Impact of a multi-star winding on the reliability of a permanent magnet generator for marine current turbine

For Marine current turbine (MCT), low speed Surface-mounted Permanent Magnet generator is a solution to satisfy the efficiency and fault tolerant requirements. This is supposed to be true if the winding is made with several non-shifted three-phase stars that could be supplied with standard modular voltage source inverters. This paper investigates the impact of the star number on the MCT energy yield if the system is conceived to operate with disconnected inverters. For this purpose, a method to calculate the extracted power according to the tidal speed for a given star number and a given activated star number is detailed. A rainflow counting method is used to account the stress due to the tidal speed change on the star converter: the impact of the star number on the resilience capability of the MCT is then quantified. By assuming a ten-year period without converter repair, according to the introduced probabilistic approach, the star number increase improves the reliability and three-star configuration appears as a trade-off.