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A Communication-Free Carrier Synchronization Strategy for Suppressing Circulating Current in Multi-Inverter Parallel Systems
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DOI：10.1109/tpel.2026.3696082.png)
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Abstract
En 中文
The parallel system of multiple three-level grid-connected inverters with an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i>-type filter has become the mainstream architecture in photovoltaic power generation due to its cost-effectiveness and flexible scalability. However, without the grid-side filter inductance, the parallel system is prone to severe switching circulating current resonance problems, which will deteriorate the power quality and significantly affect the operational stability and equipment reliability. To address this issue, this article constructs an equivalent circuit model of the parallel system to explain the formation mechanism of switching circulating currents, and then establishes a mathematical representation model to reveal the spectrum evolution based on carrier phase distribution characteristics and frequency coupling. It has been found that even minor differences in carrier frequency can lead to cumulative carrier phase deviation, which in turn leads to larger switching circulation current. On this basis, a novel phase-locked loop variable-frequency sampling synchronization strategy is proposed, which completely ensures carrier synchronization across inverters without communication or hardware changes, effectively overcoming DSP crystal oscillator frequency differences, thereby significantly suppressing the switching resonant circulating current phenomenon. Experimental results confirm the effectiveness and feasibility of this synchronization strategy.
Keywords:
Carrier synchronization
communication-free
grid-connected inverter
switching circulating current
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6.5
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1.7W
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8.3W
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