Comparison of the Trapezoidal Current and Stepped 2-Level Modulation Techniques in Modular DC-DC Converter

Abstract

For high step-ratio connectivity in direct current (DC) grid applications, a modular (DC-DC) converter (MDCC) has been proposed. To improve the performance of the MDCC, this paper discusses a trapezoidal current modulation (TCM). Com-paring with stepped 2level modulation where the sub-module (SM) capacitor voltages are balanced with a feedback control loop, TCM ensures the voltage balancing by applying an equal duty cycle for each SM in the high voltage stack with-out any additional feedback control. Three-level operation mode featured with large power transmission and high efficiency conversion, based on circulating current analysis and softswitching performance is introduced. The control schemes of this operation mode is designed to minimize both the SM capacitor voltage ripples and the peak current. An analytical simulation of the MDCC is presented using MATLAB/SIMULINK to explain the operation and discuss the results.