Coupling an energy storage to a photovoltaic (PV) system not only increases the self-consumption but also solves the over-voltage issues if the cycling of the storage is properly controlled. Whatever the application the storage is used for, the primary concern of the system owner is to maximize the profits. Therefore, this paper addresses an energy management system for a PV system coupled with battery energy storage, which maximizes the daily economic benefits while curtailing the power injection to the grid in such a way that helps to mitigate over-voltage problems caused by reverse power flow. A time dependent grid feed-in limit is proposed achieve this objective. The daily operational cost that includes the energy cost and the battery degradation cost is considered as the objective function. The non-linear constrained optimization problem is solved using dynamic programming. The analyses are made to investigate the economic benefits of charging the battery from the grid. It is found that there is a possibility for these systems for participating in load-levelling if batteries are charged from the PV system. In order for that to be feasible, the peak-hour sell-back price for the energy from storage should be higher than the off-peak utility electricity price.

A distributed control method for residential battery energy storage (BES) units coupled with photovoltaic (PV) systems is presented. The objective is to utilize customer owned BES units for solving the over-voltage issues caused by high PV penetration without significantly affecting the BES owners local objectives. 24 hour ahead active power set points of the BES unit are calculated by an optimization based scheduling algorithm. The objective function is locally decided and the optimization is performed at the local level.The BES units are charged from the excess energy from the PV systems mostly during the period the grid is under risk of over-voltage. If the set points that were calculated by the optimization, turn out not to be able to maintain the voltages within the statutory limits in real time operation, the active power set points are modified. Reactive power is also utilized when active power is not sufficient. The new set points are calculated by a central controller. The performance of the proposed method is validated in a simulation study. It is shown that the residential BES units can successfully be utilized for solving over-voltage issues without significantly affecting the primary needs of the BES owners. Keywords

This paper presents the design of a control system for a grid connected residential photovoltaic (PV) system with battery energy storage (BES). The control methods for the power electronic converters are presented and the potential of utilizing BES for participating in primary frequency regulation of the grid is investigated. The charging/ discharging rate of the battery is controlled based on the frequency droop characteristic. The performance of the control system is validated in a simulation study, in which fast response and perfect tracking of the set points are observed in (i) normal operating condition and (ii) a case where the grid frequency varies. The amount of the battery's capacity that can be utilized for this purpose depends on the quantity of power generated by the PV system, as well as the load level. The study shows that sometimes the rated capacity of the battery could be fully utilized for serving the primary frequency regulation purposes.

This paper presents a centralized voltage control scheme for unbalanced low-voltage grids experiencing over voltage problems due to high PV power penetration. Voltage control is primarily achieved by remotely controlling the active power of the distributed battery energy storage systems, which are owned by the customers. Reactive power capability of the converters are utilized for voltage control when sufficient kW capacity is not available. Distribution system operator has the control over these battery energy storage systems during the hours of high PV penetration. A method for fair utilization of battery energy storage systems by considering both rated power and energy capacity of the storage units is proposed. Delays caused by communication and computations are taken into consideration in the design of the real time controller. Results from a simulation study is presented to validate effectiveness of the real-time control scheme. The results show that the control scheme can successfully maintain the voltages at critical nodes within required limits. 1 minute computational and communication delay does not adversely affect the real time controller performance under the varying load and generation conditions considered in this paper. The utilization factor (total energy circulated through each battery units normalized to their rated energy capacity) justifies the fair utilization of battery storage units for voltage support.

This paper presents, and compares the performances of four control strategies for residential battery energy storages coupled with photovoltaic (PV) energy systems. The control strategies are: 1) rule based control, 2) optimization based control without utility constraints, 3) optimization based control with utility constraints, and 4) distributed control. The first two methods only concern about fulfilling the battery owner's requirements. In the other two methods, the utility is involved in controlling the operation of the batteries into certain extent. Therefore, the batteries intentionally contribute to lower the overvoltage risks while fulfilling the customers' needs. From the simulations it is shown that a significant reduction in reactive power support required from the converters can be achieved with optimization based control with utility constraints and distributed control schemes. Distributed control scheme shows best performance in terms of reduction in reactive power requirement, reduction in line losses and decreasing voltage unbalance. All these can be realized with little impact on the battery owner's desired objectives.