UPS Selective Tripping via Internal Impedance Identification
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Solution Overview
Problem
In power systems with multiple UPSs operating in parallel redundancy, a failed UPS can cause a chain reaction, leading to downtime in other 'good' UPSs and load devices, as existing methods require at least one cycle time (1/50 or 1/60 seconds) to determine failure and initiate selective tripping.
Innovation Solution
An uninterruptible power supply (UPS) with a control unit that identifies internal impedance using instantaneous voltage and current, employing a recursive identification process to generate a failure determination signal, allowing for selective tripping within a shorter time frame than one cycle time, utilizing a semiconductor bridge circuit and filter circuit with a trip switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional failure determination methods using one cycle-delay signals are used, then failure detection is reliable, but the tripping time is at least one cycle time (1/50 or 1/60 seconds)
Solution Approach 1:
The patent changes the detection parameter from one cycle-delay voltage and current signals to internal impedance parameters (resistance and inductance). By calculating impedance Z(s) = V(s)/I(s) and separating it into resistance Rs and inductance Ls components, the system can detect failures based on impedance variations without waiting for one full cycle, thus reducing tripping time while maintaining detection reliability.
Solution Approach 2:
The patent replaces the conventional time-based mechanical waiting period (one full AC cycle) with an electrical parameter calculation approach. By using instantaneous voltage and current measurements to compute impedance parameters through mathematical operations (Z(s) = V(s)/I(s), separating real and imaginary parts), the system achieves failure detection faster than the mechanical cycle time constraint would allow.
2Reliability
If selective tripping is implemented to prevent cascading failures, then system reliability is improved, but the complexity of failure determination increases
Solution Approach 1:
Each UPS unit independently determines its own failure status by monitoring its internal impedance parameters without requiring communication or coordination with other UPS units. The control unit calculates internal impedance using its own voltage and current measurements, compares against threshold values, and autonomously decides whether to trip. This self-service approach simplifies the overall system complexity while maintaining high reliability through distributed intelligence.
3Loss of time
If internal impedance identification is used for failure determination, then tripping time is reduced below one cycle time, but measurement precision requirements increase
Solution Approach 1:
The system continuously monitors voltage and current signals and uses feedback control to calculate impedance parameters. By establishing a feedback loop where the calculated impedance (Z(s) = V(s)/I(s)) is continuously updated and compared against threshold values, the system can detect failures rapidly with high precision. The feedback mechanism allows for real-time adjustment and refinement of measurements, compensating for noise and variations.
Solution Approach 2:
The patent performs preliminary calculations of impedance parameters using established mathematical relationships before actual failure detection is needed. By pre-defining the impedance calculation methodology (Z(s) = V(s)/I(s), separating into Rs and Ls components) and threshold values, the system is prepared to immediately identify failures when they occur, reducing measurement uncertainty and enabling faster response time.
Data Source
AI summary
UPS performance failure is determined independently by itself. Selective tripping can be done within a shorter time than one cycle of an AC output. A UPS converts a DC voltage to an AC voltage and supplies the AC voltage to a load device. A UPS has a control unit identifying a resistance value of an internal resistance as an internal impedance of the UPS by using an instantaneous value of an internal voltage and current and conducting a failure determination by detecting abnormal fluctuation of the value. It is preferred that an identification of the internal impedance is done through a system identification unit.