978-1-4799-8478-7/14/$31.00 ©2014 IEEE Six-Step Commutation with Round Robin State Machine to Alleviate Error in Hall-Effect-Sensor Reading for BLDC Motor Control Eka Firmansyah, F. Danang Wijaya, Rendy Aditya W. P., Ridwan Wicaksono Electrical Engineering & Information Technology Engineering Faculty, Universitas Gadjah Mada, Sleman, Indonesia Abstract— Hall-effect sensors are commonly applied in brushless direct current (BLDC) motor control for rotor position detection. By knowing the exact position of the rotor, inverter could supply energy in synchronize to the BLDC motor state. As the motor is categorized as synchronous motor, those sensors are vital. Working out of synchronization not only makes drive system less efficient but also threaten the inverter as current requirement will be increased. Unfortunately, the sensor works in harsh environment where high current, high temperature, and high vibration are exist. Those conditions result in some incorrect position detections. In order to improve the hall-effect position accuracy, in this paper, a simple finite state machine (FSM) called round robin technique is implemented. This technique along with conventional R-C filter in the sensor line successfully suppresses error in the rotor position detection. This results in higher inverter reliability and smoother motor operation. Keywords— brushless direct current motor; sensored control; round robin finite state machine; hall-effect rotor position detection. 1 I. INTRODUCTION Brushless direct current (BLDC) motors are gaining popularity in many areas including electric vehicle [1]. This is due to its advantage of good weight to power ratio, excellent acceleration performance, less maintenance, less acoustic and electrical noise compared to brushed DC motors [2]. The BLDC motor is actually a synchronous motor. Its rotor is comprised of permanent magnets while its rotor is made of windings [3]. It is therefore important to energize the stator winding at certain pattern in accordance to the rotor position. Fig. 1 Inverter normally used to control BLDC motor. This research is funded by Indonesia National Electric Car Project. The inverter normally used to supply the BLDC motor is depicted by Fig. 1. It is a three-phase inverter with three-legs of semiconductor switches normally made of two IGBTs or MOSFETs on each leg. Those semiconductors, therefore, has eight possible switch activation combinations. However, two of that combinations result in zero volt voltage. It leaves only six active combinations for the inverter to supply the BLDC motor as shown in Fig. 2. To gain rotor-stator synchronization, a position sensor is normally implemented. Hall-effect sensor is commonly used while other kind of position sensor like optical based sensor is also known. As depicted in Fig. 2, each hall-effect sensor combination codes corresponds to certain switch pattern for synchronization to be occurs. Therefore, the output signal of the hall-effect sensor should be noise free to guaranty the correct switching pattern to be succesfully produced. In real operating circuit, the hall-effect signal output is rarely noise-free. Certain amount of glitch occurs due to harsh environment arround them such as, high and fast-switching current, high temperature, and high vibrations give some degree of position inacuracy. Those glitches, if not properly anticipated, will result in incorrect switching pattern. This could result in inverter or motor damage, additional motor vibration, and some other issues. In this paper, a simple round- robin finite state machine is implemented to generate the switching pattern based on noisy hall-effect signal code. This technique, while simple, could improve the inverter reliability and reduce BLDC motor vibrations. Fig. 2 BLDC motor switching pattern in synchronizes to 1200 hall-effect sensors signals. 2014 IEEE International Conference on Electrical Engineering and Computer Science 24-25 November 2014, Bali, Indonesia 251