Development of Hybrid SOGI-Resonant Controller in DQ reference frame for decoupled PQ control of a VSI under nonlinear loading

Recent interest in Power Quality (PQ) enhancement and control strategies for DC/AC converters in grid-tied and islanded modes has surged. Conventional single-loop and multi-loop control topologies using PI, PR, and hysteresis controllers are widely used for system stability, current control, and PQ improvement. However, these topologies face significant challenges under non-ideal conditions, such as inverters with nonlinear or unbalanced loads. This paper addresses the challenges of simultaneous harmonic compensation and decoupled active and reactive power reference tracking by proposing a novel Hybrid SOGI-Resonant Controller (HSRC). The HSRC is designed to adapt to changing load patterns and mitigate harmonics generated by nonlinear loads. It incorporates a Second Order Generalized Integrator (SOGI) into a synchronously rotating reference frame (SRRF)-based PI-control scheme. Acting as a notch filter, the SOGI improves reference generation based on load current harmonics. The HSRC combines the benefits of Resonant controllers with cascaded PI controllers without frequent reference frame conversions. The proposed topology demonstrates significant improvement in grid-tied inverter (GTI) performance with nonlinear loads and unbalanced load combined, eliminating the need for separate controllers for positive and negative sequence signals and reducing computational burden. It provides independent control of active and reactive power alongside harmonic compensation, ensuring seamless operation under nonlinear loading conditions. The paper details the design and tuning methodology of the HSRC and verifies its efficacy through the grid-tied operation of a three-phase GTI with different loads. Results show a substantial reduction in total harmonic distortion, highlighting the HSRC's potential for enhancing power quality in practical applications.