Simulation of Five-Level DC-DC Converter with Asymmetrical Control Strategy

In this paper an asymmetrical duty cycle control strategy was proposed to the TPTL dc/dc converter. The modified converter remains all the advantages of original control strategy; meanwhile, soft-switching can be achieved using the energy stored in output filter inductance and leakage inductances of transformers (or resonant inductances).Three-phase three-level (TPTL) dc/dc converter has the advantages of lower voltage and current stress on switches, which is suitable for high power and high input voltage applications. Adopting a symmetrical control strategy, the ripple frequency of input and output current can be increased significantly, resulting in a reduced filter requirement. To further reduce the current stress on switches for higher power. The improved resonant converter features zero-voltage-switching (ZVS) realization under wide load range and higher conversion efficiency. However, wide variation in switching frequency should be concerned in the applications with wide input/output voltage range. Other alternative solutions are the non resonant soft-switching threephase converters, the upper and lower commutation cell switches are subjected to different current stresses) is improved by using MAT Lab/Simulink. The proposed concept can be implemented with five level topology using Matlab/simulink software. INTRODUCTION Over the years single phase full-bridge (FB) and threephase FB pulsewidth modulation (PWM) dc to dc soft switched converters have become popular in the field of dc to dc conversion system. For these converters metal oxide semiconductor field effect transistors (MOSFETs) are generally preferred over insulated gate bipolar transistors (IGBTs), because they can be operated at higher switching frequency and they do not have the problem of long tail current. However, these FB PWM soft switched converters are not suitable for switch mode power supply applications, where the input voltage is high. This is because the MOSFETs have to sustain high input dc link voltage. Moreover, service of auxiliary circuits is required to operate devices in soft switched mode. This requires extra components, devices and hence it leads to incurring additional cost while reducing the system reliability. In order to reduce the voltage stress to half of the input dc voltage, a three-level topology has been considered in [1] and [2] for inverter application and it has been used for realizing a dc to dc converter in [3]–[5]. The soft commutation is achieved by using phase shift PWM modulation [4], [5] which is having simple control structure and high power density can be achieved. However at high power levels, these components experience considerable current stress. In order to overcome this problem, topologies consisting of threephase inverter coupled to a three-phase high frequency transformer followed by three-phase high frequency bridge-rectifier have been proposed [6]–[9]. This results in an increase in the input current and output current frequencies by a factor of three as compared to the full bridge converter. This also results in lower current rating for the components and also a considerable reduction in size for the isolation transformer. However, the devices experience high voltage stress and the control structure is also quite involved. In an effort to overcome the aforementioned