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New Inverters for Industrial Applications

Researchers have developed a couple of novel “inverters” for driving huge electrical machines in the industry. Inverters are circuits that that convert DC voltages to a form that can be used for industrial applications. The circuits were designed by a team of researchers from the Indian Institute of Science, University of Seville (Spain), Government Engineering College, Thrissur and Norwegian University of Science and Technology. These circuit configurations can prove to be viable options for medium voltage high power drives, whose applications include steel mills, electric locomotives and electric cars.

The battery produces DC voltage, which doesn't change with time. However, most industrial appliances are designed to run on a voltage that is constantly changing, called AC voltage. In India, the AC voltage frequency is 50 cycles per second, whereas in the United States it is 60 cycles a second. Inverters convert the unchanging DC voltage to variable voltage and variable frequency AC voltage.

Inverters are at the heart of Uninterrupted Power Supply (UPS) systems that spring to life whenever there is a power cut. If you have an UPS system at home, you must have seen an inverter: it is that metal box with green lights to indicate the statuts of the battery. This ubiquitous box contains circuits that convert voltage from the battery to a form that can power lights, fans, TVs etc. Voltage from the battery, in its original form, can't be used to directly run household electrical appliances. In industries, inverters are used to drive various kinds of motors used to run  fans, pumps, drilling machines and conveyer belts.

The two circuits designed by the Indo-European team of researchers convert DC into AC power through multi-level inverters. In one of the circuits, the conversion happens through a seventeen-level inverter. Though such multilevel inverters are in vogue for sometime, they all need additional voltage sources for operation, which makes them expensive. The new design uses a component called 'capacitor'  to make them act as voltage sources, thus removing the need for many voltage sources. Also, the circuit has mechanisms to operate in full power even after component failure.

As R. Sudharshan Kaarthik, a member of the research team, explains “An additional voltage source is very expensive and very difficult to control. This topology eliminates the problem by using the capacitors as the voltage sources”. The findings are published in IEEE Transactions on Power Electronics.

The second circuit is also a multilevel topology, which elimimates low-order harmonics completely giving rise to pure AC voltage. This circuit eliminates the need for external bulky harmonic filters. The capacitors used in these circuits need to be brought to the desired voltage level during start-up by a process called 'pre-charging'. The researchers have come with a novel mechanism that takes care of  pre-charging automatically. Their results are published in IEEE Transactions on Industrial Electronics.

“Precharging is like fixing initial condition. In the proposed systems, the capacitors can be charged to its nominal value through the load current. The switching sequence itself will bring the voltages of the capacitors to their set values. No extra components or power supplies are required to do this” said co-author R. Sudarshan Kaarthik.

Link to papers:

http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6863677; http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6823724

Author Information:

Paper 1: K Gopakumar is a Professor at the Department of Electronic Systems Engineering, Indian Institute of Science Bangalore. P Roshan Kumar and R Sudarshan Kaarthik are at the Department of Electronic Systems Engineering, Indian Institute of Science. Jose I. Leon and Leopoldo G. Franquelo are at Department of Electronics Engineering, University of Seville, Seville, Spain.

Paper 2: K Gopakumar is a Professor at the Department of Electronic Systems Engineering, Indian Institute of Science Bangalore. R Sudarshan Kaarthik is at the Department of Electronic Systems Engineering, Indian Institute of Science. Jaison Mathew is with the Department of Electrical and Electronics Engineering, Government Engineering College, Thrissur. T Undeland is with the Department of Electric Power Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.

Contact Information:

Email: kgopa@cedt.iisc.ernet.in, Phone: +91 80 23600810