Power Converter Semiconductor Protection During DC-Link Start-Up
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Solution Overview
Problem
Semiconductor switches in power converters, particularly gate commutated thyristors, have limited dv/dt robustness when un-powered, leading to potential destruction during DC-link charging and circuit breaker bouncing, due to excessive voltage surges.
Innovation Solution
A protective capacitor arrangement is connected between the semiconductors and the power supply to mitigate high dv/dt, and replacing mechanical circuit breakers with semiconductor switches to prevent voltage surges during start-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If power for the gate unit is taken from the DC-link, then the converter can operate with a simpler power supply arrangement, but the gate unit is un-powered during the first part of DC-link charging and vulnerable to excessive dv/dt
Solution Approach 1:
The auxiliary power supply is activated before the main DC-link charging process to power the gate units in advance. This preliminary action ensures that the gate units are already powered and can properly control the thyristors during the critical charging phase, preventing uncontrolled commutation and excessive dv/dt that would occur with un-powered gates.
Solution Approach 2:
An auxiliary power supply is introduced as an intermediary power source between the AC grid and the gate units. This intermediary supply provides the necessary gate drive power during the transition period before the main DC-link is charged, bridging the gap between AC input and DC-link output power availability.
2Productivity
If the converter is charged from the AC side with alternating current, then the converter can be energized, but current commutation after zero crossing may cause excessive dv/dt that exceeds the thyristor's dv/dt limit
Solution Approach 1:
The gate units are powered in advance by the auxiliary power supply before AC charging begins. This preliminary powering ensures that when current commutation occurs after zero crossing, the gate units are already active and can properly control the thyristor switching, preventing uncontrolled dv/dt spikes that would damage un-powered thyristors.
3Ease of operation
If a mechanical circuit breaker opens during charging, then the charging process can be interrupted, but this causes a bouncing circuit breaker effect that generates excessive dv/dt
Solution Approach 1:
The patent replaces mechanical circuit breakers with semiconductor switches for charging control. This substitution eliminates the mechanical bouncing effect that causes excessive dv/dt. The semiconductor switches provide smooth, controlled opening and closing without mechanical contact bounce, thereby preventing voltage surges while maintaining charging control 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
The solution effectively limits dv/dt during start-up, preventing damage to semiconductors and ensuring reliable operation of power converters by ensuring the gate units are powered during critical phases and reducing the risk of parasitic turn-on.
Implementation Method 1
A capacitor arrangement, comprising at least one capacitor, is connected between the semiconductors and the power supply
Data Source
Figure 1~2b
Figure 3~4
AI summary
The present disclosure relates to a converter arrangement comprising a power converter (1), converter terminals (8), connecting the converter to an AC mains (6) via circuit breakers (7), and a capacitor arrangement (4) comprising at least one capacitor, connected in the converter arrangement between semiconductors of switches of at least one converter cell and a power supply (6) configured for charging gate units of the cell switches during start-up of the converter. The capacitor arrangement is configured to protect the semiconductors of the cell switches from voltage surges during the start-up of the converter.