Introduction: DC motors are widely used in our daily lives, from small household appliances to large industrial automotive equipment. DC motors can be broadly categorized into two main types: wound-field DC motors and permanent-magnet DC motors.

DC motors are widely used in our daily lives, from small household appliances to large industrial automotive equipment. DC motors can be broadly categorized into two main types: wound-field DC motors and permanent-magnet DC motors. Permanent-magnet DC motors include the familiar brushed and brushless DC motors.

Brushed DC Motors and Brushless DC Motors

Both are well-known motor types, but the biggest difference between them lies in their brushes. Brushed DC motors use permanent magnets as their stator, with coils wound around the rotor. Energy is transmitted through the mechanical action of carbon brushes and a commutator, which is why they are called brushed DC motors. Brushless DC motors, on the other hand, lack a mechanical component like a commutator between the rotor and stator.

In a brushed motor, the coils continuously move in the same direction due to the connection between the brushes and commutator, the resulting current and magnetic field, and the polarity relationship between the fixed magnets and the outer coils, thus rotating the rotor. In a brushless DC motor, current flowing in and out of different coils creates a changing magnetic field, which in turn rotates the outer magnets of the rotor. Brushed and brushless motors have developed significantly differently in response to the current trend toward high-efficiency motors.

The decline of brushed DC motors is due, firstly, to the fact that high-performance power devices acting as motor switches offer a more practical, cost-effective, and reliable control method, replacing the advantages of brushed motors. Second, brushless DC motors, without brushes to wear out, offer advantages in terms of electrical and mechanical noise, energy efficiency, reliability, and lifespan.

However, brushed motors remain a reliable choice for low-cost applications. With the right controller and switches, excellent performance can be achieved. Furthermore, since electronic control devices are rarely required, the entire motor control system can be quite inexpensive. Furthermore, they save space and reduce the cost of wiring and connectors, making them highly cost-effective for applications where energy efficiency is not a priority.

DC Motors and Drives

Motors and drives are inextricably linked, especially as market changes in recent years have placed higher demands on motor drives. First and foremost, high reliability is essential. Various protection features are essential, and built-in current limiting is also required to control motor current during startup, forced stop, or stall. These all enhance reliability.

Efficient drive control algorithms, such as digital motor rotation control technologies through speed and phase control, and high-precision positioning control technologies required by actuators, are essential for the development of high-performance motor application systems. This requires efficient drive control algorithms that are easy for designers to use.

Furthermore, many manufacturers now directly hardware-enable algorithms and implement them in driver ICs, making them more convenient for designers to use. Convenient drive designs are now more popular.

Stability also requires support from drive technology. Optimizing drive waveforms significantly reduces motor noise and vibration. Excitation drive technologies tailored to the specific motor magnetic circuit can significantly improve motor stability during operation. Furthermore, the drive continues to pursue lower power consumption and higher efficiency.

A typical DC motor drive method, the half-bridge drive, generates an AC trigger signal through power transistors, generating high current to drive the motor. Compared to a full-bridge drive circuit, a half-bridge drive circuit is less expensive and easier to design. However, half-bridge circuits are prone to waveform degradation and interference during oscillation transitions. Full-bridge circuits are more expensive and complex, and are also less prone to leakage.

PWM drive, a popular drive solution for DC motors, is now widely used. One reason for its increasing adoption is its ability to reduce the power consumption of the drive power supply. Many current motor PWM solutions have achieved remarkable results in wide duty cycles, improved frequency coverage, and reduced power consumption.

When using PWM for brushed motors, switching losses increase with increasing PWM frequency. When increasing the frequency to reduce current ripple, a trade-off must be made between frequency and efficiency. Sine-wave PWM drive for brushless motors also offers excellent efficiency, albeit with increased complexity.

Summary

As the functional requirements of the end market evolve, the performance and energy efficiency requirements for DC motors are steadily increasing. Regardless of whether a brushed DC motor or a brushless DC motor is used, it is necessary to select the appropriate drive technology according to the needs of the scenario to achieve more reliable, smoother and more efficient motor operation.