Power Conversion Device Short-Circuit Switch DC Component Cancellation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional power conversion devices struggle to safely and promptly break accident currents that include a DC component, which can lead to unbalanced phases and failure of the AC circuit breaker during ground faults or short-circuits.
Innovation Solution
A power conversion device with a positive-side arm and negative-side arm, each comprising multiple unit converters connected in series, an AC circuit breaker, a short-circuit switch, and a control device that detects accidents and outputs commands to balance the current by short-circuiting the DC terminals, creating a zero-point auxiliary current to cancel the DC component in the accident current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If unit converters are connected in multistages to achieve high-voltage conversion capability, then transformer weight and volume are reduced, but when DC-voltage synthetic values of phases differ, excessive short-circuit current flows between phases
Solution Approach 1:
The short-circuit switch serves as a controlled intermediary that creates a designated short-circuit path between DC terminals. This controlled short-circuit path allows the system to safely manage and restrict short-circuit current flow, preventing excessive current while maintaining the benefits of the multistage unit converter configuration.
2Reliability
If buffer reactors are installed in each phase to restrict short-circuit current, then device protection is improved, but device complexity and cost increase
Solution Approach 1:
Instead of installing separate buffer reactors in each phase, the invention merges the protection function into a single short-circuit switch connected between the DC terminals. This unified approach provides comprehensive protection against short-circuit current in all phases while reducing overall device complexity and component count.
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 safe and prompt breaking of accident currents even when a DC component is present, preventing damage to the AC circuit breaker and ensuring system stability during unbalanced phase conditions.
Implementation Method 1
a short-circuit switch which is provided between the positive-side DC terminal and the negative-side DC terminal, and which connects the positive-side DC terminal and the negative-side DC terminal via a grounded point
Implementation Method 2
This AC circuit breaker extinguishes arc discharge produced between contacts when the contacts are separated from each other and breaks the above-described excessive accident current
Data Source
Figure 1~2
Figure 3~4
Figure 5~6B
AI summary
A power conversion device which is capable of decreasing an accident current passing through an AC circuit breaker, and which is capable of breaking the accident current safely and promptly, even when a DC accident current flows in an AC system side. This power conversion device is provided between a DC terminal including a positive-side DC terminal 10a and a negative-side DC terminal 10b, and a three-phase AC terminal, mutually converts power between DC and three-phase AC, and includes a positive-side arm 2a and a negative-side arm 2b each comprising a plurality of unit converters connected in multistage, each unit converter including switching devices 11a, 11b, and a capacitor 13, the positive-side arm and the negative-side arm being connected in series between the positive-side DC terminal 10a and the negative-side DC terminal 10b in each of the three phases, and a short-circuit switch 6 which is provided between the positive-side DC terminal 10a and the negative-side DC terminal 10b, and which connects the positive-side DC terminal 10a and the negative-side DC terminal 10b via the grounded point.