UPS Current Balancing via Coupled Inductors
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Solution Overview
Problem
Current UPS systems face challenges in current share between parallel devices due to intrinsic differences in semiconductor devices, leading to unbalanced current distribution, which worsens with system scale and compact system builds.
Innovation Solution
The implementation of a series connection of switches with coupled differential mode inductors provides a cost-effective, scalable, and redundant bypass structure, compensating current unbalance through magnetically coupled windings, ensuring accurate and fault-tolerant current share in distributed bypass architectures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple parallel UPS devices are used to increase system capacity and redundancy, then system reliability and scalability are improved, but current unbalance between devices worsens due to intrinsic semiconductor differences
Solution Approach 1:
A current balancing circuit is introduced as an intermediary component between the parallel UPS devices. This circuit includes balancing resistors connected in series with each UPS device output, which actively compensate for current unbalance by adjusting the voltage drop across each device based on its actual current contribution, thereby achieving precise current sharing among devices with inherent semiconductor variations
Solution Approach 2:
The system implements a feedback mechanism where current sensors monitor the actual current output of each UPS device, and this information is fed back to control circuitry that adjusts the balancing resistor activation or values dynamically. This closed-loop feedback ensures that current share remains balanced even as operating conditions change, addressing the manufacturing precision issue while maintaining system reliability
2Area of stationary object
If compact system build is implemented to reduce space, then system footprint is reduced, but current unbalance worsens due to reduced cabling and increased wire impedance mismatch
Solution Approach 1:
The current balancing circuit with adjustable balancing resistors serves as an intermediary that compensates for the increased wire impedance mismatch inherent in compact builds. By introducing these balancing elements in series with each device, the system can offset the unequal cable impedances caused by compact routing, thereby maintaining current share accuracy despite the reduced physical space
Solution Approach 2:
The system dynamically changes electrical parameters (resistance values of balancing resistors) to compensate for the fixed physical constraints of compact routing. By adjusting these parameters based on measured current distribution, the system adapts to the specific impedance characteristics introduced by compact cabling arrangements, preserving current sharing precision
3Reliability
If distributed bypass architecture is used to improve fault tolerance, then system fault tolerance is enhanced, but current share control becomes more difficult due to lack of centralized control
Solution Approach 1:
Each UPS device in the distributed bypass architecture is equipped with its own local current sensing and balancing control circuitry. The devices autonomously monitor their own current output and adjust their balancing resistors independently based on local measurements, eliminating the need for complex centralized control while maintaining accurate current sharing across all devices
Solution Approach 2:
The current control function is segmented and distributed to individual UPS devices rather than being centralized. Each device operates as an independent control unit with its own balancing circuit, which simplifies the overall system architecture by removing complex inter-device communication requirements while enhancing fault tolerance through decentralized operation
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 achieves robust, passively controlled, and reliable current share among parallel UPS devices, particularly in phase splits with three or more devices, enhancing system reliability and scalability.
Implementation Method 1
compensating current unbalance through magnetically coupled windings
Data Source
AI summary
An uninterruptible power supply system includes: at least one AC input terminal; an AC output terminal; an DC input terminal; at least one uninterruptible power supply (UPS) device having: a DC link; a DC/AC converter connecting on a first side to the DC link and on a second side to the AC output terminal; and a DC/DC converter connecting on a first side to the DC input terminal and on second side to the DC link. The uninterruptible power supply system further includes at least two switches; and at least one coupled differential mode inductor having two windings. Each switch of the at least two switches is connected in series with at least one winding of the at least one coupled differential mode inductor forming a series connection. The series connection is connected on a first side to the at least one AC input terminal.