Current Control of Three-Phase Inverter Using Multiple Bidirectional Choppers Intended for 1.5-kV PV Systems

Abstract

This article deals with a three-phase inverter for utility-scale photovoltaic (PV) systems where multiple cascaded bidirectional choppers and a three-phase line-frequency transformer with a three-legged core are used. It can achieve a wider maximum-power-point-tracking operating voltage range and the elimination of high-frequency circulating current under the parallel operation of inverters simultaneously. Meanwhile, the conventional current control method based on three-phase <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$d-q-0$</tex-math></inline-formula> transformation suffers from system instability due to a singular point existing in the dc input voltage. For solving this problem, this article proposes a new current control for the three-phase inverter, which is based on the individual current control. The proposed PV inverter structure and the current control method are designed for application in a 1.5-kV megawatt power level PV system. The validity of the control method under active and reactive power control is proved by conducting experiments using a 1.5-kW downscaled model. Furthermore, loss analyses along with comparisons with the conventional three-level inverter are provided.