1 Introduction
With the rapid development of computer technology, network technology, and large-scale integrated circuits, dynamic signal analysis systems are showing a trend towards networking. Embedded systems, which are based on computer technology, chip technology, and software, have once again become a hot topic in research and application. Compared to general-purpose computer systems, the biggest characteristic of embedded systems is their strong purposefulness and specificity; each embedded system is designed and developed for specific applications and functions, and typically features high real-time performance, low power consumption, small size, high integration, and low cost.
Remote Energy Data Acquisition Terminals (ERTUs) are intermediate devices in energy metering systems, positioned between the metering master station and the rate-determining device (energy meter). Their main functions include energy data acquisition, processing, storage, and forwarding. Embedded technology has a long history in power systems; several years ago, China began introducing power grid monitoring systems based on embedded real-time operating systems (RTOS). With the continuous improvement of power system automation and the rapid development of embedded technology in recent years, embedded technology is increasingly widely used in various fields such as data acquisition, status monitoring, automatic devices, microprocessor-based protection, and distributed control. In particular, due to the dispersed nature of electricity users and the need for networked management, the application of embedded technology in energy metering systems will greatly improve system performance.
2. Overview of Embedded Power Harvesting Systems
Electricity data acquisition systems have broad application prospects as a technical support for electricity marketing and the future commercial operation of power grids. The system mainly consists of four parts: a master station computer system, power data acquisition devices at substations, multi-functional electronic power meters, and an information and communication network, involving professional knowledge in electronics, computers, communications, networks, power systems, and other fields.
With the establishment of the electricity market and the development of information technology, the development of power data acquisition systems has shown new characteristics: (1) Higher degree of networking. In addition to having multiple interfaces and a built-in modem, remote power data acquisition terminals (ERTUs) should also have network functions, have network interfaces, and comply with the TCP/IP standard protocol; data transmission is safe and reliable, and have user-oriented information query functions and auxiliary information release functions; (2) Automatic meter reading (ARM) is a system in which the power supply department collects the electricity consumption recorded by the electricity meters installed at the user's location through telemetry, transmission and computer systems and summarizes it to the business department, replacing manual meter reading and a series of subsequent work.
The implementation of ARM will overcome the time-consuming, labor-intensive, error-prone, and difficult nature of manual meter reading, as well as the difficulties of door-to-door meter reading, which will help improve the level of power distribution automation; (3) The Remote Energy Data Acquisition Terminal (ERTU) adopts an embedded CPU and an embedded real-time multi-tasking RTOS to form a complete embedded system. Based on the RTOS, combined with embedded Web server technology, it can realize real-time and dynamic interactive query functions, providing strong support for the decision analysis of power management personnel. The ERTU adopts timed or real-time start of meter reading tasks, reads the power information and event information in the smart energy meter through the RS-485 bus, and supports standard RS-485 serial port data output. Each ERTU device can be connected to multiple RS-485 buses, so that multiple meters of electricity information can be collected at the same time. Based on the development of the aforementioned power acquisition system, a new type of power acquisition terminal was developed in this system research. Its hardware utilizes a popular PC104 CPU, ensuring high-speed and high-reliability operation. Its bus-based design allows for easy interface expansion, and the use of an electronic disk as storage ensures data integrity even after power failure. The control platform employs a real-time embedded Linux operating system with a multi-process/thread design, allowing concurrent operation of various program modules and significantly improving system efficiency. Smart meters at each power metering point measure power. The data acquisition system collects data from these meters and stores it. The collected data is transmitted to the main station system via a dedicated line, specifically the GPRS network of a mobile company, enabling remote communication with the control center. The data acquisition system adopts a modular plug-in structure, primarily consisting of an interface module, an RS-485 acquisition module, a main control module, and a remote communication module (Modem). All modules are connected and managed through the main control module. The data acquisition device employs a timed meter reading function or can be remotely controlled. It reads the electrical energy information stored in the smart meter via an RS-485 bus and stores event information in the acquisition device in time-segmented manner. The data acquisition system has the capability to convert between different meter protocols. Corresponding acquisition programs have been written for different meters, and a program library has been established.
3. Main functions of the embedded power harvesting system
The newly developed energy acquisition system integrates data collection, storage, processing, and wireless uploading functions. The system can collect 32/64 pulse input signals with a pulse scan period of 10ms and a sampling resolution of no less than 40ms. It features hardware filtering, and software filtering based on the energy meter type and pulse width. The system provides four RS-485 interfaces, each capable of connecting up to 32 multi-functional electronic energy meters, with potential for expansion. The collection interval can be set remotely by the master station or at the system itself. Each data point read from the energy meter is added with time information and stored as time-stamped data. The system's time information is accurately synchronized via a GPS module. The system uses a GPS clock for time synchronization and can broadcast time synchronization to multi-functional electronic energy meters. This embedded energy acquisition system can communicate with both pulse-type and digital interface fully electronic energy meter terminals. It also provides a GPRS interface supporting TCP/IP protocol, uploading data to the master station server via the GPRS network. The system's functional structure diagram is shown in Figure 1.
4. System Implementation
4.1 Hardware Structure of the Data Acquisition Unit
The system's core hardware uses a standard PC104 "mezzanine bus" and an embedded operating system to provide an application platform, improving the standardization of hardware and software design and system reusability. The microprocessor uses an Intel 486 processor platform with a speed of 100MHz and is programmable. It includes an Ethernet interface supporting the TCP/IP protocol. The memory is divided into two parts: a 512kB FLASHEPROM (for storing the running program and intermediate variables) and a 64MB DiskOnChip (for storing the collected electricity data, expandable up to 1GB). A 4-channel multi-serial port card with a PC104 interface is used to expand the serial ports to eight for connecting to local electricity meters. The system also uses the following user interface devices: a monochrome LCD screen compatible with a standard LCD interface with a resolution of 320×240; and an input keyboard connected via a PC-AT keyboard interface for user input.
As can be seen above, the main PC peripherals are all concentrated on a relatively small motherboard, including: CPU, memory, bus controller, standard serial communication port, standard parallel communication port, standard IDE disk drive interface, standard VGA driver chip, LCD display interface, mouse/keyboard interface, and watchdog monitoring chip. A single motherboard, along with power supply, display, and storage devices, forms a powerful and compact industrial-grade PC.
4.2 System Time Synchronization Module
The time of the data acquisition unit is calibrated by the synchronization time signal output by the GPS standard module. The GPS module communicates with the data acquisition unit through the RS-232 interface. The electricity data collected from the electricity meter is added with time information, stored in the electronic disk, and then uploaded to the master station as time-stamped electricity data.
