Abstract: Uninterruptible power supply (UPS) is widely needed in both industrial and civil applications. To address this, an intelligent control device was developed to manage a dual-power supply system. An ARM processor is used to assess the power supply status and implement corresponding controls, achieving automatic switching between primary and backup power supplies.
Keywords: dual power supply; control system; switching device; ARM
0 Introduction
With the development of the power industry, power quality has received increasing attention. Continuity of power supply is a crucial aspect of power quality, especially important for certain power-consuming sectors such as hospitals, airports, and large production lines. Ensuring power continuity involves providing the power source with two independent power supplies—a primary and a backup—and monitoring both in real time. When one power supply fails, the system can accurately switch to the other according to a pre-defined switching procedure, maximizing power continuity. Current high-voltage dual-power switching devices have two high-voltage disconnect switches with clearly defined isolation points, ensuring better safety during maintenance. However, they require two sets of drive mechanisms working in tandem, significantly limiting the product's reliability. The control system developed in this paper uses a single drive mechanism to operate both the primary and backup power supplies, with real-time monitoring on both sides. Moreover, when a fault occurs, it can safely and reliably realize power conversion and has communication function [1]. It can realize automatic switching of dual power supply in the absence of human supervision, with a switching time accurate to 0.3s. It also has a variety of working modes such as self-starting and self-recovery, self-starting without self-recovery, and manual operation. It can be widely used in metallurgy, fire protection, chemical industry, coal mine, high-rise buildings and residential communities.
1. Main Structure
The high-voltage dual-power automatic switching system consists of two main parts: the device body and the controller. The device body, as shown in Figure 1, comprises two circuit breakers with electric operating mechanisms and accessories (auxiliary alarm contacts, etc.), mechanical interlocking mechanisms, electrical interlocking, fuses, and terminal blocks.
2 Dual Power Supply Conversion Controller
2.1 Composition
The controller consists of an ARM processor and modules for input/output, display, power supply, and RS485 communication, as shown in Figure 2. The CPU uses an S3C44BOX as the microprocessor. The enhanced features of the ARM processor on the basic RISC architecture achieve a good balance between high performance, low code size, low power consumption, and small silicon size. Input/output uses the 74LS164/165 serial interface chip, the LCD module uses an LCM122×32, the RS232/RS485 interface uses Maxim series chips for level conversion, the controller's real-time clock is implemented using a DS1302, the Flash Memory is an SSTT 39VF020 memory, and an ISSI 62LV1024 SRAM chip is used as the external data exchange area. Two-channel three-phase voltage and current sampling is completed using an isolation transformer, with a sampling accuracy of 1%. The controller power supply voltage is 220V (50Hz/60Hz) or 12V/24V DC power.
2.2 Functions
The dual power supply conversion controller monitors both the main and backup power supplies and primarily performs the following functions:
(1) Measurement and Display: It can measure the phase voltage, current, frequency, and power factor of two three-phase circuits, and detect the status of the transfer switch, such as closed, open, or tripped. If there is overvoltage or undervoltage in the two power supplies, the DC voltage signal obtained by sampling and rectification will be larger or smaller than the set required voltage. If there is a phase loss, the DC voltage obtained after rectification will be lower than the DC voltage obtained after three-phase rectification, and a zero-crossing phenomenon will occur. The system status is displayed on the panel using an LCD and LEDs.
(2) Judgment and control: After a delay judgment on the power supply quality of the two circuits, the controller has an adjustable automatic switching time of 0 min to 1.5 min to control the switching of the transfer switch. The transfer switch can be two mechanically interlocked contactors.
(3) Programming and settings: Allows users to change and set the working status "automatic/manual", "one-way priority power supply, two-way priority power supply and no priority power supply", communication parameters, and various delay parameters required for switching.
(4) DC power supply: The controller can be powered by an external DC power supply (12V~24V) or not; if not connected, the system will alarm when there is no voltage in either of the two A phases.
(5) Parameter tuning: All parameters of the controller are digitally adjusted, and each parameter can be adjusted independently, thus not affecting other parameters and improving the reliability and stability of the whole machine. During the switching process between the two power supplies, in order to stabilize the power supply circuit and ensure the accuracy and safety of the switching process, and to avoid malfunctions caused by short-term voltage changes, a manual delay is required. The delay time is selected by the user through a range switch and input to the system via a switch input.
(6) Dual power supply dual-splitting state: When the system load is in dual-splitting state, regardless of whether the two power supplies are normal or the system is in the preset state of "manual" and "automatic", the system still maintains dual-splitting state [2].
(7) Product protection functions: It has overload and short circuit protection, phase loss and open circuit protection, and undervoltage and overvoltage protection.
(8) High-performance ARM program control: Adopts a modular structure design, possesses strong anti-electromagnetic interference capability, is suitable for use in complex environments with strong electromagnetic interference, and operates without noise. It adopts an embedded installation method, has a compact structure, and saves energy and reduces consumption. It complies with national green electrical product standards. It also has RS232 and RS485 serial communication interfaces, and with the help of software running on a PC or data acquisition system, it can provide a simple and practical dual-power switching management solution for industrial and civil buildings.
2.3 Software System
In high-voltage environments, interference such as power fluctuations and electromagnetic radiation is unavoidable. When encountering strong interference, running programs may experience anomalies, errors, crashes, or even infinite loops, leading to system collapse. Therefore, in addition to adding anti-interference measures to the circuitry, the selection of the microcontroller model and certain software measures are also necessary. A watchdog program was implemented in the software to monitor system operation.
The controller's software functions primarily focus on detection and control, and is written in C language. The external hardware circuitry has already handled voltage fault detection; the program only needs to read the corresponding fault status bit inputs, perform bit checks, and then proceed to the appropriate fault handling program. Controlling the switching process is one of the core functions of the dual power supply converter controller. The software flowchart of the dual power supply converter controller is shown in Figure 3.
2.4 Anti-interference measures
Interference can affect the stable operation of the controller, so various anti-interference measures have been adopted in the circuit design:
(1) By transmitting information through isolation devices, the microcontroller is electrically isolated from various sensors, switches, etc., which can effectively prevent cross-mode interference.
(2) Arrange the ground wires reasonably, separate the digital ground and analog ground in the system, and finally connect them at one point. This avoids the interference of digital signals on analog signals.
(3) Add a decoupling capacitor to the power input terminal to reduce various high-frequency interferences.
3. Remote monitoring module
Remote monitoring consists of three main parts: equipment status and power parameter acquisition, GPRS communication network and monitoring center. Power equipment is installed on the production site, and the equipment status and power parameters are collected through the on-site control system. The GPRS communication network is the bridge for data transmission between the monitoring center and the on-site equipment. Through the GPRS network, the relevant parameters of the on-site equipment can be transmitted to the monitoring center computer on a regular basis. The monitoring center communicates bidirectionally with the on-site monitor through the GPRS network on the one hand, and provides a visual interface for users on the other hand, so that users can understand the relatively real-time operating status of the remote equipment without leaving home [3]. The structure of the remote monitoring module is shown in Figure 4.
4. Experimental Testing
According to national technical standards, this study conducted performance index tests on the successfully developed sample. The test results show that the controller can identify different set fault conditions and act accurately according to the user's requirements. The test results fully meet the design requirements and actual use needs.
5. Summary
The dual-power supply conversion controller developed in this paper can detect overvoltage, undervoltage, and phase loss faults in both power supplies. It not only supports various operating modes such as automatic transfer and reset, constant only, standby only, automatic transfer without reset, automatic trip detection, and power-off re-trip, but also accurately and reliably switches between the two power supplies. Its main features include: ① a 3-position automatic isolation switch with 3 switching positions; ② the need to release the safety lock before full disconnection to prevent source selection; ③ a manual switching mode in addition to the automatic switching system, providing a backup operating method.
References:
[1] Li Yu, Li Zhongxi. Development of an automatic switching device for intelligent dual-power supply system [J]. Power System Technology, 2003, 27(11): 68-71.
[2] Dong Xinzhou, Bi Jianguang. Analysis of transient traveling waves in power distribution lines and research on grounding line selection [J]. Proceedings of the CSEE, 2005, 25(2): 1-6.
[3] Xi Gang, Wang Wenbo, Chang Yongyu. Principles and Applications of Mobile Communication [M]. Beijing: Beijing University of Posts and Telecommunications Press, 2002.
For details, please click: Research on Intelligent Control System for High Voltage Dual Power Supply
