ABSTRACT
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.
