Applications of Inductors in Industrial Automation

Inductors, Transformers and Their Role in Industrial Automation

Inductors and transformers play a vital role in industrial automation systems, particularly in power supplies, motor control, and improving power quality. These components are essential for minimizing electrical noise, providing voltage conversion and galvanic isolation, and storing energy in magnetic fields. By carefully selecting and utlizing inductors and transformers, industrial automation systems can enhance efficiency, reduce waste, and optimize overall performance.

In this article, we'll discuss:

Importance of Inductors and Transformers in Industrial Automation
Inductor and Transformer use in power supplies
Inductor use in motor control

The Importance of Inductors and Transformers in Industrial Automation

Industrial automation is rapidly becoming more than just creating automated assembly lines to produce products faster. It is evolving into “Industry 4.0” which encompasses smart manufacturing to not only utilize robotics and cobotics (human-machine interfaces), but also industrial IoT sensors for measuring and monitoring processes, wireless communications systems for transferring essential real-time data between multiple devices, industrial instruments for test and measurement, and industrial-grade computers for analyzing data while optimizing the manufacturing portion of the supply chain.

Increasingly, deep learning, machine learning, and AI are now being used in mechatronics and intelligent systems to train equipment to recognize implicit patterns that are then used to trigger warnings and prevent problems before they arise. Industrial microcontrollers are applying tiny machine learning (TinyML) deep learning models to edge devices to improve the efficiency of AI learning while using fewer computations and less training data.

The simultaneous use of multiple power supplies and motor controllers to energize and actuate all of this automated equipment requires reliable components designed for harsh environment operation. High-frequency switching power supplies that are designed to create various voltage rails for a multitude of electrical and electronic factory automation devices create electrical noise that requires signal conditioning or signal filtering for EMI suppression.

Magnetics, such as inductors for energy storage and electrical noise reduction (including RFI suppression) and transformers for galvanic isolation and voltage conversion, are critical components in industrial automation power supplies and equipment. Step-up transformers increase voltage and step-down transformers decrease the input voltage to the desired design rail voltage, which may be 24V, 12V, 5V, or lower for logic circuits. Properly selected commercial grade and automotive grade inductors and transformers can meet the needs of rugged industrial applications.

Inductor and Transformer Use in Power Supplies

Industrial power supplies, such as AC-DC converters, DC-DC converters, and Power over Ethernet (PoE) power source equipment (PSE), provide energy at the required voltage levels to drive automated production machines, robots, wireless communication networks, IoT devices, LED lighting, and programmable logic controllers (PLC). Inductor filters that employ power inductors and common mode chokes are an integral part of these power supplies, allowing them to minimize EMI and function properly in electrically-noisy industrial environments while meeting the demands of electromagnetic compliance (EMC). Isolation transformers and transformers for PoE power source equipment (PSE) and powered devices (PD) provide electrical isolation for safety, to prevent ground loops, and to convert voltages to the required voltage rail level for the powered device.

Wire-wound inductors, such as magnetically-shielded power inductors, are common components in power supply filters. Selecting optimal power inductors, common mode chokes, and power converter transformers is facilitated by online tools such as Coilcraft’s MAGPro^TM Power Inductor Finder and Analyzer, Common Mode Choke Finder and Analyzer, and Parametric Search Tool. These free web-based tools help engineers quickly find the optimal part based on user-entered values of inductance, DC resistance (DCR), rated current, size, and other relevant parameters.

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Inductor Use in Motor Control

Industrial automation is highly dependent on AC induction motors, synchronous motors, brushless DC motors (BLDC), and stepper motors for high-speed, controlled rotational movement. Universal motors, which can theoretically operate on both AC current and DC current, are mainly used in industrial hand tools for manual assembly. Actuators are used for translational (X, Y, Z) movement.

Motor controllers and actuator controllers often require isolated gate drives that employ gate drive transformers for circuit isolation. AC to DC controllers and DC to DC controllers that provide power to motor controls at the appropriate voltage level use power inductors on the input, output, or both to “smooth out” the ripple current. Low ripple current reduces EMI and core and winding losses. High voltage inductors support the need for voltage-rated inductors for use with DC-DC and AC-DC motor controllers. AC current sensors or current sense transformers are important for monitoring and limiting current levels in industrial motor circuits, preventing possible damage.

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Importance of efficiency in industrial automation systems

Maximizing the efficiency of industrial automation equipment and processes is crucial to reducing waste, maximizing productivity, and controlling costs. Reducing the materials and energy requirements of the myriad power supplies and IoT communications equipment used in building automation helps minimize the impact of manufacturing operations on the environment and lowers overall costs.

Power over Ethernet (PoE) is an efficient method of getting power to remote sensors, cameras, industrial lighting, LED lighting, and communications equipment at distances of up to 100 meters for building automation within production facilities. It can also be used to power digital tablet and PDA charging stations for industrial personnel. PoE can eliminate the need for external high-voltage power sources by using lower-cost, lighter-weight, twisted-pair Ethernet cables to efficiently pass both power and data.

With PoE, if an Ethernet cable already exists there is no need to run a power line to the powered devices, saving materials and eliminating the need for an external wall power supply. For new locations, running Ethernet cable greatly reduces installation costs. Once installed, the monitoring and controlling of powered devices uses the same network management infrastructure as the data transfer, and shutting down or resetting devices can be done remotely.

PoE equipment includes power sourcing (PSE), midspan, and powered devices (PD). In the signal path, center-tapped 1:1 isolation transformers are used for injecting current, and common mode chokes are used to filter out EMI. Midspan devices are placed between non–PoE capable switches and PoE PD devices, using midspan power injection chokes to inject the current.

PoE operates in the low voltage telecom range, generally at 36 – 57 V, offering a safe and efficient method of providing remote power to industrial equipment. The maximum power delivered by the PSE has also evolved up to 100 W for IEEE 802.3bt. The IEEE 802.3bt standard includes eight Classes which describe PD power supply limits ranging from 3.84 W for Class 1 to 71.3 W for Class 8. Non-standard PoE devices may provide up to 90 W power to the powered device. With a 4-pair signal path arrangement, the Coilcraft WA8704-ALD PoE Signal Path Transformer can provide up to 150W.

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How inductors can improve efficiency

Switching converters for industrial automation utilize power inductors for filtering out high-frequency noise. Switched-mode converters include buck converters, boost converters, buck-boost, and SEPIC converters, all of which incorporate inductors in the filter sections. Selecting a high-efficiency inductor for each application will have a significant impact on the overall efficiency of the switching power supply. In the next section, we’ll discuss specific strategies for maximizing efficiency through proper inductor selection.

Specific strategies for maximizing efficiency with inductors

Properly sizing and selecting inductors
Minimizing losses and heat generation
Reducing current spikes and electromagnetic interference (EMI)
Using inductors in combination with other components

Inductor size is sometimes assumed to correlate with inductor loss and efficiency. Inductor DC loss is a function of the DC current and DC resistance (DCR): Idc^2 * DCR. Low DCR leads to high efficiency. From the equation for the DCR of a round wire (DCR=ρ*l*πr ²) where ρ= resistivity of wire, l = length of wire and r = radius of wire, we can see that an increase in the wire size (radius) has a larger impact on reducing DCR vs. changing the length of wire. This leads to the conclusion that larger inductors use larger wire and are therefore more efficient. However, there are other factors involved if the inductor current is not strictly DC.

If the high-frequency AC through the inductor includes substantial ripple current, winding loss due to AC resistance (ACR), sometimes called effective series resistance (ESR) and AC core loss, also factor into inductor efficiency. While larger wire size improves inductor DC efficiency, skin effect loss can reduce the advantage of using larger wire when considering AC winding loss. Therefore, larger inductors do not always have the highest efficiency.

Inductor core saturation is related to the size (effective area) of the core. A larger core area can handle more current without saturating. However, a larger core has a longer flux path which leads to higher core loss. While the Steinmetz equation has been traditionally used to calculate inductor power loss, based on measurement of a sample inductor, it is limited in frequency bandwidth to a somewhat narrow range. Measurement-based tools, such as Coilcraft’s MAGPro^TM Power Inductor Finder and Analyzer provide the most accurate measurement-based calculations of inductor core loss and winding loss, while helping the user find the smallest inductor that meets all design requirements.

Inductors are used extensively to reduce current spikes and electromagnetic interference (EMI) in the DC output of DC-DC converters or AC-DC converters. They can be combined with other inductors or capacitors to create higher order LC filters for improved attenuation. A high efficiency inductor is designed to have the lowest total losses (DC + AC) and heat generation in the smallest-possible size over a wide range of frequencies. Unless you are an expert inductor designer, using online tools, such as Coilcraft’s MAGPro^TM Power Inductor Finder and Analyzer assures maximum inductor efficiency in industrial automation systems.

Additional Resources:

What is an Inductor?
Choosing Inductors for Energy Efficient Power Applications (pdf)
Selecting the Best Inductor for Your DC-DC Converter (pdf)
Coilcraft MAGPro^TM Power Inductor Finder and Analyzer
Coilcraft MAGPro^TM DC-DC Optimizer

How Inductors Improve Power Quality in Industrial Automation Systems

Importance of power quality in industrial automation systems
Role of inductors in improving power quality
How inductors store energy in magnetic fields
How Inductors Improve Power Quality
- How inductors reduce current spikes
- How inductors filter out high-frequency noise
- How inductors regulate current

While energy efficiency is extremely important, power quality is crucial to reliable operation of electrical equipment in industrial systems. Issues with power quality can cause component and equipment failures due to overheating, and data errors in industrial communications systems. Downtime due to a power interruption or voltage interruption creates disruptions in process flows that can lead to extended supply chain delivery times.

Industrial control equipment can be sensitive to current spikes and high-frequency noise. Inductors are important components in control power supply filters that limit current spikes and reduce the amplitude of high-frequency noise and harmonics, protecting equipment from damage or interference that may cause resets. Power magnetics and RF magnetics comprise power inductors and RF inductors which temporarily store AC energy. By storing energy in the magnetic field, inductors pass DC or low frequency signals while attenuating or impeding the rate of change of current, regulating current by reducing high-frequency current spikes to minimize their impact on sensitive circuits.

Whether using a single power inductor or RF choke, or inductors combined with capacitors to create higher-order passive filters, the choice of inductor can have a major impact on the effectiveness of the filter and ultimately on the power quality of the equipment in which the filter is designed. Inductor selection involves considering DC resistance (DCR), open circuit inductance, full load inductance, rms current rating, Isat rating, and part size. The rms current rating defines the temperature rise due to current. The Isat rating defines the percentage drop in inductance, or full load inductance, giving the effective inductance at peak saturation current.

Selection of wire-wound inductors and wire-wound ferrite beads for low-pass filters and more-advanced harmonic filters for limiting current spikes and noise will have a direct impact on power quality. Therefore, the proper selection of inductor for the application is critical. Web-based tools, such as Coilcraft’s MAGPro^TM suite of Transformer & Inductor Tools, simplify the complex process of finding the optimal part for your design.

Additional Resources:

Selecting the Best Inductor for Your DC-DC Converter (pdf)
Coilcraft’s MAGPro^TM suite of Transformer & Inductor Tools

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