For decades, the majority of motor control applications have relied upon universal, brushed DC, and stepper motors given their low cost and simplicity of implementation. Continued innovation and integration of microcontroller (MCU) architectures, however, enable today's developers to cost-effectively improve motor precision, performance, power efficiency, and motor life through the use of more complex--and more intelligent--motor types and control mechanisms.
Advanced motor types
AC Induction (ACI) motors are well-suited for a wide range of high-performance applications, including white goods, pumps, fans and compressors (i.e., refrigerators and HVAC systems). ACI motors are asynchronous in operation since the motor's internal stator and rotor, controlled by varying current, rotate at different speeds. Offering excellent speed and torque control, ACI is robust, efficient at high speeds and low cost. The primary disadvantage of ACI is the need for complex feedback and control mechanisms to hold efficiency across variable and lower speeds.
Brushless DC (BLDC) motors are synchronous and control stator flux by varying current while rotor flux is held constant by permanent magnets or current-fed coils. Synchronous control can provide high position accuracy and better power efficiency (i.e., with the inherent flux of the magnets, less current is required to drive the motor). BLDC motors control position using a set number of states (see Figure 1). The more states supported, the more precisely position can be controlled but it also means more complex processing will be required. BLDC is attractive for applications where maintenance and wear impact total cost of ownership since they have no brushes. One of the fastest growing types of motors, BLDC provides efficient, reliable operation across medium-high torque, offers high power density, and can be used in combustible environments for applications such as automation, traction, precision and white goods. Since BLDC uses simple commutation techniques, systems are less complex and lighter in weight, leading to small size, high efficiency for the cost, and excellent performance at variable and low speeds.
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- Easier to control (six trapezoidal states)
- Torque ripple at commutations
- Better for lower speed
- Doesn't work with distributed winding
- Not as efficient, lower torque
- Lower cost
Figure 1: Brushless DC (BLDC) motors ease control complexity by using a set number of states. The more states supported, the more precise position can be controlled but the more complex processing that will be required.
Permanent magnet synchronous motors (PMSM) differ from BLDC motors by taking a "continuous" approach to control (see Figure 2). As such, PMSM offers low noise operation, minimal torque ripple at commutation, and works with low-cost distributed windings. Supporting a higher maximum achievable speed as well as higher efficiency and torque, they are well-suited for applications requiring precise position control, very high speed, and/or high torque such as traction, precision automation (robotics) and hybrid/electrical vehicles.
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- More complex control (continuous 3Ph sine wave)
- No torque ripple at commutation
- Higher maximum achievable speed
- Low noise
- Work with low-cost distributed winding
- Higher efficiency, higher torque
- Higher cost
Figure 2: Permanent magnet synchronous motors (PMSM) take a "continuous" approach to control to increase positioning precision. Offering low noise operation and minimal torque, PMSM is well-suited for applications requiring precise position control, very high speed, and/or high torque.