Thyristor Controller Overvoltage Protection Circuit
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Solution Overview
Problem
Existing thyristor controllers are ineffective in reliably limiting overvoltages, as the summation circuit in B6 thyristor bridges only acts between phases, failing to address overvoltages between the input and output, and varistors are unsuitable due to their sluggish characteristic curve and rapid aging.
Innovation Solution
A circuit arrangement featuring a second diode bridge with three inputs connected to the outputs of a thyristor controller, where the outputs of the diode bridges are connected in series, and individual thyristors are separated from other components by the load, using passive components to cut off voltage peaks based on mains voltage and resistance, effectively limiting overvoltages both internally and externally.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a summation circuit from B6 thyristor bridge is used, then voltage peaks are cut between phases, but it fails to limit overvoltages between input and output of the thyristor controller
Solution Approach 1:
The invention divides the overvoltage protection into two separate diode bridges: the first diode bridge handles overvoltages between phases (acting between phase inputs), while the second diode bridge handles overvoltages between input and output of the thyristor controller. This segmentation allows each bridge to specialize in protecting specific voltage pathways, ensuring comprehensive coverage without compromising reliability.
2Reliability
If varistors are used for overvoltage protection, then voltage limiting is provided, but the characteristic curve is sluggish and rapid aging occurs
Solution Approach 1:
The invention replaces varistors with diode bridges composed of diodes, resistors, and capacitors. These components are more reliable, have longer service life, and do not suffer from the rapid aging characteristic of varistors. The diode bridge circuit provides immediate response to overvoltages without the sluggish characteristic curve of varistors, ensuring both reliability and extended operational duration.
3Loss of energy
If snubber capacitance is kept small to reduce losses, then switching losses are reduced, but voltage overshoot increases
Solution Approach 1:
The invention introduces diode bridges as intermediary components between the thyristor controller and the load. These diode bridges act as mediators that clamp voltage peaks without requiring large snubber capacitances. The diodes provide a low-impedance path for surge currents, limiting voltage overshoot while keeping snubber capacitance small, thus reducing switching losses while protecting against harmful voltage spikes.
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 precise voltage peak cutoff, is robust, and adjusts automatically to mains voltage, reducing surge currents and eliminating the need for tolerance adjustments, effectively managing overvoltages in both three-phase and single-phase operations.
Implementation Method 1
a first diode bridge with two bridge members each comprising two diodes, two inputs in the electrical middle of the bridge members and a first and a second output at which the ends of the bridge members are connected to one another
Implementation Method 2
a so-called TSE (Carrier Congestion Effect) circuit is usually connected in parallel to the thyristor. This usually consists of a resistor R connected in series and a capacitance C
Implementation Method 3
The discharge resistor ensures that the snubber capacitance is continuously discharged so that it can cyclically absorb the energy stored in the inductance during operation
Data Source
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AI summary
The invention relates to a circuit arrangement for thyristor controllers, comprising: • a first diode bridge 52 with three bridge elements, each comprising two diodes, three inputs 54 at the electrical center of the bridge elements, and a first 56 and a second 58 output, at which the ends of the bridge elements are connected together, • wherein a series connection of a first and a second electrical resistor is provided between the two outputs, • wherein an electrical capacitor is connected in parallel with the second resistor. The invention also relates to a thyristor controller with a circuit arrangement according to the invention.