A Visual Basic design tool for utility connected PV inverters

There has been a rapid increase in the world-wide application of photovoltaics as a local power source to the utilities. To achieve this DC/AC power conversion is required and has resulted in a number of different power electronic solutions. The vast majority of these employ a `H´ bridges connected to the power network that can be used to unfold a rectified sinewave of current into the network or indeed generate a sinewave of current from a DC source. In the latter case the `H´ bridge devices carry bi-directional current i.e. through the switch and its body diode. The input stage to the inverter is required to boost the PV array voltage and provide electrical isolation. There are a wide variety of possible circuit topologies that may be used. This paper provides the analysis for a number of these that will allow the designer to establish values for the active and passive circuit elements including electromagnetics and thermal considerations. This analysis is incorporated into a PC package using Visual Basic and running under Windows. The format of this is based on a `question and answer´ approach, which allows the users to make design decisions such as operating temperatures etc. and input data of available components. Examples of the Visual Basic display are provided as well as SPICE based verification of some of the analysis used. It is anticipated that the tool will be expanded to include a wider range of input stages in the near future