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Publications

Publications by Mário Hélder Gomes

2010

Allocation of Reactive Power Support, Active Loss Balancing and Demand Interruption Ancillary Services in MicroGrids

Authors
Mário Hélder Gomes; João Tomé Saraiva

Publication
EPSR - Electric Power Systems Research, vol.80, no.10, pp.1267-1276

Abstract
MicroGrids represent a new paradigm for the operation of distribution systems and there are several advantages as well as challenges regarding their development. One of the advantages is related with the participation of MicroGrid agents in electricity markets and in the provision of ancillary services. This paper describes two optimization models to allocate three ancillary services among MicroGrid agents – reactive power/voltage control, active loss balancing and demand interruption. These models assume that MicroGrid agents participate in the day ahead market sending their bids to the MicroGrid Central Controller, MGCC, that acts as an interface with the Market Operator. Once the Market Operator returns the economic dispatch of the Microgrid agents, the MGCC checks its technical feasibility (namely voltage magnitude and branch flow limits) and activates an adjustment market to change the initial schedule and to allocate these three ancillary services. One of the models has crisp nature considering that voltage and branch flow limits are rigid while the second one admits that voltage and branch flow limits are modeled in a soft way using Fuzzy Set concepts. Finally, the paper illustrates the application of these models with a case study using a 55 node MV/LV network.

2006

An Active / Reactive Power Market Dispatch Model Including Soft Constraints

Authors
Mário Gomes; Tomé Saraiva

Publication
Proceedings of ORMMES06 - 19th Mini EURO Conference on Operational Research Models and Methods in the Energy Sector, Coimbra, Portugal

Abstract
This paper describes an active / reactive dispatch model based on bids transmitted by market agents to the Market Operator. The Market Operator economic schedule is then conveyed to the System Operator in order to evaluate its technical feasibility. If it is unfeasible, the System Operator runs a secondary market based on adjustment bids aiming at regaining feasibility while changing as little as possible the initial economic schedule. This secondary market is modeled as a non-linear optimization problem including the AC power flow equations, branch flow and nodal voltage limits as well as constraints related with the capability curve of synchronous generators. This problem is converted into a Symmetric Fuzzy Decision formulation admitting that branch flow and nodal voltage limit constraints have a soft nature. The resulting problem is solved using a Sequential Linear Programming, SLP, approach. The paper includes a case study based on the 24 bus IEEE Test System to illustrate its appl

2008

An active reactive bid-based market model using fuzzy sets

Authors
Mário Helder Gomes; Tomé Saraiva

Publication
IJEIS - International Journal on Engineering Intelligent Systems, vol.16, no.2, pp.121-131

Abstract
The restructuring of power systems has often originated the organization of power system operation planning in a set of chronological sequence of activities that are reasonably decoupled. This means that the Market Operator purely economic schedule together with bilateral contracts is conveyed to the System Operator to be validated from a technical point of view. The System Operator also has to schedule reactive power but some of its reactive power requirements may be unfeasible given the previous active power schedules and the alternator capability diagram. Apart from this aspect, active and reactive powers are coupled in determining the eventual violation of branch thermal limits and reactive power has a well-known local nature. While recognizing the coupling between active and reactive powers, the models presented in this paper admit that the Market Operator schedule may have to be altered either because there are branch limit or nodal voltage violations or because the System Operator requires a reactive output that can not be provided due to the previous active schedule. The changes on the initial schedule are determined by solving an optimization problem that uses adjustment generator or demand bids. Apart from that, we adopted a symmetric fuzzy programming approach recognizing that some constraints have a soft nature, namely the ones related with voltage and branch flow limits. To solve the resulting non-linear problem we used Sequential Linear Programmin

2009

A market based active/reactive dispatch including transformer taps and reactor and capacitor banks using Simulated Annealing

Authors
Mário Helder Gomes; Tomé Saraiva

Publication
EPSR - Electric Power Systems Research, vol.79, no.6, pp.959-972

Abstract
This paper describes the formulations and the solution algorithms developed to include uncertainties in the generation cost function and in the demand on DC OPF studies. The uncertainties are modelled by trapezoidal fuzzynumbers and the solution algorithms are based on multiparametric linear programming techniques. These models are a development of an initial formulation detailed in several publications coauthored by the second author of this paper. Now, we developed a more complete model and a more accurate solution algorithm in the sense that it is now possible to capture the widest possible range of values of the output variables reflecting both demand and generation cost uncertainties. On the other hand, when modelling simultaneously demand and generation cost uncertainties,we are representing in a more realistic way the volatility that is currently inherent to power systems. Finally, the paper includes a case study to illustrate the application of these models based on the IEEE 24 bus test system.

2006

A Model to Remarry the Active/Reactive Power Dispatches in Competitive Environment and Active/Reactive Marginal Prices Computation

Authors
Mário Gomes; Tomé Saraiva

Publication
Proceedings of IEEE-PESLA 2006 - IEEE/PES Transmission and Distribution T&D Latin America 2006, Caracas, Venezuela

Abstract
This paper describes a mathematical formulation for the active/reactive dispatch in electricity markets, including a number issues present in market models in force in several countries. Traditional market approaches are implemented con-sidering a sequence of activities namely in terms of active power dispatch and ancillary services. However, these two problems are coupled in the sense that dispatching reactive power is not independent from active power scheduling of generators. The proposed model admits that it is known the purely economic pool dispatch together with bilateral contracts and then it aims at dispatching reactive resources considering voltage and branch limit constraints and constraints reflecting the alterna-tor capability curve. As a sub-result, this formulation also out-puts nodal active and reactive marginal prices that can be useful to build tariff schemes. Finally, the paper includes a case study based on the IEEE 30 bus/41 branch system to illustrate the obtained

2006

Mercado de Ajustes e Determinação de Preços Marginais Nodais de Potência Activa e Reactiva

Authors
Mário Gomes; Tomé Saraiva

Publication
IST Forum ENERGIA - IST Forum ENERGIA, Lisboa, Portugal

Abstract
Esta comunicação descreve uma formulação matemática do problema de despacho de potência activa e reactiva em mercados de electricidade. Os modelos em utilização em diversos países adoptam um conjunto de etapas organizadas de forma sequencial no tempo envolvendo nomeadamente o despacho de potência activa e, em seguida, o despacho de serviços auxiliares. No entanto, estes dois problemas são acoplados no sentido em que, por exemplo, o despacho de potência reactiva não é independente da potência activa alocada aos geradores. O modelo proposto nesta comunicação admite assim que é conhecido o despacho puramente económico preparado pelo Operador de Mercado e realiza o despacho da potência reactiva considerando restrições de trânsito de potência nos ramos, limites do módulo da tensão e o diagrama de capacidade dos geradores. Como sub-resultado, são ainda obtidos os preços marginais nodais de potência activa e reactiva. A metodologia proposta é ilustrada com um caso de estudo baseado no sistema

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