1、Integration and Performance Analysis of FlywheelEnergy Storage System in an ELPH Vehicle I. INTRODUCTION Conventional Internal Combustion Engine (ICE) vehiclesbear the disadvantages of poor fuel economy andenvironmental pollution. Basis of poor fuel economy are(i) Operation of engine in lower effici
2、ency region duringmost of the time in a drive cycle and (ii) Dissipation ofvehicle kinetic energy during braking . Electricbattery operated vehicles have some advantages over the ICE driven vehicles, but their short range is a majorlacuna in their performance. The shortcomings of both ofthese can be
3、 overcome by using a Hybrid Electric Vehicle(HEV). An HEV comprises conventional propulsionsystem with an on-board Rechargeable Energy StorageSystem (RESS) to achieve better fuel economy than aconventional vehicle as well as higher range as comparedto an Electric Vehicle.HEVs prolong the charge on R
4、ESS by capturing kineticenergy via regenerative braking, and some HEVs also usethe engine to generate electricity through an electricalgenerator (M/G) to recharge the RESS. An HEVs engine is smaller and may run at variousspeeds, providing higher efficiency. Reference suggests that HEVs allow fuel ec
5、onomy and reducedemissions compared to conventional ICE vehicles by: 1. Allowing the engine to stop under vehicle stopcondition, 2. Downsizing the engine for same peak loadrequirements, as the motor will assist the engine for such higher loads, and 3. Allowing regenerative braking, not possible inco
6、nventional vehicle. In urban drive conditions, about 30% of the fuel can be saved throughregenerative braking because of the frequent stop and go conditions . Series and Parallel hybrids are the two majorconfigurations of the HEVs. Even in ParallelConfiguration of Hybrid Vehicles, there are severalp
7、ossibilities in which an arrangement between the engine,motor and transmission can be made to achieve thedesired performance from the vehicle. In general thereare two methods to couple the energy of the engine andmotor namely, (i) Speed Coupling, and (ii) TorqueCoupling.In Speed Coupling the speeds
8、of engine and motor are added in appropriate fractions to achieve the final speedof the drive, whereas in Torque Coupling the torquefrom the engine and motor are summed up in TorqueCoupler, which can be either an epicyclic gear train orsimply the rotor of the electric machine (motor). In lattercase
9、the rotor of the electric machine is integrated withthe shaft from the engine through a clutch. The parallelhybrid is considered for the present analysis because ofits significant advantages over the series hybrid, such aslower emissions, improved efficiency, simplerconfiguration and better performa
10、nce. The configurationconsidered for the analysis is Pre-transmission torquecoupled parallel hybrid drive train .There are various candidates for onboard RESS. So farlead acid batteries have dominated the industry becauseof their compactness, easy availability and low cost.However, batteries have a
11、number of disadvantages, suchas limited cycle life, maintenance and conditioning requirements, and modest power densities . Toovercome these shortcomings, research activities havefocused upon other alternatives of Energy Storage System(ESS). FESS is a prominent candidate for ESSapplications in HEVs.
12、 Flywheels in particular offer veryhigh reliability and cycle life without degradation,reduced ambient temperature concerns, and is free ofenvironmentally harmful materials .Flywheels offer many times higher energy storage per kilogram than conventional batteries, and can meet veryhigh peak power de
13、mands. Power density, which is acrucial parameter for ESS in HEVs, of an FESS is muchhigher as compared to a chemical battery. Deeper depthof discharge, broader operating temperature range adds tothe advantages of using an FESS over batteries.The FESS employed for the present analysis is anIntegrate
14、d Flywheel Energy Storage System withHomopolar Inductor Motor/Generator and High- Frequency Drive . The use of integrated design hasvarious benefits over other contemporary FESS designs.Some of these advantages are reduced system weight,lower component count, reduced material costs, lowermechanical
15、complexity, and reduced manufacturing cost. II. SYSTEM DESCRIPTION The arrangement used for analysis consists of anElectrically Peaking Hybrid Electric propulsion systemthat has a parallel configuration . Through the use of aparallel configuration the engine has been downsized ascompared to the engi
16、ne required for a similarconventional ICE vehicle. A small engine of powerapproximately equal to the average load power is used inthe model. An AC induction motor is used to supplythe excess power required by the peaking load. Theelectric machine can also absorb the excess power ofthe engine while t
17、he load power is less than thepeak value. This power, along with the regenerativebraking power, is used to charge the FESS to maintain itsState-Of-Charge (SOC) at a reasonable level.Fig. 1 shows a schematic diagram of the complete vehicleconfiguration illustrating the pre-transmission torquecoupling
18、, and the other major components of the driveThe operation of the vehicle is managed by a vehiclecontroller. It sends control signals to the motorcontroller, engine controller (throttle) and FESScontroller depending upon the control strategy and theinput signals. Basically the input signals are from
19、 the acceleration pedal and brake pedal. With the electricallypeaking principle, two control strategies for the drivehave been used . The first one is called MAXIMUMBATTERY SOC control strategy, which in particularaims at maintaining a particular range of SOC in thebattery at any instant. In this SO
20、C range, the battery ishaving maximum efficiency and thus, the bestperformance of the vehicle which is employing achemical battery, can be achieved through this strategy.Under this strategy the engine and electric motor arecontrolled so that the battery SOC is maintained at itsappropriate level for as much duration as possible. Thiscontrol strategy may be used in urban driving, in whichrepeated acceleration and deceleration is common andhigh battery SOC is absolutely important for normaldriving. This control strategy, which
