Quasi-Resonant Thyristor Interruption for Fast Fault Turn-Off
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Solution Overview
Problem
Thyristors lack controlled turn-off capability, leading to prolonged disconnection times during overcurrent faults and impacting power quality in applications like Static Transfer Switches and micro-grid disconnect switches, as they can only be switched off during zero-crossing currents.
Innovation Solution
A solid-state switching apparatus comprising anti-parallel thyristors, a quasi-resonant turn-off circuit, and a control circuit that senses current magnitude and polarity to activate selectively conductive paths for commutating and interrupting the current, allowing for faster turn-off times by applying reverse bias voltage and utilizing auxiliary thyristors and resonant components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional thyristors are used without additional turn-off circuitry, then the device complexity is low, but the turn-off time is prolonged and current interruption capability is lost
Solution Approach 1:
The patent introduces a current turn-off circuit as an intermediary system that includes resonant components (inductor and capacitor), auxiliary thyristors, and switching elements. This intermediary circuit actively manages the turn-off process by creating resonant oscillations that force current to zero and apply reverse bias voltage to the main thyristor, enabling controlled turn-off without waiting for natural zero-crossing.
Solution Approach 2:
The patent changes the operational parameters of the thyristor by introducing external circuitry that modifies the voltage and current characteristics. The turn-off circuit applies reverse bias voltage and creates controlled current oscillations, fundamentally changing how the thyristor transitions from on to off state, thereby achieving active current interruption capability.
2Reliability
If thyristors wait for zero-crossing current to turn off, then the turn-off process is simple, but the fault current can rise to high levels during overcurrent faults
Solution Approach 1:
The turn-off circuit is pre-configured with resonant components and auxiliary switching elements that are ready to immediately activate when a fault condition is detected. The circuit includes pre-charged capacitors and positioned switches that can instantly initiate the current interruption sequence, applying reverse bias and forcing current to zero without waiting for the next zero-crossing event.
Solution Approach 2:
The patent implements preliminary anti-action by preparing the turn-off circuit in advance with opposing voltage polarity. When a fault occurs, the circuit immediately applies reverse bias voltage to counteract the forward current flow, preventing the fault current from rising to damaging levels by actively opposing the harmful current direction.
3Productivity
If a break-before-make approach is used in Static Transfer Switches, then the switching sequence is simple, but the transfer gap between thyristors can be a full electrical cycle period
Solution Approach 1:
The patent introduces dynamic control to the transfer switching process by enabling active turn-off of the outgoing thyristor regardless of current phase. This dynamic capability allows the system to force immediate current interruption and transition to the incoming thyristor without being constrained by the natural AC waveform zero-crossing, thereby reducing transfer time from a full cycle to a fraction of a cycle.
Solution Approach 2:
The patent replaces the passive, waveform-dependent mechanical switching approach with an active electronic control system. The turn-off circuit uses electronic switching elements, resonant oscillations, and controlled voltage application to substitute for the natural zero-crossing mechanism, enabling precise timing control and dramatically reducing the transfer gap between thyristor transitions.
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 enables rapid current interruption, reducing turn-off times to less than 20 microseconds and improving power quality by allowing active control over current disconnection, independent of zero-crossing events.
Implementation Method 1
a quasi-resonant turn-off circuit coupled in parallel with the pair of anti-parallel thyristors, wherein the quasi-resonant turn-off circuit includes a first selectively conductive path and a second selectively conductive path
Data Source
AI summary
In one aspect, a solid-state switching apparatus is provided that includes a pair of anti-parallel thyristors, a quasi-resonant turn-off circuit, a sensor, and a control circuit. The turn-off circuit is coupled in parallel with the pair of anti-parallel thyristors and includes a first selectively conductive path and a second selectively conductive path. The sensor is configured to sense a thyristor current conducted by at least one of the pair of anti-parallel thyristors. The control circuit is configured to receive the sensed thyristor current from the sensor and determine a magnitude of the sensed thyristor current and a polarity of the sensed thyristor current. The control circuit is further configured to activate, in response to determining that the magnitude is greater than a threshold value, one of the first selectively conductive path and the second selectively conductive path based on the polarity to commutate and interrupt the thyristor current.