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Plc Controller

By the PLC-controlled thyristor AC electronic switch-PLC, electronic switches - Electrical industry

This paper introduces the electric railway series compensation device working principle and the role of Thyristor AC electronic switch. Highlighted 1600A1000V thyristor electronic switches in the programmable logic controller communication (PLC) system hardware and software and its installation in the role. Finally on the device can do a brief summary of the technical. See more exciting information

1 Overview Electric Of Railway (hereinafter referred to as electric iron) related to the harmonic problem is a common power quality and electric iron smooth building issues, my office started from the 80's efforts to study and solve the problem. Series Compensator To a certain extent, address this issue, and because of its technical difficulty is low, investment in small, easy to implement, thus the double-track electrified railway in the single renovation project has demonstrated a great advantage.

Series compensation device works in the heavy load of electric railway power lines, line inductance serious losses by investing in pre-series in the loop Capacitor Change the circuit load type, so as to achieve to improve network pressure and improve the power factor effect. Shown in Figure 1. As the power of iron overload is an exercise load, load size is not only related to the number of locomotives, but also with the locomotive truck, locomotive operations, lines of slope and other factors closely related. Capacitor switching operation is also quite frequent. If you use the machine (with contact) switches, because of its switching time relative to the network then the phase of pressure, the contact of zero absorption in the non-timely and will be due to large short-circuit power capacitor current impact, the electrical life is usually Only dozens of times. Therefore, series compensation device must use thyristor AC Electronic Switch to achieve zero power capacitor switching.

2 SCR AC electronic switch control system requirements and PLC Selection

Exchange electronic switch thyristor main circuit composed of two anti-parallel thyristor branch structure, each branch formed by two parallel thyristor, a total of four thyristors used tube (connection mode shown in Figure 2). In accordance with the electrical Chemical industry Process design requirements, SCR AC electronic switch installed in the traction transformer near the mobile home, the combined application condition of the device on the control system the following requirements:

(1) should have a high degree of reliability, to meet the electricity for the grid iron is running a long-term objective requirements;

(2) should have a sound accident alarm system, after the failure should be directed to the fault type, fault-free operation should be instructed out of the power capacitor switching state;

(3) should have a sound logic control and automatic protection function;

(4) shall ensure that the thyristor is triggered at the crossing point of voltage;

(5) should have good electromagnetic compatibility, to adapt to traction Transformer substation Field of complex electromagnetic environment.

Complete control of electronic switches can be in three ways: Development of special control using integrated circuit board; microcomputer and peripheral circuits developed using the special control circuit board; expansion module development using PLC and dedicated control system. As with the control PLC reliability, configuration flexibility, small size, powerful functions, fast and good scalability, easy maintenance, not only reduces the hardware connection, improved reliability, and by modifying the program can adapt to new requirements Therefore, the exchange of electronic switch SCR 1600A1000V selected minicomputer Siemens S7? 200 series of PLC control system as the core component.

3 PLC control system structure and its role in the exchange of electronic switches

(1) hardware structure and its role

In this device, PLC control systems, minicomputers selected Siemens S7? 200 series of the CPU222, analog expansion module EM231 and text display TD200. Distribution of resources available hardware system diagram as shown below:

CPU222 PLC control system is the CPU unit, responsible for receiving all of the switching capacity and through the A / D converted analog input and output under the control of logic control signal; EM231 responsible for the main circuit voltage, current signal for A / D conversion, and transport to the CPU unit conversion result; TD200 text display output unit responsible for monitoring CPU state, according to a combination of the various output indicators of the condition the thyristor electronic switches running status and fault type.

(2) Formation and function of software

In this device, PLC control system, the software has two parts: a text display software and logic control software. Stored in a text display text display software to display all the text and the CPU unit output combinations correspondence.

Thyristor logic control software includes all the electronic switch control logic, the software structure of the main program by the 1, 2 sub-programs, two timer interrupt program constitutes. Its main function is: According to the control requirements, to achieve the voltage and current detection, timely issue of trigger signals, as well as over voltage, over current, fan, Power supply Various categories such as fault detection and alarm signals in time, to achieve protection. The software flow chart shown in Figure 4.

4 Thyristor control strategy Thyristor AC electronic switch is a device connecting the core components of compensation, thyristor Thyristor control strategy is the key to the exchange of electronic switch technologies. To achieve zero trigger thyristors to be dependent on the main circuit voltage of phase synchronization, and once the thyristor device, synchronization signal will disappear, this is the thyristor trigger circuit design is important to note One of the problems. In addition, the thyristor does not turn, its withstand voltage and the voltage power capacitors to withstand the same phase, while the conduction circuit after the change because the circuit occurs a transition process, which is designed to note thyristor trigger circuit the problems.

5 Conclusion

PLC integration as high anti-interference ability, programming is simple, the system easy to develop, maintain and upgrade advantages, combined with text display can clearly understand the instructions of the thyristor conduction, and display all types of cut-off state fault state, the use of PLC control system of thyristor AC electronic switch of simple structure, easy maintenance and high reliability, maintainability and flexibility.

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