Magnetic Drive System Research Of Axial Blood Pump In Large Air Gap

Abstract:Blood pump as auxiliary devices in patients with heart failure, the main function is to achieve natural heart’s pumping function, so the research on the magnetic drive system is the primary problem for the clinical application。Increase the air gap of the magnetic drive system will facilitate to the impeller optimal design, which will reduce hemolysis and blood damage of the pump, but at the same time the pump’s volume also increased. Due to the large volume, only two clinical artificial heart type has been designed for children. Developed a miniaturized, intelligent, stable and durable artificial heart is the trend. Electromagnetic driving torque is the primary meet condition of the driving structure to miniaturization, the energy efficiency、temperature、quick and smooth speed adjustment will direct influence the pump’s long-term implantable and stable operation,in these aspects which lack of depth research.In this paper, based on the situation of blood pump’s from the main pole gap large(5mm),taking the rapid and stable speed control and blood pump’s miniaturization、high efficiency and low temperature rise as the target; researching on the basic science issues of driving characteristics, energy loss,temperature and speed control methods, the miniaturized and low temperature rise blood pump driving system is proposed, which provided a reference for blood pump’s magnetic driving system design.The main contents and conclusions:(1)Designed blood pump large air gap magnetic drive system. Electromagnetic driving torque as a primary objective for drive system performance, the mathematical model of the blood pump shaft load torque is established, which got the relationship between shaft load torque value with speed. Using ANSYS software numerical calculated the driving torque of ten different structure scheme which has been designed, three alveolar stator was chosen according to the results and the actual manufacturing. The preferred outer diameter was chosen28mm after analyzed the influence of the stator diameter、air gap length and thickness of permanent magnet with the driving torque、inductance and magnetic induction.(2) Establishment the energy loss mathematical model of blood pump. The energy loss mathematical model of the magnetic driver system’s stator core, permanent magnets, copper, water circuit and bearing were established. The stator core loss and permanent magnet loss of the three alveolar were analyzed by ANSOFT, the stator iron loss and permanent loss at the speed of9000rpm were0.291w and2.4wm.The energy transfer efficiency mathematical model were established, experiments show that the average transfer efficiency of driving stator and blood pump were46.85%and10.88%.(3)The research of blood pump thermal field. The theoretical model of blood pump fluid-structure interaction temperature field were established. The thermal performance parameters for temperature field simulation were identified. Simulation results show that:at the speed of8600rpm, the max temperature rise is6.976℃which appeared in the stator winding region, and the shell max temperature rise is4.024℃. The temperature related factors sensitivity of the stator phase winding, speed and shell housing thermal conductivity were analyzed, when the phase winding is3Ω, the shell maximum temperature rise is2.264℃, at the speed of8000rpm, the shell maximum temperature rise is2.707℃, both has low temperature rise.(4)System hardware and speed control strategies research.The drive> control、inverter and feedback hardware circuit of control system were designed. The startup acceleration strategy were proposed based on the blood pump mechanical-electromagnetic-hydrodynamics performance, the speed control curve were got and blood pump accelerated to9000rpm is3.9s.The constant and low-power current control strategy was proposed for blood pump steady state.