Evaluation Of A More Efficient And Cost Effective Method For Interfacing The Power From Solar And Other Types Of Distributed Dc Generation With The Ac Power System

Undergraduate research can be an important part of the engineering education. A good type of engineering project can allow students to demonstrate basis concepts, learn a generally accepted method, identify a potentially better alternative and then perform the related tests and analysis to evaluate the alternative. The results can be used in the class room as well as having the potential of being adapted as a substantially improved accepted practice. This paper will describe such an evaluation. Specifically, the generally accepted method for interfacing distributed generation devices that produce direct current (DC) with our existing alternating current (AC) power system is to install inverters to convert the DC to AC in synchronism with the AC power system. It also requires assuring safety and equipment protection. The inverter adds significant cost and has conversion losses. It is also challenging to design an inverter that produces a sine wave that is compatible with the AC system. A less than perfect sine wave will produce higher harmonics that can cause static and distorted patterns on radio and tv reception and erratic action of some radio controlled devices such garage doors. An alternative method of interfacing distributed DC power producing by distributed generation, such as photo voltaic panels and fuel cells, with the electric power system would be to convert the distribution system from AC to DC. The result would be a potentially simpler DC to DC interface. Such a system raises new issues over matching the DC voltage characteristics of distributed generation device with the DC distribution system in a manner at which losses are minimized while equipment is protected and safety is assured. This authors have performed the preliminary tests that demonstrate some inherent voltage vs solar insolation characteristic photovoltaic panels. The results show a good compatibility for interfacing and supplying power to a fixed voltage DC distribution system. This is because the open circuit voltage is nearly constant over a wide range of solar insolation, while the current is proportional to solar insolation. Similar tests are recommended to determine the compatibility of interfacing the DC power from fuel cells with a fixed DC voltage distribution system.