Sensorless torque vector speed control of a brushless DC motor

The research described in this paper was intended to evaluate a minimal-computation sensorless control technique for brushless DC motors. The motor used in the research was a cylindrical machine with surface magnets and air-gap windings. Torque vector control is a computationally economical technique for applying torque and flux control loops to electric motors. In the research described, a digital signal processor (DSP) was used to carry out position estimation and control torque and flux by controlling the drive signals to a conventional three-phase, six-switch IGBT inverter The torque vector concept operates by calculation based on a 2-phase equivalent circuit, producing values of flux magnitude and angle and torque. The torque vector control scheme demonstrated a capability for high bandwidth control, as a sampling time of only 2 μs for the inner (torque/flux) loop was achieved with a DSP which had a 50 ns single cycle execution time. The inverter switching frequency is also minimised by the strategy used.