Electromagnetic design software helps speed development of innovative contactless distributed power supply system

The system uses magnetic induction to facilitate the transfer of power and data between an input coupling device and a number of physically separate devices distributed along the length of a ‘backbone’. Principally intended for industrial control and instrumentation applications, where it will be used for powering and communicating with remote I/O sensors and actuators, the system is also likely to prove popular wherever an easily expandable, low-cost industrial control network is required.



The contactless power system is being developed by the university’s Faculty of Electrical Engineering and Information Technology under a publicly funded research programme, and is about to move from design concept to prototype evaluation. The system essentially comprises a ferrite backbone with an E-shape cross-sectional geometry and a coil wound around its central pillar – which can easily be incorporated in an industry-standard DIN rail – together with a power input coupling device and a number of pick-up modules, all incorporating wound E-shape ferrite cores, which can be positioned anywhere along the length of the backbone.



The market for such a contactless system is potentially huge; DIN rails – standardised 35 mm wide metal rails with a hat-shaped cross-section – are a ubiquitous feature of industrial control, providing simple-to-use mounting facilities inside virtually every equipment rack. But machine builders currently have to hard-wire all the power and data connections to each and every device that is mounted on the rail, and later expansion sometimes proves problematic due to physical I/O limitations. By accommodating both power and data, the contactless system should help machine builders reduce the time that it takes to build an industrial control system significantly, as well as providing uncompromised expansion capabilities.



During the course of system development, the faculty has made extensive use of Cobham Technical Services’ Opera software for numerous tasks, including evaluating the coupling efficiency of different system layouts, performing basic field measurements and assessing the effect of various types of magnetic shielding on eddy currents.



According to Professor Hans-Peter Schmidt, who is responsible for systems and simulation technology at the faculty, “Opera is proving to be extremely useful and very cost-effective. Compared to the old days, when we had to use lots of different software packages, it makes simple modelling so much easier. Opera presents a unified user interface for nearly all the simulation tasks that we perform, and it also has a very short learning curve, which makes it a great teaching tool and ideal for students who are just starting out in this discipline. Although we currently use the 2D version, next year we intend using Opera-3D for some of our more advanced simulation courses.”



Two types of contactless power system are presently being investigated. One places the ferrite backbone in an aluminium DIN rail, the other is essentially free-standing. The basic electrical test setup involves a variable waveform generator, power amplifier, current transducer, wideband oscilloscope and power meter. Considerable effort has gone into determining the optimum air gap, excitation voltage and frequency, and in assessing the effect of various conducting backplane materials, such as µ-metal foil, to suppress eddy currents.



Currently, the system is capable of achieving up to 90% power transfer efficiency with 10 pick-up modules, each demanding between 1 and 2 watts, and data transfer rates of up to 2 Mbps. It is envisaged that these performance figures will increase by at least an order of magnitude as the project progresses over the next year.



Chris Riley, Technology Manager for Cobham Technical Services, points out that the novel nature of the contactless power system makes it a very interesting simulation subject, “I don’t know of anyone else using Opera for this type of research, and it is very pleasing to see such a close correlation between predicted and measured results – many of the basic air gap measurements, for example, agree to within 2%, which is an excellent figure.”