BLDC Motor Control With HESS for Solar Based E- Vehicle · an uni-directional DC-DC Buck converter...

BLDC Motor Control With HESS forSolar Based E- Vehicle

A.Saravanan1, Dr.K.Manimala 2

1M.E(pursuing),Power electronics and Drives/EEE2M.E.,PhD,Professor /EEE

1,2Dr.SivanthiAditanar College of Engineering,Tiruchendur.

August 4, 2018

Abstract

The attention onELECTRIC VEHICLES (EV) are in-creasing for having many positive special features such aslow emission of Greenhouse Gases, high efficiency, quietoperation, fine control over the conventional vehicle, etc.Chemical battery technologies are currently the dominanttechnology in the electric car industry. It is conventionallyused as the main energy storage system (ESS) in indepen-dent moving electric propulsion vehicles[1]-[3]. However,the chemical batteries have many drawbacks such as lim-ited cycle-life, limited power density as well as high cost.To improve this, combined features of both battery and su-percapacitor system called Hybrid Energy Storage System(HESS) is proposed in this paper. HESS in Electric vehiclesprovides better performances such as highly efficient Regen-erative braking, protecting the battery from deep dischargeand better acceleration characteristics. A new regenera-tivebraking system (RBS) is proposed for EVs with HESSand driven by brushless DC (BLDC) motor. The electricalenergy available while regenerative braking is stored in bat-tery supercapacitor through the same switches available ininverter[3]. By proposing a new switching algorithm, dc linkvoltage is boosted so that energy is efficiently transferred to

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International Journal of Pure and Applied MathematicsVolume 120 No. 6 2018, 11081-11095ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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supercapacitor battery (HESS) system. To provide reliableand smooth braking operation, braking force distribution isrealized through ANN (Artificial Neural Network).Keywords:Artificial Neural Network (ANN), Brushless DC(BLDC)motor, Electric Vehicle (EV), Hybrid Energy Storage Sys-tem (HESS), Regenerative Braking System (RBS), Super-capacitor(SC).

1 Introduction

Chemical batteries are mostly used in Independent moving electricvehicles. But it has some shortcomings such as high cost due tothe fabrication material availability and disposal of used materials,limited cycle life, limited power density etc[3]. To rectify the abovesaid drawbacks double layer capacitors, known as supercapacitorsare used which offers some outstanding features such as high powerdensity,long life-cycle, and wide operating temperaturerange. Al-though the supercapacitor offers better performance in most of theterms, it cannot be used as the main ESS since its energy density isrelatively low[3]. Likewise, since the technology of the supercapac-itorsis recently developed, they are not as reliable as the conven-tional batteries. So by using hybrid energy storage system (HESS)consisting of a supercapacitor, we can effectively harness the kineticenergy of the vehicle duringbraking. This Supercapacitor systemcan assist the battery pack in peak power demands while drivingup hills and high torque requirement times and also improves thevehicle acceleration and non-pulsating smooth driving of the vehi-cle. Li-ion battery is a promising technology for vehicular applica-tions due to its high specific energy and relatively higher specificpower when compared with lead acid batteries and NiMH batteries[1]-[3]. However, cycle-life of Li-ion batteries can be considerablyreduced if the battery is exposed to fast charging and discharg-ing currents in order to meet the fast changes in torque power oftraction motor. To avoid such drawbacks supercapacitor assist isused when the fast discharge of battery happens. In this scheme,an uni-directional DC-DC Buck converter is utilized to control thepower flow between the battery and supercapacitor along with anovel controller for BLDC motor. The motor is mainly driven bythe battery pack. Solar energy available from sun rays is converted

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into electric energy by a PV panel which is used to charge a sep-arate battery during the daytime when the sun shines brightly. Anew working methodology of interaction between the battery andsupercapacitor is proposed. The presented HESS is composed ofa supercapacitor, battery pack, buck converter, and diodes withbye-passed resistor arrangements. Different operation modes of theproposed HESS are discussed in detail. Moreover, for the proposedsystem, Vector control method is used to control the speed andtorque of the vehicle. While braking, using an appropriate switch-ing algorithm for the inverter, the dc-link voltage is boosted. Thebraking energy is directly harvested by the supercapacitor moduleand battery pack without employing an additional power converter.The dc-link voltage is boosted through variation of the duty-cycle ofthe pulse width modulation (PWM) in the inverter by using vectorcontrol method. Hence, when the supercapacitor is charged to itsmaximum voltage, regenerative braking can be realized by meansof the battery pack and the efficiency is improved. Moreover, anartificial neural network (ANN) is used to achieve braking force dis-tribution for realizing reliable braking of the vehicle. Meanwhile,a PI controller is used to adjust the braking current in such a waythat the braking torque is kept constant. The remaining sectionsof the paper are organized as follows. In Section II, the structureand the working principle of the proposed HESS are discussed. InSection III, analysis of the developed RBS with vehicle dynamicsequations is presented. In Section IV, the simulation and experi-mental results of proposed HESS are presented. Finally, the mainresults are concluded in Section V.

2 WORKING PRINCIPLE OF PRO-

POSED SYSTEM

In this proposed scheme, BLDC motor is considered as main propul-sion device which is controlled by Vector control method throughthe inverter circuit. Here, the acceleration values are given as in-put. Based on the acceleration input values and actual speed andtorque from the electric vehicle, an Energy management subsys-tem calculates the required torque and speed values. Here batteryis used to supply the BLDC motor. So battery management unit

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is used to measure the State of Charge of the battery (SOC) andcalculates when the battery to be charged. The reference torqueand current values calculated from the Energy management unitis given to BLDC motor controller unit, which calculates the con-trol Firing pulses to the inverter using the PI controller and Vectorcontroller.

Fig1: Structure of the Proposed system

From the Fig1.the operation of the proposed scheme is described asfollows, for normal operation battery solely responsible for the oper-ation[3]. when power requirement is more than battery power thensupercapacitor supplies the power through uni-directional buck con-verter.while braking due to the presence of diode D1, the boostedvoltage from the inverter is used to charge the supercapacitor first,then it charges the battery through diode D2[3]. The RLimiter isused to avoid unwanted charging of supercapacitor from the bat-tery. When super capacitor charging RLimiter is by-passed throughthe parallel switch.

The solar array used in this proposed system is having the ca-pacity of assisting the battery only for a small instant of time. Oth-erwise, an additional battery is used to store the PV electric powerto supply the vehicle light and other display device loads[2]. ThePIController takes the calculated reference value of torque from thecontrolunit and actual torque value from the motor sensor. Basedon the system gain values PI controller controls the error value and,it provides the desired torque values and flux values to the vectorcontrol unit[6]-[8].Here the flux values are calculated using lookuptable method in which the flux values calculated for correspondingtorque values in laboratory experiments are tabled.In Vector con-trol method, in addition to that of reference values calculated from

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PI controller, the machine variables such as Rotor angle theta andABC phase currents are taken. based on the transformation tech-nique equations used in vector control method, independent speedcontrol is performed in vector control block.1.Braking Force Distribution through ANNTo provide reliable braking operation of the vehicle, Artificial Neu-ral Network Scheme is proposed. Suppose, the vehicle is to bestopped very early from the starting i.e. the condition when thebattery and super capacitor almost have full charge on it, the elec-trical braking method becomesunreliable.So performing electricalbraking only does not provide better braking of vehicle. To avoidthese unwanted circumstances an additional conventional brakingscheme may be used even though method wastes the energy in theform of heat. So by using ANN scheme, switch over between thebraking schemes are decided by using the values of SOCs of bothbattery and super capacitor. The test values are trained by usingANN methods.

3 VEHICLE DYNAMICS ANALYSIS

OF PROPOSED RBS

Total force required to drive a vehicle is the force which overcomesthe combinational opposite forces such as Frictional forces, Aerody-namic Forces, Uphill Resistance Forces etc. According to NewtonsSecond law of motion, the vehicle acceleration can be expressed as,(1)• Traction Force• Resistance Force•Mass Factor•Total MassV •Vehicle Speed1.Frictional Force:It is the frictional force which exists between the surface of theRoad on which the vehicle is running and the Tires of the vehicle.Frictional Force, (2)Rolling resistance CoefficientpNormal Load acting on the center of the rolling wheel(N)

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Fig 2: Dynamics of a Vehicle

2.Aerodynamic Drag ForceAerodynamic Drag is a parallel acting Force and which is in thesame direction as the airflow. The drag coefficient of a vehicle in-fluence the way it passes through the surrounding air. Reducingthe drag coefficient in an automobile improves the performance ofthe vehicle as it makes easy to improve its speed and fuel efficiency

3.Uphill Resistance:When the vehicle travels through a road with spikes, and frequentup downs etc, a component of its weight works in a directionopposite to its motion. If some amount of energy is not suppliedto overcome this backward force, then the vehicle would slow downand may stall or roll backward. If the vehicle is trading uphill at aslope of , then the weight of the vehicle, W has two components:

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Fig 3: Uphill Resistance

one perpendicular to the road surface (with a value WCos ) and theother along the road surface (with a value WSin ). The componentalong the road surface is the one that tries to restrict the motion.This type of opposing force is also called as Gradient Resistance.

From Fig 5, Fd is the supplied force by the vehicle engine to drivethe car.

4.Analysis of Operation :For Analysis of the Proposed RBS (Regenerative braking system),twophases i.e. four switches operation is considered[3]. While braking,the upper leg switches are turned off and lower leg switch is kepton.From the Fig 4, By using proper control algorithm, the energyin the windings of the BLDC motor is kept freewheeling throughthe inverter switching diodes and when the inductor has sufficientenergy which has the potential greater than the battery and su-percapacitor terminal voltage, the lower leg switchof opted to beturned on. Thus by braking electrical energy can be fed back tosupercapacitor and battery.

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Fig 4: Operation of a Proposed system for Analysis

For reliable braking, ANN (Artificial Neural Network) scheme isused[2]-[3]. By using the values of (State of Charge) SOC of thebattery and supercapacitors mechanical braking or another type ofelectrical braking systems are provided to perform desired reliablebraking.5.Switching Schemes:From the Fig 5, for normal operation of the vehicle, the BLDCmotor controller driver circuit (inverter) has normal control pulsesbased on the hall sensor outputs which is based on the position ofrotor[2]-[3].Depending on the position, corresponding switches aretriggered in upper legs and lower legs of the inverter. When wehave the wish to apply braking, because of the need to store theenergy in the supercapacitor andbattery arrangements dependingupon the values of SOC of the battery as well as the supercapacitor,proper control pulses should be given to switches of the inverter.Byadopting a special switching scheme, the energy available in boththe motor stator winding and permanent magnet rotor as in theform of magnetic energy into suitable voltage electrical energy[3].The diodes connected parallel to each switch in the inverter is actsas a freewheeling diode to circulate the energy to get the properlevel of high voltage to that of battery and the supercapacitor.Pulse width modulation (PWM) is the technique which is used toachieve the boosted voltage from the same inverter itself.

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Fig 5: Switching scheme of a proposed Regenerative Brakingsystem

4 SIMULATION & EXPERIMENTAL

RESULTS

1. Simulink Model Of Mechanics Of Vehicle SubsystemHere the vehicle dynamics are modeled with front and rear tires ar-rangements with frictional elements and mechanics of vehicle com-ponents such as mass, height, length, and ground clearance param-eters. It is shown in Fig 6. Based on the values given, the vehicledynamics block calculates the required torque value for particularrequired speed. The input required from the Engine by the vehicleis the desired torque value to drive the vehicle at the desired speed.

Fig 6: Simulink Model Of Mechanics Of Vehicle Subsystem

2. Simulink Model of Energy Management Subsystem

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The ultimate aim of this block is to calculate the reference val-ues which are used to provide required torque from BLDC motor.Also, this block determines when the battery should be charged andunplug from the charging station to prevent overcharging. Thesethings are performed by using the values of battery state of charge(SOC)and S-R flip-flop logic[1]-[4]. The reference torque values arecalculated based on the feedback parameters available from the ve-hicle dynamic block. To improve the life of the battery, batterymanagement unit is used as shown in Fig 7, to monitor the batteryperformance throughout the entire operating cycle.

Fig 7: Simulink Model of Energy Management Subsystem

3. Simulink Model BLDC Drive SubsystemBased on the reference torque value calculated from the Energymanagement unit and speed controller output, the vector controlblock calculates the firing pulses to the inverter to run the motorat the desired speed with required torque. The battery power isgiven to the input of the inverter. By adjusting the firing pulses,the required values of voltage and current values are obtained[6]-[7]. The output of the block is connected to the input of the vehicledynamics. By using proper algorithm,efficient regenerative brakingalso possible in this vector control block[10].

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Fig 8: Simulink Model BLDC Drive SubsystemTable 1: Speed Vs Torque Look Up Table For Acceleration Inputs

Based on the Equations (1)-(5), For particular Mass and other pa-rameters the torque required to drive the vehicle is predicted. Forsimplification, here for Mass of 1400 Kg(approximately) and otherstandard parameters the drive torque required is assumed as 256N-m.4. The output of Electric Vehicle:The Acceleration values are given here in the form of positive andnegative numerical values in the range of 0-1. Based on the accel-eration the drive torque reference is calculated and which is usedto produce actual torque value. In this model for 0-4 seconds, 0.7value of acceleration is given. For that particular acceleration ,carspeed will be 0-36 km/hr with high increasing value of slope. Dur-ing 0-4 seconds the reference drive torque will be calculated nearly180 N-m. But the actual drive torque produced by the proposedsystem is mismatch with the reference one due to the insufficientbattery capacity. Initially, the vehicle acceleration will be high.After reaching particular speed(50 km/hr) the slope of thespeedofvehicle will be reduced which satisfies Newton’s second law of mo-tion. For normal operation, the positive power indicates the power

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flows from battery to motor. While braking the power flows frommotor to battery through an inverter which is here considered asnegative power[10]. To reduce the deviation from the reference an-dattained parameters, the future work is to be carried out.

Fig 9:Output of Electric Vehicle

5 CONCLUSION

In this paper, a new RBS based on utilization of HESS is proposedfor EV which is driven by BLDC motor. While regenerative brak-ing of energy regeneration, the kinetic energy of the vehicle(BLDC)is harvested by the supercapacitorand battery using the appropri-ate switching templates of the inverter. Hence, the need for addi-tional power electronics interfaces is eliminated. Meanwhile, ANNcontroller is utilized to control the braking force distribution be-tween rear and front wheels of the EV to ensure reliable braking.Moreover, the PI controller is used to control the duty-cycle of thePWM in the inverter to realize constant torque braking.In compar-ison with other similar types of the regenerative braking schemes,the proposed method has the superiorities of being simple and highefficient.

References

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[4] Roman Nadolski, Krzysztof Ludwinek, Jan Staszak, Marek-Jakiewicz Kielce University Of Technology, DepartmentOf Electrical Machines And Mechatronic Systems Utiliza-tion Of BLDC Motor In Electrical Vehicles”, PublishedIn PrzegldElektrotechniczny (Electrical Review), ISSN 0033-2097, R. 88 Nr 4a/2012

[5] S. Sashidhar And B. G. Fernandes Department Of Electri-cal Engineering, IIT Bombay, ”Braking Torque Due To CrossMagnetization In Unsaturated IpmBLDC Machines And ItsMitigation, Published In: IEEE Transactions On Magnetics,Vol. 53, No. 1, January 2017

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[9] Yu Xiaobo, Li Xiao Gao Yong, Sensor-Less Brushless DcMotor Control System Design For Electric VehicleElectron-ics,Communications and Control (ICECC), 2011 InternationalConference onNingbo, China.

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BLDC Motor Control With HESS for Solar Based E- Vehicle · an uni-directional DC-DC Buck converter...

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