Proc. of the IEEE International Conference on Smart Instrumentation, Measurement and Applications (ICSIMA) 26-27 November 2013, Kuala Lumpur, Malaysia
Electric Vehicle Energy Management System using National Instruments’ CompactRIO and LabVIEW °
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Syaifuddin Mohd∇1, Saiful A. Zulkifli 2, Redhata G. A Rangkuti*3, Mark Ovinis∇4 and Nordin Saad ∇ Mechanical Engineering Department, ° Electrical and Electronics Engineering Department, Universiti Teknologi PETRONAS, Bandar Sri Iskandar, Malaysia.
[email protected];
[email protected];
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[email protected] *
Project Department, PETRONAS Carigali Muriah Ltd., Jakarta, Indonesia. 3
[email protected] limited energy storage density of today’s batteries, full-electric vehicles have yet to achieve the same driving range as the ICEV. An energy management system is therefore required to achieve efficient usage of this limited energy storage. In a project to convert a conventional vehicle to an EV for the PROTON Green Mobility Challenge (PGMC) 2012 competition, the propulsion system is converted to an electric propulsion system consisting of a 3-phase AC induction motor, a motor controller and an energy storage device – a LiFePO4 rechargeable battery pack. To achieve optimum performance of the propulsion system, three areas are investigated in this project: • Improvement of motor drive system • Efficiency of electric propulsion system • Power control strategy for different driving objectives
Abstract—This paper describes development of an electric propulsion system, energy management system (EMS) and battery management system (BMS) to convert a conventional internal-combustion-engine vehicle to a full electric vehicle. An EMS is designed, built and tested with the objective of optimizing electric power consumption of the converted electric vehicle and extend its driving range. The ‘driver-assist’ system monitors vehicle performance via an on-board data acquisition system. It tracks, among others, vehicle speed, motor speed, power consumption, battery and motor temperature and battery state of charge (SOC) and gives feedback in terms of suggested actions for the driver. The EMS is implemented on National Instruments’ CompactRIO embedded controller, programmed on LabVIEW Real-Time software. The paper also describes development of a graphical driver interface (GDI), based on the web server function of the CompactRIO, implemented via TCP-IP connection with a tablet PC. The GDI not only offers the driver control of the EMS and in-vehicle data logging, but also remote monitoring and control of the EMS via a wireless 3G internet connection.
II. ELECTRIC VEHICLE OVERVIEW Electric vehicles are propelled by an electric motor powered by a motor drive, controller and battery pack. Electric motors have numerous benefits compared to internal combustion engines, including: • Electric motors convert up to 85% of the chemical energy of batteries to power the wheels. • EVs release zero pollutants. Even though the power plant generating electrical energy may be using fossil fuels and still produce emissions, the emissions source is removed from the streets to a centralized location where emission can be more effectively controlled. • Electrical energy can be produced from truly zeroemission and renewable energy sources such as hydro, solar and wind. • Electric motors offer smoother and quieter operation and require less maintenance. • Possibility of obtaining electrical energy from renewable energy sources reduces dependency on fossil fuels.
Keywords- Electric Vehicle Propulsion; Energy Management System; Real-Time Embedded System; Battery Management System; In-Vehicle Data Logging; Graphical Driver Interface
I. INTRODUCTION In the past several decades, internal combustion engine vehicles (ICEV) have experienced continuous improvement in fuel performance, vehicle control and safety measures. However, efficiency of the internal combustion engine (ICE) remains relatively low - at best, only about 30% of the energy generated during combustion is converted to mechanical power, while the significant portion is wasted to the environment as heat. Electric motors are more efficient than the ICE. With zero exhaust emission, electric motor-powered vehicles help reduce serious air pollution problems attributed to ICEV [1]. Electric vehicles (EV) have many advantages over the ICEV; apart from zero emissions and higher efficiency, an EV has noiseless and smoother operation, and is independent of fossil fuels for its immediate on-board energy source. Full electric, hybridelectric and fuel-cell vehicles are clear alternatives to conventional ICEVs for years to come. However, due to the
However, electric vehicles suffer the following drawbacks associated with the on-board energy storage (batteries) [2]: • EVs have shorter driving range: about 160-300 km per full battery charge, while petrol vehicles can sometimes go farther than 400 km before re-fuel. • Re-charge time: battery packs need four to eight hour to be fully re-charged. Even fast charging to 80% of its capacity needs around 30 minutes.
This project is partly funded by PROTON Holdings Berhad, for the competition PROTON Green Mobility Challenge (PGMC), October 2012.
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The complete motor drive system s includes a Curtis motor controller 1238R, a main contactor, a key switch relay and a Molex Mini 840 dashboard dispplay. Specifications of the Curtis AC50 induction motor are sum mmarized in Table I [3]. Graphs of motor torque, battery voltage, horsepower and RMS current vs. speed are shown in Fig. 3 [33].
• The battery pack consisting of many individual battery units need to be replaced after several years and this can be very costly. • Significant vehicle space is needed to install the battery pack, which is also very heavy. III. ELECTRIC MOTOR AND MOTOR CONTROLLER
B. Motor Controller Motor controller model Currtis 1238R is used to control the AC50 induction motor. It provides p flexibility and power through inclusion of a fieldd-programmable logic control, embedded in a state-of-the-art motor m controller [5]. The embedded logic controlller runs a fully functional fieldoriented AC motor control opeerating system (OS) that can be user-tailored via parameter moddification. The OS also contains logic to execute OEM-developped software, called VCL, which can be used to enhance conntroller capabilities beyond the basics. The VCL (Vehicle Conntrol Language) is an innovative programming language develooped by Curtis. Several electric vehicle tasks are distinctively built into the VCL code [5].
A. Electric Motor Options for EV m as illustrated There are several options for the electric motor, in Fig. 1. A squirrel cage motor is an asyncchronous induction motor widely used in various applications due to its relatively low price, high strength and good dynamic peerformance, which makes it a good option for EV propulssion. A switched reluctance (SR) motor has low manufacturinng price but it has high torque variations and noisier operation. Permanent-magnet brushless DC motors (BLDC) ( have been in broad use with EVs due to its high pow wer density, lower weight, compact size and simplified hardwaare. BLDC motors are implemented in Toyota Prius and Hondaa Civic. However, the rare-earth materials used for the permannent magnets are a significant environment concern [1]. Hybrid-field excited permanent magnet motor m offers better performance, as its field can be strengtheneed and weakened, but it has higher manufacturing price and com mplexity of control is increased. In this project, an AC inductioon motor has been provided by the competition organizer, whicch is manufactured by Curtis. The exact motor model is Curttis AC50 (Fig. 2), widely used in electric vehicle applicatioons [3]. An AC induction motor is a commutator-less mootor that offers a number of benefits over conventional DC motor drive: low weight, small dimensions, low price, and highh efficiency [4].
TABLE I. CURTIS AC50 INDU UCTION MOTOR SPECIFICATIONS Curtis AC50 In nduction Motor Diameter Weight Voltage Ampere Rating Motor Efficiency Peak Power Torque RPM
8 inches 122 lb 72-108 Volt 550 Amp 89% 52 HP 115 ft/lbs 6500
Fig. 1. Electric motor options for EV
Fig. 3. Torque, horsepower, voltagee and current vs speed of Curtis AC50
Fig. 2. Curtis 1238R (top) and National Instruments’ Com mpactRIO (bottom)
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IV. STRATEGIES FOR EV OPTIMIZZATION In order to achieve best performance of the t EV propulsion system, two areas of study are investigated: • Enhancement of the motor drive systtem by increasing thermal limits of the motor and motor m controller: increased levels of motor torque will w increase the continuous motor current which in turrn increases motor temperature. To overcome this problem m, a liquid cooling system over the motor and motor controller c can be implemented as illustrated in Fig. 4. With W liquid cooling, it is possible to extend the maximum speed s of the motor as shown in the graph of Fig. 5.
Fig. 4. Liquid cooling system for electtric motor
• Efficiency of the electric propulsion n system: A more efficient system consumes less power and thus prolongs battery life. It is critical for the motor control c strategy to ensure that the motor operates most of o the time in the high-efficiency regions of the motor eff fficiency map (Fig. 6). This energy management and suupervisory control cannot be implemented by the Curtis motor controller; instead, it is programmed on a seeparate controller hardware. V. ENERGY MANAGEMENT SYSTEM (EMS) ON NATIONAL O INSTRUMENTS’ COMPACTRIO
Fig. 5. Motor peak torque with liquid cooling
The main function of the EMS is to monittor various vehicle parameters and to assist the driver in operatting the vehicle, to ensure the electric motor operates with hiigh efficiency. To reduce development time of the EMS, a modular, m embedded real-time controller CompactRIO from Natioonal Instruments is used (Fig. 2). NI CompactRIO (cRIO) is a reconfigurable d acquisition. It system for integrated real-time control and data has a rugged hardware architecture which includes I/O modules, reconfigurable FPGA chassis, and real-time controller. The user-programmer is able to develop and customize a variety of embedded control and monitoring applications. VI. LABVIEW REAL-TIME SOFTTWARE Fig. 6. Efficiency map of induction mootor
The CompactRIO is programmable usinng LabVIEW, also from NI, a graphical programming environm ment which can be used to develop advanced measurement, test and control applications. LabVIEW provides a lot of feaatures and tools to create user-defined interfaces, differentiablee by its graphical programming language along with an inttegrated compiler, linker and debugging tools. LabVIEW differrs from most other programming languages in two majoor ways. First, programming is implemented by wiring mutually m graphical icons on a block diagram, which is then coompiled directly to machine-executable code. The graphical representations r in LabVIEW contain programming concepts similarly s found in text-based language, such as data types, evvent handling, and object-oriented programming.
VII. BATTERY MANAG GEMENT SYSTEM (BMS) In this project, 13 units of o LG Chemicals’ Lithium-ion batteries are used for the vehiccle’s energy storage. An off-theshelf BMS from Orion is ussed to manage and protect the battery pack, installed in the vehicle v behind the batteries. The 13 units of batteries are conneccted in series, with each battery consisting of 4 cells each (2 in series and 2 in parallel). The battery pack has a maximum continuous charging current of 172 Amps, a maximum continuuous discharging current of 460 Amps at SOC50 for 30 seconnds at 25 °C and a maximum discharging current of 600 Ampps. The Orion BMS is chosenn because of its high level of immunity to electrical noise and a voltage transients found in automotive environments. Furthermore, F it has a dual programmable controller-area-nnetwork (CAN) interface which
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has enabled CAN messages to be integrateed with the CANenabled CompactRIO for telemetry purposes.. The basic features of this BMS include cuurrent and voltage protection (from over-charge and over-diischarge), thermal protection (over-temperature protection wiith fan controls), passive cell balancing (to maximize ussable capacity of batteries), internal resistance monitoring of individual i cells (to determine battery condition) and state of charge c monitoring (SOC, coulomb counting with dynamic drift correction). Coulomb counting is susceptible to accumulated error and this must be corrected. In this project, the coulomb counting method m is used in conjunction with the open circuit voltage method m with takes into account charging efficiency and self-disccharging rate for a more accurate SOC estimation. For this appplication, 13 cell voltage taps, a total pack voltage tap, a Hall H Effect current sensor and four temperature sensors are useed. Inputs required of the user include the specifications for thhe battery cell, the battery cell's SOC versus the open cell vooltage at different working temperatures, the cell’s chargingg efficiency over different operating temperature and the cell’s self-discharging rate over different range of temperature. These cell characteristics will define the safe and optimum operating conditions for the battery cells, to extend its life. During charging, the BMS controls the flow of current into the battery pack (based on manufacturer’s chargee current limit) via an ON/OFF digital signal sent to a Manzaniita battery charger. Internal shunt resistors are used to dissipate excess e energy from the cell in the pack with higher voltage. During discharging, the BMS stops the flow of current out off the battery pack (based on discharge current limit).
EMS also sends a signal to thee Curtis motor controller to coordinate on the level of re--generative braking to ensure optimum state-of-charge of thee battery pack. C. Graphical Driver Interface (GDI) ( Design A driver interface is designed and implemented on a touchscreen, Windows-based tablet PC, to display various vehicle parameters, receive inputs from m the driver and relay decisions of the EMS to the driver. TABLE II. SUBSYSTEMS & CAB BLE TYPES OF ELECTRIC VEHICLE Part
Sub bsystem Name
A
Touch-screenn driver interface (GUI)
B
Gearbox & differential gear
C
Curtis AC C50 induction motor
D
Curtis 12338R motor controller
E
Energy Management System (EMS) controller/CompactRIO
F
Battery pack & Orion Baattery Management System (BMS)
G
LED indicator panel for gear-shift assist
No
Power/Signal Type
Cable Type
1
Ethernet network
UTP CAT-5 cable
2
3-phase motor power
Heavy-gauge power cable
3
DC bus link +/-
Heavy-gauge power cable
4
Various signals
Single/multi-core signal cable
NTATION VIII. EMS DESIGN & IMPLEMEN
A. System Layout and Schematics t EV, while Fig. Table II lists the different sub-systems of the 7 and 8 show the layout and schematics resppectively. The subsystems are connected to each other usingg certain types of cable, which are also listed in Table II. B. Energy Management System Design The EMS communicates with the Currtis 1238R motor controller using RS232 serial connectionn. A serial data acquisition program is developed on LabVIEW and deployed to the CompactRIO. Early EMS designs are deeveloped alongside bench test experiments (see below). Inputs to the EMS controller include: • Battery state of charge (SOC) • Battery voltage • Motor current • Motor speed • Vehicle speed • Gear position m controller & • Various temperatures of motor, motor battery pack Based on the above inputs and specific control c algorithms to achieve different race objectives of the PG GMC competition, the EMS controller continuously makees decisions and provides suggestions to the driver on timing for shifting of the transmission gear - whether to maintain currrent gear position, up-shift or down-shift - to obtain optimum performance. The
Fig. 7. EV Subsystems Layout
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Fig. 9 shows an early GDI design, duriing the bench test stage. The final design which is deployed on the tablet PC wn in Figs. 10 and located in the dashboard of the EV, is show 11, which also show different tabs of the inteerface program. Invehicle data logging is another feature of thee EMS, which can be activated via the GDI. Among the param meters that can be logged include battery pack voltage, batterry state of charge, motor current, motor speed, vehicle speed, gear position and battery temperature. Both digital and analog data can be loggedd by the EMS. The logged files are saved in the built-in flashh memory of the CompactRIO, which can later be post-processed using 3rd party software such as Microsoft Excel. Fig. 9. RPM and current reading progrram of EMS during bench test
D. EMS and Propulsion System Bench Test Bench testing for the EMS, motor and motor m controller is accomplished in the lab, outside of the vehhicle, as shown in Fig. 12. The list of components for the bench test is given in Table III. A control box consisting of throtttle potentiometer, brake potentiometer, power switch and reverse direction switch, is employed, to replace actual innstruments in the vehicle.
+
DC/DC
+
- Converter -
Key Switch
+
Fig. 10. Main tab of EMS as viewed on o Tablet PC
-
12 Volt RS2 32
RJ45
DIO Module AO Module
M NC
AI Module
Power Steering Motor
Various parameters: EMS
P NC
(CompactRIO)
Brake Vacuum Pump
• • • • • • •
Batteryy state of charge Batteryy voltage Motor current Motor speed Vehiclee speed Driver’s accelerator on positio Driver’s brake pedal on positio
Fig. 11. Second tab of EMS as viewedd on Tablet PC LED Indicattor
Tablet PC (GUI)
Throttle
Brake
High-Voltage Contactor Fuse (400 A) Manual Contactor
-
+ Battery Bank
Fig. 8. EV schematics Fig. 12. Bench test for EMS and propuulsion system
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TABLE III. COMPONENTS OF EMS AND PROPULSION SYSTEM BENCH TEST No
Component
1
Curtis AC50 Induction Motor
2
Curtis 1238R Motor Controller
3
Molex Display 840
4
General Control Box & Relay
5
Battery Pack 72 Volt
6
Main Contactor
7
Battery 12 Volt
8
LabVIEW GDI
9
NI CompactRIO Real-Time Controller
E. Battery Charging and BMS Bench Test Charging test for the battery management system (BMS) is also achieved in the lab. An off-the-shelf battery charger is used - Manzanita Micro PFC-50. An image of the battery charging and BMS bench test is shown in Fig. 13 while schematics of the entire EV system including the BMS and battery charger is shown in Fig. 14. The Orion BMS has a thermal management system consisting of thermistors for measuring battery temperature, an ON/OFF output and PWM output for control of an external exhaust fan. IX. CONCLUSION An electric vehicle energy management system (EMS) is described in this paper, developed and implemented using National Instruments’ CompactRIO. The EMS is a controller separate from the motor controller. Along with a battery management system (BMS), the EMS is used to convert a conventional vehicle to an all-electric vehicle (EV). The main objective of the EMS is to monitor vehicle conditions and assist the driver in operating the vehicle, to ensure the electric motor operates with high efficiency. The BMS serves to ensure that the battery cells have a balanced state of charge (SOC) and to manage thermal conditions of the battery pack. Together, the EMS and BMS improve the EV’s performance by optimizing its energy usage to extend the converted vehicle’s driving range.
Fig. 14. Schematics of entire EV system with BMS and battery charger
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Fig. 13. Bench test of battery charging with BMS
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