S. Raiti

Local voltage regulation in LV distribution networks with PV distributed generation

The increasing connection of distributed generation (DG) in distribution networks may affect the quality of power offered to customers. One of the most relevant issues is the possibility to have unacceptable voltage rise at the point of common coupling (PCC). This work focuses on the problem of voltage control in LV distribution networks in the presence of photovoltaic (PV) DG. The paper presents a local voltage control strategy based on PV generation curtailment as an alternative to on/off operation, typically required by distribution operators to prevent overvoltage at the PCCs by means of overvoltage protections embedded in the PV unit. To show the effect of the proposed local voltage control, a simulation tool, developed in MATLABreg Simulinkreg environment, has been implemented by means of appropriate numerical models for network components and PV generators

Integration of multiple PV units in urban power distribution systems

Abstract The amount of power and energy that can be injected into the distribution system by dispersed generation (DG) is constrained by technical issues related to electrical components rating and distribution system operation. In this context, the aim of the paper is to study the voltage profile of a LV feeder in order to assess the maximum value of the power that can be injected into multiple load points of the feeder by PV units without violating the voltage constraints. To perform this study an analytical method with integral approach is used: the distribution of generators and loads along the feeder is represented by means of continuous functions and constant current model. The main result of the proposed study is that, with reference to a set of contiguous generation units, it is possible to derive analytical relationships between the position of the point of maximum/minimum voltage on the feeder and the characteristics of the distributed generation (e.g. length of the concerned feeder portion, position of the generators and overall current injected by the generators).

Study of the impact of PV generation on voltage profile in LV distribution networks

The present paper aims at assessing the effects produced on the distribution system by dispersed generators directly connected to LV networks. In particular, the introduction of photovoltaic (PV) generation systems has been studied, since such systems are the only ones having a natural inclination to be easily integrated into high density urban LV distribution networks. In the proposed study some aspects of the quality of power supplied to the customers will be dealt with taking into consideration slow voltage variations. In this regard the effect of dispersed generation (DG) on the voltage profile of a LV distribution feeder has been examined. With reference to a different kind of load distribution along the line, analytical expressions have been derived to determine the limit value of the power that can be injected into the distribution network without causing overvoltages. These expressions have been developed under some simplifying hypothesis related both to the DG unit and to the distribution network.

Distributed generation in LV distribution networks: voltage and thermal constraints

The paper deals with the problem of assessing the amount of power that distributed generation (DG) can inject into LV distribution feeders without violating some technical constraints, such as the limitation posed by voltage constraints and lines thermal rating. The problem is studied following an analytical approach. The maximum value of the power that can be injected into the feeder by DG without violating the thermal constraints is analytically compared to the that which can be injected without violating the voltage constraints, in order to assess which of the two limitations is the most restrictive depending on the system operating conditions. The results obtained are also discussed by means of some numerical examples.

Voltage sensitivity analysis in radial MV distribution networks using constant current models

The paper presents some results of studies conducted on the development of analytical tools useful to allow real time control of voltages and power fluxes in active distribution networks in presence of distributed generation (DG) in the framework of Smart Grids implementation. The analytical tools can nevertheless be useful at the planning stage to guide some choices made by distribution planners. Specifically, a simple approach for calculating voltage sensitivity indexes with respect to active and reactive power changes at any node in a radial distribution network is investigated. The paper presents first stage results obtained by using two constant current models for loads and generators to obtain node voltages and their sensitivities. Subsequent stages of the study will perform a comparison with different models, such as the constant power one, and will assess the viability of the various approaches. Then, in this paper voltage sensitivity indexes are formulated with respect to active and reactive components of net node currents and the influence of some simplifying assumptions has been assessed. Numerical results are provided as the outcome of calculations performed on a test distribution network using MATLAB®.

Probabilistic Load Flow for Distribution Networks with Photovoltaic Generators Part 2: Application to a Case Study

Connections of distributed generators (DG) to distribution systems are increasing in number, though they may often be associated with the need of costly grid reinforcements or new control issues to maintain optimal operating conditions. Appropriate analysis tools are required to check distribution networks operating conditions in the evolving scenario. For example, load flow (LF) calculations are typically needed to assess the allowed DG penetration level for a given network in order to ensure that voltage and current limits are not exceeded. In the first part of this paper the solution of the LF problem in distribution networks with photovoltaic (PV) DG has been dealt with. Suitable models for the active power produced by PV DG units and the power absorbed by the loads have been used for representing the uncertainty for solar energy availability and loads variation. The proposed models have been incorporated in a radial distribution probabilistic load flow (PLF) program that has been developed by using Monte Carlo techniques. In this paper a practical case study is presented to show the results of the proposed method used for probabilistic predictions of power flows at the various sections of distribution feeders and voltage values at all nodes of a given network.

Integrated protection scheme to coordinate MV distribution network devices, DG interface protections and micro-grids operation

The present work deals with the research of novel technical solutions to improve service continuity in MV distribution networks in presence of dispersed generation (DG). In particular, the paper focuses on the development of new criteria to manage both network protections and DG interface protections in a coordinated way, also in view of allowing portions of MV distribution networks to operate as intentional islands, in other words as temporary autonomous micro-grids, in case of faults or anomalies in the main distribution system.

Probabilistic Load Flow for Distribution Networks with Photovoltaic Generators Part 1: Theoretical Concepts and Models

Connections of distributed generation (DG) systems to distribution systems are increasing in number, though they may often be associated with the need of costly grid reinforcements or new control issues to maintain optimal operating conditions. Appropriate analysis tools are required to check distribution networks operating conditions in the evolving scenario. Load flow (LF) calculations are typically needed to assess the allowed DG penetration level for a given network in order to ensure that voltage and current limits are not exceeded. The present paper deals with the solution of the LF problem in distribution networks with photovoltaic (PV) DG. Suitable models for the active power produced by PV DG units and the power absorbed by the loads are to be used for representing the uncertainty for solar energy availability and loads variation. The proposed models have been incorporated in a radial distribution probabilistic load flow (PLF) program that has been developed by using Monte Carlo techniques. In this paper the theoretical concepts and the software implementation are described. The developed program allows probabilistic predictions of power flows at the various sections of distribution feeders and voltage profiles at all nodes of a network. In the second part of the paper the application to a practical case study is presented to show the results of the proposed method.