Monday, November 26, 2001		Article

Test gadgets with software
Sumesh Raizada

EVER since the invention of electric bulb, probably the first electrical device, there has been a continuous research and development in the field of electricity. Electric motors, transformers, alternators and several other devices that developed later on, played an important part in the industrial revolution. However, the discovery of semiconductors like silicon and germanium has led to another industrial revolution in the past couple of decades throughout the world. Apart from television, radio, calculators and computers, scientists have now come out with electronic products that have numerous industrial and commercial applications.

While the digital electronics deal mainly in products like computers, video, CD players, cameras, there is another equally important field, mainly called power electronics. It involves devices and components that controls electrical as well as electronic appliances and provides power supply to them. These are mainly AC to DC converters, DC to AC Inverters, thyristor-controlled drives and several microprocessor-based equipment. Now, with the aid of computers, further advancement in this relatively lesser-known but important field of electronics has occurred and offers vast career opportunities for the professionals in design, manufacturing and testing. Those with a background in physics, electronics, electrical and computers can opt for this growing area of Power Electronics.

Power electronics refers to the control and conversion of electrical power by semiconductor devices. Earlier, mercury-arc rectifiers were used for controlling electrical power but their applications were limited to industrial electronics only. Later, silicon-controlled rectifiers or SCRs were developed that had applications in areas such as electrical drives, power supplies, aviation electronics, high frequency inverters, etc. Power electronics devices have applications in control of electrical power ranging from a few watts to several MW. It not only controls but also converts one form of electrical power to another. The main forms of conversion are AC to DC or DC to AC conversions. However each form has its own utility and varied applications.

Electronic power converters refer to a power electronic circuit that converts voltage and current from one form to another. These converters can be broadly classified as Rectifiers that convert an AC voltage to a DC voltage and Inverters that convert a DC voltage to an AC voltage. Besides, there are chopper or a switch-mode power supply that converts a DC voltage to another DC voltage and Cycloconverter that convert an AC voltage to another AC voltage. SCRs, diodes and other semiconductor devices are the main components that are utilised in the power electronic devices.

Rectifiers have application in variable speed DC drives, Battery chargers, DC power supplies and Power supply for electroplating. While, inverters have applications in emergency lighting systems, AC variable speed drives, uninterrupted power supplies or UPS and frequency converters. Though Inverters are mostly designed with SCRs yet other semiconductor devices such as bipolar junction transistors, MOSFETs, insulated gate bipolar transistors and MOS-controlled thyristors are also used nowadays due to inherent advantages offered by them. Presently only the inverters with a high-power rating, such as 500 KW or higher, are built with SCRs, while those for domestic application and low power outputs are built with MOSFET technology.

Power BJT or a MOSFET are normally used in a switch-mode power supply. A switch-mode power supply can be a Step-down SMPS, Step-up chopper, Fly-back converter and Resonant converter. The typical applications for a switch-mode power supply or a chopper are DC drive, battery charger and DC power supply. Cycloconverter that converts AC-to-AC voltage have application mainly in controlling the speed of an AC traction motor.

Analysis of power electronic circuits is extremely complicated, as these circuits normally do not operate in a steady state, which refers to the state of a circuit characterised by either a DC response or a sinusoidal response. Since the responses are non-sinusoidal, harmonic analysis is necessary. In order to obtain the time response, it is extremely essential to make use of a computer program. The qualified computer professional from the field of software as well as hardware thus plays an important role in design as well as testing of power electronic equipment. A software professional design programs and simulation technique for testing the devices in a virtual state.

To design and build control circuitry of a power electronic device, a professional has to be qualified and proficient in several disciplines. They are involved in design of analogue and digital electronic circuits, microcontrollers and digital signal processors, etc. Many power electronic circuits have an electrical machine as their load. Computer simulation is done to optimise the design of a power electronic system.

In order to simulate, knowledge of software package such as MATLAB and the know-how to model nonlinear systems is essential. Other power electronic packages that a person should be aware of are Pspice and MathCad. Besides, proficiency in Java applet so as to illustrate how the circuit operates is also important. Another important software package that is applied in testing is Caspoc. It is used for animation of the circuit and control devices, animation of objects like motors, meters and cars, etc. Caspoc is most commonly used for modeling and simulation of power electronics and electrical drives as it combines the ease of drag and drop schematic development. With this software, one can model any type of power electronics circuit and devices like SMPS, inverters and rectifiers.

Though most of the universities and engineering colleges offer course in power electronics both in graduation as well as post graduation, University of Birmingham, UK, offers a unique postgraduate course that covers computer-aided power electronics. It provides an overview of power electronic converters and systems including the main device, operating principles, characteristics, applications, modelling analysis and simulation techniques for power electronic systems. The course also provides exposure to the circuit analysis and modelling techniques for power electric systems. Students are also exposed to arithmetical techniques and algorithms for undertaking power electronics simulations and CAD or simulation systems.

Prospects are bright for those opting for this career that is highly technical but undoubtedly interesting as it offers a lot of opportunity and scope for research and development. Graduate or diploma engineers in electrical, electronics or computers and physics graduate with computer proficiency have a scope of growing in this field. Professionals are employed in research institutions and universities for carrying out advanced research. Manufacturers of computers and electronic appliances like television, washing machine, etc., UPS or inverter manufacturers, industrial electronic firms that develop control circuits and devices for AC or DC drives have career opening for professionals in design, development, production, testing and quality assurance.

The job responsibilities include evaluation of new and existing product applications to meet customer needs, electrical and mechanical testing, manufacturing process development, investigation of new concepts and materials in power electronic circuit, participation in industry standards development and to provide marketing and sales support. Those who are looking for openings in Power Electronics can search the same on the Internet where a number of Websites are available. One such site is CareerAnalog.com, which provides links to power and other electronics jobs.