Modeling and Analysis of a DC Electrical System and Controllers for Implementation of a Grid-Interactive Building
As the penetration of photovoltaic (PV) systems on building rooftops increases, the accumulated effect of the rooftop PV power outputs on electric network operation is no longer negligible. Energy storage resources (ESRs) have been used to smooth PV power outputs, particularly when building load becomes low. In commercial buildings, the batteries of plug-in electric vehicles (PEVs) can be regarded as distributed ESRs. This paper proposes a DC electrical system in a commercial building that
... building that enables PEVs to compensate for rooftop PV power fluctuation and participate in tracking signals for grid frequency regulation (GFR). The proposed building system and associated controllers are modeled considering steady-state and dynamic operations of the PV system and PEV batteries. Simulation case studies are conducted to demonstrate the performance of the proposed building system under various conditions, determined by such factors as the maximum voltage, minimum state-of-charge, and desired charging end-time of PEVs batteries. Energies 2017, 10, 427 4 of 21 system consists mainly of three devices: for example, an AC-DC bidirectional converter, a rooftop PV generator, and PEV batteries, which are connected to a common DC link in parallel. The proposed system structure and control scheme have been generalized such that additional PV generators, PEVs batteries, and controllable or uncontrollable building loads can be easily included. As shown in Figure 1 , the AC-DC converter acts as an interface between the AC distribution network and the DC electrical system in a building, which enables the commercial building to act as a large-scale inverter-interfaced ESR, as well as an intermediate aggregator, under the control of central or local dispatching centers. It is well known that behind-the-meter ESRs have the huge potential to provide various ancillary services (e.g., grid frequency/voltage regulation and spinning reserve provision) to AC networks. However, as the penetration of behind-the-meter ESRs continues to increase, it is expected that an ISO will encounter difficulties in simultaneously controlling a number of small-scale ESRs in buildings, which are usually distributed over a wide range of location. These may be with respect to the number of communication links required, the integration of the various communication protocols, or the real-time processing of transferred data [26, 34, 35] . As an intermediate aggregator, the proposed building system can be effectively used to mitigate the requirements of ISO's communications systems.