Conversores CC-CC modulares para desenvolvimento de carregadores de baterias off-board para veículos elétricos

Abstract

Off-board battery chargers for electric vehicles (EVs) have powers exceeding 10 kW, and due to the involved power levels, they are typically developed with two stages of electrical power processing. Thus, the first stage consists of an AC-DC converter (rectifier), and the second stage is formed by a DC-DC converter that regulates voltage and current to the batteries. Therefore, aiming at the development of off-board batttery chargers for EVs, this undergraduate thesis studied the second stage formed by modular DC-DC converters of the Buck family with independent inputs and outputs connected in series. This technique facilitates the use of power MOSFETs with lower onstate resistance (RDS(on) ) commercially available, thereby increasing the overall system efficiency. To further improve overall efficiency, each modular DC-DC converter uses three-state switching cells (TSSC). The advantages of the proposed DC-DC converter include reduced voltage and current stress on semiconductors and other components, a reduced output LC filter due to its operation at twice the switching frequency, and the autotransformer helps balance the current through the switches as the average voltage across it is zero. Additionally, it maintains the control characteristic of the classic Buck CC-C converter. A disadvantage is the need for many semiconductors and auxiliary sources for MOSFET biasing.Another important highlight is the use of the master-slave control technique formed by a voltage loop and a current loop. The thesis presents qualitative and quantitative analyses, a design example, and simulation and experimental results for four modules connected in series. Each module has the following specifications: input voltage Vi1 -Vi4 = 30 V to 50 V; output power Po1 -Po4 = 95 W; output voltage Vo1 -Vo4 = 10.5 V to 13.5 V, and switching frequency fs = 25 kHz.