Contents I. Introduction
In Recent years, the offshore wind power is developing rapidly. The development of offshore wind energy conversion system indicates a trend toward employing large wind turbines with higher power rating to improve efficiency and reduce the cost of offshore wind power. In 2018, the average power rating of newly installed onshore wind turbines and offshore wind turbines are 2.7 and 6.8 MW in Europe, respectively [1]. Commercial high power wind turbines include some wind turbines from companies in the world [2], [3]. Permanent magnetic synchronous generator (PMSG)-based wind turbines feature low maintenance cost and high efficiency, so they have been considered a promising solution to high power wind turbine applications. For onshore PMSG-based wind turbines, the voltage rating of the PMSG is usually lower than 1 kV, such as 690 V. However, PMSG voltage rating of 690 V is relatively low for high power applications due to the large current which causes high power loss and high cost of cables and connections [4]. Therefore, medium voltage or high voltage PMSGs are promising for new designs of high power wind turbines [5].
