Parallel UPS Circuit Neutral Point Current Balance
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Solution Overview
Problem
Conventional online UPS systems face challenges in achieving current balance among multiple parallel-connected units, leading to inefficiencies, increased costs, and electromagnetic interference (EMI) due to the use of magnetic elements like inductors, which are difficult to manufacture and control independently.
Innovation Solution
The introduction of a decoupling switch with a reverse parallel-connected diode between the battery set and the neutral, allowing independent current control for each UPS mode, reducing the number of inductors and increasing the utilization rate of magnetic elements, while also incorporating additional control switches to manage EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple UPSs are parallel-connected with a jointly used battery set, then wire saving and improved total reliability are achieved, but current unbalance occurs among the UPS units
Solution Approach 1:
A neutral point is introduced as an intermediary connection between multiple UPS units and the battery set. This neutral point serves as a common reference that allows independent current control for each UPS while maintaining system-wide current balance through the shared neutral connection.
Solution Approach 2:
The battery connection is segmented into individual UPS-to-battery paths that converge at a common neutral point. This segmentation allows each UPS unit to independently control its current while the neutral point ensures overall system balance, resolving the current unbalance issue in parallel configurations.
2Stability of the object's composition
If inductors are used in the PFC circuit for voltage conversion, then stable voltage is provided to the inverter, but EMI is generated and inductor utilization rate is only 50%
Solution Approach 1:
Multiple inductors from different UPS units are merged into a single shared inductor that serves all parallel-connected UPS units. This consolidation reduces the total number of inductors, increases utilization rate above 50%, and reduces EMI through combined magnetic fields while maintaining voltage stability through coordinated control.
Solution Approach 2:
The shared inductor performs multiple functions: it provides voltage conversion for multiple UPS units simultaneously, acts as an EMI filter for the entire system, and serves as a common energy storage element. This multi-functionality resolves the contradiction by making the inductor more efficient while reducing overall EMI.
3Ease of operation
If conventional PFC circuits are used with separate battery connections for each UPS, then independent current control is achieved, but manufacturing costs and system volume increase
Solution Approach 1:
Multiple separate battery connections are merged into a single shared battery set with a common neutral point. This merging reduces system volume and manufacturing costs by eliminating redundant components while maintaining independent current control capability through the shared neutral architecture.
Solution Approach 2:
The shared battery set and neutral point structure serves multiple UPS units simultaneously, providing a universal power source and control reference. This multi-functional design reduces overall system complexity and volume while preserving independent current control for each unit.
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 enables current balance among multiple UPS modes, reduces the volume and manufacturing costs, and minimizes EMI by allowing independent current control and reducing the reliance on magnetic elements, thereby enhancing the overall efficiency and reliability of the parallel-connected UPS system.
Implementation Method 1
a first rectifying bridge including a first and a second bypass diodes coupled to a first middle point coupled to the second terminal of the first inductor
Implementation Method 2
a first PFC boost converter including a first PFC circuit outputting a second and a third DC voltages, and including a first inductor having a first terminal coupled to the positive terminal
Implementation Method 3
including silicon-controlled rectifiers (SCRs) SCR1-SCR2
Data Source
AI summary
The configurations of a parallel-connected UPS circuit are provided in the present invention. The proposed circuit includes a neutral, a battery having a positive and a negative terminals, and a plurality of PFC boost converters, each of which includes a PFC circuit including an inductor having a first terminal coupled to the positive terminal and a second terminal, a rectifying bridge coupled to the second terminal of the inductor, and having a first terminal and a second terminal coupled to the negative terminal, a switch bridge having a first terminal coupled to the first terminal of the rectifying bridge and a second terminal coupled to the second terminal of the rectifying bridge, and a control switch having a first terminal and a second terminal coupled to the neutral.