As the penetration level of renewable energy sources, such as photovoltaic (PV) and wind power, becomes more and more prevalent, their unpredictable and intermittent nature increases the probability of a mismatch between the produced power and the demand. The reliability, stability, and power quality of the grid degrade if proper actions to overcome these problems are not taken into account. One solution is to utilize an electrical energy storage (EES), such as a battery.

The purpose of this thesis is to provide an insightful and meaningful comparison between the different power electronic topologies utilized in PV-EES distributed generation (DG) systems. One- and double-stage schemes and ac-interfaced batteries are investigated and compared. The topologies are compared on the basis of part count, component sizing, reliability, efficiency, modularity, and control system complexity. The constraints in each approach are identified. The comparisons are conducted by analyzing the topologies and performing real-time simulations.

Based on the aforementioned analysis, it is shown that the addition of the bidirectional dc-dc converter (double-stage inverter) is necessary if the battery terminal voltage is lower than that required for the direct (single-stage) inverter connection. The same applies to the PV modules. Furthermore, the double-stage topology allows more flexibility in the dc-link voltage selection. Thus, the employed control techniques can operate the inverter in a more effective way leading to lower total harmonic distortion (THD) as well as a reduction in the hardware requirements (e.g. filter size). Also, due to the cascaded control scheme of the inverter, faster regulation of the PV voltage can be implemented in the double-stage scheme. However, the single-stage inverter is more efficient owing to the less power conversion stages involved. As demonstrated by simulations with real irradiance data, the battery can be used for intermittency mitigation to compensate the fluctuations in the PV power (power balance), thus providing constant power to the grid.