Development of hybrid car calibration system based on NI CompactRIO

    Challenge: In view of the characteristics of hybrid electric vehicles, a hybrid electric vehicle calibration system based on NI CompactRIO was developed. During the test bench and vehicle debugging stage, the system can be used to modify the calibration parameter variables inside the vehicle controller online to achieve the purpose of optimizing the performance of the vehicle.

Application: Use NI's CompactRIO real-time controller, Labview Real-Time, Labview FPGA, Labview RIO, and Labview Real-Time Application tools to develop this automated test system.

Products used:

    Labview 8.5 software development platform

    Labview Real-Time Module

    Labview FPGA Module

    Labview RIO Module

    NI CompactRIO-9014 with 128MB

    Real-time DRAM controller

    NI CompactRIO-9104 8-slot reconfigurable

Embedded chassis

    NI 9853 2-Port High-Speed ​​CAN Module

introduce

    Hybrid vehicles combine the advantages of traditional vehicles and electric vehicles. As a relatively mature new energy source, they have been widely developed. The vehicle control unit (VCU) is used to achieve vehicle energy management and power system control, and is the control center of hybrid vehicles. The control parameters in the VCU are one of the key factors in achieving hybrid vehicle performance, and corresponding optimization and calibration work must be carried out.

    The calibration of automotive ECU is a very complex process. On the one hand, it is due to the complexity of the working conditions of the controlled system; on the other hand, there are influences between many control parameters. The optimization of the operating parameters and control parameters of the ECU requires the use of special tools for analysis and modification, so the calibration system of the ECU was born. The selection of the calibration system is related to the calibration quality, calibration time and calibration cost. Therefore, the selection of a complete and applicable ECU calibration system is one of the key factors for the successful development of the ECU. Taking the above factors into consideration, the NI CompactRIO system was finally selected to develop the hybrid vehicle calibration system on this platform. Its compact shape can be placed in any free position in the car without affecting the space of the vehicle; the sturdy design allows stable operation even in harsh driving conditions; anti-interference measures can eliminate the influence of various interferences on the system during driving; the Labview graphical programming language liberates engineers from complex programming work and greatly shortens the development cycle; the hot-pluggable I/O module with built-in signal conditioning enhances the openness and flexibility of the system, and engineers can access the underlying hardware resources.

Hybrid Electric Vehicle Design

The single-axle parallel hybrid solution studied in this paper is a mild hybrid form of front-engine front-wheel drive.

    After a lot of scheme selection and design, the engine, ISG motor, super capacitor and dual clutch are integrated. The disc-type integrated ISG motor is directly installed on the output end of the internal combustion engine crankshaft, the motor rotor is directly connected to the engine crankshaft, and the stator is fixed on the engine body. The motor replaces the flywheel and the original starter and generator.

    The power of the hybrid system of this scheme is mainly driven by the internal combustion engine, and the motor is auxiliary driven. The dynamic response of the internal combustion engine power output is slow and the torque output control accuracy is poor, while the instantaneous power drive response of the motor is fast, the torque output control accuracy is high, and the energy recovery efficiency is high. Therefore, the working characteristics of the motor are used to optimize the engine working conditions, and hybrid control strategies such as idle stop, fast start, deceleration oil cut-off, acceleration assistance, motor constant power generation and deceleration braking energy recovery are formulated.

Benefits of NI CompactRIO Systems

    NI CompactRIO is a compact and rugged industrial control and acquisition system that uses reconfigurable I/O (RIO) and FPGA technology to achieve ultra-high performance and customizable functions. It includes a real-time controller and a reconfigurable FPGA chip, suitable for reliable independent embedded or distributed application systems; it also includes hot-swappable industrial I/O modules and built-in signal conditioning that can be directly connected to sensors/regulators. This design makes the low-cost architecture open and users can access the underlying hardware resources.

    FPGA (Field Programmable Gate Array) is a further development of programmable devices such as PAL, GAL, PLD, etc. Its logic functions are completed by the regularly arranged logic cell array inside. The logic cell array includes three parts: configurable logic module, input and output module and internal connection. Engineers can reconfigure the logic module and I/O module inside FPGA through software programming to realize customized logic.

    FPGA technology has many advantages, including custom I/O hardware timing and synchronization, high reliability, digital signal processing and analysis, etc. These advantages provide a flexible and low-cost solution for the rapidly growing automotive electronic test technology. FPGA can be directly connected to digital and analog I/O, and different sampling rates and triggers can be defined for each channel. With the application of FPGA technology, advanced signal processing and analysis can be performed on any sensor signal. In many signal processing systems, the underlying signal preprocessing algorithm has to process a large amount of data and has high requirements for processing speed, but the algorithm is relatively simple and can be programmed using FPGA. In addition, it is very convenient to implement digital filtering operations, fast Fourier transforms, windowing and other signal processing and analysis on the collected signals on FPGA.

System design

    Hybrid vehicle calibration is different from traditional engine calibration. Due to the more complex working conditions and environment, higher requirements are placed on the stability of the calibration system. The calibration hardware environment finally developed is shown in Figure 1. The communication master end consists of a portable PC and the NI CompactRIO system, and the communication is completed through TCP/IP; the communication slave end is the msCAN of the vehicle controller. The calibration method uses CCP, a vehicle calibration protocol based on the CAN bus, so the NI CompactRIO system is connected to the vehicle controller through the CAN bus.

Figure 1 Calibration system hardware architecture

    The CAN network of a hybrid vehicle consists of four control units, including the vehicle control unit (VCU), engine management system (EMS), motor control unit (MCU), and information status display controller (DPLY). All these control systems communicate through the CAN bus. When designing the vehicle CAN network, a node is reserved for vehicle CAN network monitoring in the development phase. The calibration system is also connected to the CAN network through this node, thereby establishing a connection with the vehicle controller VCU. The main control PC is the top layer of the calibration system. It can monitor the vehicle CAN network data online and modify the vehicle controller calibration parameters online, thereby uniformly controlling and managing the system. The CAN communication module uses the NI 9853 two-channel high-speed CAN acquisition module to collect vehicle CAN network signals with a resolution of 25ns and supports 11-bit and 29-bit arbitrary IDs. This solution has the characteristics of high integration, saves equipment investment, and simplifies the working environment of calibration personnel.

System software design

    The software design of the hybrid vehicle calibration system fully considers the hardware characteristics of the CompactRIO system. The software programming mainly includes three parts: the underlying FPGA program, the RT program, and the host computer host program.

    The bottom FPGA program realizes data acquisition of each board, transmission of correction coefficients of each IO channel, DMA transmission of data to RT, etc. The RT program is responsible for communicating with the bottom FPGA, flashing indicator lights of the RT system, controlling user switches, TCP/IP network communication with the host computer Host, FTP data transmission, calibration, interpretation and recording of test data, etc. The host computer Host program is responsible for configuring the overall test system channel, communicating with RT, and can monitor specific channels of the acquisition board in real time, view data saved on RT, etc.

    The entire software supports different sampling rates, supports the recording and conversion of CAN frames, and the storage of TDMS file formats. The data recording of the controller is displayed by the flashing indicator light on the front panel, and the data recording can be paused through the custom switch on the front panel. The system has expanded the U disk, and the data will be automatically stored in the U disk. After powering off, you only need to copy the data in the U disk to the host computer.

    After developing the program that runs on the FPGA target using the Labview graphical language, compile the program and download the compiled file to the FPGA chip. The RT program can be downloaded to the NI CompactRIO real-time system through the Labview Real-Time Application tool, so that the RT program will run automatically as soon as the system is powered on.

    According to the basic functions of the calibration system, the host computer software is divided into the following modules: CAN communication control module, vehicle controller calibration module, and CAN network data monitoring module. The main function of the CAN communication configuration module is to configure the relevant information of the CAN channel, so as to drive the NI 9853CAN card to send and receive CAN data; most of the calibration work is completed under the vehicle controller calibration module. In general, there are two tasks to be performed by this module: reading RAM area data and displaying it on the PC, and downloading data to the RAM area. Figure 2 shows the calibration interface. All instructions in the calibration process are displayed in the form of controls on the front panel. When the user clicks on a certain instruction, the module should be able to receive the user's calibration instruction and start the management of the corresponding thread. The main function of the CAN network data monitoring module is to process the vehicle CAN network message obtained by the CAN card and finally display it on the monitoring interface. The CAN messages obtained from the CAN card are still in the form of data frames. In order to provide a friendly interface for testers, it is necessary to convert between decimal data and the binary data used in the controller. At the same time, the application needs to perform corresponding data analysis based on the ID number of the CAN message sent by each controller, and display it on the front panel in the most intuitive way possible, so that R&D personnel can understand the working conditions of the vehicle, engine and motor in real time.

Figure 2 Calibration interface

in conclusion

    There are multiple interference sources when the car is driving, such as spark discharge caused by motor brushes, electromagnetic signals generated by pulse switch contacts in certain circuits, interference from various electrical equipment during operation, etc. These noises have serious interference on the measured signals and test equipment, which will cause large data acquisition errors. Therefore, the anti-interference ability of the acquisition equipment is particularly important. Through long-term real-vehicle road tests, the anti-interference measures of the equipment can eliminate the impact of various interferences on the system during driving, ensure accurate and reliable acquisition of vehicle CAN network data, and perform online calibration of vehicle controller parameters. Its real-time performance and reliability have been verified, fully meeting the requirements of hybrid vehicle calibration tests, and playing a very important role in the control strategy debugging of hybrid vehicles.