The Difference Between Brushless DC Motors and Stepper Motors

A brushless DC motor (BLDC, also known as an electronically commutated motor (ECM or EC motor) or synchronous DC motor) is a synchronous motor that uses direct current (DC) power. Essentially, a brushless DC motor is a permanent magnet synchronous motor with position feedback, using a DC power input and an inverter to convert it into three-phase AC power.

There are various types of motors, but the brushless DC motor is currently the most ideal speed-regulating motor. It combines the advantages of both DC and AC motors, possessing the excellent adjustment performance of DC motors and the simple structure, no commutation sparks, reliable operation, and ease of maintenance of AC motors. Therefore, it is widely welcomed in the market and used in automobiles, home appliances, industrial equipment, and other fields.

A stepper motor is an open-loop controlled motor that converts electrical pulse signals into angular or linear displacement; it is also called a pulse motor. Under non-overload conditions, the motor's speed and stopping position depend only on the frequency and number of pulse signals, and are not affected by load changes. When a stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in a set direction, called the "step angle." The stepper motor rotates step by step at fixed angles. The angular displacement can be controlled by controlling the number of pulses, thus achieving precise positioning. Simultaneously, the speed and acceleration of the motor can be controlled by controlling the pulse frequency, thus achieving speed regulation. Stepper motors are widely used in peripherals of digital computers, as well as printers, plotters, and disk drives.

The main differences between brushless DC motors and stepper motors are as follows:

1. Brushless DC motors have higher speeds than stepper motors.

2. The driving principles of brushless DC motors and stepper motors differ. Brushless DC motors rely on alternating power supplies provided by Hall effect sensors for positioning and control of rotation. Stepper motors are directly driven by single-phase pulse voltages and do not require Hall effect sensors for positioning. The rotation angle can be precisely positioned by controlling the number of pulses applied to the motor.

3. Due to the different driving principles, brushless DC motors are generally used in applications where high control precision is not required. Stepper motors are used in applications requiring high control precision.

DC brushless motors can be categorized into three main applications:

Continuous load applications: Primarily used in fields requiring a certain speed but not high precision, such as fans, water pumps, and hair dryers. These applications are relatively low-cost and often use open-loop control.

Variable load applications: Primarily used in applications where the speed needs to vary within a certain range, demanding higher requirements for motor speed characteristics and dynamic response time. Household appliances such as spin dryers and compressors are good examples, as are oil pump control, electrical controllers, and engine control in the automotive industry. These applications have relatively higher system costs.

Positioning applications: Most industrial and automatic control applications fall into this category. These applications often involve energy transfer, thus requiring specific dynamic response and torque, and placing higher demands on the controller. Photoelectric sensors and synchronization devices may be used for speed measurement. Process control, mechanical control, and transportation control are many applications in this category.

Key characteristics of stepper motors include:

1. The accuracy of a typical stepper motor is 3-5% of the step angle, and this accuracy is non-cumulative. 2. The maximum permissible surface temperature of a stepper motor.

Overheating a stepper motor will first cause the magnetic material to demagnetize, leading to a decrease in torque and even loss of steps. Therefore, the maximum permissible surface temperature of the motor depends on the demagnetization point of the magnetic material. Generally, the demagnetization point of magnetic materials is above 130 degrees Celsius, and some even reach above 200 degrees Celsius. Therefore, a surface temperature of 80-90 degrees Celsius is perfectly normal for a stepper motor.

3. The torque of a stepper motor decreases as the speed increases.

When a stepper motor rotates, the inductance of each phase winding generates a back electromotive force (EMF). The higher the frequency, the greater the back EMF. Under its influence, the phase current decreases as the frequency (or speed) increases, resulting in a decrease in torque.