PV Micro-Inverter Topology Using LLC Resonant Converter

Abstract

In this paper, a DC–single-phase AC power converter with an LLC resonant converter is presented for a photovoltaic (PV) micro-inverter application. This application requires the leakage current suppression capability. Therefore, an isolated power converter is usually combined for DC/AC systems. The LLC resonant converter is the one of the isolated power converter topologies, and it has good performance for conversion efficiency with easy control. On the other hand, a double-line frequency power ripple has to be compensated for in order to improve the performance of the maximum power point tracking (MPPT). Therefore, a bulky electrolytic capacitor is usually necessary for the power converter. However, the electrolytic capacitor may limit the lifetime of the micro-inverter. This paper introduces the PV micro-inverter with a LLC resonant converter. In addition, the active power decoupling circuit is applied in order to compensate the double-line frequency power ripple by the small capacitor in order to eliminate the electrolytic capacitor. Finally, the transformer design is considered in order to reduce the transformer losses. As a result, the conversion efficiency of the LLC converter is improved by 1% when the litz wire has many strands.

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“…The authors of [6] discussed combining PV modules, power electronics and energy storage components in one device. This is similar to micro-inverters with an MPPT for PV modules [101]. However, they are all still on a device level.…”

Sliding-mode controller for a photovoltaic system based on a Cuk converter

“…The first ones usually adopt step-up converters to match the low-voltage provided by the PV modules with the high-voltage required by commercial grid-connected inverters [5][6][7][8][9][10]. Instead, the second systems have more diverse requirements; for example, PV systems interacting with stand-alone AC loads usually adopt step-up converters [5,[11][12][13], but PV systems designed for battery charging or to interacting with DC loads often use step-down converters [14,15]. Figure 1 depicts some of those types of PV systems: Type I uses a step-up dc/dc converter to perform the maximum power point tracking (MPPT) control on the PV source, which ensures the extraction of the maximum power from the PV string.…”

Control of Single-Phase Electrolytic Capacitor-Less Isolated Converter for DC Low Voltage Residential Networks

“…Most topologies use passive elements in their essence that act as filters for harmonic content caused by the switching of the semiconductors and, in the particular case of single-phase converters, the occurrence of ripple at the double of the line frequency in the output current, which can cause instability in the dc network [23]. This problem is usually solved by adding extra capacity value to the output filter or is naturally diminished when connected directly to batteries when there is energy storage.…”

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