Bipolar Double Voltage Cell for Multilevel Converters

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Solution Overview

Problem

Multilevel converters face challenges in reducing the number of components in the conduction path while maintaining fault current limitation and bipolar voltage contribution capability, particularly in half-bridge and full-bridge cell topologies.

Innovation Solution

A cell design with two sections of series-connected switching units and an interconnecting section, allowing for bipolar voltage contributions and fault current blocking with a reduced number of components by using a combination of capacitors and switching units.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If full-bridge cells are used, then fault current blocking ability and bipolar voltage contribution are improved, but the number of components doubles compared to half-bridge cells

Engineering Contradiction:

Improvefault current blocking abilityVSAvoidnumber of components

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The cell is divided into two distinct sections: a first section with a first energy storage element and switching units, and a second section with a second energy storage element and switching units. This segmentation allows each section to be optimized independently, reducing the total component count while maintaining full-bridge functionality for fault current blocking and bipolar voltage contribution.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The interconnecting section merges the first and second sections by electrically connecting the switching units and energy storage elements in a configuration that enables bipolar voltage contribution with fewer components than a traditional full-bridge cell. The merging creates a hybrid topology that achieves full-bridge capabilities with reduced complexity.

Inventive Principle:

Principle #5Merging (Combining)

2Device complexity

If clamped double cells are used, then the number of components is reduced compared to full-bridge cells, but bipolar voltage contribution capability is lost

Engineering Contradiction:

Improvenumber of componentsVSAvoidbipolar voltage contribution capability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The switching units in the interconnecting section are configured to dynamically switch between different conduction paths, enabling the cell to provide both positive and negative voltage contributions. This dynamic switching capability restores bipolar voltage contribution that was lost in static clamped double cell configurations.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The switching units serve multiple functions: they enable bipolar voltage contribution, provide fault current blocking, and allow flexible connection configurations between the two sections. This multi-functionality compensates for the reduced component count while maintaining full operational capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If half-bridge cells are used, then the number of components is minimized, but fault current blocking ability and bipolar voltage contribution are limited

Engineering Contradiction:

Improvenumber of componentsVSAvoidfault current blocking ability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Dividing the cell into two sections with separate energy storage elements and switching units enables each section to contribute to fault current blocking independently, providing enhanced protection capability while maintaining a component count lower than traditional full-bridge cells.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The interconnecting section acts as an intermediary between the two sections, providing the necessary electrical connections and switching paths to enable fault current blocking and bipolar voltage contribution without requiring the full component set of a traditional full-bridge cell.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS9461557B2Bipolar double voltage cell and multilevel converter with such a cell

Publication Date: 2016.10.04 HITACHI ENERGY LTD

AI summary

A multilevel converter cell includes a first section with a first group of series connected switching units in parallel with a first energy storage element, where a junction between a first and second switching units of the first group of series connected switching units forms one cell connection terminal, a second section with a second group of series connected switching units in parallel with a second energy storage element, where a junction between a third and fourth switching units of the second group of series connected switching units forms another cell connection terminal, and an interconnecting section with a third group of series-connected switching units comprising a fifth, sixth and seventh switching unit, with the fifth and sixth switching units connected in parallel with the first energy storage element and the sixth and seventh switching units connected in parallel with the second energy storage element.