Investigation of Control Frequency for Maglev Artificial Hearts

Abstract

　We have constructed a maglev control system consisting of microcomputers and PWM amplifiers to miniaturize the digital control system of a ventricular assist device (VAD). The maglev control's high-speed arithmetic processing capability is essential to realizing the maglev control's stability. Unfortunately, the microcomputer has limited arithmetic processing capability. We evaluate the effect of the control frequency on the maglev control's stability with the control simulation and experiments. Simulation results showed that the control system oscillated and became less stable as the control frequency was reduced. The control frequency at which instability occurred was estimated to be 1.5 - 4 kHz from the phase margin and gain crossing frequency. When the vibration performance of the actual machine was evaluated for each control frequency, the axial vibration amplitude was maximum around the control frequency estimated by the simulation. Therefore, the actual machine and control system used in this experiment required a sampling frequency of 1.5 - 4 kHz or higher.