Microcomputer based Harmonic Estimation of Thyristor Converter Waveform using Recursive Discrete Fourier Transform

Abstract

The paper presents an application of recursive discrete Fourier transform (RDFT) method involving real number computations for estimating the harmonic magnitudes in the waveforms of a 6 pulse, full wave thyristor bridge circuit. The signal is modelled in state variable form as the output of a dynamic system. A dead-beat spectral observer in discrete time, operating at the Nyquist sampling rate estimates the harmonic amplitude components recursively since it performs one step per-sample updating. The estimates rapidly converge to yield the transform coefficient after exactly the requisite number of samples decided by Nyquist rate, even in the presence of numerical truncation errors. A microcomputer based instrumentation scheme for on-line implementation of the RDFT is suggested.

Indexing terms:

• On-line harmonic estimation
• Microcomputer Instrumental recursive estimation
• Thyristor converter harmonic estimation