Semiconductor technology keeps the simplicity of brushed motors
Unexpectedly, brushed motors and incandescent lamps have much in common: they were invented and optimized in the 19th century, and their ease of use made them ubiquitous in our daily lives in the 20th century. They were also influenced by regulations that focused on energy efficiency in the 21st century. . Most incandescent lamps have disappeared, but the more energy-efficient brushless motors are still a slow alternative to brush motors. This is partly due to cost and because of the significant technical challenges involved in implementing a brushless motor system. Semiconductor technology has led to the disappearance of cheap but inefficient incandescent lamps, as well as the ability to move the brushed motor to the same end.
The motors are everywhere, but unlike light bulbs, they are not so obvious. When there is an inanimate physics moving, it is most likely driven by a motor. These motors drive our home refrigerators, dishwashers and washing machines. They open the door, run the escalator, the vertical elevator and the train to send us to work. They make coffee, cool the computer and run the air conditioner while we work. In modern cars, 20 to 50 motors are used to power a variety of different functions such as adjusting mirrors, headlights and seats, fuel pumps, pumps and windshields, and assisting braking and steering. In the future, the motor will even be responsible for letting the car move by itself.
In the past century, most of the motors selected for these applications were brushed motors because they are very easy to use. Like a light bulb, it works as long as it is energized – the reverse voltage passes through the terminal and the motor reverses direction. When you change the voltage, the speed changes. This simplicity may be caused by a mechanical switch (commutator) inside the motor that rotates it. The commutator consists of a rotating copper slip ring and a slip joint (called a brush) that is connected to the rotating motor coil, which causes current to flow from the stationary motor housing to the slip ring. When the motor coil assembly rotates, the coil terminals slide past the brush, indicating that current flows through the coil, maintaining rotation in such a manner.
Figure 1: Schematic diagram of brushed motor
Although the commutator makes the brushed motor easy to use, it is also a major source of problems. The commutator is subject to mechanical wear and limits the life of the motor. Brush wear produces dust and reduces motor performance. In addition, an arc is generated when motor current flows between the coils along the slip ring. Such brush arcs generate ozone and cause noise and electronic radiation that can interfere with electrical equipment such as telephones, radios, and wireless communication networks. In dusty or flammable environments, brushing the arc can be dangerous because it can cause a fire or even an explosion. The commutator uses a mechanical brush that also limits the motor's energy efficiency by up to 70%, while the brushless motor achieves up to 90% energy efficiency (as Nicola Tesla showed up as early as the end of the 19th century). If brushless motors are more energy efficient, more reliable and more environmentally friendly than brushed motors, why are brush motors still so common today?
Just like incandescent and LED lights, replacing some cheap and simple things with something more complicated and expensive usually requires strong pressure from the government until mass production lowers the price. International energy efficiency standards (such as Energy Star in North America and Eco-Design in the European Union) force companies to comply. In addition, consumers are increasingly concerned about the environment and energy conservation, and now are more willing to spend money on energy-saving products, either for conscientious reasons, or to reduce electricity bills. Therefore, energy efficiency is seen as a purely regulatory requirement and is seen as a way for engineers to differentiate their products from their competitors. Similarly, in the automotive sector, automakers have been asked to improve fuel economy through ever-tightening CO2 emissions standards. This can be done in many creative ways, but a sustainable approach is to drive systems that are traditionally connected to the engine and motor. The latter can be better optimized for the task at hand and only run when necessary. A good example is the power steering system, which must provide maximum steering support with an idling engine while parked. When the power steering system is still connected to the engine, it consumes a lot of power on the bus, and the steering is minimal, so the power steering system in the car becomes the first application to use a brushless motor. As regulations become more stringent, brushless motors are being designed into hydraulic pumps to provide brake support, engine cooling fans, fuel pumps, oil/pumps, and more.
Although the replacement of conventional brushed motors with brushless motors is a fast way to improve energy efficiency and reliability while eliminating noise and pollution, the implementation of brushless motors is a major challenge for engineers. Work that had previously been mechanically done by the commutator is now done electrically using a three-phase inverter. The inverter requires a gate driver, which is typically controlled by a microcontroller implementing complex motor control algorithms. Therefore, engineers developing these applications not only need to be competent in hardware design and microcontroller programming, but also need to have an in-depth understanding of motor physics to design the maximum energy efficiency into the system. Brushed motor application designers often do not have these skills, so they are reluctant to use brushless motors.
These engineers need a ready-made solution that allows the brushless motor to operate without the need for in-depth design and programming expertise. The goal is to make brushless motor application development as simple as brush motor development, so that application engineers can focus on their expertise to the application rather than how to rotate the motor. Similar to LED lights replacing incandescent lamps, the semiconductor industry can support the shift to brushless motor deployments by addressing the complexity of motor control systems for customers. Advantageously, some companies are beginning to address the challenge.
An example is ON Semiconductor, which has used its "easy-to-use" motor driver experience for stereo equipment, disk drives and cooling fans, focusing on the development of brushless motors for industrial and automotive applications. In particular, the company introduced a highly integrated LV8907 motor driver IC that makes brushless motors as easy to use as brush motors without any software development. The LV8907 can be used in 12 V industrial and consumer applications, and is compatible with automotive requirements, requiring only six power switches and several discrete resistors and capacitors. The IC is responsible for starting up, eliminating the need for sensors to commutate and operate the various safety features required for brushless motors. After the motor and application related parameters are uploaded via the SPI interface, a pulse width modulated signal (PWM) is required to control the motor speed - just like a brushed motor application. All relevant parameters can be stored in the device's embedded non-volatile (OTP) memory and will remain fixed throughout the life of the application.
Although a switch can be used for fixed speed mode, the LV8907's built-in PI speed control loop combined with PWM input supports precise regulation of motor speed under different supply voltage and load conditions. Thanks to the integrated protection of the device, the application is protected from overcurrent, overvoltage and overtemperature and other fault conditions. In the case of a stall, the LV8907 will stop driving the motor and restart after setting the interval.
In short, the transition from brushed to brushless motors is already underway, and for reasons of energy efficiency, and increasingly stringent government regulations are accelerating this development. However, as this transition involves significant technical challenges, they still have obstacles to increase the range of brushless motor applications. By introducing intelligent motor control solutions for brushless motors, the semiconductor industry is providing more and more products to eliminate these obstacles. Therefore, brushless motors, like LED lights, may become more common as new technologies are introduced in the 21st century to meet environmental challenges. Perhaps soon, brush motors have become history like incandescent lamps.
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