Mitigation of Oscillations in Grid Converters Enabled Microgrids Based on Proportional Resonance and Model Predictive Control

Abstract

This paper proposes a robust control scheme for three phase LCL-filtered gird converters enabled microgrids to mitigate high frequency and subsynchronous or supersynchronous oscillations. Three phase LCL-filtered grid converter is partitioned into two components, i.e., LC filter component and grid side inductor component. The interconnection voltage of LC filter is regulated by model predictive control (MPC) with disturbance observer. The grid side current is regulated by proportional resonance (PR) control. The merits of MPC and PR can be combined. MPC can inherently realize active damping without additional control and reduce modulation delay, which improves the dynamic performance. PR control not only makes the steady state error zero, but also reduces the complexity of control compared with the overall grid converter is controlled by MPC. By analyzing the frequency response of transfer function and output impedance, the phase margin of the proposed control is sufficient, and the output impedance of grid converters is always resistive or inductive at the whole frequency when system and control parameters vary, which suppress the subsynchronous and high frequency oscillations. The comparative analysis of simulation results validates the effectiveness and robustness of the proposed control in current tracking, harmonic suppression and response to grid impedance varies.