Design and Performance Analysis of Coupled Dual Axial Flux PM Machines for Left Ventricular Assist Devices

This study aims to design a small-sized embedded axial flux permanent magnet synchronous motor (AFPMSM) for a left ventricular assist device (LVAD) pump. The power density per unit volume of the AFPMSM structure is much higher than conventional radial flux permanent magnet machines, so it is preferred for the geometry of the pump structure. For further enhancement in torque density and reliability, dual motors have been fitted into the pump structure successfully. AFPMSM is first analyzed analytically to shrink the design space, and then finite element analysis (FEA) methods were employed to give the motor its final shape. Experimental validations were performed by measuring the back-emf, torque, efficiency, and loss values of the prototyped AFPMSMs. The measured torque constant of 9.58 mNm/Arms ensures that the phase current of 0.35 Arms is sufficient for the LVAD pump when both motors are running at the same time. Compared to other commercial and non-commercial LVAD models, the proposed twin motor structure is superior in terms of volume and weight. Furthermore, it has advantages in terms of patient and device safety due to its natural fault-tolerant structure. Finally, due to the hidden embedded motors, blood flow can be created quite smoothly without any significant impeding effect caused by the motors. This resulted in increased pump efficiency and the desired motor power and torque. In this way, smaller yet more powerful motors can be used.