基于公共低压直流母线AC-AC隔离型模块化多电平级联变换器

AC-AC Type Isolated Modular Multilevel Cascade Converter Based on Common LVDC Bus

文中提出一种新型单级式隔离型模块化多电平级联变换器(isolated modular multilevel cascade converter,I-MMCC),其具有中压三相交流(medium voltage three-phase AC,MVAC_((T-P)))、中压单相交流(medium voltage single phase AC,MVAC_((S-P)))和低压直流(low voltage DC,LVDC)3种电压端口。该变换器可实现从LVDC到MVAC的单级式功率变换,MVAC_((T-P))与MVAC_((S-P))电压端口能够实现同频或变频的AC-AC功率自由变换,其单极性调制策略可避免隔离型AC-AC矩阵变换器双向开关管换流暂态过程中出现的电压尖峰等问题。首先,介绍I-MMCC子模块拓扑结构与调制策略,并建立子模块及单相I-MMCC平均等效数学模型;其次,分析MVAC_((T-P))与MVAC_((S-P))端口变频–变压工作原理、稳态功率与端口特性,对单相交流端口基于正交虚拟电路概念,建立控制模型,并推导出MVAC_((S-P))、MVAC_((T-P))端口功率约束关系。最后,通过搭建一套实验样机验证所提出拓扑结构的有效性和优越性。

This paper introduced a novel single-stage isolated modular multilevel cascaded converter(I-MMCC),which has triple ports of three-phase medium-voltage AC(MVAC_((T-P))),single-phase medium-voltage AC(MVAC_((S-P)))and low-voltage DC(LVDC).The converter can realize single-stage power conversion from LVDC to MVAC,and MVAC_((T-P))and MVAC_((S-P))port can realize flexible AC/AC power conversion for same or changeable frequencies.Its unipolar modulation strategy can avoid the voltage spike during the transient commutation process of bidirectional switches in isolated AC-AC matrix converter.The topology and modulation strategy of I-MMCC sub-module were proposed at first.The average equivalent model of sub-module and single-phase I-MMCC was established,respectively.In addition,the working principles towards frequency and voltage conversion of MVAC_((T-P))and MVAC_((S-P))port were introduced.The steady-state power and port characteristics of the two ports were analyzed as well.Based on the concept of orthogonal virtual circuit,the control model of single-phase AC port was established,and the power constraints of MVAC_((S-P))and MVAC_((T-P))ports were deduced.Finally,a set of laboratory prototype was built to verify the effectiveness and superiority of the proposed converter.