Parallel Power Converter DC Bus Isolation for Cascading Failure Prevention
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Solution Overview
Problem
Conventional uninterruptible power supply systems face issues with varying output voltages and cross currents between power converters, leading to potential failures when one converter fails, causing others to malfunction due to overcurrent flow.
Innovation Solution
A power conversion system with interconnected DC buses through wirings and a control circuit that stops operation when excessive current is detected, ensuring uniform input voltages and isolating failed converters to prevent cascading failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC buses of multiple power converters are connected in parallel to suppress output voltage variation, then uniform input voltages are achieved and cross current is reduced, but when one converter fails with short-circuit, overcurrent flows from other converters causing cascading failures
Solution Approach 1:
The patent divides the DC bus system into segmented sections by introducing isolation switches between individual power converter DC buses. This segmentation allows the system to maintain electrical connectivity for voltage uniformity while enabling isolation of faulty units, preventing overcurrent from affecting the entire system.
Solution Approach 2:
The patent introduces current detectors and isolation switches as intermediary components between power converters. These intermediaries monitor current flow and automatically isolate failed converters, acting as a protective barrier that prevents harmful overcurrent from propagating through the parallel-connected DC bus system.
2Adaptability or versatility
If conventional parallel connection of power converters is used, then system redundancy is achieved, but cross current flows between converters with different output voltages
Solution Approach 1:
The patent implements a control mechanism where current detectors continuously monitor the DC bus connections and provide feedback to the control circuit. When voltage differences cause cross current, the feedback signal triggers the isolation switch to open, eliminating the cross current while maintaining the redundant parallel architecture.
Solution Approach 2:
The patent makes the DC bus connection dynamic by introducing controllable isolation switches that can change their state based on system conditions. This allows the system to adaptively connect or disconnect individual converters, optimizing performance by preventing cross current while maintaining redundancy capability.
3Reliability
If isolation switches and current detectors are added to prevent cascading failures, then failure range is limited, but device complexity increases
Solution Approach 1:
The patent implements a self-service protection mechanism where the system automatically detects and isolates failed converters without requiring external intervention or complex control systems. The current detectors and isolation switches work autonomously to protect the system, adding minimal complexity while achieving reliable failure isolation.
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 solution effectively reduces cross currents and limits failure range, ensuring continued operation and preventing other converters from failing when one fails, while also simplifying the system design by reducing the number of current detectors needed.
Implementation Method 1
a capacitor connected to the DC bus, for smoothing the DC voltage
Data Source
AI summary
An uninterruptible power supply system includes a plurality of uninterruptible power supply devices, and each uninterruptible power supply device includes a conversion circuit, an inversion circuit, a DC positive bus, a DC negative bus, and a capacitor. The uninterruptible power supply system includes a first wiring connected between DC positive buses of two uninterruptible power supply devices, and a second wiring connected between DC negative buses of the two uninterruptible power supply devices. The operation of all uninterruptible power supply devices is stopped in response to an absolute value of a current flowing through a bundle of the first and second wirings exceeding an upper limit value.