Three-Phase Isolated PFC Converter With Defined Neutral Point
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Solution Overview
Problem
Conventional three-phase PFC rectifiers with galvanic isolation are bulky and heavy due to the use of inductors and DC link capacitors, and the neutral point potential is undefined, leading to undesirable variations.
Innovation Solution
A power converter design with three input stages, each connected to a transformer winding, where the input stage receiving the lowest voltage is statically connected to a common circuit node, and the others operate in a switched mode, defining the neutral point potential and reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional two-stage PFC rectifier with inductors and DC link capacitor is used, then galvanic isolation between input and output is achieved, but the device becomes bulky and heavy
Solution Approach 1:
The patent removes the bulky inductors and DC link capacitor from the conventional two-stage PFC rectifier architecture. Instead, it uses three single-phase PFC circuits with transformers that directly provide galvanic isolation, extracting the unnecessary heavy components while maintaining the essential isolation function through the transformer windings alone.
Solution Approach 2:
The patent merges the functions of the first stage (rectification) and second stage (isolation) into a single integrated stage. The three single-phase PFC circuits with their transformers simultaneously perform rectification and provide galvanic isolation, eliminating the need for separate stages and bulky components.
2Productivity
If all three input stages operate in switched mode, then power factor correction is achieved, but switching losses increase
Solution Approach 1:
The patent implements dynamic operation where the switching state of the three input stages changes based on the instantaneous values of the three-phase input voltages. At any given moment, only two stages operate in switched mode while the third operates in continuous conduction mode, creating a dynamic switching pattern that reduces overall switching losses while maintaining PFC functionality.
Solution Approach 2:
The patent changes the operating parameters of the input stages based on the instantaneous voltage conditions. By detecting which phase has the lowest voltage magnitude and adjusting which stage operates in which mode, the system optimizes the switching parameters to minimize losses while achieving the required power factor correction.
3Device complexity
If the neutral point potential is left undefined in conventional designs, then circuit simplicity is maintained, but potential variations cause operational issues
Solution Approach 1:
The patent implements a control mechanism that detects the instantaneous values of the three input voltages, identifies the lowest voltage phase, and uses this feedback information to determine which input stage should be connected to the common circuit node. This feedback-based control ensures the neutral point potential remains well-defined and stable throughout operation.
Solution Approach 2:
The patent introduces a common circuit node that serves as an intermediary connection point for the three input stages. By controlling which stage connects to this node based on voltage conditions, the system mediates the neutral point potential to ensure it remains well-defined without significantly increasing overall circuit complexity.
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 ensures a well-defined neutral point potential, maintains power factor correction, and reduces switching losses by operating only two input stages in switched mode, thus optimizing the converter's efficiency and size.
Implementation Method 1
three transformers each including a first winding and a second winding inductively coupled with the first winding
Data Source
AI summary
A power converter includes three input nodes each configured to receive a respective one of three alternating input voltages, and an output; three transformers each comprising a first winding and a second winding inductively coupled with the first winding; an input circuit with three input stages each coupled to a respective one of the input nodes, the first winding of a respective one of the transformers and a common circuit node; and an output circuit coupled to the second winding of each of the transformers and the output. The method includes detecting the lowest input voltage, which is that one of the input voltages having the lowest magnitude; connecting that one of the input nodes receiving the lowest input voltage to the common circuit node by the input stage connected to that one of the input nodes receiving the lowest input voltage.