This diploma thesis deals with maintaining possibilities for appropriate climatic conditions in outdoor greenhouse. The importance for growing plants is an appropriate temperature, humidity and adequate supply of water. The aim of the study is to suggest an apparatus sustaining beforehand defined conditions in the greenhouse with minimal requirements for maintenance. Apparatus uses analogue control by applying photosezistor and thermistor. For power supply are DC-DC converters used.

This diploma thesis deals with maintaining possibilities for appropriate climatic conditions in outdoor greenhouse. The importance for growing plants is an appropriate temperature, humidity and adequate supply of water. The aim of the study is to suggest an apparatus sustaining beforehand defined conditions in the greenhouse with minimal requirements for maintenance. Apparatus uses analogue control by applying photosezistor and thermistor. For power supply are DC-DC converters used.

AC-DC converters find application in every day life as a front-end to DC-DC and DC-AC converters. Active three-phase converters shape the three-phase input current to be sinusoidal and to be in-phase with the input voltage, as well as to provide a steady DC output voltage. This thesis investigates various active three-phase rectifier and control topologies and identifies a rectifier and control topology most suitable for use in converting a variable voltage variable frequency generator output to a DC voltage. In this dissertation, design relations are derived for determining the plant transfer response (for the suitable topology/controller), design equations are derived for designing/choosing the filter components, and guidelines are derived that will assist in choosing the right semi-conductor components and to give an estimation of expected system efficiency. The dissertation investigates the implementation of both analogue and digital control and provides implementation methodologies for both controllers. Expected results are verified by simulation and a build-up prototype. It was shown that the VIENNA rectifier is able to convert a generator type input, with variable input voltage amplitude and variable frequency, to a constant DC-bus voltage whilst controlling the input current to be sinusoidal and in phase with the input voltage. The rectifier was able to maintain a constant DC voltage at the output for input voltages as low as half the rated input voltage and for an equivalent output power of half the rated output power. This suggests that the VIENNA rectifier, controlled as a dual-boost rectifier, is suitable for applications that require power factor corrections and simultaneously operate from a wide input voltage range. / Dissertation (MEng (Electrical Engineering))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / MEng / unrestricted