Multi-Level Power Converter Inductor Segmentation
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Solution Overview
Problem
Multi-level converters used for renewable energy sources face challenges in efficiently managing secondary energy storage, particularly in isolating it during faults and reducing inductance per switching cell while maintaining smooth current flow.
Innovation Solution
The solution involves arranging the inductor in the arm circuit, allowing for lower inductance and enabling alternative operational modes by controlling switching devices, including integrated gate-commutated thyristors, gate turn-off thyristors, and insulated-gate bipolar transistors, with a secondary inductor connected in series to reduce transient current flow between converter arms, and using capacitors or supercapacitors for energy storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the inductor is arranged in the arm circuit with lower inductance, then the self-inductance of the first inductor is reduced, but the current rating of the cell inductor becomes higher
Solution Approach 1:
The patent divides the inductor function into two separate components: the first inductor (L1) in the arm circuit with reduced inductance, and the second inductor (L2) connected in series with the secondary energy storage. This segmentation allows L1 to have lower inductance for reduced volume while L2 handles the current rating requirements, resolving the contradiction between reduced self-inductance and higher current rating requirements.
2Adaptability or versatility
If the secondary energy storage is integrated into the converter circuit, then the converter can manage energy from renewable sources, but the converter cannot isolate the secondary energy storage in case of fault
Solution Approach 1:
The patent introduces switching devices (third and fourth switching devices) as intermediaries between the secondary energy storage and the converter circuit. These switching devices enable the controller to isolate the secondary energy storage during faults while maintaining its integration for normal operation, thus resolving the contradiction between adaptability and reliability.
3Volume of moving object
If the inductor has lower inductance, then the inductance per switching cell is reduced, but the transient current flow between converter arms increases
Solution Approach 1:
The second inductor (L2) connected in series with the secondary energy storage acts as an intermediary that limits transient current flow between converter arms. This allows the first inductor to have lower inductance for reduced cell size while L2 compensates by suppressing harmful transient currents.
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 self-inductance of the first inductor, enables isolation of secondary energy storage during faults, and provides a smoother current flow with higher current ratings for the cell inductor, enhancing the converter's operational efficiency and fault tolerance.
Implementation Method 1
The power converter requires an inductance per switching cell in order facilitate a smooth current to and from the secondary energy storage
Implementation Method 2
The primary energy storages of the switching cells are usually capacitors
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A multi-level power converter for one or more phases. The converter comprises one or more converter arms (3) comprising a plurality of serial connected switching cells (20). Each switching cell (20) comprises a plurality of switching devices (40a, 40b, 40c, 40d), a primary energy storage (50),a secondary energy storage (52) and a first inductor (54). The switching devices are arranged to selectively provide a connection to the primary energy storage, wherein each switching cell comprises a bridge circuit (60) comprising the switching devices and the primary energy storage, a battery circuit (62) connected to the bridge circuit and comprising the secondary energy storage, and an arm circuit (64) providing a connection between two adjacent switching cells. The first inductor of each switching cell is arranged in the arm circuit.