When operating in marine environments, the power conversion link of direct-drive grid-connected permanent magnet synchronous generator (PMSG) units may be subject to various types of faults, such as short-circuit faults in the generator windings and open-circuit faults in the converter. Due to the high maintenance cost, once a generator fault occurs, it will cause huge economic losses. For this reason, it is significant to investigate the impact of different faults of grid-connected wind power units on the generator. In this article, the coupled electromagnetic–thermal converter calculation model is established for a direct-drive offshore PMSG with a rated power of 5 MW and a rated speed of 15 r/min. In addition, the generator loss distributions under four types of machine-side converter open-circuit faults and four types of grid-side inverter open-circuit faults are calculated. Particular attention is given to the distribution of the eddy-current loss of the rotor magnet box. On this basis, the transient effects of different faults on the temperatures of the generator windings and permanent magnets are investigated. The dimensionless number global rise time is used as the evaluation index in this research. The index reveals the impact of different faults on the generator stability by indicating the time it takes for the generator’s key components to reach the temperature tolerance limit. The findings provide a basis for enhancing the transient operation capability of wind generators under extreme fault conditions.

Abstract In this paper, we design and fabricate a Schottky-metal-insulator-semiconductor (MIS) cascode anode GaN lateral field-effect diode (CA-LFED) to achieve ultralow reverse leakage current ( I LEAK ). The device based on AlGaN/GaN high-electron-mobility-transistor (HEMT) includes a normally-off MIS-controlled channel that is cascoded with a high barrier height Schottky contact. At reverse bias, the high electric-field is effectively prevented by the normally-off MIS-controlled channel edge. Together with the high barrier height Schottky contact, this feature significantly suppresses the I LEAK . Supported by the device fabrication, the CA-LFED with high breakdown voltage (BV) > 600 V shows an ultralow I LEAK of 3.6 × 10 −9 A/mm as well as a low forward voltage drop ( V F ) of 2.2 V. The performance suggests that the CA-LFED can be a promising candidate for ultralow I LEAK and better V F - I LEAK trade-off GaN power diode applications.