State flow approach for multiple power sources management

Transcription

1 State flow approach for multiple power sources management A. Naamane 1, A. Kaiss 2 1 LSIS/UMR 7296, Aix-Marseille Université, Avenue Escadrille Normandie-Niemen, Marseille, France. 2 IUSTI/UMR CNRS 7343, Aix-Marseille Université, 5 rue Enrico Fermi, Marseille, France. aziz.naamane@lsis.org Abstract The renewable energy sources are, and will be more and more, brought to function on the same site. However, they have not yet the subject of a real overall energy management strategy. As several systems rely on multiple energy sources, power distribution strategy must be implemented by matching the supply and the demand. The balance between production and consumption must be carefully conducted to ensure the availability of power. This paper advocates the use of the state flow approach as an alternative mean to manage the multi power source distribution for multiple supply systems by a load matching switch. Keywords: power management, solar, wind energies, stateflow, energy storage 1. Introduction Solar and wind energy systems are being considered as promising power generating sources due to their availability and topological advantages for local power generations in remote areas. Utilization of solar and wind energy has become increasingly significant, attractive and cost-effective, since the oil crises of early 1970s.However, a drawback, common to solar and wind options, is their unpredictable nature and dependence on weather and climatic changes, and the variations of solar and wind energy may not match with the time distribution of load demand. This short coming not only affects the system s energy performance, but also results in batteries being discarded too early. Generally, the independent use of both energy resources may result in considerable over-sizing, which in turn makes the design costly. It is prudent that neither a stand-alone solar energy system nor a wind energy system can provide a continuous power supply due to seasonal and periodical variations [1] for stand-alone systems. Fortunately, the problems caused by the variable nature of these resources can be partially or wholly overcome by integrating these two or more energy resources in a proper combination, using the strengths of one source to overcome the weakness of the other. The use of different energy sources allows improving the system efficiency and reliability of the energy supply and reduces the energy storage requirements compared to systems comprising only one single renewable energy source. Of course, with increased complexity in comparison with single energy systems, the optimum design of a hybrid system becomes complicated through uncertain renewable energy

2 supplies and load demand, non-linear characteristics of the components, high number of variables and parameters that have to be considered for the optimum design, and the fact that the optimum configuration and optimum control strategy of the system are interdependent. This complexity makes the hybrid systems more difficult to be designed and analyzed. This paper addresses decentralized control strategies of multi-sources and multi-users energy systems. The objective is to describe, by using the stateflow approach, a decentralized multi-sources, multi-users energy system. 2. Multi- energy sources structure To illustrate the possibility to propose a power distribution switch that maximizes the total available power from the different power sources, the example of a multi-energy system of figure 1 is taken. This hybrid system contains three energy sources: solar, wind and a battery. It is obvious that other energies sources could be added with the same principle. Bus AC To grid Wind turbine Generator Inverter AC PV modules / Converter Batteries / Converter Figure 1: Configuration of multi-sources hybrid energy systems. The amount of energy produced depends mainly on weather conditions, hence the importance of maximizing the amount of energy produced. The main difficulty of such a distributed management of the energy problem is to use the most possible appropriate way all the possible sources of production in relation to all identified needs. For this, it should switch on an ad hoc manner some sources to some users, depending on the state's energy system at time t and on the forecasts of its operation in the near future. HRsource1 HRsource2 HRsource3 Hrsource HRsourcek Switch HRUser1 HRUser2 HRUser HRUsern HRsBattery HRUCharger Figure 2: Switching of multi-sources and multi-users energy system. The switch is then a connection function between users and power sources. The various connection configurations constitute solutions of such a multi-sources and multi-users energy system. Thus the control of an energy system consists in choosing among these connection configurations that will be the most appropriate at a given time allowing an optimum use of the majority of the produced energy. 3. Stateflow chart approach

3 A Stateflow chart is an example of a finite state machine. A finite state machine is a representation of an event-driven (reactive) system. In an event-driven system, the system makes a transition from one state (mode) to another, if the condition defining the change is true.so Staeflow is based on finite State Machines concept that has been developed (Moore, Mealy) to account for the operation of discrete event system. In these systems the passage from one State to another is governed by discrete events. Figure 3.State transition diagram The example of the management of energy derived from several sources is represented by the Simulink model represented by figure 3. the Simulink model takes into account with stateflow, various modes of operation of the system associated with the changes of energy productions related to weather changes. There is in effect the presence of a block State logic, built with stateflow, issuing several signals switch intended precisely to modify the State of the switch. With stateflow, simulink can now simulate the operation of complex hybrid systems involving the continuous and the discrete event aspects. This allows to simulate continuous systems operating on several different modes which the chain is managed by stateflow. Description of the used variables in stateflow chart: The system s inputs : P: Consumer Power Demand PPv: Power provided by the photovoltaic panels PEol: Power provided by the windturbine PB: Power supplied by the battery The system s outputs PV: switch On / Off - PV Wind: relay On / Off - windturbine Drums: relay On / Off - battery Local variables: Test: the M function introduced in the chart i: the resulttest function The obvious conditions used are presented in the following table:

4 Table 1: strategy Conditions The machine that it has designed presented in figure 4.1 is composed of an initial state and of seven States of actions. These States are enabled if the condition of the junction is validated and the actions will be performed later. States are bounded between them at the beginning and at the end by connecting junctions that allow splitting a transition in several transitions and introduce points of decisions. Figure 4 control Conditions diagram 4. Simulation results and interpretation

5 Figure 4 : simulation results According to this last figure, the general state of the switch is well defined, and the power source that supplies the desired power is well defined too. 5. Conclusion The optimum design of a multiple power source supply system becomes complicated through uncertain renewable energy supplies and load demand. The optimum configuration

6 and optimum control strategy of systems supplied by multiple power sources need to dispatch the power by matching the supply and demand in accordance with the power management tasks. Accurate load matching is especially critical for renewable energy sources such as photovoltaic panel and wind aero turbines, because it impacts on the available power utility. Energy management is nowadays a subject of great importance and complexity. It consists in choosing among a set of sources able to produce energy that will give energy to a set of loads by minimising losses and costs. The sources and loads are heterogeneous, distributed and the reaction of the system, the choice of sources, must be done in real-time to avoid power outage For efficient management of hybrid renewable and classical energy systems, stateflow approach has been presented in this paper, it can be advantageously used to tackle the power management issues with the possibility to match the production and the demand. The future developments of this study will focus on practical tests. First, a dspace card will be used to validate the principle in an experimental way. This work could be extended to develop an architecture proposal for an intelligent and autonomous demandresponse energy management system, based on a fully interactive ICT infrastructure that meets specific requirements, the main purpose of which, by the cooperation between a house and the grid, is to help the end user to achieve energy savings References [1] B.B.F. Wittneben, The impact of the Fukushima nuclear accident on European energy policy, Environmental Science & Policy, vol. 15, no. 1, pp. 1-3, [2] Lagorse, J.; Simoes, M.G.; Miraoui, A.; A Multiagent Fuzzy-Logic-Based Energy Management of Hybrid Systems Industry Applications, IEEE Transactions on Issue 6, pp , 2009 [3] G Dawei, J Zhenhua, and L Qingchun. Energy management strategy based on fuzzy logic for a fuel cell hybrid bus. Journal of Power Sources, 1(185), [4] C Abbey and G Joos. Energy management strategies for optimization of energy storage in wind power hybrid system. In PESC record IEEE annual power electronics specialists conference, [5] S Abras, S Ploix, S Pesty, and M Jacomino. A multi- agent design for a home automation system dedicated to power management. In Christos Boukis, Aristodemos Pnevmatikakis, and Lazaros Polymenakos, [6] R. Frik and P. Favre-Perrod,.Proposal for a multifunctional energy bus and its interlink with generation and consumption,. Diploma thesis, High Voltage Laboratory, Swiss Federal Institute of Technology (ETH) Zurich, [7] B. Kl ockl and P. Favre-Perrod,.On the in_uence of demanded power upon the performance of energy storage devices,. in Proc. of the 11 th International Power Electronics and Motion Control Conference (EPEPEMC), Riga, Latvia, 2004 [8] M. Manfren, P. Caputo, G. Costa, Paradigm shift in urban energy systems through distributed generation: Methods and models, Applied Energy, vol. 88, no. 4, pp , [9] MANWELL J.F. Hybrid energy systems. In: CLEVELAND C.J. (ed.) Encyclopedia of Energy, Volume 3. London: Elsevier, 2004, pp [10] CLARKE J.A. Energy simulation in building design. 2nd Ed. Oxford : Butterworth Heinemann, 2001, 362 pp. ISBN [11] SONTAG R., LANGE A. Cost effectiveness of decentralized energy supply systems taking solar and wind utilization plants into account. Renewable Energy, 2003, vol. 28, n 12, pp ISSN

7 [12] Fouzia. OUNNAR, Aziz NAAMANE - Patrick PUJO - Kouider nacer M'SIRDI "Pilotage multicritère d'un système énergétique multi-sources et multi-utilisateurs», 1er Congrès International en Génie Industriel et Management des Systèmes, Fès (Maroc), 04 fev 2012 to 18 avr 2012