Cold Source Compressor Restart Control Using Dynamic Pause Periods
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Solution Overview
Problem
The restart of a compressor in refrigeration systems is often unsuccessful due to overcurrent issues caused by liquid back, leading to repeated stoppages and a high likelihood of complete operation failure.
Innovation Solution
A cold source unit with a controller that performs first and second start retry controls, pausing the compressor for increasing time periods to discharge liquid refrigerant, including the use of a heater for liquid discharge promotion when necessary, to reduce the likelihood of overcurrent during restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the compressor is restarted immediately after stoppage due to overcurrent, then the response time is short, but the liquid refrigerant remains in the compressor causing repeated overcurrent and complete stoppage
Solution Approach 1:
The pause time period is made dynamic rather than fixed. The controller adjusts the pause time based on the number of times start retry control has been performed - using a first time period for initial retries and a second, longer time period after exceeding a first criterion value. This dynamic adjustment optimizes the balance between quick restart response and sufficient liquid discharge time.
Solution Approach 2:
The controller changes the time period parameter based on the retry count. When the number of start retry control performances exceeds the first criterion value, the controller switches from using the first time period to the second time period (which is longer). This parameter change adapts the system to the accumulated liquid refrigerant condition.
2Reliability
If a fixed pause time is used for compressor restart, then the control is simple, but it cannot adapt to different liquid accumulation conditions leading to restart failure
Solution Approach 1:
The control system uses dynamic time period selection based on retry count. The controller maintains simplicity by using a clear conditional logic: if retry count exceeds the first criterion value, use the second (longer) time period; otherwise, use the first time period. This provides adaptability without excessive complexity.
3Reliability
If the compressor pauses for a longer time to discharge liquid refrigerant, then the restart success rate improves, but the system response time decreases
Solution Approach 1:
The system dynamically adjusts pause duration based on the retry history. For initial retries (first time period), the pause is shorter to maintain responsiveness. After exceeding the first criterion value, the pause extends to the second time period to ensure liquid discharge and prevent complete stoppage, optimizing the reliability-productivity trade-off at different stages.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach increases the success rate of compressor restarts by ensuring sufficient discharge of liquid refrigerant, reducing the risk of overcurrent and subsequent stoppages, thereby improving the reliability of refrigeration system operation.
Implementation Method 1
a heater to heat the liquid refrigerant in the compressor
Data Source
Figure 1~2
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AI summary
A cold source unit (100) includes a compressor (1) and a controller (30) to control the compressor (1). When the controller (30) detects overload on the compressor (1), the controller (30) performs first start retry control of restarting the compressor (1) after pausing the compressor (1) for a first time period. When the number of times the first start retry control is performed exceeds a first criterion value, the controller (30) performs second start retry control of restarting the compressor (1) after pausing the compressor (1) for a second time period longer than the first time period.