Harmonic Compensation and Frequency Support of Microgrids Using Battery Energy Storage System With Hardware-in-the-Loop Validation

Abstract

Converter-dominated microgrids (MGs), an emerging class of converter-dominated power systems (CDPS), feature extensive converter-interfaced distributed energy resources (DERs) and power-electronic loads such as variable-frequency drives (VFDs). A representative example is the Natural Energy Laboratory of Hawaii Authority (NELHA) MG located in Hawaii, which exhibits converter-dominated behavior due to extensive power-electronic interfacing and large motor-drive loads. In particular, its VFD-driven pump systems draw non-sinusoidal currents that cause notable harmonics at the point of common coupling (PCC), motivating a unified approach that combines harmonic mitigation with fast primary frequency support. This paper proposes a multifunctional battery energy storage system (BESS) control strategy that performs shunt active power filtering and droop-based primary frequency control within a single converter. The proposed controller integrates shunt active power filter (SAPF) harmonic-current reference generation into the BESS droop loop, enabling the BESS grid-side converter to inject both the active power required for frequency support and the compensation currents required to cancel load harmonics at the PCC. By leveraging the existing BESS inverter and DC-link, the approach avoids a separate dedicated SAPF inverter and DC-link capacitor, reducing additional hardware and semiconductor utilization. Hardware-in-the-loop (HIL) tests of a NELHA-inspired microgrid model validate the effectiveness of the proposed control strategy, demonstrating harmonic mitigation together with stable frequency response and power sharing under nonlinear-load conditions. Furthermore, an FFT-based analysis of the proposed HIL case yields a grid-current THD of 0.92%. For comparative context, this result is evaluated against literature-reported THD values of 1.18% for a conventional hysteresis-controlled SAPF and 5.88% for an existing fixed-switching-frequency active harmonic-filtering method. The proposed system also provides integrated droop-based primary frequency support.