Teardown:The power inverter-from sunlight to power grid

Focus:

A teardown of SMA Solar Technology’s Sunny Boy series of transformerless solar power inverters reveals the architecture, control methods, and key components used in this design of this grid-tied inverter card series. The article begins by explaining the role of the inverter in photovoltaic power systems, gives a brief description of the Sunny Boy series inverter and its key features. Next, maximum power point tracking (MPPT) is explained and SMA’s choice of an MPPT algorithm is discussed. Then, the operation of the inverter’s dc-dc stepup converter stage is described including an explanation of transformerless switching and how it satisfies the UL 1741 safety standard. Other inverter requirements are also discussed as well as operation of SMA’s H5 topology, which adds an extra switch to the standard H4 bridge. The final section discusses the functions performed by the control processor, Sunny Boy’s use of Texas Instruments’ TMS320F2812 digital signal controller for this purpose, and the inverter’s use of Avago gate-drive optocouplers in the H5 bridge circuit.

What you’ll learn:

• How to understand operation of grid-tied solar power inverters, particularly the transformerless kind
• How to understand the architectural and component choices that have been made in the design of a commercially available solar power inverter

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Author & Publication:

Steve Tarnovich, Contributing Technical Editor , EDN, Feb 16 2012

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