Two-Terminal M2LC Subsystem With Unequal Capacitor Sizing

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Solution Overview

Problem

Existing Modular Multilevel Converter (M2LC) cell configurations require two identical storage capacitors, which increase size and cost, and do not optimize energy output distribution between terminals.

Innovation Solution

The M2LC subsystems utilize three or four switching devices and capacitors, where one capacitor handles fundamental output current and another operates at switching frequency, allowing for reduced capacitor sizes and independent voltage control, enabling efficient energy distribution and minimizing control complexity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If two identical storage capacitors are used to achieve voltage states, then voltage control capability is improved, but device size and cost increase

Engineering Contradiction:

Improvevoltage control capabilityVSAvoiddevice size and cost

Core Design Contradiction:

Adaptability or versatilityVSQuantity of substance

Solution Approach 1:

The patent applies asymmetry by using two capacitors of different sizes (first capacitor and second capacitor with different capacitance values) instead of identical capacitors. The larger capacitor handles fundamental output current while the smaller capacitor operates at switching frequency, reducing overall device size and cost while maintaining the ability to achieve multiple voltage states through coordinated switching of all four switching devices

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent applies local quality by assigning different functional roles to different capacitors based on their size characteristics. The first (larger) capacitor is optimized for handling fundamental output current, while the second (smaller) capacitor is optimized for switching frequency operations. This localized optimization allows each capacitor to be sized appropriately for its specific function, reducing total component size and cost while maintaining overall system performance

Inventive Principle:

Principle #3Local quality

2Device complexity

If switching devices are configured to share current, then device complexity is reduced, but control precision requirements increase

Engineering Contradiction:

Improveswitching device configurationVSAvoidcontrol precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent applies merging by having switching devices share current paths and control functions. Multiple switching devices can conduct current through common paths, and the control system manages coordinated switching to achieve desired voltage states. This sharing approach reduces the number of completely independent circuits needed, simplifying overall device complexity while the control system handles the increased coordination requirements

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20120068756A1Two-Terminal M2LC Subsystem and M2LC System Including Same

Publication Date: 2012.03.22 BENSHAW INC

AI summary

A two-level two-terminal modular multilevel converter subsystem. The subsystem includes a first capacitor and a second capacitor. The modular multilevel converter subsystem is configured to selectively place the first capacitor in series with the second capacitor. The modular multilevel converter subsystem is also configured to selectively place the first capacitor in parallel with the second capacitor relative to first and second output terminals of the modular multilevel converter subsystem.