Heat Pump Compressor Speed Limiting to Prevent Hunting Oscillation
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Solution Overview
Problem
Conventional heat pump cycle devices experience hunting oscillation in compressor rotational speed when outside air temperatures are low, leading to discomforting noise due to frequent changes in compressor speed.
Innovation Solution
Implementing a limited speed operation that restricts the compressor's rotational speed to a predetermined lower speed until the intake refrigerant temperature reaches a higher threshold, preventing sudden changes and oscillations by delaying the return to normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the compressor rotational speed is reduced when the intake refrigerant temperature falls below a threshold temperature to protect the heat pump cycle devices, then the compressor is protected from damage, but the rotational speed of the compressor repeatedly increases and decreases in an oscillatory manner (hunting oscillation), producing discomforting noise
Solution Approach 1:
The control device performs preliminary action by setting a predetermined time period after detecting low intake refrigerant temperature, during which the compressor rotational speed is constrained to be equal to or lower than a predetermined value. This preliminary constraint prevents the hunting oscillation from occurring in the first place, rather than reacting to temperature fluctuations after they occur.
Solution Approach 2:
The control device dynamically adjusts the maximum allowed rotational speed of the compressor based on the intake refrigerant temperature. When the temperature is below the threshold, the rotational speed is limited to a predetermined value for a specified time period, creating a dynamic response that smooths out oscillations while still protecting the system.
2Speed
If the compressor rotational speed is immediately returned to target rotational speed when the intake refrigerant temperature rises above the threshold temperature, then the system responds quickly to temperature changes, but sudden changes in rotational speed occur, causing hunting oscillation
Solution Approach 1:
The control device establishes a predetermined time period that begins when the intake refrigerant temperature rises above the threshold. During this time period, the rotational speed is gradually increased rather than immediately returning to the target speed, preventing sudden changes that would cause hunting oscillation.
Solution Approach 2:
The control device changes the parameter of maximum allowed rotational speed from a fixed value to a time-dependent value. The rotational speed constraint is maintained for a predetermined time period after temperature threshold crossing, and this time parameter smoothing prevents abrupt speed changes and associated hunting oscillation.
Data Source
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AI summary
Based on a determination at step 115 as to whether an intake refrigerant temperature Ts is at least -32°C, and decisions at steps 145 and 150, either a normal operation or a speed control operation is performed. From a state where the intake refrigerant temperature Ts is less than -34°C, which is when a speed reduction operation is performed, if the intake refrigerant temperature Ts reaches at least -32°C but has not previously reached -20°C, a limited speed operation is performed at step 155. During the limited speed operation, a maximum allowed rotational speed of a compressor (11) is limited to a predetermined speed lower than that of the normal operation. Under different circumstances, if the intake refrigerant temperature reaches at least -32°C, the normal operation is performed at step 160.