Single-Stage Multistring PV Inverter With an Isolated High-Frequency Link and Soft-Switching Operation

A grid-tied multistring photovoltaic (PV) inverter with a high-frequency ac (HFAC) link, soft-switching operation, and high-frequency (HF) galvanic isolation is introduced. This single-stage topology can handle an arbitrary number of PV strings with different electrical parameters, locations, and orientations. Using a dedicated maximum power point tracker for each PV string, this inverter can harvest the highest possible power from each string independently, even though they might be at dissimilar irradiance levels and operating temperatures. The isolated HFAC link is formed by the magnetizing inductance of a small-sized HF transformer and two small ac capacitors without the use of bulky short-life electrolytic capacitors. The link is responsible for transferring the PV strings' power to the grid along with creating zero-voltage switching for the power devices. Therefore, the converter has the advantages of high power density, high reliability, as well as high efficiency. After describing the control scheme and the operating algorithm of the proposed multistring inverter, a detailed analysis is carried out. The experimental results of the developed 1-kW two-string prototype with different PV strings at various PV conditions are also shown. The results verify the effectiveness of the topology in tracking the maximum power of each string independently without affecting the operating condition and control of the other string.