A Review of Architectures and Concepts for Intelligence in Future Electric Energy Systems <s> IV. ESS INTEGRATION <s> This paper presents the analysis, design, and experimentation results of a photovoltaic energy management system with battery backup. The proposed system is capable of both grid-connected and islanded operations. The main advantage of the proposed system is that, in grid-connected mode, the inverter works as a current source in phase with the grid voltage, injecting power to the grid and controlling the dc-link voltage. The dc/dc converter manages the battery charge. In islanded mode, the inverter control is reconfigured to work as a voltage source using droop schemes. The dc/dc converter controls the dc-link voltage to enable the maximum power point tracking reference to be followed. An operation protocol is proposed to ensure the quality of the energy supply and minimize energy loss. A battery bank is connected to the dc link as energy storage for islanded operation mode. The aim of this paper is to show that the proposed system performs correctly, without dangerous transients for the inverter or the loads. Simulation and experimental results on a 3-kW prototype show the feasibility of the proposed control strategy. <s> BIB001 </s> A Review of Architectures and Concepts for Intelligence in Future Electric Energy Systems <s> IV. ESS INTEGRATION <s> In this paper, a coordinated voltage control scheme utilizing electrical energy storage (EES) is presented, for future distribution networks with large, clustered distributions of low carbon technologies (LCTs) in terms of both feeder and phase location. The benefits of the EES integrated scheme over conventional voltage control schemes are demonstrated by realizing a set of network scenarios on a case study network both in simulation and in network in the loop (NIL) emulation at a smart grid laboratory facility. The case study uses a rigorously validated model of an actual GB distribution network with multiple EES installations. It was found that the EES integrated voltage control scheme is able to provide increased capability over conventional voltage control schemes and increase the value of EES to network operation. <s> BIB002 </s> A Review of Architectures and Concepts for Intelligence in Future Electric Energy Systems <s> IV. ESS INTEGRATION <s> Increasing penetration of photovoltaic (PV), as well as increasing peak load demand, has resulted in poor voltage profile for some residential distribution networks. This paper proposes coordinated use of PV and battery energy storage (BES) to address voltage rise and/or dip problems. The reactive capability of PV inverter combined with droop-based BES system is evaluated for rural and urban scenarios (having different \mbi R/X ratios). Results show that reactive compensation from PV inverters alone is sufficient to maintain acceptable voltage profile in an urban scenario (low-resistance feeder), whereas coordinated PV and BES support is required for the rural scenario (high-resistance feeder). Constant, as well as variable, droop-based BES schemes are analyzed. The required BES sizing and associated cost to maintain the acceptable voltage profile under both schemes are presented. Uncertainties in PV generation and load are considered, with probabilistic estimation of PV generation and randomness in load modeled to characterize the effective utilization of BES. Actual PV generation data and distribution system network data are used to verify the efficacy of the proposed method. <s> BIB003 </s> A Review of Architectures and Concepts for Intelligence in Future Electric Energy Systems <s> IV. ESS INTEGRATION <s> Local PV storage systems are emerging in Germany as PV feed-in tariffs have dropped below electricity prices for households. These PV storage systems provide the opportunity to increase the local consumption of locally generated PV energy. The so called self-consumption does not imply an explicit benefit for highly PV penetrated distribution grids suffering PV related voltage rises. Hence, this paper introduces several local voltage control strate-gies using PV storage systems. These strategies focus on adding a voltage control capability to self-consumption strategies through a combination of voltage dependent battery charging, automatic reactive power provision as well as PV power curtailment. Their potential to smooth the grid integration of PV while increasing self-consumption is assessed through grid simulations and an economic evaluation. In conclusion, PV storage systems which are capable of voltage control can improve PV grid integration and provide a benefit to storage system owners. <s> BIB004
The increasing share of intermittent and distributed generation units into the power system is the main driver for the integration of stationary storage systems into the power system. Future demand for storage will include both long-term largescale storage such as hydrogen or natural gas and small-scale short-term storage systems such as batteries or flywheels within the distribution system [56] , [57] . The number of possible applications for grid-connected stationary storage is large. Depending on the methodology and the granularity of the segmentation between 9 and 16, distinguished services are reported in the literature [57] -  . Requirements to controls and ICT strongly depend on the necessary service or combination of services and the storage technology in use. A common picture showing the state of the art for all services and control architectures is hence not possible. This review focuses on the implementation and operation of ESS providing services for power quality. The most important service discussed is voltage control to maintain power quality and to allow for a higher hosting capacity of renewable sources  - BIB001 . Fig. 3 shows a simulation study of an ESS providing voltage control for a local PV generator  . It absorbs all active power above a defined threshold (e.g., 1.02 per unit) to avoid intolerable voltage levels. When they fall below the defined threshold, the ESS starts the discharging. The storage system is not the only component participating in voltage control schemes. Often, such functions are provided by DER-based inverter systems and/or OLTC BIB002 , BIB003 . In a number of cases, the analyzed storage systems also provide additional services such as local consumption of DER BIB004 . For the case of voltage control, different architectures, ranging from autonomous control with and without remote configuration ability to central control, are analyzed.