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How to reduce circulating current in a modular inverter?

The reduction methods for modular inverters are compared in terms of efficiency, performance, and reliability. The possible approaches for circulating current reduction are categorized into three groups–hardware, control, and modulation. Each reduction method is discussed according to the category.

Why do parallel inverters reduce circulating current?

The common mode voltage of each inverter is distributed more equally in a carrier cycle, and thus the circulating currents of paralleled modules are mitigated . Furthermore, the reduction methods for low-frequency circulating current can be divided into two categories based on control and modulation [40–67].

How circulating current flows between inverters?

The circulating current flows between inverters due to DC-offset voltage and fluctuation of AC output voltages. This strategy uses the fundamental voltage and phase droop scheme to allow the inverters to share their load currents and uses a DC-offset droop scheme in order to eliminate DC circulating current.

What are parallel inverter control methods?

Parallel inverter control methods have been explained in the presented work with their exceptional characteristics shown in Table 4. Droop control and active load sharing are also shown. Generally, there are two groups of active load sharing control namely current sharing control and power-sharing control.

What causes a circulating current in a parallel inverter?

This circulating current is caused by initial voltage variations across inverters connected to the same DC bus and the same load [8, 9]. Parallel inverters in the traditional method need separate isolating transformers to cut the route for the circulating currents .

Can inverters be connected in parallel to DC and AC buses?

When inverters are linked in parallel to both common DC and AC buses, we must address both the zero-sequence and cross-sequence circulating-current problems . The DC bus was considered to be a constant voltage source in this research. Fig. 2. Zero-sequence circulating current path.