Improving Solar Inverter Reliability: Techniques For Protecting Output Power Switches Focus: This article focuses on the reliability of inverters used in off-grid and grid-tied,
residential photovoltaic systems at power levels from several hundred watts up to about 20
kW. In such applications, the design of the output power stage (mainly the MOSFET power
switches) needs attention to achieve improvements in inverter failure rates. This article
discusses the benefits of applying foldback current limiting and other techniques in
protecting the MOSFETs. It discusses the differences between inverters with transformer
outputs and those that are transformerless, the vulnerability of power MOSFETs in
inverters, including the greater stress on MOSFETs in transformerless inverters. It
explains the benefits of using foldback current limiting (two possible techniques) to
protect the MOSFETs (typically not done in solar inverters). The potential benefits and
limitations of using TI’s UCC5870 isolated MOSFET driver to protect the power MOSFETs are
also discussed. Finally, the vulnerability of transformerless inverters to delivering high
levels of dc in certain failure modes is explained along with a circuit solution to guard
against this problem.
What you’ll learn: - How to improve the reliability of inverters for residential photovoltaic systems
- How to protect the power MOSFETs in solar inverters by applying foldback current limiting
- How to use a dc detector to prevent transformerless inverters from delivering dc under short
circuit and other conditions
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Author & Publication: Jerry Steele, Red Hill Labs, Tucson, Ariz., How2Power Today, Jan 14 2022
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