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Industrial Electronics and Electric Drives - a short overview
Ehab H.E. Bayoumi
Editor in Chief, International Journal of Industrial Electronics and Drives
Industrial electronics and electric drives technology have made significant developments after several decades of the dynamic evolution of power semiconductor devices, converters, pulse width modulation (PWM) techniques, advanced control and simulation techniques. Recently its applications have been fast expanding in industrial, commercial, residential, transportation, utility, aerospace, renewable energy systems, electric/hybrid vehicles and military environments, primarily due to reductions in cost and size and improvements in performance. In the global industrial automation, energy conservation and environmental pollution control trends of the 21st century, the widespread impact of industrial electronics is inevitable. It appears that the role of industrial electronics on our society in the future will be as important and versatile as that of information technology today.
In this review article, the significance of industrial electronics will be discussed. The recent advances of industrial electronics, power converters, electric drives and new trends in industrial electronics and motor drives, along with some possible research and development areas, will then be highlighted.
2. Industrial Electronics
Solid-state power semiconductor devices constitute the heart of modern industrial electronic apparatus, and today their evolution has been possible primarily due to device progression [1-7]. Power semiconductor growth has closely followed the evolution of microelectronics. Researchers in microelectronics have worked resolutely to enhance semiconductor processing, device fabrication and packaging, and these efforts have contributed to the successful development of so many advanced power devices available today.
The invention of IGBTs has been a crucial achievement in the history of power semiconductor devices . Modern IGBTs are available with trench-gate and punch-through technologies for lower conduction drop . This self-controlled hybrid device combines the advantages of power MOSFETs and BJTs. Its power rating is increasing continuously with the improvement of electrical characteristics. IGBT IPMs are available with built-in gate drivers, control and protection. It appears that in the future, insulated gate devices (power MOSFETs and IGBTs) will continue to dominate in industrial electronic applications. High-power integrated gate-commutated thyristors (IGCTs) (or GCTs) have been introduced in recent years and are available with forward and reverse blocking capabilities. High-power IGBTs and IGCTs are now serious competitors in multi-megawatt converters. In high power rating, both IGBTs and IGCTs have comparable switching frequency and permit snubberless operation. There are a number of other devices, such as MOS-controlled thyristors, static induction thyristors, injection-enhanced gate transistors, MOS turn-off thyristors, etc., that have not yet been established commercially. In addition, there are also a number of new devices under development [4-7].
Globally, electrical energy consumption is increasing dramatically in order to keep up with our living standards. Most of the world’s electricity is produced by fossil fuel and nuclear power plants. The burning of fossil fuels causes environmental pollution comprising the generation of greenhouse gases that contribute to global warming, whereas nuclear plants have safety and waste disposal problems. Industrial electronics assist energy conservation effectively by improving efficiency of utilisation. According to the estimate of Electric Power Research Institute (EPRI) of the USA, around 60 to 65% of grid energy in the USA is consumed in electrical machine drives, and 75% of these are pump-, fan- and compressor-type drives. The majority of these pumps and fans are employed in industrial environments for the control of fluid flow. It is reported that currently around 97% of medium- to high-power drives for such applications operate at fixed speed , where flow is controlled by mechanical methods such as throttling control, dampers or flow control valves, resulting in a substantial amount of energy loss. Only 3% of these drives are operated at variable frequency speed control with fully open throttle that can improve efficiency by up to 30% at light load.
Industrial electronics-based load-proportional speed control in air conditioning can save as much as 30% of energy compared to traditional thermostatic controls. For this reason, the majority of Japanese homes use variable-speed air conditioning to save energy. It has been estimated that roughly 24% of grid energy in the USA is consumed in lighting. Industrial electronics-based high-frequency compact fluorescent lamps (CFLs) can typically be four times more efficient than traditional incandescent lamps, as well as giving much longer life. Light-dimming control of CFLs can further improve energy efficiency . CFLs are expected to completely replace incandescent lamps in the near future. Solid-state LED lamps with higher efficiency and longer life are also around the corner. High-frequency induction cooking and microwave ovens also save energy compared to traditional surface-mounted ovens. According to the EPRI estimate, 15% of grid energy can be saved easily by the widespread (but economical) application of industrial electronics .
3. Power Converters
A power converter, consisting of a pattern of power semiconductor switches and one or several passive components, helps to convert and control electrical power from ac to dc, dc to dc, dc to ac, or ac to ac . Converter development has essentially followed device progression. Certainly, the most common type of converter operates on a utility system. Diode or thyristor-based converters distort the ac line current and create utility system power quality problems. It is more economical to solve these problems by using a PWM-type front-end converter with self-controlled devices (such as power MOSFETs, IGBTs, GTOs or IGCTs) that shape the line current to be sinusoidal, and the displacement power factor (DPF) can be programmed to be unity, leading or lagging. In addition, the line voltage sag problem can easily be compensated. Considering the present trend, it appears that eventually phase-controlled converters and cycloconverters will become obsolete for operation in utility systems.
Converting dc to ac voltage is known as inverting. It is carried out by voltage-fed and current-fed inverters, with the former superior in overall figure-of-merit considerations. Therefore, this class of inverters has been accepted almost universally for general power processing applications. Voltage-fed inverters can be two- or multilevel types, depending on the level of handling power. Recently, research into multilevel inverters and their applications has been very prominent in literature [3, 4]. Multilevel inverters with higher numbers of levels are vital for handling higher power at high voltage. In general, their applications could comprise high-power motor drives and utility system applications (such as STATCOM and HVDC inverters). The inverter is normally maneuvered in PWM mode for motor drive, but in steppedwave mode (with coupling transformers) for STATCOM [4–6]. Flexible ac transmission systems (FACTS)  are basically an industrial electronic method of regulating the bus voltage and controlling the flow of active (P) and reactive (Q) power (often called unified power flow controlling) in the transmission system of a utility grid. Since the transient response of STATCOMs for supplying and absorbing energy pulses is very fast, the units can also control transient stability and generator oscillation problems of the utility system. FACTS applications will continue to grow in future with higher converter levels and higher power ratings as we gain more experience in this area [2, 3].
In a motor drive, high dv/dt deteriorates machine insulation, causes bearing current problems and machine terminal voltage boost when there is a long cable between the inverter and the motor. To overcome these problems, soft-switched converters have been proposed. Soft-switched power conversion is considered one of today’s hot applications. It is a high-frequency link power conversion, where the load requires galvanic isolation from the source through a high-frequency transformer [1-4]. One popular application area of soft-switched converters is resonant-link dc–dc converters.
Future emphasis on converters will be mainly in industrial electronic building block integration, automated design, simulation, manufacturing and testing.
4. Motor Drives
The electrical machine, the workhorse of the modern variable frequency ac drive, has gone through slow but sustained growth during the past century. The initiation of powerful digital computers, new and improved materials, coupled with extensive research, has resulted in higher power density, higher efficiency, and many performance enhancements of machines. The progression of power semiconductor devices, various converter topologies, advanced PWM techniques and improved control and estimation methods gradually brought high-performance ac drives of various types into the market place, pushing dc drives toward obsolescence .
It is interesting to note that recently, voltage-fed multilevel inverters are finding almost universal acceptance for large-power four-quadrant induction and synchronous motor drives, replacing the traditional thyristor-based cycloconverters and current-fed inverters. Permanent magnet synchronous machines (PMSMs), particularly brushless dc drives with trapezoidal machines, are more popular in the lower end of power. Generally, PMSM drives are more expensive than cage-type motors, but have the advantages of higher efficiency (lower life-cycle cost) and lower rotor inertia. Particularly, axial-flux (compared to radial flux) PMSMs are showing more promise for direct wheel drive EV/HEV applications . As the cost of high-energy NdFeB magnets decreases in future, PM machine drives will gradually find increased acceptance.
It is interesting to note that switched reluctance motor (SRM) drives are getting wide attention in the literature [4, 8]. The SRM is simple in construction, economical and robust, and is often compared with the induction machine, although it is the closest relative of the synchronous reluctance machine. However, the SRM drive has inherent pulsating torque and acoustic noise problems, and needs an absolute position encoder like a self-controlled PMSM drive – although extensive research has mitigated some of these problems.
5. New Trends
Some of the new trend areas in industrial electronics and electric drives can be outlined as follows:
1- Research in batteries, FCs, PV cells, microchips, ultracapacitors, superconducting magnet energy storage, etc.
2- AI-based intelligent and evolutionary control and estimation techniques, particularly with neural networks (NNWs), particle swarm optimisation (PSO), ant colony optimisation (ACO) and bacteria foraging optimisation (BFO), will also impact industrial electronics evolution . A large number of ANN topologies yet remain unexplored for innovative industrial electronics applications, along with hybrid AI techniques such as neuro-fuzzy, neuro-genetic, neuro-fuzzy genetic, etc.
3- Development of large and economical ANN-ASIC chips is essential for industrial applications of intelligent systems . Currently, FPGAs are becoming very powerful with embedded DSPs for implementation of NNWs.
4- Sensorless online precision estimation of machine variables (particularly absolute position in synchronous machines and in induction machines at zero or near-zero frequency region) and machine parameters require further exploration, although significant advances have been made recently in these areas.
5- Online diagnostics of converter and machine faults, along with utility power quality diagnosis and the corresponding fault-tolerant control, are important topics for reliability improvement of industrial electronic systems. Control, estimation, monitoring, fault diagnostics and fault-tolerant control will eventually be implemented on a single DSP/ASIC chip.
6- It is expected that converters, controls and machines will eventually be integrated as an intelligent machine of the future, particularly in the lower end of power rating. There are, of course, myriads of application-oriented topics which are incremental in nature .
The International Journal of Industrial Electronics and Drives (www.inderscience/ijied) is a fully refereed international journal that presents state-of-the-art research work in the area of industrial electronics, power converters and drives. The thrust is towards those investigations which have significant potential for industrial applications. The journal highlights new topologies or control methodologies and also reporting of the limitations faced by the existing industrial drives and converter units.
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