Modular input-parallel output-series DC/DC converter control with fault detection and redundancy

Large offshore wind farms require extensi ve sub-sea cables within the collection network. Present solutions are based aro und medium-voltage AC collection networks. Recent studies have highlighted the poten tial benefits of DC collection networks. However, achieving DC/DC conversion at th e required voltage and power levels presents a significant challenge for wind-tu rbine power electronics. This paper proposes an alternative DC collection network based around a modular DC/DC converter with input-parallel output-series (IPOS) connection. This modular topology can overcome the limitations imposed by semiconduct or voltage ratings and provides fault-tolerant operation. Small-signal analysis of the converter is presented to be used to facilitate controller design for the converter inpu t and output stages. A new master- slave control scheme and distributed voltage sharin g controllers are proposed that ensure power sharing under all operating conditions , including during failure of a master module. This control scheme achieves fault-t olerant operation by allowing the status of master module to be reallocated to any he althy module. The proposed control scheme is validated using simulation and experiment ation, considering active power sharing between modules with parameter mismatch