Thyristor Blocking Time Reduction in Electric Machine Power Systems
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Solution Overview
Problem
Existing power supply systems for high-power electric machines, such as those in hydroelectric power stations and wind turbines, take too long to block thyristors during faults, leading to extended periods where the electric machine is not supplied, due to the time required for current dissipation in electrical resistors.
Innovation Solution
Applying a negative voltage to thyristor terminals for a duration greater than the predetermined deactivation time, and using a control method that calculates and applies control signals to quickly switch the output terminals between positive and negative input terminals to ensure thyristor blocking, reducing the blocking time of the protection device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical resistors are used in series with thyristors to limit overcurrents, then overcurrent protection is improved, but the time required to block thyristors increases due to prolonged current dissipation
Solution Approach 1:
The patent extracts the current dissipation function from the electrical resistors and transfers it to a dedicated dissipation circuit. This allows the main thyristors to be blocked quickly without waiting for current dissipation through series resistors, as the dissipation occurs in a separate path. The electrical resistors are removed from series connection with thyristors, eliminating the delay caused by their presence during blocking.
Solution Approach 2:
The patent introduces an intermediary dissipation circuit that temporarily handles the current dissipation task. This intermediary circuit allows the main power path to be quickly interrupted while providing a separate path for current dissipation, thus mediating between the need for quick blocking and the need for safe current dissipation.
2Reliability
If the duration of negative voltage application to thyristor terminals is increased beyond the predetermined deactivation time, then thyristor blocking reliability is improved, but the control complexity increases
Solution Approach 1:
The control system applies negative voltage to thyristor terminals in advance and maintains it for a predetermined extended period to ensure reliable blocking before the actual fault condition occurs. This preliminary action guarantees that thyristors are fully deactivated and will not conduct during fault conditions, improving blocking reliability through proactive control.
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
This approach significantly reduces the time necessary to block thyristors, minimizing the period during which the electric machine is not supplied and enhancing fault protection and system recovery.
Implementation Method 1
a converter of a direct current input into a polyphase alternating current output comprising a plurality M of phases
Implementation Method 2
a storage bank comprising at least one storage capacitor arranged between the input terminals of the converter
Implementation Method 3
each switching branch comprising two thyristors connected head-to-tail and in parallel
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
This power supply system for an element (18), consisting of a rotor (18) and a stator, of an electrical machine, comprises: - a converter (30) of an input direct current into an output polyphase alternating current having a plurality M of phases, the converter (30) comprising two input terminals (42A, 42B), the converter (30) being disposed at the input of said element (18) and being suitable for delivering the polyphase alternating current to said element (18), - control means (32) for the converter (30), - a storage bank (34) comprising at least one storage capacitor (66, 68) disposed between the input terminals (42A, 42B) of the converter, and - a device (36) for protecting the element (18) against overvoltages and/or overcurrents of said polyphase alternating current, disposed between the converter (30) and said element (18), and comprising a plurality of switching branches (76) arranged between the respective phases of the polyphase alternating current,Each switching branch (76) comprises two thyristors (78) connected back-to-back and in parallel. The control means (32) are adapted to apply a negative voltage across the terminals of at least one thyristor (78) for a duration exceeding a predetermined turn-off time of said thyristor (78).