Application of human-machine interface in intelligent silicon-controlled rectifier device

1 System composition and working principle

1.1 System composition

The system consists of 5 parts: transmitter, PLC host, analog input and output module, touch screen, thyristor rectifier, etc. The system control structure is shown in Figure 1. In the control part, SIEMENS's S7-200 PLC is selected to process the sampling signal quickly and reliably, and the programming software is STEP 7-MicroWIN 32 V3.2; SIEMENS's TP270B touch-type human-machine interface (HMI) is selected to display and record real-time temperature values ​​and various fault information, and the configuration software is SIMATIC Pro-Tool V6.0. MPI (multi-point) communication is adopted between HMI and PLC. By defining the component attributes set on the HMI screen and the data exchange address with the PLC, the register corresponding to the relevant components on the HMI can read and write the PLC storage unit.


Figure 1 System control structure


1.2 Working principle

The thyristor rectifier outputs a DC voltage of 0 to 45V, which is continuously adjustable; and outputs a DC current of 0 to 1600A, which is continuously adjustable. The temperature of the main silicon element is sampled by the sensor, and the measured temperature signal is sent to the PLC after amplification and A/D conversion. The data is processed by software, and the processed data is sent to the HMI for real-time display. The over-temperature alarm and over-temperature trip temperature limit values ​​are set on the HMI. When the temperature of the main silicon element is too high and exceeds the limit value, the PLC will output an over-temperature alarm signal and an over-temperature trip signal, and display specific information on the HMI. At the same time, the current and voltage of the excitation coil are precisely controlled by PI, and the parameter values ​​of the PI algorithm can be set on the HMI. The data acquisition processing, fan operation and fault alarm in this system are completed by the PLC and HMI through the compilation of corresponding software.

2 System software design

SIMATIC ProTool is an HMI configuration software launched by Siemens. The software consists of two parts: ProToolCS (configuration system) and ProTool RT (running system) for process visualization. The software has multiple functions such as alarm recording, report printing, trend curve, etc., and supports communication protocols of third-party manufacturers other than Siemens. Based on it, this system has carried out a series of application developments such as screen design, communication configuration, alarm setting, and safety protection design.

2.1 Touch screen screen design

The touch screen screen design not only requires the realization of all control functions (input and display parameters, storage records, alarms, etc.), but also needs to be simple and clear, so that operators can perform operations correctly. Considering the process variables and actual functions that the system needs to monitor, a total of 5 groups of screens are configured. The following introduces several basic screens.

⑴ Main screen

The top of the designed monitoring main screen is the real-time display curve of the excitation current, and below it are two display boxes that display the excitation current and voltage values ​​in real time. There is also an input box for setting the current value. When the hand is pressed in this position, a digital option box can pop up to facilitate the input of the current setting value. There are two fine-tuning keys on the right side of the box. Each press can add or subtract 1. At the bottom of the main control interface is the equipment operation status display box, which can display the system status in real time (system on, off, fault information, etc.). The lower right corner of the monitoring main screen is the function selection pop-up menu, which is mainly composed of the working status bar, parameter setting bar, alarm record bar, etc. As shown in Figure 2.

(2) Real-time display of temperature, current and voltage

During display, the touch screen reads only one digital value from the PLC at a time in each time unit (clock pulse) and adds it to the corresponding physical value displayed on the operating unit. Three groups of real-time data are configured in this program, each of which displays three analog quantities: temperature, excitation current and voltage of the silicon main component.

⑶ Parameter setting

In this screen, the operator can set and adjust the automatic start/stop temperature of the fan, the over-temperature alarm temperature and over-temperature trip temperature of the silicon main component, as well as the over-current value and over-voltage value. Operators with the highest level of authority can also set the parameters () in the PID algorithm, which makes it very convenient to perform online parameter setting of the system.

⑷ Fault record

Whenever an alarm signal is generated, an alarm message window will pop up on the touch screen interface, and the alarm light will flash. Archive the alarm message and create a screen configuration message view to save and display all alarm messages since the system was running. Prompt the alarm number, the date and time of the alarm, the cause of the alarm, and whether it is confirmed.

2.2 Security Protection Design

ProTool allows users to use passwords to prevent other unauthorized personnel from using controls, thereby increasing the security of the system. ProTool provides password levels from 0 to 9. Password level 0 does not require a password; password levels 1 to 8 are assigned according to the importance of the function; password level 9 is only authorized to system administrators. In response to the needs of security management and operation, the system defines two levels of passwords: system administrator level 9 and operator level 1. The system administrator level password is required for PID parameter setting. Other operations, such as temperature alarm limit and power-on soft start time, also require password input to log in first. Enter the password, touch the "Login" button, and then touch other function buttons to enter the sub-screen equal to or lower than the password level. After the sub-screen operation is completed and returned to the main screen, touch the "Exit" button, the password will become invalid, and the password must be re-entered to enter the sub-screen again. If the "Exit" button is not touched, the system will automatically revoke the password after 1 minute.


Figure 2: Monitoring main screen


2.3 Communication between HMI and PLC

There are three communication modes between Siemens HMI and PLC: PPI (point-to-point) communication mode, MPI (multipoint) communication mode and PROFIBUS-DP communication mode.

MPI (multipoint) communication mode is adopted in this system. Since the MPI interface is RS485 structure, PLC and HMI are connected through RS485 line, and its transmission rate is 187.5k baud rate. An MPI network can have multiple network nodes, and its address is set in the S7-200 hardware configuration. The MPI address of the HMI in this system is "1"; the MPI address of the CPU is "2". The HMI and the process communicate through variables through PLC. Usually, the data exchanged between PLC and operating unit is process data. For this purpose, a variable pointing to an address on PLC is created in the configuration. The touch screen reads the value from the specified address and displays it. Similarly, the operator can input data on the touch screen that will be written to a certain address on the PLC.

3 Conclusion

The 1600A/45V intelligent thyristor rectifier device combines PLC and touch screen together, and uses the corresponding software of PLC and touch screen to control and process each sampling value. It has great advantages in real-time display, data recording, and alarm of temperature, current, and voltage. The operator can not only conveniently observe and grasp the real-time operating temperature of the device, but also quickly troubleshoot according to the alarm message; with the help of historical records, the management personnel can also analyze and query important data, which can greatly improve the level of operation management. At present, the device has been applied in Ganzhou Jinhuan Magnetic Separation Equipment Co., Ltd.