Hybrid Smart Converter Transformer for Enhanced HVDC Reliability and Reduced Complexity

The HVDC transmission is typically utilized for connecting long distance or asynchronous AC networks. The two most common HVDC technologies are voltage source converter HVDC (VSC-HVDC) and line commutated converter HVDC (LCC-HVDC). Although VSC-HVDC has enhanced control features along with non-dependence upon synchronous machines for commutation, it suffers from higher cost and higher losses due to the involvement of high-speed switching, requires sophisticated gate driver circuitry, has a weak overload capability and suffers from lower reliability due to higher component count. This paper focuses on the highly mature LCC-HVDC technology and aims at enhancing its reliability along with reduced control complexity by proposing a novel transformerless power electronics-based module integrated between the neutral and ground of HVDC inverter-side transformer. The module introduces a variety of smart features in conventional converter transformer, such as, harmonics isolation, voltage regulation, voltage and impedance balancing. This enhances LCC-HVDC robustness against commutation failure, reduces DC power recovery time and control complexity while protects it against certain natural and man-made disturbances, such as, solar storms and high-altitude nuclear detonations. The proposed approach is evaluated in PSCAD/EMTDC for the CIGRE HVDC benchmark model that highlights its promising performance.