PLC Controller Power-Cut State Restoration
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Solution Overview
Problem
Programmable logic controllers (PLCs) face challenges in restoring their state before a power cut without information corruption, as existing techniques do not adequately address the process of writing information for state restoration during a power cut, leading to unstable reactivation.
Innovation Solution
A controller with a nonvolatile storage system that includes a first and second area, where the file system unit stops writing target information into the first area during a power cut and prioritizes writing power-cut retaining information into the nonvolatile storage using auxiliary power, ensuring stable restoration of the state before the power cut without increasing the number of components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated nonvolatile memory is installed for storing power-cut retaining information, then the reliability of state restoration is improved, but the device complexity increases due to additional components
Solution Approach 1:
The nonvolatile memory is divided into a first area for normal operation data and a second area for power-cut retaining information. This segmentation allows the system to maintain reliability by dedicating specific storage space for restoration data while using existing memory infrastructure, avoiding the need for completely separate dedicated memory components.
Solution Approach 2:
The existing nonvolatile memory is made multi-functional by allocating different areas for different purposes: the first area handles normal operation data while the second area stores power-cut retaining information. This universal usage of existing memory components eliminates the need for additional dedicated memory hardware, reducing device complexity while maintaining restoration reliability.
2Loss of time
If the PLC writes power-cut retaining information during normal operation, then the restoration speed is improved, but the loss of information increases due to potential power cut during writing
Solution Approach 1:
The PLC performs preliminary writing of power-cut retaining information during normal operation when power is stable. By proactively storing restoration data before power cuts occur, the system prepares advance restoration information that can be quickly retrieved after power restoration, reducing restoration time while minimizing the risk of information loss during the writing process.
Solution Approach 2:
The critical power-cut retaining information is extracted and stored in a separate second area of nonvolatile memory, distinct from normal operation data in the first area. This extraction isolates the restoration-critical data, allowing it to be managed independently and reducing the risk that power cuts during normal operations will corrupt the restoration information.
3Device complexity
If the PLC uses existing nonvolatile memory for power-cut retaining information, then the device complexity is reduced, but the reliability of information retention deteriorates due to potential data interference
Solution Approach 1:
The nonvolatile memory is segmented into distinct first and second areas, with the second area specifically dedicated to power-cut retaining information. This segmentation within the existing memory prevents data interference between normal operation data and restoration data, maintaining information retention reliability while avoiding additional hardware components.
Solution Approach 2:
The second area of nonvolatile memory is given special local quality by being designated exclusively for power-cut retaining information. This localized designation ensures that restoration-critical data receives focused protection and management, improving information retention reliability in that specific region without requiring entirely separate memory hardware.
Data Source
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AI summary
A controller allows, after a power cut, stable restoration of the state before the power cut without increasing the number of components. A control unit (30) included in a PLC (1) generates power-cut retaining information (42) to be retained at a power cut, and stores the generated power-cut retaining information (42) into a main memory (16). The control unit (30) includes a file system unit (34) for reading and writing target information from and into a nonvolatile memory (14). When the file system unit (34) receives a power cut notification indicating a cut of power fed while reading or writing target information from or into a nonvolatile memory (14), the file system unit (34) stops the reading or writing process, and writes the power-cut retaining information (42) stored in the main memory (16) into the nonvolatile memory (14) using power fed from the auxiliary power supply.