UPS Module Current Balancing via Single Sensor
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Solution Overview
Problem
Existing multiple-module uninterruptible power supplies (UPS) face challenges in accurately controlling output current among modules due to variations in component characteristics, requiring expensive current sensors for each module, which increases costs and complicates current balancing.
Innovation Solution
A UPS system with subcontrollers in each module that measure input and output voltages, uses a single aggregate output current sensor, and calculates DC bus voltage targets to ensure equal output current distribution among modules, eliminating the need for individual current sensors and compensating for module variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple current sensors are used to measure output current of each module, then output current control precision is improved, but device cost increases
Solution Approach 1:
The patent combines multiple individual current measurements into a single aggregate current measurement. Instead of using separate current sensors for each module, the system uses one current sensor to measure the total output current, then distributes this measurement across modules using calculated current references based on module efficiency characteristics.
Solution Approach 2:
The patent creates a virtual copy of current measurement information through calculation. By measuring aggregate current and using stored efficiency data, the system calculates what each module's current contribution should be, effectively copying the measurement information needed without physical duplication of sensors.
2Measurement precision
If individual current sensors are installed for each module, then output current measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple individual measurement functions into a single measurement function. One current sensor measures the aggregate current, and the control system combines this single measurement with efficiency data to determine individual module current references, reducing sensor quantity and system complexity.
Solution Approach 2:
The patent introduces an intermediary calculation process that mediates between the single aggregate current measurement and the individual module current control. The efficiency characteristics stored in memory act as an intermediary, allowing the system to derive individual current references from the collective measurement without direct sensing of each module.
3Manufacturing precision
If module variations are compensated using individual current sensors, then current balancing accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent performs preliminary characterization of each module's efficiency characteristics during manufacturing or initialization. These efficiency values are stored in memory before operation, allowing the control system to compensate for module variations using pre-acquired data rather than requiring expensive individual sensors during operation.
Solution Approach 2:
The patent changes the approach from direct physical measurement to using efficiency parameters stored in memory. By utilizing these pre-determined efficiency characteristics and adjusting current references based on calculated values, the system achieves accurate current balancing without the manufacturing cost of multiple sensors.
Data Source
AI summary
In the preferred embodiments, an uninterruptible power supply has multiple UPS modules connected in parallel. Each module has an AC-DC-AC converter and a subcontroller for controlling the operation of the AC-DC-AC converter. A single current sensor senses a total aggregate current flowing from all the modules. Each subcontroller can detect an input voltage, output voltage, and DC bus voltage of each module. Also, each module has unique operating characteristics (e.g., efficiency curve and a responsiveness coefficient K). Operating characteristics data are stored in a memory accessible by the subcontroller. Based on the voltage and current measurements, and the operating characteristics of each module, the subcontrollers perform calculations to determine a DC bus voltage target (unique for each module) that results in each module providing the same output current. Accordingly, only one current sensor is needed, and, consequently, the cost of the UPS device can be reduced.