Model predictive control methods of leakage current elimination for a three-level T-type transformerless PV inverter

Abstract

This study presents finite control set model predictive control (FCS-MPC) methods to eliminate leakage current for a three-level T-type transformerless photovoltaic (PV) inverter without any modification on topology or any hardware changes. The proposed FCS-MPC methods are capable of eliminating the leakage current in the transformerless PV system by applying the defined candidate voltage vector (VV) combinations with only six medium and one zero VVs (6MV1Z) or three large and three small VVs, which generate constant common-mode voltage to perform the optimisation in every control period. With fewer VVs used for the optimisation, the computational burden can be significantly reduced. Furthermore, comparative analysis is performed to show that among these proposed methods, the 6MV1Z method can achieve satisfactory performances in both grid current tracking and neutral point potentials balance control even with less number of candidate VVs, which exhibits the FCSMPC as an alternative control strategy to be used in the grid-connected transformerless PV system. Finally, experiments are performed to validate the analysis and the effectiveness of the proposed methods.