Discontinuous Modulation Scheme for a Differential-Mode Ćuk Inverter

Siamak Mehrnami,Sudip K Mazumder

doi:10.1109/tpel.2014.2314688

Abstract

The differential-mode Ćuk inverter (DMCI) is a single-stage inverter with low device count. It offers advantages over other topologies because of compactness, higher power density, and reduced cost. It is a promising topological configuration for renewable-/alternative-energy applications with isolated as well as nonisolated structures. The continuous modulation scheme (CMS), which was introduced originally for this inverter, activates all the modules of the DMCI. The new discontinuous modulation scheme (DMS) deactivates one module in each half line-cycle leading to discontinuous operation of modules. This paper outlines the DMS and a mechanism to realize it. The experimental open-loop and closed-loop results of the DMCI using CMS and DMS are provided along with a comparison of their performances. It is shown that, the DMS reduces the circulating power and hence mitigates the losses. The voltage ratings of the devices also are reduced with the DMS. In contrast, the CMS has wider linearity in its normalized dc-voltage gain and yields reduced harmonic distortion of the output voltage. For DMS, to achieve comparable linearity in normalized dc-voltage gain and distortion, harmonic compensation under closed-loop control is a pathway that has been demonstrated.

Highlights

For low-cost inverter applications, ranging from renewable energy to alternative energy to vehicular applications, with need for galvanic isolation, high-frequencylink (HFL) inverters have emerged as a potential front runner [1]-[7]
In this paper, a detailed analysis on the performance of the DMCI operating with discontinuous modulation scheme (DMS) as well as continuous modulation scheme (CMS) is provided in Sections III and IV based on theoretical and experimental results. These results demonstrate the positive impact of DMS on the DMCI with regard to efficiency and reduction in device breakdown voltage rating while at the same time, requiring relatively complex closedloop compensation in order to achieve satisfactory total harmonic distortion (THD) and transient response
An experimental hardware prototype was developed for the DMCI to validate and compare the results obtained using the two modulation schemes focusing on energy-conversion efficiency, device rating, output-voltage distortion, and transient response of the inverter

Summary

INTRODUCTION

For low-cost inverter applications, ranging from renewable energy to alternative energy to vehicular applications, with need for galvanic isolation, high-frequencylink (HFL) inverters have emerged as a potential front runner [1]-[7]. For DMCI, and as evident from the illustration, one of the main drawbacks of the CMS is that it leads to circulating power in the converter yielding extra loss This circulating power enhances the peak current and peak voltage of the switching devices. The activation of each of the modules of the DMCI using DMS in alternate half of each line cycle yields a reduction in the order of the inverter by two as compared to the system order obtained using CMS. The flow of power flow in the DMCI in the positive and negative halves of the line cycle are illustrated, respectively, in Fig. 7(b) and Fig. 7(c)

Circulating Power

Device Rating

EXPERIMENTAL RESULTS

Distortion

CONCLUSIONS