Discrete Motor Frequency Control to Avoid Refrigeration Resonance
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Solution Overview
Problem
Variable speed electric motors in refrigerant systems often encounter undesirable conditions such as mechanical and acoustic resonance, leading to noise, excessive vibration, and potential damage due to operational frequencies that pass through resonance frequencies during start-up, shutdown, and adjustments to meet thermal load demands.
Innovation Solution
The motor controller alternates the operating frequency between multiple discrete frequencies to maintain an average desired frequency, thereby avoiding the undesirable characteristics associated with continuous operation at a single frequency, ensuring continuous variable speed operation while minimizing resonance-related issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the motor operates at a single desired frequency to maintain stable cooling capacity, then the system efficiency is improved, but mechanical and acoustic resonance occurs causing noise and excessive vibration
Solution Approach 1:
The motor controller alternates the motor operation between at least two different frequencies in a periodic manner, where the frequencies are selected such that their combination results in an average operating frequency that provides the desired cooling capacity while avoiding resonance conditions. This periodic frequency switching eliminates the harmful resonance effects associated with continuous operation at a single frequency.
2Adaptability or versatility
If the motor frequency is varied continuously to meet thermal load demands, then the adaptability is improved, but the system passes through resonance frequencies causing noise and vibration
Solution Approach 1:
Instead of continuous frequency variation, the controller uses periodic switching between discrete frequencies to adapt to thermal load demands. The motor operates at one frequency for a period, then switches to another frequency, maintaining adaptability while avoiding the harmful resonance frequencies that occur during continuous frequency transitions.
3Object-affected harmful factors
If stepless control is used to avoid resonance frequencies, then the harmful factors are reduced, but the resonance frequencies cannot be entirely avoided
Solution Approach 1:
The continuous frequency range is segmented into discrete frequency levels. Instead of using stepless control that continuously sweeps through frequencies, the system divides the operating range into specific discrete frequency steps, selecting combinations of these segmented frequencies that avoid resonance zones while achieving the desired average operating frequency and cooling capacity.
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
A variable speed electric drive for use in refrigerant systems (20) includes an electric motor (40) for driving an associated component (22) at a variable speed that is a function of an operating frequency of the motor (40); and a control (42) for supplying alternating discrete drive frequencies to the electric motor to provide a continuously variable speed drive of the associated component (22). The control (42) cycles the drive frequency to the electric motor (40) among the at least two discrete frequencies so that the variable average resultant speed at which the associated component (22) is driven is a function of a combination of the selected at least two discrete frequencies.