Leakage Current Mitigation in Transformerless Microinverter for Grid-Connected Photovoltaic System

Transformerless inverters are cost-effective and power-effective but require a high-gain step-up DC-DC converter for solar energy applications. On the other hand, using transformerless microinverters can lead to safety issues due to the parasitic capacitance of the solar panel, which causes leakage current that leads to performance problems. This paper introduces a new model predictive control (MPC) to mitigate PV leakage current. The proposed controller is designed to control a two-stage transformerless grid-connected PV system with PV parasitic capacitances. The control part is divided into three main controllers: 1) the maximum power point tracking (MPPT) perturb and observe (P&O), which will control the Quadratic Boost Converter (QBC), a single switch high gain DC-DC converter; this control part will control the single switch to track the PV maximum power point optimally; 2) A PI controller that controls the DC-Link capacitor and guarantees the power transfer from the PV side to the grid side; 3) the proposed MPC that will control the nine-level crossover switch cell (CSC) inverter to reduce the leakage current across the parasitic capacitance while maintaining the unity power factor, low grid current Total Harmonic Distortion (THD), and maintaining fixed voltage for the CSC flying capacitor. A simulation was conducted to verify the performance of the proposed controller and ensure its effectiveness. A grid current THD of less than 5% is achieved, and a stable operation is validated. Additionally, leakage current mitigation from 0.35 to 0.18 A(rms) is achieved.