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This video demonstrates the initial rotor position detection in a sensorless motor system using the RL78/G1F microcontroller. By using the initial rotor position detection solution, startup and continuous position detection on a sensorless BLDC motor can be performed.

A sensorless BLDC motor control cannot use back electromotive force to detect the rotor position while the rotor is stopped or in an extremely low speed state. For this reason, it is necessary to pull the rotor into a specific position for control at startup. But this causes an unexpected rotor motion, such as reverse rotation, whereby the startup is not smooth and is slow. The RL78/G1F can make efficient sensorless initial rotor position detection by using its built-in functions and eliminate unnecessary motion at startup, allowing a smooth, fast and high-torque startup of sensorless BLDC motors.

In the motor startup demo, you can see the comparison of the startup behavior with and without the initial position detection. In the subsequent continuous initial position detection demo, you can see the actual rotor position detection by this solution in manual low-speed rotation.

Please see the demos of how the sensorless BLDC motor’s initial rotor position detection can be realized by using the built-in functions of the RL78/G1F. You can experience the effect!

Note: Since the demo uses a 2-pole motor, there are electrically equivalent positions for every 180-degree mechanical angle.

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