Controls and operation of variable frequency drives
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Solution Overview
Problem
In HVACR systems, undesired or un-commanded compressor rotation poses significant issues, leading to potential damage and increased wear due to existing limitations in current approaches, particularly in systems using electric motors driven by variable frequency drives.
Innovation Solution
A system comprising a refrigerant circuit with a compressor, condenser, expander, and electric motor, where a controller analyzes system conditions to identify risks of un-commanded rotation and controls the power supply to oppose rotation, using methods such as short circuit conditions or DC current to prevent unwanted rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If variable frequency drives are used to control electric motors in HVACR systems, then energy efficiency and motor control are improved, but the risk of undesired compressor rotation increases due to limitations in existing control approaches
Solution Approach 1:
The controller proactively prevents undesired compressor rotation by detecting pressure differentials across the compressor and applying counteracting electrical forces through the VFD before rotation can occur. This preliminary anti-action eliminates the harmful effect while maintaining energy-efficient VFD operation.
Solution Approach 2:
The system continuously monitors pressure conditions across the compressor and uses this feedback to control the VFD output. When a pressure differential indicating potential reverse rotation is detected, the controller adjusts the motor drive signals in real-time to prevent rotation, creating a closed-loop control system that maintains reliability.
2Reliability
If existing control approaches are used to mitigate undesired compressor rotation, then some protection is provided, but substantial issues remain due to limitations in these approaches
Solution Approach 1:
The VFD control system performs multiple functions: it provides energy-efficient motor control during normal operation and simultaneously prevents undesired rotation when pressure differentials are detected. This multi-functionality eliminates the need for separate protection mechanisms, reducing overall system complexity while maintaining reliability.
Solution Approach 2:
The controller uses the existing VFD hardware and pressure sensor data to self-regulate and prevent compressor rotation without requiring additional dedicated protection components. The system serves its own protection needs through intelligent control of the existing drive electronics.
3Measurement precision
If the controller monitors system conditions to identify rotation risks, then protection accuracy is improved, but the complexity of control increases
Solution Approach 1:
The controller uses feedback from existing pressure sensors to monitor the pressure differential across the compressor. This feedback mechanism provides accurate detection of rotation risk conditions using already-available system data, avoiding the need for additional complex sensing systems.
Solution Approach 2:
The pressure differential serves as an intermediary indicator of potential compressor rotation risk. Rather than directly sensing rotation or complex mechanical states, the controller monitors the pressure difference across the compressor, which indirectly but reliably indicates rotation risk, simplifying the detection mechanism.
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
The solution effectively prevents undesired compressor rotation, reducing the risk of damage and wear by accurately identifying and mitigating un-commanded rotation conditions, thereby enhancing the reliability and longevity of HVACR system components.
Implementation Method 1
the controller being configured to control the power supply to provide a short circuit condition effective to provide an electrical resistance to current generated by rotation of the motor
Implementation Method 2
the controller being configured to control the power supply to provide a DC current to the motor effective to urge the motor to a predetermined alignment and resist rotation of the motor
Data Source
AI summary
A system includes a refrigerant compressor, an electric motor and configured to drive the refrigerant compressor, and a controller. The controller is configured to operate the compressor in a liquid clearing start mode where electrical current through the motor is prevented from exceeding a predetermined current limit for a period of time not to exceed a predetermined period of time, and is configured to operate the compressor in a run mode in response to determining the motor exceeds a predetermined speed threshold at or before expiration of the predetermined period of time, wherein the run mode does not prevent electrical current through the motor from exceeding said predetermined current limit.