Hardware system design of electric locomotive logic control unit test bench

0 Introduction

The electric locomotive logic control unit (LCU) is an important control part of the electric locomotive. It uses modern electronic components to replace the original contact relays on the electric locomotive, thereby improving the safety and reliability of the electric locomotive control system. At present, all new electric locomotives produced in my country are equipped with LCU, and the old electric locomotives are also equipped with this device after overhaul. However, since the operating environment of electric locomotives is usually very harsh, after the locomotive logic control unit has been used for a period of time, it may cause LCU failure, so the LCU must be regularly inspected comprehensively. This paper mainly proposes a feasible design scheme for the hardware system of the LCU test bench for SS4G electric locomotives.

1 System Structure of LCU Test Bench

The LCU test bench system in this paper adopts a modular design concept. The main functional modules of the system are composed of a host computer, a communication module, a data acquisition and control module, a programmable power supply and monitoring module, and a simulated load module. The block diagram of the LCU test system is shown in Figure 1.

1.1 Host computer

The host computer is the core part of this test bench. Its main function is to imitate the control signal of the electric locomotive and send it to the LCU. At the same time, it detects the operation of the LCU according to the feedback data to find errors and analyze the causes. In addition, the host computer also has the function of drawing the LCU logic ladder diagram; according to the LCU logic ladder diagram, it can automatically or manually complete the logic test table function; automatically or manually complete the LCU test function, and has the function of printing test reports and continuously enriching the fault database. The CPU used in this host computer is Celeron 1.8 GHz, the memory is 512 MB, the operating system is WindowsXP. 80 GB hard disk space. At the same time, it has a good operating interface and human-computer interaction capabilities, and the graphical interface is simple and intuitive, and the operation is convenient and simple.

1.2 Communication module

The communication module is mainly responsible for the communication between the host computer and other functional modules, and simulates another chassis to complete the online test when performing a single chassis test. This design uses RS485 as the communication protocol of the host computer, and other modules use the CAN bus for communication. In the design, in order to prevent the bus interference signal from entering the system and affecting the stability of the system operation, this design isolates the data between the microcontroller and the CAN bus. The structural block diagram of its communication module is shown in Figure 2.

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1.3 Data acquisition and control module

The main function of the data acquisition and control module is to convert the logic control command (5 V) sent by the communication module into the logic control command (110 V) that the LCU can receive, and collect the LCU output signal and send it back to the host computer for detection. The data acquisition and control module consists of 8 identical circuit boards, which correspond to the LCU of the SS4G electric locomotive under test.

The specific working principle of the data acquisition and control module is: the host computer sends relevant control commands to this module through the CAN bus of the communication module, and then the single-chip microcomputer controls the on or off of the 24-way photoelectric switch according to the command. Provide 24 input logic control signals for the LCU board (high level is 70~135 VDC, low level is OV). In order to ensure the correctness of the 24-way logic control signal, this design uses 24-way photoelectric feedback circuits to convert it into TTL level signals, and then send it back to the single-chip microcomputer for judgment. The output of each LCU control board has 14 high outputs and 4 low outputs, so the collection of its output signals is also divided into 14 high output collections and 4 low output collections. They share an AD converter and use time-sharing multiplexing to perform AD conversion on each output. In addition, when detecting the high output of the LCU, it is also necessary to detect its output voltage under load.

In this design, we also use time-division multiplexing to test the high output under load. In addition, this module also has a self-test function. The structural block diagram of the data acquisition and control module is shown in Figure 3.

1.4 Programmable power supply and monitoring module

The program-controlled power supply and monitoring module mainly provides working power for the LCU test bench and monitors the power supply in real time. This program-controlled power supply has four different output voltages (DC70 V, DC75 V, DCll0 V and DCl37 V), which can test the working condition of the LCU under different voltages. In order to ensure the safety of the test bench equipment and the LCU under test, this module is designed with overcurrent and overvoltage alarm and protection functions. When the industrial computer sends a voltage adjustment command to the program-controlled power supply and monitoring module through the CAN bus of the communication module, the single-chip microcomputer can control the program-controlled power supply to adjust the output voltage. Under normal working conditions, the output voltage and current can be sampled in real time through the Hall sensor to monitor the working condition of the power supply. When the voltage or current is found to be abnormal, the voltage and current can be detected after a delay of 100 to 500 μs (to prevent current glitches). If it is still abnormal, the solid-state relay will be turned off immediately, and the power supply abnormality data will be sent to the upper computer. Figure 4 shows the structure diagram of the program-controlled power supply and monitoring module.

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1.5 Simulation load module

When testing the LCU, it is also necessary to test its working condition under high output with load. Therefore, this design also provides a simulated load unit to simulate the load on the electric locomotive. Each LCU control board corresponds to a set of optional loads (a total of 8 sets are required), and each set of loads has 4 optional resistance values ​​(330 ohms, 220 ohms, 110 ohms and 55 ohms are selected according to the actual situation of the SS4G electric locomotive); in addition, it is also required to have a load self-test function, which should be able to determine whether the load resistance is short-circuited, open-circuited or abnormal. Its working principle is that during normal operation, the single-chip microcomputer selects the resistance value through 4-way photoelectric switches as the load of the LCU high output. The load self-test is to select the resistance value to be tested by the single-chip microcomputer, and at the same time, the conduction switch of the self-test power supply is turned on to energize the resistance to be tested, and then the voltage of the resistance is converted into AD and fed back to the single-chip microcomputer for detection. The structural block diagram of its simulated load module is shown in Figure 5.

2 Hardware Circuit Design

The hardware system of this test bench is an embedded system with the 16-bit high-performance microcontroller MB90F543G produced by Fujitsu as the core. MB90F543G has two CAN bus interfaces that comply with the V2.0 standard, which is very convenient for the expansion of the CAN bus. It also has 8-channel 8/10-bit A/D converters and 8 interrupt priorities, 34 interrupt sources, and a 4-byte instruction queue, which can enhance the speed of instruction execution.

2.1 CAN bus interface circuit

Since the MB90F543G microcontroller itself has two CAN controllers, it can be expanded by simply adding a CAN transceiver. This system uses the PCA82C-250C chip produced by Philips as the CAN transceiver. This chip is fully compatible with the ISO/DIS 11898 standard and has high transmission speed (up to 1Mbps), strong anti-interference ability, and can support up to 110 node connections. Therefore, it has been widely used. In this design, in order to protect the CAN transceiver, a surge protection chip NUP2105 is also added. The CAN bus interface circuit in this system is shown in Figure 6.

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2.2 RS485 interface circuit

The RS485 conversion interface is located between the host computer and the communication module. It is mainly used for the host computer to transmit commands to other functional modules and receive feedback data from other modules. This design uses the 6LBCl84 chip as the RS485 transceiver. Similarly, the NUP2105 surge protection chip is added to protect the 6LBCl84 and avoid burning the device. The RS485 interface circuit is shown in Figure 7.

2.3 LCU input control and feedback circuit

The LCU input control circuit is used to control the on and off of the LCU input voltage, that is, to provide a logic input signal for the LCU. The feedback circuit is used to sample the LCU input logic signal and feed it back to the microcontroller to verify whether the LCU input logic meets the requirements. This system uses a KP4010 photoelectric switch to control the on and off of the circuit. The circuit is shown in Figure 8.

2.4 AD conversion circuit

The system uses TLV2556IDW chip as AD converter. TLV2556IDW is a 12-bit AD converter produced by TI. It has 11 analog voltage input channels and programmable output data length. In order to improve the stability of the system and the accuracy of AD conversion, this design also uses ADuMl311BRWZ data isolation chip to isolate data between the AD converter and the microcontroller. In the design, 4 LCU low outputs use 4 analog input ports respectively, while 14 LCU high outputs use 1 analog input port through time-division multiplexing. Its AD conversion circuit is shown in Figure 9.

3 Conclusion

According to the characteristics of the SS4G electric locomotive logic control unit, this paper designs the hardware system of the LCU test bench in detail. Since this design adopts a modular design concept, the system design is simple and easy to maintain. The sub-modules and their functions in the system can fully meet the test requirements of the current electric locomotive logic control unit.