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In this paper, a modulation strategy based on the circuit-level decoupling concept is proposed and investigated for the three-level four-leg neutral-point-clamped (NPC) inverter, with the aim of delivering power to all sorts of loads, linear/nonlinear and balanced/unbalanced. By applying the proposed modulation strategy, the four-leg NPC inverter can be decoupled into three three-level Buck converters in each defined operating section. This makes the controller design much simpler compared to the conventional four-leg NPC inverter controllers. Also, this technique can be implemented with a simple logic and can be processed very quickly. Moreover, the switching loss is reduced substantially and the dc-link capacitors' voltages balance is also achieved without any feedback control. The proposed modulation technique is verified by the experiment.