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Energy Storage in the Emerging Era of Smart Grids Part 7

Tham khảo tài liệu 'energy storage in the emerging era of smart grids part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 168 Energy storage in the Emerging Era of Smart Grids where Lk is the transformer leakage inductance plus any series inductance n is the transformer turns ratio Side B to Side A and Ũis the angular frequency. To transfer power from Side A to Side B A-to-B mode Vac A should lead Vac Band is considered as positive. In B-to-A mode Vac A should lag Vac Band is negative. This leading or lagging phase shift is simply implemented by proper timing control of converter switches. Lk is an important element which determines the maximum amou nt of transferable power with given switching frequency. Therefore apart from other practical limitations it is possible to reach a high power density converter with a low leakage transformer. In most unidirectional dc-dc converters only the input bus has voltage variations and the output voltage is usually regulated. However in many IBDC applications both de buses have voltage variations imposed by other sections of the systems. In this regard an important design parameter in an IBDC wh ich affects soft switching range and other performance characteristics isthe voltage ratio defined as Achieving soft switching over the entire operating range of a converter is always challenging. To have zvs for the switches in a bridge leg the current leaving the leg pole the center of the leg should lag the pole voltage. In other words the zero crossing of the leg output current should occur after its voltage zero crossing. It is shown that for the DAB Fig. 6 soft switching can be achieved in all switches ford 1 and over the entire control range De Doncker et al. 1991 Kheraluwala et al. 1992 . Compared to the traditional hard-switched PWM converters the phase shift converter usually has higher circulating current and thus more conduction losses. However as the switching frequency increases the loss reduction caused by soft-switching overweighs the conduction losses and thus the overall efficiency improves. Some of the advantages of this converter can be