quinta-feira, 10 de novembro de 2016
Power Conversion Technology for Grid-connected PV Inverter-WOO-JUN CHA -DOCTORAL THESIS-DEPARTMENT OF ELECTRICAL ENGINEERING POHANG UNIVERSITY OF SCIENCE AND TECHNOLOGY-SOUTH KOREA
This thesis proposes hardware circuits and control algorithm of grid-connected photovoltaic (PV) inverters having high efficiency. PV inverter can be classified into singlephase and three-phase inverter according to power capacity. A micro-inverter system is proposed for the single-phase inverter. This system is composed of step-up dc-dc converter that uses an active-clamp circuit with a series-resonant voltage doubler and a high efficiency inverter with single-switch-modulation. During the step-up dc-dc stage, the active-clamp circuit provides zero-voltage switching turn-on, recycles the energy stored in the leakage inductance of the transformer, and limits switch voltage stress. A series-resonant voltage doubler is used on the transformer secondary side to remove the reverse-recovery problem of the rectifier diodes. During the inverter stage, to improve efficiency and reliability in the proposed inverter, only single switch is modulated at switching frequency without shoot-through problem. This whole process minimizes power losses and eliminates a mismatch of a capacity between the PV panel and PV inverter, so the proposed micro-inverter is suitable for use in a single-phase grid connected PV inverter. A prototype design and experimental results are given to verify the proposed system. A novel space-vector modulation (SVM) for a three-phase PV inverter with simple software implementation is proposed. The conventional SVM algorithm for the three-phase PV inverter requires complex computations, such as square root and arctangent, and a sector selection algorithm. The proposed SVM algorithm can determine directly on-state times of switches without complex computations and complex sector selection algorithm. Experimental results show high performance of the proposed algorithm for the three-phase PV inverter.