Control scheme for low voltage ride-through compliance in back-to-back NPC converter based wind power systems

The increasing influence of wind power in the power system operation has caused the power system operators to include wind power plants in the control of the overall power system, both in steady-state and transient operation. Therefore, the grid connection requirements of the power system operators involve wind power systems. Low voltage ride-through requirement is probably the most demanding grid connection requirement to meet, at least from the point of view of the wind energy conversion system. In presence of grid voltage dips, the low voltage ride-through compliance produces a mismatch between the generated active power and the active power delivered to the grid. The management of this mismatch supposes a challenge for the wind energy conversion system. In this work, a control scheme for the back-to-back neutral-point-clamped converter is proposed. Under grid voltage dip, the controllers for generator-side and grid-side converters work concurrently to meet the low voltage ride-through requirement by storing the active power surplus in the inertia of the generator and keeping constant the dc-link voltage. Simulation results verify the proposed control scheme.