What changes in a brushless DC motor to control its operation?

The correct answer revolves around how a brushless DC motor operates and what specifically is adjusted to control its performance. In a brushless DC motor, the rotor's movement is influenced by changes in the magnetic field generated by the stator. This is accomplished by altering the polarity of the field windings.

By changing the polarity to the field windings, the motor can effectively control the direction of the magnetic field, which in turn influences the rotor's position and speed. This method eliminates the need for brushes, which are typical in traditional DC motors, resulting in greater efficiency, reduced maintenance, and a more dynamic response to control signals.

While adjusting the speed of the rotor may be a goal, it is fundamentally tied to the changes in the polarity of the field windings. Similarly, although frequency of the voltage supply is related to how motors can sometimes be driven, brushless DC motors typically use pulse-width modulation (PWM) to achieve speed control rather than modifying the input frequency. Temperature changes can impact motor performance, but they are not a direct method of controlling operation. The focus on polarity changes reflects the unique design and functionality of brushless DC motors, signifying its operational characteristics.