Single-Sensor Undervoltage Protection for Three-Phase Compressors
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Solution Overview
Problem
Existing 3-phase voltage monitors disconnect the load at a set voltage threshold, which can deny cooling even when the compressor is under low load conditions and capable of operating at lower input voltages without stalling, leading to system shutdowns and potential food spoilage.
Innovation Solution
The implementation of adaptive undervoltage protection using a single current sensor, which monitors the current between the relay and the compressor motor, allowing the system to continue operating at lower input voltages if the compressor is under low load and not stalling, thereby reducing unnecessary shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a set voltage threshold is used to disconnect the load, then the compressor motor is protected from stalling and excessive heat buildup, but the system experiences unnecessary shutdowns when the compressor is under low load conditions and capable of operating at lower voltages
Solution Approach 1:
The system changes from using a fixed voltage threshold parameter to using a dynamic current-based parameter. The processor monitors actual current draw and compares it against threshold values to dynamically determine undervoltage conditions, allowing the system to adapt to varying load conditions rather than applying a static voltage cutoff that causes unnecessary shutdowns during low-load operation
Solution Approach 2:
The system implements feedback by continuously monitoring current sensor readings and using this information to adjust undervoltage detection decisions. The processor receives real-time current data, evaluates whether the compressor is operating under conditions where low voltage would cause harmful effects, and only triggers undervoltage protection when actual current indicates a genuine risk of stalling or overheating
2Device complexity
If a single current sensor is used instead of multiple voltage sensors, then device complexity is reduced, but the ability to accurately monitor all three phases for undervoltage conditions is compromised
Solution Approach 1:
The system substitutes direct voltage measurement (electrical measurement) with current measurement (electrical measurement through current sensor). Instead of using multiple voltage sensors to directly monitor each phase voltage, the system uses a single current sensor to monitor current draw, which serves as an indirect but reliable indicator of undervoltage conditions affecting compressor operation
Solution Approach 2:
The single current sensor serves multiple functions: it detects undervoltage conditions, monitors load levels, determines compressor operating status, and prevents both overcurrent and undervoltage shutdowns. This multi-functional approach replaces what would traditionally require separate voltage sensors for each phase, achieving the same protective goals with reduced component count
Data Source
AI summary
Exemplary embodiments are disclosed of a relay control or contactor configured to provide adaptive undervoltage protection for a three-phase load using a single current sensor. The current sensor is electrically connected with a corresponding one of a first, second, or third relay for providing information about current from the corresponding relay to a load. The information may be usable to determine a failure condition when: after the relays are energized, the information indicates that: there is no current across the corresponding one of the first, second, and third relays thereby indicating that the corresponding one of the first, second, and third relays is open and the load is running on two phases; or the current across the corresponding one of the first, second, and third relays is at lock rotor current for more than a determined amount of time indicating that the load is running on two phases.