Design and Analysis of High-Gain Medium-Voltage DC-DC Converters for High-Power PV Applications

Medium-Voltage (MV) DC grids for collecting and integrating Photovoltaic (PV) systems offer an effective solution to overcome the problems introduced due to AC grid. The direct conversion of the PV power to MV DC grid increases the efficiency and reduces the cost when compared to MV AC grid. In MV DC grid connected PV systems, a high gain DC-DC converter is required to convert the unregulated PV DC voltage to a regulated MV DC voltage. In this paper, voltage Re-Lift and Super Re-Lift Luo converters, are used as high-gain DC-DC converters to integrate the solar energy into the MV DC grid. Design, modelling and analysis of the operation of these converters at MV high-power levels are presented. Also, performance assessment for the two different DC-DC converter topologies is conducted. Both the voltage Re-Lift and the Super Re-Lift Luo converters have high output voltage transfer gain, high power density, high efficiency, and high output voltage with small ripples. However, the Voltage-Lift Luo converter increases the output voltage in arithmetic progression, while the Super Lift Luo converter increases the output voltage in geometric progression. Digital simulations are carried out to validate the analysis and the comparison of the two converters performance using Matlab/Simulink platform for 10kV DC grid and 1MW PV power plant.