Control of Neutral-Point-Clamped Converter in Distributed Power Generation to fulfil Low Voltage Ride-Through Requirements

Grid connection requirements established by power system operators have been updated in recent years, in order to include distributed power generation plants operation in the transient operation control of the overall electric power system. Among them, low voltage ride-through requirements demand wind power plant to remain connected to the network in presence of grid voltage dips. It is well-known that grid voltages present positive, negative and zero sequence components under faulty condition, hence regulators based on symmetrical components are well suited to control grid-connected converters. In this work, a neutral-point-clamped topology has been considered as an active front end of a distributed power generation system. In order to achieve balanced grid currents under any grid condition, negative-sequence grid voltage is feed forwarded, working concurrently with the linear quadratic regulator current controller. An outer loop for dc-link voltage control is implemented using a proportional-integral regulator. Power flow mismatch during grid fault condition causes dc-link voltage increase, therefore generator-side regulation is needed to avoid improper dc bus voltage evolution.