Power Electronics Topologies for Solar Photovoltiac Energy System Applications

Abstract

Owing to economic aspects, Central inverter is the dominating candidate in large-scale PV installations despite its lower energy harvest compared to other topologies like string inverters especially under partial shading conditions. This dissertation focuses on developing a new fractional rated converter to harvest maximum power point from PV systems for different environmental conditions e.g. dust, temperature, and shading effects. The first approach emphasizes on balancing the voltages from different strings in a PV farm and ensure higher energy yield from central inverters. The voltage approach balancing has a higher efficiency and energy density at lower cost. A new MPPT algorithm has been designed and tested through simulation to conform the functionality of the proposed topology. The second approach is an extension to voltage balancing topology to develop based on it a complete energy harvesting system that balances the voltage and current from the non-linear source which is the PV. The two-stage converter characterized by the fractional power rating, high efficiency, scalability and lower cost of the energy produced. The approach is designed for PV strings with voltage of 1500V DC to achieve maximum power point tracking (MPPT) through the fractionally rated stages mitigating the effects of environmental conditions. The proposed system is shown to be scalable to suite large-scale solar PV power plants. A design example of 1.1 MW PV power and lab-prototype of 400 W has been built to validate the proposed concept. The third part theme investigated a dual phase output inverter actively decouples the double line frequency harmonics integrated with power optimizer. The inverter employs a half bridge with passive elements (L-C) to balance the output to actively decouple the double line frequency. The closed loop control adjusts for varying load conditions. Further, an integrated power optimizer (PO) provides interface of solar-pv and battery to the dc-link. The PO stage (half bridge) is controlled such that maximum power point tracking (MPPT) is achieved for the connected pv-array and independent charge/discharge functions of the battery. Simulation and experimental results verify the performance of the proposed technique under balanced, unbalanced load, non-linear conditions as well as fault condition.