DC Grid Protection Coordination With SSCBs and Pre-Charging

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Solution Overview

Problem

DC distribution systems face challenges in protecting against short circuits and other fault sources due to the fast self-protection functions of power electronics in converters, which can lead to damage from voltage reversal and high current peaks, and result in selectivity issues with active front ends.

Innovation Solution

A method for coordinating protective devices in a distribution network using solid-state circuit breakers (SSCBs) that can disconnect fault regions within 10 μs, combined with electromechanical switches and pre-charging apparatuses to manage fault currents and restore voltage, allowing for selective operation and minimizing power losses and costs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If semiconductor switches (SSCBs) are used for fast fault interruption, then fault current interruption speed is improved (within 10 μs), but power loss and cost increase significantly

Engineering Contradiction:

Improvefault current interruption speedVSAvoidpower loss

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The protective device is divided into two functional segments: a semiconductor switch (IGBT) for fast fault detection and initiation (within 10 μs), and an electromechanical switch for the actual current interruption. This segmentation allows each component to perform its optimal function - the semiconductor provides speed while the electromechanical switch provides energy efficiency for the interruption task.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control unit acts as an intermediary that receives fault signals from the semiconductor switch and triggers the electromechanical switch. This intermediary coordination enables the system to achieve fast fault response through the semiconductor while using the electromechanical switch for the energy-efficient interruption of fault current.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If semiconductor switches are used throughout the distribution network, then fault response time is improved, but device complexity and cost increase

Engineering Contradiction:

Improvefault response timeVSAvoidnumber of semiconductor switches

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

Instead of uniformly deploying semiconductor switches throughout the entire distribution network, the invention applies them selectively only at critical locations where fast fault detection is most beneficial. The electromechanical switches handle routine protection tasks, reducing overall system complexity while maintaining fast response where needed.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system dynamically coordinates between semiconductor and electromechanical switches based on fault conditions. The semiconductor switch provides fast initiation capability, while the electromechanical switch provides reliable interruption - creating a dynamic hybrid protection scheme that adapts to different operational requirements.

Inventive Principle:

Principle #15Dynamics

3Loss of energy

If conventional electromechanical switches are used, then power loss is reduced, but fault current interruption speed is insufficient for high current peaks

Engineering Contradiction:

Improvepower lossVSAvoidfault current interruption speed

Core Design Contradiction:

Loss of energyVSSpeed

Solution Approach 1:

The semiconductor switch performs preliminary action by detecting the fault condition and initiating the tripping sequence within 10 μs. This preliminary detection and signal generation prepares the system for rapid response, while the electromechanical switch executes the actual interruption, combining the benefits of fast detection with energy-efficient switching.

Inventive Principle:

Principle #10Preliminary action

4Adaptability or versatility

If self-protection functions of power electronics are relied upon, then selectivity is improved, but protection reliability deteriorates due to voltage reversal and uncontrolled rectifier operation

Engineering Contradiction:

ImproveselectivityVSAvoidprotection reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The coordinated protective device acts as an intermediary between the power electronic converter's self-protection and the main distribution network protection. It provides a controlled interface that prevents uncontrolled rectifier operation and voltage reversal issues while maintaining selectivity through the semiconductor switch's fast response capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The semiconductor switch provides preliminary anti-action by detecting fault conditions and triggering the protection mechanism before voltage reversal or uncontrolled rectifier operation can occur. This preemptive action prevents the harmful effects while maintaining system selectivity.

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS12237125B2Method for coordinating protective devices in a distribution grid

Publication Date: 2025.02.25 SIEMENS AG

AI summary

In a method for coordinating a distribution grid of different levels of electromechanical switches and automatically electrically closable apparatuses in a DC circuit, the distribution grid is arranged between feed-in devices and loads and includes at least one busbar. Each of the apparatuses includes an electrical switch to open or close the DC circuit, a fault current detection device, a tripping unit, and a pre-charging apparatus.