Power Conversion Device Zero-Phase Current Limiting Transformer
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Solution Overview
Problem
Existing power conversion devices require a single-phase reactor to limit zero-phase current, which increases complexity and cost, and lacks voltage sensors for effective current control.
Innovation Solution
A power conversion device using a three-phase transformer with voltmeters to measure line-to-line voltages and control unit cells, eliminating the need for a reactor by utilizing the inductance of secondary windings for current limitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-phase reactor is used to limit zero-phase current, then zero-phase current is limited, but device complexity and cost increase
Solution Approach 1:
The patent merges the current limitation function into the transformer by utilizing the inductance of the transformer's leakage flux. The transformer is designed with specific winding configurations (delta-connected primary windings, star-connected secondary windings with neutral point) that inherently provide the necessary inductance to limit zero-phase current, eliminating the need for a separate single-phase reactor while maintaining the current limitation function.
Solution Approach 2:
The transformer is designed to perform multiple functions simultaneously: voltage transformation, isolation, and zero-phase current limitation. By configuring the windings in delta and star connections with specific grounding arrangements, the transformer's leakage inductance serves as the limiting impedance for zero-phase current, making the device multi-functional and reducing overall system complexity.
2Reliability
If a single-phase reactor is used to limit zero-phase current, then zero-phase current is limited, but cost increases
Solution Approach 1:
The patent merges the current limitation function into the transformer by utilizing the inductance of the transformer's leakage flux. The transformer is designed with specific winding configurations (delta-connected primary windings, star-connected secondary windings with neutral point) that inherently provide the necessary inductance to limit zero-phase current, eliminating the need for a separate single-phase reactor while maintaining the current limitation function.
Solution Approach 2:
The transformer is designed to perform multiple functions simultaneously: voltage transformation, isolation, and zero-phase current limitation. By configuring the windings in delta and star connections with specific grounding arrangements, the transformer's leakage inductance serves as the limiting impedance for zero-phase current, making the device multi-functional and reducing overall system complexity.
3Measurement precision
If voltage sensors are added to measure line-to-line voltages for effective current control, then current control precision is improved, but device complexity increases
Solution Approach 1:
The patent introduces voltmeters as intermediary measurement devices to detect line-to-line voltages. These voltmeters provide the necessary voltage information to the control unit, which then calculates and controls the zero-phase current. This intermediary approach enables precise current control through voltage measurement rather than direct current measurement, simplifying the control architecture.
Solution Approach 2:
The control unit receives voltage information from voltmeters and uses this feedback to adjust the switching states of unit cells, thereby controlling the zero-phase current. The system continuously monitors line-to-line voltages and adjusts the output accordingly, implementing a closed-loop control mechanism that improves current control precision.
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 limits zero-phase current without a reactor, reducing device complexity and cost while enabling compact size and efficient reactive power transfer.
Implementation Method 1
a three-phase transformer 11 with at least three legs 113uv, 113vw, 113wu on each of which a primary winding 111uv, 111vw, 111wu and a secondary winding 112uv, 112vw, 112wu are wound for magnetic coupling
Data Source
Figure 1
Figure 2(a)~2(d)
Figure 3(a)~3(d)
AI summary
A power conversion device (1, 1A, 1B), which limits a zero-phase current without using a reactor, includes clusters (12uv, 12vw, and 12wu) in each of which six unit cells (121) are connected in series; and a transformer (11) that has legs (113uv, 113vw, 113wu) on each of which a primary winding (111uv, 111vw, 111wu) and a secondary winding (112uv, 112vw, 112wu) are wound for magnetic coupling. The both ends of the secondary winding (112uv, 112vw, 112wu) are connected to the both ends of the cluster (12uv, 12vw, 12wu).