While the pace of development in the field of motor drives and motion control may have slowed over the past 60 years, innovation in mature technologies continues. Advances in the following five areas are expected to continue driving the development of the motor drive and motion control industry.
1. Advances in motor drive technology
Motor drive technology provides reliable power to countless manufacturing and production lines worldwide. One of the biggest developments in this field over time has been the variable frequency drive (VFD), which provides reliable speed and torque control for AC induction motors in industrial applications. New VFDs can control permanent magnet AC synchronous motors, increasing their versatility. Servo and stepper drives have achieved significant performance improvements in torque and position control for various types of servo and stepper motors. They complement various applications with their respective lower power ranges.
Hardware and software innovations are the driving forces behind the development of these motor drives. Key hardware developments include power switching transistors and microprocessors. Software innovations include the development of new software tools that can perform complex control algorithms that were previously impossible. With improved usability, software has also made motor drives more user-friendly.
In particular, it significantly reduces the size and weight of the frequency converter. Large cabinets give way to compact electronic enclosures, which can be installed near the motor to fit specific manufacturing plant layouts, and some can even be installed on the motor itself, depending on the power requirements of different applications.
In the 1990s, a class of so-called "miniature drives" emerged, one model of which was only 0.19 kW and could fit in a technician's shirt pocket. Yes, this was an impractical application, but it vividly illustrates that anything is possible. Servo drives and stepper drives have also benefited from the continuous miniaturization of electronic control.
2 Power switching devices and microprocessors
Power switching transistors, which regulate the input current/voltage waveform for motor control, are the core of motor drives. In early drives, silicon controlled rectifiers (SCRs) (a type of solid-state switch) and gate-turn-off thyristors (power semiconductors) served as power switches. These represented mature technologies and were only seen in limited applications in certain high-power driver programs.
With the rapid development of computer and digital technologies, motor drives have gradually shifted to designs based on digital microprocessors (MPUs), which still dominate today. A newly emerging type of semiconductor—the Insulated Gate Bipolar Transistor (IGBT)—has become the primary power switching device for motor drives. The IGBT combines the best characteristics of a MOSFET input with a bipolar transistor output. Other features include fast switching and lower losses due to the insulated gate. For example, advancements in IGBTs have led to faster switching speeds and the ability to operate at higher voltages.
The capabilities of microprocessors and digital signal processors (DSPs) are constantly improving. Higher computing speeds allow for faster responses to load dynamics and near real-time communication with other parts of the motion system. Memory can be compressed into microchips, enabling the implementation of more complex motion control algorithms in both software and hardware.
3. Controlling complexity
Multifunctional AC inverters offer three main motor control methods. Open-loop control is the first and simplest method. It provides reasonable speed regulation and operates without feedback devices. Flux vector control (FVC) represents the highest level of inverter performance and has several variations. Field-oriented FVC simulates the characteristics of DC and AC motors by independently controlling the current components that generate magnetic flux and torque, thus achieving optimal control of motor torque and power. FVC uses feedback devices (typically encoders) to obtain motor shaft position and speed information. The control algorithm relies on a complex motor model and implements separate speed and torque loops. Full vector control can provide high torque at low speeds (sometimes even close to zero speed).
Between these two extremes lies sensorless vector control (also known as open-loop vector control, SVC), an alternative that improves the low-speed torque, speed regulation, and starting torque capabilities of open-loop control inverters. Although SVC inverters operate without feedback, they can estimate torque current, excitation current, and their vector relationships using motor current and voltage signals to achieve precise motor control. They also rely on an accurate motor model. Newer inverters are capable of providing all of these control types, even including open-loop control, which is useful in some applications.
4. The impact of software
These formulas and motor models have existed for a long time, but their application in dynamic motion control programs and algorithms only became possible after the widespread adoption of computers. Meanwhile, the performance of MPUs, digital signal processors, and microchips used in motion controllers and frequency converters has continuously improved, enabling higher execution speeds and significant memory increases. Multiple motor control topologies mentioned above can be integrated into a single frequency converter, which is also more economical. A simple change in software parameters can alter the control mode.
Computer simulations using appropriate software allow for virtual prototyping and testing before hardware construction, enabling the evaluation of different motion control system designs. Image credit: Yaskawa Electric.
Another benefit of motion control software is its ability to assist in setting up frequency converters and motors, especially servo drives. Simulation is another area of software innovation. It allows for the "virtual prototyping" of motion control systems using software before building the hardware.
5. Mechatronics
Traditionally, mechanical and electronic systems were physically separate units. The field of motion control underwent a dramatic transformation in the mid-1990s when the integration of motors and controls became widespread. Many manufacturers introduced a range of products: first, integrated motors that combined AC induction motors and frequency converters. Then, similar combined units could also include servo and stepper motors and their respective controllers.
A prime example of mechatronics is combining a motor and inverter components into a single package. An exploded view of an integrated stepper motor illustrates this technology, which is also applicable to other types of motors. Image credit: Applied Motion
Configuring motors with onboard electronic control units offers users various benefits, such as lower installation costs, elimination of long wiring between the motor and inverter, reduced cabling, fewer system components, easier diagnostics and maintenance, and a simpler control architecture. However, the success rate of integrated motors has been lower than expected, primarily due to issues in the induction motor and inverter sectors. Nevertheless, these induction motor/inverter combinations still have a market, with maximum power outputs up to 22kW, and can be used in appropriate applications and hybrid power control architectures.
