Precise removal of decaying dc in DFT algorithm for power system measurement

In this paper we present an approach which precisely removes the errors due to decaying dc offset from Discrete Fourier Transform (DFT). Decaying dc has a continuous spectrum spanning the whole subsynchronous frequencies, making it difficult to be suppressed. DFT as one of the most favorable approaches in power system measurement cannot tackle decaying dc and its results are erroneous in presence of decaying dc. The DFT-based approach proposed in this paper is based on using two different sampling frequencies, one double of the other, and it can extract the part of DFT result which is due to decaying dc component in the form of a formula. Simulations are performed for signals with one decaying dc component and also with multiple concurrent decaying dc components and the results demonstrate that the proposed approach, irrespective of the amplitude and the time constant of the decaying dc component, estimates the phasor of the signal precisely in presence of one decaying dc component and with negligible error in presence of multiple concurrent decaying dc components.