Power Conversion Device Charging Unit Downsizing via Transformer Segmentation
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Solution Overview
Problem
Conventional power conversion devices using three-winding transformers for DC-AC power conversion face issues with inrush overcurrent during capacitor charging, leading to heat generation and increased size of the charging unit due to excitation currents flowing through the charging resistor.
Innovation Solution
The power conversion device places the charging unit between the secondary and tertiary windings of the three-winding transformer, preventing excitation currents from flowing through the charging resistor, thus avoiding heat generation and allowing for a downsized charging unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the charging unit is placed in the primary side of the three-winding transformer, then the capacitor can be charged from the power system, but excitation current flows through the charging resistor causing heat generation and increased size
Solution Approach 1:
The patent segments the transformer windings into primary, secondary, and tertiary windings with distinct functions. The charging unit is connected to the secondary and tertiary windings rather than the primary winding, separating the charging function from the excitation current path. This segmentation allows the charging resistor to only handle charging current without carrying excitation current, reducing heat generation and enabling a smaller charging unit size.
2Use of energy by moving object
If the charging unit is placed in the primary side of the three-winding transformer, then the capacitor can be charged, but the size of the charging unit must be increased to withstand heat generation
Solution Approach 1:
The patent segments the transformer windings into primary, secondary, and tertiary windings with distinct functions. The charging unit is connected to the secondary and tertiary windings rather than the primary winding, separating the charging function from the excitation current path. This segmentation allows the charging resistor to only handle charging current without carrying excitation current, reducing heat generation and enabling a smaller charging unit size.
3Device complexity
If a three-winding transformer is used to suppress short-circuit current, then a buffer reactor becomes unnecessary, but the charging unit still experiences heat generation from excitation currents
Solution Approach 1:
The patent segments the transformer windings into primary, secondary, and tertiary windings with distinct functions. The charging unit is connected to the secondary and tertiary windings rather than the primary winding, separating the charging function from the excitation current path. This segmentation allows the charging resistor to only handle charging current without carrying excitation current, reducing heat generation and enabling a smaller charging unit size.
Solution Approach 2:
The secondary and tertiary windings act as intermediary elements between the power system and the capacitor charging circuit. By routing the charging current through these intermediate windings rather than directly through the primary winding, the patent creates a path that supplies charging current while isolating the charging resistor from excitation currents, thereby reducing heat generation.
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 reduces the size of the charging unit and improves efficiency by eliminating energy losses from excitation currents, resulting in a more compact and cost-effective power conversion device.
Implementation Method 1
a three-winding transformer 4 connected between the positive-side phase arm 2a and the negative-side phase arm 2b
Implementation Method 2
unit converters which include a DC voltage source such as a capacitor
Implementation Method 3
a charging unit that includes a charging resistor for suppressing this inrush overcurrent of the charging current
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A power conversion device enabling a downsizing of a charging unit is provided. The power conversion device includes, in each phase, a positive side phase arm including unit converters connected to a DC positive side terminal and connected in multi stage, each unit converter including a switching element and a capacitor, a negative side phase arm including unit converters connected to a DC negative side terminal and connected in multi stage, each unit converter including a switching element and a capacitor, a three-winding transformer connected between the positive side phase arm and the negative side phase arm, and a plurality of charging units each including a charging resistor and a disconnection switch connected in parallel with each other. The three-winding transformer includes a secondary winding connected to the positive side phase arm and a tertiary winding connected to the negative side phase arm, and a negative side of the secondary winding and a negative side of the tertiary winding are connected with each other in each phase and among three phases. The charging units are connected between the positive side phase arm and the secondary winding, and between the negative side phase arm and the tertiary winding, respectively.