An Active AC Grid to DC Microgrid Interface Using a Bidirectional Bridgeless Flyback Converter
The usage of power electronics in power systems is one of the key techniques for boosting the development of microgrids. Particularly, in the case of public lighting systems, power electronics converters are applied to both the LED driving stage and the grid interfacing stage. From the point of view of the grid, the latter stage usually behaves as a high power factor (PF) load. However, recent trends in these systems imply a manifold of different storage and renewable energy microgeneration units connected to the DC bus of each street lamp. All together are usually known as lighting smartgrids. The present work aims for keeping the DC bus stable, injecting or extracting energy whereas maintaining high PF with respect to the AC grid. This idea is performed by means of a power droop control that provides the current reference to the grid-tie power converter: a bidirectional bridgeless discontinuous conduction mode (DCM) Flyback converter. This paper defines, explains and implements a power droop control as well as a novel unified switching pattern for the bidirectional DCM Flyback converter, suitable for both inverter and rectifier operating modes. Another contribution is that the proposed switching pattern enables for a smooth transition between these modes. The proposed strategy provides the pulses for every switch at the interfacing stage in the adequate sequence, thus simplifying the design and implementation of the power and control stages. The proposed switching pattern is validated through experimental results.