A Stabilizer for Inverters Operating in Grid-Feeding, Grid-Supporting and Grid-Forming Modes

An adaptive stabilization technique is presented in this paper to enable stable operation of inverters operating under weak grids. The large impedance associated with a weak grid can deteriorate the stability of inverters in grid-feeding, grid-supporting, and grid-forming modes of operation. In this paper, the gain of the cross-coupling current terms are adaptively varied using a direct model reference adaptive control (MRAC) approach to enhance the stability of inverters in weak grids. The direct MRAC approach does not require a parameter estimation stage, instead, the parameters are updated according to an adaptation law derived using the Lyapunov stability criterion to ensure that the response of the system follows the response of a stable reference model. The inner current loops are present in a controller operating in a synchronously rotating frame, irrespective of the operating mode of the inverter, making the presented technique suitable for various modes of inverter operation. The efficacy of the developed scheme is verified for various weak grid scenarios through simulation studies carried out in the MATLAB/Simulink environment.