Coaxial multi-stage magnetic suspension centrifugal compressor

Abstract

The application discloses a coaxial multi-stage magnetic suspension centrifugal compressor, which comprises a compressor shell, a main shaft, a driving motor and at least three centrifugal impellers. The compressor shell is internally formed with a gas compression flow channel. The main shaft is axially arranged in the compressor shell. The rotor of the driving motor is fixedly sleeved on the main shaft. The centrifugal impellers are fixedly installed on the main shaft and coaxially arranged with the rotor of the driving motor, and jointly form a multi-stage compression unit. A magnetic suspension bearing system comprises a radial magnetic bearing for providing radial support force and an axial magnetic bearing for providing axial support force. The main shaft is supported in a non-contact mode in the compressor shell by the magnetic suspension bearing system. The four-stage centrifugal impellers are coaxially connected in series with the permanent magnet synchronous motor rotor, and the magnetic suspension bearing is matched, so that a very high total compression ratio is distributed to each stage of impellers, and the compressor can easily cope with the extreme temperature difference requirement and improve the overall energy efficiency ratio level.

Description

Technical Field

[0001] This invention relates to the field of heat pump compressor technology, and in particular to a coaxial multi-stage magnetic levitation centrifugal compressor. Background Technology

[0002] Centrifugal compressors, as core power equipment in large-scale refrigeration, heating, and industrial process systems, use high-speed rotating impellers to perform work on gas, converting mechanical energy into pressure and kinetic energy. This kinetic energy is then further converted into pressure energy by stationary components such as diffusers, thus achieving gas compression. To overcome the pressure ratio limitations of single-stage compression and broaden the operating temperature range, multi-stage centrifugal compression technology has emerged. This technology connects multiple impellers coaxially in series, progressively pressurizing the gas to achieve a higher overall pressure ratio, meeting the demands of operating conditions from cryogenic to high-temperature environments.

[0003] In recent years, the introduction of magnetic levitation bearing technology has brought revolutionary progress to centrifugal compressors. By levitizing the rotor using electromagnetic force, mechanical contact and friction are completely eliminated, eliminating the need for complex lubrication systems. This results in improved efficiency, reduced maintenance costs, and extremely low vibration and noise. Magnetic levitation centrifugal compressors have thus become a solution for large-scale central air conditioning and industrial refrigeration applications.

[0004] Currently, common magnetic levitation bearings employ permanent magnet bias or hybrid magnetic circuit designs. When heat pump systems operate in high-temperature heating mode for extended periods, the permanent magnets risk demagnetization at high temperatures, leading to decreased bearing capacity and control failure. Simultaneously, the rotor displacement detection systems often utilize eddy current sensors, whose operating temperature range is typically limited. Under extreme high or low temperature conditions, measurement accuracy drifts or even fails, directly impacting the stability of the levitation control. With four or more stages of impellers connected coaxially, the rotor system has a large length-to-diameter ratio, resulting in dense critical speeds at ultra-high speeds and extremely stringent dynamic balance requirements. Existing control strategies have limited ability to suppress rotor misalignment. Under disturbances such as sudden load changes, surge boundaries, or thermal deformation caused by wide-temperature-range operation, rotor instability can easily occur, leading to contact and rubbing against the protective bearing, resulting in failure. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide a coaxial multi-stage magnetic levitation centrifugal compressor to solve the problems mentioned in the background art.

[0006] The technical solution adopted by this invention to solve its technical problem is: a coaxial multi-stage magnetic levitation centrifugal compressor, comprising: The compressor housing has a gas compression flow channel formed inside it; The main shaft passes through the compressor housing along the axial direction; A drive motor, the rotor of which is fixedly mounted on the main shaft; At least three centrifugal impellers are fixedly mounted on the main shaft and coaxially arranged with the rotor of the drive motor, together forming a multi-stage compression unit; A magnetic levitation bearing system, comprising a radial magnetic bearing for providing radial support force and an axial magnetic bearing for providing axial support force, wherein the main shaft is suspended and supported within the compressor housing in a non-contact manner via the magnetic levitation bearing system; The gas compression channel is connected in series with each stage of the centrifugal impeller, so that the gas can be sequentially transported and compressed.

[0007] As a further improvement of the present invention: the drive motor is a permanent magnet synchronous motor, the stator of the permanent magnet synchronous motor is fixed inside the compressor housing, and the rotor of the permanent magnet synchronous motor is fixedly mounted on the middle part of the main shaft.

[0008] As a further improvement of the present invention: the centrifugal impeller includes a first-stage impeller, a second-stage impeller, a third-stage impeller and a fourth-stage impeller, the first-stage impeller, the second-stage impeller, the third-stage impeller and the fourth-stage impeller are coaxially connected in series along the axial direction of the main shaft and are located on both sides of the permanent magnet synchronous motor.

[0009] As a further improvement of the present invention: diffusers are respectively provided between the first-stage centrifugal impeller and the second-stage impeller and between the third-stage impeller and the fourth-stage impeller in the compressor housing. A bend, a return flow device and a volute are sequentially provided after each diffuser. The diffuser, bend, return flow device and volute are sequentially connected to form a continuous flow channel that guides the gas from the previous stage to the next stage. The second-stage impeller is connected to the third-stage impeller through the volute and the interstage pipe.

[0010] As a further improvement of the present invention: the magnetic levitation bearing system includes at least two radial magnetic bearings and one axial magnetic bearing. The radial magnetic bearing is an electromagnetic bias bearing. A control coil is wound on the stator core of the radial magnetic bearing for independently controlling the displacement of the main shaft in each degree of freedom by adjusting the control current. The axial magnetic bearing includes a thrust disk fixed on the main shaft and a corresponding electromagnetic stator.

[0011] As a further improvement of the present invention: the diffuser flow area is gradually increased, and the volute flow area is gradually increased.

[0012] As a further improvement of the present invention: inside the compressor housing, protective bearings are also provided on both axial sides of the magnetic levitation bearing system. A radial safety air gap is provided between the inner ring of the protective bearing and the main shaft. The rolling elements of the protective bearing are made of ceramic material.

[0013] As a further improvement of the present invention, it also includes a control unit for coordinating the control of the drive motor and the magnetic levitation bearing system, and multiple displacement detection units for detecting the spatial position of the main shaft; The control unit is signal-connected to the displacement detection unit and the magnetic levitation bearing unit, and is configured to adjust the output force of the magnetic levitation bearing system in real time according to the feedback signal of the displacement detection unit, so as to control the offset of the high-speed rotating spindle. Methods for controlling the spindle offset include: In cycles The radial displacement of the spindle is detected in real time by an inductive displacement sensor. and Obtain the rotation speed and pressure at all levels ; The control unit executes the UFRC-PID composite control algorithm, and the total control force command... Feedforward control force PID feedback control force and robust decoupling compensation force Composite generation, specifically: Based on real-time operating condition parameter vector Through the pre-stored perturbation mapping function, Calculate the feedforward control force: Calculate displacement deviation: r is the reference position; The adaptive PID output force is calculated as follows: Wherein, the gain matrix , , Operating parameters Estimate states that are not directly measured using a state observer. And calculate the robust decoupling compensation force: in, The observer gain matrix; Overall control force: ; Will The excitation current is converted to drive the magnetic bearing, generating electromagnetic force that acts on the spindle, achieving closed-loop control and reducing the radial offset of the spindle. It is stable in the 1-2 micrometer range.

[0014] As a further improvement of the present invention, it also includes an emergency power failure protection circuit integrated inside the compressor. The emergency power failure protection circuit includes an energy storage capacitor module, a voltage detection module, and a switching control module. The energy storage capacitor module is composed of multiple large-capacity electrolytic capacitors connected in parallel, and the total capacity of the energy storage capacitor module is not less than 44000μF. The voltage detection module is used to monitor the status of the main power supply. The switching control module is configured to switch the windings of the permanent magnet synchronous motor to the energy storage capacitor module when the power is lost, so as to use rotational inertia to generate electricity to maintain the power supply of the magnetic levitation bearing system for a short time.

[0015] As a further improvement of the present invention: the emergency power failure protection circuit includes a power failure protection method, specifically: The DC bus voltage of the compressor inverter is monitored in real time. When the DC bus voltage drops below the first set threshold within a preset time, it is determined to be a sudden power outage. An emergency response is triggered, the pre-installed energy storage capacitor module is connected to the DC bus, and the permanent magnet synchronous motor driving the compressor is controlled to switch from electric mode to generator mode. Based on the remaining energy of the system after switching, a deceleration trajectory is planned to smoothly decrease from the current speed to a preset low speed threshold. During the deceleration process, the electrical energy generated by the permanent magnet synchronous motor in power generation mode is used in conjunction with the energy storage capacitor module to supply power to the magnetic levitation bearing system and control unit, so as to maintain the suspension of the main shaft during the deceleration period. When the spindle speed drops to the first set threshold, the spindle is controlled to approach the protective bearing along a preset progressive spatial trajectory, while the excitation current of the magnetic levitation bearing is gradually reduced until the spindle lands on the protective bearing at a contact speed lower than the allowable impact speed, so as to achieve a soft landing.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention, by connecting a four-stage centrifugal impeller coaxially with a permanent magnet synchronous motor rotor and using magnetic levitation bearings, distributes an extremely high total compression ratio to each impeller stage. This allows the compressor to easily handle extreme temperature differences, from -40°C cryogenic refrigeration to 130°C high-temperature heating, significantly expanding its application boundaries in high-pressure, wide-temperature-range scenarios such as industrial heat pumps and process cooling. The magnetic levitation bearings completely eliminate mechanical friction and complex lubrication systems, reducing traditional friction losses by approximately 30% and improving heat exchange efficiency due to the oil-free design, thus enhancing the overall energy efficiency ratio of the compressor.

[0017] 2. The UFRC-PID composite control algorithm integrates high-precision feedforward based on real-time operating conditions, adaptive PID feedback, and robust decoupling compensation. It can perform closed-loop control at a frequency of no less than 50kHz, dynamically stabilizing the radial offset of the high-speed rotor within an accuracy of 1-2 micrometers. This ensures smooth operation under complex airflow disturbances, with extremely low vibration and noise, and improves the dynamic stability of the rotor system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

[0019] Figure 2 This is a cross-sectional structural diagram of the present invention.

[0020] The following are the labels in the diagram: 1. Compressor housing, 2. Permanent magnet synchronous motor, 3. Main shaft, 4. Radial magnetic bearing, 51. Diffuser, 52. Bend, 53. Return valve, 54. Volute, 6. Interstage pipe, 7. Thrust disc, 81. First stage impeller, 82. Second stage impeller, 83. Third stage impeller, 84. Fourth stage impeller, 9. Protective bearing, 10. Thrust bearing. Detailed Implementation

[0021] In order to clearly and completely understand the technical solution, the present invention will be further described in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0023] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0024] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0025] An embodiment of the present invention provides a coaxial multi-stage magnetic levitation centrifugal compressor, comprising: The compressor housing 1 has a gas compression flow channel formed inside it; The main shaft 3 is axially inserted into the compressor housing 1; The drive motor has its rotor fixedly mounted on the main shaft 3; At least three centrifugal impellers are fixedly mounted on the main shaft 3 and coaxially arranged with the rotor of the drive motor, together forming a multi-stage compression unit; A magnetic levitation bearing system, comprising a radial magnetic bearing 4 for providing radial support force and an axial magnetic bearing for providing axial support force, wherein the main shaft 3 is suspended and supported in the compressor housing 1 in a non-contact manner by the magnetic levitation bearing system; The gas compression channel is connected in series with each stage of the centrifugal impeller, so that the gas can be sequentially transported and compressed.

[0026] According to the present invention, the coaxial multi-stage magnetic levitation centrifugal compressor has at least three centrifugal impellers coaxially arranged with the main shaft 3 and the motor rotor to form a series multi-stage compression unit, achieving an ultra-high overall compression ratio and reducing the aerodynamic and thermal loads of each impeller stage. This allows it to maintain high adiabatic efficiency even at extremely high outlet pressures or extremely low suction pressures. The gas flow channels are connected in series to ensure continuous airflow through each stage, improving the overall energy efficiency ratio. The magnetic levitation bearing system enables the main shaft 3 to be suspended in a non-contact manner, eliminating the mechanical friction loss of traditional oil-lubricated bearings, improving transmission efficiency, and allowing the rotor to reach ultra-high speeds of tens of thousands of revolutions per minute without worrying about wear and lubrication issues. The non-contact support method can eliminate the main sources of vibration and noise, making the compressor run smoothly.

[0027] In one embodiment of the present invention, the drive motor is a permanent magnet synchronous motor 2. The stator of the permanent magnet synchronous motor 2 is fixed inside the compressor housing 1, and the rotor of the permanent magnet synchronous motor 2 is fixedly mounted on the middle of the main shaft 3. The permanent magnet synchronous motor 2 uses permanent magnet excitation, which eliminates rotor excitation losses compared to asynchronous motors, resulting in higher efficiency and power factor. Directly connecting it to the main shaft 3 avoids energy loss during transmission, achieving extremely high conversion efficiency from electrical energy to mechanical energy, directly improving the overall energy efficiency of the machine. Simultaneously, the permanent magnet synchronous motor 2 has excellent speed regulation performance and control precision. Through a matching frequency converter, it can achieve wide-range, high-precision stepless speed regulation, meeting the requirements of the magnetic levitation bearing system for rapid speed adjustment, thus coping with load changes, achieving surge protection, and optimizing partial load efficiency.

[0028] In one embodiment of the present invention, the centrifugal impeller includes a first-stage impeller 81, a second-stage impeller 82, a third-stage impeller 83, and a fourth-stage impeller 84. These four impellers are coaxially connected in series along the axial direction of the main shaft 3 and are located on both sides of the permanent magnet synchronous motor 2. The use of four-stage adjustable impellers in series achieves an ultra-high total pressure ratio, distributed across the four compression stages. This ensures that each impeller only needs to withstand a moderate pressure ratio and temperature rise, avoiding the problem of drastic efficiency drops and excessive material stress in single-stage compression under high pressure ratios. This allows the compressor to stably and efficiently cover extreme operating conditions from -40°C cryogenic refrigeration to 130°C high-temperature heating, fundamentally expanding the application boundaries of the equipment in demanding fields such as industrial heat pumps and process cooling. The symmetrical arrangement of the four impellers on both sides of the permanent magnet synchronous motor 2 results in a more balanced mass distribution of the entire rotor system, reducing residual dynamic imbalance forces generated during high-speed rotation from the source.

[0029] In one embodiment of the present invention, diffusers 51 are respectively arranged between the first-stage centrifugal impeller and the second-stage impeller 82 and between the third-stage impeller 83 and the fourth-stage impeller 84 inside the compressor housing 1. A bend 52, a return flow device 53 and a volute 54 are arranged sequentially after each diffuser 51. The diffusers 51, bends 52, return flow devices 53 and volute 54 are connected sequentially to form a continuous flow channel that guides gas from the previous stage to the next stage. The second-stage impeller 82 is connected to the third-stage impeller 83 through the volute 54 and the interstage pipe 6. The flow area of ​​the diffusers 51 and the volute 54 are arranged to gradually increase.

[0030] The diffuser 51 is the core component for energy conversion. Its gradually increasing flow area allows the kinetic energy of the high-speed gas exiting the impeller to be efficiently converted into pressure energy (static pressure). Each impeller stage is followed by a diffuser 51, forming the basic efficiency unit from kinetic energy harvesting (impeller) to kinetic energy conversion (diffuser 51). This multi-stage, repetitive energy conversion pattern is the fundamental flow path for achieving ultra-high adiabatic efficiency in the entire machine. In a multi-stage series structure, the gas needs to change direction and reshape the flow field from the outlet of the previous stage to the inlet of the next stage. The bend 52 is responsible for changing the airflow direction with minimal loss; the return flow device 53 (usually with guide vanes) is responsible for eliminating the circumferential rotational component of the airflow and uniformly guiding it into the inlet of the next stage impeller 81, effectively avoiding severe separation or turbulence when the airflow turns and enters the next stage, maintaining stable flow in the multi-stage compressor under a wide range of operating conditions and preventing inter-stage stall. The first and second stage impellers (groups 82) and the third and fourth stage impellers (groups 84), located on the same side of the motor, each form a relatively independent compression module. Gas is collected in the middle via a volute (54) and then transported across the motor area via interstage pipes (6), solving the flow channel interruption problem caused by the motor occupying axial space and achieving a compact structure. Simultaneously, the gradually expanding cross-section design of the volute (54) assists in diffusion during gas collection, further improving the pressure rise efficiency of single-stage compression.

[0031] In one embodiment of the present invention, the magnetic levitation bearing system includes at least two radial magnetic bearings 4 and one axial magnetic bearing. The radial magnetic bearings 4 are electromagnetic bias bearings, and control coils are wound on the stator core of the radial magnetic bearings 4 for independently controlling the displacement of the main shaft 3 in each degree of freedom by adjusting the control current. The axial magnetic bearing includes a thrust disk 7 fixed on the main shaft 3 and a corresponding electromagnetic stator. The radial magnetic bearings 4 are electromagnetic bias bearings, designed for high-temperature heat pump operation (exhaust temperature can reach above 130°C during heating), solving the defect of permanent magnet bias bearings being prone to demagnetization at high temperatures. Since the excitation magnetic field is entirely generated by the current of the control coil, its strength and stability are not affected by temperature, ensuring the bearing's load-bearing capacity throughout the entire operating temperature range (-40°C to 130°C). The control coils wound on the stator core allow for independent control of the displacement of the main shaft 3 in each degree of freedom by adjusting the control current. Each radial bearing can independently control at least two orthogonal directions (such as X and Y). Combined with the axial bearing, this constitutes a complete electromagnetic levitation of the main shaft 3 in all five degrees of freedom. The control unit can adjust the current of each coil in real time through algorithms to generate the required electromagnetic force, instantly compensating for any minute rotor misalignment. This allows the main shaft 3 offset to be controlled within 1-2 micrometers, suppressing high-speed rotor micro-vibration. The axial magnetic bearing employs a thrust disk 7 and a corresponding electromagnetic stator structure. The thrust disk 7 is fixed to the main shaft 3 and forms an air gap with the electromagnetic stators on both sides, providing bidirectional, high-load-bearing axial active control. For multi-stage centrifugal compressors, the axial force exerted by the gas on the impeller is enormous and complex. This axial magnetic bearing can detect and counteract changing axial forces in real time, maintaining the rotor's axial position. Working in conjunction with the radial bearing, it ensures the rotor's stable suspension in space, avoiding friction and collision in any direction.

[0032] In one embodiment of the present invention, protective bearings 9 are provided on both axial sides of the magnetic levitation bearing system inside the compressor housing 1. A radial safety air gap is provided between the inner ring of the protective bearing 9 and the main shaft 3. The rolling elements of the protective bearing 9 are made of ceramic material.

[0033] Protective bearings 9 are positioned on both axial sides of the magnetic levitation bearing system. Their function is to act as a barrier in the event of complete failure of the magnetic levitation system, such as power outages, control malfunctions, or severe overloads, catching the falling high-speed rotor and preventing a catastrophic collision between the rotor and stator. A radial safety air gap is provided between the inner ring and the main shaft 3 to ensure that the main shaft 3 is suspended in the center position during normal operation of the magnetic levitation system, with no contact between it and the inner ring of the protective bearing 9, thus preventing any mechanical friction from occurring in the protective bearing 9. The rolling elements are made of ceramic material, which has high temperature resistance and can maintain its performance even at the high temperature remaining on the rotor after the magnetic bearing is powered off, avoiding the risk of steel bearings softening or seizing due to high temperatures; its low density and high hardness can withstand the huge instantaneous impact and centrifugal force when the high-speed rotor falls, with minimal wear; its self-lubricating properties perform even better during short periods of dry running.

[0034] In one embodiment of the present invention, the main components of this application are: High-speed impeller: A core component and a key part of the centrifugal compressor, responsible for performing work on the gas. A closed impeller typically consists of a cover, a disc, and blades. It is usually made of high-strength alloy or titanium alloy. The impeller is matched with a high-speed motor via a rotor, rotating at extremely high speeds.

[0035] Spindle 3: The function of spindle 3 is to support the rotating parts mounted on it and transmit torque.

[0036] Diffuser 51: An annular space surrounding the impeller. As the gas flows out of the impeller, it still maintains a relatively high velocity. To fully utilize this velocity energy and increase the gas pressure, a diffuser 51 with a gradually increasing flow area is installed behind the impeller; its cross-sectional area gradually increases, making it a key component for energy conversion.

[0037] Permanent Magnet Synchronous Motor 2: Modern and more advanced technology adopts a variable frequency drive permanent magnet synchronous motor 2, which directly drives the impeller to achieve the required speed, resulting in higher efficiency and a more compact structure.

[0038] Magnetic levitation bearing: Supports the rotor to operate at high speed and stably. Magnetic levitation technology is a hallmark of modern high-end centrifuges. It uses electromagnetic force to suspend the main shaft 3 in the air, completely eliminating mechanical friction, resulting in extremely high efficiency and eliminating the need for a lubrication system.

[0039] Imported regulating valve: Located at the front end of the air inlet, it is used to adjust the opening and closing angle of the blades and control the flow rate of gas entering the compressor. It is a key component for energy regulation.

[0040] Thrust plate 7: In a multi-stage centrifugal compressor, the thrust plate 7 is used to balance the axial force caused by unequal gas forces, ensuring the normal operation of the rotor.

[0041] Thrust bearing 10: During normal operation of the centrifugal compressor, the pressure difference between the inlet and outlet creates an axial thrust pointing towards the low-pressure side (inlet side). The compressor's balancing device can balance most of the axial force, and the residual axial force is borne by the thrust bearing 10, whose thrust block is called the main thrust block. Additionally, during startup, the impact of the airflow often generates an axial thrust in the opposite direction, causing the rotor to move towards the high-pressure side; therefore, an auxiliary thrust block is added opposite the main thrust block. This type of thrust bearing is called a double-end thrust bearing 10.

[0042] Bend 52: In a multi-stage centrifugal compressor, the gas must bend between stages, so bend 52 is used. Bend 52 is a curved annular space formed by the casing and partitions.

[0043] Return valve 53: The channel connected after bend 52 is the return valve 53. The function of the return valve 53 is to ensure that the airflow enters the next stage evenly in the required direction. It consists of baffles and guide vanes. The guide vanes are usually arc-shaped and can be cast as one piece with the cylinder or manufactured separately and then bolted together.

[0044] The volute 54 is mainly used to collect the gas behind the diffuser 51 or the impeller and lead the medium gas out of the compressor to the delivery pipeline or gas cooler. In addition, during the gas collection process, in most cases, due to the gradual increase in the outer diameter and the gradual increase in the flow area of ​​the volute 54, it also plays a certain role in slowing down and diffuser.

[0045] Protective bearing 9: Employing a precision, high-speed, stable, wear-resistant ceramic protective bearing 9, its function is to support the rotor for high-speed operation, prevent residual axial force on the rotor, limit axial movement of the rotor, and maintain the rotor in a defined axial position. When the machine is shut down and stops working, the rotor loses its magnetic levitation support and becomes suspended in the air; in this case, the protective rotor may fall, causing friction and potentially leading to mechanical failure.

[0046] The working process of a coaxial four-stage heat pump compressor (centrifugal compressor) can be divided into the following nine main steps: Step 1: Inhalation and Flow Low-temperature, low-pressure refrigerant vapor (usually Freon-based substances such as R134a, R1234ze, R507A, etc.) is drawn from the evaporator into the compressor inlet. The inlet valve adjusts its opening according to the system load demand, controlling the gas flow rate into the impeller.

[0047] Step 2: First-level compression acceleration and increase in kinetic energy Gas enters a high-speed rotating impeller. The blades on the impeller drive the gas to rotate and do work on it. Under the action of strong centrifugal force, the gas is thrown from the center (hub) of the impeller to the edge (rim). In this process, the gas velocity is greatly increased, gaining enormous kinetic energy. At the same time, due to the centrifugal force, the gas pressure also increases slightly.

[0048] Step 3: Gas deceleration and pressure energy conversion After leaving the impeller, the high-speed airflow enters the bladeless diffuser 51, whose cross-sectional area gradually increases. According to Bernoulli's equation in fluid mechanics, with the expansion of the flow channel, the fluid velocity decreases while the pressure increases significantly. This process is similar to a high-speed car suddenly going uphill, where the speed decreases but the potential energy increases. Here, most of the gas's kinetic energy is effectively converted into the pressure energy (potential energy) we need.

[0049] Step 4: Second-stage impeller 82 compression The impeller rotates at speeds of thousands to tens of thousands of revolutions per minute, imparting a powerful centrifugal force to the gas. This process increases the gas's kinetic energy, causing it to be thrown towards the impeller edge, resulting in a significant increase in its velocity, pressure, and temperature.

[0050] Step 5: Gas collection and discharge The gas, after being compressed twice, is further pressurized by diffuser 51 and then collected in volute 54. The flow channel design of volute 54 also gradually increases its cross-section, which can further reduce the airflow velocity and increase the pressure. The gas collected in volute 54 is then led out of the compressor and transported through 2-3 stage pipelines to the third-stage compressor impeller for further compression and pressurization.

[0051] Step 6: Third-stage impeller 83 compression Due to the high pressure requirement, the gas compressed to the interstage pressure by the three-stage impeller 83 will be guided to the next stage (fourth stage) impeller through the bend 52 and the return flow device 53 for repeated compression, so that the gas velocity and pressure will increase again during the flow process.

[0052] Step 7: Gas deceleration and pressure energy conversion The high-speed gas then enters the diffuser 51 (an annular flow channel fixed behind the impeller). As the cross-sectional area of ​​the flow channel gradually increases, the gas velocity decreases, and the kinetic energy is converted into static pressure energy, further increasing the gas pressure.

[0053] Step 8: Fourth-stage impeller 84 continuous compression The compressor's multi-stage impeller compresses the gas to the required refrigerant gas pressure for the system.

[0054] Step 9: High-pressure gas output The gas after final stage compression is collected by the volute 54, whose spiral design reduces airflow vortex losses. Finally, the high-temperature, high-pressure refrigerant gas is discharged from the compressor exhaust port and transported to the downstream system through the outlet pipe to enter the condenser for the next step of condensation and heat release process.

[0055] In one embodiment of the present invention, it further includes a control unit for coordinating the control of the drive motor and the magnetic levitation bearing system, and multiple displacement detection units for detecting the spatial position of the main shaft 3. The control unit is signal-connected to the displacement detection unit and the magnetic levitation bearing unit, and is configured to adjust the output force of the magnetic levitation bearing system in real time according to the feedback signal of the displacement detection unit, so as to control the offset of the high-speed rotating main shaft 3. Methods for controlling the offset of spindle 3 include: In cycles The radial displacement of spindle 3 is detected in real time by an inductive displacement sensor. and Obtain the rotation speed and pressure at all levels ; The control unit executes the UFRC-PID composite control algorithm, and the total control force command... Feedforward control force PID feedback control force and robust decoupling compensation force Composite generation, specifically: Based on real-time operating condition parameter vector Through the pre-stored perturbation mapping function, Calculate the feedforward control force: Calculate displacement deviation: r is the reference position; The adaptive PID output force is calculated as follows: Wherein, the gain matrix , , Operating parameters Estimate states that are not directly measured using a state observer. And calculate the robust decoupling compensation force: in, The observer gain matrix; Overall control force: ; Will The excitation current is converted to drive the magnetic bearing, generating an electromagnetic force that acts on spindle 3, achieving closed-loop control and causing the radial offset of spindle 3 to... It is stable in the 1-2 micrometer range.

[0056] Feedforward control Based on real-time operating conditions (speed, pressure at each stage), major disturbances (such as the 84 gas force in the fourth-stage impeller) are calculated and counteracted in advance, eliminating most predictable disturbances before they affect the rotor. Adaptive PID feedback. Then, the residual unknown perturbation is handled, and its gain matrix is... , , It can adaptively adjust to different operating conditions, ensuring optimal control performance under varying loads and temperatures. Robust decoupling compensation. The inherent gyroscopic effect, mass imbalance, and coupling interference between degrees of freedom of the high-speed rotor are intelligently counteracted through a state observer. This is achieved through the operation condition parameter vector. By sensing the compressor's operating status in real time and adjusting the feedforward model and PID parameters accordingly, the control system can automatically adjust to the optimal control strategy, thereby maintaining ultra-high efficiency and stability across the entire operating range and effectively expanding the compressor's safe and efficient operating range.

[0057] In one embodiment of the present invention, an emergency power failure protection circuit integrated inside the compressor is also included. The emergency power failure protection circuit includes an energy storage capacitor module, a voltage detection module, and a switching control module. The energy storage capacitor module is composed of multiple large-capacity electrolytic capacitors connected in parallel, and the total capacity of the energy storage capacitor module is not less than 44000μF. The voltage detection module is used to monitor the status of the main power supply. The switching control module is configured to switch the winding of the permanent magnet synchronous motor 2 to the energy storage capacitor module when the power is lost, so as to use rotational inertia power generation to maintain the power supply of the magnetic levitation bearing system for a short time.

[0058] In one embodiment of the present invention, the emergency power failure protection circuit includes a power failure protection method, specifically: The DC bus voltage of the compressor inverter is monitored in real time. When the DC bus voltage drops below the first set threshold within a preset time, it is determined to be a sudden power outage. An emergency response is triggered, the pre-installed energy storage capacitor module is connected to the DC bus, and the permanent magnet synchronous motor 2 driving the compressor is controlled to switch from electric mode to generator mode. Based on the remaining energy of the system after switching, a deceleration trajectory is planned to smoothly decrease from the current speed to a preset low speed threshold. During the deceleration process, the electrical energy generated by the permanent magnet synchronous motor 2 in the power generation mode is used in conjunction with the energy storage capacitor module to supply power to the magnetic levitation bearing system and control unit, so as to maintain the suspension of the main shaft 3 during the deceleration period. When the spindle speed of the spindle 3 drops to the first set threshold, the spindle 3 is controlled to approach the protective bearing 9 along a preset progressive spatial trajectory, while the excitation current of the magnetic levitation bearing is gradually reduced until the spindle 3 lands on the protective bearing 9 at a contact speed lower than the allowable impact speed, so as to achieve a soft landing.

[0059] By monitoring the DC bus voltage in real time and quickly determining when a power outage occurs, the system can connect the energy storage capacitor and switch the motor to generator mode. At this moment, the permanent magnet synchronous motor 2 becomes a generator, and the rotor's enormous rotational inertia becomes a temporary power source. Working in conjunction with the capacitor's energy storage, it continuously supplies power to the critical magnetic levitation control system, overcoming the weakness of traditional magnetic levitation systems where a power outage results in a fall. This transforms the unprotected free-fall impact into a controlled deceleration process with energy support. During the deceleration phase, the system plans the optimal deceleration trajectory based on the remaining energy, such as the controller adjusting the current rotor speed. Estimate the total remaining energy of the system and plan a smooth deceleration reference trajectory. For example, using an exponential or S-shaped curve: , Optimized settings based on available energy and safety constraints. Motor controller based on... Adjust the generator torque to achieve the actual rotational speed. The curve is tracked to gradually decrease. Simultaneously, the magnetic bearing controller adaptively adjusts the bearing control parameters based on the changes in dynamic characteristics caused by the decrease in rotational speed, maintaining suspension stability and ensuring a smooth decrease in rotational speed to avoid rotor dynamic instability due to stall. During the low-speed landing phase, its control logic switches from maintaining precise center suspension to guiding a gradual approach, controlling the rotor to slowly move towards the protective bearing 9 along a predetermined spatial trajectory while gradually reducing the magnetic force. This ensures that the contact speed between the rotor and the protective bearing 9 is strictly controlled at an extremely low level below the permissible impact speed.

[0060] It also includes anti-surge control, which performs the following steps during compressor operation: High-frequency pressure signal acquisition and feature extraction: The dynamic pressure signal in the compressor intake pipe is acquired in real time at a sampling frequency of not less than 10 kHz, and the pressure signal is preprocessed and filtered; based on the processed pressure signal, at least one time-domain feature value reflecting the pressure pulsation intensity and one frequency-domain feature value reflecting the pressure oscillation frequency are calculated in real time. Real-time surge risk assessment: Based on the current compressor operating parameters and the time-domain and frequency-domain characteristic values ​​calculated in real time, a surge proximity index is calculated using a preset surge prediction model; when the surge proximity index exceeds a preset safety threshold, the operating point is determined to be close to the surge boundary, and an active intervention command is immediately triggered; Multi-actuator coordinated active intervention: After triggering the active intervention command, at least two of the following adjustment actions are executed synchronously or sequentially to bring the compressor operating point out of the surge risk zone: Control the hot gas bypass valve to increase its opening within 100-300 milliseconds to quickly reduce the exhaust back pressure; The adjustable guide vanes for controlling the air intake can be adjusted to increase the air intake volume. The inverter controlling the compressor slightly increases the output frequency; Risk Relief and Status Restoration: After the active intervention is performed, the surge proximity index is continuously monitored; when the index falls back to a safe range and stabilizes for a preset time, the risk is determined to be relieved, and the hot gas bypass valve, adjustable intake guide vane and frequency converter are controlled to gradually restore to the set state before the intervention.

[0061] By acquiring dynamic pressure signals at a frequency of at least 10 kHz and combining time-domain and frequency-domain feature extraction, the system can capture early surge precursor signals that are undetectable by traditional methods. Quantitative assessment using the surge proximity index allows for intelligent determination of the approaching risk boundary before the operating point reaches the traditional fixed surge line. Rapidly opening the hot gas bypass valve within 100-300 milliseconds instantly reduces back pressure; simultaneously adjusting the inlet guide vanes and increasing the rotational speed directly increases flow capacity and alters the compressor characteristic curve, pulling the operating point back from the edge of the surge cliff to the core of the safe zone. After successful intervention, the risk is continuously monitored until completely eliminated, and the actuator is gradually restored to its pre-intervention optimized settings.

[0062] In summary, after reading this invention document, those skilled in the art can make various other corresponding modifications to the technical solutions and concepts based on this invention without creative mental effort, and all of these modifications fall within the scope of protection of this invention.

Claims

1. A coaxial multi-stage magnetic levitation centrifugal compressor, characterized by, include: The compressor housing has a gas compression flow channel formed inside it; The main shaft passes through the compressor housing along the axial direction; A drive motor, the rotor of which is fixedly mounted on the main shaft; At least three centrifugal impellers are fixedly mounted on the main shaft and coaxially arranged with the rotor of the drive motor, together forming a multi-stage compression unit; A magnetic levitation bearing system, comprising a radial magnetic bearing for providing radial support force and an axial magnetic bearing for providing axial support force, wherein the main shaft is suspended and supported within the compressor housing in a non-contact manner via the magnetic levitation bearing system; The gas compression channel is connected in series with each stage of the centrifugal impeller, so that the gas can be sequentially transported and compressed.

2. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 1, characterized in that, The drive motor is a permanent magnet synchronous motor. The stator of the permanent magnet synchronous motor is fixed inside the compressor housing, and the rotor of the permanent magnet synchronous motor is fixedly mounted on the middle part of the main shaft.

3. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 2, characterized in that, The centrifugal impeller includes a first-stage impeller, a second-stage impeller, a third-stage impeller, and a fourth-stage impeller. The first-stage impeller, the second-stage impeller, the third-stage impeller, and the fourth-stage impeller are coaxially connected in series along the axial direction of the main shaft and are located on both sides of the permanent magnet synchronous motor.

4. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 3, characterized in that, The compressor housing contains diffusers between the first-stage and second-stage centrifugal impellers and between the third-stage and fourth-stage impellers. Behind each diffuser, a bend, a return flow device, and a volute are sequentially arranged. The diffusers, bends, return flow devices, and volutes are connected in sequence to form a continuous flow channel that guides gas from the previous stage to the next stage. The second-stage impeller is connected to the third-stage impeller through the volute and interstage pipes.

5. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 4, characterized in that, The magnetic levitation bearing system includes at least two radial magnetic bearings and one axial magnetic bearing. The radial magnetic bearings are electromagnetic bias bearings. The stator core of the radial magnetic bearings is wound with a control coil, which is used to independently control the displacement of the main shaft in each degree of freedom by adjusting the control current. The axial magnetic bearing includes a thrust disk fixed on the main shaft and a corresponding electromagnetic stator.

6. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 5, characterized in that, The diffuser flow area is gradually increased, and the volute flow area is gradually increased.

7. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 1, characterized in that, Inside the compressor housing, protective bearings are also provided on both axial sides of the magnetic levitation bearing system. A radial safety air gap is provided between the inner ring of the protective bearing and the main shaft. The rolling elements of the protective bearing are made of ceramic material.

8. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 6, characterized in that, It also includes a control unit for coordinating the control of the drive motor and the magnetic levitation bearing system, and multiple displacement detection units for detecting the spatial position of the spindle; The control unit is signal-connected to the displacement detection unit and the magnetic levitation bearing unit, and is configured to adjust the output force of the magnetic levitation bearing system in real time according to the feedback signal of the displacement detection unit, so as to control the offset of the high-speed rotating spindle. Methods for controlling the spindle offset include: In cycles The radial displacement of the spindle is detected in real time by an inductive displacement sensor. and Obtain the rotation speed and pressure at all levels ; The control unit executes the UFRC-PID composite control algorithm, and the total control force command... Feedforward control force PID feedback control force and robust decoupling compensation force Composite generation, specifically: Based on real-time operating parameter vector , through pre-stored disturbance mapping function, Calculate feedforward control force: Compute displacement deviation: r is the reference position; The adaptive PID output force is calculated as follows: wherein the gain matrix , , is a working condition parameter Estimating non-directly measured states by state observers and computing a robust decoupled compensation force: wherein, is the observer gain matrix; Total control force of synthesis: ; Will Convert to excitation current drive magnetic bearing, generate electromagnetic force acting on the spindle, realize closed loop control, make the spindle radial offset Stable in the range of 1-2 microns.

9. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 6, characterized in that, It also includes an emergency power failure protection circuit integrated inside the compressor. The emergency power failure protection circuit includes an energy storage capacitor module, a voltage detection module, and a switching control module. The energy storage capacitor module is composed of multiple large-capacity electrolytic capacitors connected in parallel. The total capacity of the energy storage capacitor module is not less than 44,000 μF. The voltage detection module is used to monitor the status of the main power supply. The switching control module is configured to switch the windings of the permanent magnet synchronous motor to the energy storage capacitor module when the power is lost, so as to use rotational inertia to generate electricity to maintain the power supply of the magnetic levitation bearing system for a short time.

10. A coaxial multi-stage magnetic levitation centrifugal compressor according to claim 9, characterized in that, The emergency power failure protection circuit includes a power failure protection method, specifically: The DC bus voltage of the compressor inverter is monitored in real time. When the DC bus voltage drops below the first set threshold within a preset time, it is determined to be a sudden power outage. An emergency response is triggered, the pre-installed energy storage capacitor module is connected to the DC bus, and the permanent magnet synchronous motor driving the compressor is controlled to switch from electric mode to generator mode. Based on the remaining energy of the system after the switch, a deceleration trajectory is planned to smoothly decrease from the current speed to a preset low speed threshold. During the deceleration process, the electrical energy generated by the permanent magnet synchronous motor in power generation mode, together with the energy storage capacitor module, powers the magnetic levitation bearing system and control unit to maintain the levitation of the main shaft during the deceleration period. When the spindle speed drops to the first set threshold, the spindle is controlled to approach the protective bearing along a preset progressive spatial trajectory, while the excitation current of the magnetic levitation bearing is gradually reduced until the spindle lands on the protective bearing at a contact speed lower than the allowable impact speed, so as to achieve a soft landing.

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