RBE202TC Programmable Logic Controllers and Network Communications
Laboratory 1 (40%)
The Variable Frequency Drive (VFD) System
Figure 1 - Power circuit of the electromagnetic-relay based VFD control system
Figure 2 - Control circuit of the variable frequency drive (VFD) system
Figures 1 and 2 provide a detailed representation of the power circuit and control circuit involved in an electromagnetic relay-based variable frequency drive (VFD) control system, specifically tailored for driving a three-phase AC motor.
In Figure 1, the functionality of the motor drive is illustrated with two primary terminals: the FWD (forward) terminal, which initiates the motor's rotation in the forward direction, and the REV (reverse) terminal, which facilitates rotation in the reverse direction. This dual terminal system allows for versatile operational control, enabling users to select the desired motor direction based on specific application needs.
The motor drive is designed to operate in three distinct speed modes, accommodating varying operational requirements. The specific conditions and logic that dictate which speed mode is engaged are detailed in Table 1. This ensures that users can optimize performance based on factors such as load requirements and operational efficiency.
In the event of a system fault, the motor drive responds by opening TB, which is a normally closed contact, effectively interrupting power to the motor, and closing TC, a normally open contact, to signal an alert or lockout condition. This safety feature is crucial for preventing damage to the motor and ensuring the overall safety of the system. Once the operator has diagnosed and resolved the fault, they can utilize the RST (reset) terminal on the motor drive to restore normal operation, thereby resetting the system and preparing it for further use.
Overall, this comprehensive VFD control system allows for greater control, flexibility, and safety in operating three-phase AC motors across a variety of applications.
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Speed Mode
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X1, X2 and X3 Logic
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Forward Direction
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Reverse Direction
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Low
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X1 HIGH
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FWD HIGH and REV LOW
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REV HIGH and FWD LOW
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Intermediate
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X1 HIGH and X2 HIGH
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FWD HIGH and REV LOW
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REV HIGH and FWD LOW
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High, rated
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X1 HIGH and X2 HIGH and X3 HIGH
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FWD HIGH and REV LOW
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REV HIGH and FWD LOW
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Table 1 - Variable speed control using the VFD motor drive in Figure 1
In this assignment, you are tasked with modifying the existing circuits to support an additional function and then designing a PLC based control system to achieve the control requirement of the modified electromagnetic-relay based control system.
Individual Report (30%):
Complete the following tasks and report them in a technical report.
1. Please modify the circuits in Figures 1 and 2 to include a motor reversing function within the electromagnetic-relay-based control system. Create a new schematic diagram following the NEMA standards. Clearly state the modifications you have made and describe the working principle of the updated electromagnetic-relay-based VFD control circuit based on the provided information and your design. Your descriptions should specifically focus on how the electromagnetic relays facilitate the various functions.
i. To start the system
ii. Variable speed control in forward direction
iii. To change motor rotation direction from forward to reverse direction
iv. To stop the system
v. Fault control
2. Create a PLC-based control system and draw a schematic diagram. Clearly label the different parts of the diagram, including the power circuit and control circuit. Explain how your design works, including any safety features you used.
3. Detail the input/output (I/O) allocation for the PLC in a table format. Create a Ladder Diagram (LAD) program based on your I/O allocation and the schematic diagram from Task 2. Present the LAD program and provide a description of its functionalities.
4. Simulate your LAD program using Automation Studio. Describe your hardware configuration and the key steps used for the simulation and report your simulation results.
Your report should comprise, but not limited to, the following sections.
• Title page
• Summary
• Introduction
• Design
• Results and discussion
• Conclusion
• References
• Appendix
Submission requirements
Deadline: 4th May 2025, 23:59
Length of report: Maximum of 1500 words not including figures and references
Mode of submission: In Word or PDF, online submission via Learning Mall
Referencing style. IEEE style.
(For more information regarding IEEE referencing style, please refer to the document named “BRIEF_GUIDE_TO_REFERENCING_WITH_IEEE_SYSTEM.pdf”.)
Lab Presentation (10%):
You are to present your work near the end of the module. You will be all divided into separate sessions. The presentation schedule will be released during the semester and please take note of your session date and time. The lab presentation is assessed by the module leader. Anyone who fails to turn up for their presentation will receive a mark of zero for this part of assessment.
Your presentation at the PLC lab (TC-A-4014) should include, but not limited to, the following items.
i. How the control requirement is achieved using a PLC-based control system.
ii. Your LAD program.
iii. The key steps for simulation and the corresponding simulation results.
The presentations will proceed according to the name list in each session. Therefore, first named person in each session will start and progress down the list. Students will be given 15 minutes for their presentation.