Harmonic filtering and fault ride-through of diode rectifier unit and modular multilevel converter based offshore wind power integration

The diode rectifier unit (DRU) is promising in offshore wind power integration due to its reliability and economy. Offshore AC voltage control is the key technology of the DRU-based scheme. In this paper, a low-cost offshore wind power integration system based on the DRU and the modular multilevel converter (MMC) in parallel on the rectifier side is proposed. The low-capacity MMC rectifier is controlled to establish the offshore AC voltage amplitude and frequency, maintain all offshore wind active power transmitted by the DRU, and provide reactive power compensation and AC harmonic filtering for the DRU. Besides, the fault ride-through strategies of both the offshore fault and the onshore fault are proposed. Moreover, the calculation method of the rated capacity of the MMC rectifier is derived. The time domain simulations of the hybrid system under typical operating conditions are investigated in PSCAD/EMTDC, and the feasibility of the proposed scheme is verified. A hybrid offshore wind power integration system based on the diode rectifier unit and the low-capacity modular multilevel converter (MMC) in parallel on the rectifier side is elaborated. The control strategy of the MMC rectifier is proposed, combining AC voltage control, active power control, reactive power compensation, and AC harmonic filtering. The fault ride-through strategies of both the offshore fault and the onshore fault are proposed.image