Transformerless Large-Scale Grid-tied PV System Using Sensorless Boost Modular Multilevel Inverter with DC Fault Blocking Capability

The scalability of Modular Multilevel Converters (MMCs) has eased the integration of large-scale Renewable Energy Sources (RESs) to Medium Voltage (MV) network. In this paper, the integration of a grid-connected large-scale Modular Multilevel Inverter (MMI)-based 1 MW PhotoVoltaic (PV) plant is analysed. The proposed MMI employs Full-Bridge-SubModules (FB-SMs) topology. Unlike the conventional Half-Bridge (HB)-based MMI, FB-SMs enable a boosting operation; avoiding typical configurations where step-up transformers are required. That is, better power density and specific power can be provided. Moreover, the FB circuit inherits DC faultblocking capability. Therefore, a DC-fault protection system is investigated as same as normal operation to foster the system reliability. A sensorless sorting algorithm is adopted to perform the MMI’s capacitors voltage balancing, hence the firing of FBSMs. The sensorless approach reduces hardware complexity and cost, especially in case of high number of MMI levels. The proposed system is investigated using MATLAB simulation platform.