Active Thyristor Turn-Off in Power Converter Protection
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Solution Overview
Problem
Existing power converter systems face challenges in efficiently deactivating thyristor-based protective devices, leading to delayed restoration of normal operation due to the inability to precisely control thyristor turn-off times, especially during transient events, which increases the expense and complexity of the protective circuitry.
Innovation Solution
A method and device that actively control the thyristors in the external rectifier bridge using a sequence of voltage pulses to commutate the current back to the power converter, ensuring reliable and efficient turn-off of the thyristors by synthesizing the thyristor turn-off sequence based on the power converter topology and conducting states, minimizing stress on components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thyristors in the external rectifier bridge are used for overvoltage protection, then the power converter is protected from surge currents, but the thyristors cannot be precisely turned off until rotor currents naturally fall to zero, causing delayed restoration of normal operation
Solution Approach 1:
The patent applies preliminary action by detecting error situations (overvoltage or overcurrent conditions) before they become critical and activating the protective device in advance. The control device monitors DC bus voltage and rotor currents continuously, and triggers the thyristor bridge protection mechanism proactively when threshold values are approached, preventing catastrophic failures before they occur.
Solution Approach 2:
The patent implements feedback by continuously monitoring the operational state of the protective device and the power converter system. The control device receives feedback signals about DC bus voltage, rotor currents, and thyristor conduction states, and uses this information to determine when to activate or deactivate the protective device, ensuring timely restoration of normal operation after the error condition is resolved.
2Reliability
If the protective device remains activated until stator is separated from the grid, then complete protection is ensured, but normal power converter operation is interrupted for extended periods
Solution Approach 1:
The control device continuously monitors system parameters including DC bus voltage, rotor currents, and grid connection status. When the error condition is detected, the protective device is activated. The feedback mechanism tracks when the error condition resolves itself, and automatically deactivates the protective device to restore normal operation, balancing protection completeness with operational availability.
Solution Approach 2:
The protective device is designed to be self-regulating through the control logic that automatically detects when protection is no longer needed and deactivates the thyristor bridge accordingly. The system serves itself by monitoring its own state and making autonomous decisions about when to activate or deactivate protection, eliminating the need for manual intervention and maximizing operational availability.
3Strength
If freewheeling diodes and brake choppers are over-rated to handle transient surge currents, then the power converter can withstand surge currents, but the expense and complexity of the protective circuitry increases
Solution Approach 1:
The patent segments the protection function into a separate external thyristor-based rectifier bridge that operates independently from the main power converter. This segmentation allows the protective function to be optimized separately, using cost-effective thyristor technology for surge protection while keeping the main power converter components (freewheeling diodes and brake choppers) at their normal ratings, thereby reducing overall system complexity and cost.
Solution Approach 2:
The external thyristor rectifier bridge acts as an intermediary protective device between the rotor and the main power converter. It mediates the surge current handling by providing an alternative path for transient currents, protecting the main power converter components from having to be over-rated. This intermediary structure simplifies the main converter design while maintaining surge protection capability.
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 quick and secure deactivation of the thyristor-based protective device, reducing the delay in restoring normal power converter operation and minimizing the load on components, thus improving the reliability and efficiency of the protection mechanism.
Implementation Method 1
controllable switching elements that can be controllably switched at a high-frequency to convert the DC voltage of the DC intermediate circuit into a multiphase AC voltage
Implementation Method 2
a brake chopper that dissipates the excess energy out of the intermediate circuit to a brake resistor transforming it into heat therein
Implementation Method 3
The protective crowbar effectively short circuits the rotor terminals, so that the currents in the power converter can quickly be reduced to zero
Implementation Method 4
actively controlling the switching elements of the power converter device to produce a sequence of voltage pulses of suitable polarity and amplitude to serve as a thyristor turn-off sequence which is applied to the protective device to force commutation of the current from the protective device to the power converter device
Data Source
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AI summary
A method is disclosed to protect a power converter arrangement with a power converter that has a DC side that is connected to a DC intermediate circuit, an AC side, and controllable switches that can be controllably switched at a high frequency to invert the DC voltage of the DC intermediate circuit into an AC voltage. A protective device that can be activated and deactivated is provided to protect the power converter from overload by connecting an external thyristor rectifier bridge with a brake resistor (Rb ext) to the AC side of the power converter. If a predetermined error situation is detected (51), the external thyristors are triggered to turn on, to activate the protective device (52). If it is detected that the predetermined error situation has disappeared (53), the external thyristors are turned off (54) by ending the triggering of the thyristors and actively controlling the power converter switches to produce a sequence of voltage pulses of suitable polarity and amplitude to serve as a thyristor turn-off sequence that is applied to the protective device to force commutation of the current from the protective device to the power converter, to deactivate the protective device. A power converter arrangement with a device to protect against overload is also disclosed.