Kalman filtering based algorithm for low frequency power systems subharmonics identification

With the wide use of power electronics equipment such as rectifiers, inverters, cycloconverters and SCRs in power system control, as well as the off-on switching of voltampere compensators in transmission and distribution systems, electric utilities have experienced an increase in the levels of harmonic frequencies on the electrical delivery system. The off-on switching of the equipment may produce damped transients of high and/or low frequency on the voltage and/or current waveforms. This paper presents a new application of the linear Kalman Filtering Algorithm (KF) for identifying the amplitude and damping factors of these transients (subharmonics). The frequencies of these subharmonics are assumed to be known in advance and are fractions of the system nominal frequency (power frequency). Modelling of these transients to fit the linear Kalman filtering algorithm, as well as the methods of identification are also offered in the body of the paper. The proposed algorithm is applied to actual recorded data of a dynamic load, which is a variable frequency drive controlling a 3,000 HP induction motor connected to an oil pipe line compressor. The data given for this load are the three-phase currents at different motor speed.