Title: Principle of Brushless DC Motor Control

Introduction: In the realm of motor control, the ability to precisely regulate the rotation and speed of motors is paramount. This control is facilitated by motor drive systems, also known as electronic speed controllers (ESCs). ESCs are categorized into brushed and brushless types, depending on the type of motor they are paired with.

Brushed DC motors feature a stationary permanent magnet with coils wound around the rotor. Rotation is achieved by intermittently changing the magnetic field direction through a brush and commutator contact. In contrast, brushless DC motors lack brushes and commutators; their rotors consist of permanent magnets while the coils remain stationary. To enable rotation in brushless DC motors, an electronic speed controller is required to continually alter the direction of current within the fixed coils, ensuring repulsion between the coils and the permanent magnets to sustain rotation.

While brushed motors can operate without an ESC by directly supplying power, they lack speed control. On the other hand, brushless DC motors necessitate an ESC for operation. The ESC converts DC power into three-phase AC power to drive brushless DC motors.

Early ESCs primarily featured brushed motor control. The distinction between brushed and brushless ESCs lies in their compatibility with the respective motor types. Brushed motors utilize carbon brushes, distinguishing them from brushless motors where the rotor is composed of magnetic blocks and the stator remains stationary. The nomenclature of brushed and brushless ESCs is derived from these motor distinctions. In technical terms, brushed ESCs output DC power, while brushless ESCs output three-phase AC power. DC power, found in batteries with positive and negative terminals, contrasts with AC power, which oscillates between positive and negative along a single wire. Understanding these distinctions lays the foundation for comprehending three-phase AC power and DC power.

Brushless ESCs receive DC input, stabilize voltage with a filtering capacitor, and split the power into two branches: one for the ESC's Battery Eliminator Circuit (BEC) and another for MOSFET usage. Upon activation, the ESC's microcontroller initiates MOSFET oscillation, producing the characteristic sound of brushless motor operation. Some ESCs feature throttle calibration functionality to ensure proper throttle positioning before entering standby mode. The microcontroller within the ESC adjusts voltage output, frequency, and drive direction based on PWM signals to control motor speed and direction. During motor operation, three sets of MOSFETs within the ESC work in tandem to generate a frequency of 8000Hz, effectively mimicking an inverter or speed controller used in industrial motor applications.

Brushless ESCs require DC input typically supplied by lithium batteries. Their output consists of three-phase AC power capable of directly driving motors. For aerial models like quadcopters, specialized ESCs with three signal input lines for PWM control are essential. Quadcopters feature four propellers arranged in a cross configuration to counteract inherent spinning tendencies. The small diameter of each propeller disperses centrifugal forces, unlike traditional rotorcraft propellers that concentrate inertial centrifugal forces. As a result, quadcopters require high-speed ESCs for rapid response to attitude changes, as conventional PPM ESCs with approximately 50Hz update rates are inadequate for the swift adjustments needed in quadcopter flight control.

Conclusion: In summary, the principle of brushless DC motor control involves the use of electronic speed controllers to convert DC power into three-phase AC power for driving brushless motors. Understanding the intricacies of ESC operation, from throttle calibration to PWM signal processing, is crucial for optimizing motor performance in various applications, including aerial models like quadcopters. Specialized ESCs with high-speed communication interfaces play a critical role in ensuring stable flight dynamics and rapid response capabilities, making them indispensable components in modern motor control systems.