In today’s world, motors are ubiquitous, powering everything from household appliances to industrial machinery. The importance of optimizing motor control for energy efficiency cannot be overstated, given that motors account for a significant portion of global energy consumption. This article delves into the structure of motors, the use of variable frequency drives (VFDs), and the solutions for motor control applications, including hardware support and advanced algorithms.
The prevalence of motors
Motors are integral to our daily lives, found in household appliances like washers, dryers, dishwashers, and pool pumps. They are also essential in automotive applications, with modern cars containing anywhere from 40 to 100 motors, depending on the model and trim level. Industrial environments are heavily reliant on motors, particularly in robotics and factory automation. Figure 1 shows the range of motor applications from household appliances to automotive and industrial.
Figure 1 The range of applications involving motors highlights the prevalence of this technology and thus the importance of considering their energy consumption and efficiency. Source: Microchip
According to the Energy Information Administration, approximately 50% of global energy consumption is attributed to motors. In industrial applications, this figure can exceed 80%. For instance, in the United States, the total energy consumption in 2022 was 4.07 trillion kilowatt-hours, equating to a daily consumption of 11.2 billion kilowatt-hours. Improving motor efficiency by just 1% could save 56 million kilowatt-hours of energy daily.
Key trends in motor efficiency
Figure 2 shows the four avenues to improve motor efficiency: energy efficiency motors, the use of drives and better electronics, advanced algorithms, and the integration of IoT. This section will touch upon these four topics and go into more detail.
Figure 2 The four avenues to improve motor efficiency: energy efficiency motors, the use of drives and better electronics, the integration of IoT, and advanced algorithms. Source: Microchip
Energy efficient motors
One of the primary trends in motor efficiency is the transition from traditional motors, such as AC induction motors, to more efficient types like brushless DC (BLDC) motors, permanent magnet synchronous motors (PMSM) and interior permanent magnet (IPM) motors. These motors offer higher efficiency and improved performance. Additionally, advancements in materials, such as the use of amorphous metals and rare earth magnets, have further enhanced motor efficiency.
Material advancements
In the realm of motor technology, advancements in materials and design have significantly enhanced the efficiency and performance of motors over the past century. As shown in Figure 3, a motor typically consists of end bells, a rotor, bearings, and a stator with windings.
Figure 3 The basic structure of a motor where rotor and stator coils materials have shifted from aluminum to copper. Source: Microchip
Over the years, the materials used in these components have evolved. For instance, the transition from aluminum to copper in the rotor and stator coils has improved conductivity and efficiency. Additionally, advancements in manufacturing tolerances have reduced noise and further increased efficiency.
One notable trend in motor technology is the use of amorphous materials in rotors and stators. Traditionally, silicon steels were used, but they had high eddy current and hysteresis losses. These are now being replaced by amorphous materials like metallic glasses, which have lower losses and thus higher efficiency.
For permanent magnet motors, stronger magnets, such as those made from rare earth materials like neodymium, iron and boron, provide more torque and efficiency. However, due to sustainability concerns, alternatives like aluminum, nickel, chromium, and ferrite-based magnets are being explored for their good properties over a range of temperatures and strong magnetic fields.
Motor structure
The transition from journal bearings to ball bearings has played a significant role in reducing friction and improving tolerances, thereby enhancing motor efficiency. Over the past century, motors have become considerably smaller while maintaining the same power output. As shown in Figure 4, a modern 5-horsepower, squirrel-cage rotor, three-phase induction electric motor (SCIM) is substantially smaller and weighs approximately 20% of what a motor with the same power rating did in 1910. This reduction in size can be attributed to the use of lighter and more efficient materials, as well as advancements in thermal and electrical insulation.
Figure 4 A timeline of the reduction in mass for a 3.7 kW SCIM motor from 1910 to 2020. Source: Hitachi
Lighter motors are particularly beneficial for automotive applications, where reducing weight can lead to increased efficiency and the ability to integrate motors into more compact spaces. As we continue to explore new materials and designs, the potential for even greater efficiency and performance in motor systems remains promising.
Variable frequency drives
Variable frequency drives (VFDs) have become increasingly popular for controlling motor speed and improving efficiency. VFDs adjust the motor’s speed to match the load requirements, reducing energy consumption. The transition from insulated gate bipolar transistors (IGBTs) to silicon carbide (SiC) and gallium nitride (GaN) technology in VFDs has also contributed to higher efficiency and faster switching.
VFD impact
Variable Frequency Drives (VFDs) have revolutionized motor control by allowing precise control over motor speed and torque. This technology optimizes motor performance and significantly improves system efficiency. A VFD adjusts the frequency and voltage supplied to the motor, enabling it to operate at the most efficient point for a given load.
For instance, traditional motor systems often operate at full power, with flow rates controlled by throttling valves, leading to substantial energy losses. In contrast, VFDs eliminate the need for throttling by adjusting the motor speed to match the required flow rate, thereby reducing energy consumption and increasing overall system efficiency. As shown in Figure 5, studies have shown that switching to a VFD can more than double the efficiency of a motor system, from around 31% to 72%.
Figure 5 Switching to a VFD can more than double the efficiency of a motor system, from around 31% to 72%. Source: [1]
Motor control hardware
As shown in Figure 6 a range of power management devices are necessary to effectively benefit from VFDs.
Figure 6 Basic block diagram of supporting power management devices for motor control. Source: Microchip
AC-DC converters utilizing SiC in tandem with gate drivers enable precision switching for efficient power conversion. MCUs with motor-specific peripherals and specialized algorithms, e.g. dsPIC33 digital signal controllers (DSCs), can be optimized to convert DC to variable AC. Finally, integrated sensors offer real-time feedback on current, voltage and temperature, enhancing system reliability.
Advanced control algorithms
Traditional methods, such as V/F control for AC induction motors, are cost-effective and straightforward but may not offer the highest efficiency. More advanced algorithms, such as six-step commutation for BLDC and PMSM motors, can offer sensor or sensor-less precision torque control. Field-oriented control (FOC), for example, uses a single-cycle MAC with data saturation as well a zero overhead looping and barrel shifting for high performance speed, position, and torque control. Figure 7 shows a sample block diagram for FOC of a motor using the least FPGA resources to execute a full motor control algorithm.
Figure 7 The block diagram for modular sensorless BLDC motor control algorithm using coordinate rotation digital computer (CORDIC) with sine-cosine required for FOC of motors. Source: Microchip
The Zero-Speed/Maximum-Torque (ZS/MT) control algorithm is a new variation of the sensorless FOC algorithm that enables the adoption of sensorless control techniques in high-torque or low-speed motor control applications. ZS/MT eliminates the need for Hall effect sensors by using a reliable initial position detection (IPD) method based on high-frequency injection (HFI) to determine the exact rotor position at zero and low speeds, making it ideal for applications like drilling machines, garage door openers, automotive starters and e-bikes.
Integration with IoT and AI/ML
The integration of IoT and AI technologies has revolutionized motor control. Sensors are used to detect current, torque, and rotor position, among other parameters, information that is then fed to MCUs for processing. With the integration of ML, these systems can perform predictive maintenance by analyzing sensor data to predict potential motor failures or maintenance needs.
Predictive maintenance ensures that motors operate at peak efficiency and performance, reducing the likelihood of unexpected breakdowns. By continuously analyzing parameters such as current, torque and vibration, predictive maintenance ensures efficient motor operation and minimizes downtime. Systems can, for instance, employ a classification model to determine the operational state of a motor, identifying whether it is functioning normally or experiencing anomalies such as an unbalanced load or a broken bearing, by monitoring the quiescent current of the motor.
Optimizing motor control
Optimizing motor control for energy efficiency is crucial for reducing global energy consumption and improving the performance of various applications. By transitioning to efficient motors, utilizing VFDs, implementing advanced control algorithms and integrating IoT and AI technologies, significant energy savings can be achieved. As the demand for energy-efficient solutions continues to grow, advancements in motor control technology will play a vital role in meeting these needs.
Pramit Nandy is a product marketing manager at Microchip Technology Inc., focused on motor control applications. Nandy has been with Microchip since 2021 and his previous experience includes a product marking manger position with Onsemi. He holds a master’s degree in electrical engineering from Arizona State University.
Reference
- T. de Almeida, F. J. T. E. Ferreira and D. Both, “Technical and economical considerations in the application of variable-speed drives with electric motor systems,” in IEEE Transactions on Industry Applications, vol. 41, no. 1, pp. 188-199, Jan.-Feb. 2005, doi: 10.1109/TIA.2004.841022.
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