Multi-Port DC Transfer Switch Using Negative-Voltage Current Commutation
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Solution Overview
Problem
Conventional DC transfer switches in LCC-HVDC transmission systems face issues of environmental harm due to SF6 gas, bulkiness due to low-frequency LC circuits, and high costs from multiple two-port switches, which are inefficient for high-frequency operations and require extensive energy absorption.
Innovation Solution
A multi-port DC transfer switch utilizing a controllable negative voltage source with shared current commutation branches and controllable conduction switches, incorporating vacuum switches and a square wave resonant DC circuit breaker to facilitate rapid current transfer across multiple branches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional two-port DC transfer switches are used to achieve operation mode switching in LCC-HVDC transmission systems, then the switching requirements can be met, but multiple independent switches are required which increases device complexity and cost
Solution Approach 1:
The patent applies multi-functionality by designing a single multi-port DC transfer switch that can perform multiple operation mode switching functions (metallic return transfer, earth return transfer, neutral bus switching) that previously required separate two-port switches. The switch integrates multiple ports and shared current commutation branches to handle different switching scenarios within one device, reducing the total number of switches needed in the system.
Solution Approach 2:
The patent combines multiple functional components into a unified structure. The multi-port DC transfer switch merges multiple main branches, shared current commutation branches, and controllable conduction switches into a single integrated device. This consolidation eliminates the need for separate independent switches while maintaining all required switching capabilities.
2Reliability
If SF6 gas is used as arc extinguishing medium in conventional DC transfer switches, then arc extinction can be achieved, but environmental harm is caused due to SF6 being a strong greenhouse gas
Solution Approach 1:
The patent replaces the harmful SF6 gas with vacuum as the arc extinguishing medium. Vacuum switches use the vacuum environment itself to extinguish arcs, eliminating the need for SF6 gas entirely. This substitution maintains arc extinction capability while removing the environmental harm associated with SF6 greenhouse gas emissions.
3Reliability
If low-frequency LC oscillation circuits are used in conventional DC transfer switches, then current commutation can be achieved, but the equipment becomes bulky due to the low frequency requirements
Solution Approach 1:
The patent introduces dynamic control through controllable conduction switches that can rapidly change their conduction state. This dynamic switching capability allows the system to achieve current commutation without relying on low-frequency LC oscillation circuits, thereby reducing the size of inductors and capacitors needed while maintaining reliable current transfer functionality.
4Adaptability or versatility
If multiple independent two-port switches are configured to meet different switching requirements, then all operation modes can be supported, but the cost increases due to multiple arresters needing to absorb energy
Solution Approach 1:
The patent merges the energy absorption function into the shared current commutation branches that are common to all main branches. By using shared branches with controllable switches, the system can transfer current between different ports without requiring multiple independent arrester groups, thereby reducing energy loss 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
Reduces the need for high-cost equipment like capacitors and reactors, minimizes environmental impact by replacing SF6 with vacuum switches, and enhances operational speed through high-frequency current transfer.
Implementation Method 1
the current commutation path is composed of LC oscillation circuit. The working process of the DC transfer switch is as follows: responding to the separating brake signal, the mechanical switch contacts are separated, the arc is generated between the contacts, and the arc resistance presents a nonlinear change; due to the negative impedance characteristics of the arc, the oscillating current in the LC circuit diverges and oscillates.
Implementation Method 2
the arc is generated between the contacts, and the arc resistance presents a nonlinear change; due to the negative impedance characteristics of the arc, the oscillating current in the LC circuit diverges and oscillates. When the sum of the load current and the oscillating current superimposed on the load current path passes across zero, the arc of the mechanical switch is extinguished
Implementation Method 3
minimizes environmental impact by replacing SF6 with vacuum switches
Data Source
AI summary
The invention discloses a multi-port DC transfer switch based on a controllable negative voltage source, which belongs to the technical field of power equipment. It includes X (X=5 or 3) main branches, a current commutation branch and X groups of controllable conduction switches. The main branch is composed of through-current vacuum switch, and the current commutation branch is composed of a controllable negative voltage source and a square wave resonant DC circuit breaker in series. The five main branches at the sending terminal are connected to the positive rectifier at the sending terminal, etc., and the three main branches at the receiving terminal are connected to the positive rectifier at the receiving terminal, etc., which are connected to the current commutation branch through the controllable conduction switches.