Inferring Polished Rod Position from Torque Current of the Motor

It is well known that the dynamic position of the rod pumping aid in the diagnosis of onshore oil wells and can be used to control the pumping unit. Even today the acquisition of the position of the polished rod is made using physical transducers of position. However, this paper shows that the dynamic position of the polished rod can be inferred from torque current (which is given by sensorless vector AC-drive) of a threephase induction motor using a nonlinear autoregressive model with exogenous input based on wavelet network (wavenet). The set of input-output data was collected from a pumping unit system installed in an oil-well developed for tests. The model orders were evaluated using Akaike's final prediction error (FPE). The results obtained in the validation step show that, for the experimental set used in this work, the best estimated model may be used in place of the physical transducer of position. Key-Words: Sucker-rod pumping; polished rod position, system identification; NARX model; wavenet; wavelet.