DEVELOPMENT OF A PRECISE CONTROLLER FOR AN ELECTROHYDRAULIC TOTAL ARTIFICIAL-HEART - IMPROVEMENT OF THE MOTORS DYNAMIC-RESPONSE

In an electrohydraulic total artificial heart developed at the Nationa l Cardiovascular Center (Osaka, Japan), two blood pumps are pushed alt ernatively by means of the bidirectional motion of a brushless DC moto r for pump systole and diastole. Improvement in the dynamic response o f the motor is very important to obtain better pump performance; this was accomplished by using power electronic simulation. For the motor t o have the desired dynamic response, it must be commutated properly an d the damping ratio (zeta), which represents transient characteristics of the motor, must lie between 0.4 and 0.8. Consequently, all satisfa ctory specifications with respect to power consumption must be obtaine d. Based on the simulated results, the design criteria were determined and the precise controller designed to reduce torque ripple and motor vibration, and determine motor stop time at every direction change. I n in vitro tests, evaluation of the controller and dynamic response of the motor was justified in terms of zeta, power consumption, and moto r stop time. The results indicated that the power consumption of the c ontroller and the input power of the motor were decreased by 1.2 and 2 .5 W at zeta = 0.6, respectively, compared to the previous system. An acceptable dynamic response of the motor, necessary for the reduction of torque ripple and motor vibration, was obtained between zeta = 0.5 and zeta = 0.7, with an increase in system efficiency from 10% to 12%. The motor stop time required for stable motor reoperation was determi ned to be over 10 msec, for a savings in power consumption of approxim ately 1.5 W. Therefore, the improved dynamic response of the motor can contribute to the stability and reliability of the pump.