GaN-based single-phase differential PV inverters

Differential PV inverters have the benefits of second-order ripple elimination and leakage current suppression. Therefore, the need for additional components such as switch, inductor, capacitor, and transformer to achieve the power decoupling function and galvanic isolation can be avoided. In recent years, GaN devices used to improve the performance of differential PV inverters, which have the advantages of high switching frequency, high operating temperature, and high operating voltage. However, using GaN devices cannot guarantee better performance of inverters because the GaN device performance depends on the design parameters, such as switching frequency and operating temperature. To fully utilise the benefits of the GaN device, the design challenges and the complex trade-offs between components associated with inverters need to be addressed. Therefore, this thesis investigates impacts of GaN devices-based single-phase differential PV inverters with the aim to optimise inverter efficiency, power density, and cost using systematic design and control approaches. In single-phase differential inverters, active power decoupling methods are often aimed to reduce the total capacitance as much as possible, which sacrifices the overall efficiency and volume of the inverter. To address that, a trade-off analysis of all the active and passive components of the GaN-based differential buck inverters is developed through detailed mathematical modelling. Then, a multi-objective optimisation method based on geometric programming is presented to optimise the efficiency and power density. The design method is based on power loss and volume of the inverter by considering the dominant design parameters. As a result, the maximum limit of design trends can be obtained, which gives more freedom to choose the best design. The aforementioned multi-objective optimisation methods require extensive mathematical models and more system information to find an optimal design. It increases the computational complexity, needs multiple conditions to eliminate unwanted solutions, and requires more time to choose the optimal design. Therefore, an ANN-based multi-objective design method is developed to improve accuracy and reduce computational burdens. A buck-type differential inverter is used to verify the ANN-based design method in both simulation and experiment. The previous two studies are based on buck-type differential inverters, which need an additional front-end DC-DC converter for solar PV application to meet the wide voltage requirements. This inverter requires an additional hardware controller, reduces efficiency and power density, and increases cost. Single-stage inverters are widely popular in industrial and commercial applications because of their higher efficiency and simple control. A novel single-stage buck-boost inverter topology based on GaN devices is proposed, simulated, and experimentally verified the performances. It has been observed that the maximum efficiency of the prototype is 97.89%, the power density is improved to 3.5kW/dm3 and the components cost of the prototype is £136.16