A New Approach for the Computation of Harmonics and Interharmonics Produced by Line-Commutated AC/DC/AC Converters

Abstract

A new approach for modeling line-commutated ac/dc/ac conversion systems is presented and discussed. It is based on the modulation function theory taking advantage of a two-step procedure in which two different models are used. The goal is to achieve a reduction of the computational burden with respect to the time domain models and better modeling accuracy with respect to classical modulation function approaches. The proposed model constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Comparative tests validate the proposed method and demonstrate its computational efficiency and result accuracy.

A new approach for the computation of harmonics and interharmonics produced by AC/DC/AC conversion systems with PWM inverters

“…This impedance involves both the conduction and the commutation conditions, so it depends on their duration, i.e., the overlapping angle m [1].…”

“…This means to assume the mean value for the Z eq previously defined, so ignoring the modulation effects of the alternating of the rectifier conduction and commutation conditions [1]. In order to also take into account the effects of the rectifier conduction and commutation cycles on the supply side impedance as seen by the DC side, it is possible to consider again the circuit of Figure 2b), replacing the DC Equivalent Load by means of the series of the DC resistance and inductance and the e.m.f source v o'o (t) obtained at the end of the iteration process (Figure 7).…”

“…The computation of the harmonics and interharmonics produced by AC/DC/AC conversion systems is the object of extensive research activity [1][2][3][4][5][6][7][8][9][10]. In addition to the typical problems caused by harmonics, such as overheating and the reduction of useful life, interharmonics create several new problems, such as sub-synchronous oscillations, voltage fluctuations, and light flicker, even for low-amplitude levels [10].…”

“…In addition to the typical problems caused by harmonics, such as overheating and the reduction of useful life, interharmonics create several new problems, such as sub-synchronous oscillations, voltage fluctuations, and light flicker, even for low-amplitude levels [10]. Typically, attention is devoted to those systems in which both AC/DC and DC/AC conversions are operated by line commutated converters at different frequencies that intermodulate originating interharmonics; this is the case of HVDC systems [3,4] and high-power adjustable speed drives (ASDs) [1]. Less attention has been devoted to different systems, such as ASDs using PWM inverters, due to the assumption that the DC-link capacitor, which was used in this case, practically reduces the intermodulation between the two converters to zero [5,6].…”

A new frequency approach for light flicker evaluation in electric power systems

“…Recent studies have demonstrated that modern distributed energy resources, in particular wind turbines, are able to produce interharmonics in a wide range of frequency from DC to some kilohertz [15]. Moreover, in [16][17][18], it was demonstrated that interharmonic components produced by adjustable speed drives can cover all the frequency range from DC.…”