Super Capacitor based Battery Power Management for Hybrid Vehicles

Super Capacitor based Battery Power Management for Hybrid Vehicles

Super Capacitor based Battery Power Management for Hybrid Vehicles

Ashish Parimi

Department of Electrical and Electronics Engineering , Matrusri Engineering College,

Saidabad, Hyderabad-500059

Abstract:- This paper presents super capacitor and battery association methodology for Hybrid vehicle. This has currently lead-acid batteries with a rated voltage of 540 V, two motors each one coupled with one alternator. The alternators are feeding a DC-bus by rectifiers. The main objective is to study the management of the energy provided by two super capacitor packs. Each super capacitor module is made of 108 cells with a maximum voltage of 270V. This is carried out for studies and innovating tests for the Hybrid Vehicle applications. The multi boost and multi full bridge converter are studied to define the best power management scheme. A good power management strategy by using multi boost and the multi full bridge converter . The experimental and simulation results of the two converter are presented.

Keywords:- «Supercapacitors», «Boost converter», «Full bridge converter», «Power management»

1. INTRODUCTION

   In the last few years the pollution problems and the increase of the cost of fossil energy (oil, gas) have become planetary problems. The car manufacturers started to react to the urban pollution problems in nineties by commercializing the electric vehicle. But the battery weight and cost problems were not solved. The batteries must provide energy and peaks power during the transient states. These conditions are severe for the batteries. To decrease these severe conditions, the super capacitors and batteries

   (a) First solution (b) Second Solution Figure1: Converter topologies for ECCE Hybrid Vehicle

2. DC/DC CONVERTERS TOPOLOGIES AND MODELLING

   2.1. Multi boost and Multi full bridge converters modelling

   • Figure 2a shows the multi boost converter topology. The general model for this topology [2] is given by equation (1); where (1) and (n) define respectively the duty cycle and parallel input converter number.

     d

     associate with a good power management presenting a

     L (I sc

     ) Vsc

     V

     promising solution.

     Supercapacitors are storage devices which enable to supply

     n dt n

     n 1 bus1

     the peaks of power to hybrid vehicle during the transient states. During the steady states, batteries will provide the energy requested. This methodology enables to decrease the weight and increases the lifespan of the batteries. Hybridization using batteries and super capacitors [1] for transport applications is needed when energy and power management are requried during the transient sates and steady states. The multi boost and multi full bridge converters will be investigated because of the high power. For range problems, traction batteries used until now cannot satisfy the energy needed for future vehicles. To ensure a good power management in hybrid vehicle, the multi boost and multi full bridge converters topologies and their control are developed. Two topologies proposed for the power management in ECCE Hybrid Vehicle are

     n 1,2, , N p

     I L Vbus1 Pbus1 Pbus2 Pbusn

     d

     (I bat ) Vbat Vbus1

     dt

     I c I ba k I

     h t L

     The voltage drops in the Ln and inductances are given by equation (2).

     d

     multi boost converters control during super capacitor modules discharge. These modules being identical, the energy management between the modules and the hybrid vehicle DC-link enables to write the super capacitors

     V L

     Ln n dt

     (I )

     sc n

     current references (4).

     Isc = Isc1 + Isc2 + + Iscn

     d

     1

     V

     bus1

     V dt (Ibat )

     Iscrefn

     = (Ich Ibatref )

     N p Vscn

     1. Iscref

     = Iscref1 + Iscref2 + + Iscrefn

     Figure-2: Multi boost Converter topology, Multi full bridge converter topology

     (2)

     To simplify the super capacitors current references estimation, the multi boost converter efficiency () was fixed at 85%.

   • The multi full bridge converter [5] control strategy proposed in this paper consists to establish the full bridge converters standardized voltage [6]. The control law which result from the multi full bridge converter modeling is presented by equation(5), where (m) defines the transformer turns ratio.

   V V

   The converter average model has a nonlinear behavior because of crosses between 1control variable and Vbus1

   1

   U mod

   bat

   parameter. The Vbus1, Vsc1, Vsc2, Vscn , Ich and Vbat variables can to disturb the control, they must be measured and used in the estimate of the control law to ensure a dynamics of control [3]. The multi boost converter [4] topology control law which results from the boost converter modeling is presented by 1 duty cycle (3); where Np = max(n) is the maximum number of parallel converters.

   V =

   scn

   m Vscn

   Vsc1 + Vsc2 + + Vscn

   N

   p

   The multi boost converter control strategy is presented in Fig.3 (a). It ensures the super capacitor modules discharge with variable current. The super capacitors reference current (Iscref) is obtained starting from the power management between batteries and hybrid vehicle DC – link. This control strategy includes the super capacitors and batteries current control loops. PWM1 signal ensures the

   This standardized voltage is compared with two triangular carrier waves of amplitude Vmax = 1V with a switching frequency of 20 kHz. The inverter control strategy is presented in Fig. 3(b); where Q1, Q2, Q3 and Q4 are the control signals applied to K1, K2, K3 and K4 switches. The simulations and experimental parameters are presented in table below.

   1. Multi boost control

   Figure 3. Multi boost and Multi full bridge converters control strategy

3. DESIGN

   During the super capacitors discharge, the batteries current reference (Ibatref) is fixed at 13A so that, the super capacitors modules provide hybrid vehicle power request during the transient states. For these tests,

   the hybrid vehicle request (Ich) was fixed at 53A .

   Simulation Design Parameters

   Battery:Nickel-Metal-Hydride,(Nominal, Rated)=(1.2*30,1.5*30)V,100%charge

   Super capacitor : Capacitance:6800e-6 Active Load : 45V

   IGBT/Diode:(Internal,Snubber)=(1e-3,1e5)Ohm, Snubber Capacitance:inf

   *All the results are plotted with respect to time.

   1. Boost converters simulation and experimental results

      Figure-4. Super capacitor -module voltage results

      Figure 5. Super capacitor- modules current results

      Figure-6: DC-link Load current

      Figure 7. DC-Battery current

   2. Full bridge converters experimental results

   Wiring in power electronic design is a general problem for electrical energy system and the voltage inverters do not escape to this problem. The switch action of semiconductors causes instantaneous fluctuations of the current and any stray inductance in the commutation cell will produce high voltage variations. Semiconductors, when switching off, leads to high voltage transitions which is necessary to control within tolerable limits. The energy stored in parasitic inductances, during switching on, is generally dissipated by this semiconductor.

   Figure-8:Full bridge converter with chopping devices

   In the case of the single-phase inveter, each cell includes two switches and a decoupling capacitor placed at the cell boundaries, which presents a double role. It enables to create an instantaneous voltage source very close to the inverter. The (C) capacitor associated to an inductor enables to filter the harmonic components of the currents which are generated by the inverter. Parasitic inductances staying in the mesh include the capacitor inductance, the internal inductance of semiconductors and the electric connection inductances.

   A good choice of the components with an optimal wiring enables to minimize parasitic inductances. Using the semiconductors modules solves the connection problems between components. All these efforts can become insufficient, if residual inductances remain too high or if the inverter type is the low voltages and strong currents for which the voltage variations are much important. In both cases, the use of the chopping devices is necessary. These devices must be placed very close to the component to avoid any previous problem.

   During switching off of the semiconductors, the corresponding current stored in wiring inductances circulates in the following meshes C1, D1 ; C 2 , D2; C3, D3 and C4 , D4 which limits the voltages applied to the switches. When electrical energy is fully transferred in C1, C2, C3 and C4 capacitors, the current becomes null and the meshes become closed. The C1, C2, C3 and C4 capacitors are used only for transient energy tank and it is necessary to recycle this switching energy while controlling the voltage at the semiconductors boundary. This function is ensured by R1, R 2, R3 and R4 resistances. R 1, R2, R3 and R 4 resistances are identical and C1, C2, C3 and C4 capacitors are also identical.

   Full bridge converter simulation results for Np = 2:

   The simulation has been made for Np = 2 [7] . The maximum and minimum voltages of the super capacitor modules are respectively fixed at 270V and 135V. The hybrid vehicle requested current (Ich) is respectively fixed at 100A from 0 to 0.5s, 400A from 0.5s to 18s and 100A from 18s to

   20s. Battery reference current (I bat) is fixed at 100A independently of the hybrid vehicle power request. Super capacitor module voltage (Vsc) presented in Fig.9 (a) are identical. The currents amplitude (Isc) presented in Fig.9 (b) are also identical. Control enables to maintain the battery current (Ibat) at 100A; but around 0.5s and 18s the battery current control loop has not enough time to react . The important power of the transient states is ensured by the super capacitors module(IL) Fig. 10(b). Simulation parameters are presented in TABLE II.

   Symbol value Name

   Battery current smoothing

   25µH

   inductance

   The parameters used for experimental tests are presented in

   TABLE I and the principle of such circuits [8] is given in

   m 3 Planar transformer turns ratio 604V-

   Fig. 8.

   Symbol Value Name

   Vbus1

   432V DC-link voltage Super capacitors currents

   R1= R2=R3

   = R4 10 Chopping circuits resistances C1=C2=C3=

   C4 220µF Chopping circuits capacitors

   Battery current smoothing

   L1=L2 50µH

   smoothing inductances

   25µH

   inductance

   M 3 Planar transformer turns ratio 60V-

   Vbus1

   43V DC-link voltage Super capacitors voltage

   C 6800 µFsmoothing capacitor

   Super capacitors currents

   L1 50µH

   smoothing inductance

   TABLE I: FULL BRIDGE EXPERIMENTAL PARAMETERS

   Figure-9: (a): Super capacitor modules voltages

   , (b): Super capacitor modules currents

   Figure-10: DC-link Load current

   Figure-11: Battery current

4. CONCLUSION

In this paper, multi boost and multi full bridge converter topologies and their control strategies for batteries and super capacitors coupling in the hybrid vehicle applications were proposed. The system control is ensured by PIC18F4431 microcontroller type which includes 9 analog inputs and 8 PWM outputs.

For low voltage and high current applications such as super capacitors, the full-bridge converter seems to be less interesting because of its higher cost (many silicon and passive components), and a lower efficiency.

For reasons of simplicity and cost, the multi boost converter is the most suitable topology regarding the multi full bridge converter topology. It enables a good power management in hybrid vehicle.

ACKNOWLEDGEMENT:

We take this opportunity to acknowledge with thanks and hereby wish to express our deep sense of gratitude to (M.V.Subramanyam Asst. professor) Department of Electrical and Electronics Engineering, for his guidance, valuable suggestions and encouragement at every step in completing this project successfully.

We are thankful to express our high regards to our Head of the Department(Prof.Dr.G.Ravindranath) for encouraging us in successfully completing this project.

We thank our parents and friends who helped us in completing our project successfully.

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