The Flexible Grid-connection Research of Two-level High-power Offshore Wind Power Grid Inverter

In this paper, we present a high-power offshore wind power grid inverter of two-level. We design an inverter of 30MW as a sample, the dc bus voltage is 35KV. The switching devices of the main circuit withstand the high voltage and current through IGBTs in serious and in parallel. The control strategy for the inverter concludes the voltage loop control, the current loop control and the phase-locked loop control. The voltage loop is designed to keep the dc-link voltage steady. The current loop is designed to make the current of the grid side have little harmonic components and track the active current given from the voltage loop quickly. The phase-locked loop is designed to make the gird current have the same direction with the grid voltage. We controlled the active current and reactive current independently. Simulation results successfully validate the proposed control strategy of grid-connection.