Brushless speed control for a novel brazilian axial ventricular assist device

ABSTRACT

OBJECTIVES: The reduction in size of these systems, which increases their reliability, biocompatibility and robustness, is essential to the complete implantation of the VADs, which is the main focus of the current state of art. Continuous flow VADs are actuated by brushless motors due to their reliability. The objective of the current project was to implement and simulate sensorless speed control in order to actuate VAD. METHODS: In order to increase the robustness of the system even further, a strategy that does not use Hall sensors can be implemented. The sensorless strategy to control speed that was implemented in this work aims to detect the position of the rotor by using the coil of the inactive phase in order to sense the variation in magnetic flux, which comes in the form of back-electromotive forces. RESULTS: A three phase inverter to electrically commute the motor's phases, a conditioning circuit that obtains the back-electromotive forces and a speed controller were developed. The speed control and the commutation logic were implemented by using a microcontroller. The results that were obtained in computational simulations indicated that the three-phase inverter, the commutation logic and the controller reached the project requirements. The implemented microcontroller commutation logic presented the expected behavior. Commutation signals were obtained in six stages, necessary for the correct activation of the phases of the brushless motor. The controller was validated in terms of its step response, demonstrating low overshoot and fast control action in the system. CONCLUSIONS: To further enhance the robustness of the system, an alternative strategy that eliminates the use of Hall sensors can be employed. The sensorless speed control strategy, implemented in this study, detects the position of the rotor by measuring variations in magnetic flux through the coil of the inactive phase, thus relying on back-electromotive forces for detection.