FOPID-Controlled Hybrid Transformerless PV Inverter for Single-Phase Grid Integration with Improved Leakage Current Suppression and Reactive Power Support

Abstract: This study uses simulations to test a better control method for a nine-switch hybrid transformerless single- phase photovoltaic (PV) inverter that is meant to work with the grid. The proposed inverter design puts together DC-side decoupling, AC-side isolation, and middle voltage clamping into one structure that works together. In all scenarios, this configuration preserves the common-mode voltage at half of the DC-link voltage. Because of this, the leakage current is substantially lower, with a maximum value of 5 mA, which is around 11 to 22 times lower than what is seen in many well-known transformerless inverter topologies. A four-layer hierarchical control structure is employed to make both the dynamic response and the steady-state accuracy better. At the primary level, finite control set model predictive control (FCS-MPC) makes sure that the grid current is tracked accurately. A fractional-order super-twisting sliding mode controller (FO-STSMC) with a fractional order of 0.87 makes this even stronger. It is incredibly stable even when things go wrong or the system is unsure. A two-stage multi-variable compensating notch filter in a cascade is used to get rid of harmonics. It gets rid of dominant harmonics at 100 Hz and 150 Hz by more than 44 dB. A fractional-order PID (FOPID) controller also acts as the outer supervisory layer and allows you adjust the system with five different parameters. Simulation experiments run in MATLAB/Simulink show that the system works very well, with a grid current total harmonic distortion (THD) of 0.30%, a quick transient response, and the ability to inject reactive power effectively. The system is also compliant with IEEE 1547-2018 and EN 50549, which means it is ready for deployment in the real world.

Keywords: Fractional-order PID, fractional-order super-twisting sliding mode control, leakage current suppression, model predictive control, multi-variable compensating filter, reactive power injection, transformerless PV inverter, VtCM consistency.