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| 8 Electric Motors DC Motors Brushless DC (BLDC) Motors Brushed DC Motors AC Motors Induction Motors Permanent Magnet Synchronous Motors (PMSM) Special Motors Stepper Motors Servo Motors Figure 3: A high-level view of motor classific tions. (Source: Author) HP8K/HT8K Dual Channel Enhancement Mode MOSFETs mouser.com/rohm-hp8k-ht8k-mosfets

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• Allistair WinningMatt CampbellJoseph DowningRudy RamosRicky FloresKatie SandovalKevin Hess, Sr. VPMarketingRussell Rasor, VPGlobal Supplier MarketingHeidi Elliott, Director Marketing CommunicationRaymond Yin, Director Technical Content
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• Demystifying Motor Selection
• Diving Deeper into Control
• An Introduction to Electric Motors
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• Powering Up Electric Motor Drives
• Designing for Movement and Position
• Ensuring Efficiency through Isolation and Sensing
• Mouser and Mouser Electronics are registered trademarks of Mouser Electronics, Inc. Other products,
• logos, and company names mentioned herein may be trademarks of their respective owners. Reference
• designs, conceptual illustrations, and other graphics included herein are for informational purposes only.
• Copyright © 2024 Mouser Electronics, Inc.
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• Electric motors are an essential part of our everyday lives. Although usually hidden from view, they perform countless tasks that make our lives easier, enhance our comfort, and make us more productive. At home, washing machines, vacuum cleaners, microwav
• Motors are available in a wide variety of sizes; for example, one of the world's largest and most powerful motors is the 105MW two-pole electric motor that Siemens has developed for a Chinese energy storage project. At the opposite end of the spectrum, on
• Being an integral part of many applications means an enormous market for electric motors. According to MarketsandMarkets Research, it was worth US$134 billion in 2022, and that figure is expected to rise to US$186 billion in 2027, providing a compound ann
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• Increased efficiency can be achieved in the fabrication of the motor itself through more precise manufacturing techniques and
• advanced materials; supporting components can also be designed to drive the motor more efficiently. For example, variable-speed drives (VSD) and variable-frequency drives (VFD) match the motor's rotation to the load's requirements, ensuring that the syste
• Advanced materials that have been brought to the market relatively recently, such as gallium nitride (GaN) and silicon carbide (SiC), can deliver power to the motor more efficiently. Those power devices are often supported by complex digital computing
• technologies to control the power flow to the motor accurately. Using these technologies can make electric motors considerably more energy efficient, reducing running costs while improving the performance of the systems.
• Additionally, governments and trade organizations around the world use legislation to promote the use of more efficient drives. The United States began regulating electric motors in 1992 as part of its Energy Policy Act. Five years later, the country intr
• Governing bodies have used these IE classifications to mandate a minimum level of efficiency for motors. For example, (EU) 2019/1781, the EU regulation on electric motors and variable speed drives, came into force on July 1, 2021. It expanded on previous
• Motor Operation and Types
• At its most basic level, the electric motor is a simple machine that converts electrical energy into mechanical motion. This process is possible because of the interaction of magnetic fields, where opposite poles attract and similar poles repel. In most m
• As shown in Figure 1, when power is supplied to the rotor, an electric field is created, and the north pole of the electromagnet is repelled by the north pole of the permanent magnet while being attracted to its south pole. It rotates to match the opposin
• Figure 2 shows the main constituent parts of a DC motor. The electromagnet windings, also known as the armature, are part of the rotor construction, which usually also contains a core, bearings, and an axle to allow it to rotate freely. The permanent magn
• In a motor, poles always come in pairs, and the pole count of a motor is the number of permanent magnetic poles. Therefore, a single permanent magnet would be used in a two-pole motor, such as the one shown in Figure 2. Depending on the number of poles in
• The other main category of electric motors is the AC motor, which, as the name suggests, works off an AC power supply. AC motors are like DC motors in that they use a rotor and a stator. However, the stator has multiple coils that energize in pairs in a s
• Both AC and DC motors have further subdivisions, as shown in Figure 3. Later articles will give more details on these types of motors, how they operate, and the applications where they can be best employed.
• Comparison of Benefits
• Every application is different; choosing between an AC motor or a DC motor requires many complex decisions, which this guide will address later. Generally, AC motors are more robust and, because of the way they operate, have higher torque levels than DC m
• The Future of Electric Motors
• Electric motors have been around almost as long as electricity has been reliably harnessed. Only 34 years separated Alessandro Volta's invention of the battery in 1800 and Moritz Jacobi's development of an electric motor with usable mechanical power. Sinc
• Sources
• 1
• "Electric Motors Market Size, Share,
• Industry Analysis [2022-2030],"
• MarketsandMarkets, November 2024,
• https://www.marketsandmarkets.com/
• Market-Reports/electric-motor-market-
• alternative-fuel-vehicles-717.html.
• 2
• "Electric Motors and Variable Speed
• Drives," European Commission, accessed
• January 26, 2024, https://commission.
• europa.eu/energy-climate-change-
• environment/standards-tools-and-labels/
• products-labelling-rules-and-requirements/
• energy-label-and-ecodesign/energy-
• efficient-products/electric-motors-
• and-variable-speed-drives_en.
• 3
• Fluke, "New Testing Approach Matches
• Real World Conditions," Blog, May 9,
• 2021, https://www.fluke.com/en-us/
• learn/blog/power-quality/testing-
• matches-real-world-conditions.
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• the rotor, the rotor does not require power like in a DC motor. The magnetic field generated by the stator induces a current in the rotor, which, in turn, produces its own magnetic field that interacts with the stator's magnetic field, causing the rotor t
• AC motors can be single or three-phase, with three-phase motors using three AC currents, which are out of phase with each other in a triangle of coils. At any time during operation, one coil attracts the rotor, one repels, and one is neutral. As the rotor
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• Electron motionBrushDC Power supplySplit-ring commutatorRotationNSDC MOTOR
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• About the author: Allistair Winning
• Since graduating with a BSc in Electronic Systems from the University of the West of Scotland in 1997, Allistair has worked in electronics media across marketing, PR, and journalism roles. During that time, he worked as the editor of Electronics Engineeri
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• Electric MotorsDC MotorsBrushless DC (BLDC) MotorsBrushed DC MotorsAC MotorsInduction MotorsPermanent Magnet Synchronous Motors (PMSM).Special MotorsStepper MotorsServo Motors
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• In the first article of this series on electrical motors, we looked at AC and DC motors and gave an overview of their operation. Since those motor designs were first introduced, they have been improved and now feature several subcategories. This article w
• AC Motors
• Two main types of AC motors are used extensively today: induction and synchronous. All AC motors discussed in this article rely on the stator to create a rotating magnetic field, which interacts with the rotor's magnetic field to produce torque. The main
• The motors are built with a casing that is hollow in the center. In all examples here, the stator comprises a ring of electromagnets situated around the inside of the casing (Figure 1). The electromagnets are arranged in pairs of poles—with at least one p
• The number of poles affects the speed of the rotor and the torque. When an AC supply is connected, current flows in the coils to produce a magnetic field. The sinusoidal nature of an AC supply means that the magnetic field rotates around the rotor. A moto
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• This formula gives a result in revolutions per second, which can be multiplied by 60 to provide the number of revolutions per minute. As the speed of the motor is related to the frequency of the supply, if a different speed is required, then a variable-fr
• AC motors can be used in single-phase or three-phase topology. However, a single-phase design would not have enough poles to generate a rotating field, and extra winding will be required to provide it. The additional winding must be out of phase with the
• AC Induction Motors
• AC induction motors (also known as asynchronous motors) are often chosen for their simplicity. They have only one moving part—the rotor—which makes them robust and reliable. Their simple design also means that they are very cost-effective. Additionally, i
• The rotor of an AC induction motor can be constructed in several different ways, including as a metal axle or a loop of wire. Still, it is most frequently a "squirrel cage" design for higher efficiency. This type of motor is made from parallel conductive
• The rotating magnetic field induces a current in the rotor bars, which, in turn, generate magnetic fields that interact with the original magnetic field from the stator. This process produces force on the rotor bars, causing the rotor to rotate to "catch
• AC induction motors offer a cheap, reliable design widely used for both industrial and domestic use cases. For example, single-phase motors can usually be found in smaller applications, such as compressors, fans, mixers, toys, and drilling machines. Three
• AC Synchronous Motors
• As the name suggests, in a synchronous motor, the rotor speed and the stator magnetic field speed of rotation are the same. One of the downsides of induction motors is that the slip necessary for them to operate makes them unsuitable for precisely timed a
• For the motor to operate properly, the rotor needs to generate its own magnetic field. The reason for this, especially in larger motors, is the rotor's inertia, which stops it from self-starting and synchronizing with the stator magnetic field. Generating
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• The rotor of an excited synchronous motor has windings that match those in the stator. A DC power supply is used to energize the windings in the rotor to produce a constant magnetic field, allowing the rotor to interact and sync with the rotating magnetic
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• Non-exited synchronous rotors use ferromagnetic materials instead of current to provide the magnetic field in the rotor. There are three main types of non-excited rotor designs: hysteresis, synchronous reluctance, and permanent magnet synchronous.
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• The hysteresis motor rotor is fabricated from layers of material that exhibit a wide hysteresis loop fixed around a solid non-magnetic (usually aluminum) core. The rotor exhibits high retentivity, making it difficult to change the magnetic polarities caus
• Hysteresis motors are simple, silent, and reliable. They require no excitation to start and synchronize smoothly. They also do not draw large amounts of current during startup and operation. They are often used in equipment that needs constant speed and w
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• The rotor of a synchronous reluctance motor is fabricated from a soft magnetic material with properties that create areas of high and low magnetic permeability. Both the rotor and stator are constructed with salient poles. This type of construction can ca
• Reluctance is lowest when the salient poles on the rotor and stator are aligned and highest when they are at maximum misalignment. The rotor always moves from high reluctance to low reluctance, producing torque. This torque will pull the rotor to the near
• Synchronous reluctance motors have grown in popularity recently as electronics have made motor control easier. The design is also simple, cost-effective, rugged, and easy to manufacture. However, the sophisticated drive system required can increase its ov
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• The rotor of a permanent magnet synchronous motor (PMSM) uses magnets to create field poles that generate the required magnetic field. The magnets are either embedded in the rotor or fixed on top. Fixing the magnets to the rotor surface means the design i
• PMSMs feature smooth torque over the whole speed range, quick acceleration and deceleration, and low noise, making them ideal for applications like robotics.
• Hybrid Designs
• Other types of AC motors include designs that take advantage of the best features of two different types of motors. For example, the permanent magnet synchronous reluctance motor combines the high efficiency and flexible control of a synchronous reluctanc
• DC Motors
• DC motors provide high torque when starting, are easy to control, and have less complex rectification. There are two main types of DC motors: brushed and brushless.
• Brushed DC
• The brushed DC motor typically has a permanent magnet stator that supplies a fixed magnetic field. The rotor is constructed from electromagnetic poles, which are energized by brushes that must have contact with the rotor. The interaction of the magnetic f
• Although this design has been in use for over a hundred years, advances in component and material technology have kept brushed motors a viable solution for low-end, cost-effective applications. The design has limitations, but modern MOSFET and IGBT switch
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• Brushless DC
• Like the AC synchronous reluctance motor, brushless DC (BLDC) motors (Figure 3) have gained popularity due to advances in electronics. The design of the BLDC motor shares some similarities with AC motors in that its operation relies on creating a rotating
• The ability to control the speed of the motor precisely by adjusting the voltage to the electromagnetic coils makes BDLC motors ideal for precision applications, such as driving the rotors in drones.
• Conclusion
• This exploration of electric motors reveals a landscape rich in diversity and specialization. AC motors, particularly induction and synchronous types, stand out for their robustness and reliability in a range of applications, from industrial machinery to
• DC motors, notably BLDC variants, excel in precision and efficiency. Their design evolution, propelled by advancements in electronic control systems, renders them ideal for applications requiring high starting torque and accurate speed control, such as dr
• Selecting the right motor type for each application is critical, and no single design fits all. As technology progresses, electric motors will continue to evolve, offering ever-more tailored and efficient solutions for an array of applications.
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• The first two articles in this series examined the basic operation of different electrical motors. In some simple applications, such as computer fans, electric motors that operate at a single speed and in a single direction can be run directly from the po
• There are several different types of motors, each with pros and cons. Getting the best performance and efficiency out of these motors almost always involves implementing a suitable control circuit. Some control methods are simple and require only a few ba
• Brushed DC
• The brushed DC motor is an older design used today mainly because of its low cost. In many applications, designers will incorporate brushed DC motors without control circuits to keep costs down. However, if the speed of the motor needs to be changed or th
• Brushless DC
• Brushless DC (BLDC) motors operate similarly to AC motors, with the stator creating a rotating magnetic field that causes the permanent magnet rotor to rotate. Voltage is used to energize the electromagnets in the windings of the stator in a specific orde
• For smoother rotation, sinusoidal control can provide continuous current change. This type of control usually has an inverter adjusting the voltage and current into each stator winding. A PWM produces the sinusoidal effect as the duty cycle is lengthened
• Sinusoidal control is far more complex than the simple PWM control required for a brushed DC motor, requiring three voltages to be generated and coordinated. As shown in Figure 2, sensors feed a decoder with positional data from the rotor, which is then u
• While sinusoidal control is ideal for providing a smooth, noiseless output, trapezoidal control (Figure 3) maximizes the motor's torque. In this technique, only two windings of equal magnitude are energized at a time, while the third winding is set to zer
• Trapezoidal control can also be achieved without the Hall sensors by measuring the back-EMF generated by the rotation of the rotor to calculate the correct energizing sequence. As only two windings are energized at any point, no current flows in the non-e
• Another option for controlling BDLC motors is using vector control, also known as field-orientated control (FOC). We will look at vector control in more detail in the AC Motors section, as it is most often used in those applications. Vector control perfor
• AC Motors
• AC motors also have a stator that creates a rotating magnetic field by energizing electromagnets in a defined sequence. The speed of the motor is tied to the frequency of the input, so if a change in rotor speed is required, the frequency of the current t
• Scalar Control
• Scalar control operates by keeping the magnetic field generated by the stator at a constant strength. To achieve this, the controller adjusts the voltage and frequency of the power delivered to the electromagnets on the stator. While changing the frequenc
• Vector Control
• Vector control allows the frequency and phase angle of the power delivered to the stator windings to be adjusted. It also controls the current's magnetic flux and torque components, making it the most complex control technique. As such, it is a very effic
• The torque in a motor is caused by the interaction of the electric fields generated by the rotor and stator and is at its highest when those fields are orthogonal. Vector control was developed to keep the two fields orthogonal during the motor's operation
• It is possible to use vector control in several types of motors—including newer hybrid designs, such as permanent magnet-assisted synchronous reluctance motors—by selecting the correct mathematical model for the motor type. This feature can ease future mi
• For example, Microchip Technology's Digital Signal Controller range combines the features of a microcontroller and a DSP (Figure 4).
• Conclusion
• Efficient control of electrical motors is pivotal for optimizing performance across a wide array of applications, from simple household appliances to complex industrial machinery. Various control methods, each with unique advantages and challenges, cater
• The future of motor control looks promising, with continual improvements in microcontroller technologies and software development tools. Many well-known companies are at the forefront, offering integrated solutions that simplify the implementation of comp
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• Torque CommandMotor CurrentSinusoidalLookupPWM ModulatorIAIBICCurrent SensorDECODERPosition SensorABCBLDC Motor
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• Torque CommandMotor CurrentPI ControllerPWM ModulatorIAIBICCurrent SensorDECODERPosition SensorSTATORROTORBLDC MotorABCNS
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• In the previous article in this series, we looked at how the control of electric motors is getting more sophisticated to maximize speed, torque, and efficiency. The highlighted solutions required powerful microcontrollers processing complex algorithms to
• Some of the most popular motor types used today would not be viable without those control methods; for example, permanent magnet synchronous motors (PMSM) and brushless DC (BLDC) motors require extensive mathematical calculations to operate effectively. M
• In this article, we will examine the architectures and components that go into powering electric motors.
• Architecture
• The most widely used method of delivering power to the stator coils in three-phase AC and BLDC motor control designs is by using an inverter (Figure 1). In the vast majority of three-phase AC motor designs, the supply voltage is initially converted to DC,
• Various types of inverters can be used depending on the topology and the number of phases in the motor design. Still, the most popular way of delivering the PWM signal is through a three-phase, two-level configuration Figure 2. In this case, the inverter
• Power Components
• MOSFETs and IGBTs have traditionally been used to act as switches in inverter designs to deliver power. MOSFETs can potentially switch at up to 100kHz but are more often used at speeds in the tens of kHz. They use a manufacturing process similar to that o
• At those higher voltage and current levels, IGBTs are usually the preferred choice of switching devices. An IGBT's structure is similar to a MOSFET, but an extra P+ layer is added at the collector, making it act like a MOSFET driving a PNP transistor (Fig
• Key Parameters
• For both MOSFETs and IGBTs, current handling and peak-voltage ratings are the primary traits needed to meet the requirements of the motor's load. After those specifications, the two devices have secondary and tertiary requirements.
• The most important secondary parameters of MOSFETs are drain-source on-resistance (R
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• DS(ON)
• and gate capacitance. Lower on-resistance reduces resistive losses and lowers the voltage drop when the device conducts, directly resulting in greater efficiency. However, it is not as straightforward as it seems. The gate capacitance is a factor in how q
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• For IGBTs, the on-state voltage drop is a critical specification to consider. This drop includes both the diode drop across the P-N junction and the voltagedrop across the driving MOSFET.
• Contrary to a pure power MOSFET, the on-state voltage drop of an IGBT does not fall below the threshold of a diode.
• Selecting the right component is not just a matter of choosing the right figures from a datasheet because the parameters change during operation. Both the R of the MOSFET and the on-state voltage drop of the IGBT are affected by both temperature and curre
• The Wide Bandgap Revolution
• Until recently, silicon MOSFETs and IGBTs were the components of choice to power electric motors. Many applications remain perfectly acceptable options, but now further choices are available due to the commercialization of wide bandgap technologies. Over
• The bandgap is the energy required for electrons and holes to transition from the valence band to the conduction band. While silicon has a bandgap of 1.12eV, SiC and GaN have band gaps of 3.26eV and 3.39eV, respectively. The breakdown fields of the three
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• The very low gate capacitance of GaN designs also leads to lower switching losses. A great example of how GaN transistors can change power designs can be seen in USB chargers for cell phones, which have shrunk in size, even as their power-handling capabil
• On the other hand, SiC switches a lot slower than GaN while still being faster than silicon solutions. The wide bandgap material offers additional power delivery benefits, such as high voltage and current handling, high thermal conductivity, and robustnes
• Of course, there are trade-offs required to get that better performance. Wide bandgap semiconductors are much harder to drive than MOSFETs and IGBTs, leading to increased design time and complexity. Additionally, one of the most significant advantages of
• Based on initial cost, IGBTs and MOSFETs are less expensive than SiC and GaN transistors, which means they may be a better option for many cost-sensitive applications. However, although SiC and GaN transistors are more expensive than their silicon counter
• All of the types of transistors we have described are perfectly acceptable choices depending on the needs of the application. In fact, as shown in Figure 4, there are significant overlaps at around the 100kHz/10kW level, and all four transistor types may
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• is 3.5MV/cm, GaN is 3.3MV/cm, and silicon is 0.3MV/cm. These figures mean that GaN and SiC are over ten times more capable of maintaining higher voltages. In practical terms, the two wide bandgap materials can switch faster and handle higher voltages for
• Although the bandgap figures look similar for GaN and SiC, their electron mobility figures are very different, and those play a large part in dictating how the new materials are used for power-handling applications. Electron mobility measures how fast an
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• Those better specifications mean that GaN can switch rapidly, ten times faster than silicon MOSFETs.
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• All the different types of electrical motors we have looked at so far in this series have been designed for one simple task: to transform electrical power into rotational mechanical force. The torque generated can be directly utilized or tailored to the l
• Linear Motion
• Turning rotational torque into linear force opens a broader range of applications for electrical motors in areas such as manufacturing, packaging, transportation, and defense applications. There are a few different ways of providing linear motion, includi
• Adding a linear actuator to a motor's output transforms rotational to linear motion quickly and easily. Linear actuators commonly feature devices such as ball screws or lead screws (Figure 1). Both work on a similar principle: Turning the threaded screw p
• Linear actuator designs often include gears, making them suitable for loads that require large amounts of force. The downside of the extra force is that linear actuators tend to be slower than other methods of providing linear motion. Their other drawback
• An alternative way of achieving linear motion is to use a motor designed for that specific purpose. Linear motors operate similarly to conventional motor types, with a rotor, a stator, poles, electromagnets, and permanent magnets. Like conventional motors
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• along the inside of the tube. This type of design can provide both high speed and high force. Tubular linear motors are highly efficient because the force generated by permanent magnets and stator coils is perpendicular to the magnetic field and the curre
• Both linear actuators and linear motors are more precise, efficient, and versatile than hydraulic and pneumatic methods of providing linear motion. As applications for linear motion become more sophisticated and demanding, these advantages are increasingl
• actuators are ideal for applications that require simultaneous high force and high speed.
• Positioning
• Motors can also be deployed in applications that require highly precise positioning, such as pick-and-place machines, printers, robotics, and power tools. Traditional motor designs can be used for positioning applications, but their accuracy is typically
• stepper motors and servo motors.
• Stepper Motors
• Stepper motors are an adaptation of the motors highlighted in previous articles in this series but are specifically designed for positional precision. They
• are most often based on BLDC motors, variable reluctance motors, and hybrid synchronous motors. These motors can be effective positioning devices, but their accuracy depends on the quality of the angular sensor used. Stepper motors are designed to have ma
• The other main physical difference between the stepper motor and BLDC motor designs is that the stepper motor has more poles on the rotor (Figure 3). The larger the number of poles, the more steps the motor can take in one 360° rotation. This usually rang
• in practice, stepper applications often use a sensor to detect the rotor position because of possible slippage through excess speed, load, and other issues (such as vibration, temperature changes, load variations, and mechanical wear and tear). Alternativ
• The stepper motor moves forward or backward in small increments; when it arrives at its target position, it will stay in place as long as the stator coils remain energized and there is no further instruction to move from the controller. Control is achieve
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• Servo Motors
• Stepper motors excel in applications that require a combination of accurate positioning, tight speed control, and low-speed torque. Conversely, servo motors offer a better solution for applications requiring greater speed with higher torque, such as heavy
• The most basic servo system comprises a motor, a control circuit, and a simple feedback device like a potentiometer. Unlike the stepper motor, a servo motor is always a closed-loop system. Servo motor designs can range from very simple to highly sophistic
• Piezoelectric Motors
• Piezoelectric motors differ significantly from all the motors previously discussed in this article. This type of motor uses piezoelectric materials—substances that are mechanically stressed when exposed to an electrical current. The properties of piezoele
• Conclusion
• When considering motor designs for movement and positioning, electrical motors extend beyond the basic conversion of electrical power into rotational force. From the precision and efficiency of linear actuators and motors to the exacting control provided
• A second type of linear motor design that has been growing in popularity recently is the tubular linear motor. Here, disc-shaped permanent magnets are embedded in a long tube, with the stator electromagnetic windings arranged
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• small number of steps. Stepper motors can also be used with linear actuators to provide precise linear motion applications.
• A technique called microstepping was developed to deliver high-resolution stepping without an
• expensive and complex rotor. This technique can also help smooth the motion of the motor. Microstepping uses a PWM signal to control the current in the windings, allowing the rotor to stop between poles, which increases the number of steps available. It d
• Microstepping can also be used in place of gearing in some applications, but while it does not introduce back-EMF or reduce system speed, it can't multiply the torque in the same way that gears can. There is also a danger of introducing smaller steps than
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• So far, this series of articles on motor control has focused on the construction and function of electrical motors and ways to control and supply power to them. However, these are not the only features required to design a complete system that allows the
• Isolation
• Isolation protects a circuit by creating a physical break in the current path (Figure 1), which is essential for most motors to operate. These motors use high voltages to function, usually delivered by MOSFETs arranged in an H-bridge configuration. The tw
• Motors can generate a lot of electrical noise, and engineers must often specially choose system components to mitigate that noise or at least protect against it. Electric motor designs also feature isolation to protect sensitive components from noise and
• Voltages on the control side continue to decrease as smaller semiconductor processes are used to increase the efficiency of the circuit. This trend has led to many microcontrollers using voltages of 1V or lower. At the same time, the introduction of wide-
• There are several ways of isolating the circuit's areas, and the best solution will depend on each application's size, performance, longevity, and reliability requirements. These solutions can include relays, optical isolation, capacitive isolation, and m
• Relays
• Mechanical relays can be one of the simplest ways of protecting sensitive circuits from high-voltage anomalies. They have contacts that physically separate and connect to isolate the circuit, giving high protection. Relays are also capable of switching hi
• Optical Isolation
• Optical isolation is a technique that converts electrical signals to photons and back to electrons to provide isolation. In optical isolation devices—called optocouplers—an LED generates a photonic representation of the control signal, and a photosensitiv
• Optocouplers can provide isolation at levels up to several kilovolts. The speed at which data can be transmitted is limited by how fast the LED can switch, but today's optocouplers can operate at tens of megabits per second (Mbps), which is sufficient for
• Optocouplers also have several drawbacks. They can be relatively expensive and require external biasing, which makes them less efficient than other isolation techniques. Also, high currents and temperatures can lead to the diffusion of atoms out of the LE
• Capacitive Isolation
• As the name suggests, capacitors are also used for isolation purposes. These devices are manufactured from two conductive plates separated by a dielectric material. The capacitor is made to act like a transformer by coupling the voltage on one conductor t
• Magnetic Isolation
• Magnetic isolation uses operating principles like those of a transformer, consisting of two coils and a core. The coils are both wound around the core but are electrically isolated from each other. When the primary coil is energized by a current, a magnet
• Sensing
• Electric motor solutions almost always integrate a feedback loop to provide the controller with information on the rotor's position, speed, and acceleration to deliver precise and efficient control. There are different ways of taking these measurements, a
• Resolvers
• Resolvers provide one of the most accurate ways of measuring rotor position. They use transformer principles and are constructed using a single primary coil, either fixed to or built into the rotor. The primary coil is paired with two secondary windings f
• Encoders
• Several types of encoders can be used to provide positional feedback. They all have unique benefits and drawbacks.
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• Optical encoders consist of an LED and two photosensors that are situated at a 90° angle from each other. The LED and photosensors are separated by a glass or plastic disk that rotates with the rotor. The disk has alternating opaque and clear lines or slo
• technology has improved their performance considerably.
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• Capacitive encoders use a rotor, a transmitter, and a receiver. The rotor contains a sinusoidal pattern, and the transmitter's reference signal is modulated predictably. The encoder detects the changes in capacitance-reactance and translates them into inc
• Sense Resistors
• Current sensing is an alternative method of calculating the position of a rotor. It is a simple technique that uses a resistor placed in series with each motor winding. The voltage across the resistors is sensed and monitored by the motor controller. The
• Conclusion
• This article has focused on two of the main functions electric motor systems require to operate—isolation and sensing—but there are many more parts with their own role in the design. Engineers must choose even the most basic components and connectors with
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• position, a third photosensor can be used as a reference.
• As optical encoders rely on vision, their performance can be hampered by any contamination or blockages that obscure a slot. The disk can also be damaged by vibrations from the motor or warped by temperature extremes. Additionally, the LEDs can degrade ov
• Magnetic encoders use a disk with several poles around the circumference. Sensors—such as Hall effect devices to detect voltage change or magnetoresistive devices to detect a change in magnetic field—are placed equidistantly from each other and output a s
• Magnetic encoders are rugged and capable of withstanding the shock and vibration found in electrical motors (Figure 3). Their operation is unaffected by oil, dirt, moisture, or other contaminants. However, they are susceptible to temperature extremes and
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