Purpose -The purpose of this paper is to consider both sides of a back-to-back AC-DC-AC interface. Design/methodology/approach -The paper presents a mathematical analysis, simulation, laboratory test in scaled model. Findings -The two main findings comprised concept of control methods for grid AC-DC-AC converter applied in renewable energy sources with variable speed operation under distorted grid. Active filtering functionality in case of non-linear current of a parallel load. Second, a control algorithm dedicated for two-level AC-DC converter applied in industrial networks with high-order harmonics compensation working under hard conditions -balanced and unbalanced voltage dips.Research limitations/implications -The paper shows preliminary results for AC-DC-AC converter and active filter (AF) during voltage dips and for harmonics compensation. Control methods and/or topology should be improved and tested in scale and after at high-power system. Practical implications -Power quality supplied/received to/from the grid can be increased. In case of low-cost system only AF can be applied to existing non-linear receivers. Moreover, in case of full AC-DC-AC converter energy saving and production is possible. Originality/value -Presented control methods give satisfactory results. Paper presents laboratory results for grid and machine side two different power circuits during steady states and transients. Moreover, active filtering operation during voltage dips is presented.
The paper is a comprehensive laboratory comparison study of two galvanic isolated solution off-board battery chargers: (1) Si-based cost-effective case, and (2) SiC-bidirectional ready for vehicle to grid concept case. All circuits are modular, and in both cases the DC/DC converter can be replaced according to the end user requirements (the coupled transformer remains the same and is constructed based on 12xC100 cores to avoid additional choke). In the case of single active bridge, an active RCD snubber is proposed to protect against overvoltage above 1kV in the DC_2 circuit. The dual active bridge is equipped with soft-star modulation using a zero vector to reduce in-rush current in case of no-load operation, while the AC/DC grid connected converter remains bidirectional to assure the highest power quality at the point of common coupling. All tests were made with real second-used batteries, which improves environmental, economic and technical feasibility of such systems for prosumers. The total efficiency of both AC/DC/DC converters (>97% in SiC and >94% in Si versions) was investigated in the same laboratory conditions.
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