| As a medical device that assists the heart to pump blood normally,the blood pump has become one of the main treatment methods for end-stage heart failure.At present,the blood pump has been developed to the third generation,which is characterized by the introduction of suspension technology to enable the impeller to achieve non-contact support,thereby eliminating mechanical wear,prolonging service life,and reducing blood damage.As the key technology of the third-generation blood pump,magnetic levitation technology is characterized by a small suspension gap,high control precision,and controllable stiffness.However,full passive and full active magnetic levitation systems can not completely meet the requirements due to their structural characteristics.Therefore,it is of great significance to develop the hybrid magnetic levitation technology for centrifugal blood pumps.To explore a radial hybrid magnetic levitation system for Centrifugal Blood Pump,a prototype of the radial hybrid magnetic levitation blood pump was designed and manufactured,and a software and hardware system for magnetic levitation control of blood pump was developed.A parameter self-tuning PID controller based on improved particle swarm optimization(PSO)was designed and implemented,good control performance was obtained in the system control simulation,and has been verified by experiments.(1)The prototype of the centrifugal radial magnetic suspension blood pump was designed and manufactured.The structural design parameters and theoretical levitation force of the magnetic bearing were calculated based on the equivalent magnetic circuit method,the designed magnetic suspension structure is permanent magnet passive suspension in the axial direction and inclined direction,and active control in radial two degrees of freedom.It lays a theoretical foundation for the following simulation and control strategy of blood pump support and experimental verification.(2)The support stiffness and radial coupling characteristics of the magnetic bearing of the blood pump were simulated based on Maxwell software.The magnetic simulation result shows that the stiffness of the passive support is 6.5N/mm and 1.7～2.4 N×m/rad respectively,indicating that it has a good passive support performance.The magnetic field distribution of the bias magnetic field,control magnetic field,and the mixed magnetic field are simulated,the simulation result shows that there is no magnetic field coupling between the two degrees of freedom in the radial direction,which validates the assumption of decoupling between the radial direction and the superposition of the magnetic paths.The magnetic stimulation experiments of radial coupling characteristics and support stiffness are carried out,the simulation result shows that the force-current relationship between the two radial degrees of freedom is far from the equilibrium position and the direction of deviation is slightly opposite to the control direction.The simulation result shows that the current stiffness is 6.742 N/A,and the displacement stiffness is 14.780 N/mm,which is less than the theoretical calculation value under the ideal condition because of the magnetic leakage.The above results show that the rotor can be effectively controlled within the designed air gap.(3)The mathematical model of the magnetic levitation system of the blood pump was established and the system performance was analyzed.The result shows that the system is completely controllable and observable,but the openloop system is unstable and the feedback control is needed.On this basis,a PID controller is designed.According to the closed-loop transfer function,the constraint relation of the parameters of the PID controller was obtained.Aiming at the problem that the PID control parameter tuning depends on the experience and the process is tedious and is difficult to obtain the desired control effect,a parameter self-tuning PID controller based on improved particle swarm optimization was proposed with taking system overshoot,steady-state error and integral of time times absolute error as the optimization objective.The simulation results show that the improved PSOPID controller has a better overall performance than the standard PSOPID controller and the traditional PID controller.(4)To verify the validity of the designed radial hybrid magnetic levitation structure and control method for the centrifugal blood pump,the experimental platform of the blood pump prototype was built,and the magnetic suspension control program was programmed based on STM32.Three groups of experiments were carried out on the blood pump prototype experimental platform: the static levitation of the impeller rotor,the steady response of the impeller rotor,and the anti-disturbance of the impeller rotor.The results of the experiments show that the radial magnetic suspension structure and control method of the centrifugal blood pump designed in this paper has a good dynamic performance and stability. |
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