed, controlling the stator current vector to move according to the calculated current vector trajectory, thereby realizing flux-weakening speed expansion. A voltage limit ellipse, a current limit circle and a flux weakening control current vector track are calculated, so that direct-axis and quadrature-axis current components of the stator can be accurately adjusted under different working conditions, the rotating speed of the motor is controlled within a target range, and the problem that the speed adjusting precision is not high enough is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor speed regulation, and particularly relates to a method and system for regulating the speed of a motor by adjusting field weakening. Background Art

[0002] In the field of motor control, speed regulation technology is of great importance. It is the key to ensuring the stable operation of motors according to different working conditions requirements and is widely used in various industrial production, transportation and other scenarios.

[0003] Traditional motor speed regulation methods, such as voltage control and frequency control, although they can meet some speed regulation requirements, will have problems of reduced efficiency and increased energy consumption under high-speed operation or low-load conditions. At the same time, when the DC side voltage of the inverter reaches the maximum value, it will cause the current regulator to saturate. To expand the speed regulation range and achieve constant power speed regulation during high-speed operation above the base speed, field weakening control becomes a necessary means.

[0004] Although field weakening speed regulation technology has broad prospects in fields such as electric vehicles and industrial automation due to advantages such as fast response speed and wide speed regulation range, there are still many deficiencies in the existing technology. For example, the speed regulation accuracy is poor and it is difficult to meet the requirements of high-precision control; under different load and speed conditions, parameters need to be frequently adjusted, and the operation is cumbersome; and the stability of the control system is poor and it is easily affected by external interference. Summary of the Invention

[0005] To solve the above problems existing in the existing field weakening speed regulation method, the present invention provides a method and system for regulating the speed of a motor by adjusting field weakening.

[0006] In a first aspect, the technical solution of the present invention provides a method for regulating the speed of a motor by adjusting field weakening, including the following steps: Detect the operating state of the motor and obtain the operating state data; Calculate the voltage limit ellipse and the current limit circle according to the operating state data; Calculate the current vector trajectory that simultaneously satisfies the constraints of the voltage limit ellipse and the current limit circle; Calculate the target speed of the motor according to the motor operating state data and the motor parameters; By adjusting the direct-axis current component and the quadrature-axis current component of the motor stator, and combining the target speed of the motor, control the stator current vector to move along the calculated current vector trajectory to achieve field weakening speed expansion.

[0007] As a further limitation of the technical solution of the present invention, the operating state data includes the current actual speed, current and voltage; the step of calculating the voltage limit ellipse and the current limit circle according to the operating state data includes: Calculate the voltage limit ellipse equation according to the parameters and operating state of the motor; Calculate the current limit circle equation according to the rated current and operating state of the motor.

[0008] As a further limitation of the technical solution of the present invention, when the stator voltage reaches the limit of the inverter output voltage, the voltage limit ellipse equation is:

[0009] In the formula, and are the inductances of the stator quadrature axis and direct axis respectively; and are the stator quadrature axis current component and direct axis current component respectively; is the magnetic flux of the motor permanent magnet; is the limit of the inverter output voltage, that is, the stator terminal phase voltage, , is the DC bus voltage, is the rotational speed.

[0010] As a further limitation of the technical solution of the present invention, when the stator current reaches the rated current, the equation of the current limit circle is:

[0011] In the formula, is the current vector amplitude, and are the stator quadrature axis current component and direct axis current component respectively, is the rated current of the motor.

[0012] As a further limitation of the technical solution of the present invention, the steps of calculating the current vector trajectory that simultaneously satisfies the voltage limit ellipse and current limit circle constraints specifically include: Judge whether the motor is operating below the base speed according to the current actual rotational speed of the motor; If so, determine that the motor is operating in the constant torque region, and select the current vector trajectory inside the current limit circle to ensure the maximum torque output; If not, determine that the motor enters the field weakening speed regulation region, and calculate the current vector trajectory so that the current vector trajectory is between the voltage limit ellipse and the current limit circle.

[0013] As a further limitation of the technical solution of the present invention, the calculation formula of the current vector trajectory is: .

[0014] The calculation formula of the motor target rotational speed is:

[0015] In the formula, p is the number of pole pairs of the motor.

[0016] As a further limitation of the technical solution of the present invention, the steps of realizing field-weakening speed regulation by adjusting the direct-axis current component and quadrature-axis current component of the motor stator and combining with the target speed to control the stator current vector to move along the calculated current vector trajectory include: According to the difference between the given voltage of the electromotive force and the feedback voltage of the electromotive force calculator, adjust the input of the excitation current regulator, change the excitation magnetic flux of the motor, and further adjust the direct-axis current component of the stator; at the same time, according to the deviation between the target speed and the actual speed, and the current vector trajectory, adjust the armature voltage of the motor, so as to control the quadrature-axis current component of the stator; through the coordinated adjustment of the direct-axis and quadrature-axis current components of the stator, make the stator current vector move along the calculated current vector trajectory, and realize the field-weakening speed regulation of the motor.

[0017] In a second aspect, the technical solution of the present invention further provides a speed regulation system for controlling field-weakening, the system includes a motor, and the method described in the first aspect is used to perform speed regulation control on the motor.

[0018] As a further limitation of the technical solution of the present invention, the system further includes a first potentiometer, a second potentiometer, a speed regulator, a first current regulator, a first converter, and a tachogenerator coaxially connected to the motor and rotating with the motor; The tachogenerator is connected to the speed regulator, the speed regulator is connected to the first current regulator, the first current regulator is connected to the first converter, the power supply supplies power to the motor through the first converter, a first acquisition module is arranged on the connection line between the power supply and the first converter, a second acquisition module is arranged at the power supply end of the motor, the second acquisition module is connected to the electromotive force calculator through a voltage isolator, the first acquisition module is connected to the electromotive force calculator, and the electromotive force calculator is connected to the excitation current regulator through an electromotive force regulator; the excitation current regulator is connected to the excitation power electronic converter through a function generator, and the excitation power electronic converter is connected to the coil of the motor; a third acquisition module is arranged at the output end of the excitation power electronic converter, and the third acquisition module is connected to the excitation current regulator; the system uses the method described in the first aspect to perform speed regulation control on the motor.

[0019] The first potentiometer is used to provide a speed given voltage to the speed regulator, and the second potentiometer is used to provide an electromotive force given voltage to the electromotive force regulator; The difference between the speed voltage fed back by the tachogenerator and the speed reference voltage is input to the speed regulator. The difference between the speed regulating voltage output by the speed regulator, i.e., the current reference voltage, and the voltage collected by the first acquisition module is input to the first current regulator. The first converter supplies power to the motor according to the output voltage of the first current regulator. After the voltage collected by the second acquisition module passes through the voltage isolator and is subtracted from the voltage collected by the first acquisition module, it is input to the electromotive force calculator; after the output voltage of the electromotive force calculator is subtracted from the electromotive force reference voltage, it is input to the electromotive force regulator. After the output voltage of the electromotive force regulator is subtracted from the voltage collected by the third acquisition module, it is input to the field current regulator. The output of the field current regulator passes through the function generator and the field power electronic converter to control the field current of the motor, thereby regulating the magnetic flux of the motor.

[0020] The speed regulation process of this system includes: In the field weakening speed increase stage above the base speed, when the motor speed increases and the back electromotive force increases, at this time, the electromotive force regulator outputs the field current reference voltage according to the comparison result between the electromotive force reference voltage and the feedback voltage output by the electromotive force calculator. The difference between the voltage collected by the third acquisition module and the field current reference voltage is input to the field current regulator. By adjusting the input of the field current regulator, the field magnetic flux of the motor is changed, affecting the direct-axis current component of the stator. At the same time, the speed regulator and the first current regulator adjust the armature voltage of the motor through the first converter according to the deviation between the target speed and the actual speed and the requirements of the current vector trajectory, thereby controlling the quadrature-axis current component of the stator. Through the coordinated regulation of the direct-axis and quadrature-axis current components of the stator, the stator current vector moves along the calculated current vector trajectory, realizing the field weakening speed increase of the motor and enabling the motor to operate stably at a higher speed.

[0021] Detect the voltage of the motor, and the electromotive force calculator detects the voltage and current , and uses the formula: to indirectly detect the electromotive force, and the electromotive force calculator calculates the feedback signal of the electromotive force It is used to subtract the given electromotive force voltage and then input it into the electromotive force regulator. The tachogenerator detects the motor speed. After obtaining the operating state data such as voltage, current, and speed, the voltage limit ellipse and current limit circle calculated in combination with the inherent parameters of the motor determine the boundary range of voltage and current during motor operation, providing constraint conditions for subsequent control. After obtaining the data of the voltage limit ellipse and current limit circle, the current vector trajectory that satisfies both constraint conditions is calculated. This trajectory determines the position where the stator current vector of the motor should be in different operating states to ensure the safe and efficient operation of the motor. By adjusting the first potentiometer, the speed given voltage is changed, and this voltage is compared and operated in the speed regulator with the actual speed feedback signal of the motor detected by the tachogenerator. The speed regulator combines the rated parameters of the motor and the current operating state data (such as current, voltage, etc.) to calculate the target speed of the motor, outputs it to the current regulator, and then outputs the corresponding voltage to the motor through the first converter.

[0022] The beneficial effects of the technical solution of the present invention are as follows: Based on the motor operating state parameters and the motor's own parameters, the voltage limit ellipse, current limit circle, and field-weakening control current vector trajectory are calculated, enabling precise adjustment of the direct-axis and quadrature-axis current components of the stator under different working conditions, thereby controlling the motor speed within the target range and effectively solving the problem of insufficient speed regulation accuracy.

[0023] According to the real-time operating state of the motor, the stator current vector is automatically adjusted, eliminating the need for manual frequent intervention to adjust parameters, greatly simplifying the operation process, reducing the operation difficulty and workload. By detecting the motor operating state and adjusting the current vector trajectory in real time, the saturation of the current regulator is avoided, ensuring the stable operation of the motor under various working conditions. By seeking the maximum torque / current trajectory, the motor can operate with the minimum stator current under different torque requirements, reducing the energy consumption of the motor. During the field-weakening control process, the stator current components are reasonably adjusted to maintain voltage balance and improve the operating efficiency of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present invention, the drawings required for description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a flowchart of the method provided by the embodiment of the present invention.

[0026] Figure 2 It is a diagram showing the stator current vector trajectory of a cylindrical rotor motor.

[0027] Figure 3 It is a diagram of the constant torque and maximum torque current trajectory.

[0028] Figure 4 It is the power output characteristic diagram of a permanent magnet synchronous motor.

[0029] Figure 5 It is the circuit diagram of an operational amplifier for analog implementation of an electromotive force calculator.

[0030] Figure 6 It is the structure diagram of the speed loop in a field-weakening control system.

[0031] Figure 7 It is the speed control system diagram for controlling field weakening. Specific implementation manner

[0032] To make the objectives, features, and advantages of the present invention more obvious and understandable, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the specific embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without making creative efforts belong to the scope of protection of this application.

[0033] As Figure 1 shown, an embodiment of the present invention provides a method for adjusting the speed of a motor by adjusting field weakening, including the following steps: S1: Detect the operating state of the motor and obtain the operating state data; including parameters such as speed, current, and voltage; S2: Calculate the voltage limit ellipse and current limit circle according to the operating state data; During high-performance field-weakening speed regulation, in different working regions, due to different control laws, in order to obtain the optimal control effect, different current and voltage vector trajectories are usually selected. Therefore, the current and voltage vector trajectories at this time need to be calculated. The voltage limit ellipse is restricted by the output voltage of the inverter. When the PMSM operates stably, the voltage vector amplitude is: (1) When the PMSM operates stably and the stator resistance voltage drop is ignored, the voltage equation can be simplified to: (2) According to equations (1) and (2), we get: (3) In the formula, and are the inductances of the stator quadrature axis and direct axis respectively; and are the stator quadrature axis current component and direct axis current component respectively; is the magnetic flux linkage of the motor permanent magnet; is the limit of the inverter output voltage, i.e., the stator terminal phase voltage, , is the DC bus voltage, is the rotational speed.

[0034] When the current regulator saturates, the stator terminal phase voltage is = At this time, the rotational speed The corresponding operating trajectory at is the ellipse in the dq coordinate system shown in Equation (3), and it is called the voltage limit ellipse at the rotational speed At a certain rotational speed The stator current can only operate within this elliptical trajectory. And as the rotational speed increases, the voltage limit ellipse will gradually shrink.

[0035] Limited by the inverter output current and the rated current of the motor itself, when the PMSM operates stably, the magnitude of the current vector is: (4) In the formula, is the magnitude of the current vector, and are the quadrature-axis current component and direct-axis current component of the stator respectively, is the rated current of the motor.

[0036] S3: Calculate the current vector trajectory that simultaneously satisfies the voltage limit ellipse and current limit circle constraints; The current vector trajectory is a circle centered at the origin in the dq coordinate system, and this circle is called the current limit circle, as Figure 2 shown. When the motor operates stably, the stator current vector can neither exceed the voltage limit ellipse nor exceed the current limit circle, and must be within the voltage limit ellipse and current limit circle. As when, the range of the current vector is restricted within the sawtooth region.

[0037] When the motor operates at a certain rotational speed , from the voltage balance equation: (6) The field-weakening control current vector trajectory can be obtained: (7) S4: Calculate the target rotational speed of the motor according to the motor operating state data and motor parameters; The calculation formula for the target rotational speed of the motor is: (8) In the formula, p is the number of pole pairs of the motor.

[0038] S5: By adjusting the direct-axis current component and quadrature-axis current component of the motor stator, and combining with the target speed of the motor, control the stator current vector to move along the calculated current vector trajectory, so as to achieve field-weakening speed increase.

[0039] According to Figure 3 it can be known that the constant-torque trajectory of a non-salient-pole motor is , a series of horizontal lines parallel to the d-axis on the plane. It is not only axisymmetric about , but also positive in the second quadrant (operating in the motor state) and negative in the third quadrant (operating in the braking state). Whether in the second quadrant or the third quadrant, the stator current vector corresponding to any point on the constant-torque trajectory of a certain command value results in the same value of the motor torque. This involves the problem of seeking a stator current vector with the smallest amplitude, because the smaller the stator current, the higher the motor efficiency and the lower the required inverter capacity. In , the plane diagram, the point on the constant-torque trajectory of a certain command value that is closest to the coordinate origin is the space vector of the minimum current required to generate this torque. Connecting the minimum current points required to generate different torque values forms the maximum torque / current trajectory of the motor. It can be easily known from this: the maximum torque / current trajectory of a non-salient-pole motor is axis. Therefore, the = 0 control of a non-salient-pole motor is the maximum torque / current ratio control.

[0040] In some embodiments, the steps of calculating the current vector trajectory that simultaneously satisfies the voltage limit ellipse and current limit circle constraints specifically include: Judge whether the motor is operating below the base speed according to the current actual speed of the motor; If so, determine that the motor is operating in the constant-torque region, and select the current vector trajectory inside the current limit circle to ensure the maximum torque output; If not, determine that the motor enters the field-weakening speed regulation region, and calculate the current vector trajectory so that the current vector trajectory is between the voltage limit ellipse and the current limit circle.

[0041] Figure 4 In interval 1 is the = 0 normal control interval, and interval 2 is the field-weakening speed increase control interval.

[0042] The following takes the stator current vector trajectory Figure 3 shown in Figure 3 as an example to analyze the field-weakening speed increase control process of a non-salient-pole PMSM. Figure 3 In the torque corresponding to point is , which is the motor at speed The maximum torque output at this time (both the voltage and current reach the limit values, so is the turning speed at the maximum torque of the motor). When the speed increases to ( ), the maximum torque / current locus intersects the voltage limit ellipse at point B, and the corresponding torque is . If the stator current vector deviates from the maximum torque / current locus at this time and moves from point B along the voltage limit ellipse to point C, the current does not reach the limit value during this process, but when moving to point C, a larger torque ( ) will be output, thereby increasing the output power of the motor when operating above the turning speed. If the speed is to be further increased, the stator current can move from point C along the current limit circle to point, but the torque will decrease. It can be seen from the analysis that when the stator current vector changes from B→C→ , gradually increases, weakening the permanent magnet flux. Under the condition of constant inverter capacity, the purpose of weak magnetic speed expansion is achieved. And the higher the speed, the smaller the output torque. Region 3 is when reaching (i.e., the output reaches the maximum output power), if speed expansion is still required, it is necessary to change according to the locus of → . However, if the center coordinate ( , 0) falls outside the current limit circle, that is, , then this region does not exist.

[0043] For the weak magnetic control mode to satisfy Equation (7), as Figure 2 shown, by controlling , the output power of the converter can be made constant, and the operating range of the motor can be extended to the high-speed region. In the above scheme, when the motor speed reaches a relatively high speed, the back electromotive force of the motor increases, which will cause the stator terminal voltage to be greater than the bus voltage, forcing the voltage difference required for the stator current to track its command value to decrease to 0 (even negative). At this time, the dq axis current regulators of the inverter will start to saturate. By adjusting , , controlling the current vector locus, avoiding the saturation of the current regulator, so that the PMSM can smoothly and quickly transition from constant torque speed regulation to the weak magnetic working mode and perform stable speed increase.

[0044] In a specific embodiment, by adjusting the direct-axis current component and quadrature-axis current component of the motor stator, combined with the target speed, controlling the stator current vector to move along the calculated current vector locus, the steps to achieve weak magnetic speed expansion include: According to the difference between the given voltage of the electromotive force and the feedback voltage of the electromotive force arithmetic unit, the input of the excitation current regulator is adjusted to change the excitation magnetic flux of the motor, and further adjust the direct-axis current component of the stator; at the same time, according to the deviation between the target speed and the actual speed, and the current vector trajectory, the armature voltage of the motor is adjusted to control the quadrature-axis current component of the stator; through the coordinated adjustment of the direct-axis and quadrature-axis current components of the stator, the stator current vector is moved along the calculated current vector trajectory to achieve the field-weakening speed increase of the motor.

[0045] As Figure 7 shown, the technical solution of the present invention also provides a speed regulation system for controlling field-weakening, including a speed regulator ASR, a first current regulator ACR, a first converter UPE, a motor, and a tachogenerator TG coaxially connected to the motor and rotating with the motor; The tachogenerator TG is connected to the speed regulator ASR, the speed regulator ASR is connected to the first current regulator ACR, and the first current regulator ACR is connected to the first converter UPE. The power supply supplies power to the motor through the first converter UPE. A first acquisition module TA1 is arranged on the connection line between the power supply and the first converter UPE. A second acquisition module TA2 is arranged at the power supply end of the motor. The second acquisition module is connected to the electromotive force arithmetic unit AE through a voltage isolator TVD. The first acquisition module TA1 is connected to the electromotive force arithmetic unit AE. The electromotive force arithmetic unit AE is connected to the excitation current regulator AFR through an electromotive force regulator AER; the excitation current regulator AFR is connected to the excitation power electronic converter VFC through a function generator GTFC, and the excitation power electronic converter VFC is connected to the coil of the motor; a third acquisition module TA3 is arranged at the output end of the excitation power electronic converter, and the third acquisition module is connected to the excitation current regulator; the method described in the above embodiment is used to perform speed regulation control on the motor.

[0046] The system further includes a first potentiometer RP1 and a second potentiometer RP2; the first potentiometer is used to provide a speed given voltage to the speed regulator ASR, and the second potentiometer is used to provide an electromotive force given voltage to the electromotive force regulator AER; In the embodiment of the present invention, the first potentiometer RP1 and the second potentiometer RP2 are respectively connected to the power supply. By adjusting the output speed given voltage of the first potentiometer RP1, the speed given voltage minus the voltage fed back by the tachogenerator is input to the speed regulator ASR, and the output speed regulation voltage of the speed regulator ASR, that is, the current given voltage and the voltage collected by the first acquisition module TA1 are input to the first current regulator ACR, and the voltage output by the first current regulator ACR to the first converter UPE, and the first converter UPE regulates the power supply to the motor according to the output voltage of the first current regulator ACR The voltage collected by the second acquisition module TA2 is output through the voltage isolator TVD , and is subtracted from the voltage collected by the first acquisition module , and then input to the electromotive force calculator AE; the electromotive force calculator AE outputs a voltage , and the electromotive force given voltage is output by adjusting the second potentiometer RP2 , and the electromotive force given voltage is subtracted from the voltage output by the electromotive force calculator AE , and then input to the electromotive force regulator AER. The electromotive force regulator AER outputs a voltage , and is subtracted from the voltage collected by the third acquisition module , and then input to the field current regulator AFR. The output of the field current regulator passes through a function generator and a field power electronic converter to control the field current of the motor, thereby regulating the magnetic flux of the motor.

[0047] The speed regulation process of this system includes: In the field weakening speed increasing stage above the base speed, the electromotive force given voltage is adjusted by the second potentiometer. The electromotive force regulator adjusts the input of the field current regulator according to the difference between the electromotive force given voltage and the feedback voltage of the electromotive force calculator, and then changes the field magnetic flux of the motor, and further adjusts the direct-axis current component of the stator; at the same time, the speed regulator and the first current regulator adjust the armature voltage of the motor according to the deviation between the target speed and the actual speed, as well as the current vector trajectory, so as to control the quadrature-axis current component of the stator; through the coordinated adjustment of the direct-axis and quadrature-axis current components of the stator, the stator current vector moves along the calculated current vector trajectory, realizing the field weakening speed expansion of the motor.

[0048] The voltage of the motor is detected, and the electromotive force calculator calculates through the detected voltage and current , using the formula: Indirectly detect the electromotive force, and the tachogenerator detects the motor speed. After obtaining the operating state data such as voltage, current, and speed, the voltage limit ellipse and current limit circle calculated in combination with the inherent parameters of the motor determine the boundary range of voltage and current during motor operation, providing constraint conditions for subsequent control. After obtaining the data of the voltage limit ellipse and current limit circle, calculate the current vector trajectory that simultaneously satisfies the two constraint conditions. This trajectory determines the position where the stator current vector of the motor should be in different operating states to ensure the safe and efficient operation of the motor. By adjusting the first potentiometer, change the speed set voltage, and this voltage is compared and operated in the speed regulator with the actual speed feedback signal of the motor. The ASR combines the rated parameters of the motor and the current operating state data (such as current, voltage, etc.) to calculate the target speed of the motor, outputs it to the current regulator, and then outputs the corresponding voltage to the motor through the first converter.

[0049] In the field weakening speed increase stage above the base speed, when the motor speed increases and the back electromotive force increases, at this time, the electromotive force regulator adjusts the input of the field current regulator according to the comparison result of the electromotive force set value and the feedback value, and then changes the field magnetic flux of the motor, affecting the direct-axis current component of the stator. At the same time, the speed regulator and the first current regulator adjust the armature voltage of the motor through the first converter according to the deviation between the target speed and the actual speed and the requirements of the current vector trajectory, so as to control the quadrature-axis current component of the stator. Through the coordinated adjustment of the direct-axis and quadrature-axis current components of the stator, the stator current vector moves according to the calculated current vector trajectory, realizing the field weakening speed increase of the motor and enabling the motor to operate stably at a higher speed.

[0050] Voltage regulation speed control below the base speed: The RP2 provides the electromotive force set voltage at the base speed , and make , , the AER is saturated, which is equivalent to the open-loop of the electromotive force loop; the output limit value of the AER is set to the full-magnetic set value and added to the field current regulator AFR, and the AFR adjusts to keep the magnetic flux at the rated value; use RP1 to adjust the speed, at this time, the speed and current double-closed-loop system plays a control role; Field weakening speed increase above the base speed: Adjust RP1 to increase the speed set voltage to increase the speed. , the AER starts to desaturate, reducing the field current set voltage, thereby reducing the field magnetic flux to increase the speed.

[0051] In the embodiment of the present invention, an operational amplifier can be used to form an analog calculation circuit to implement the electromotive force calculator AE, and the specific circuit is as Figure 5 shown. Equivalently, the electromotive force calculator AE includes an operational amplifier, and the voltage isolator TVD outputs the voltage Two resistors connected in series are connected to the first input terminal of the operational amplifier, and the connection terminal of the two resistors is grounded through a capacitor The voltage collected by the first acquisition module TA1 is connected to the first input terminal of the operational amplifier through the passing resistor, the output terminal of the operational amplifier is connected to the first input terminal of the operational amplifier through the resistor R1, and the second input terminal of the operational amplifier is grounded through the resistor The output of the operational amplifier is the output of AE .

[0052] The speed regulator ASR adopts a linear PI regulator, which cannot guarantee excellent control performance throughout the field-weakening speed regulation range. In this application, a division link is added behind the speed regulator ASR as shown in Figure 6 so that its output (representing Te*) is divided by the magnetic flux and then sent to the current regulator ACR as the input quantity Figure 6 in the link, ignoring the influence of the small time constant 1 / of the current loop, then dividing by and multiplying by The two non-linear links are adjacent and can be cancelled out, simplifying the controlled object of the speed regulator ASR into a linear one. The speed regulator ASR can be designed according to the method of a linear system, and the parameters can change in real time with the magnetic flux

[0053] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein

Claims

1. A method for regulating the speed of a motor by adjusting weak magnetic field, characterized in that: The steps include: Detect the running status of the motor and obtain the running status data; Calculate the voltage limit ellipse and current limit circle based on the operating status data; Calculate the current vector trajectory that satisfies both the voltage limit ellipse and the current limit circle constraints; Calculate the motor target speed based on the motor operating status data and motor parameters; By adjusting the direct-axis current component and the quadrature-axis current component of the motor stator and combining the motor target speed, the stator current vector is controlled to move according to the calculated current vector trajectory to achieve magnetic field weakening speed expansion.

2. The method for regulating the speed of a motor by adjusting weak magnetic field according to claim 1, characterized in that: The operating status data includes the current actual speed, current and voltage; The steps of calculating the voltage limit ellipse and the current limit circle according to the operating status data include: Calculate the voltage limit ellipse equation according to the motor parameters and operating status; Calculate the current limit circle equation based on the rated current and operating status of the motor.

3. The method for regulating the speed of a motor by adjusting weak magnetic field according to claim 2, characterized in that: When the stator voltage reaches the limit of the inverter output voltage, the voltage limit ellipse equation is: In the formula, and are the inductances of the stator quadrature and direct axes, respectively; and They are the stator quadrature-axis current component and the direct-axis current component respectively; is the flux linkage of the motor’s permanent magnet; is the limit of the inverter output voltage, that is, the stator terminal phase voltage, , is the DC bus voltage, is the rotation speed.

4. The method for regulating the speed of a motor by adjusting weak magnetic field according to claim 3, characterized in that: When the stator current reaches the rated current, the equation of the current limit circle is: In the formula, is the current vector magnitude, and are the stator quadrature-axis current component and the direct-axis current component, is the rated current of the motor.

5. The method for regulating the speed of a motor by adjusting weak magnetic field according to claim 4, characterized in that: The steps of calculating the current vector trajectory that satisfies both the voltage limit ellipse and the current limit circle constraints specifically include: Determine whether the motor is running below the base speed based on its current actual speed; If so, the motor is determined to be operating in the constant torque region, and the current vector trajectory is selected to be within the current limit circle to ensure the maximum torque output; If not, it is determined that the motor has entered the weak magnetic speed regulation area, and the current vector trajectory is calculated so that the current vector trajectory is between the voltage limit ellipse and the current limit circle.

6. The method for regulating the speed of a motor by adjusting weak magnetic field according to claim 5, characterized in that: The calculation formula of the current vector trajectory is: The formula for calculating the motor target speed is: Where p is the number of pole pairs of the motor.

7. The method for regulating the speed of a motor by adjusting weak magnetic field according to claim 6, characterized in that: By adjusting the direct-axis current component and quadrature-axis current component of the motor stator and combining the target speed, the stator current vector is controlled to move according to the calculated current vector trajectory. The steps to achieve magnetic field weakening speed expansion include: According to the difference between the given voltage of the electromotive force and the feedback voltage of the electromotive force operator, the input of the excitation current regulator is adjusted to change the excitation flux of the motor, thereby adjusting the stator direct-axis current component; at the same time, according to the deviation between the target speed and the actual speed, as well as the current vector trajectory, the armature voltage of the motor is adjusted to control the stator quadrature-axis current component; through the coordinated adjustment of the stator direct-axis and quadrature-axis current components, the stator current vector moves according to the calculated current vector trajectory, thereby realizing the weak magnetic speed expansion of the motor.

8. A speed control system for controlling weak magnetic field, characterized in that: The system includes a motor, and the system uses the method according to any one of claims 1 to 7 to control the speed of the motor.

9. The speed regulation system for controlling weak magnetic field according to claim 8, characterized in that: The system also includes a first potentiometer, a second potentiometer, a speed regulator, a first current regulator, a first converter, and a speed measuring generator coaxially connected to the motor and rotating with the motor; The speed measuring generator is connected to the speed regulator, the speed regulator is connected to the first current regulator, the first current regulator is connected to the first converter, the power supply supplies power to the motor through the first converter, a first acquisition module is provided on the connection line between the power supply and the first converter, a second acquisition module is provided at the power supply end of the motor, the second acquisition module is connected to the electromotive force operator through a voltage isolator, the first acquisition module is connected to the electromotive force operator, the electromotive force operator is connected to the excitation current regulator through the electromotive force regulator; the excitation current regulator is connected to the excitation power electronic converter through a function generator, the excitation power electronic converter is connected to the coil of the motor; the output end of the excitation power electronic converter is provided with a third acquisition module, the third acquisition module is connected to the excitation current regulator; The first potentiometer is used to provide a speed setting voltage to the speed regulator, and the second potentiometer is used to provide an electromotive force setting voltage to the electromotive force regulator.

10. The speed regulation system for controlling weak magnetic field according to claim 9, characterized in that: The speed regulation process of this system includes: In the weak magnetic speed-up stage above the base speed, when the motor speed increases, the back electromotive force increases. At this time, the electromotive force regulator outputs the given excitation current voltage according to the comparison result between the given electromotive force voltage and the feedback voltage output by the electromotive force operator. The difference between the voltage collected by the third acquisition module and the given excitation current voltage is input to the excitation current regulator. By adjusting the input of the excitation current regulator, the excitation flux of the motor is changed, affecting the stator direct-axis current component; at the same time, the speed regulator and the first current regulator adjust the armature voltage of the motor through the first converter according to the deviation between the target speed and the actual speed, as well as the requirements of the current vector trajectory, so as to control the stator quadrature-axis current component; through the coordinated adjustment of the stator direct-axis and quadrature-axis current components, the stator current vector moves according to the calculated current vector trajectory, thereby realizing the weak magnetic speed expansion of the motor.

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