Modular Multilevel Converter Fault Current Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modular multilevel power converters face high costs and increased mechanical and design complexity due to the high cost of capacitors required for energy storage, particularly in medium-voltage applications.
Innovation Solution
Regulating and controlling fault currents to reduce the energy stored in capacitors, using output chokes and magnetically coupled branch chokes to influence energy storage, and modulating common-mode voltage and internal currents to minimize capacitor requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitor size and energy storage capacity are increased to ensure reliable operation, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements dynamic control of fault currents during fault conditions, adjusting current forms and frequency spectra in real-time to minimize energy storage requirements. This dynamic approach allows the system to maintain reliability with reduced capacitor sizes by adapting the fault current characteristics rather than relying on oversized energy storage
Solution Approach 2:
The invention changes key operating parameters including current form, frequency, and frequency spectrum during fault conditions. By modifying these parameters dynamically, the system can control the energy stored in capacitors and maintain reliable operation with reduced capacitance values, thereby reducing device complexity
2Reliability
If capacitor energy storage capacity is increased to handle fault currents, then reliability is improved, but cost increases
Solution Approach 1:
The patent employs parameter changes by adjusting the frequency and frequency spectrum of fault currents. This allows the system to maintain fault tolerance with reduced energy storage capacity, directly lowering capacitor costs and overall manufacturing expenses
Solution Approach 2:
The invention implements feedback control mechanisms that monitor fault conditions and adjust current characteristics in real-time. This feedback enables the system to maintain reliability without requiring oversized capacitors, as the control system dynamically optimizes the fault current response
3Ease of manufacture
If capacitor size is reduced to lower cost, then manufacturing cost decreases, but the ability to handle fault currents is worsened
Solution Approach 1:
The patent uses dynamic control strategies that adjust fault current characteristics based on real-time system conditions. This dynamic approach compensates for reduced capacitor size by actively managing the fault current response, maintaining handling capability despite smaller energy storage
Solution Approach 2:
The invention changes current parameters including frequency and frequency spectrum to optimize fault current handling with reduced capacitance. By modifying these parameters, the system maintains adequate fault current handling capability while using smaller, less expensive capacitors
4Object-generated harmful factors
If output voltage harmonics are reduced to improve power quality, then power quality is improved, but device complexity increases
Solution Approach 1:
The patent employs a modular multilevel converter structure that segments the power conversion function into multiple discrete modules. This segmentation naturally produces low-harmonic output voltages while maintaining a manageable modular structure that can be scaled and configured flexibly
Solution Approach 2:
The invention achieves multiple functions within a unified modular framework: the same modular structure provides both low-harmonic output and flexible fault handling capabilities. This multi-functionality reduces overall device complexity compared to separate systems for each function
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a method for operating a modular multilevel converter (M) which has several electrically connected converter modules (SM) for each phase, each of which has an energy storage device (CSM) for storing electrical energy, wherein in the event of a fault, energy stored by at least one energy storage device (CSM) is influenced by a regulation and/or control of at least one load current (iL1 to iL3) of a phase of the multilevel converter (M) affected by the fault.