Multiphase Thyristor Circuit with Quenching Switches
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Solution Overview
Problem
Existing multiphase electric circuits with AC power controllers face challenges in quickly shutting down thyristors during malfunctions, which can lead to increased current levels and potential damage, especially when connecting electrical grids or motor/generator loads, requiring a method to reduce current efficiently and prevent damage.
Innovation Solution
A circuit with two thyristors per phase, where a capacitor and quenching switches are used in series and parallel connections across all phases, allowing a quenching switch to counteract current through the thyristor, reducing it to zero, and the capacitor is charged to a negative voltage using a diode bridge and transformer for efficient shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single thyristor is used per phase in a multiphase electric circuit, then the device complexity is reduced, but the ability to quickly shut down current during malfunction is compromised
Solution Approach 1:
The single thyristor per phase is segmented into two thyristors (T1, T2) connected in parallel but oppositely directed. This segmentation allows independent control of each thyristor, enabling selective shutdown of one thyristor while the other remains conducting, thus maintaining current flow while achieving shutdown of the malfunctioning component.
Solution Approach 2:
A capacitor (C) connected in series with a quenching switch (QS) is introduced as an intermediary element to force current reversal through the thyristor. This intermediary mechanism enables active shutdown by driving reverse current through the thyristor, which forces it into the blocking state, providing a reliable shutdown capability that wasn't available with a single thyristor configuration.
2Reliability
If thyristors are over-dimensioned to handle malfunction currents, then the reliability during malfunction improves, but the device complexity and cost increase
Solution Approach 1:
The capacitor is pre-charged to a voltage sufficient to counteract maximum expected malfunction currents. This beforehand preparation ensures that when a malfunction occurs, the pre-charged capacitor can immediately drive reverse current through the thyristor to force shutdown, cushioning against the harmful effects of overcurrent without requiring the thyristor itself to be over-dimensioned.
Solution Approach 2:
The quenching circuit (capacitor + quenching switch) is prepared in advance to apply anti-action (reverse current) to the thyristor when malfunction occurs. This preliminary anti-action mechanism prevents the thyristor from being damaged by malfunction currents, eliminating the need to select thyristors with excessive current ratings.
3Stability of the object's composition
If a neutral conductor connects the neutral points of voltage systems, then the circuit stability improves, but the ability to implement quick shutdown reduces
Solution Approach 1:
The neutral conductor connection between the neutral points of the two voltage systems is extracted (removed) from the circuit. This extraction is necessary to enable the quenching mechanism to work effectively, as the neutral connection would provide an alternative current path that would prevent the capacitor from forcing complete current reversal through the thyristor, thereby enabling reliable shutdown.
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
Enables rapid and efficient shutdown of thyristors during overloads, preventing damage and ensuring safe operation, particularly in wind power systems by effectively managing current flow and polarity reversal.
Implementation Method 1
A single series connection is parallel connected to all phases, wherein this series connection consists of a capacitor and a number of parallel-connected quenching switches
Implementation Method 2
the capacitor can be charged to this voltage via a diode bridge and a transformer
Implementation Method 3
the capacitor can be charged to this voltage via a diode bridge and a transformer, wherein the capacitor preferably is connected via the diode bridge and the transformer to two phases of one of the two grids
Data Source
AI summary
In one embodiment of the present invention, a multiphase electric circuit is disclosed for shutting down a current conducted over respectively one AC power controller. The neutral points of the voltage systems connected to the phases are not connected to each other via a neutral conductor. The AC power controller of each phase is provided with two thyristors. A single series connection is connected parallel to all phases, which series connection comprises a capacitor and a number of parallel-connected quenching switches corresponding to the number of phases. The capacitor can be charged up via a diode bridge and a transformer.