Unit Power Factor Converter to Charge Embarked Supercapacitors

Transcription

1 Unit Power Factor onverter to harge Ebarked Supercapacitors M. Becherif,, M. Y. Ayad, A. Henni 3, A. Aboubou 4, M. Wack SeT aboratory, UTBM University Rue Thierry Mieg 9000 Belfort (cedex), France F-ab fuel ell aboratory Rue Thierry Mieg 9000 Belfort (cedex), France 3 Alsto Power Syste, Energy Manageent Business, Alsto France 4 MSE aboratory, Biskra University, 07000, Algeria phone: :+33 (0) , fax: +33 (0) , e-ail: Mohaed.becherif@utb.fr Abstract The use of supercapacitors (Ss) in ebedded syste is quite suitable because of their appropriate characteristics in ter of high power capacitance, low serial resistance and their response tie. The supercapacitor is a regular capacitor but with the exception that it offers very high capacitance in a sall package. Rather than a battery, the supercapacitor energy storage is by eans of static charge not by an electro-cheical process. There are three types of electrode aterials suitable for the supercapacitor. They are: high surface area activated carbons, etal oxide and conducting polyers. The high surface electrode aterial, also called Double ayer apacitor. It stores the energy in the double layer fored near the carbon electrode surface. The electrolyte ay be aqueous or organic. The aqueous variety offers low internal resistance but liits the voltage to one volt. In contrast, the organic electrolyte allows.5 volts of charge, but the internal resistance is higher. To operate at higher voltages, supercapacitors are connected in series. On a string of ore than three capacitors, voltage balancing is required to prevent any cell fro reaching over-voltage. This paper deals with the conception of an ebarked power source using supercapacitors which are charged by eans of Unit Power Factor (UPF) electronic converter. These supercapacitors ensure the power supply of an electrical network iniature rail of 50W. The operating principle of this device and soe siulation results obtained under Saber software are presented. I. INTRODUTION Until now, the ost used direct storage eleent in electric power supply applications are undoubtedly the accuulators which allow an acceptable autonoy. Their ain disadvantage is their low power density. However, the capacitors have high power capability but they can only be considered for applications which require little energy. So, there was thus a relatively lack in ters of storage devices for high power and high energy applications. With their energetic features situated between those of the batteries and capacitors, the Ss are certainly one of the ost suitable electrical engineering coponents able to fill the deficit of electrical energy storage [],[]. Therefore, these new coponents for an interesting energy storing device filling the gap between the electrolytic capacitors and conventional batteries. So, Ss offer large perspectives for a best anageent of the ebarked electrical energy by the ean of hybridizing different power sources. In such hybrid power source, Ss are used as an auxiliary power unit (APU) added to a ain classical source. In this way the resulted power device will be characterized by the association of advantages of two electrical energy features that is to say a high specific energy cobined to a high specific power available in a quite long period of tie (about soe tens to a hundred of seconds). We notice that this association is ade possible thanks to power electronic converters [3],[4]. Moreover, this type of power eleents cobination allows dissociating the ean power sizing fro the peak transient power sizing in order to optiize the volue and weight of whole the ebarked power syste. In the reference [5] the authors study the association of a photovoltaic generator to Ss in order to ensure the electric train feeding. Two packs of Ss have been used: the first one (SPack) is outside of the train and it is charged fro a second pack (SPack) under a high current (fast charging). SPack is located at the train station where it is charged with a low current (slow charging) fro a photovoltaic generator. In this way the train is periodically supplied by an Energy Transferring Mode (ETM: fro Pack to Pack). In this paper we are interesting to add a new low charging ode for the second Ss pack (SPack) starting fro the A network. Indeed this charger is justified by the fact that the sun is an uncertain energy source. So, when the sky is overcast it is necessary to use another power source that is to say the A network in order to win a high reliability of the train feeding. We notice that the ebarked power supply is constituted with a D-bus on which the only used power sources (SPack) and electrical loads are connected by eans of power converters. In each train station the Ss are charged through a D-D converter connected to a D link ensured by the doestic one phase s sinusoidal electrical network by eans of diodes rectifier and a boost. This double stage converter offers the possibility to charge the Ss in UPF ode.

2 This UPF charger is especially considered here in the point of view of its sizing process and its control strategy. So, after exposing the proposed power converter and explaining the use control ethod, soe siulations and experiental results are given and copared in a testing and validating process. II. UPF HARGER TOPOOOGY AND SIZING The load is a iniature train on the scale /4th fed by eans of Ss (SPack) which are supplied by the necessary energy at the stopping stations fro (SPack). The charging of Ss on the quay (SPack) is carried out double stage A-D and D-D conversion. The A-D converter is based on using controlled rectifier with UPF allowing to absorb a sinusoidal current in phase with the voltage and thus to liit the haronics creation in the network, see Fig.. The first converter is an A-D one cobining a diodes double-bridge rectifier and a boost converter. It realises a conversion with sinusoidal absorption and supplies power to the D voltage stage consisting of the capacitor. The control technique of this chopper iposes an inductive current having the shape of a rectified sinusoid. Taking into account the voltage variation fro the rectifier (fro to the axiu value of the network voltage), the chopper ust necessarily be a boost one. The second D-D converter is a siple buck converter; it allows controlling the electrical current charging the Ss. I U PF D U h S siultaneously on the continuous part of the rectifier. However, it ust be noticed that the A-D conversion only through the diode double-bridge inverter has a very powerfactor (about 0.6), because of the network current has an ipulse for rich in odd haronics. These ipulses quasi centred copared to the sinusoid contribute to defor the sinusoidal wavefor of the network voltage by creating a voltage decreases through its internal ipedance. TABEAU Electrical specifications of the UPF charger Maxiu Power P ax 50 W Network voltage V n 30 V / 50 Hz Ss voltage V S 5...0V Average voltage <U red > 0.8V The voltage factor for F. The rate voltage undulation V 48%. The proposed solution for this proble is to replace a traditional converter A-D by a controlled rectifier with UPF consuing a sinusoidal current in phase with the voltage. III. EXPERIMETA BENH For the experiental bench (on Fig. 3), we have chosen the SKM 4 A power MOSFET odule with SKHI A/B driver. For the rectifier, we will use the GBP-35A diode odule. By using these eleents, we find the efficiency of the syste is equal to 83% (7% of losses including coutation and conduction MOSFET losses, coutation and conduction MOSFET losses, and inductance losses). INDUT - V D D V S APAIT Fig.. UPF charger topology DRIVER After charging the Ss, the power is provided fro these storage eleents to the load by using a boost converter (Fig. ). DRIVER S D 3 NETWORK AND RETIFIER V S U Dis V D I load Fig. 3. Realised syste Fig.. Discharging Ss to the load In order to size the above converter we started fro the electrical specifications of the iniature train. So, on the base of these specifications one can deduce those of the searched A-D-D converter, see tab. In order to be able to reduce the rate of voltage undulation V D, the capacitor is placed III. STATE SPAE MODEING This section gives the dynaic odel of the syste of Fig.. It is coposed of a charging achine, a diodes-bridge converter, a Boost converter, a D Bus, a Buck converter and a Supercapacitor. The design of the wind generator as well as the storage device using supercapacitors was explained in [7].

3 The wind generator is coposed by a echanical propeller and a Peranent Magnet Synchronous Machine (PMSM) giving a rated electric power of 50W. The PMSM is driven under a variable speed (situated between 7rd/s and 78rd/s on the basis of the wind profile of Wide hen-nord Pas de alais- France). The PMSM is a single phase achine for which the equivalent electrical schee is given by the Fig. 4. i R For the Buck converter he odel is (see Fig. 5): di [ UhVD RSi V0 ] (4) dt Finally, the S is odeled by: dv dt (5) 0 i 0 + kv0 Where + kv > ω e V The syste can be odeled by a state space approach using the following state space vector: Fig 4. Single phase achine odel The achine paraeters are: R 0.4Ω ; 0. H ; p ; Φ 0.9 ax Wb The electroagnetic torque is given byte pφ f i Where φ f is the achine agnetic flux, p is the poles pair nuber and i is the stator current. According to Fig., the achine inductance can be considered in serial with the Boost inductance, and then an equivalent inductance is adopted + eq () The achine state space is di dt [ e V Ri ] () The current and voltage after the diode bridge are: i ; U V Sign( i ) d i d V S R S V 0 0 +kv 0 Fig. 5 Supercapacitor electrical odel The D bus is odeled by: dv dt D id [ U PFi Uhi ] (3) T [ x ; x ; x ; x ] [ i ; V ; i ; ] T x 3 4 D V0 (6) The control vector is: T [ U ; U ] [ U ; ] T u (7) PF Uh Note that U Uh U Dis, the subscript h indicates the charge ode and Dis the discharge one. The dynaic of the syste is: 3 4 eq [ e R x U x σ ] [ U x σ U x ] 0 [ U x R x x ] x3 + kx 4 S 3 3 With σ if i 0 else σ, + kx > IV. ONTRO STRATEGY OF THE HARGER In this section we give soe details about the control strategy of both the converter stage i.e. A-D (double bridge rectifier cobined to the boost chopper) and D-D (buck chopper) stage. A. Regulation of boost charger converter The boost regulation is of type of power-factor correction. It akes it possible to have a current in phase with the voltage in the chopper input. (8)

4 The Fig. 6 shows, the control schee of the boost converter in which the easured voltage V D is ultiplied by the ratio of the axiu current value to the axiu voltage value; the output agnitude is then copared with the easured current value of the boost converter (flowing the inductor ). The result of this hysteretic coparison is used to control the converter. This regulation perits to have a current in phase with the voltage, which reduce pollution in haronic on the network. However, by using this type of regulation, we do not choose the duty cycle, neither the chopping frequency of the converter. Hence, it should be ade sure that the converter supports the frequencies iposed by this control, and to take into account in the inductance sizing. V D I MAX V MAX I +_ I Fig. 6: ontrol of the boost converter U PF The current gain I MAX allows regulating the charging current value of the S to the reference. The voltage gain V MAX allows to be brought back to a sinusoid whose aplitude is only defined by the current gain I MAX. The effective voltage of the rectifier is equal to 7V; we obtain the value of the gain voltage V MAX equal to 0.03 V. In order to regulate the coutation frequency of the converter, we use a controlled PWM as for exaple the one resulting fro the coparison of a duty cycle with a serrated signal. B. Regulation of the Ss buck converter The Fig. 7 shows the control schee of Ss charging. First of all, the voltage value of the D stage ust be of 5±0.5V; a hysteretic regulator has been used to verify this condition. Then, the Ss are charged under a constant current (.5A) ensured also by a hysteresis regulator with A of bandwidth.. ontrol of the end of charge In order to stop the charge of the Ss when its voltage reached 0V, we added a condition on the control of the Ss voltage. The S current reference is equal to zero when the S voltage is greater than V Sax. D. Regulation of the Ss discharging The Fig. 8 chows the control schee of Ss discharging. Fro the power needed by the load and dividing by the Ss voltage, the discharging Ss reference is generated. P V S +_ U Dis Fig. 8: ontrol of the Ss discharging V. SIMUATION RESUTS The siulations have been achieved by using the Saber software. In this section we present the siulation results highlighting the different functionalities of the studied converter. We are interested in the current and voltage wavefors in the ost iportant points of the converter. The Fig. 9 proofs that the proposed converter really absorbs a sinusoidal current fro the A network. However, we see a great peak of this current in the beginning of the converter operating. This phenoenon is certainly due to considering a perfect voltage source, i.e. without internal ipedance, but also because of the capacitors filter. Hence, an inductance of 0. H has been added, between the rectifying bridge and the source, in order to decrease the current. I MIN I MAX A I MIN A if V D < V DMAX V D else I 0 I I A +_ U h V DMAX endif Fig. 9: Rectifier phase current Fig. 7: ontrol of the Ss converter with: I MIN A and I MAX 3 A. Figures 0 and present respectively the input current of the boost and its reference ( I I and I ). ref

5 Fig. shows the wavefors of the Ss current and voltage v s. One can notice the existence of hysteric bandwidth of current; by exaining its zoo, one ay clearly see that this current vary between V and 3V. In the sae tie the D link voltage V s is varying also within a voltage hysteretic bandwidth equals to V around 5V. Indeed, this value of D link voltage is the guarantee of the Ss charging until 0V. For that reason we chose to start the Ss charging only when the D stage voltage reaches 5V±0.5V. So, the final value of the duty cycle of the buck chopper is about Fro 0s to 8s, corresponds to the load of the capacitors situated between the two choppers. Fro 8s to 37s, the chopper series charges the supercondensateurs with constant current. At the end, the capacitor voltage on the D link decrease to 4.5 V. It is necessary thus to wait the end of this part, that this voltage reached 5.75 V to start to Ss charging. Fro 56s to 6s, we start to charge the Ss, but because the capacitors voltage which decreases again to 4.4 V, the set point of the charging current was not reached. Fig. 0: Inputs boost current reference and easured values The wavefors presented in the Fig. 3 correspond respectively to the S converter control the detection of the charging authorization, the Ss current, the D link voltage and the Ss voltage (redundancy with Fig. 4). Fig.3: ontrol of the S converter, charging authorization, Ss current, condition on the charging Ss voltage, Ss current, D link voltage and the Ss voltage Fig. : D link current wave for Fig.4: ontrol of the S converter, charging authorization, Ss current, condition on the charging Ss voltage, Ss current, D link voltage and the Ss voltage Fro 56s to 6s, we continue the charging of the Ss until we obtain the liiting voltage value of 0 V. VI. VAIDATION EXPERIMENTA TEST BENH Fig. :. Ss current and voltage In order to test the proposed control strategy of the syste shown in Fig., an experiental test bench has been ade. This bench is based on the studied device. The wind generator is replaced with the single phase A network through a transforer. The rest of the circuit has been build

6 according to the real characteristics described below. On Fig. 5 the different coponents of the bench are shown. For the control strategy ipleentation, the dspace real tie interface (RTI) DS04 has been used. For conditioning the easureent and the control signals between the RTI and the power sides of the syste, an electronic card has been developed. Fig. 6 (top) shows the experiental wavefors of the boost current following well its reference varying as the absolute value of a sine function. The presence of soe current delay in the tracking is caused by the delay in the data acquisition and control devices. The siulation wavefors of the figure 0 are then validated. The input A voltage tie variation and the coand signal of the boost switch are presented in Fig. 6 (botto). These results prove that the device sizing and the control strategy are satisfactory. Thus, it can be concluded that the charger is now ready to be explored in order to check the device perforances. Fig. 5: Experiental Set-up. Fig. 6: Experiental Wavefors for currents, control and voltage (V /0). VII. ONUSION In this article, a supercapacitors charger with unit factor power was presented. The design and the sizing were discussed. The control of this syste was developed to achieve an unitary power factor. The state space odelling of the whole syste is given. Soe siulation, by using SABER environent, was presented. These results give the good functioning and the experientations validate the proposed schees, sizing and control strategies. VIII. REFERENES [] F. Belhachei, S. Raël, B. Davat, "A Physical based odel of power electric double-layer supercapacitors", IEEE-IAS'00, Roe, October 000 [] B.E. onway, "Electrocheical supercapacitors Scientific fundaentals and technological applications", Kluwer Acadeic/Plenu Publishers, New York, 999. [3] A. Rufer, "A Supercapacitors-Based Energy-Storage Syste for Elevators with Soft outated Interface", IEEE transactions on industry applications, vol. 38, pp. 5-59Septeber/October 00. [4] M. Y. Ayad, S. Raël, S. Pierfederici, B. Davat Supercapacitors for ebarked systes as a storage energy device solution in Proc. ESSAP 004 (DROM 7),, BEFORT, Novebre 004. [5] M. Becherif and E. Mendes, "Stability and robustness of Disturbed-Port ontrolled Hailtonian syste with Dissipation, 6th IFA World ongress, Prague, 005. [6] M. Becherif, R. Ortega, E. Mendes and S. ee, Passivity-based control of a doubly-fed induction generator interconnected with an induction otor, 4nd onf. on Decision and ontr., pp , Maui, Hawai USA 003. [7] M. Becherif, M.Y. Ayad, A. Djerdir and A. Miraoui, Electrical train feeding by association of supercapacitors, photovoltaic and wind generators, IEEE-IEP, 007. [8] M. Becherif, M.Y. Ayad and A. Miraoui, Modelling and passivity-based control of hybrid sources: Fuel cell and supercapacitors. In 4st IEEE-IAS, USA, 006. [9] M. Y. Ayad, M. Becherif, A. Djerdir and A. Miraoui, Sliding Mode ontrol of D Bus Voltage of a Hybrid Sources using Fuel ell and Supercapacitors for Traction Syste, International Syposiu on Industrial Electronics (IEEE-ISIE 07), Spain 007. [0] A. Henni and H. Siguerdidjane, Robust nonlinear control of a agnetic suspension syste. IEEE A 003, pp: vol. [] S. Poullain, F. Heliodore, A. Henni, J.. Thoas and E. ourbon, Modelling of the dynaic characteristics of the D line for VS transission schee. Seventh International onference on A-D Power Transission, pp: