Low cost sensorless position detection for brushless DC motor

This paper describes a low cost sensorless position detection scheme for a brushless DC motor. This method is based on interruption of the 3 phase-currents and reading the back-EMF. The hardware for measuring the back-EMF is very simple. The method is possible thanks to the flexibility of the modern DSP. The proposed scheme shows how it is possible to get rotor position information with a good accuracy (5°). This precision allows a sinusoidal alimentation. The method takes information about the rotor in a few microseconds (~100 μs) and when it wants. That means it is robust and does not need to wait a back-EMF zero crossing. The goal of this paper is to prove that sensorless sinusoidal alimentation with a very limited number of components is also possible in a wide speed range. The paper presents the method as well as a wide range of experimental results showing the feasibility and the robustness of the proposed method with 2 different brushless DC motors. The speed range starts at about 1% and stops higher than 100% of the nominal speed