Parallel UPS Bypass Switching for Balanced Power Sharing
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Solution Overview
Problem
In parallel uninterruptible power supply (UPS) systems operating in bypass mode, achieving even load distribution among multiple UPS units is challenging due to manufacturing differences and impedance mismatches, leading to potential overloading and system malfunctions, with existing solutions increasing cost, complexity, and weight while offering only partial load sharing accuracy.
Innovation Solution
A distributed control unit system where each UPS communicates with others to monitor current signals, set a reference RMS value, and adjust activation delays for bypass switches, ensuring balanced current sharing without a master-slave relationship and physical impedance adjustments, allowing for precise control of bypass switches to maintain continuous output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If physical impedance adjustments (inductors, cable length modifications) are used to achieve load sharing, then bypass-power sharing accuracy is improved, but device complexity, cost, and weight increase
Solution Approach 1:
The patent replaces physical impedance adjustments (mechanical/electrical components like inductors and cable modifications) with an electronic control system that uses activation delays and RMS value comparisons to achieve load sharing. This substitution eliminates the need for additional physical components while maintaining or improving sharing accuracy.
Solution Approach 2:
The patent changes the control parameter from physical impedance values to temporal parameters (activation delays) and electrical parameters (RMS values). By controlling when bypass switches are activated and comparing RMS values, the system achieves precise load sharing without modifying physical characteristics of the system components.
2Measurement precision
If physical impedance adjustments are made to achieve load sharing, then bypass-power sharing accuracy is improved, but system weight increases
Solution Approach 1:
The patent replaces heavy physical impedance components (inductors, modified cables) with lightweight electronic control circuitry that measures RMS values and controls activation timing. This substitution dramatically reduces system weight while achieving the same or better load sharing performance.
3Power
If more than four UPS units are coupled in parallel, then system power capacity and redundancy are improved, but load distribution becomes increasingly unbalanced
Solution Approach 1:
The patent implements a feedback mechanism where each UPS control unit monitors the RMS value of current in its bypass line, compares it with reference values from other UPS units, and adjusts its bypass switch activation delay accordingly. This continuous feedback loop maintains balanced load distribution even as the number of parallel UPS units increases beyond four.
Solution Approach 2:
The patent introduces dynamic activation delays that are adjusted in real-time based on load conditions and RMS value comparisons. This dynamic control allows the system to adapt to changing load distributions when additional UPS units are added, maintaining balance where static impedance adjustments would fail.
4Device complexity
If manufacturing differences and impedance mismatches are accepted, then device complexity is reduced, but bypass-power sharing accuracy deteriorates
Solution Approach 1:
The patent enables each UPS unit to automatically measure its own bypass line current RMS value, compare it with other units, and self-adjust its activation delay without requiring external calibration or manual impedance matching. This self-service approach compensates for manufacturing differences and impedance mismatches while adding minimal system complexity.
Data Source
AI summary
A UPS system includes a plurality of UPSs coupled in parallel and each having a bypass switch and a controller that is in communication with the controller of the other UPSs and including: a first unit monitoring the current flowing through a bypass line of its UPS and determining the effective value of the current strength; a second unit collecting the effective values of all of the UPSs having the bypass switch closed and defining a reference effective value corresponding to the lowest collected effective value; a third unit determining a delay for closing the bypass switch of said UPS, the delay being zero if the effective value of its UPS is equal to the reference effective value; and a fourth unit keeping the bypass switch closed if the delay is zero, or opening it for a duration corresponding to the delay before closing it.