Control and analysis of low inertia miniature synchronous motors

Miniature motors are available in sizes as small as 1.9 mm in diameter by 10 mm in length. Position sensors have not yet been implemented in these small synchronous motors below 8 mm in diameter. Open-loop control is optimal with sine-wave driving electronics, but in this case the electronic box is far from being as small as the motor. Open-loop control, like for stepping motors is usually performed, and works well at high speed. This paper presents a pulse frequency modulation (PFM) technique that can be implemented with small microcontrollers and can significantly reduce the irregularities of movement at any speed. Analysing and measuring the rotation of these small motors is an interesting and difficult problem per se. Adequate test equipment is a requirement to evaluate both open-loop and future closed-loop control algorithms