Common-ground-type Five-level Single-phase Transformerless PV Grid-connected Inverters

Aiming at the problems of the existing single-phase transformerless photovoltaic grid-connected inverters topology with large leakage current and grid-connected current harmonics, a new common-ground five-level single-phase transformerless photovoltaic grid-connected inverter was proposed. This inverter topology required seven power switches, two capacitors, and a filter. The main advantages of the new inverter are: 1) The neutral point of the grid is directly connected to the negative terminal of the photovoltaic cell, completely eliminating leakage current; 2) There are a total of five voltage platform order outputs, which makes the waveform closer to a sine wave and reduces grid-connected current harmonics. The new topology used model predictive control to make the control more flexible and to track the given quickly. This article introduced the working principle, modalities and control strategies of the new topology in detail, and compared it with several traditional topologies. The proposed topology leakage current suppression capability and ability to reduce grid-connected current harmonics are higher than the traditional topology. Finally, through the simulation of 1kVA system, and design prototype, relevant experimental results were obtained. It can be proved that the proposed topology worked effectively in photovoltaic grid-connected systems, and provided a reliable basis for the application of the new topology in practice. © 2021 Chin. Soc. for Elec. Eng.