Control And Topology Improvements In Half-bridge Dc-dc Converters

Efficiency and transient response are two key requirements for DC-DC converters. Topology and control are two key topics in this dissertation. A variety of techniques for DC-DC converter performance improvement are presented in this work. Focusing on the efficiency issue, a variety of clamping techniques including both active and passive methods are presented after the ringing issues in DC-DC converters are investigated. By presenting the clamping techniques, a big variety of energy management concepts are introduced. The active bridge-capacitor tank clamping and FET-diode-capacitor tank clamping are close ideas, which transfer the leakage inductor energy to clamping capacitor to prevent oscillation between leakage inductor and junction capacitor of MOSFETs. The two-FET-clamping tank employs two MOSFETs to freewheeling the leakage current when the main MOSFETs of the half-bridge are both off. Driving voltage variation on the secondary side Synchronous Rectifier (SR) MOSFETs in self-driven circuit due to input voltage variation in bus converter applications is also investigated. One solution with a variety of derivations is proposed using zerner-capacitor combination to clamping the voltage while maintaining reasonable power losses. Another efficiency improvement idea comes from phase-shift concept in DC-DC converters. By employing phase-shift scheme, the primary side and the secondary side two MOSFETs have complementary driving signals respectively, which allow the MOSFET to be turned on with Zero Voltage Switching (ZVS). Simulation verified the feasibility of the proposed phase-shifted DC-DC converter. From the control scheme point of view, a novel peak current mode control concept for half-bridge topologies is presented. Aiming at compensating the imbalanced voltage due to peak current mode control in symmetric half-bridge topologies, an additional voltage compensation loop is used to bring the half-bridge capacitor voltage back to balance. In the proposed solutions, one scheme is applied on symmetric half-bridge topology and the other one is applied on Duty-cycle-shifted (DCS) half-bridge topology. Both schemes employ simple circuitry and are suitable for integration. Loop stability issues are also investigated in this work. Modeling work shows the uncompensated half-bridge topology cannot be stabilized under all conditions and the additional compensation loop helps to prevent the voltage imbalance effectively

Grid Integration of DC Buildings: Standards, Requirements and Power Converter Topologies

Residential dc microgrids and nanogrids are the emerging technology that is aimed to promote the transition to energy-efficient buildings and provide simple, highly flexible integration of renewables, storages, and loads. At the same time, the mass acceptance of dc buildings is slowed down by the relative immaturity of the dc technology, lack of standardization and general awareness about its potential. Additional efforts from multiple directions are necessary to promote this technology and increase its market attractiveness. In the near-term, it is highly likely that the dc buildings will be connected to the conventional ac distribution grid by a front-end ac-dc converter that provides all the necessary protection and desired functionality. At the same time, the corresponding requirements for this converter have not been yet consolidated. To address this, present paper focuses on various aspects of the integration of dc buildings and includes analysis of related standards, directives, operational and compatibility requirements as well as classification of voltage levels. In addition, power converter configurations and modulation methods are analyzed and compared. A classification of topologies that can provide the required functionality for the application is proposed. Finally, future trends and remaining challenges pointed out to motivate new contributions to this topic

Isolated and Bidirectional DC-DC Converter for Electric Vehicles

O estado da arte iniciou com a análise na literatura de topologias de conversores DC-DC. Técnicas de modulação são estudadas com vista a melhorar a eficiência de conversão, realçando as vantagens e limitações inerentes das mesmas. Após a análise da literatura, o foco projeto passou a ser a topologias de dupla ponte com dispositivos ativos e com isolamento galvânico intermédio entre as duas pontes (conhecido em inglês por dual active bridge). Algumas técnicas de modulação que permitem o funcionamento do conversor são analisadas no documento e suportadas com resultados obtidos em ambiente de simulação. O dimensionamento do transformador de potência é realizado assim como a descrição dos passos. É relizado uma análise de mercado de dispositivos de comutação com a tecnologia "Silicon Carbide" e são apresentados estimativas de perdas e eficiência de operação na utilização de transistores com a techonoloa SiC no conversor analisado. Os resultados são obtidos com recurso a simulações computacionais que através de modelos de aproximação permitem aproximar o conversor a uma situação mais proxima da real. Em termos de implementação, é esperado a implementação um circuito de comando para dois MOSFETS com tecnologia SiC com a configuração em meia ponte ligada a uma carga

Grounding and Charging Strategy for Ships during Cold Ironing Operation

In order to minimize the pollution that ships generate at ports, ships can be connected to the utility grid during charging, also known as shore-to-ship connection or cold ironing operation. The pollution can also be remarkably reduced if the ships are full-electric or hybrid. With the utilization of a common DC bus, several ships can be charged simultaneously. However, due to the common DC bus, the ships are not galvanic isolated from each other such that leakage current can occur among the ships and the quay when the current leaks to the ground during a fault. Hence, this paper proposes a complete charging and grounding strategy, which will provide galvanic isolation between the ships and the quay. The charging and grounding strategy are verified through simulations in the Matlab/Simulink environment. An isolated and ideal PSFB DC-DC converter with a rated power of 400 kW was proposed to obtain galvanic isolation. The proposed converter obtained a stable output during nominal and half load from the simulation results. In addition, two grounding systems on the shore-side and the ship-side were proposed. On the shore-side, a double grounding TN-C grounding system with a NGR resistor was designed such that the leakage current can easily be detected when a ground fault occurs. On the ship-side, an IT system with HRMG resistors was designed to reduce the leakage current such that the risk of corrosion was reduced and provided safety for personnel. As a result, a fault on the shore-side did not affect the ship-side grounding system and opposite. Faults that can appear on the charging system were found through research and simulated with the complete charging and grounding system to verify that the grounding system was optimally designed. The results during a fault on the system showed that the shore-side grounding system was not optimally designed because the NGR did not reduce the fault current to a lower value than 25 A. The common DC bus was created from an uncontrolled rectifier that suffered a substantial power dissipation. As a result, the output of the PSFB DC-DC converter was unstable. Therefore, a resistor was added to the TN-C grounding configuration during simulations of the charging system to achieve a stable output of the DC-DC converter. The IT grounding configuration on the ship-side reduced the fault current to 6 mA during a LG fault, and personnel safety was kept at a safe level when a person touched one of the DC lines. However, it was shown that the personnel safety was not obtained when a person touched the energized chassis due to a dangerous voltage potential

Design and Analysis of Reconfigurable Resonant Converter with Ultra Wide Output Voltage Range

In this article, a reconfigurable isolated dc/dc converter is proposed suitable for a wide output voltage range of 180–1500 V for efficient onshore charging in maritime applications. The proposed circuit concept can also fulfill the requirements of other heavy-duty battery charging applications, especially those operating within the shore environment—such as straddle carriers, forklifts, reach stackers, and terminal tractors. The circuit topology consists of two interleaved LLC resonant converters each connected to a three-winding transformer. Through the use of additional circuitry, the topology can be adapted to operate at peak efficiency in three output voltage ranges. Furthermore, the topology is able to alleviate the current and voltage stresses on the semiconductor devices in comparison to the conventionally employed LLC resonant converters. The operation of the circuit is explained and its steady-state model is developed. In order to validate the performance of the converter, an 11-kW prototype is designed, tested, and analyzed. The experimental results attest that the proposed reconfigurable resonant converter is able to achieve an extremely wide output voltage range while maintaining a high power transfer efficiency

Integrated fuzzy and phase shift controller for output step voltage control in multilevel inverter with reduced switch count

A modified multilevel inverter with a configurable level generation is proposed in this paper. The MLI is composed of a modified boost converter at the front end followed by a level generation circuit and a H-bridge configuration. The front-end converter is biased with a PV source with a Hybrid boost resonant converter. The switches are triggered out of phase through a MPP tracker which uses Fractional INC MPPT. The secondary side of the circuit is composed of a derived voltage doubler along with the voltage regulator. The output of the doubler is regulated through a level converter which integrates a fuzzy controller and a phase shift controller. The modified multilevel inverter uses a low-voltage PV source as input and generates a variable-step multilevel output voltage with lower harmonic distortion and it is suitable for low-power PV applications