DC motors are widely used in our daily lives, from small household appliances to large industrial and automotive equipment. Broadly speaking, DC motors can be categorized into two main types: wound magnetic field DC motors and permanent magnet magnetic field DC motors. Permanent magnet magnetic field DC motors include the familiar brushed and brushless types.
Brushed DC motors and brushless DC motors
As two commonly discussed types of motors, the biggest difference between them lies in the brushes. Brushed DC motors use permanent magnets as the 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, do not have a commutator between the rotor and stator.
Brushed motors rotate because the coils move continuously in the same direction due to the connection state of the brushes and commutator, the generation of current and magnetic field, and the polarity relationship between the fixed magnet and the outer side of the coil. Brushless DC motors rotate because the magnetic field changes due to the inflow and outflow of current into different coils, causing the outer magnet to rotate the rotor. Brushed and brushless motors have developed in very different ways in the current trend of high-efficiency motor development.
The decline of brushed DC motors is due to two main reasons: first, high-performance power devices are more practical, economical, and reliable in controlling motors, replacing the advantages of brushed motors; second, brushless DC motors do not have brush wear, and therefore have advantages in 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, they can achieve excellent performance. Furthermore, they require almost no electronic control devices, making the entire motor control system quite inexpensive. In addition, they save space for wiring and connectors, and reduce cable and connector costs, making them very cost-effective for applications where energy efficiency is not a primary concern.
DC motors and drives
Motors and drives are inseparable, especially in recent years as market changes have placed higher demands on motor drives. Firstly, there are high requirements for reliability; various protection functions are essential, and built-in current limiting is also required to control motor current during start-up, forced stop, or stall. These all enhance reliability.
Efficient drive control algorithms, such as digital control of motor rotation achieved through speed and phase control, and high-precision positioning control required by actuators, are indispensable for the development of high-performance motor application systems. This necessitates the availability of efficient drive control algorithms that designers can easily use.
Moreover, many manufacturers now directly implement algorithms in hardware and apply them to driver ICs, making it more convenient for designers to use. Convenient driver design is now more popular.
Stability also requires the support of drive technology. Optimizing the drive waveform has a significant impact on reducing motor noise and vibration. Excitation drive technology suitable for various motor magnetic circuits can greatly reduce the instability of the motor during operation. In addition, there is the continuous pursuit of lower power consumption and higher efficiency in drive systems.
A typical driving method for DC motors is the half-bridge drive. Its function is to generate an AC trigger signal through a power transistor, thereby producing a large current to drive the motor. Compared to a full-bridge drive, the half-bridge drive circuit is less expensive and easier to implement. However, the waveform can be degraded and interference can occur during the oscillation transition in a half-bridge circuit. Full-bridge circuits are more expensive and more complex, and are less prone to current leakage.
PWM (Pulse Width Modulation) drives are currently very popular and widely used in DC motors, partly because they reduce power consumption. Many modern PWM solutions for motors have achieved significant advancements in improving duty cycle width, expanding frequency coverage, and reducing power consumption.
When a brushed motor is driven by PWM, the switching losses increase with the PWM frequency. To reduce current ripple by increasing the frequency, a trade-off between frequency and efficiency is necessary. Sine wave excitation PWM drive for brushless motors is also an excellent solution in terms of efficiency, although it is more complex.
summary
As functional demands in the end-market evolve, the requirements for the performance and energy efficiency of DC motors are gradually increasing. Regardless of whether a brushed or brushless DC motor is used, it is necessary to select the appropriate drive technology based on the specific scenario to achieve more reliable, stable, and efficient motor operation.
