State-Feedback Reshaping Control of Voltage Source Converter
Admittance reshaping is a widely used strategy to address the converters low-frequency stability issues in weak grid, caused by the PLL and its interaction with the dc and ac voltage control. However, the asymmetric control of the d- and q-axis current references and the coupling between the converter ac and dc side restricts the damping capability of Single-Input-Single-Output feedbacks. This phenomena gets even worse in presence of nearby converters. This paper extends the concept of admittance reshaping to Multi-Input-Multi-Output (MIMO) control. A full state-feedback is added to the current reference of the converter to increase the damping of the conventional multi-loop control. A systematic offline algorithm is delegated to design the feedback, and a scalar coefficient is employed to activate/deactivate online the reshaping feedback, making the proposed solution user-friendly. The proposed control is analyzed both in time- and frequency-domain and tested in parallel-operation with other converters, and shows higher damping capability than conventional solutions and good robustness with respect to grid impedance and operating point variations. Experimental tests under ac and dc disturbances are conducted both in lab setup and in Hardware-In-the-Loop.
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