Parallel UPS Control via Master-Slave Current Sharing
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Solution Overview
Problem
Coordinating power distribution among multiple uninterruptible power supplies (UPS) in parallel configurations is complex and unstable, leading to increased power distribution costs and reliability challenges.
Innovation Solution
Implementing a master/slave configuration where one UPS controls the load voltage and another determines a reference output current value based on actual output currents from other UPS, with a controller adjusting the duty cycle of a control signal to synchronize output currents, and using current transformers for isolation and communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple uninterruptible power supplies are coordinated in parallel configuration, then power distribution capacity increases, but system complexity and instability increase
Solution Approach 1:
The system divides the parallel UPS coordination into distinct functional segments: master UPS units handle voltage control and current measurement, while slave UPS units handle current control only. This segmentation allows each unit to have simplified control logic while maintaining overall system capacity.
Solution Approach 2:
Current transformers serve as intermediary devices that isolate the control circuits from the power circuits. They provide electrical isolation while enabling communication of current measurements between UPS units, reducing interference and improving stability.
2Power
If multiple uninterruptible power supplies are coordinated in parallel configuration, then power distribution capacity increases, but power distribution costs increase
Solution Approach 1:
The master UPS units continuously measure the actual output current and provide feedback to slave UPS units. This feedback mechanism enables automatic load sharing adjustment, ensuring optimal power distribution that minimizes energy losses and operational costs.
3Reliability
If master/slave configuration is implemented with current transformation, then electrical isolation and safety improve, but device complexity increases
Solution Approach 1:
Current transformers act as intermediary devices that provide electrical isolation between the power circuit and control circuit. This isolation improves safety and reliability by preventing ground loops and electrical interference, while the standardized transformer design keeps the added complexity manageable.
Data Source
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AI summary
Systems and methods of operating uninterruptible power supplies in parallel in a power distribution system to provide power to a load are provided. At least one uninterruptible power supply inverter provides power to the load. A communication interface provides a measured value of at least one of inverter output current of a first uninterruptible power supply and a measured value of the load current to a second uninterruptible power supply, and receives a measured value of at least one of inverter output current of the second uninterruptible power supply and the load current. A controller controls the uninterruptible power supplies to operate in one of a master state and a slave state. In the master state the uninterruptible power supply is configured to control the voltage to the load, and in the slave state the uninterruptible power supply is configured to determine a reference output current value based at least in part on at least one of the measured value of inverter output current of the second uninterruptible power supply and the measured value of the load current. The uninterruptible power supply in the slave state drives its inverter output current toward the reference output current value to provide its share of the load current.