Guide to Power Electronics Design: Low-Power Components and Applications: Introduction (part 2)

Power Quality and Modern Components

During the last decade, many industrial processes have dramatically expanded their use of electronic equipment with very sophisticated microelectronic components. Meanwhile many consumer electronic products and personal computers, etc. are used by many millions of individuals at their residences too. Downsizing of individual semiconductor components in processor and memory chips, is evident from the exponential growth in the number of components per chip in popular microprocessors such as the Intel family. With the downsizing of semiconductors in the components, the quality of AC power systems becomes critical for the reliable operation of the products and systems. Common problems such as blackouts, brownouts, sags, spikes, and lightning related transients, etc. propagating into the systems could create serious problems in the systems. With more and more nonlinear subsystems (such as switchmode power supplies, switched rectifiers, etc.) used at the interface between utility power input and the systems, the power quality problem is worsened due to the non-linear nature of the currents drawn from the utility.

Above: Fig. 1 Exponential growth in number of transistors per chip in Intel processor family (Intel Corp, USA)

For this mason, power factor correction, and harmonic control, etc., which were specifically relevant to the electrical power environments historically, are now becoming mandatory with low power systems too. Many organizations, such as component manufacturers, system designers as well as standardization groups are placing heavy emphasis on these concepts.

Power factor corrected switchmode power supplies, power factor corrected energy saving lamps, etc. are gradually becoming the modem design trends. AC voltage regulators, power conditioners and UPS systems, etc. are becoming a very fast growing market segment due to power quality issues.

While these systems use the state of the art power semiconductors, etc., highly sophisticated systems with superconducting magnetic energy storage (SMES), etc. are also installed as trial systems in critical locations. Superconducting magnetic energy storage was originally proposed for use by utilities to store energy to meet peak electricity demands.

The systems were to store large amounts of electrical energy to provide thousands of megawatts of power for several hours at a time. However, smaller storage systems have developed much faster. The first commercially available unit of this kind rapidly stores and delivers smaller amounts of electricity over a brief period (about a megawatt for a few seconds). This new technology excels in handling power disturbances, which are increasingly expensive problems in industrial facilities.

Above: Fig. 2 Basic power electronic system

Systems Approach

Taking a systems approach, every application in power electronics can be represented by a load, and a drive consisting of four basic elements, control driver device circuit. Most of the progress in the near future is expected to originate either from the side of the control unit (i.e., more sophisticated software) or from the device side. In both cases, advances in silicon technology open up new possibilities, especially in order to cut costs for a given application.

Another area where a large effort is being spent, both in research and development, concerns the combination of these building blocks. In the first stage, this includes the integration of the driver into the actual device. This effort is presently under way in the sense of replacing the conventional current fed drive by a voltage fed one.

Ultimately, the integration of all three blocks, control driver device, is the goal. This applies mainly to the region of low power where dissipation problems are less severe.

In the case of industrial applications of power electronics, the operating environment will impose additional requirements beyond the mere functional performance. Qualities like reliability, safety, maintainability, and availability need to be considered too and will influence both the design and the selection of components for a given system.

Specialized Applications

Frequently, new applications for power electronics are being suggested and created. Some are extensions of other fields; others are fields unto themselves. Here are several new applications that are becoming a reality:

• Magnetically levitated (MAGLEV) trains with advanced electromagnetic propulsion and power systems.

• Plasma fusion technology with very high power electronics systems.

• Megawatt amplifiers in small sizes.

• Smart power management and distribution systems for high speed fault detection and power re-routing.

The capability of superconductors to generate a large magnetic field allows a MAGLEV train to levitate a passenger vehicle above a track so that physical contact is not needed. Slowed only by air friction and track coil resistance, the train can then travel at speeds approaching 500 Km/h. Mechanical propulsion is difficult without physical contact or noisy turbines. Therefore, the train must be propelled electromagnetically. Similarly, power to the passenger compartment must be inductively coupled from the guideway.

Controlled thermonuclear plasma fusion systems require regulated high power supplies, to heat hydrogen isotopes to temperatures that will initiate fusion reactions. Examples of these heating systems are gyrotrons and neutral beams.

Both systems require modulation of their input supplies. The power requirements of these systems are staggering; hundred of kilovolts at hundreds of amperes for several seconds at a time. Novel solid state power electronics provides a way to attain higher power with lower cost, easier maintenance, greater ruggedness, and smaller size. A series modulator using IGBT-based switching modules can provide discrete modulation with sub-microsecond switching times. They also are not subject to parasitic oscillations and x-rays, so higher voltages up to the megavolt level are possible.

Some existing industrial applications require amplifiers that can provide megawatt power levels. For example, amplifiers that produce +_ 450V at 2,000 A to drive a large electromagnetic linear motor have been reported. It consists of six parallel, 400A, 1200V IGBTs in each leg of an H-bridge and operates at up to 10KHz switching frequency. Active overcurrent and overvoltage regulation and protection are provided with the amplifier. These power amplifiers can be used for applications such as seismic exploration. References 2 and 3 provide some details related to very special applications.

Advanced power management and distribution is undergoing change as solid state power controllers become available. These devices can be circuit breakers, relays, and power controllers all in one package. They can operate three to four orders of magnitude faster than mechanical circuit breakers and relays. The speed and easy interface with other electronics of these devices offer capabilities far beyond those of mechanical circuit breakers and relays. Fast turn-off gives solid state power controllers the ability to limit current by relying on the inductance inherent in any power distribution system. Easy interface with other electronics, such as microprocessors, makes smart operation and remote control possible. A microprocessor can use information from a variety of sensors to decide the status of the power controller.

This section has provided an overview about the power electronics industry, including high power and specialized applications. The next sections provide the details related to power electronic components and techniques used in power electronic systems handling power in the range of few watts to about 100 kw.

References:

1. Thollot, Pierre A. "Power Electronics Technology & Applications." IEEE, 1993.

2. De Winkel, Carrel C., James P. Losleben, and Jennifer Billmann. "Recent Applications of Super Conductivity Magnet Energy Storage." Power Quality Proceedings ( USA), October 1993, pp 462-469.

3. Marcel, P. J., P. E. Gaudreav, Robert A. Wiesenseel, and Jean-Paul Dionne. "Frontiers in Power Electronics Applications." Power Quality Proceedings, October 1993, pp 796-801.

4. Sevens, Rudy and Jack Armijos. "MOSPOWER Applications Handbook." Siliconix Inc., 1984.