Voltage Control on LV Distribution Network: Local Regulation Strategies for DG Exploitation

Abstract

The presence of Dispersed Generation (DG) in LV distribution networks affects voltage profiles along distribution feeders, specifically over-voltages may occur at the DG Point of Common Coupling. This study focuses on a voltage control system that exploits DG units in order to mitigate overvoltage violations. The proposed approach is based on a local-corrective control strategy that modulates the reactive power injected/absorbed by the DG power plants. A chronological analysis is carried out on an annual basis to assess the performance of the control laws proposed and the sensitivity of the LV network characteristics on voltage regulation, i.e., the effectiveness of the LV reactive injections regulation model. From the results obtained by extensive numerical simulations it can be pointed out that the local-corrective regulation approach is a viable solution useful to increase the Hosting Capacity (HC) of existing networks, without the need for complex new infrastructures that entail huge investments. Finally, a novel DG coordination procedure is proposed, this approach has been designed in order to minimize the communication channel requirements, i.e., to allow coordinated voltage control without requiring complex real time apparatus and calculations (measurements, state estimation, Optimal Power Flow, etc.), considered to be impractical for LV grid applications.

Voltage Control Methodologies in Active Distribution Networks

“…Nowadays, Grid Codes already rule the direct contribution of DG units to voltage control at the PCC. In [26], with respect to the Italian scenario, authors have already investigated the possible solutions proposed by the national grid code and pointed out the achievable performances. In all the proposed control laws, a DG unit is going to contribute to the voltage control simply by evaluating the real-time voltage phase at the PCC; eventually, maximum/minimum thresholds are imposed to the control law, in order to preserve the dynamic stability.…”

“…Thus, all the methods involve two conditions: a normal operating situation, and a situation where first thresholds are violated. Among all the presented strategies in [26], the volt-var control, illustrated in Figure 3, shows better performances regarding increasing the HC and containing energy losses. Interestingly, papers [54,55] study similar Local Strategies applied in the LV grids of photovoltaic plants [54] and prosumers [55], and similar conclusions are drawn regarding the volt-var control.…”

“…Other papers study the combination of various methods with power factor control, in order to gain some advantages such as reliability, efficiency and flexibility [24,25]. Finally, in [26], the authors investigate various local voltage control strategies where the control variable (i.e., DGs power factor or reactive power output, for instance) linearly varies with the controlled/monitored quantity, such as the nodal voltage or real power output. These control laws are designed to comply with the regulatory requirements [17], and the paper identifies the achievements obtainable from all.…”

Voltage Control in Active Distribution Grids: A Review and a New Set-Up Procedure for Local Control Laws

“…In [5], [31], 4 different local control strategies have been exploited according to European technical standards, as listed in the following: LawA) control of tangent of φ according to the PCC voltage (tan φ = f (u)); LawB) control of reactive power according to the PCC voltage (q = f (u)); LawC) control of tangent of φ according to the real power injected (tan φ = f (p)); LawD) control of reactive power according to the real power injected (q = f (p)). In Fig.…”

“…The fast increasing of DG connections may affect the supply quality. In fact, voltage profile along the feeder have been influenced and over voltage at the DG's Point of Common Coupling (PCC) may occur [5], [6]. The voltage increase along the feeder leads to power flow decreasing in the HV/MV transformer which cause load compensation decreasing.…”