Abstract
Power quality and energy efficiency are of great importance in motor control. The motor of any medical device needs to have a smooth torque and minimal vibration in order to maximise its energy efficiency and patient comfort. Furthermore, in rotary blood pumps, excessive energy wasted due to vibration is converted into uncontrolled movement of the mechanical parts and thus could reduce the life of the motor-pump. Besides mechanical or hydraulic origin, one of the causes of vibration in any pump is torque ripple resulting from motor phase commutation. In this paper, using relevant equipment, two extreme scenarios were examined for vibration and electrical efficiency comparison due to power quality in a blood pump: one trapezoidal control with a trapezoidal phase current output; the other a field oriented control (FOC) with a non-distorted sinusoidal phase current. The test motor-pump was the Arteriovenous Fistula Eligibility (AFE) System that is used prior to haemodialysis. The trapezoidal technique was implemented utilising the Allegro a4941 fan driver (Allegro Microsystem, 2012), and the FOC technique was implemented using the Texas Instrument digital signal processor (TMS320F28335). The aim was to reduce the energy wasted over vibration, and to achieve smooth operation of the AFE System. Vibration was measured with a one-axis accelerometer; results showed considerably lower vibration due to less current ripple associated with the FOC control as well as lower power consumption.
Highlights
In medical applications, in wearable medical devices, a motor must function with smooth torque and minimal fluctuation over its operational speed range in order to maximise efficiency and patient comfort by reducing motor vibration and acoustic noise
This paper studies the vibration and power consumption improvement of the Arteriovenous Fistula Eligibility (AFE) System motor with a field oriented control (FOC) instead of its current trapezoidal controller based on the power quality improvement
Motor vibration is a important factor in medical devices, as it is associated with power consumption, durability of mechanical parts, patient comfort, and haemolysis in blood pumps
Summary
In wearable medical devices, a motor must function with smooth torque and minimal fluctuation over its operational speed range in order to maximise efficiency and patient comfort by reducing motor vibration and acoustic noise. Vibration that exists in a motor may be due to (i) hydraulic sources (such as operating away from the best efficiency point and flow turbulence [3]); (ii) the mechanical sources (such as unbalanced impeller, bent shaft, eccentricity, cogging torque, and electro motive force (EMF) waveform imperfections [4,5,6]); or (iii) torque ripple resulting from ineffective motor commutation [7,8]. Besides the design and point of operation, the choice of motor commutation is a critical factor in the quality of operation of a motor, and could be a source for electromagnetic torque ripple (the periodic change of output torque) [9,10]
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