Parallel Converter Reactive Power Control for Circulating Current Suppression
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Solution Overview
Problem
Circulating currents in power supply systems connected in parallel or series combinations lead to adverse effects such as overcurrent protection and current leakage, affecting the normal operation of the power supply system.
Innovation Solution
A power supply system and converter design that adjusts actual output reactive power based on target and compensated reactive power, using phase differences or modulation ratios between common-mode output currents and voltages to minimize voltage differences between converters, thereby suppressing circulating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple converters are connected in parallel or series-parallel to increase power capacity, then the power transmission capability is improved, but circulating current is generated causing overcurrent protection and current leakage
Solution Approach 1:
The patent changes the operating parameters of converters by dynamically adjusting output reactive power based on common-mode voltage differences. By monitoring and adjusting reactive power parameters, the system eliminates circulating current while maintaining parallel connection configuration for high power capacity.
Solution Approach 2:
The patent implements a feedback control mechanism where the converter controller continuously monitors common-mode output voltages of parallel-connected converters and adjusts output reactive power accordingly. This closed-loop feedback eliminates circulating current by compensating for voltage differences between parallel converters.
2Object-affected harmful factors
If common-mode voltage difference between parallel converters is reduced to suppress circulating current, then circulating current is suppressed, but control complexity increases
Solution Approach 1:
The patent enables converters to autonomously adjust their own output reactive power based on locally measured common-mode voltage differences. Each converter independently calculates and implements compensation without requiring complex inter-converter communication or centralized control, thereby suppressing circulating current while maintaining simple control architecture.
3Object-affected harmful factors
If output reactive power is adjusted to control common-mode output voltage, then circulating current is suppressed, but total output reactive power may be affected
Solution Approach 1:
The patent applies partial adjustment of output reactive power specifically targeted at eliminating common-mode voltage differences. By applying only the necessary reactive power compensation to suppress circulating current rather than uniformly adjusting all converters, the system maintains total output reactive power while eliminating harmful circulating current.
Data Source
AI summary
A power supply system, a converter, and a circulating current suppression method of the converter. The power supply system includes at least two converters that are coupled between a direct current power supply and an alternating current grid. Each converter obtains target output reactive power when an output current of the converter starts to increase from an initial current, obtains a reactive power compensation parameter based on the three-phase output voltages. Further, each converter obtains compensated output reactive power of the converter based on the reactive power compensation parameter and adjusts actual output reactive power of the converter based on the target output reactive power and the compensated output reactive power, so that an absolute value of a difference between common-mode output voltages of any two of the at least two adjusted converters is less than a difference threshold.