Parallel UPS PWM Synchronization via Local Voltage Zero Crossing
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Solution Overview
Problem
In parallel UPS systems, high frequency circulating currents arise due to unsynchronized PWM pulses, requiring additional wiring and a 'master-slave' relationship for synchronization, which decreases system reliability.
Innovation Solution
The method synchronizes PWM pulses with locally measured critical bus voltage zero crossings, eliminating the need for communication and 'master-slave' relationships, thereby increasing system reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a master-slave synchronization method is used to synchronize PWM pulses in parallel UPS systems, then PWM pulse synchronization is achieved, but additional wiring is required and system reliability decreases due to single point failure
Solution Approach 1:
Each UPS unit independently synchronizes its PWM pulses by detecting the zero-crossing point of its own output voltage waveform. The control method uses local measurements and self-adjustment without requiring external synchronization signals or master-unit coordination, thereby eliminating additional wiring and single-point-failure risks while achieving PWM pulse synchronization across all parallel units
Solution Approach 2:
The synchronization function is segmented and distributed to each UPS unit individually rather than centralized in a master unit. Each unit's controller independently performs zero-crossing detection and PWM pulse width adjustment based on its own output voltage, dividing the synchronization task into autonomous local operations that eliminate dependency on inter-unit communication wiring
2Reliability
If PWM pulses are not synchronized in parallel UPS systems, then system complexity is reduced, but high frequency circulating currents are generated
Solution Approach 1:
The control method employs feedback by continuously monitoring the output voltage waveform of each UPS unit, detecting its zero-crossing point, and using this information to adjust the PWM pulse width accordingly. This closed-loop feedback mechanism ensures PWM pulses are synchronized to the actual output voltage, eliminating high-frequency circulating currents while maintaining system stability
Solution Approach 2:
The method dynamically changes the PWM pulse width parameter based on the detected zero-crossing point of the output voltage waveform. By adjusting the pulse width to coincide with the zero-crossing moment, the control system synchronizes PWM pulses across parallel units and eliminates circulating currents without requiring complex synchronization infrastructure
Data Source
AI summary
A method for pulse width modulated pulse synchronization in a parallel UPS system uses the locally measured critical bus voltage to detect a zero crossing and adjust the PWM pulse to coincide with the zero crossing. No communication between the units is required to perform synchronization, and no “master” and “slave” relationship exists to thereby increase the total system reliability.