Dually Fed Permanent Magnet Synchronous Generator Condition Monitoring Using Generator Current

Paper in proceeding, 2013

As the number of installed wind turbines steadily increase in the world, better and more efficient maintenance procedures are needed. Condition monitoring is one method which increases the efficiency of maintenance as it provides information on the current state of the turbine, which in turn determines when and what type of maintenance is needed. This paper presents an extension of a previously derived method that is able to detect generator winding faults as well as faults in the mechanical part of the drive train. The method is here applied on a setup consisting of a generator with dual windings connected to two completely isolated, individual controlled inverters. Furthermore, the investigated method includes the use of an observer system for estimating the generator rotor position and generator speed, extending the original method to a sensorless operation. The observer system consists of a flux observer and a phase looked loop. The simulated model is based on data from a direct driven wind turbine generator in the MW range. Since the machine in this paper is dually fed, faults in the electrical system are more easily detected by comparing the outputs from both converters, which under normal conditions are identical. With the knowledge on how the observer is constructed and how it reacts to parameter errors, it is shown that the resulting effects of the phase looked loop during an electrical fault can be utilized when determining in which part of the generator the fault has accorded, without the need to look at the two different outputs individually. It is also shown that mechanical imbalances are detectable but nothing is gained by having a system consisting of two sets of separated electrical windings compared to a system with a single electrical winding. Differentiating between electrical and mechanical faults is possible by observing the frequency content in the monitored quantities, as mechanical faults creates and oscillation at the generators mechanical rotating frequency where electrical faults frequency content is a multiple of the generators electrical frequency.