2.1 Construction of BLDC Motors

BLDC motors can be constructed in several different physical configurations. In the conventional (also known as inrunner) configuration, the permanent magnets are part of the radially center core. In the outrunner (or external-rotor) configuration, the radial-relationship between the coils and magnets is reversed. The stator coils in the outrunner configuration form the center core of the motor, while the permanent magnets spin within an overhanging rotor which surrounds the core. For this application, the inrunner configuration was selected. Figure 2 shows that the rotor is in the center with the permanent magnets and that the stator contains the windings. The inrunner configuration has lower rotor inertia and more efficient heat dissipation when compared to the outrunner model. The most common BLDC motor topology uses a stator structure consisting of three phases. As a result, a standard six-transistor inverter or six-mosfet inverter is the most commonly used power stage.