Enhanced DC-link voltage control of PMSG-based wind turbine generators by machine-side converter during asymmetrical grid faults

Abstract

Under asymmetrical grid fault conditions, oscillating active power can occur on the grid-side converter (GSC) of permanent magnet synchronous generator (PMSG)-based wind turbine generators. The oscillating active power flows into the DC-link, causing voltage oscillations that can lead to a shortened lifetime of DC-link capacitors and additional harmonics injected into the grid. While conventional methods can mitigate the oscillating active power through negative sequence current injection by the GSC, this hinders the grid support of the GSC regarding negative sequence reactive current during grid fault. To address this issue, a novel control scheme is proposed that uses the machine-side converter (MSC) to transfer the oscillating power to the motor. Firstly, the active power capacity of the MSC is analyzed and compared with that of GSC, and the results show that MSC has enough capacity to accommodate the oscillating active power. On this basis, a novel MSC control scheme is proposed to transfer the oscillating active power on the DC-link to the motor, which has a much larger inertia to buffer the power oscillation. Compared with conventional methods, the proposed control scheme relieves the GSC from mitigating the power oscillation to support the grid. Simulation studies using DIgSILENT PowerFactory are presented to verify the effectiveness of the proposed control scheme for PMSG-based wind turbine generators.