Parallel Power Conversion System Voltage Equalization
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Solution Overview
Problem
Conventional uninterruptible power supply systems face issues with cross currents between output terminals of multiple inverters due to voltage variations, requiring uniform input voltages and additional components like voltage detectors and pre-charging circuits, leading to system enlargement.
Innovation Solution
A power conversion system with interconnected power conversion devices and fuses that match DC bus voltages across devices, using annular wiring to equalize voltages and reduce the need for multiple voltage detectors and pre-charging circuits, thereby downsizing the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage detectors and pre-charging circuits are provided for each uninterruptible power supply device to uniform input voltages and prevent cross currents, then the reliability and stability of voltage control is improved, but the device complexity and system size are enlarged
Solution Approach 1:
The patent merges the voltage detection function into a single centralized detector that monitors the common DC bus voltage, rather than requiring individual voltage detectors in each uninterruptible power supply device. This consolidation maintains voltage control stability while reducing the overall number of components and system complexity.
Solution Approach 2:
The single voltage detector serves all uninterruptible power supply devices by monitoring the common DC bus voltage, making it a universal component that performs the voltage detection function for the entire system rather than being dedicated to individual devices. This multi-functional approach reduces redundancy and system size.
2Reliability
If pre-charging circuits are provided for each uninterruptible power supply device to charge capacitors before starting, then the reliability of starting operation is improved by preventing inrush current, but the device complexity and system size are enlarged
Solution Approach 1:
The patent merges the pre-charging function into a single centralized circuit that charges capacitors through the common DC bus, rather than requiring separate pre-charging circuits in each uninterruptible power supply device. This consolidation maintains starting reliability by preventing inrush current while reducing the overall number of components.
Solution Approach 2:
The common DC bus acts as an intermediary that enables a single pre-charging circuit to serve multiple uninterruptible power supply devices. The pre-charging circuit charges the DC bus, which then supplies charged capacitors to all connected devices, eliminating the need for individual pre-charging circuits at each device.
3Adaptability or versatility
If output voltages at multiple inverters vary, then the adaptability to different operating conditions is improved, but cross currents flow between output terminals causing harmful effects
Solution Approach 1:
The patent connects the DC buses of multiple uninterruptible power supply devices in common, creating an equipotential structure where all devices share the same DC voltage reference. This equipotential connection prevents potential differences between devices that would otherwise cause cross currents to flow between output terminals, while still allowing individual devices to adapt their output voltages to different operating conditions.
Data Source
AI summary
First to n-th (n is an integer of 2 or more) power conversion devices are connected in parallel to a load. First to n-th fuses are provided in first to n-th wirings, respectively. Each of the first to n-th power conversion devices includes a converter, an inverter, and a DC bus supplying a DC voltage from the converter to the inverter, and capacitors connected to the DC bus. An i-th (1≤i≤n−1) wiring includes the DC bus of an i-th power conversion device and the DC bus of an (i+1)-th power conversion device. The n-th wiring is connected between the DC bus of the n-th power conversion device and the DC bus of the first power conversion device.