Wide-speed-range permanent magnet synchronous motor with variable air-gap flux and control method

Abstract

The application discloses a wide-speed-adjustable permanent magnet synchronous motor with variable air-gap magnetic flux and a control method, and relates to the technical field of motors. The synchronous motor comprises a screw rod, a first screw rod fixing seat, a second screw rod fixing seat, a stator and a rotor assembly. The first screw rod fixing seat and the second screw rod fixing seat are fixed at two ends of the screw rod. The rotor assembly is coaxially arranged outside the screw rod and is coaxially arranged with the stator. The rotor assembly and the screw rod are rotatably and axially movably matched. The rotor assembly is of an axial sectional structure. At least two rotor sections with differentiated electromagnetic parameters are arranged along the axial direction of the screw rod. The magnetic circuit structure with different axial sectional air-gap magnetic fluxes is formed between each rotor section and the stator. Without relying on the traditional flux-weakening control, the air-gap magnetic flux is changed in a mechanical mode, the back electromotive force and the torque characteristics of the motor are adjusted, wide-range speed adjustment is realized, the efficiency reduction and the additional loss caused by the flux-weakening control are avoided, and the overall operation performance of the motor is improved.

Description

Technical Field

[0001] This invention relates to the field of motor technology, specifically to a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux and its control method. Background Technology

[0002] In the die-casting manufacturing field, die-casting equipment needs to repeatedly switch between high-speed feed / retract and low-speed, high-thrust die-casting modes. During high-speed operation, the back electromotive force (EMF) of a traditional permanent magnet synchronous motor increases sharply with increasing speed, easily exceeding the inverter bus voltage limit and restricting further speed increases. To address this issue, conventional technology employs a field-weakening control strategy, which actively weakens the air gap flux by applying a d-axis demagnetizing current to reduce the back EMF and maintain high-speed operation. However, field-weakening control relies on a reverse magnetic field to counteract the main magnetic field of the permanent magnet. This process not only generates significant additional armature losses, leading to a decrease in system efficiency, but also exacerbates motor temperature rise, affecting long-term operational reliability. Furthermore, field-weakening control requires a complex current regulation mechanism, and its dynamic response capability is insufficient in scenarios with frequent switching between die-casting modes, making it difficult to balance high-speed stability and high torque output requirements, thus limiting overall control performance. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art, and proposes a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux and a control method. Without relying on traditional field weakening control, the air gap flux is changed mechanically to adjust the back EMF and torque characteristics of the motor, thereby achieving wide-range speed regulation. This avoids the efficiency reduction and additional losses caused by field weakening control and improves the overall operating performance of the motor.

[0004] This invention provides a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux. The synchronous motor includes a lead screw, a first lead screw fixing seat, a second lead screw fixing seat, a stator, and a rotor assembly. The first lead screw fixing seat and the second lead screw fixing seat are respectively fixed to both ends of the lead screw. The rotor assembly is sleeved on the outside of the lead screw and arranged coaxially with the stator. The rotor assembly and the lead screw are rotatably and axially movable. The rotor assembly is used to connect to a die-casting device.

[0005] The rotor assembly is an axially segmented structure, with at least two rotor segments having different electromagnetic parameters arranged along the screw axis. Each rotor segment forms a magnetic circuit structure with unequal axial segmented air gap magnetic flux with the stator. The rotor assembly moves axially synchronously with the die-casting device. The axial overlap area between the rotor assembly and the stator is dynamically adjusted during the synchronous displacement stage to achieve wide speed regulation operation under weak magnetic conditions.

[0006] Furthermore, the rotor assembly includes a first rotor and a second rotor. The first rotor has an axial stack height of L1 and a corresponding air gap of g1. The second rotor has an axial stack height of L2 on the side closer to the die-casting device. The inner diameter is reduced so that the corresponding air gap increases to g2, satisfying g1 < g2. Unequal air gap magnetic flux is formed by the difference in segmented air gap size.

[0007] Furthermore, the rotor assembly forms a segmented permanent magnet structure based on the first rotor and the second rotor;

[0008] The first rotor permanent magnet uses high-grade magnets, while the second rotor permanent magnet uses low-grade magnets. Unequal air gap magnetic flux is formed by the difference in magnetic field strength between the axially segmented permanent magnets of the first and second rotors.

[0009] Furthermore, the rotor assembly forms a segmented permanent magnet quantity difference structure based on the first rotor and the second rotor. The permanent magnet thickness and pole arc coefficient of the first rotor and the second rotor are different, and unequal air gap magnetic flux is formed by the axial segmented permanent magnet quantity difference.

[0010] Furthermore, when the rotor assembly is displaced along the lead screw axial direction, under high-speed operating conditions, the rotor assembly and the stator are in a state of unequal segmented air gap magnetic flux.

[0011] Under die-casting conditions, the rotor assembly enters the equal air gap region and switches to a state of equal air gap magnetic flux.

[0012] Furthermore, the operation of the permanent magnet synchronous motor is divided into a high-speed feeding stage, a die-casting stage, and a high-speed retraction stage.

[0013] Furthermore, the dynamic characteristics of the permanent magnet synchronous motor satisfy the following:

[0014] ;

[0015] ;

[0016] in, For back potential, For torque, The back electromotive force coefficient, The torque coefficient, For air gap flux, This refers to the rotational speed of the permanent magnet synchronous motor. This is the armature current.

[0017] This invention also provides a speed control method for a permanent magnet synchronous motor, applicable to the wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux, comprising the following steps:

[0018] Based on the unequal air gap magnetic flux structure of the motor axial segment, the effective air gap magnetic flux value required for high-speed operation is determined, and the overlapping area ratio of the rotor segment and the stator is obtained according to the effective air gap magnetic flux value.

[0019] The axial displacement of the rotor assembly is controlled according to the overlapping area ratio, so that the rotor segment and the stator form a corresponding overlapping area, thereby obtaining the target low magnetic flux state.

[0020] The drive armature circuit outputs q-axis torque current and shuts off d-axis demagnetizing current, thus creating a non-weakening speed increase for the permanent magnet synchronous motor under low magnetic flux conditions.

[0021] Furthermore, the control method also includes:

[0022] Real-time detection of the axial overlap area between the rotor assembly and the stator to obtain the current air gap flux;

[0023] Based on the current air gap flux, the increasing trend of the air gap flux is obtained, and the increase in back EMF is determined according to the increasing trend of the air gap flux.

[0024] The armature current is reduced according to the rise of the back EMF, so that the terminal voltage is maintained within the bus voltage limit, thus completing the smooth switching between high-speed and die-casting conditions.

[0025] Furthermore, the step of obtaining the increasing trend of the air gap magnetic flux based on the current air gap magnetic flux, and determining the increase in back EMF based on the increasing trend of the air gap magnetic flux, includes:

[0026] Calculate the difference between the current air gap flux and the air gap flux at the previous time point, calculate the real-time change of air gap flux per unit time, and mark the real-time change as the increasing trend of air gap flux.

[0027] The back electromotive force of the permanent magnet synchronous motor is calculated based on the increasing trend of the air gap magnetic flux.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] Through the aforementioned structure and working principle, the motor can adjust its back EMF and torque characteristics by mechanically changing the air gap flux without relying on traditional field weakening control (i.e., without injecting d-axis demagnetizing current), thus achieving a wide range of speed regulation. This avoids the efficiency reduction and additional losses caused by field weakening control, improving the overall operating performance of the motor. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux in an embodiment of the present invention;

[0031] Figure 2This is a cross-sectional view of the structure of the wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux in an embodiment of the present invention;

[0032] Figure 3 This is a cross-sectional view of the rotor assembly of a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux in an embodiment of the present invention.

[0033] Figure 4 This is a cross-sectional view of the rotor assembly of a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux in an embodiment of the present invention.

[0034] Figure 5 This is a flowchart of the control method for a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux in an embodiment of the present invention. Detailed Implementation

[0035] To further illustrate the technical means and effects adopted by this application to achieve its intended purpose, the specific implementation methods, structures, features, and effects according to this application are described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0036] Example 1:

[0037] Please refer to Figure 1 As for Figure 4 This invention provides a wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux. The synchronous motor includes a lead screw 1, a first lead screw fixing seat 2, a second lead screw fixing seat 5, a stator 4, and a rotor assembly 3. The first lead screw fixing seat 2 and the second lead screw fixing seat 5 are respectively fixed to both ends of the lead screw 1. The rotor assembly 3 is sleeved on the outside of the lead screw 1 and arranged coaxially with the stator 4. The rotor assembly 3 and the lead screw 1 are rotatably and axially movable. The rotor assembly 3 is used to connect to a die-casting device. The die-casting device can be connected to the rotor assembly 3 through a mechanical connecting rod, coupling, or gear and rack mechanism, thereby realizing the synchronization of the movement of the die-casting device and the axial displacement of the rotor assembly 3.

[0038] The variable air gap flux permanent magnet synchronous motor is a type of permanent magnet synchronous motor that can achieve stable operation over a wide speed range by adjusting the magnetic flux in the motor's air gap. This motor can effectively extend its speed range without relying on traditional field weakening control.

[0039] Furthermore, the first lead screw fixing seat 2 and the second lead screw fixing seat 5 are support components used to firmly fix both ends of the lead screw 1 in the motor structure, ensuring that the lead screw 1 remains stable during axial displacement.

[0040] The rotor assembly 3 has an axially segmented structure, with at least two rotor segments having different electromagnetic parameters arranged along the axial direction of the lead screw 1. Each rotor segment and the stator 4 form a magnetic circuit structure with unequal axial segmented air gap magnetic flux. The rotor assembly 3 moves axially synchronously with the die-casting device. The axial overlapping area between the rotor assembly 3 and the stator 4 is dynamically adjusted during the synchronous displacement stage to achieve wide speed regulation operation under weak magnetic conditions.

[0041] By arranging at least two rotor segments with differentiated electromagnetic parameters along the axial direction of the lead screw 1, this segmented structure allows the rotor to have different electromagnetic characteristics at different axial positions. Different rotor cores made of different materials can be used at different axial positions, or slots of different shapes can be opened on the rotor core to change its permeability.

[0042] Furthermore, the rotor assembly 3 can perform axial synchronous displacement with the die-casting device. When the die-casting device performs feed or retraction movements, the rotor assembly 3 will move synchronously along the axial direction of the lead screw 1. This synchronous displacement action can be achieved through the threaded engagement between the lead screw 1 and the rotor assembly 3; when the lead screw 1 rotates, the rotor assembly 3 moves axially. Alternatively, a guide rail can be provided on the lead screw 1, and the rotor assembly 3 can engage with the guide rail via a slider. An external drive mechanism can control the axial movement of the rotor assembly 3, and this movement can be linked to the motion signal of the die-casting device.

[0043] Specifically, the rotor assembly 3 includes a first rotor 31 and a second rotor 32. The first rotor 31 has an axial stacking height of L1 and a corresponding air gap of g1. The second rotor 32 is located on the side closer to the die-casting device, with an axial stacking height of L2. The inner diameter is reduced to increase the corresponding air gap to g2, satisfying g1 < g2. Unequal air gap magnetic flux is formed through the difference in segmented air gap size.

[0044] Furthermore, the axial stack height L1 of the first rotor 31 refers to the length of the first rotor 31 along the motor axis, which determines the effective magnetic circuit length when the first rotor 31 coincides with the stator 4. The corresponding air gap g1 refers to the radial distance between the first rotor 31 and the stator 4, which can affect the magnitude of magnetic reluctance and magnetic flux density. The axial stack height L2 is the length of the second rotor 32 along the axial direction. The inner diameter reduction means that the inner diameter of the second rotor 32 is reduced relative to the first rotor 31 or other parts of the rotor assembly 3, which leads to an increase in the radial distance between it and the stator 4, thereby increasing the corresponding air gap to g2.

[0045] The first rotor 31 and the second rotor 32 refer to two independent or semi-independent axial segments within the rotor assembly 3. Structurally, they can be independent physical components, mechanically connected to form a single rotor assembly 3, or they can be two regions on the same rotor body divided by different designs. Their function is to provide different electromagnetic characteristics to achieve axial segment differences in air gap magnetic flux. The air gap of the first rotor 31 is smaller than that of the second rotor 32, enabling unequal air gap magnetic flux effects. By setting different sized air gaps in different axial segments of the rotor assembly 3, the magnetic reluctance in the magnetic circuit changes when the stator 4 coincides with different rotor segments, resulting in different magnetic flux through the air gap. The smaller the air gap, the smaller the magnetic reluctance and the larger the magnetic flux; the larger the air gap, the greater the magnetic reluctance and the smaller the magnetic flux.

[0046] Specifically, in this embodiment, the first rotor 31 can adopt a conventional permanent magnet synchronous motor rotor structure, maintaining a standard air gap g1, for example, 0.5 mm, between its outer diameter and the inner diameter of the stator 4. The second rotor 32 can be designed such that its outer diameter is smaller than that of the first rotor 31 at the end near the die-casting device, making the air gap g2 between it and the inner diameter of the stator 4 significantly larger than g1, for example, 1.0 mm. These two rotor segments can be fixed to the lead screw 1 by key connection, bolt connection, or interference fit, ensuring that they can move axially as a whole with the lead screw 1. When the motor requires high speed and low torque output, the rotor assembly 3 can be moved to a position where the stator 4 mainly coincides with the second rotor 32, at which time the air gap magnetic flux is small; when the motor requires low speed and high torque output, the rotor assembly 3 can be moved to a position where the stator 4 mainly coincides with the first rotor 31, at which time the air gap magnetic flux is large.

[0047] Specifically, in another embodiment, the rotor assembly 3 can form a segmented permanent magnet structure based on the first rotor 31 and the second rotor 32;

[0048] The permanent magnet of the first rotor 31 is made of high-grade magnet steel, and the permanent magnet of the second rotor 32 is made of low-grade magnet steel. Unequal air gap magnetic flux is formed by the difference in magnetic field strength of the axial segmented permanent magnets of the first rotor 31 and the second rotor 32.

[0049] The first rotor 31 uses high-grade magnets, specifically N52SH or UH series magnets, which have higher remanence density and coercivity. The first rotor 31 generates strong magnetic flux in the air gap, which is mainly responsible for providing the rated torque and power density of the motor.

[0050] The second rotor 32 can use low-grade magnets such as N35 or N30. Because the magnetic field strength of low-grade magnets is weaker, the second rotor 32 generates a weak magnetic flux in the air gap. When the motor is running, the first rotor 31 and the second rotor 32 can rotate coaxially, exhibiting a parallel or series axial magnetic circuit distribution. Due to the difference in magnet performance along the axial length, the air gap magnetic flux density is distributed in a stepped or gradually changing manner along the axial direction, creating an effect of "unequal air gap magnetic flux."

[0051] Furthermore, the magnet structure design based on the different magnetic strengths of the first rotor 31 and the second rotor 32 can reduce eddy current losses in the permanent magnets. The axially unequal magnetic flux design formed by the first rotor 31 and the second rotor 32 allows for the artificial modulation of the spatial distribution of the air gap magnetic field, making it closer to a sine wave. This helps reduce the cogging torque and torque ripple of the motor, improving operational smoothness.

[0052] Specifically, in another embodiment, the rotor assembly 3 can form a segmented permanent magnet quantity difference structure based on the first rotor 31 and the second rotor 32. The permanent magnet thickness and pole arc coefficient of the first rotor 31 and the second rotor 32 are different, and unequal air gap magnetic flux is formed by the axial segmented permanent magnet quantity difference. The segmented permanent magnet quantity difference structure of the rotor assembly 3 means that in the axial segmented design of the rotor assembly 3, the effective amount of permanent magnet material used in different rotor segments is different. This difference can be achieved in a variety of ways, such as changing the physical size, shape or arrangement of the permanent magnets, thereby affecting the magnetic field strength and distribution generated.

[0053] Furthermore, the permanent magnets of the first rotor 31 and the second rotor 32 have different thicknesses. Since the thickness of the permanent magnet is one of the key parameters affecting its magnetic flux output capability, a thicker permanent magnet can usually generate a stronger magnetic field. By designing the difference in thickness, two magnetic fields of different intensities are formed.

[0054] The first rotor 31 and the second rotor 32 have different pole arc coefficients, that is, the ratio of the arc length of the permanent magnet along the circumferential direction to the pole pitch of the first rotor 31 and the second rotor 32 is different. This can affect the area effectively covered by the permanent magnet in the air gap and the uniformity of the magnetic field distribution. Different pole arc coefficients will result in different magnetic flux coupling between the permanent magnet and the stator 4 winding.

[0055] The unequal air gap flux achieved by varying the amount of permanent magnets used in axial segments refers to the ability of different segments of the rotor assembly 3 along the axial direction to generate inherently different air gap fluxes when they coincide with the stator 4, through differentiated design of parameters such as the thickness or pole arc coefficient of the permanent magnets. This design gives each rotor segment unique magnetic field characteristics, thereby dynamically changing the magnetic flux coupled with the stator 4 as the rotor assembly 3 moves axially, achieving the desired unequal air gap flux effect.

[0056] Specifically, in this embodiment, the rotor assembly 3 can be composed of two axial segments, namely a first rotor 31 and a second rotor 32. The first rotor 31 can be equipped with a permanent magnet with a radial thickness of 5 mm and a pole arc coefficient of 0.8. The second rotor 32 can be equipped with a permanent magnet with a radial thickness of 3 mm and a pole arc coefficient of 0.6. When the rotor assembly 3 is axially displaced on the lead screw 1, if the first rotor 31 coincides with the stator 4, the motor will operate in a higher air gap flux state determined by the thicker permanent magnet and the larger pole arc coefficient. Conversely, when the rotor assembly 3 is displaced until the second rotor 32 coincides with the stator 4, the motor will operate in a lower air gap flux state determined by the thinner permanent magnet and the smaller pole arc coefficient. This structure allows the motor to achieve precise segmented adjustment of the air gap flux through simple mechanical displacement, thereby adapting to different operating conditions.

[0057] The motor can precisely construct axially segmented unequal air gap flux by differentiating the amount of permanent magnets used inside the rotor assembly 3, such as varying the thickness of the permanent magnets or the pole arc coefficient. This design avoids the complexity of achieving flux differences by changing the physical air gap size or the grade of permanent magnets, making flux adjustment more flexible and controllable. During axial displacement of the rotor assembly 3, the motor can smoothly and efficiently switch between different air gap flux states according to actual needs, thereby achieving wide speed range operation under non-weakening magnetic conditions. This effectively improves the motor's operating efficiency and control accuracy under different operating conditions, especially providing optimized performance in scenarios requiring switching between high torque output and high-speed operation.

[0058] Specifically, when the rotor assembly 3 is axially displaced along the lead screw 1, the overlapping area between the rotor assembly 3 and the stator 4 is small under high-speed conditions, resulting in unequal air gap magnetic flux in segments. Switching between these flux states can be achieved through mechanical displacement, electromagnetic control, or a combination of both. For example, by changing the relative axial position between the rotor assembly 3 and the stator 4, rotor segments with different electromagnetic parameters can be aligned with the stator 4, thereby altering the overall air gap magnetic flux distribution. The small overlapping area between the rotor assembly 3 and the stator 4 under high-speed conditions typically requires the motor to have a low back EMF to avoid voltage saturation and achieve higher speeds. When the axial overlapping area between the rotor assembly 3 and the stator 4 is small, it means that only a portion of the rotor segments are effectively coupled to the stator 4, or the coupled rotor segments have a low magnetic flux density.

[0059] During die casting, rotor assembly 3 enters the equal air gap region, switching to a state of equal air gap magnetic flux. This involves moving rotor assembly 3 to a position where only a portion of the permanent magnets are aligned with stator 4, or aligning the rotor segment with the stator 4 with a larger air gap. It is then in a state of unequal segmented air gap magnetic flux, meaning the magnetic flux distribution in the motor's air gap is uneven in the axial direction.

[0060] This means that there are differences in air gap flux density in different regions along the motor axis. This difference can be achieved in several ways, such as by using different permanent magnet grades, amounts of permanent magnets (e.g., thickness or pole arc coefficient), or different air gap sizes in different axial segments of rotor assembly 3. This non-uniform flux distribution becomes more pronounced when the overlap area between rotor assembly 3 and stator 4 is small, thus providing the required low flux characteristics during high-speed operation. During die-casting, rotor assembly 3 enters the equal air gap region. Die-casting typically requires the motor to output a large torque, which necessitates a high air gap flux. By axially moving rotor assembly 3 to fully align its high flux density or uniform flux distribution rotor segment with stator 4, the air gap flux distribution between rotor assembly 3 and stator 4 becomes relatively uniform or reaches maximum effective flux.

[0061] Specifically, the operation of the permanent magnet synchronous motor is divided into a high-speed feed stage, a die-casting stage, and a high-speed retraction stage. During the high-speed feed stage, to reduce back electromotive force and allow the motor to reach higher speeds, the rotor assembly 3 is driven to a specific axial position, resulting in a smaller axial overlap area between it and the stator 4. At this position, due to the segmented axial structure of the rotor assembly 3, for example, only some rotor segments with lower magnetic flux density may be effectively coupled to the stator 4, or the rotor assembly 3 may be moved to a region with a larger air gap in its axial segmented structure, thus placing the motor in a state of unequal segmented air gap magnetic flux.

[0062] During die casting, a high torque output from the motor is typically required. In this condition, the control system drives the rotor assembly 3 to move axially along the lead screw 1, bringing it into a pre-defined equal air gap region. In this region, the axial overlap area between the rotor assembly 3 and the stator 4 reaches its maximum or optimal coupling state, and the structural design of the rotor assembly 3 ensures that the air gap magnetic flux distribution is relatively uniform and the magnetic flux is large within this region. This uniform and high magnetic flux state enables the motor to generate strong electromagnetic torque, meeting the high torque output requirements of the die casting process.

[0063] After the die-casting process ends, the motor enters the retraction phase. To quickly return to its original position and prepare for the next cycle, rotor assembly 3 moves in the opposite direction along the lead screw 1. During this process, the air gap magnetic flux state switches from an equal state back to an unequal state. This means that rotor assembly 3 gradually exits the equal air gap region and returns to a state with a smaller overlap area with stator 4 and uneven magnetic flux distribution, thereby reducing the back EMF again and enabling the motor to complete the retraction action at high speed.

[0064] Specifically, the dynamic characteristics of the permanent magnet synchronous motor satisfy the following:

[0065] ;

[0066] ;

[0067] in, For back potential, For torque, The back electromotive force coefficient, The torque coefficient, For air gap flux, This refers to the rotational speed of the permanent magnet synchronous motor. This is the armature current.

[0068] back potential This represents the electromotive force induced in the stator winding 4 when the motor rotates, and its magnitude is related to the motor's back electromotive force constant. air gap flux and rotational speed Proportional. Torque This represents the mechanical torque output by the motor, the magnitude of which is related to the motor's torque constant. air gap flux and armature current Proportional. These relationships reveal the air gap magnetic flux. It plays a central role in determining the electrical and mechanical output characteristics of an electric motor. For example, back EMF. The calculation can be performed based on the motor design parameters and operating status. The specific calculation formula is: where:

[0069] ;

[0070] in, Back potential, Electrical angular velocity is determined by the operating conditions. ( For mechanical rotation speed, (where the extreme logarithm is) : Permanent magnet flux linkage, determined by the remanence density of the permanent magnet. The magnetic circuit cross-sectional area, the number of turns in series per phase, and the winding coefficient are all determined by these factors.

[0071] Torque The calculation can be performed by measuring the armature current. This is combined with magnetic flux information, or measured directly using a torque sensor. Among these, the air gap magnetic flux... Air gap flux refers to the magnetic flux generated by permanent magnets in the air gap of a motor. It is a key physical quantity connecting the stator and rotor magnetic fields. In permanent magnet synchronous motors, the magnitude of the air gap flux directly affects the motor's back electromotive force and torque output capability. Adjustments can be made in various ways, such as changing the magnetic properties of the permanent magnet, adjusting the geometry of the air gap, or changing the relative position of the permanent magnet and the stator winding 4.

[0072] In this application, The dynamic changes are mainly achieved by altering the axial overlap area or air gap size between the rotor segment and the stator 4 through the axial displacement of the rotor assembly 3. The dynamic variation of speed and torque output is matched, which means that the air gap flux is actively controlled. The size of the motor can be flexibly adjusted to change the back EMF and torque output characteristics, making it adaptable to different operating conditions and speed and torque requirements.

[0073] Example 2:

[0074] Please refer to Figure 5 This invention also provides a speed control method for a permanent magnet synchronous motor, comprising the following steps:

[0075] S1: Based on the unequal air gap magnetic flux structure of the motor axial segment, determine the effective air gap magnetic flux value required for high-speed operation, and obtain the overlapping area ratio of the rotor segment and stator 4 according to the effective air gap magnetic flux value; set the magnetic flux reference for the motor in high-speed operation state, which can be calculated and determined by considering factors such as the speed, power requirements and back EMF limitation of high-speed operation through pre-conducted motor characteristic tests, simulation analysis or mathematical models established based on motor design parameters, and after considering factors such as the speed, power requirements and back EMF limitation of high-speed operation.

[0076] In this embodiment, a mathematical model is set based on motor design parameters, based on the permanent magnet synchronous motor. The shaft voltage equation and torque equation, neglecting the voltage drop across the resistor under high-speed steady-state conditions, express the inverter's output voltage capability as a voltage-limiting ellipse. The current capability of the motor and inverter is represented by a current circle. .

[0077] Furthermore, For stator direct-axis inductance, For stator quadrature axis inductance, This represents the direct-axis component of the stator current. The quadrature-axis component of the stator current. It is a permanent magnet flux chain. This represents the maximum output phase voltage amplitude of the inverter. The maximum allowable current amplitude, It represents the electric angular velocity.

[0078] Given speed With torque command Subsequently, within the intersection of the current circle and the voltage ellipse, the model is solved analytically or numerically for a set of optimal solutions. This causes the air gap flux linkage amplitude to This ensures that the voltage margin is maintained for high-speed operation while meeting voltage limits, and also guarantees the required output torque.

[0079] In practical applications, this model is often used as the core of the field weakening control algorithm. It is first obtained through offline parameter identification. The nonlinear characteristics of current variation are studied, and a three-dimensional lookup table or fitted analytical expression of speed-torque-minimum flux linkage is pre-established in the controller. During operation, the controller reads the DC bus voltage, motor speed, and torque commands in real time, and obtains the minimum effective air gap flux reference value through table lookup or real-time solution. Then, combined with the flux linkage observer, a closed-loop regulation is formed to dynamically correct the direct-axis current. This enables efficient and stable flux control of the motor under high-speed operating conditions.

[0080] Furthermore, in this embodiment, based on the magnetic flux characteristic curves of the motor at different axial positions of the rotor assembly 3, and combined with the target high-speed speed, a magnetic flux that can both meet the back EMF margin requirement and avoid magnetic circuit saturation can be selected, and the overlapping area ratio of the rotor segment and the large stator 4 can be obtained when the motor is in the state of the effective air gap magnetic flux value.

[0081] S2: Control the axial displacement of rotor assembly 3 according to the overlapping area ratio, so that the rotor segment and stator 4 form a corresponding overlapping area, thereby obtaining the target low magnetic flux state. The air gap magnetic flux is precisely adjusted mechanically to achieve the target low magnetic flux state determined in the previous steps. This can be achieved using a lead screw 1 transmission mechanism in conjunction with a servo motor for precise position control. The servo motor drives the lead screw 1 to rotate, causing the rotor assembly 3, which engages with the lead screw 1's thread or ball bearing slider, to move axially. The axial position of rotor assembly 3 is detected in real time by an encoder, and according to a preset magnetic flux-position correspondence, the rotor assembly 3 is moved to the position where it forms the required overlapping area with the stator 4, thereby obtaining the target low magnetic flux.

[0082] Furthermore, in another embodiment, a linear actuator or electromagnetic drive device can be used to directly drive the rotor assembly 3, and the real-time position can be fed back by a position sensor. The controller adjusts the driving force according to the feedback signal so that the rotor assembly 3 can accurately stop at the axial position that can generate the target low magnetic flux.

[0083] Furthermore, the position sensor can be an eddy current displacement sensor, which is installed on the outside of the motor end cover or bearing housing, with the probe aligned with the rotor shaft end face or shoulder. The operating parameters of the eddy current displacement sensor are: outputting a 4-20mA or voltage signal, and displaying the axial displacement value in real time (accuracy up to ±0.01mm). By acquiring the axial displacement of the rotor and stator, the overlapping area data of the rotor and stator can be obtained, so as to adjust the relative position of the rotor and stator in real time to achieve the target low magnetic flux axial position.

[0084] S3: Drives the armature circuit to output q-axis torque current and shuts off the d-axis demagnetizing current. This creates a field-weakening-free speed increase for the permanent magnet synchronous motor under low flux conditions. A vector control (FOC) strategy can be employed, decomposing the stator 4 current into d-axis current (flux component) and q-axis current (torque component) through coordinate transformation. In high-speed operation mode, the controller sets the d-axis current command to zero and controls only the q-axis current to generate the required torque. The magnetic field inside the motor is entirely provided by the permanent magnets, and the armature current does not produce a demagnetizing effect, thus avoiding stator 4 winding losses caused by the d-axis demagnetizing current.

[0085] Furthermore, in another implementation, a direct torque control (DTC) strategy can be adopted. By directly controlling the stator 4 flux linkage and torque, the controller will adjust the amplitude of the stator 4 flux linkage according to the speed and voltage limits during high-speed operation, keeping it at a low level, but without actively injecting demagnetizing current, ensuring that the armature current is mainly used to generate torque.

[0086] This application fully utilizes the variable axial segmented air gap flux of the motor to transform the flux adjustment required for speed increase from traditional electrical field weakening to mechanical displacement adjustment. First, a target low flux value is determined based on the requirements of high-speed operation. Then, by precisely controlling the axial displacement of the rotor assembly 3, the overlapping area of ​​the rotor and stator 4 is physically changed, thereby achieving dynamic adjustment of the air gap flux. Once the target low flux state is reached, the armature circuit control strategy ensures that only q-axis torque current is output without injecting d-axis demagnetizing current. This method cleverly combines mechanical field adjustment with electrical control, enabling the motor to avoid stator 4 winding losses caused by d-axis demagnetizing current during speed increase, thus achieving wide-range field-weakening-free speed increase operation while maintaining high efficiency.

[0087] Specifically, the control method further includes:

[0088] The axial overlap area of ​​rotor assembly 3 and stator 4 is detected in real time to obtain the current air gap flux. Real-time detection of the axial overlap area between rotor assembly 3 and stator 4 is crucial for accurately understanding the current operating status of the motor. This detection can be achieved by installing a linear displacement sensor on the lead screw 1 or rotor assembly 3. For example, a grating ruler, magnetostrictive displacement sensor, or eddy current displacement sensor can be used to directly measure the axial position of rotor assembly 3, and then calculate its overlap area with stator 4. Alternatively, an indirect estimation can be made by establishing a mapping relationship between the axial position of rotor assembly 3 and air gap flux in the motor controller, combined with motor operating parameters (such as speed and current). Obtaining the current air gap flux is essential. This forms the basis for subsequent voltage balance control. This can be achieved by pre-calibrating the correspondence between the axial position of rotor assembly 3 and the air gap flux, and then substituting the detected axial overlap area into the relationship curve or lookup table. Alternatively, the air gap flux can be directly measured by installing a Hall sensor or flux sensor in the motor stator 4 windings.

[0089] Furthermore, by establishing a mapping relationship between the axial position of rotor assembly 3 and air gap flux in the motor controller, and combining this with motor operating parameters (such as speed and current), indirect estimation can be performed. Specifically, this can be done as follows:

[0090] In permanent magnet synchronous motors, when the rotor is axially offset, the change in the overlapping area of ​​the stator and rotor leads to an increase in the effective magnetic flux linkage of the permanent magnets. The back electromotive force amplitude changes approximately linearly. Consequently, the controller changes. It uses a voltage model or directly samples the line voltage to obtain the current back electromotive force amplitude. Combined with electric angular velocity Nominal permanent magnet flux under the rated overlapping area The axial offset can be estimated. ,in The rate of change of flux linkage per unit displacement (pre-calibrated by the motor structure). Final overlapping area. , This is the rated overlapping area. For linear coefficients related to the shape of the iron core (such as rectangular iron cores) (For stacking thickness width), by utilizing the existing voltage and speed signals of the controller, no additional sensors are required, enabling simple and suitable online real-time estimation operations.

[0091] Based on the current air gap flux, the increasing trend of the air gap flux is obtained, and the increase in back EMF is determined according to the increasing trend of the air gap flux; this can be achieved through the algorithm module of the motor controller based on the current air gap flux. The rate of change of the back EMF and the motor speed, combined with motor parameters (such as the back EMF constant), are used to calculate or predict the back EMF in real time. The rate of increase.

[0092] Furthermore, the algorithm module is a calculation program built into the motor controller. The motor controller acquires the stator voltage and stator current signals of the motor, obtains the net voltage component through subtraction, and then integrates over time to continuously calculate the air gap flux vector at the current moment. Based on this, the algorithm module synchronously performs differential calculations on the flux amplitude to obtain the rate of change of flux. Combined with the real-time speed signal obtained from the encoder or Hall sensor, it uses the built-in dynamic mathematical model of the motor (including parameters such as back EMF constant and stator resistance) to dynamically calculate the instantaneous value of the back EMF and its upward trend. The output result can be directly used for flux reference correction in the field weakening region, overvoltage protection early warning, or as an input for speed loop feedforward control to ensure that the system can respond to voltage saturation risks in advance during high-speed dynamic processes.

[0093] Specifically, the step of obtaining the increasing trend of the air gap magnetic flux based on the current air gap magnetic flux, and determining the increase in back EMF based on the increasing trend of the air gap magnetic flux, includes:

[0094] Calculate the difference between the current air gap flux and the air gap flux at the previous time point, calculate the real-time change of air gap flux per unit time, and mark the real-time change as the increasing trend of air gap flux.

[0095] The back electromotive force of the permanent magnet synchronous motor is calculated based on the increasing trend of the air gap magnetic flux.

[0096] Furthermore, a motor operation model can also be established based on the increasing trend of the air gap flux, where the air gap flux... When the change occurs, the back electromotive force is calculated using simulation. The expected change is used to determine the magnitude of the increase.

[0097] Specifically, the armature current is reduced according to the rise in back EMF, keeping the terminal voltage within the bus voltage limit and achieving a smooth switch between high-speed and die-casting conditions. Synchronously reducing the armature current is a key means of effectively lowering the motor terminal voltage and preventing it from exceeding the bus voltage limit. This can be achieved by using a current regulator in the motor controller to gradually or rapidly reduce the given value of the armature current when a rising trend in back EMF is detected, based on a preset control strategy or algorithm. Alternatively, the duty cycle of the PWM modulator can be adjusted to directly control the inverter output voltage, thereby indirectly reducing the armature current. Maintaining the terminal voltage within the bus voltage limit is the core objective of this control method, aiming to ensure the safe and stable operation of the motor. This can be achieved by setting a voltage feedback loop in the motor controller to monitor the motor terminal voltage in real time and compare it with the bus voltage limit; once it approaches or exceeds the limit, the current reduction strategy is immediately triggered. Alternatively, feedforward control can be used to adjust the armature current in advance based on the predicted rise in back EMF, proactively controlling the terminal voltage within a safe range. Achieving a smooth transition between high-speed and die-casting operating conditions aims to ensure the continuity and stability of motor operation during the switch between different conditions, avoiding shocks or overvoltages. This can be achieved by gradually adjusting the armature current during the condition switch using a smooth current feed curve or ramp function, avoiding sudden current changes.

[0098] By combining real-time monitoring, trend analysis, and active control, a closed-loop voltage balance control system is formed. Firstly, by continuously monitoring the axial overlap area of ​​rotor assembly 3 and stator 4, the system can accurately obtain the current air gap flux. This real-time data is fundamental to understanding the current electromagnetic state of the motor. Secondly, based on the acquired air gap flux... By analyzing the back EMF and its changing trends, combined with operating parameters such as motor speed, the controller can accurately predict the rise in motor back EMF. This predictive capability allows the system to intervene before the back EMF actually rises and may cause overvoltage. Finally, once it is predicted that the back EMF may cause the terminal voltage to exceed the bus voltage limit, the controller will immediately and synchronously reduce the armature current. Since the armature current directly affects the motor terminal voltage, by precisely adjusting the armature current, the system can effectively suppress the rise effect of back EMF, thereby stably maintaining the motor terminal voltage within the bus voltage limit. The synergistic effect of this series of steps ensures that even when the motor switches between high-speed and die-casting conditions, the air gap flux remains within the limit. Even with dynamic changes, the motor can operate smoothly and safely, avoiding system instability or damage caused by excessive voltage. This control method fully utilizes the variable air gap flux of the motor, enabling the motor to operate efficiently and reliably over a wide speed range through intelligent voltage management.

[0099] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux, characterized in that, The synchronous motor includes a lead screw, a first lead screw fixing seat, a second lead screw fixing seat, a stator, and a rotor assembly. The first lead screw fixing seat and the second lead screw fixing seat are respectively fixed to both ends of the lead screw. The rotor assembly is sleeved on the outside of the lead screw and arranged coaxially with the stator. The rotor assembly and the lead screw are rotatably and axially movable. The rotor assembly is used to connect to the die-casting device. The rotor assembly is an axially segmented structure, with at least two rotor segments having different electromagnetic parameters arranged along the screw axis, including a first rotor and a second rotor. The corresponding air gap of the first rotor is g1, and the corresponding air gap of the second rotor is increased to g2 by reducing the inner diameter of the side closer to the die-casting device, satisfying g1 < g2. The difference in segmented air gap size forms unequal air gap magnetic flux, so that the first rotor and the second rotor form a magnetic circuit structure with unequal axial segmented air gap magnetic flux between the stator. The rotor assembly moves axially along the lead screw with the die-casting device. Under high-speed conditions, the axial overlap area between the rotor assembly and the stator is small, resulting in a segmented air gap flux unequal state. Based on the motor's axial segmented air gap flux unequal structure, a wide-range speed regulation operation control without field weakening is achieved. Under die-casting conditions, the axial overlap area between the rotor assembly and the stator reaches the maximum or optimal coupling state, switching to an equal air gap flux state to output a larger torque. The process of achieving wide-range speed regulation without field weakening includes the following steps: determining the effective air gap flux value required for high-speed operation; obtaining the overlap area ratio between the rotor segment and the stator based on the effective air gap flux value; controlling the axial displacement of the rotor assembly based on the overlap area ratio to form a corresponding overlap area between the rotor segment and the stator, thereby obtaining the target low flux state; driving the armature circuit to output the q-axis torque current and turning off the d-axis demagnetizing current, thus achieving field weakening-free speed expansion for the permanent magnet synchronous motor under low flux conditions; real-time detection of the axial overlap area between the rotor assembly and the stator to obtain the current air gap flux; obtaining the increasing trend of the air gap flux based on the current air gap flux; determining the rise in back EMF based on the increasing trend of the air gap flux; reducing the armature current based on the rise in back EMF to maintain the terminal voltage within the bus voltage limit, thereby completing the smooth switching between high-speed operation and die-casting operation. The real-time detection of the axial overlap area between the rotor assembly and the stator to obtain the current air gap flux includes: obtaining the current back electromotive force amplitude. Combined with electric angular velocity Nominal permanent magnet flux under the rated overlapping area Estimate axial offset ,in Determine the overlapping area as the rate of change of magnetic flux per unit displacement. , This is the rated overlapping area. The linear coefficient is related to the shape of the iron core; the current air gap flux is obtained through the mapping relationship between the axial position of the rotor assembly and the air gap flux in a pre-calibrated manner.

2. The wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux according to claim 1, characterized in that, The rotor assembly forms a segmented permanent magnet structure based on the first rotor and the second rotor; The first rotor permanent magnet uses high-grade magnets, while the second rotor permanent magnet uses low-grade magnets. Unequal air gap magnetic flux is formed by the difference in magnetic field strength between the axially segmented permanent magnets of the first and second rotors.

3. The wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux according to claim 1, characterized in that, The rotor assembly is based on a first rotor and a second rotor to form a segmented permanent magnet content difference structure. The permanent magnet thickness and pole arc coefficient of the first rotor and the second rotor are different. Unequal air gap magnetic flux is formed by the difference in the axial segmented permanent magnet content.

4. The wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux according to claim 1, characterized in that, The operation of the permanent magnet synchronous motor is divided into a high-speed feeding stage, a die-casting stage, and a high-speed retraction stage.

5. The wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux according to claim 1, characterized in that, The dynamic characteristics of the permanent magnet synchronous motor satisfy: ； ； in, For back potential, For torque, The back electromotive force coefficient, The torque coefficient, For air gap flux, This refers to the rotational speed of the permanent magnet synchronous motor. This is the armature current.

6. The wide-range speed-regulating permanent magnet synchronous motor with variable air gap flux according to claim 1, characterized in that, The step of obtaining the increasing trend of the air gap magnetic flux based on the current air gap magnetic flux, and determining the increase in back EMF based on the increasing trend of the air gap magnetic flux, includes: Calculate the difference between the current air gap flux and the air gap flux at the previous time point, calculate the real-time change of air gap flux per unit time, and mark the real-time change as the increasing trend of air gap flux. The back electromotive force of the permanent magnet synchronous motor is calculated based on the increasing trend of the air gap magnetic flux.

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