Lifecycle Energy Production Evaluation and Improvement of PM Synchronous Generators for Wind Turbines Considering Accumulative Demagnetization

Previous methods for evaluating the lifecycle energy production (LEP) of permanent magnet synchronous generators (PMSGs) for wind turbines usually neglect the risk of irreversible demagnetization in PMs. This is because demagnetization is typically prevented at the design stage by lowering stator currents and thus PM temperature. However, this approach comes at the cost of reduced output power. This article reveals that allowing a certain degree of demagnetization can enhance LEP, even though the postdemagnetization annual energy production declines. Unlike prior work focusing on single-event demagnetization, this study considers accumulative demagnetization caused by multiple short-circuit faults. When fault conditions, such as short-circuit type, rotor position, and rotor speed, vary between consecutive faults, irreversible demagnetization can accumulate. With this effect, LEP becomes a function of the output power after each fault and the time intervals between faults. To address this, a novel LEP evaluation method is developed with the uncertainty of fault occurrences considered. Using this method, LEP of a PMSG is evaluated under various rated stator currents, corresponding to different levels of rated output power. Results show that by balancing stator current and demagnetization level, the optimal LEP can increase by up to 4.93% compared with that when demagnetization is avoided.