Ultra-sparse AC-link converters

Due to their remarkable merits, the soft-switching ac-link universal power converters have received noticeable attention during the last few years. These converters, which can appear as dc-dc, dc-ac, ac-dc, or ac-ac, are compact, reliable, and expected to offer longer life time compared to the other types of converters. However, they require more switches, which make the control process more involved. The sparse ac-link buck-boost converters were proposed to partially solve this problem. The sparse configuration reduces the number of switches from 24 to 20 in a three-phase ac-ac configuration. This paper proposes a modified configuration, which further reduces the number of switches without changing the principles of operation. This converter, which is named Ultra-Sparse ac-Link Buck-Boost converter, reduces the number of switches from 24 to 16, in a three phase ac to ac case, and from 16 to 10, in a dc to three-phase ac configuration. The proposed converter is applicable to systems with unidirectional flow of power, such as PV and wind power generation. Despite reducing the number of switches, the partial resonance time, during which no power is transferred, is as short as the original configuration. The proposed converter is expected to offer higher reliability compared to the original converter; and higher reliability and efficiency compared to the sparse configuration. Another important feature of this configuration is that it can be fabricated by IGBT modules, which are more compact and more cost-effective compared to the discrete devices. This paper presents the principles of the operation of this configuration, and compares the efficiency, the failure rate and the current rating of the switches in the ultra-sparse, sparse and original configurations. Moreover, it evaluates the performance of the proposed converter through simulation and experiment.