Low-Frequency Circuit Breaker for Wind Generators
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Solution Overview
Problem
Current circuit breakers for wind generator systems are inadequate for cutting off low-frequency fault currents, particularly in permanent-magnet-type wind generators, as they lack cost-effectiveness and efficiency, with existing solutions like direct-current circuit breakers being large and costly, and thyristor switches causing conduction losses.
Innovation Solution
A low-frequency circuit breaker comprising a semiconductor switch and a mechanical switch, connected in parallel and series with an alternating-current path, utilizing anti-parallel thyristors and a circuit breaker control circuit to detect abnormalities and switch current flow through the thyristors for efficient cutoff, reducing conduction losses and maintaining constant current flow through mechanical switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a direct-current circuit breaker is used in a wind generator system, then the circuit breaker can cut off fault currents, but the circuit breaker becomes large and costly
Solution Approach 1:
The circuit breaker is divided into two distinct parts: a mechanical switch for normal current conduction and a semiconductor switch (thyristor) for fault current interruption. Each component is optimized for its specific function, allowing the mechanical switch to be smaller than a full-featured DC circuit breaker while the thyristor handles only the fault current interruption task.
Solution Approach 2:
The mechanical switch acts as an intermediary that carries normal operating currents, allowing the semiconductor switch to be smaller and less expensive since it only needs to handle fault currents. This mediator approach enables the system to achieve DC circuit breaker functionality with reduced size and cost.
2Weight of stationary object
If a thyristor switch is used to cut off current, then the circuit breaker can be smaller and cheaper, but conduction loss increases due to continuous conduction
Solution Approach 1:
The circuit breaker dynamically switches between two operational modes: During normal operation, the mechanical switch conducts current with low loss. When a fault is detected, the system transitions to using the thyristor switch for current interruption. This dynamic switching optimizes both size/cost and energy loss characteristics.
Solution Approach 2:
The mechanical switch is opened periodically or on-demand rather than remaining closed continuously, allowing the system to use the low-loss mechanical conduction path during normal operation while reserving the thyristor path for fault conditions. This periodic activation minimizes overall energy loss.
3Loss of energy
If a mechanical switch is used for current conduction, then conduction loss is low, but the switch cannot quickly interrupt fault currents
Solution Approach 1:
The mechanical switch serves as the primary current path with low conduction loss, while the thyristor switch acts as a backup intermediary that activates only when fault currents need to be interrupted. This arrangement allows the system to maintain low losses during normal operation while having rapid fault interruption capability when needed.
Solution Approach 2:
The thyristor switch is prepared and positioned to immediately take over current conduction when a fault occurs, while the mechanical switch continues carrying the load current. This preliminary arrangement ensures that fault interruption can occur rapidly without requiring the mechanical switch to open under high fault current conditions.
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
The solution provides a cost-effective, low-loss circuit breaker capable of efficiently cutting off abnormal low-frequency currents in wind generator systems, reducing the risk of semiconductor device damage and maintaining minimal operational losses.
Implementation Method 1
the first and second thyristors are made conductive by supplying a gate signal to the first and second thyristors
Implementation Method 2
the conduction current through the alternating-current path is switched to flow through the thyristors by opening the mechanical switch
Data Source
AI summary
An object is to obtain a low-frequency circuit breaker which has a simple configuration and a small size as a whole and is advantageous in view of costs. There is provided a low-frequency circuit breaker, in which a semiconductor switch and a mechanical switch are connected in parallel with each other. The semiconductor switch is configured by connecting a thyristor and a thyristor in anti-parallel with each other. These members are controlled by the circuit breaker control circuit.