Digital simulation and model validation of brushless DC machines

Concerns the simulation and validation of brushless DC drive models. The combination of an AC machine, rotor position feedback and drive amplifier is normally classed as a brushless drive. With the improvement in power electronic device technology, brushless DC drives are increasingly displacing conventional DC machines in high performance servo applications. A brushless machine is similar to a permanently excited synchronous machine in that the rotor carries permanent magnets which give rise to a very low inertia system whilst the stator typically has a three phase star-connected winding. The stator winding may be either distributed or concentrated leading to two generic machine types: those driven by trapezoidal and those by sinusoidal waveforms. The drive amplifier uses the position feedback information to synthesise the appropriate armature currents. Brushless drives were investigated because very high performance drives were required to meet the specification of a particular engineering problem. Demanding positional control of the drives was required (to within 0.0025 radians at 2500 r/min carrying high inertial loads). In order to achieve the best performance from the drives obtained, simulation was used to predict behaviour and performance, to aid design and attain greater understanding of the systems