Hybrid Modular Multilevel Converter Thyristor IGBT Design

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Solution Overview

Problem

Modular multilevel converters (MMCs) for high voltage direct current (HVDC) systems face challenges such as high conduction losses, circulating current issues, and limited power handling capability due to the use of IGBTs, which underutilize the power handling capabilities of thyristors.

Innovation Solution

A hybrid modular multilevel converter (HMMC) design that incorporates chain links formed by submodules with both semi-controlled and fully controlled devices, including thyristors and IGBTs, with inductors to limit circulating current and enhance power handling, allowing thyristors to carry full load current while IGBTs handle only a fraction, reducing conduction losses and improving fault handling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If IGBTs are used in MMCs for high voltage conversion, then the converter achieves high voltage capability and modular design, but conduction losses increase and power handling capability is limited

Engineering Contradiction:

Improvepower handling capabilityVSAvoidconduction loss

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

The patent combines two different semiconductor device technologies (IGBTs and thyristors) into a hybrid converter system. The IGBT-based submodules provide high voltage capability and modular design, while the thyristor-based series switch provides high power handling capability and low conduction losses, achieving synergistic benefits from both technologies

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent creates a composite semiconductor device architecture by integrating IGBT modules and thyristor valves in series. This composite structure allows the system to leverage the advantages of both device types: the controllable switching of IGBTs and the low-loss conduction of thyristors

Inventive Principle:

Principle #40Composite materials

2Power

If the number of IGBTs in conduction path is increased to achieve required output voltage, then voltage generation capability is improved, but conduction losses increase

Engineering Contradiction:

Improveoutput voltage capabilityVSAvoidconduction loss

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

The patent segments the voltage generation function between two distinct components: IGBT-based submodules that provide modular voltage steps, and a thyristor-based series switch that provides additional voltage multiplication. This segmentation allows each component to operate in its optimal efficiency range

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the conduction path configuration by introducing a series-connected thyristor switch that remains conductant during power transfer, thereby reducing the number of IGBTs that need to conduct simultaneously and reducing overall conduction losses

Inventive Principle:

Principle #35Parameter changes

3Reliability

If thyristors are used to increase power handling capability, then surge current handling and reliability are improved, but control capability during DC side fault is lost

Engineering Contradiction:

Improvesurge current handling capabilityVSAvoidcontrol capability during fault

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent introduces an intermediary control mechanism that uses the controllable IGBT submodules to manage fault conditions. During DC side faults, the IGBT submodules can be rapidly switched to block fault current, while the thyristor provides stable high-power conduction during normal operation

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements preliminary fault detection and response mechanisms where the controllable IGBT submodules are positioned to detect and respond to DC side faults before they propagate through the entire system, allowing rapid isolation of fault conditions

Inventive Principle:

Principle #10Preliminary action

4Loss of energy

If chain links with inductors are added to limit circulating current, then circulating current is reduced, but device complexity increases

Engineering Contradiction:

Improvecirculating current lossVSAvoidconverter structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent designs the chain link inductors to serve multiple functions: limiting circulating current between parallel chains, filtering harmonic currents, and providing magnetic energy storage for power oscillation damping. This multi-functionality reduces the need for separate dedicated components

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11532996B2Hybrid modular multilevel converter

Publication Date: 2022.12.20 INDIAN INSTITUTE OF TECHNOLOGY BOMBAY

AI summary

Accordingly, the embodiments herein provide a hybrid modular multilevel converter. The hybrid modular multilevel converter includes one or more chain links, one or more high voltage switches and a plurality of inductors. The one or more chain links are formed by sub modules. The one or more high voltage switches are formed by semi-controlled devices or fully controlled or any other suitable semiconductor devices. The plurality of inductors are arranged in the one or more chain links to limit circulating current among the one or more chain links. The one or more chain links are configured to enhance a power handling capability of the hybrid modular multilevel converter.