A Medium-Voltage DC-Collection Grid for Large-Scale PV Power Plants With Interleaved Modular Multilevel Converter

Abstract

There is a growing interest in deploying medium-voltage dc-collection grid technologies in renewable energy applications to improve energy efficiency. Existing dc-collection grids incorporate medium-voltage dc/dc converters that suffer from bulky passive components such as a step-up transformer along with additional conversion stage to incorporate MPPT function. In response to these concerns, this article proposes a new medium-voltage dc-collection grid method for large-scale PV plants with an interleaved modular multilevel (IMMC) dc-dc boost converter. The proposed IMMC converter is synthesized with lower voltage half-bridge SiC inverter blocks connected in series to support medium-voltage dc-dc conversion. The half-bridge blocks of the IMMC employ SiC switches, along with high-frequency PWM operation enable compact size/weight along with high-efficiency conversion. Simulation results are shown for 1500-V (dc) to 16-kV (dc) conversion with four series-connected IMMC inverter blocks powered from two PV plants. A power-sharing stage is an integral part of the proposed converter. This enables two series-connected PV plants to supply unequal power under partial shading conditions. Control of the power-sharing stage for varying insolation from PV (1000-500 W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) due to the shading effect is shown. A design example for 1-MW PV power plant block based on the specifications derived from Kuwait Shagaya 60-MW solar power plant is discussed. Experimental results on a scaled-down laboratory prototype are included in this article.