An Integrated Active Power Filter–Ultracapacitor Design to Provide Intermittency Smoothing and Reactive Power Support to the Distribution Grid

Grid integration of distributed energy resources (DERs) is increasing rapidly. Furthermore, smart grid technologies are making the grid more bi-directional providing opportunities to consumers to supply power back to the grid. Energy storage technologies like battery and ultracapacitor (UCAP) can be integrated through grid-tied inverters to support variable DERs such as solar and wind. In these cases, the energy storage with active power capability can improve grid performance by providing active and reactive power support. In this paper, the concept of providing active/reactive power support and renewable intermittency smoothing to the distribution grid by UCAPs is presented. UCAPs have a higher number of charge-discharge cycles and higher terminal voltage per module when compared to batteries which make them ideal for providing grid support. The UCAP is integrated into the dc-link of the active power filter (APF) through a dc-dc converter. The dc-dc converter provides a stiff dc-link voltage which improves the performance of the grid tied-inverter. Design and control of both the dc-ac inverter and the dc-dc converter are very important in this regard and presented. The simulation model of the overall system is developed and results are compared to the results from an experimental hardware setup.