Thyristor Switch Phase Control for Simultaneous Turn-Off
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Solution Overview
Problem
In thyristor switches, variations in thyristor characteristics lead to some thyristors being turned off while others remain on, causing unwanted stress and potential breakdown due to uneven element operation timing.
Innovation Solution
A static switch with a controller that detects the phase of the power supply voltage and sets a target phase for gate signal interruption to prevent stress by ensuring all thyristors are turned off simultaneously, using a phase detecting unit and gate signal generating unit to manage the gate signal based on the power factor angle of the load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate signal is interrupted to turn off the thyristor switch, then the power supply to the load is interrupted, but due to variations in thyristor characteristics, some thyristors may remain in on-state causing unwanted stress and potential breakdown
Solution Approach 1:
The controller performs preliminary detection of the power supply voltage phase angle before interrupting the gate signal. By detecting whether the phase angle is within the predetermined range (around the zero-crossing point of the power supply voltage), the controller determines the appropriate timing to interrupt the gate signal, ensuring all thyristors turn off simultaneously and avoiding unwanted stress.
2Duration of action of stationary object
If the gate signal is interrupted at any timing, then the switching operation is simple and fast, but the uneven turn-off timing of thyristors accelerates deterioration and reduces the life of the thyristor switch
Solution Approach 1:
The controller continuously monitors the power supply voltage phase angle and uses this feedback information to determine the optimal timing for interrupting the gate signal. By comparing the detected phase angle with the predetermined range, the controller adjusts the gate signal interruption timing to ensure uniform turn-off of all thyristors, thereby extending the switch life without excessive complexity.
3Reliability
If the gate signal is blocked when load current is zero or almost zero, then thyristors are protected from damage due to ignition scattering, but the load current may not be properly controlled during normal operation
Solution Approach 1:
The controller applies different control strategies based on the local condition of the power supply voltage phase angle. When the phase angle is within the predetermined range (near zero-crossing), the controller blocks the gate signal to protect thyristors from ignition scattering. When the phase angle is outside this range, the controller allows normal gate signal operation for proper load control. This localized control approach protects thyristors while maintaining normal operation capability.
Data Source
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AI summary
A thyristor switch (1) is constituted of a pair of arms connected in anti-parallel, each of the arms including a plurality of thyristors connected in series. A controller (4) includes a phase detecting unit (10) configured to detect a phase of a power supply voltage supplied from an alternating-current power supply (2), and a gate signal generating unit (20) configured to interrupt a gate signal when an open command is provided to the static switch and the phase of the power supply voltage detected by the phase detecting unit (10) matches a target phase. The target phase is set outside of a phase range where interruption of the gate signal is prohibited, the phase range being set so as to include a zero crossing point at which a load current is switched in polarity.