D. Menniti

Harmonic and interharmonic distortion modeling in multiconverter systems

The problem of modeling multi-power converter systems in presence of harmonic and interharmonic distortion is considered. Specifically, current source rectifiers are considered as distortion sources, some supplying DC motors and the remaining supplying inverters feeding AC machines. The classical analogue, frequency domain and time domain models proposed in the literature to study harmonic distortion in a multi-power converter system are considered and, for each model, suitable extensions to include the interharmonic distortion are presented and critically analysed. The results of several experiments are reported to show the usefulness and to compare the accuracy of the different extensions considered. >

Harmonic and interharmonic distortion in current source type inverter drives

Current source inverter drives are sources of harmonic and nonharmonic distortion in supply systems. The nonharmonic components have frequencies that change with motor speed so conventional filters might not be effective in reducing their amplitude. The distortion calculation at the design stage allows preventive actions to minimise the distortion at source by varying DC link and/or AC motor parameters. The aim of the paper is to discuss the modeling of the supply side current distortion and to analyse the effects of nonideal supply conditions. The main utilizable models, both analogue and numerical, are discussed and analysed. Several laboratory and numerical experiments are reported to compare the different model characteristics and to analyse the current distortion sensitivity to the supply voltage distortion and unbalance. >

Purchase-Bidding Strategies of an Energy Coalition With Demand-Response Capabilities

The implementation of demand-response programs (DRP) has gained interest as a means to alleviate energy consumption during peak-hours. Two explanations account for the success of such programs which involve both utilities and electricity consumers, with the latter often organized into coalitions: the system operator meets its goal of reducing the load peak; simultaneously, electricity consumers achieve economic benefits when reducing consumption during peak hours. In this paper, a Monte Carlo-based algorithm has been proposed for the formulation of multiple purchase offers in the day-ahead energy market (DAEM) by coalitions in which consumers vary in their sensitivity to DRP, manifesting different responsiveness to hourly tariffs based on the hourly market clearing prices. Being able to monitor how coalition members use air-conditioning in the presence of variable hourly energy tariffs, the coordinator can then define a purchase-bidding strategy, depending on how price-sensitive the coalition is. Simulation results show that the presence of a price-sensitive demand leads not only to a subsequent reduction in energy prices during peak-hours but also leads to a decrease in their inter-hour volatility.

Energy Management System for an Energy District With Demand Response Availability

During recent years the electricity supply chain (electricity production, consumption, distribution, storage, and load management) has changed. In this context a new term appears: the prosumer, that is both a consumer and producer of energy in the same entity. In the paper, an energy management approach of several prosumers aggregated in a coalition, the energy district (ED), and coordinated through a central control entity, the coalition coordinator, is proposed. The aim of the coalition coordinator is to maximize the coalition utility also reducing in this way the reverse energy flows at the point of delivery by an appropriate demand response program. The application on an Italian residential housing area is illustrated. The numerical results demonstrate the effectiveness and attractiveness of the proposed energy management scheme.

An incremental conductance method with variable step size for MPPT: Design and implementation

In this paper the authors propose a novel method for tracking the maximum power point of a PV array. This method is derived by the well known incremental conductance method and the novelty consists in varying the duty cycle of the dc-dc switching converter used as MPPT tracker using a variable step size instead of a fixed step size. A practical way to determine the minimum and the maximum values of the variable step size is explained in detail. The laboratory results demonstrate the effectiveness of the proposed method both in terms of speed in MPP tracking and accuracy in the MPP individuation.

In the future Smart Cities: Coordination of micro Smart Grids in a Virtual Energy District

In the future Smart City, new information and communication technologies will enable a better management of the available resources. The Smart Grid infrastructure is emerging as a complex system where fine-grained monitoring and control of energy generating and/or consuming entities within the electricity network is possible. This will result to better approaches that will boost energy efficiency. To make real this vision, (open) platforms providing access to the smart meter data as well as potential management and value-added functionalities are needed. These will offer basic energy services that can be commonly used by application developers. In this context, this paper proposes a new market platform in order to coordinate the energy exchanges among several micro Smart Grids aggregated in a Virtual Energy District. Some numerical results in Matlab/Simulink environment are presented to validate the proposed platform.

Power management by grid-connected inverters using a voltage and current control strategy for Microgrid applications

This paper presents the application of a suitable control strategy for multibus microgrid applications. The control strategy, used with each distributed generation system in the microgrid is developed so as to combine the advantages of the current control and the voltage control strategies. The performance of the proposed application in terms of power management has been verified in simulation on a microgrid test.

A new method for SSSC optimal location to improve power system Available Transfer Capability

In recent years, an increased interest was devoted to the problem of flexible AC transmission system devices location. In literature, most of proposals consist in iterative analyses, exhaustively looking for the branch that maximizes or minimizes an objective, such as least transmission losses or best power transfer capability. In this paper, attention is particularly focused on the static synchronous series compensator and a method is proposed to determine the device best location that maximizes the power system available transfer capability measured as the maximum system load increase before any operating limit is reached. The proposed method always performs an exhaustive analysis although conducted by modelling the transmission network by means of the simplified DC load flow equations embedded within an opportune optimisation model. Tests carried on networks modelled also by means of the AC load flow representation have demonstrated the validity of the proposed DC load flow based method

Grid-interfacing active power filters to improve the power quality in a microgrid

This paper proposes the application of the strategy control approach used for the shunt active power filter previously proposed by the authors to the inverter interface of each single micro-sources present in a Microgrid. In particular the attention has been focused on the power quality and var supporting issues. The main advantage of the proposed strategy control approach lies on the fact that all sensitive loads connected to the Point of Common Coupling (PCC) are immunized from the power quality problems. Moreover, the proposed control approach requests only local information. The effectiveness of the proposed control strategy approach applied to a Microgrid is illustrated.

Management of storage systems in local electricity market to avoid renewable power curtailment in distribution network

The increase of small size generation systems may cause congestions, hitherto unexpected, on the distribution network. To reduce the impact of congestions, the use of storage systems is one of the main countermeasure. In the paper, a storage management strategy based on a local energy market is proposed, in order to maximize the utility of an users community in which local market takes place. The numerical results obtained and shown in the paper demonstrate the effectiveness of the proposed management strategy2.