Hybrid Load Breaker with Semiconductor Switch for DC Arc Prevention

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Solution Overview

Problem

Existing load breaker arrangements for photovoltaic plants face challenges in safely switching off DC currents without causing switching arcs, leading to contact fusing and inefficiencies, especially when dealing with higher currents and the need for manual operation or high-cost solutions.

Innovation Solution

The use of two relays and a semiconductor switching element, controlled by an electronic unit, allows for automatic and manual switching off of DC currents with galvanic separation, preventing arcs and enabling efficient operation across a range of currents, including higher values, through a combination of automatic and manual control mechanisms.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If DC relays are used to interrupt current through switching contacts, then current switching capability is achieved, but switching arcs occur leading to contact burn and fusing

Engineering Contradiction:

Improvecurrent interruption capabilityVSAvoidswitching arc and contact burn

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A semiconductor switching element (IGBT) is introduced as an intermediary between the control coil and the switching contacts. The semiconductor element is connected in parallel with the switching contacts and is switched on before the contacts open, taking over the current flow and preventing arc formation at the contacts. This mediator protects the mechanical switching contacts from harmful arcs while maintaining reliable current interruption capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If gates are used for higher currents up to several 100 A, then contact fusing risk is reduced, but device size and cost increase significantly

Engineering Contradiction:

Improvecontact fusing resistanceVSAvoiddevice size and cost

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The switching function is segmented into two parts: a mechanical relay for galvanic separation and contact isolation, and a semiconductor switching element for current interruption. This segmentation allows the use of a smaller, less expensive relay while the semiconductor element handles the high current switching, achieving both reliability and cost-effectiveness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The mechanical system (gate) that would handle both galvanic separation and current interruption is replaced by a hybrid system combining a simple mechanical relay with an electronic semiconductor switch. The semiconductor element substitutes for the bulky mechanical current-interrupting mechanism, reducing device size and cost while maintaining the ability to handle high currents.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If relays are used for lower currents not exceeding 30 A, then device size and cost are reduced, but contact fusing occurs easily

Engineering Contradiction:

Improvedevice size and costVSAvoidcontact fusing resistance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The semiconductor switching element serves as a protective intermediary that absorbs the harmful switching arc energy before it can reach the relay contacts. By switching on the semiconductor element before the relay contacts open, the current is diverted through the semiconductor path, preventing arc formation and contact burn even in small, cost-effective relays designed for lower currents.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 prevents switching arcs, allows for safe and efficient current interruption, reduces the risk of contact fusing, and provides a cost-effective and space-efficient solution for photovoltaic plants, enabling reliable automatic and manual operation.

Implementation Method 1

a semiconductor switching element (4) interrupting the DC current for the switching contacts (K1, K2) to be de-energized

Methodology Applied

Scientific EffectSemiconductor switching: Diode

Implementation Method 2

The relay incorporates a control coil through which an electric current flows for a metal armature to attract

Methodology Applied

Scientific EffectElectromagnetic attraction: Electromagnet

Implementation Method 3

The overcurrent function is mostly realized by a wire wound about a bi-metal spring and deforming the spring at high current

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS8213133B2Load breaker arrangement

Publication Date: 2012.07.03 SMA SOLAR TECH AG

AI summary

A load breaker arrangement includes first and second input terminals, respectively, and first and second output terminals. The arrangement also includes two relays connected in series with one another, wherein the two relays are coupled between the second input terminal and the second output terminal, a semiconductor switch connected in parallel with one of the two relays, and a third relay coupled between the first input terminal and the first output terminal. A control circuit, in a load breaker mode, turns on the semiconductor switch while the two relays and the third relay are closed, then opens the one of the two relays in parallel with the semiconductor switch, then opens the semiconductor switch to break a current between the second input and second output terminals, and then opens the other of the two relays not in parallel with the semiconductor switch and opens the third relay.