Development of intelligent control system for high voltage dual power supply

0 Introduction

With the development of the power industry, people pay more and more attention to the quality of power. The continuity of power supply is an important aspect of power quality, which is particularly important for some power-consuming departments, such as hospitals, airports, and large production lines. The way to ensure the continuity of power supply is to provide the power supply object with two independent power supplies, the main and the backup power supply, and monitor both power supplies in real time. When one side of the power supply fails, it can accurately complete the switch to the other side of the power supply according to the set switching program to maximize the continuity of power supply. The new high-voltage dual power supply switching device now has two high-voltage isolation switches with obvious isolation breaks. It better ensures the safety of maintenance, but requires two sets of drive mechanisms to be linked, so the working reliability of the product is greatly restricted. The control system developed in this paper can drive the main and backup power supplies with one set of drive mechanisms, and both sides can achieve real-time monitoring. When a fault occurs, it can realize power conversion safely and reliably, and has communication function. It can realize automatic switching of dual power supplies without anyone on duty. The switching time is accurate to 0.3s, and it has multiple working modes such as automatic start and automatic recovery, automatic start without automatic recovery, and manual. It can be widely used in metallurgy, fire protection, chemical industry, coal mines, high-rise buildings, residential areas and other places.

1 Main structure

The high-voltage dual power automatic switching system consists of two parts: the device body and the controller. The device body is shown in Figure 1, which consists of two circuit breakers with electric operating mechanisms and accessories (auxiliary alarm contacts, etc.), mechanical interlocking mechanisms, electrical interlocking, fuses, wiring terminals, etc.

Figure 1 Device body

2 Dual Power Conversion Controller

2.1 Composition

The controller consists of ARM and input/output, display, power supply and 485 communication modules, as shown in Figure 2. The CPU uses S3C44BOX as the microprocessor. The enhanced features of ARM on the basic RISC structure enable the ARM processor to achieve a good balance in high performance, low code size, low power consumption and small silicon chip size. The input/output uses the serial interface chip 74LS164/165, the LCD module uses LCM122×32, the RS232/RS485 interface part uses the Maxim series chip for level conversion, the real-time clock of the controller is implemented with DS1302, the Flash Memory uses SSTT's 39VF020 memory, and the ISSI's 62LV1024SRAM chip is used as the external data exchange area. The sampling of the two-way three-phase voltage and current is completed by an isolation transformer, and the sampling accuracy is 1%. The power supply voltage of the controller is 220V (50Hz/60Hz) or 12V/24V DC power supply.

Figure 2 Controller structure

2.2 Functionality

The dual power conversion controller monitors the main and backup power supplies and mainly implements the following functions:

(1) Measurement and display: It can measure the two-way three-phase voltage, current, frequency, power factor, and detect the state 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 zero crossing will occur. The system status is displayed on the panel using LCD and light-emitting diodes.

(2) Judgment and control: After the controller makes a delayed judgment on the power supply quality of the two circuits, it has an adjustable automatic switching time of 0min to 1.5min to control the switching of the transfer switch. The transfer switch can be two mechanically interlocked contactors.

(3) Programming and settings: Allows the user to change and set parameters such as the working status "automatic/manual", "one-way priority power supply, two-way priority power supply and no priority power supply", communication parameters, various delays required for conversion, etc.

(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 A-phase voltage on both circuits.

(5) Parameter setting: All parameters of the controller are digitally adjusted, and each parameter can be adjusted separately, so it will not affect other parameters, which improves the reliability and stability of the whole machine. In the process of switching between two power sources, in order to stabilize the power supply circuit, ensure the accuracy and safety of the switching process, and avoid false operations caused by short-term voltage changes, artificial delay is required. The delay time is selected by the user through the step switch and input into the system by the switch quantity.

(6) Dual power supply dual split state: When the system load is in the dual split state, regardless of whether the two power supply groups are normal and whether the system is in the "manual" or "automatic" preset state, the system will still maintain the dual split state.

(7) Product protection function: overload and short circuit protection, phase failure and circuit break protection, loss of voltage and undervoltage protection.

(8) High-performance ARM program control: It adopts modular structure design, has strong anti-electromagnetic interference ability, is suitable for use in complex environments with strong electromagnetic interference, and operates without noise. It adopts embedded installation, compact structure, energy saving and consumption reduction, and complies with national green electrical product standards. It also has RS232 and RS485 serial communication interfaces. With the help of software running on 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 a high-voltage environment, it is inevitable to encounter interference such as power fluctuations and electromagnetic wave radiation. When encountering strong interference, the running program will produce exceptions, errors, runaway, or even dead loops, causing the system to crash. Therefore, in addition to adding anti-interference measures to the circuit, the selection of microcontroller models and some software measures are also necessary. A watchdog program is set in the software to monitor the operation of the system.

The software functions of the controller are mainly detection and control, and are written in C language. The external hardware circuit has completed the determination of voltage faults. The program only needs to read the corresponding fault status bit input and enter the corresponding fault handling program after bit judgment. The control of its switching process is one of the core functions of the dual power conversion controller. The software flow of the dual power conversion controller is shown in Figure 3.

Figure 3 Dual power conversion controller software flow

2.4 Anti-interference measures

Interference will affect the stable operation of the controller, so a variety of anti-interference measures are taken in circuit design:

(1) Transmitting information through isolation devices and electrically isolating the microcontroller from various sensors, switches, etc. can better prevent cross-mode interference.

(2) Arrange the ground wire reasonably, separate the digital ground and analog ground in the system, and finally connect them at one point to avoid interference of digital signals on analog signals.

(3) Add decoupling capacitors at the power input end to weaken various high-frequency interferences.

3 Remote monitoring module

Remote monitoring includes three parts: equipment status and power parameter collection, GPRS communication network and monitoring center. Power equipment is installed at the production site, and the equipment status and power parameters are collected through the on-site control system; the GPRS communication network is a 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 at regular intervals: the monitoring center communicates with the on-site monitor through the GPRS network on the one hand, and provides users with a visual interface on the other hand, so that users can understand the relatively real-time operating status of remote equipment without leaving home. The structure of the remote monitoring module is shown in Figure 4.

Figure 4 Remote monitoring module diagram

4 Experimental testing

According to national technical standards, this study conducted performance index tests on the successfully developed samples. The test results show that the controller can identify different set fault conditions and act accurately according to user requirements. The measured results fully meet the design requirements and actual use needs.

5 Conclusion

The dual power conversion controller developed in this paper can detect overvoltage, undervoltage and phase failure of dual power supplies, and can not only realize the working modes of automatic switching and self-recovery, normal only, standby only, automatic switching without automatic recovery, automatic tripping detection, power failure and re-tripping, but also accurately realize the reliable switching between the two power supplies. The main points are as follows: ① It is equipped with a 3-position automatic isolation starter with 3 switching positions; ② In order to prevent the source selection from fully disengaging, the safety lock must be unlocked first; ③ In addition to the automatic switching system, the operating mechanism also retains the manual switching mode, providing a backup operation method.