Design of an intelligent high-frequency switching power supply monitoring module

　　Since the 1990s, the national telecommunications department has gradually accelerated the requirements for network management of communication equipment, requiring that all equipment that constitutes the communication network must have the ability to be intelligent and communicate, and power supply equipment is no exception [1]. The application of computer technology has made communication power supply a high-tech product that integrates computing technology, control technology, and communication technology, greatly improving the performance and functions of the product, thereby realizing automatic testing, automatic diagnosis, and automatic control of the system, and realizing remote communication, telemetry, and remote control of the power supply system [2]. Therefore, high-frequency switching power supplies have also entered the stage of intelligent control. This paper designs and implements a monitoring module for an intelligent high-frequency switching power supply.

　　1. The principle and characteristics of high-frequency switching power supply

　　Intelligent high-frequency switching power supply has the characteristics of highly flexible combination and self-monitoring, especially in the field of communication. It is widely used because of its small size, low noise, easy maintenance and can be incorporated into the computer monitoring system of the communication system. The circuit principle block diagram of the high-frequency switching power supply is shown in Figure 1. It is mainly composed of AC power distribution, rectifier module, DC power distribution module, charging module, main monitoring module and related circuits, among which the charging module and the main monitoring module have built-in microprocessors. This high-frequency switching power supply converts 220V (or 380V) AC power into stable and reliable 48V or 24V DC power to power the load (such as program-controlled switches, optical terminals, etc.), and float charge or balance charge the battery pack. When the AC power input is interrupted, the battery pack supplies power to the load through the system to ensure continuous and uninterrupted power supply to the load. When the AC power returns to normal, the system automatically charges the battery pack and quickly replenishes the power after the battery is discharged in large quantities.

　　The power supply has the following features:

　　The AC input voltage has a wide adaptability range: three-phase 380±30% (266~494V), single-phase 220±30% (154~286V); the
        active power factor correction technology is used to make the power factor ≧0.99 and the overall efficiency is high;
        the PWM edge resonance technology is used, which, on the one hand, reduces the power loss of the switching devices during high-frequency switching and improves the overall efficiency, making the overall efficiency as high as more than 90%, and on the other hand, reduces electromagnetic interference, and the power supply system can be installed in the program-controlled computer room;
        the system adopts microcomputer control, Chinese character display, and keyboard operation, which is easy to master and use, greatly facilitating users.

　　

        Figure 1 High-frequency switching power supply block diagram

　　2. Composition of the main monitoring module of intelligent high-frequency switching power supply

　　Since this power supply system is required to have extremely high reliability, it is very important to monitor and control its operating conditions effectively. As an independent module, the system main monitoring module can monitor the operating conditions of each unit of the entire power supply system, and has the function of collecting, displaying and setting the operating parameters of the system. It can also communicate with an external computer (generally a PC) to form a local or remote centralized monitoring system. When communicating with an external computer interface, the main monitoring module is called the lower computer and the external computer is called the upper computer. Therefore, the main monitoring module must also be able to continuously receive commands from the upper computer, and operate the power supply system according to the commands or send the operating status and parameters of each unit of the power supply system back to the upper computer, control the input and exit of each module, complete the human-computer dialogue, and realize communication with an external computer or a remote host.

　　2.1 Working principle and composition of monitoring module

　　Figure 2 is a block diagram of the main monitoring module [4]. As an independent module, the main monitoring module of the system can monitor the working status of the entire power system, control the input and output of each module, and complete the human-computer dialogue. The module consists of an AT89C52 single-chip microcomputer, an AC/DC power distribution parameter acquisition unit, a display and operation unit, and a serial port communication unit. The monitoring module and the rectifier module exchange information through RS-485 serial communication. This allows the hardware design of the monitoring module to be unrestricted by the number of rectifier modules to be monitored, so that the number of power modules in the system can be expanded arbitrarily. The serial communication method is also used with the host computer. The serial port is expanded through the 8250 chip. For local centralized monitoring, the RS-485 serial port can be used. For remote monitoring, the RS-232 serial port can be used, and communication is carried out through a modem (MODEM) and a telephone line. The system uses a large-screen LCD and keyboard to realize local human-computer interaction. The main monitoring module detects the DC bus voltage and current. When the voltage or current is greater than the upper limit setting value, it commands the rectifier module to reduce the voltage and limit the current. According to the working conditions of each rectifier module, it determines the exit and input of each module, so that the entire power supply system works in a stable state. In addition, the main monitoring system also detects the fluctuation of the grid voltage, sends out an alarm signal, and records the fault information.

　　

        Figure 2 Monitoring system composition block diagram

　　The AC detection unit is mainly composed of a three-phase AC voltage detection board, a three-phase display board, etc. The three-phase AC voltage detection board is installed in the upper AC power distribution part of the cabinet. Its function is to send the isolated AC power signal to the controller, and the controller detects the AC power parameters to determine whether the input AC power is "over-limit" or "phase-missing". When it is "over-limit" or "phase-missing", the controller will issue an alarm. The switching unit sends the frequency signal of the controller to control the output voltage of the rectifier to each rectifier, and sends the detected signal of each rectifier to the controller. These signals include: the frequency signal of the control rectifier output voltage, the voltage signal of the current sharing bus, the current signal of each rectifier, and the alarm signal of the rectifier. The DC detection unit mainly includes a battery current detection board and a battery protection board. Detect whether the load branch DC circuit breaker is disconnected, detect whether the battery branch fuse is disconnected, detect the battery branch current and send it to the controller. The controller detects, displays, and alarms the signals sent by the AC detection unit, the switching unit, and the DC detection unit; and controls the working status of the rectifier. Status query, system operation and parameter setting are implemented through the keyboard.

　　2.2 Main functions of the controller

　　Detection: system AC power supply, battery status, rectifier status, battery current, main branch current and fault content;
        Control: system power on/off, equalization charging on/off, rectifier on/off, battery test on/off;
        Parameter setting: system parameter setting, number of rectifier cabinets;
        Battery parameters: equalization charging voltage, floating charging voltage, overvoltage value, undervoltage value, charging current limit value, conversion current, etc.;
        Monitoring parameters: equipment number, communication interface, dialing method, telephone number and fault reporting on/off, etc.;
        Communication: realize three remote controls through the interface, and output the system alarm signal to the system fault monitor through the fault interface.

　　3. Monitoring system software implementation

　　3.1 Implemented Functions

　　This system adopts a centralized management and independent control mode. Each module's single-chip microcomputer has its own independent control program and communication program with the monitoring module. When an individual module fails, it will not affect the operation of the entire machine. The main monitoring module software adopts a modular structure design, and various functions are completed by corresponding interrupt subroutines. The monitoring module software mainly completes the following functions:

　　(1) Receive data sent by each module;
        (2) Send control commands to each module;
        (3) Human-computer interaction interface. The main control microcontroller in the monitoring module is the host, and the microcontroller in the rectifier module is the slave. They use a 10-bit asynchronous communication format of N, 8, 1, and a baud rate of 4800B. The data sent by the slave to the host can only be sent after the host issues a permission command, that is, the module selected by the address code has the right to send data to the monitoring module.

　　3.2 Main monitoring program

　　The main monitoring software adopts modular structure design, and various functions are completed by corresponding interrupt subroutines. Figure 3 shows the main program flow chart. System initialization includes initialization of MCU internal control registers, register area and data area, etc. Self-test includes RAM self-test and self-test of each sensor of the control system. After the self-test passes, the interrupt and PTS are opened, and the display initialization subroutine is called. The display system main menu can use the keyboard to select each submenu, including operation parameter menu, status menu, fault record menu and parameter setting menu, etc. To ensure safe operation, the parameter setting menu is only available to authorized management and maintenance personnel, and a password is required to operate. [page]

　　

  Figure 3 Main program

　　This monitoring system uses 8×4 Chinese characters to display. Considering that there are many parameters to be monitored, one screen cannot display all of them. Therefore, a menu-based operation method is adopted, that is, select the menu information displayed on the display screen, press the appropriate function key on the keyboard of the alarm module panel, and the system's microprocessor responds to the information sent by the key to achieve the corresponding function. Therefore, the keys include numeric keys and function keys. The program adopts a tree-like branching structure, as shown in Figure 4, the keyboard program flow chart.

　　

        Figure 4 Keyboard program flow chart

　　The core part of the monitoring software is the serial port receiving interrupt subroutine. This subroutine must complete serial port communication, data reception and verification, format conversion, access, control, etc. Due to the large amount of monitored data, each type of data must have a fixed format and adopt an error detection and retransmission mechanism to ensure the correctness of the data. The data processing subroutine mainly completes A/D conversion, data comparison and judgment, digital signal output feedback control, clear interrupts, etc. Figure 5 is a flow chart of the serial port receiving interrupt subroutine.

　　

        Figure 5 Flowchart of the serial port receiving interrupt subroutine

　　4. System anti-interference measures

　　The performance of the monitoring module directly affects the operation of the entire switching power supply. If the anti-interference measures are not fully considered, once interference enters the monitoring module, it will cause false detection and false alarm, which will cause the entire system to fail. This system adopts a combination of hardware anti-interference and software anti-interference in its design.

　　4.1 Hardware Anti-interference Measures

　　In order to improve the input impedance of analog quantity and reduce loss, a voltage follower is added before A/D conversion. After the detected signal voltage is converted into current, a resistor is added to restore it to a voltage signal. A high-precision 12-bit dual-integral A/D converter ICL7109 is used. In order to eliminate the noise interference of digital quantity, a 10uF filter capacitor group is added to the circuit. When the entire system completes the serial port communication with the computer, 6N136 is used for isolation. The watchdog circuit composed of MAX706 is used to improve the anti-interference measures of MCU

4.2 Software Anti-interference Measures

　　Mainly use digital filtering and digital zeroing technology to eliminate the deviation of the switch circuit and A/D conversion circuit, smooth the signal, and eliminate and reduce interference. Specify the format of various data, adopt the verification, error detection and retransmission mechanism to improve reliability. A large number of redundant instructions are used to improve the reliability of software execution.

5. Conclusion

　　The intelligent high-frequency switching power supply and the battery form an uninterruptible power supply system, which can be widely used in places that require high-power DC power supply, such as post and telecommunications, water conservancy and electricity, public security, railways, and computing centers. The switching power supply using the monitoring module in this article can realize the "three remote" and other functions through operation tests, with convenient maintenance, high reliability, normal operation, and all indicators can meet the requirements.