Modified Transformerless Series-Connected Current Source Converter Without Series-Connected Switches

Transformerless series-connected current source converters (SC-CSCs) were recently proposed. Compared with existing ones, they eliminate the transformer, giving significant reductions in cost and size. However, they need the use of series-connected switches in medium/high-voltage applications, and as a result, very complicated voltage balancing schemes are required. To address this challenge, a modified transformerless SC-CSC is proposed. In the modified one, the series-connected switches are replaced with a cascaded half-bridge converter, while the left remains the same as existing ones. By doing so, the need for series-connected switches is eliminated, while the advantages of original converters are well retained. In addition, the cascaded half-bridge converter has inherent voltage balancing, reduced switching frequencies, and a unique zero-load feature. The operation principle of the modified converter is presented. The performance is verified by both simulations and lab-scaled experiments.