Sammendrag
A generalized and versatile approach for control of
the circulating currents of Modular Multilevel Converters (MMC)
has been recently proposed by using Lagrange Multipliers in the
ABC frame. This approach is capable of analytically obtaining the
differential current references associated with the desired operating
conditions imposed to the optimization procedure. Previous implementations
of this control approach have been sensitive to harmonic
distortion of the control signals when applied to systems with a low
number of levels, and have depended on average value calculations
of sinusoidal variables, slowing down the dynamics of the control
and making the tuning of the control system difficult under certain
conditions. This work demonstrates that the performance of the
versatile Lagrange-based control can be improved by introducing
adaptive filtering based on Second Order Generalized Integrators
(SOGIs) for processing the system variables needed for calculating
the circulating current references. In addition to improved control
dynamics and easier tuning of system controllers, the use of the
adaptive filters provides inherent capability for operation under
frequency variations, and is therefore suitable for control of MMCs
operating in weak grids as well as for high- or medium-voltage
motor drives.
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