## 1 Introduction
### Active Distribution Network Management
#### 1.1.2 Centralized Management Schemes  
Centralized voltage control schemes are based on information about a large portion--or even totality--of the distribution network, in order to determine the control actions to be implemented. Typically, these methods control not only the substation voltage level but also other resources with voltage control capabilities, such as energy storage devices, flexible loads, and controllable DG units. Usually, the network nodes' voltages are either measured or estimated and obtained through an Advanced Metering Infrastructure (AMI) or similar. Centralized voltage control schemes may rely heavily on data and communication infrastructure, sensors and advanced control systems, but are able to ensure coordinated and optimized management of the available resources. By comparison, decentralized control schemes are simpler to implement, but the lack of coordination between devices often leads to sub-optimum solutions. A typified approach to centralized control schemes is the use of optimization techniques. In Reference [12], the authors propose an Optimal Power Flow (OPF) algorithm to perform the voltage control of the LV network, recurring to energy storage devices and flexible loads. Similar approaches to the coordination of DER can also be found in References [13; 14]. In Reference [15], the authors propose a genetic algorithm to determine the optimal operating point for several controllable resources. It was shown that the algorithm was able to keep the voltage values within the predefined limits for a set of simulated scenarios. In Reference [16], the authors propose an algorithm to determine the optimal dispatch of energy storage devices. The problem is represented by a nonlinear programming model that was formulated using an exponential voltage-dependent load model. In Reference [17], a two-level hierarchical energy management system for microgrid operation based on a robust model predictive control strategy is proposed. The objective function is formulated as the minimization of the cost of the energy drawn from the main grid, increasing self-consumption from local RES. Simulation results using data from a real urban community showed that when compared with an equivalent (non-robust) deterministic methodology (i.e., without considering uncertainty), show that the proposed solution achieved lower energy costs and obtained a more uniform grid power consumption, safer battery operation, and reduced peak loads. Centralized voltage control techniques based on optimization methods can be complex and demanding from a computational power and hardware point-of-view, requiring dedicated systems to run the algorithms, such as Advanced Distribution Management Systems (ADMS), developed specifically to support the operation of the LV network. Given the large number of LV networks, simpler alternatives are sought in order to enable efficient monitoring and control of LV distribution grids with large integration of DER. In Reference [18], a method for the coordination of multiple energy storage systems is proposed for voltage control in LV distribution networks. The performance of coordinated control is compared with non-coordinated control using both a real-time digital simulator and a Matlab model of a real UK low voltage distribution network with a high installed capacity of solar PV. The proposed coordinated control scheme is able to use the ES devices more evenly and therefore reduces the costs of battery replacement. In Reference [19] are shown the results from a demonstration trial of a hierarchical control scheme, that combines a centralized algorithm with decentralized algorithms embedded in the inverters of DER. The control algorithm was demonstrated in a real LV network and the results obtained have shown that the proposed approach was able to keep the voltage values within the predefined limits, thus enabling a larger deployment of renewable energy in the network.