Analysis, modeling and simulation of N-port converter for grid connected PV system

The renewable energy sources such as wind, solar, and fuel cell are needed to produce electric energy to meet increasing demand on energy, shortage of fossil fuels, and global concern about fossil emission levels. Specifically solar energy has seen tremendous growth because of its several advantages such as being pollution free, little maintenance, emitting no noise and, long life time. Grid connected solar photovoltaic (PV) systems have great potential to be a distributed power source because of their modular characteristics and ease of installation. In 2011 more than 62,500 PV systems have been interconnected by utilities in the US, and the forecasts show that this number will increase to over 150,000 in 2015. Power electronics forms a major role in connecting PV systems into grid. Multilevel converters have been increasingly used in these systems to take care of high voltage levels and reduced harmonic distortion. There are some different multilevel topologies, and applications. In this thesis, a cascaded multilevel H-bridge inverter as a part of N-port multilevel converter is developed and analyzed to integrate PV system into grid. This N-port multilevel converter uses dual active bridge (DAB) converters as a front-end DC to DC converter to control power to grid and cascaded multilevel H-bridge (CHB) as a DC to AC inverter. The average model of DAB and CHB converters is developed in MATLAB ® /Simulink ® and power electronics simulation software PSIM® . A system level controller is designed which includes P & O maximum power point tracking (MPPT) for the PV, and d-q axis grid current controller for the CHB inverter. In addition the phase-shift sinusoidal PWM is developed to the 11-level CHB. The entire N-port converter system for three phases with 15 ports is modelled in PSIM ® and the controller performance is verified.