NPC Power Converter Fault Protection via Switch Isolation
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Solution Overview
Problem
Neutral point clamped (NPC) power converters face operational issues due to short circuit conditions caused by inoperable NPC diodes, leading to increased fault current that can damage DC bus capacitors, and existing protection methods like crowbar circuits add cost and complexity.
Innovation Solution
A fault protection system for NPC power converters, comprising a DC bus, a switching network with series-connected switches and NPC diodes, and a control module that monitors and controls the switching network to detect and manage fault conditions by switching switches to an open position, determining the non-operational diode, and maintaining the corresponding switch in that position to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a crowbar circuit is employed to protect the power converter from fault conditions, then the power converter is protected from damage, but the cost and complexity of the system increases
Solution Approach 1:
The patent extracts the protection function from a separate crowbar circuit and integrates it into the existing switching network by utilizing the existing switches and diodes. The control module detects faults and selectively opens specific switches to isolate the faulty NPC diode, eliminating the need for additional crowbar circuitry while maintaining protection functionality.
Solution Approach 2:
The switching network components (switches and diodes) serve dual purposes: they perform their primary power conversion function and simultaneously provide fault protection. When a fault is detected, the control module manipulates these existing components to block fault current, allowing the system to protect itself without external assistance from separate protection circuits.
2Power
If NPC diodes are used in the power converter, then the converter can operate at higher voltage levels, but short circuit conditions can occur when NPC diodes fail
Solution Approach 1:
The control module continuously monitors the switching network and detects NPC diode failures before they can cause catastrophic damage. Upon detecting a faulty NPC diode, the control module immediately opens the corresponding switches in the same leg to prevent fault current from charging the DC bus capacitors to dangerous voltage levels, thereby preventing the harmful short circuit condition from developing.
Solution Approach 2:
The switches in each leg act as intermediaries between the NPC diodes and the DC bus capacitors. When an NPC diode fails, the control module opens these switches to mediate and block the fault current path, preventing the harmful interaction between the faulty diode and the capacitors that would otherwise lead to dangerous voltage levels.
3Device complexity
If fault current flows through DC bus capacitors when NPC diodes fail, then the capacitors can be damaged, but eliminating the need for protection circuits increases system simplicity
Solution Approach 1:
The patent merges the protection function with the existing switching network structure. The same switches and diodes used for normal power conversion operations are also used for fault protection. By combining these functions into a single integrated system controlled by the control module, the patent eliminates the need for separate protection circuits while still preventing capacitor damage from fault current.
Data Source
AI summary
A neutral point clamped (NPC) power converter fault protection system is provided, and include a DC bus, a switching network, and a control module. The switching network is connected to the DC bus. The switching network includes at least two leg circuits. Each of the at least two leg circuits includes at least two switches connected in series and two NPC diodes. Each of the two NPC diodes corresponds to one of the at least two switches. Each of the at least two switches has an open position. The two NPC diodes are connected between a corresponding one of the at least two leg circuits and the DC bus. The control module is in communication with the switching network. The control module includes control logic for monitoring the switching network to detect a fault condition.