UPS Current Sensor for Unity Power Factor with Non-Linear Loads
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Solution Overview
Problem
Existing UPS systems with power factor correction fail to account for non-linear currents drawn by additional components like battery chargers, leading to suboptimal power factor operation.
Innovation Solution
A current sensing device is strategically placed to measure the net current from the AC supply, ensuring it is sinusoidal and in phase with the AC voltage, even when individual components like the battery charger and input rectifier have non-sinusoidal currents, by controlling switch S1 based on feedback from the current sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the current sensor measures only the rectifier current, then the power factor correction can be implemented for the rectifier, but the non-linear current drawn by the battery charger causes the overall power factor to deteriorate
Solution Approach 1:
The patent combines the measurement of currents from multiple sources (rectifier and battery charger) into a single net current measurement. The current sensor is positioned to measure the algebraic sum of currents from both the rectifier and battery charger, allowing unified power factor correction control that accounts for all load components rather than treating them separately
2Loss of energy
If the current sensor is placed to measure net current including battery charger, then unity power factor can be achieved for the overall system, but the measurement and control complexity increases
Solution Approach 1:
The patent introduces a current sensor as an intermediary measurement device that captures the combined effect of multiple current sources. This single measurement point serves as a mediator that simplifies the control system by providing one comprehensive feedback signal representing the net current, eliminating the need for multiple separate sensors and complex synchronization logic
3Adaptability or versatility
If additional UPS components like battery charger are connected to the AC supply, then the UPS functionality is enhanced, but the non-linear currents drawn by these components cause power factor deterioration
Solution Approach 1:
The patent implements a feedback control mechanism where the current sensor continuously monitors the net current drawn from the AC supply, and this measurement is fed back to the rectifier control system. The control system adjusts the rectifier switching based on this feedback to compensate for the non-linear currents from the battery charger, maintaining unity power factor despite the presence of additional components
Data Source
AI summary
A UPS has a current sensor for controlling operation of a UPS main power circuit positioned in series with the AC supply voltage so as to measure the net current used by each component connected to the UPS main power circuit. Feedback from the current sensor received by a control circuit is used to achieve unity power factor operation with the UPS. The current sensor location and operation is adaptable to both single phase and three phase operation.