RF Telemetry Design for Electric Vehicle

6th International Conference on Advanced Technology & Sciences (ICAT'Riga)

Sep 12-15, 2017, Riga/LATVIA

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RF Telemetry Design for Electric Vehicle Hande N. Kilickir, Akif Demircali, Selim Koroglu, Selami Kesler, Mustafa Tumbek, Arda Kilic Dept. of Electrical and Electronics Eng., Pamukkale University Pamukkale, Denizli, Turkey, 20070 [email protected], [email protected], [email protected], [email protected], [email protected], [email protected]

Abstract— Electric vehicles are promising solutions to today’s transportation and environmental problems. To improve the electric vehicles and use them safely could be possible with the online monitoring and recording the important parameter of the vehicle at the whole operating period. However, it is a complicated problem and has some restrictions about the range, reliability and stability. In this work, a telemetry system is presented to overcome these struggles. The proposed system uses the RF signals to transfer the data and reliable and stable ARM microprocessors to proceed communication assignment. Functional operation of the proposed telemetry system is tested in the competition of International Tubitak Efficiency Challenge Electric Vehicle and the results are presented in this paper. Keywords— Electric vehicles, RF signals, Telemetry, CAN communication, System design

I. INTRODUCTION Telemetry is a system that collects, sends and receives some information from vehicle to the place where monitoring or recording is needed. Knowledge of some basic parameters of the vehicle especially in competitions has crucial importance for the reliability of the vehicle’s components and sustainability of the race. Telemetry is also necessary for development and adjustments of the vehicle management. Moreover, telemetry system provides advantages to improve the safety condition of the driver and warnings to prevent from failures [1]. In literature, telemetry system is implemented in several ways for the vehicles. Most of the researchers uses the General Packet Radio Service (GPRS) [1]-[3], radio frequency (RF) [4], [5]and other telemetry system[5], [6]. GPRS is preferred for the ease of implementation and it is a very robust and proven option that offers the bigger coverage warranty. However, RF signals more appropriate for the local applications like vehicle races. RF range depending on the used module is sufficient and provides reliable communication depending on the selected communication protocol [4]. In this paper, RF telemetry system including transmitter and receiver modules is designed for the electric vehicle and implementation results are presented. The proposed system is used for the vehicle ALATAY in the competition of International Tubitak Efficiency Challenge Electric Vehicle. This paper is structured as follows. The first section states the needs for this work and gives an introduction to the subject. The second section presents the structure of the telemetry system and detailed information about the communication protocols and hardware-software designs of telemetry. Section

III represents the results of implementation studies, and discussion of the obtained results. Finally, conclusions are given in Section IV. II. TELEMETRY SYSTEM DESIGN The constructed telemetry system has two parts; one part carries out the data collection process and includes transmitter module inside the vehicle. In addition to these assignments, the system provides to display collected data to inform the driver with familiar interface from commercial vehicles. Second part of the telemetry system is produced portable outside of the vehicle with receiver module and visualization tools. Designed telemetry system has several communication modules to support different communication protocols. Transmitter module is placed inside the vehicle and sends information to receiver module about battery status, temperature and vehicle speed. Transmitter module obtains these data from the main controller unit (MCU) of the vehicle via Controller Area Network (CAN) bus communication. Data is transferred from transmitter to receiver module by NRF24L01 communication module. Transferred data is get with the same communication module and shown on the TFT screen of the receiver module as shown in the Fig. 1.

Fig. 1 General telemetry system design

In this application, the following modules are used as shown in the Fig. 1: • A main controller unit (MCU) which collects information about the battery voltage and temperature and calculates the state of charge of the battery. MCU is also

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calculates the vehicle speed from the back-EMF voltages and sends this information to the CAN bus. The presented MCU is based on the STM32F407VG, a small and powerful ARM Cortex M4 32 bit microcontroller. This model has been chosen, basically because of its 168 Mhz speed and useful peripherals in relation with the communication. • A display unit at the vehicle front console. • A transceiver unit that is located inside the vehicle reads data from the CAN bus and sends the data with RF signals. • A second transceiver unit, held at the support service area, is receiving the data to monitor the vehicle condition.

A. Communication Protocol In telemetry system, vehicle main controller and transmitter module communicate with CAN communication protocol. Obtained data by transmitter module is sent with NRF24L01 module via Serial Peripheral Interface (SPI) communication protocol to receiver card. These communication protocol between modules are shown in Fig. 2. CAN communication protocol is a communication protocol that is frequently used in vehicles and that the secure communication is in the front-line. The MCU unit in the vehicle communicates with inverters and steering angle sensor via this communication method. As the vehicle has 2 motors and 2 inverters, electronic differential application is used. Therefore, the speed and torque references to be sent to these two inverters are also implemented by CAN communication. Also, as shown in Fig. 2, high-safety CAN communication is used between the MCU and the telemetry transmitter because of the importance of the data. The NRF24L01 module is used to send the information to be sent by the MCU. This module is a highly integrated, ultra-low power, 2Mbps RF transceiver integrated circuit (IC) for the 2.4 GHz frequency band. The specified module sends the requested information using the SPI communication protocol. SPI is an interface bus commonly used to send data between microcontrollers and small peripherals. It uses separate clock and data lines along with a select line to choose the target device. In telemetry application, RF signals and information are transmitted synchronously with SPI protocol in wireless environment. As shown in Fig. 2, the MCU in the vehicle also communicates with the display unit at the vehicle front console using the UART. UART stands for Universal Asynchronous Receiver / Transmitter. It's not a communication protocol like SPI and CAN, but a physical circuit in a microcontroller, or a stand-alone IC. A UART's main purpose is to transmit and receive serial data. One of the best things about UART is that it uses only two wires to transmit data between devices like CAN.

Fig. 2 Communication protocols used in the vehicle.

B. Hardware Design In this section, open circuit of transmitter-receiver card is shown. Fig. 3. shows the main connection diagram of the designed telemetry system. The same microprocessor with the MCU, STM32F407 is used in the transmitter circuit. This microprocessor has 100 pins that are set so that pins can be used during communication with other peripherals as shown in Fig. 3. In the circuit drawings, the resistance and capacitors on the sides of the microcontroller form the minimum circuit. This is necessary for the microcontroller to protect from the sudden voltage drops that can occur during the operation of the target circuit. In addition, there are boot and reset buttons necessary to boot and restart the system. Besides that, power supply of the microcontroller and the transmitter is achieved with the regulator circuits that reduces the 12 V to 5 V or 3.3 V as needed.

Fig. 3 Telemetry main scheme.

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Transmitter and receiver cards are designed in Proteus ISIS/Ares program as shown in Fig. 4. Because of the importance of size and weight in electric vehicles, it is important that the printed circuit board (PCB) should be as compact as possible.

Fig. 4 PCB designs of transceiver modules.

C. Software Design For the information exchange of the designed telemetry system, a flow diagram was created as shown in Fig. 6. As can be seen, the flow chart starts with the creation of the pre-set of the communication method. The information to be sent is then combined into a packet and sent in every 1 second with the SPI protocol. The information is transmitted by the MCU to the transmitter, which is speed, battery and temperature information. The transmitted information in relation to the battery includes current of the battery, the lowest and highest cell voltages, the total voltage of the battery module and the state of charge (SOC) information. In terms of temperature, motor and battery temperature are separately measured and sent.

Fig. 6 Telemetry system flow diagram

After the design of PCB and production, transceiver modules are get ready to be used. Fig. 5. shows the final appearance of designed telemetry module from top and bottom.

III. IMPLEMENTATION RESULTS In addition, we designed a protection box for the receiver module in SolidWorks as shown in the Fig. 7. Final view of telemetry system’s screen can be seen from the Fig. 8.

Fig. 7 Designed protection box for the receiver module. Fig. 5 Final appearance of designed telemetry module from top and bottom.

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IV. CONCLUSIONS In electric vehicle races, traceability of the vehicles and directions according to the results obtained from this monitoring is of utmost importance. For this reason, there is a need for a reliable, consistent telemetry system that can fulfill the required tasks. Therefore, in this study, a telemetry system with the desired characteristics was designed and used successfully in the competition of International Tubitak Efficiency Challenge Electric Vehicle. ACKNOWLEDGEMENT This work was supported by the Scientific and Technological Research Council of Turkey under Grant 114E023, and by the Pamukkale University under the Grant PAU-ADEP/2017. REFERENCES [1] Fig. 8 Final view of telemetry system’s screen.

The transmission was tested in a distance of 1000 m and operated without problems. There were no problems in the operation of the designed telemetry system even though many vehicles were found in the race field and each tried to communicate with similar methods.

[2]

ALATAY vehicle won the first prize in the category of domestic product award in the participated competition with the help of telemetry design and other designs, which is one of the 6 main topics evaluated by the competition committee. Fig. 9 shows this award and some of the team advisors.

[4]

[3]

[5]

[6]

Fig. 9 Domestic product award given to the ALATAY vehicle.

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