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DC-Link Voltage Control of Neutral Point Clamped Power Converters Using Extended State Observer

This paper employs linear extended state observer (LESO) in the dc-link voltage control for a three-phase three-level NPC power converter, which works in rectifier mode. Three-loop control scheme is adopted, which consists of voltage loop, current loop and capacitor voltage balance loop. In the voltage loop, the LESO estimates the external load randomly connected to the dc-link, and uses the estimated value to compensate a PI controller. To test the effectiveness and robustness of adding LESO, simulations are carried out with three different loads, from small to large. The results show that: first, adding LESO to the voltage loop can significantly improve the dc-link voltage transient performance, in terms of much less voltage drop, and less recovering time; second, with LESO, the controller is more robust in the face of load disturbance variation.