An Auxiliary Power Supply Based Nine Switch Photovoltaic Grid-Tied (AP-H9) Inverter Using Model-Free Predictive Control

In order to solve the problem of large leakage current and poor parameter robustness of three-phase H8 inverter, an auxiliary power supply based nine switch transformerless photovoltaic grid-tied (AP-H9) inverter is proposed. The inverter limits the common mode voltage of the system to 2/3 times of the DC side voltage without increasing the system loss and control difficulty, so as to effectively suppress the system leakage current. At the same time, a model-free predictive current control method based on the ultra-local model is proposed. The gain and dynamic part of the ultra-local model of the inverter are updated online using the voltage and current information of the past two times, and then the predictive voltage vector of the next time is obtained. This method does not require the accurate model of the inverter and any system parameters. Finally, an experimental prototype with TMS320F28335 as the control chip is developed. The simulation and experimental results show that the proposed inverter and its control strategy can effectively suppress the leakage current of the photovoltaic grid connected system and improve the robustness of the system.