Modular Multilevel Converter DC Fault Isolation
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Solution Overview
Problem
Existing DC fault isolation systems face challenges in reducing fault isolation response time, DC fault current magnitude, component count, improving system reliability, and stability, with many requiring passive component charging or using semiconductor devices solely for fault current interruption.
Innovation Solution
The system employs a modular multilevel converter (MMC) with AC/DC converters that interrupt current flow through one arm and transmit AC current through another, utilizing a controller to detect faults, limit current, and isolate faults quickly by creating an intentional short circuit, allowing the DC circuit breaker to isolate the fault under zero current conditions without precharging capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive component charging is performed before fault isolation, then system reliability is improved, but fault isolation response time increases
Solution Approach 1:
The power converter is pre-configured with charged capacitors and ready-to-switch semiconductor devices before a fault occurs. This preliminary preparation eliminates the need for charging operations during fault isolation, enabling immediate response while maintaining system reliability through pre-charged energy storage components.
2Object-generated harmful factors
If semiconductor devices are used solely to interrupt fault current, then fault current magnitude is reduced, but device complexity increases
Solution Approach 1:
The power converter is designed to perform multiple functions: normal power conversion operation and fault current interruption. By integrating both functions into a single device with bidirectional switching capability, the system reduces fault current magnitude without requiring separate dedicated fault protection devices, thereby managing complexity.
Solution Approach 2:
Instead of using unidirectional switches that only block current in one direction, the invention employs bidirectional switches that can interrupt current in both directions. This inverted approach allows a single switch to replace what would traditionally require multiple unidirectional devices, reducing overall system complexity while maintaining fault current suppression capability.
3Stability of the object's composition
If DC circuit breaker is used for fault isolation, then system stability is improved, but offline time increases
Solution Approach 1:
The power converter acts as an intermediary device between the fault location and the DC circuit breaker. It rapidly redirects fault current through its bidirectional switches before the circuit breaker operates, enabling the breaker to isolate the fault under near-zero current conditions. This mediation allows the circuit breaker to maintain system stability while minimizing its own operation time and reducing offline period.
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 fault isolation response time, minimizes fault current magnitude, decreases system downtime, enhances reliability, and maintains stability by quickly isolating faults and resuming normal operation without precharging, thus improving overall system performance.
Implementation Method 1
operating an AC/DC converter in response to a DC fault by interrupting current flow through a first arm of the converter and transmitting AC current through a second arm of the converter
Data Source
AI summary
Unique systems, methods, techniques and apparatuses of a DC fault isolation system are disclosed. One exemplary embodiment is a power conversion system comprising a converter including a midpoint connection structured to receive AC power, a first converter arm, a second converter arm, and a control system. The control system is configured to operate the converter a fault condition mode in response to a DC fault condition, wherein the fault condition mode operates at least one full bridge cell of the second converter arm so as to interrupt current flowing between the midpoint connection and the second DC bus rail and operates the first converter arm so as to allow the AC power to flow between the midpoint connection and the first DC bus rail in response to detecting the DC fault condition.