AC-DC Interface Auxiliary Windings for Fast Fault Isolation

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Solution Overview

Problem

Existing interface arrangements between AC and DC systems, particularly in cell-based multilevel converters, face challenges in handling faults such as overvoltages and high currents due to single-phase-to-ground and DC pole-to-ground faults, which are difficult to manage with existing surge arresters and AC breakers, especially in high voltage environments.

Innovation Solution

An interface arrangement that includes a converter, a transformer with auxiliary windings, and a controllable short-circuiting device connected between the auxiliary windings and ground, which is activated by a fault detecting unit to quickly short-circuit the auxiliary windings and reduce voltage and current stresses, allowing for faster fault handling and isolation of the AC source.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If surge arresters are used to handle overvoltages in cell-based multilevel converters, then overvoltage protection is provided, but the solution becomes difficult to implement due to the cell structure

Engineering Contradiction:

Improveovervoltage protectionVSAvoidimplementation difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention divides the overvoltage protection function into two parts: the existing cell-based converter structure remains unchanged, while a separate neutral point clamping circuit is added. This segmentation allows the protection function to be implemented without redesigning the entire converter structure, making it easier to manufacture and integrate into existing cell-based multilevel converters

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The neutral point of the converter is introduced as an intermediary element for overvoltage protection. By clamping the neutral point voltage to ground through controlled switching, the invention provides overvoltage protection without directly modifying the cell structure, thus maintaining ease of implementation while achieving reliable protection

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If DC pole to ground fault protection is implemented, then high current protection is provided, but existing solutions are insufficient for cell-based multilevel converters

Engineering Contradiction:

Improvehigh current protectionVSAvoidcompatibility with cell-based converters

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The neutral point clamping circuit serves multiple functions: it provides overvoltage protection, facilitates AC breaker opening, and protects against DC pole to ground faults. This multi-functionality makes the invention universally applicable to cell-based multilevel converters without requiring separate protection circuits for each fault type, thereby improving both reliability and adaptability

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 solution enables fast and effective handling of pole-to-ground and single-phase-to-ground faults in both symmetrical and unsymmetrical systems, reducing the need for large and costly surge arresters and AC breakers, while ensuring the AC breaker can open promptly to isolate the fault, thereby protecting the converter and reducing operational stresses.

Implementation Method 1

a transformer having a primary side with a first set of primary windings for being coupled to said AC system and a secondary side with a second set of secondary windings coupled to said converter

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

a short-circuiting device connected between said third set of auxiliary windings and ground... which is activated by a fault detecting unit to quickly short-circuit the auxiliary windings and reduce voltage and current stresses

Methodology Applied

Scientific EffectElectrical short-circuiting: Conduction (electrical)

Data Source

PatentEP2771956B1Interface arrangement between ac and DC systems for reliable opening of the circuit breaker in time

Publication Date: 2016.05.25 ABB (SCHWEIZ) AG

Figure 1~2
Figure 3~4

AI summary

The present invention relates to an interface arrangement for coupling between an AC system (10) and a DC system (11). The arrangement comprises a converter (12) for conversion between AC and DC and having a DC side with a first and a second terminal (T1, T2) for connection to the DC system and an AC side with a group of terminals (T3) for being coupled to the AC system, a transformer (18) having a primary side with a first set of primary windings for being coupled to the AC system and a secondary side with a second set of secondary windings coupled to the converter, where the transformer is equipped with a third set of auxiliary windings and a short-circuiting device (24) is connected between the third set of auxiliary windings and ground.