A brushless DC geared motor consists of a motor body and a driver, and is a typical mechatronic product. The stator windings are typically configured in a three-phase symmetrical star connection, very similar to a three-phase asynchronous motor. Magnetized permanent magnets are attached to the rotor, and a position sensor is installed inside the motor to detect the rotor polarity. The driver, composed of power electronics and integrated circuits, functions to: receive start, stop, and brake signals from the motor to control these actions; receive position sensor signals and forward/reverse signals to control the switching of power transistors in the inverter bridge, generating continuous torque; receive speed commands and speed feedback signals to control and adjust the speed; and provide protection and display functions.
DC motors offer advantages such as fast response, high starting torque, and the ability to provide rated torque from zero speed to rated speed. However, these advantages are also their disadvantages. To generate constant torque under rated load, the armature magnetic field and rotor magnetic field must be maintained at a constant 90° angle, which requires carbon brushes and a commutator. Carbon brushes and commutators generate sparks and carbon dust during motor rotation, which can damage components and limit their application.
AC motors, without carbon brushes and commutators, are maintenance-free, robust, and widely applicable; however, achieving performance equivalent to DC motors requires complex control techniques. Rapid advancements in semiconductors have significantly increased the switching frequency of power components, improving drive motor performance. Microprocessors are also becoming increasingly faster, enabling AC motor control to be placed in a rotating two-axis Cartesian coordinate system. By appropriately controlling the current components of the AC motor on both axes, similar control to dc brush gear motor can be achieved, with performance comparable to DC motors.