Francesco Lamberti

A smart strategy for voltage control ancillary service in distribution networks

The expected impact of distributed generation (DG) into Smart Grid represents a great challenge of the future for power systems. In particular, the integration of DG based on renewable energy sources (RESs) in distribution networks, without compromising the integrity of the grid, requires the development of proper control techniques to allow power delivery to customers in compliance with power quality and reliability standards. This paper proposes a coordinated local control approach that allows distribution system operator (DSO) and independent power producers (IPPs) to obtain benefits offering the voltage regulation ancillary service to DSO and maximizing allowable active power production for each RES unit belonging to the same IPP. The control is based on a cooperation of data transfer between DSO and IPPs. In order to realize such cooperation, a nonlinear constrained optimization problem is formulated and solved by sequential quadratic programming (SQP) method. The validation of the proposed control technique has been conducted through several time series simulations on a real MV Italian distribution system.

Impact analysis of distributed PV and energy storage systems in unbalanced LV networks

The integration of distributed PV units in LV distribution networks with co-located energy storage systems (ESSs) allows increasing the amount of consumed local electrical energy while significantly raising the PV penetration. The installation of ESSs may in addition promote the self-consumption of energy and reduce the mismatch between the demand and the PV power generation making such power source dispatchable. A Monte Carlo simulation is performed by varying residential load profiles, sizes and locations of PV units and ESSs in order to assess the impact that a local and independent control of co-located PV units and ESSs have on the grid. Time series unbalanced power flow simulations are carried out considering different scenarios on a typical LV Italian distribution network. The results are evaluated in terms of benefits on voltage profiles pointing out a significantly reduction of voltage problems on the network at each penetration level.

Estimating the load response to voltage changes at UK primary substations

The development of Smart Grid technologies and the need to defer investments for expanding and reinforcing distribution networks have attracted new attention to aspects of Conservation Voltage Reduction (CVR). Based on the fact that the demand of certain loads can change with voltage, it is plausible to envisage the active management of voltage regulation devices in order to increase/decrease the demand during certain periods for the benefit of the distribution network (e.g., peak shaving) or the whole system (e.g., fast reserves). The extent of this voltage-driven demand response is however entirely dependent on the instantaneous load composition. In order to quantify the benefits of such a scheme, this work proposes a methodology to estimate the time-varying residential load response to primary substation voltage changes whilst complying with voltage limits at low voltage. This is applied to a small UK distribution network downstream an OLTC-enabled 33 kV/6.6 kV substation with 351 residential, 2 commercial and 1 industrial customers (total peak demand of 932 kW). The results, only considering part of the residential loads modeled with time-varying ZIP parameters, suggest that - even considering voltage constraints- there is considerable load response that can be unlocked from residential loads. However, this is highly dependent on the time of the day.

Impact assessment of energy storage and electric vehicles on smart grids

The impact of non-scheduled Renewable Energy Sources on distribution networks and the forecasted deployment of Electric Vehicles can lead up to severe power quality stress (i.e. peak demand), in the next future. In order to alleviate these problems, IPP can offer a peak shaving ancillary service to DNOs by means of Energy Storage Systems (ESSs) integration, which represents a technological promising solution. Here, we analyze the sizing of ESSs, installed at the DG connection bus, by Monte Carlo simulations and assess the solutions for a real Italian MV network taking into account several proposed indices related to the ESS cost and size.

Co-located storage systems with renewable energy sources for voltage support in distribution networks

Recently, new standards and incentives are spreading the installation of energy storage systems (ESSs) to promote, inter alia, the renewable energy sources (RES) penetration. ESSs can be used for supporting producers and distribution system operators to give more flexibility to the grid in terms of dispatching capability of RES, load shifting, peak shaving, ancillary services. This paper proposes a local voltage control method based on the capability of ESSs to exchange power with the network in order to maximize, as much as possible, the active power production avoiding the disconnection of generators when voltage limits are violated. The method is applied to a real Italian test MV network and the obtained results are encouraging.

Assessing the performances of residential ESSs control by means of a Monte Carlo analysis

The integration of energy storage systems (ESSs) co-located with distributed PV units in LV networks allows increasing self-consumption of energy and supporting DSO for grid management. In fact, ESSs may help the distribution network in reducing the mismatch between demand and PV generation making such power source dispatchable. Here, we perform a Monte Carlo analysis to assess the impact that two different control strategies have on the grid: a classical consumer strategy and a control that allows providing an ancillary service to DSO for improving voltage quality. In the last, we propose a control strategy based on the limitation of the charging/discharging periods of the ESSs in two time periods. We implement Monte Carlo simulations to assess the charge/discharge time intervals of ESSs. Unbalanced power flow simulations take into account the variation of power demand, penetration and locations of PV/ESSs for a summer day on a LV Italian network.

Centralized Scheduling Approach to Manage Smart Charging of Electric Vehicles in Smart Cities.

Electric vehicles (EVs) are emerging as the future of individual mobility systems in smart cities since they reduce greenhouse gas emissions and fossil fuel dependence. However, the deepening penetration of battery EVs forecasted for the incoming years could cause significant stress on distribution networks (DNs), as well as the need to address the growing energy demand. In order to limit the negative drawbacks associated with EVs charging demand, the paper proposes a centralized approach for the EVs smart charging, and its performance are compared with the uncontrolled charging approach. An optimization framework is formulated in order to reduce both the overall peak power demand and the EVs charging cost according to the electricity prices during the day. Finally, several Monte Carlo simulations are carried out to evaluate the benefits introduced by the proposed scheduling strategy on a real case study, in terms of charging cost for EVs’ users, satisfaction of EVs charging needs, and flattening of the load profile.

Ancillary services provided by residential ESSs in LV networks: Assessing the opportunity costs

The increasing penetration of distributed generation in LV distribution systems brings new challenges for distribution system operators (DSOs). For instance, the unpredictable generation of photovoltaic (PV) units may increase the effort of DSO in maintaining the demand/supply balance in the network. To this end, co-located energy storage systems (ESSs) can be a precious resource for improving the operation of PV units and increasing self-consumption of solar energy. On the other hand, DSO can take advantage of these assets by envisaging an ancillary service for improving voltage profiles based on the ability of ESSs to shift local demand/generation from a period to another period in time. To identify a fair remuneration for customers involved in providing the proposed ancillary service, we assess the opportunity cost of the forgone alternative: the cost of not self-consume solar energy. The proposal is tested on a typical LV Italian distribution network considering different scenarios and policies.

Long-term performance in providing voltage support by PV and storage systems in distribution networks

Many distribution utilities are facing with the challenge to integrate increasing amounts of photovoltaic (PV) systems. Battery energy storage systems (BESSs) can be used for supporting producers and distribution system operators to give more flexibility to the network in terms of dispatching capability of PV, load shifting, peak shaving, ancillary services. This paper proposes to support locally voltage profiles by means of PV with co-located BESS in order to maximize, as much as possible, the active power production reducing the exchange of reactive power. If BESSs are not able to support voltage profiles, the modulation of the PV production is taken into account. Long-term analysis is performed on a real Italian test MV network taking into account the capability curves of power-electronic PV and BESS interfaces.

Comparison of voltage control methods for incrementing active power production

Due to the increasing development of Distributed Generation (DG) based on renewable energy sources (RESs), currently voltage control represents an important issue in distribution power systems. In this paper, we propose a comparison between two voltage control methods that allow obtaining the maximum available power production from wind turbines and photovoltaic systems. Both methods suppose a wind and photovoltaic plants belonging to an Independent Power Producer (IPP) able to control each RES units. The first method is based on a coordinated local control approach that takes advantage of a mixed Distribution Network (DN) sensitivity analysis; the second one is based on a cooperation of data transfer between Distribution Systems Operator (DSO) and IPP in order to maintain voltage levels within mandatory limits. The comparison is conducted by means of a time series simulation analysis on a real MV Italian distribution system.