Pre-charge Pressure Estimation of a Hydraulic Accumulator Using Surface Temperature Measurements

Pitch systems form an essential part of today’s wind turbines; they are used for power regulation and serve as part of a turbine's safety system. Hydraulic pitch systems include hydraulic accumulators, which comprise a crucial part of the safety system, as they are used to store energy for emergency shut-downs. However, accumulators may be subject to gas leakage, which is the primary failure mode. Gas leakage affects performance of the accumulator and, in extreme cases, compromises the safety function of the pitch system. This paper deals with the development of a robust algorithm to detect gas leakage in piston-type accumulators. The approach presented is based on a State Augmented Extended Kalman Filter (SAEKF), which utilizes an extended thermal model of the accumulator as well as temperature measurements along the accumulator surface to determine the gas temperature. Based on the gas temperature, an estimate for the pre-charge pressure of the accumulator is presented. The method is experimentally validated and addresses the drift problems in estimating the gas leakage evident from previous research. Additionally, the method is able to identify and isolate gas leakage to a single accumulator out of a bank of accumulators.