Conférence Internationale des Energies Renouvelables (CIER’14) Monastir, Tunisie - 2014
Modelling of hybrid energy conversion system: wind turbine/photovoltaic source associated with battery/ultracapacitor storage A. Djellad#1, P.O. Logerais*2, A. Omeiri#3, O. Riou*4, F. Delaleux*5, J.F. Durastanti*6 #
LEA, Université Badji Mokhtar-Annaba B.P.12, 23000 Annaba, Algérie 1
[email protected] [email protected]
3
*
CERTES, Université Paris-Est IUT de Sénart, rue Georges Charpak, 77567 Lieusaint, France 2
[email protected] 4
[email protected] 5
[email protected] 6
[email protected]
Abstract — Hybrid solar-wind energy systems put to use two renewable energy sources, which allow improvement of the efficiency and a better power reliability. In the present paper, the elements of a standalone hybrid system are studied. The system consists of a hybrid wind turbine (WT) and solar photovoltaic (PV) array power source and a hybrid battery/ultracapacitor energy storage. Each element is finely modelled in the Matlab/Simulink environment. The assumptions and physic laws are presented for each element of the system. The output voltage of the rectifier connected to the Permanent Magnet Synchronous Generator (PMSG) is obtained according to wind speed. The storage by battery/ultracapacitor of photovoltaic energy is simulated. The results are depicted and will aid in the future to size and optimize the hybrid system. Keywords— Wind turbine; photovoltaic module; ultracapacitor; battery; multibranch circuit model; simulation.
I. INTRODUCTION Hybrid solar–wind systems are interesting in remote area power generation applications due to advancements in renewable energy technologies and substantial rise in prices of petroleum products [1,2]. Solar and wind energy systems are promising power generating sources due to their availability and topological advantages for local power generations. Hybrid solar/wind energy systems put to use two renewable energy sources which allow improving the system efficiency and the power reliability. Even though they enable to reduce the energy storage requirements for standalone applications, storage with different time responses permits to overcome the intermittency [3]. Batteries are conventional devices for storing electrical energy but ultracapacitors are
complementary with their high power densities and elevated number of cycles. In the present paper, a standalone system consisting of a hybrid wind turbine (WT) and solar photovoltaic (PV) array power source combined with a hybrid battery/ultracapacitor energy storage is studied. The fine modelling of each element of the system is depicted. Individual simulation results are shown and discussed to envisage the dimensioning of the overall system. Results of the wind turbine production are shown. The storage by battery/ultracapacitor storage of photovoltaic energy is simulated with a photovoltaic source.
II. SYSTEM DESCRIPTION The wind/PV hybrid power system is presented in Fig. 1. It consists of both a wind power and photovoltaic (PV) power units, lead acid battery, ultracapacitors, inverter and controller. Wind power unit uses a variable speed fixed pitch wind turbine with folding tail vane to directly drive permanent magnet synchronous generator (PMSG). Power electronics interface employs diode bridge rectifier and DC/DC converter to achieve power conversion and regulation. PV power unit requires DC/DC converter to adjust power output. The two energy sources are connected in parallel to a common DC bus line through their individual DC/DC converter, which make two different power units achieve decoupling: PV power and wind power can supply loads power commonly or separately.
Conférence Internationale des Energies Renouvelables (CIER’14) Monastir, Tunisie - 2014
In expression (1), Cp depends aerodynamic characteristics of constant, Cp gets larger when constant, there is a value of The curve family of Cp versus where 0=0< 1< 2< 3< 4.
on and , representing the the turbine. If is kept gets less. Similarly, given making Cp maximum [8]. and is illustrated in Fig. 3
0.35 Pitch=0 deg Pitch=2 deg Pitch=4 deg Pitch=6 deg Pitch=8 deg
Power Coefficient Cp
0.3
Fig. 1 Configuration of standalone wind/PV hybrid power system.
0.25 0.2 0.15 0.1 0.05 0 0
1
2
3
4 5 6 Tip-Speed Ratio
7
III. MODELLING Fig. 3 Curve family of Cp versus
The wind turbine with PMSG is connected to uncontrolled diode rectifier (DC bus) for supplying battery and supercapacitor (see Fig. 2).
Fig. 2 Structure of wind turbine based on PMSG.
The proposed model is based on the steady-state aerodynamic power characteristics of the wind turbine. The wind turbine analyzed is a classic three-bladed horizontal-axis (main shaft) wind turbine design with the corresponding pitch controller [4,5]. The output mechanical power available from a variable speed wind turbine can be expressed in the following way [6]:
9
10
and .
In terms of wind speed, the operation range of the turbine can be divided into maximum power point tracking (MPPT) mode and nominal power mode. When the wind speed is between cut-in and nominal speeds, the turbine will operate in MPPT mode requiring the power conversion coefficient to be the maximum Cpmax. As illustrated in Fig. 3 the pitch angle and the tip-speed ratio should be 0 and opt respectively [9]. The optimal rotor speed at different wind speeds can be calculated by:
When the wind speed exceeds nominal speed, the turbine will operate in nominal power mode. In this case, the pitch angle is regulated to control the wind power captured by the turbine. Fig. 4 presents the characteristic of the wind speed V . Between V1 and V8, it operates in nominal power mode, where V1
