Transformerless Modular Current Source Inverter for High-Power Medium-Voltage PV System

Current source inverters (CSI) are a promising candidate for connecting intermittent photovoltaic systems to medium voltage grids. Traditional PV systems require additional bulky low-frequency step-up transformers. CSIs have numerous merits, such as inherent short-circuit protection, high scalability, and modular structure. Also, they can eliminate the need for the transformer without adding extra complications to the system like voltage/power imbalance in distributed dc buses, complicated design, or additional conversion stages. This paper proposes a modular transformerless series-connected CSI (SC-CSI) for medium voltage grid-tied applications. The inverter has buck-boost voltage regulation, which is beneficial in applications with highly variable voltage sources. A simulation of the proposed circuit is carried out to validate the effectiveness of the proposed solution and control strategy.