Parallel Power Converter Load Sharing via Shared Command Bus
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Solution Overview
Problem
Existing parallel connected power converter systems face challenges in accurate load sharing during transients due to lower bandwidth control loops and reliance on matched output resistances, leading to voltage sag and inaccurate current sharing.
Innovation Solution
A power supply system with multiple power converters connected in parallel, utilizing a shared command bus for current command signals, where a primary master converter drives the bus unless faulty, and a secondary master converter takes over, ensuring effective load sharing and redundancy without external control systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lower bandwidth auxiliary control loop is used to force load sharing, then load sharing is achieved, but accurate current sharing during load transients cannot be maintained
Solution Approach 1:
The control system is segmented into two independent loops: a high-bandwidth main voltage regulation loop and a lower-bandwidth auxiliary load sharing loop. The main loop operates at full bandwidth to maintain accurate voltage regulation and fast transient response, while the auxiliary loop handles load sharing at reduced bandwidth. This segmentation allows each loop to optimize its performance for its specific function without compromising the other.
2Reliability
If droop current sharing technology is used, then load sharing is achieved, but output voltage regulation deteriorates
Solution Approach 1:
The control architecture separates voltage regulation and load sharing functions into distinct loops. The main voltage regulation loop operates independently at full bandwidth to maintain precise output voltage regulation, while the auxiliary load sharing loop uses droop characteristics to distribute load current. This eliminates the trade-off present in traditional droop methods where voltage regulation must be compromised for load sharing.
Solution Approach 2:
An auxiliary control loop acts as an intermediary that introduces minimal disturbance to the main voltage regulation loop. The auxiliary loop generates small correction signals based on load sharing requirements without significantly affecting the primary voltage control function, thus maintaining both voltage regulation accuracy and load sharing capability.
3Reliability
If error amplifier outputs are tied together, then current commands are common, but offset and noise are converted directly into differences in output current
Solution Approach 1:
The control system separates the error amplifier stages from the load sharing control. Each power converter maintains its own independent error amplifier for voltage regulation, while a separate auxiliary control loop implements load sharing through current sensing and comparison. This segmentation prevents offset and noise from being directly converted into output current differences while still achieving common current commands through the auxiliary loop's coordinated control.
Data Source
AI summary
A power supply system includes multiple power converters, each having an input and an output. The outputs of the power converters are connected together in parallel to produce a single system output. There is a shared command bus that is coupled to each one of the power converters. A control loop in (associated with) a designated one of the power converters is operable to generate a current command signal to be output onto the shared command bus. All of the parallel connected power converters in the power supply system are configured to receive the current command signal from the shared command bus and to adjust an amount of electrical current being supplied by that power converter in response to the current command signal.