Design and Comparison of passive component requirements of a matrix converter and voltage-source based back-to-back converter

Abstract

A filter is required to eliminate the high frequency switching ripple present in the input current of AC/AC pulse-width modulated (PWM) converters. Design of such filters requires an estimation of the higher harmonic components present in various voltages and currents. Due to pulse-width modulation (PWM), the matrix converter generates switched currents at its input and the back-to-back converter generates switched input voltages which flows distorted currents. This dissertation presents simple closed form analytical expressions for the RMS input current ripple of the matrix converter and RMS input voltage ripple of a DC-link based back-to-back converter. The design of DC-link capacitor in a back-to-back converter requires the estimation of ripple current flowing through it which is also analytically computed. The expressions evaluated are independent of variation of load frequency, output alignment angle, switching frequency, etc. and is a function of known parameters like the modulation indices of the converters, the load and its power factor, DC-link voltage, etc. A systematic step-by-step procedure is presented to design various input filter components from the specifications of allowable THD in the grid current, permissible distortion in the input voltage, allowable inverter current ripple and reactive current drawn by filter capacitor. The converters are modeled for the grid frequency component in order to evaluate the design for input power factor, voltage drop across the filter, maximum possible real power transfer, etc. A damping resistance has been designed ensuring minimum ohmic loss. The analytical estimation of the ripple quantities and the proposed design procedure have been validated by simulations in MATLAB/Simulink and experiments on a laboratory prototype. A comprehensive comparison between the passive filter component requirements of a matrix converter and a DC-link based back-to-back converter is studied under different operating conditions. An input L-C filter of matrix converter is compared with an LCL filter and DC-link capacitor of a back-to-back converter. To compare size, volume and lifetime of passive components, the analysis with a quantitative and qualitative comparison of the passive component values along with their current and voltage ratings is also presented under different load power rating and variation of switching frequency.