Analysis of Harmonics and Ripple Current in Multi-module Converters with Increasing Number of Modules for High Power Applications

Abstract

Controlled rectifiers are considered as the most important hardware part in the field of HVDC systems in transmission lines and can be used for a number of power electronics based system operation, control and utility applications. In this paper, a brief design of a 12-pulse, 24-pulse, 36-pulse and a 48-pulse converter connected to the grid is presented along with the harmonic and ripple current analysis with its comparison statistics and thus providing a justification for the suitable ones. The performance of the 12, 24, 36 and 48-pulse converters are compared for their effectiveness in both quantitatively as well as qualitatively. Further, comparison of the 48-pulse converter on its THD and current ripple which is connected towards the grid with simple pulse width modulation technique is also proposed. It combines all features of the low switching concepts and DC current reinjection techniques. Some basic topological explanation of the controlled rectifiers and simulation results using MATLAB are also presented in this paper in order to justify the harmonic analysis. The simulation results along with the quantitative results shows the effectiveness of the proposed scheme for the cancelation or the elimination of the harmonics result in maximum harmonic mitigation, for high power utility applications, the 48-pulse converter is most fitting to improve the conversion efficiency, low di/dt and dv/dt and active and reactive power controllability. Keyword: Controlled INTRODUCTIONMultipulse converters are suitable for high-power applications with the advantages of ideal harmonic performance and low switching frequency, but it also has an drawbacks of poor regulation and less controllability. With very low switching frequency a bidirectional pulse width modulation (PWM) converter based on multipulse structure has got the same harmonic performance [1]. The harmonic performance and linear regulation capability of such converters can also be analyzed theoretically. The general structure of the multilevel converter is to synthesize a sinusoidal voltage from several levels of voltages, typically obtained from capacitor voltage sources. The so-called 'multilevel' generally starts from three levels. A three-level converter, also known as a 'neutral-clamped' converter, consists of two capacitor voltages in series and uses the center tap as the neutral [13]. To get high dynamic performance the controller parameters are optimized with adequate gain phase margin. A 3-kVA prototype can be built so that the simulation and experiment results could be validated and the proposed converter could be used for high-power conversions [3]. The performance analysis of a 2-level, 24-pulse voltage source converters (VSCs) for high voltage DC (HVDC) system can be used for power quality improvement [4]. High Voltage Direct Current (HVDC)

A New Aluminum Pot Line Rectiformer Scheme with Effective Harmonic Suppression Capability

“…Aluminum Bahrain (ALBA) company consumes more than 1.6GW DC power to feed their five pot lines. Conventional pot line scheme is consisting of six Rectiformers connected in parallel and each is phase shifted in order to achieve 72 pulse system which effectively reduces the harmonic currents at PCC [1]. The ideal characteristic harmonic orders penetrating into the network in this case will be [2]- [3]:…”