Hybrid Voltage Current Control for UPS Fault Isolation
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Solution Overview
Problem
Existing power systems with uninterruptible power supplies (UPSs) face challenges in managing DC fault current components during bolted faults, leading to large and potentially damaging currents that require oversized chokes for fault isolation, which is impractical and inefficient.
Innovation Solution
Implementing a hybrid voltage/current limiting control system that includes a controller to determine when a bridge current reaches a predetermined limit, modifying the capacitor voltage in the inverter to quickly re-center the fault current and reduce the DC fault current component, allowing for smaller choke sizes and efficient fault isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fault isolation methods are used without hybrid voltage/current control, then fault currents can be isolated, but oversized chokes are required which increase system size, cost, and complexity
Solution Approach 1:
The system dynamically changes the operating parameters of the inverter by modifying the capacitor voltage reference during fault conditions. The controller detects bridge current limits and adjusts the voltage parameter to reduce the DC fault current component, thereby reducing the required choke size while maintaining fault isolation capability
Solution Approach 2:
The patent implements a dynamic control system that continuously monitors bridge current and adapts the capacitor voltage in real-time during fault conditions. This dynamic adjustment allows the system to respond to changing fault conditions, reducing the need for oversized static components like chokes
2Reliability
If oversized chokes are used for fault isolation, then DC fault currents can be limited, but system cost and efficiency decrease
Solution Approach 1:
By changing the capacitor voltage parameter dynamically during fault conditions, the system achieves DC fault current limitation without requiring expensive oversized chokes. This parameter-based control approach reduces material costs and manufacturing complexity
3Ease of operation
If bridge current is not limited, then system operation is simpler, but DC fault current components cause damage and require oversized protection components
Solution Approach 1:
The controller implements feedback control by continuously monitoring the bridge current and comparing it against predetermined limits. When the limit is reached, the system automatically adjusts the capacitor voltage to reduce the DC fault current component, providing simple automated protection without complex manual intervention
Solution Approach 2:
The capacitor voltage acts as an intermediary control variable that mediates between the bridge current limit requirement and the fault current reduction goal. By adjusting this intermediate parameter, the system achieves fault current limitation while maintaining operational simplicity
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 enables rapid re-centering of fault currents, reducing the size of chokes by half compared to traditional methods, effectively eliminating large DC fault currents and enhancing the reliability and efficiency of UPS systems.
Implementation Method 1
modify, in response to the determination, a capacitor voltage in the inverter of the at least one UPS to reduce a DC fault current component of a load current in the inverter
Data Source
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AI summary
A system (300) is provided. The system includes a plurality of uninterruptible power supplies (UPSs) (302), each UPS of the plurality of UPSs including an inverter (330), a ring bus (306), and at least one controller (309) communicatively coupled to the plurality of UPSs, the at least one controller configured to determine when a bridge current in at least one UPS of the plurality of UPSs reaches a predetermined bridge current limit, and modify, in response to the determination, a capacitor voltage in the inverter of the at least one UPS to reduce a DC fault current component of a load current in the inverter.