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SUPPLEMENT AUTOMATION SOLUTIONS FOR MACHINE BUILDING


55thannIversary


the evolution of AC drive teChnology


From quasi-square waves to silicon carbide. Dominic Bowker, general manager UK and Ireland at Inovance, looks at how AC drives have evolved from simple speed controllers into intelligent power conversion systems, and why silicon carbide could represent the next important stage in their development


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ver six decades, AC drive technology has transformed the way machines use electric motors. At its most basic level,


an AC drive solves a simple problem. When an AC motor is connected directly to the mains supply, its speed is largely determined by the supply frequency and the motor design. However, most industrial applications


don’t want a motor to run at one fixed speed. Production machinery, pumps and fans may need to respond to changing operating conditions and demands. Engineers historically relied on gearboxes, belts, clutches, valves or dampers, but this added mechanical complexity and, in many flow-control applications, wasted energy. AC drives control the conversion of electrical


energy into mechanical motion as efficiently and smoothly as possible. This article explores how this has been achieved over the years and how technology is evolving to push the limits of what is possible.


the eArly dAys of AC motion Control Modern AC drives began to emerge during the late 1960s and became widely established through the 1970s. Early drives used relatively crude switching techniques, including quasi- square-wave or stepped output waveforms. These systems could vary speed, but the waveform supplied to the motor was far from ideal. It contained significant harmonic content, which could increase motor heating, torque ripple, acoustic noise and electrical interference. What the industry needed was a way to switch high voltages and currents quickly, efficiently and reliably. A major step forward came in the 1990s


with the commercial adoption of the Insulated Gate Bipolar Transistor, or IGBT. IGBTs gave drive designers a practical way to switch high voltages and currents rapidly and reliably at industrial power levels. Using pulse width modulation (PWM), the drive rapidly switches its DC bus to synthesise a variable output voltage. Although this voltage consists of high-frequency switching pulses, the motor’s inductance smooths the resulting current into a waveform much closer to the sinusoid required for efficient torque production. IGBTs reduced harmonics and improved speed and torque control. Combined with increasingly


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capable digital control algorithms, they enabled effective flux vector control, allowing AC motor packages to deliver strong low-speed torque and dynamic performance previously associated mainly with DC motors.


from dC motors to more effiCient AC motor Control DC motors, although highly controllable, use brushes and commutators that require regular maintenance. As vector-controlled AC drives matured, many applications moved away from DC systems towards lower-maintenance AC motor and drive packages. IGBTs also began to appear on the input


side of drive systems. Conventional drives use diode or thyristor rectifiers, so braking energy is typically dissipated as heat in braking resistors. Active Front End (AFE) technology replaces these with a controlled IGBT switching stage, allowing energy to be returned to the electrical supply, while also achieving low harmonic distortion and near-unity power factor. As IGBT-based power stages


became the established architecture for drives, drive technology also advanced in other areas. Over the past two decades, many of the major developments have been in control electronics, software, communications, diagnostics, connectivity, functional safety and ease of use.


intelligent, sAfer, more user-friendly drives Modern drives can communicate over high-speed, industrial Ethernet networks such as EtherCAT and PROFINET, allowing multiple axes to be synchronised accurately within a machine. This supports faster, more coordinated production, while the drive itself can provide diagnostic information, support integrated safety functions and be commissioned through intuitive software tools. Functional safety has also become an


important part of drives, including Safe Torque Off (STO), which prevents the drive from producing torque when required. Newer drive systems


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support advanced safety functions that monitor stopping, speed and direction. These functions can help reduce external safety hardware and wiring, simplify panel design, improve diagnostics and support compliance with modern safety requirements.


AC drives: A key Component in modern AutomAtion The AC drive has evolved from a standalone speed controller into an intelligent component within the wider automation system. As drive technology becomes more cost-effective and easier to apply, its use has expanded beyond industrial machinery into everyday infrastructure applications. Pumps, fans, compressors and HVAC systems are good examples of this move. Rather than controlling flow mechanically through valves, dampers or other restrictions, motor speed can be matched more closely to process demand. This reduces energy consumption, improves controllability and reduces reliance on some mechanical control components. Today, drives support much of the


infrastructure behind modern life. They help move water, control air, manufacture food, handle materials, operate lifts and cranes, support marine systems, run production equipment and test new technologies. Most people rarely see them, but their contribution to industrial productivity and energy efficiency is considerable.


the emergenCe of siliCon CArbide The growth of electric vehicles (EVs) is driving major investment in motors, inverters and test equipment. EV traction systems demand compact, efficient power conversion, while battery simulators, motor test rigs and e-mobility development systems are creating similar requirements within industrial environments. This is where Silicon Carbide (SiC)


semiconductor technology is beginning to play a more important role. Compared with conventional silicon devices, SiC offers lower switching losses, higher switching frequencies and improved thermal performance. For drive designers, this creates opportunities for greater power density, improved efficiency and more compact cooling and filtering. These advantages are


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