MOTION SYSTEM APPLICATIONS
Intelligent drives
power IoT applications The most basic function of a dc drive is to control the speed of a dc motor. The best way to control the speed is by varying either the armature voltage or the field current. This is because the speed of dc motors is directly proportional to the armature voltage and inversely proportional to motor flux, which is a function of field current. Known for providing tight speed control and full torque at any speed, dc drives have an edge over more traditional ac drives that have a more narrow speed range and limited torque control. Also, dc drives are simple to start up, troubleshoot and maintain. Even dc motor brushes have become more robust and are less likely to require maintenance or replacement than they once were. On the other hand, ac drives are used to control the speed of an ac motor. For an ac motor, speed is determined by the number of motor poles and the frequency. A typical way to control frequency is via pulse width modulation (PWM). A PWM drive outputs a train of pulses to a motor and by modulating the pulse width, making it either narrower or wider, delivers an ac current waveform to the motor. One of the most common types of ac drives is the variable frequency drive (VFD). They operate by switching output devices on and off, which can be transistors, IGBTs (insulated gate bipolar transistors), or thyristors. VFDs can be either constant voltage or constant current, with constant voltage types being more common. They use PWM to control both the frequency and the voltage applied to the motor. VFDs have a number of significant benefits including energy savings. Controlling the amount of current drawn by the motor can decrease energy costs because the motor will not run at full load all of the time. This is becoming more important as motor efficiency continues to be a top design priority. Also, on motor start-up, VFDs can provide a crucial advantage. Without a VFD, an induction motor on start-up has to handle a high initial in-rush current. As the motor speeds up and approaches a constant speed, the current levels off from the peak in-rush values. With a VFD, the motor’s input starts off with low voltage and a low frequency, avoiding the problem of high in-rush currents. Eliminating the in-rush currents upon start-up also gets rid of the excessive torque on components, increasing the life of the motor and reducing maintenance costs and the need for repair.
INTELLIGENT DRIVES FOR THE IIOT Both ac and dc drives continue to evolve, adding functions and offering more intelligence across a range of industrial applications. Intelligent
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DESIGN WORLD — MOTION
Drives - DC - MC 11-19.indd 46
11 • 2019
The NORD DRIVESYSTEMS application test area consists of an oval conveyor belt with rising and falling sections, as well as a bypass section with input and discharge points from the main route.
drive technology is key to digitalization and production automation, because it enables networked and autonomous production processes in smart factories. Companies like NORD DRIVESYSTEMS supply drive solutions (both hardware and software) and communications and application support for Industry 4.0 environments. NORD DRIVESYSTEMS drive units support intelligent IIoT digitalized production with advanced maintenance services. The industrial motor drives are built for easy integration with internal PLCs and a host of communication options for decentralized motion designs. In fact, the drives work with all common fieldbuses and Ethernet-based protocols and include analog and digital interfaces for sensors and actuators. The integrated PLC in the drive electronics allows autonomous control of sequences and movements to reduce the computational burden on the central controls. The drives also facilitate scalable design to accommodate changes to automation installations’ complexity, quantity, and size. NORD drives are prepared for integration into a cloud and can be connected to various external cloud systems. Fast, efficient and comprehensive evaluation of analog and digital data by the intelligent PLC in the drive electronics forms the basis for modern maintenance and servicing concepts such as condition monitoring and predictive maintenance. Due to continuous monitoring of the field level, linking of communication, sensors, process data, and vital parameters of the drive, deviations from the normal state can be quickly detected. Drive operators can motioncontroltips.com | designworldonline.com
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