Parallel UPS Ring Bus Fault Detection for Power Quality
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Solution Overview
Problem
In known power systems with multiple UPSs, transient conditions caused by a UPS failure can lead to reduced power quality due to saturation of PDU isolation transformers and inadequate fault current, affecting the power supplied to critical loads.
Innovation Solution
A controller is used to monitor and control UPS systems with a ring bus configuration, incorporating static switch modules to bypass chokes during faults, and a fault detection method that distinguishes between UPS and load faults by analyzing current differences, ensuring rapid disconnection of faulty units and maintaining power quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple UPSs are coupled to a load to provide power redundancy, then reliability is improved, but power quality deteriorates due to transient conditions and transformer saturation
Solution Approach 1:
A ring bus configuration with choke inductors is introduced as an intermediary between multiple UPS systems and the load. The chokes act as current-limiting elements that prevent transient currents from saturating the PDU isolation transformer when a UPS fails, thereby maintaining power quality while preserving redundancy benefits
Solution Approach 2:
The system segments the power distribution into distinct sections with individual chokes for each UPS connection point on the ring bus. This segmentation isolates fault currents to specific segments, preventing system-wide transformer saturation and enabling localized fault management while maintaining overall system reliability
2Reliability
If a UPS fails in a parallel configuration, then redundancy is maintained, but fault current becomes inadequate to clear the fault
Solution Approach 1:
The ring bus configuration with choke inductors pre-establishes a current path that limits fault current magnitude to prevent transformer saturation. When a UPS fails, the choke's inductive reactance naturally limits the fault current to a level that prevents saturation while still enabling the protective device to clear the fault, eliminating the need for high-magnitude fault currents
3Reliability
If PDU isolation transformer saturates during UPS failure, then fault isolation is achieved, but power quality to load deteriorates
Solution Approach 1:
The choke inductors are pre-installed in series with each UPS connection to the ring bus, creating a current-limiting barrier before fault conditions occur. When a UPS fails, these pre-positioned chokes immediately limit the transient current magnitude, preventing transformer saturation before it can degrade power quality to the load
Data Source
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AI summary
An uninterruptible power supply (UPS) system (100, 300) is provided. The UPS system includes a plurality of UPSs (102, 104, 106, 302, 304, 306), a ring bus (118, 314, 410, 510) that electrically couples the UPSs (118, 314, 410, 510) together, a static switch (340, 342, 344) coupled between an associated UPS of the UPSs (118, 314, 410, 510) and the ring bus (118, 314, 410, 510), and a controller (200). The controller (200) receives current data representative of an inverter current and a load current associated with the associated UPS. An output capacitor (606) of the associated UPS is coupled to a node that conducts the inverter current and the load current. The controller (200) further calculates a measured current based on the received current data, determines a voltage of said output capacitor (606), generates a derived current based on the determined voltage and a predetermined capacitance of said output capacitor (606), compares the measured current and the derived current to identify a fault location, and controls said static switch (340, 342, 344, 408) based on the identified fault location.