Design and implementation of communication power supply monitoring system based on single chip microcomputer

The communication power supply is the "heart" of the communication network. The stable and reliable operation of the communication power supply system is directly related to the stability and reliability of the communication. At present, the power supply mode of large-scale communication power supply mostly adopts the centralized power supply mode. Once a power supply failure occurs, it will directly cause the paralysis of the entire communication system.

The traditional maintenance method of communication power supply mainly relies on manual supervision, which is labor-intensive and inefficient. It often causes major communication blockages due to equipment failures that are not handled in a timely manner. Therefore, remote real-time monitoring of communication power supply equipment running on the network is conducive to timely detection of power supply failures and reducing human factors, which is very important for ensuring the stable and reliable operation of the power supply system.'

At present, high-frequency switching power supply system equipment is widely used in communication power supply systems, which are highly intelligent. During operation, the power supply system has many specific operating requirements. For example, if the power supply system cannot output the specified current and voltage or the output current and voltage exceed the allowable fluctuation range, and the noise voltage is higher than the allowable value for more than 10 seconds, it is considered a system failure. If the voltage, frequency or waveform distortion in the original AC system exceeds the specified range and lasts for more than 60 seconds, it is also considered a failure.

To this end, in order to ensure the reliability of the communication power supply system, the communication department should try to introduce two mains inputs from two different places, and set up two mains power automatic switching devices; the equipment used should be high-frequency switching rectifier equipment with high reliability.

Modular and hot-swappable structures are used for easy replacement, and backup equipment is configured reasonably. The power supply mode should vigorously promote decentralized power supply, and communication equipment using the same DC voltage should use more than two independent power supply systems. In order to shorten the average fault repair time of the equipment as much as possible, it is necessary to frequently analyze the operating parameters, predict the time of fault occurrence and eliminate it in time. It is also necessary to improve the level of technical maintenance and adopt centralized maintenance, remote telecommunication, and telemetry maintenance.

The implementation of centralized monitoring and management is an inevitable trend in the development of network technology, a requirement of modern communication networks, and an effective measure for enterprises to reduce staff and increase efficiency. Various power supply equipment should be intelligent, standardized, and comply with open communication protocols.

1 Framework structure and overall design requirements

The main function of the communication power supply monitoring system is to monitor the operating status of the power supply at any time; monitor various quality characteristic indicators such as voltage fluctuation, frequency fluctuation, waveform distortion rate, instantaneous surge, transient pulse, three-phase imbalance, etc.; when a fault occurs, it can take corresponding measures and alarm in time. According to the basic mode of centralized maintenance and unified management of communication power supply, the monitoring system is a multi-level distributed computer monitoring network in structure, which can generally be divided into four levels: central monitoring center, regional monitoring center, station monitoring center and front-end field processing part (including intelligent equipment, battery tester, front-end acquisition equipment). The framework structure of the whole system should adopt a tree structure (see Figure 1). The tree structure has good scalability to meet the needs of the continuous development of the communication industry.

Figure 1 Communication power supply monitoring system framework diagram

The main functions of the communication power supply monitoring system are designed as follows:

(1) Real-time monitoring and display of the operating parameters and corresponding working status of each communication power supply equipment. When a device fails, it has an audible and visual alarm function to promptly prompt the staff to troubleshoot the fault; (2) When a fault occurs, it can realize the accurate switching of the master and slave power supplies in a timely manner, and at the same time ensure that the voltage is of the same frequency, phase, and amplitude during switching; (3) It has a complete protection function for the communication power supply system to prevent the system from overvoltage, overcurrent, frequency or phase deviation, and overheating, and take timely measures when the above phenomena occur; (4) Communication function: It has the functions of communication between the master and slave units, and communication with the monitoring center (host computer); (5) It has the function of recording historical data and status.

2 Hardware Circuit Design

DS80C320 is a high-speed, low-power 8-bit microcontroller launched by DALLAS, USA. It uses a newly designed processor core, removes redundant clock and storage cycles, and can increase the execution speed of each identical instruction by 1.5 to 3 times at the same crystal speed. It is compatible with 80C51/80C32 and uses the standard 8051 instruction set.

This system monitors the current, voltage, temperature, frequency and phase of the communication power supply system in real time, and sends the corresponding data to the microprocessor. At the same time, it collects the voltage, working current and ambient temperature of the battery, calculates the internal resistance of the battery regularly and sends it to the memory and microprocessor; and sends the data to the host computer through the microprocessor. The specific modules are divided into microprocessor and peripheral modules, voltage acquisition and test model, current acquisition and test model, temperature acquisition and test model, frequency and phase measurement module, input and display module, control quantity output input module and communication module, as shown in Figure 2.

Figure 2 Monitoring system hardware block diagram

In this system, the microprocessor uses the DS80C320 chip, which improves the reliability of the entire system. At the same time, the corresponding external memory is expanded to accurately record the state of the battery. According to the acquisition accuracy requirements and the characteristics of the collected quantity, the current, voltage and temperature test acquisition module uses AD's high-performance 12-bit successive approximation analog-to-digital converter AD574A to complete the conversion time of 25 s, the linear error is ±1/2 LSB, there are internal clock pulse sources and reference voltage sources, single-channel unipolar or bipolar voltage input, 28-pin dual vertical plug-in package, and ADG508A is used to expand the analog input channel. The frequency and phase difference acquisition test module converts the signal into a square wave through a zero-crossing comparator with hysteresis characteristics, and then sends it to the single-chip microcomputer through a dual four-choice switch 4052, which can fully meet the requirements of the servo system. The frequency and phase difference are calculated through the timer. The main function of I/O control is to realize the effective control of the power supply circuit breaker and the effective switching of the main power supply, backup power supply and backup generator. The input and display module uses 8-bit 7-segment LED display, and the displayed content includes operating data such as current, voltage, frequency and phase difference. These data can be simply selected by pressing buttons, and the operating status is prompted by light-emitting diodes and buzzers. The hardware part of this system uses serial port 1 and RS485 standard interface IZ1 to realize communication with the host computer, and complete functions such as data transmission and remote alarm.

3 System Software Design

3.1 System Software Process

The system software is developed using Labwindows/CVI, a software development platform for measurement and control launched by NI. LabWin-dows/CVI is an interactive C language development platform launched by National Instruments (National Instruments, NI for short). LabWin-dows/CVI organically combines the powerful and flexible C language platform with professional measurement and control tools for data acquisition, analysis and display. It greatly enhances the functions of C language by using its integrated development environment, interactive programming method, function panel and rich library functions, and provides an ideal software development environment for developers and designers familiar with C language to write detection systems, automatic test environments, data acquisition systems, process monitoring systems and other application software.

The flow chart of the main program of the system software is shown in Figure 3.

Figure 3 Main program flow chart

3.2 Main algorithms and functions of the software

3.2.1 Determination of battery intelligent charging and discharging algorithm

Correct and reasonable charging and discharging can effectively extend the service life of the battery. This system has a built-in data model for the battery charging and discharging algorithm. It uses the data collected and uploaded by the lower computer to automatically generate a capacity corresponding curve for comparison and operation, which is used to determine the lower computer's management of the battery's charging and discharging, thereby realizing the battery's intelligent charging and discharging function.

There are many intelligent battery charging and discharging algorithms. The algorithm used in this system is: neural network algorithm.

The neural network algorithm is an artificial intelligence technology that uses computers to simulate the brain's signal processing process. It is composed of a large number of simple neurons that are widely connected to form a complex nonlinear system. It automatically summarizes the collected data and obtains the inherent laws of the data. The battery is a highly nonlinear system, and it is usually difficult to establish a reasonable and accurate mathematical model for its charging and discharging process. Therefore, under the condition of external excitation, the neural network algorithm can use the learning ability and parallel structure of the neural network to simulate the nonlinear characteristics of the battery to estimate the SOC value.

SOC estimation uses a typical three-layer neural network, in which the number of neurons in the input and output layers is determined by the actual system needs, and the number of neurons in the middle layer depends on the system complexity and analysis accuracy requirements. In the neural network method, the system input includes battery voltage, ambient temperature, charge and discharge current, battery internal resistance, cumulative discharge power, etc. Whether the input type and quantity are selected appropriately will directly affect the calculation amount and accuracy of the method model.

3.2.2 Digital filtering algorithm

According to the characteristics of this system with high acquisition accuracy and slow changes in the collected analog quantity, the median filter method is adopted to extract data close to the true value from the sampled data column. Median filtering is to continuously sample a certain measured parameter N times (generally N is an odd number), and then arrange the N sampling values ​​from small to large, or from large to small, and then take the middle value as the current sampling value. Median filtering is more effective in removing pulse interference caused by fluctuations caused by accidental factors or errors caused by sampler instability. It can perform multi-cycle sampling on current, voltage, temperature and other data, and compare it with the effective sampling value after each sampling. If the change amplitude does not exceed a certain amplitude, the sampling is valid; otherwise, it is considered invalid and abandoned.

4 Anti-interference measures

Since there are high-power devices in the system and they have certain electromagnetic interference, once the interference enters the system, it will cause false alarms at best, and even cause the entire system to be paralyzed or even cause major accidents in serious cases. This system has taken anti-interference measures from both hardware and software aspects to ensure the reliable operation of the monitoring system.

In terms of hardware, optical coupling devices are used to isolate the microcontroller from various sensors, switches, and actuators to prevent cross-mode interference. At the same time, decoupling capacitors are added to the power input end to weaken various high-frequency interferences to improve the hardware's anti-interference ability.

In terms of software, the internal programmable hard logic watchdog provided by DS80C320 is used to ensure the security of the program.

5 Conclusion

Compared with conventional power supply systems, the communication power supply system should be able to automatically, continuously and in real time monitor the operation/fault status and operation parameters of all transformers and distribution equipment, and should also have the ability to automatically handle faults in an emergency. Practice has proved that the communication power supply monitoring system based on DS80C320 has excellent performance, fully meets the requirements of high stability of the power supply system, has good anti-interference ability, and ensures the safe and reliable operation of the entire intelligent building.