R & D of the Advanced Electric Vehicle at CATARC

The breakthrough of key technology on battery electric vehicles is critical to of hybrid and fuel cell electric vehicles. This paper introduces the technical configuration of the new advanced electric vehicle and design of lightweight vehicle and integrated assembly. The Electric Vehicle developed at CATARC acquires many creative results, such as control strategy of vehicle, CAN Bus technology, heat management system of lithium-ion battery pack, fault diagnosis, safety management for high-voltage system and body comfort control. Also, this paper evaluates the vehicle performance and defines the technical scheme by using simulation tools. Simulation results are also validated by vehicle test. At last, the test results on the performance of electric vehicle are systematically introduced.


INTRODUCTION
Electric vehicles contain electric motor and drive, traction battery and its management system, etc.Many technologies of battery electric vehicles are the basics of hybrid and fuel cell electric vehicles.Successful experiences indicate that the companies such as TOYOTA and GM which have the most advanced technology on hybrid and fuel cell electric vehicles have advanced technology on battery electric vehicles.The key technologies on battery electric vehicles are critical to hybrid and fuel cell electric vehicles.
At the goal of innovation of science and technology and industrialization, comprehensive and systematic R&D of the advanced battery electric vehicle was carried on at CATARC.The emphases are design of weight reduction, integrated assembly, distribution control system based on double bus, battery heat management, fault diagnosis, high-voltage safety management, recording and analysis of the data of fleet vehicles, and supervising management system based on wireless telecommunication technology, etc. [1] . [2]e technical configuration of the advanced electric vehicle is described in Fig. 1.

VEHICLE CONFIGURATIONS
It can be seen that research of new type battery electric vehicles is system engineering on complete vehicle development [3] .It emphasizes on sustaining constructing on platform supporting research and development as well as focuses on the field of advanced automotive electronic technology.It not only carried out technology innovation of complete vehicle design, but also developed intelligent supervising management system based on wireless long-distance communication technology.

Design for Weight Reduction
Weight Reduction is always an important research content of auto technology, and the problem stands out.Through analyzing vehicle using condition and requirement, we can optimize the parameter of the voltage and capacity of battery, requirement of power , speed and torque of motor, complete vehicle performance, traction battery and motor were chosen accordingly.
We reduce the weight of electric drive assembly and on-board energy storage system for configuration optimization that includes integration and modularization design among motor, motor drive, powertrain, cooling system, air condition, brake vacuum system, and also includes integration on on-board energy system which is composed of battery module, management system and on-board charger.The electric vehicle used lightweight material, for instance, in frame of battery pack, plates of pack, and wheel hub.Fig. 2 is the integrated electric drive assembly.
CAD techniques are used to perform finite element analysis on body bearing frame pieces, achieve optimization of configuration by combining calculation and test.

Fig. 2 Integrated Electric Dive Assembly
Vehicle control system of the advanced electric vehicle is network configuration that have two buses, which are high speed CAN bus in powertrain and low speed bus in body system.Each node in high speed CAN bus is the ECU of each subsystem.Low speed bus sets node according to physical position.The principle is area autonomy based on space position.Electric components were linked nearby to ECU on one node, and communicated with the bus through ECU.Low-speed bus had two choices, one is low speed CAN bus, the other is LIN bus.
In the former one, the configurations of both high-speed CAN bus and low-speed CAN bus are independently controlled.We can build high speed CAN bus according to ISO11898 and J1939 and J2284 [4] , and build low speed fault tolerant CAN according ISO 11519-2 [5] .Node control unit controls local executing components according to local sensors and signals from CAN bus, while transmitting the signals that needs to be shared with other nodes to CAN bus.Fig. 3 is the vehicle control net configuration used in advanced electric vehicle, and control system is double bus net configuration, i.e. high speed CAN bus in driving system and low speed bus in body system.Fig. 4 is the network topology in body comfortable system.Fig. 3  Distribution control system based on double bus not only solved the problems such as complex circuitry and wiring harness, but also improved communication and resources sharing ability, at the same time, it supports X-By-Wire technology further.

Fault Diagnosis and Safety Management
Technique for High-Voltage System [6] An important character of battery electric vehicles is high voltage and large current.Electric vehicles, with similar performance as traditional vehicles, have higher voltage than safe voltage, while the impedance is very small.The current may achieve even hundreds amperes, and instantaneous short circuit current can increase several times.For these reasons, design of high voltage power system must consider the safety of people and vehicle.
In the development of new type electric vehicle, we studied safety control of high voltage and protection strategy, including condition analysis before switching on high-voltage system, prevention while instantaneous crash, high-voltage system real-time supervising in operation, management strategy considering kinetics safety and electric safety.The advanced electric vehicle was equipped with the Diagnosis and Safety Unit (DSU) specially designed.The unit s major function is state inspect and malfunction diagnosis for each tache of electric car drive chain, then start correspond function of strategy in invalidation and safe prevention to insure the safety and reliability [7] .Fig. 5 shows the structure of Diagnosis and Safety Unit.

Battery Thermal Management System
Condition of battery pack directly influenced the performance such as acceleration characteristics, cruising range, regenerative braking, etc.The cost and cycle life of battery influence the cost and reliability of vehicle.Battery got heat during charging and discharging because of battery ohm polarization, electrochemistry polarization, electrochemistry reaction and overcharge oxygen complex.The heat can do harm to electrode and septum materiel, which can influence electrode performance and life, and then cycle life, efficiency characteristics, capacity, safety and reliability [8] .Thus it is very important to control overheat of modules in pursuit of normal use of great capacity battery.Another problem, which influences the module that is composed of many cells, is that batteries in the pack differ from each other on temperature, which will lead different state of charge, and then it leads imbalance among cells, which reduces the capacity and life of the modules.We designed Battery Thermal Management System (BTMS), by the system battery working in the best temperature range, and keeping temperature balanced.BMTS had some functions, such as cooling the battery when the ambient temperature is high, and heating when cold to keep the battery in the best condition, even BTMS can exhaust automatically the dangerous gas from battery pack.
Fluid analysis software -FLUENT and general finite element analysis software -ANSYS are used to analyze gas flow condition in the pack, such as distribution of gas speed and temperature, in the meantime lots of research tests are performed.Many parameters are optimized based on influence factors, such as battery pack size, battery layout in battery pack, pack material, structure of cooling system, and control strategy of actuator for forcing ventilation.For ensure the design of battery thermal managements, the hardware-in-loop simulation test was performed.At the temperature of 20 20 Temperature difference among all the cells is less than 3 .

On-line Supervising and Calibration Technology
On-board recording instrument based on multi communication ports is very important to vehicle powertrain system matching and operation analysis.On-board recording instrument should record the information of vehicle operation, motor state, battery state, etc.Data analysis software related to electric vehicle carried out data rerunning and analysis, including statistic analysis.
For the convenience of matching and optimization, the ECU of each subsystem supervised and calibrated data on-line.Controlled objects and management strategy were parameterized, and could be supervised and calibrated on-line through communication ports.

Vehicle Intelligent Management System
During calibration, testing and demonstration, we introduced GPS, GSM/GPRS and GIS to intelligent management such as communication and dispatching and tracking.Through vehicle intelligent monitoring platform, on-board terminal transmits vehicle information to the central monitor management center, which makes it easy to manage the fleet.In the meantime wireless remote testing, calibration and analysis can also be achieved.Developing further can achieve remote diagnosis and assistance.

Simulation and Validation
Power performance, economic performance and cost of battery electric vehicle can be influenced by many factors, such as nominal power and peak power of motor, rated speed and highest speed of motor, high-efficiency area distribution of motor, battery capacity and quantity.Vehicle performance was evaluated by simulation software CRUISE.Combining the design goal of complete vehicle, the basis technology and the requirement of main capability index are decided, such as high-efficiency area distribution of motor, peak power of battery, and so on.Fig. 6 shows the process of some parameters in Tianjin city drive cycle.We can get some key data such as maximum discharge current and variation of SOC, and then we can work out the cruising range after a complete charge in Tianjin city drive cycle (Table 1 shows the result).Fig. 7 shows the operating point distribution in Tianjin city drive cycle, and we can get the energy consumption distribution.In the meantime, it can give the special requirement of high-efficiency area distribution of motor and optimize index of vehicle economic performance.
Table 1 is the comparison between test results and simulation results.It can be seen that power performance simulation result is similar with test one, but cruising range in real city cycle is less than simulation result by 7%.The main cause is that cells in the pack are not balance, and it is difficult to model exactly in simulation.The specifications for the battery electric car and its prototype gasoline car are shown in table 2.  3 shows the comparison between the battery electric car and its prototype gasoline car.We can see that acceleration performance dropped in 0~50 km/h and 0~100km/h test, but other performance index meets technique requirement of prototype car, and the direct gear acceleration is much better than prototype.

Table 3 Power Performance Comparison between
Electric Car and Prototype

Economic Performance
Table 4 shows comparisons on energy consumption and economic performance between electric vehicles and gasoline vehicles at speed of 40 km/h and in city drive cycle.It is evident that economic performance of electric vehicle is much better than of traditional gasoline vehicle., and radiation interference characteristic meet the requirement among the bandwidth 9kHz~1GHz.Fig. 9 is plane polarization peak scan process at vehicle left side.We can see that measure data is much lower than standard limit.

CONCLUSION
Research and development of the advanced electric vehicle at CATARC embodied innovation of science and technology, and gained several creative achievements, such as lightweight design and integrated assembly, battery heat management system, and fault diagnosis and safety management for high-voltage system, body comfort control, etc.
The key technologies involved in battery electric vehicles are common issues that hybrid vehicles and fuel cell vehicles must confront.The breakthrough of key technology on battery electric vehicles is critical to hybrid and fuel cell vehicles.Because of environmental protection characteristics and universality of energy sources, battery electric vehicles will become of mainstream in future of transportation.

Fig. 5
Fig. 5 Diagnosis and Safety Unit

Fig. 6
Fig. 6 Running Parameter in Tianjin City Drive Cycle

Condition Vacuum Assist Steering Assist Charger High Speed CAN Bus Low Speed Bus Head Light Node Assemble Switch Node Vehicle Controller Power Seat Rear Lamp Diver Door Other Nodes Fault Diagnose ECU
Vehicle Control System Configuration Fig. 1 Technical Configuration of advanced electric vehicle

Table 1
Comparison between Test and Simulation Results

Table 4
Comparisons on Economic Performance ability.Complete vehicle was tested according to GB/T 18387-2001-Electric Vehicle Electro -magnetic Radiant Intensity Limit and Measurement Band 9kHz~30Hz and GB/T 14023-2000-Engine Light by Spark Radiation Interference Characteristic Limit and Measurement