Abstract

Document Sections

I. Introduction

II. Circulating Current

III. Proposed Method to Eliminate Circulating Current

IV. Simulation and Experimental Results

V. Discussion

VI. Conclusion

Abstract:

Parallel pulsewidth modulation rectifiers are a good solution for high-power ac–dc applications, which enhance quality and reliability. However, the main and inevitable shortcoming of parallel structures is a generation of circulating current. Various methods are proposed to reduce or eliminate circulating current, most of which tend to change or limit the switching pattern of parallel converters. This article presents an interfacing circuit with low rating elements, which eliminates the circulating current without any limitation for the switching pattern of parallel converters. Therefore, voltage and current waveforms are in high quality. Moreover, unlike previous methods that had complex control and high mathematical computations, the presented method has simple control. Therefore, multiple modules can be implemented in a modular fashion with a fast dynamic response. Simulation and Laboratory results are presented to validate the analysis.

INTRODUCTION

he use of parallel PWM rectifiers (PPWMR) is essential in a wide range of applications in electrical industry such as renewable energy systems and motor drives [1, 2]. High power conversion, higher reliability, enhanced power quality, improved current and voltage waveforms are among the benefits of parallel structure. The main problem with the application of such structures is the inevitable creation of circulating current, which will damage semiconductor devices, increase losses, cause distortion in current and voltage waveforms, reduce efficiency and reliability of the system [3, 4]. Circulating currents are categorized as high and low frequency components [1, 5] which are due to different switching states of parallel rectifiers and different control system of converters respectively. Also, different design components and unbalanced voltages are of concern in low frequency circulating currents.

Low frequency circulating currents are normally reduced using a droop control strategy [6] and also PI controllers which are dependent on circuit performance in different states. Among these strategies are PI controller with feed forward controller [7], deadbeat control method [8], using a PIR with Manuscript received November 12, 2020; revised April 18, 2021 and June 16, 2021; accepted July 14, 2021. H. A Porkia and J. Adabi are with the Faculty of Electrical and Computer Engineering, Babol Noshirvani University of Technology, Babol 47148- 71167, Iran (e-mail: j.adabi@nit.ac.ir). F.Zare is a Professor with School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Australia, (e-mail: f.zare@uq.edu.au). feed forward term which requires information of switching vectors in each period [9], improved D-∑ digital method [10], finite-time controller and zero-vector feed forward control method [5]. [11-14] introduces a strategy based on an average model. [15] investigated elimination of circulating current due to third harmonic order.

Main solutions for high frequency circulating current reductions are mainly classified in three main categories: Filters, PWM strategies and topology reconfiguration. Each of which has its advantages and disadvantages. Coupled inductor (CI) [16-18], common mode inductor (CMI)[19], inter-phase inductor [20] and modified LCL (MLCL) [6] are the main structures in the category of filter-based techniques. Mainly, they have issues regarding size, cost and losses. However, according to [3, 6], MLCL leads to internal common mode resonance current and external zero-sequence resonance circulating current.