Abstract
Medium-scale photovoltaic (PV) systems using cascaded H-bridge multilevel inverters have a capability to perform individual maximum power point tracking (MPPT) for each PV panel or each small group of panels, resulting in minimization of both power losses from panel mismatch and effect of partial shading. They also provide high power quality, modularity, and possibility of eliminating dc-dc boost stage and line-frequency transformer. However, each PV panel in the system is subjected to a double-line-frequency voltage ripple at the dc-link which reduces the MPPT efficiency. This paper proposes a dc-link voltage ripple reduction by third-harmonic zero-sequence voltage injection for improving the MPPT efficiency. Moreover, a control method to achieve individual MPPT control of each inverter cell is also presented. The validity and effectiveness of the proposed methods were verified by computer simulation.
Highlights
Renewable energy technology has undergone a substantial development in the last three decades
In the central inverter topology, several PV strings (PV panels connected in series) are connected in parallel with one blocking diode per string to form a single dc-link and are connected to the grid via a central inverter
This paper presents a dc-link voltage ripple reduction in each cell of the three-phase cascaded H-bridge multilevel PV system by injecting the third-harmonic zero-sequence voltage to improve the maximum power point tracking (MPPT) efficiency
Summary
Renewable energy technology has undergone a substantial development in the last three decades. This is similar to that of the moduleintegrated inverter topology In this case, it is possible to achieve the distributed MPPT control by each H-bridge inverter individually [10, 11] that greatly optimizes the energy yield from the PV panels. The system can be extended to a largecapacity PV system in which the dc-link of each H-bridge inverter can be connected to several PV strings with one dedicated dc-dc converter per string that is similar to the concept of multistring inverter topology [12, 13] This kind of system can achieve a power rating of a few megawatts with the voltage rating in the medium-voltage level. The validity and effectiveness of the methods presented in this paper are verified by computer simulation
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