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KR-102963800-B1 - PLC CONTROL SYSTEM

KR102963800B1KR 102963800 B1KR102963800 B1KR 102963800B1KR-102963800-B1

Abstract

It implements a redundant control environment that enables rapid switching and recovery at low cost, without replacing existing PLCs with expensive dedicated redundancy equipment. A PLC control system according to one aspect of the present invention is a PLC control system that receives a sensor signal from an external facility and outputs a control signal, comprising: a first PLC control unit that receives the sensor signal and generates a first control data; a second PLC control unit that receives a signal identical to the sensor signal in parallel and generates a second control data; a control output selection unit connected to the output paths of the first PLC control unit and the second PLC control unit, and controlled to transmit either the first control data or the second control data to an external facility according to an input selection control signal; and a switching control unit that generates a selection control signal to the control output selection unit according to whether the first PLC control unit is abnormal or user input, wherein the control output selection unit may be controlled such that the second control data is selected when a selection control signal from the switching control unit is applied while the first control data is selected.

Inventors

  • 양희원

Assignees

  • 주식회사 상하

Dates

Publication Date
20260512
Application Date
20251126

Claims (7)

  1. In a PLC control system that receives sensor signals from external equipment and outputs control signals, A first PLC control unit that receives the above sensor signal and generates first control data; A second PLC control unit that receives a signal identical to the sensor signal in parallel to generate second control data; A control output selection unit connected to the output paths of the first PLC control unit and the second PLC control unit, respectively, and controlled to transmit either the first control data or the second control data to an external facility according to an input selection control signal; and It includes a switching control unit that generates a selection control signal to the control output selection unit according to whether there is an abnormality in the first PLC control unit or user input, and The control output selection unit is controlled so that the second control data is selected when a selection control signal from the switching control unit is applied while the first control data is selected, and The above control output selection unit is, It includes a plurality of switching elements connected in series to the output paths of the first control data and the second control data, respectively. The plurality of switching elements are configured to conduct either the output path of the first control data or the output path of the second control data according to the selection control signal, and The above control output selection unit internally calculates a switching judgment index, which is a weighted switching criterion considering load state, current magnitude, or output response delay, and then switches. The above conversion judgment index is defined as in the following mathematical formula 2, and [Mathematical Formula 2] (Here is the load current magnitude of the output path, is the response delay time for control commands, ε is the contact resistance of the switching element, and α, β, and γ are weights representing the importance of each element on the switching timing. The first PLC control unit and the second PLC control unit are configured to continue receiving the sensor signal and storing the input history, respectively, even after the control output is switched by the switching control unit. The above input history is utilized as diagnostic data for comparing and analyzing the abnormal occurrence sections between the first PLC control unit and the second PLC control unit, and The above input history may consist of a combination of time stamps and state variables, and the difference in input logs between the two control units is calculated by a comparison index D(t) defined by the following mathematical formula 3, and [Mathematical Formula 3] (Here is the input value of time point t stored in the first PLC control unit, and is the input value at the same point in time stored in the second PLC control unit), PLC control system.
  2. In Article 1, The above switching control unit is, A PLC control system characterized by detecting an abnormal signal from the first PLC control unit or receiving a switching command signal input from a user to generate the selection control signal.
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  5. In Article 1, The sensor signal is configured to pass through a noise removal unit provided in a common input path before being input to the first PLC control unit and the second PLC control unit, and A PLC control system characterized by the above-mentioned noise removal unit including at least one of a filter element that blocks high-frequency noise components, a surge absorption element, or a ground isolation circuit.
  6. In Paragraph 5, A PLC control system characterized by additionally connecting the noise removal unit to the output path of the control output selection unit to prevent distortion of the control signal transmitted to external equipment.
  7. In Article 1, The first PLC control unit or the second PLC control unit periodically receives environmental condition data indicating internal humidity or the possibility of corrosion, and A PLC control system characterized by outputting a control signal to drive an external gas supply source or an air circulation source when the above environmental state data is greater than or equal to a preset threshold value, thereby controlling the circulation of internal air in a space accommodating the first PLC control unit and the second PLC control unit.

Description

PLC Control System The present invention relates to a PLC control system used in industrial automation processes, and more specifically, to a PLC control system that implements redundant control using a relay-based switching method while maintaining an existing PLC. As industrial automation facilities become more advanced, Programmable Logic Controllers (PLCs) are used as core control devices in most sites, including power plants, water purification plants, pumping stations, chemical plants, and manufacturing lines, to automatically control various valves, motors, and pumps based on sensor input values. While PLCs have long been established as the standard control method in industrial settings due to their high reliability and stability, they have a critical limitation: if the control device itself fails or communication is disrupted, it acts as a Single Point of Failure (SPOF), causing the entire process to immediately halt. Particularly in infrastructure facilities requiring continuous 24-hour operation, such as pumping stations or water treatment plants, failure to recover within minutes of a PLC failure can lead to severe operational disruptions; therefore, the application of redundancy technology capable of immediate recovery in emergency situations is essential. To address this, major PLC manufacturers in the existing market, such as LS Electric, Mitsubishi, and Siemens, have been releasing dedicated product lines that support redundancy at the CPU or I/O module level. For example, LS Electric's XGR/XGI series offers a dual-CPU redundancy configuration; it is designed to operate two control processors in parallel internally, so that if one module fails, the other module automatically takes over control. However, these dedicated redundant PLCs are several times more expensive than standard PLCs, and above all, they face very high barriers to adoption in actual field environments, as they require the complete removal of existing single-unit PLCs and their replacement with dedicated redundant modules. Furthermore, existing redundant PLCs are often compatible only within the same product family from the same manufacturer, and it is difficult to apply dedicated redundancy modules as is to equipment installed with various sensor, relay, and I/O wiring configurations depending on site conditions. Consequently, when attempting to introduce redundant PLCs, inconveniences arise, such as the need to rewire all input and output terminals or configure a separate gateway to integrate communication protocols between the existing and new PLCs. Since these installation processes result in high engineering costs and prolonged equipment shutdowns, they are actually applied only restrictively in new plants where a complete overhaul of the facility is unavoidable, while small and medium-sized businesses with existing facilities continue to maintain risky operation methods based on a single PLC. Existing redundant PLC systems face numerous technical limitations not only in terms of cost but also in terms of maintenance. Since dedicated redundancy modules handle switching automatically within the system, operators find it difficult to intuitively verify whether the switch has actually occurred, and it is challenging to quickly diagnose the specific section where an error occurred if one arises after the switch. Furthermore, it has been reported that in some systems, data logs are reset or input values are momentarily lost during redundancy switching, resulting in the loss of information necessary to trace control history or analyze the cause of failures. In other words, there are situations where this opaque structure—where "a switch has occurred but the reason for it is unknown"—actually becomes a burden for the maintenance personnel. Furthermore, most redundant PLC products released to date merely "redundantly duplicate control logic" and lack protection against external environmental factors (power noise, moisture, dust, vibration, etc.). Consequently, they fail to provide a fundamental solution when actual failures occur in external terminal blocks, cables, or relay contacts rather than within the PLC's internal circuitry. In particular, despite the frequent contact failures caused by moisture and corrosion in water treatment, civil engineering, and underground facilities, as well as the numerous malfunctions resulting from power noise in power plants and heavy industry facilities, existing redundant PLCs remain limited to simple CPU redundancy without considering these external environmental factors. The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the detailed description of the invention provided below; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings. FIG. 1 is a drawing illus