Refrigerant Compressor VFD Phase Shift to Reduce Harmonic Distortion
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Solution Overview
Problem
Refrigerant compressors with variable frequency drives (VFDs) create harmonic distortion in electrical systems, leading to losses, poor power factor, excessive heating, and early component failure due to their non-linear load characteristics, which existing multiple rectifier configurations attempt to mitigate but at increased cost and complexity.
Innovation Solution
Configuring multiple variable frequency drives in refrigerant loops with phase shift transformers to demand current at different phases, effectively canceling harmonic frequencies and reducing total harmonic distortion, using a combination of six pulse, twelve pulse, and eighteen pulse configurations to achieve sinusoidal current profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If multiple rectifier configurations (twelve pulse, eighteen pulse) are used in variable frequency drives to reduce harmonic distortion, then harmonic cancellation is improved, but device complexity and cost increase
Solution Approach 1:
The system divides the VFD population into multiple groups, where each group contains VFDs configured with the same phase shift. This segmentation allows harmonic cancellation to be achieved through group coordination rather than requiring complex multiple rectifier configurations within each individual VFD, thereby reducing device complexity while maintaining harmonic reduction benefits
Solution Approach 2:
Phase shift transformers are introduced as intermediary devices between the power source and the VFDs. These transformers provide the necessary phase shifts to enable harmonic cancellation across different VFD groups, achieving the harmonic reduction effect of complex multiple rectifier systems through a simpler external phase shifting approach rather than internal rectifier complexity
2Loss of energy
If multiple rectifier configurations are used to achieve harmonic cancellation, then power factor is improved, but device complexity and cost increase
Solution Approach 1:
VFDs are segmented into groups with identical phase shift configurations, allowing the system to achieve improved power factor through coordinated group operation rather than requiring each individual VFD to have complex multiple rectifier configurations, thus reducing device complexity while maintaining energy efficiency
Solution Approach 2:
Multiple VFDs within a group are configured with identical phase shift settings, creating copies of the same phase shift configuration. This copying approach simplifies the overall system design compared to using unique complex multiple rectifier configurations in each VFD, while still achieving the power factor improvement through cumulative harmonic cancellation effects
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 configuration significantly reduces harmonic distortion, achieving equivalent harmonic cancellation to more expensive multiple rectifier systems while being cost-effective and reliable, by using multiple six pulse VFDs in a refrigerant loop to mimic the performance of single, more expensive twelve or eighteen pulse VFDs.
Implementation Method 1
a second variable frequency drive drives a second compressor and is connected to a second compressor winding in the phase shift transformer being at a 30° phase shift relative to the first compressor winding
Data Source
AI summary
Compressors in a refrigerant loop are driven by variable frequency drives. The variable frequency drives are configured to demand current from an alternating current power source at different phases relative to one another such that at least one current harmonic frequency at the alternating current power source is cancelled.