UPS Control Apparatus Phase-Locked Zero-Cross Switching
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Solution Overview
Problem
Off-line uninterruptible power systems lack phase locking function, leading to instantaneous short circuits and excessive switching stress on the switch unit due to delayed switching times, which can result in switch unit damage.
Innovation Solution
The implementation of a control apparatus that generates a base triangular wave signal to determine if its cross-over value is within a predetermined range at the zero-crossing point of the mains voltage, allowing for phase-locked switching and adjusting the frequency of the base triangular wave signal to optimize switching timing, thereby preventing instantaneous short circuits and reducing switching stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase locking function is added to prevent instantaneous short circuit, then reliability is improved, but device complexity increases
Solution Approach 1:
A phase lock detection module is introduced as an intermediary component that detects the phase difference between mains voltage and conversion voltage, and generates phase lock detection signals to control the switching timing. This mediator enables phase-locked switching without requiring complex overall system redesign, thereby improving reliability while limiting complexity increase to a specific functional module.
2Reliability
If switching is performed at zero crossing point to reduce switching stress, then switch unit reliability is improved, but switching precision deteriorates due to delay time
Solution Approach 1:
The control apparatus performs preliminary detection of the zero crossing point of the mains voltage using the phase locked loop before actual switching occurs. By detecting the zero crossing point in advance and using it to trigger the switching action, the system compensates for the inherent delay time in the switch unit, ensuring that switching occurs precisely at the zero crossing point rather than after the delay.
Solution Approach 2:
A feedback mechanism is implemented where the phase lock detection module continuously monitors the phase difference between mains voltage and conversion voltage, and adjusts the switching timing based on this feedback. The phase lock detection signal is generated based on the detected phase difference, creating a closed-loop control system that maintains precise zero-crossing switching despite variations in system response time.
3Manufacturing precision
If frequency adjustment of base triangular wave signal is implemented to optimize switching timing, then switching precision is improved, but control complexity increases
Solution Approach 1:
The frequency of the base triangular wave signal is adjusted as a controllable parameter to optimize switching timing. The phase locked loop detects the zero crossing point of the mains voltage and adjusts the frequency of the triangular wave signal accordingly, enabling precise synchronization between the inverter output and the mains voltage. This parameter adjustment approach allows flexible control of switching timing without requiring fundamental changes to the control architecture.
Data Source
AI summary
An uninterruptible power system includes a power conversion apparatus, a switch unit and a control apparatus. The switch unit outputs a mains voltage in a line mode, and output an alternating conversion voltage in a battery mode. The control apparatus is configured to generate a base triangular wave signal according to the mains voltage. When the uninterruptible power system is in a battery mode and the control apparatus detects the regeneration of the mains voltage, the control apparatus is configured to determine whether a cross-over value of the base triangular wave signal is within a predetermined range when the mains voltage is at a zero-cross point. The control apparatus is configured to control the switch unit to output the mains voltage instead of the alternating conversion voltage when the cross-over value of the base triangular wave signal is within the predetermined range.