Hybrid Series Converter: A DC Fault-Tolerant HVDC Converter With Wide Operating Range

A compact, efficient and dc fault-tolerant hybrid series converter (HSC) topology is proposed in this article for high-voltage direct current (HVdc) applications. It contains a parallel and a series chain link (CL) per phase. The parallel CL (PCL) supports the dc-link, whereas the series CL (SCL) enables the HSC to have enhanced operating range and dc fault-tolerant capabilities. A new control technique is proposed to control the SCL submodules (SMs) capacitor voltage for its entire operating range. The performance of HSC and its control technique is evaluated using PSCAD/EMTDC for various conditions. The capability of HSC to work in the undermodulation and overmodulation index range and for HVdc system is examined. Furthermore, the response of HSC during pole-to-pole dc fault and ac faults is analyzed to substantiate its dc fault blocking and ac fault ride-through capabilities. The results obtained validate that the HSC exhibits superior performance over the existing ones. The SMs’ capacitor size design methodology in HSC and for other existing topologies is described. The loss calculation of the HSC is carried out to determine its efficiency and is compared with the prominent converter topologies. A three-phase 13-level HSC experimental setup is developed to validate its feasibility and also to reconfirm the simulation outcomes.