Optimal Compensation of Harmonic Propagation in a Multi-Bus Microgrid

This paper discusses how an Active Power Filter (APF) can be utilized for system-wide harmonic mitigation in a microgrid with multiple sources of harmonic distortion located at different buses. A two-bus microgrid system with independent nonlinear loads at both buses is first investigated analytically, and it is demonstrated that it is possible to derive a harmonic current injection from the APF that will minimize the harmonic distortion at both buses. However, analytical optimization of the APF current will be sensitive to parameter variations, will deteriorate when the APF reaches current saturation and cannot be easily extended to larger systems with many loads at different buses. A more practically applicable method for calculating the APF current references, by using the framework of Model Predictive Control (MPC) is instead proposed for the investigated system. Under realistic operating conditions, this approach can obtain further improvement in the system-level harmonic mitigation. The characteristics and performances that are obtained with the analytical solution and the MPC-based control are assessed by time domain simulations in the Matlab/Simulink environment. The results clearly indicate how an MPC-based system-oriented compensation can maximize the utilization of a single APF in a multi-bus Microgrid.