HIGH EFFICIENCY BASE DRIVE DESIGNS FOR POWER CONVERTERS USING SILICON CARBIDE BIPOLAR JUNCTION TRANSISTORS

This thesis explores the base driver designs for Silicon Carbide Bipolar Junction Transistors (SiC BJTs) and their applications for power converters. SiC is a wide bandgap semiconductor which has been the focus of recent researches as it has overcome the several of physical restrictions set by the silicon material. Compared with silicon bipolar devices, SiC BJTs have several advantages including a higher maximum junction temperature, higher current gain and lower switching power losses. Transient power losses are low and temperature-independent in a wide range of junction temperatures. With junction temperature capable of being between 25ºC to 240ºC, SiC BJTs have been of great interest in industry. As a current-driven device, the base driver power consumption is always a major concern. Therefore, high efficiency base drive designs for SiC BJT need to be investigated before this power device can be widely used in industry

Deploying SiC BJTs in an 800-V switched-mode power supply for hybrid & electric vehicles

An SMPS for hybrid electric vehicle and electric vehicle applications is presented. The use of SiC BJTs in the primary-side switching circuitry is investigated. Practical deployment aspects are addressed. Particular attention is given to the design of the BJT base driver stage and a bespoke turn-on switching-aid circuit. Mathematical design calculations are not presented, but the proposed circuitry is demonstrated in a 1-kW isolated-output DC-DC converter operating from 800 V and supplying 48 V at a switching frequency of 60 kHz. Full-load efficiency was evaluated at 93.3% using a calorimeter

Design and Realization of a Novel Buck-Boost Phase-Modular Three-Phase AC/DC Converter System with Low Component Number

Scalability and modularity are key features for future power converters, such that these systems can be easily employed in many applications with different electrical specifications. In this thesis, the potential of a new bidirectional phase-modular three-phase AC/DC converter with buck-boost capability is evaluated by means of studying two potential application cases and developing a hardware prototype for one of them. The DC-DC inverting buck-boost converter is a well-known and established topology. By connecting three such systems in parallel, a phase-modular bidirectional buck-boost DC-AC converter employing a minimum number of active components results, where for given AC voltage amplitudes, an arbitrary DC voltage can be generated and vice versa. Such a three-phase converter was not yet described in literature and this project aims at investigating the fundamental topology properties, as well as its performance limits. A hardware demonstrator is designed for one potential application in order to verify the basic operation and the expected high performance in terms of efficiency and power density.Comment: 80 pages, Master Thesis at ETH Zuric

Isolated Single-stage Power Electronic Building Blocks Using Medium Voltage Series-stacked Wide-bandgap Switches

The demand for efficient power conversion systems that can process the energy at high power and voltage levels is increasing every day. These systems are to be used in microgrid applications. Wide-bandgap semiconductor devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) are very promising candidates due to their lower conduction and switching losses compared to the state-of-the-art Silicon (Si) devices. The main challenge for these devices is that their breakdown voltages are relatively lower compared to their Si counterpart. In addition, the high frequency operation of the wide-bandgap devices are impeded in many cases by the magnetic core losses of the magnetic coupling components (i.e. coupled inductors and/or high frequency transformers) utilized in the power converter circuit. Six new dc-dc converter topologies are propose. The converters have reduced voltage stresses on the switches. Three of them are unidirectional step-up converters with universal input voltage which make them excellent candidates for photovoltaic and fuel cell applications. The other three converters are bidirectional dc-dc converters with wide voltage conversion ratios. These converters are very good candidates for the applications that require bidirectional power flow capability. In addition, the wide voltage conversion ratios of these converters can be utilized for applications such as energy storage systems with wide voltage swings

Plug-In Grid Compatible Next Generation Power Converters

The utilization of the DC low voltage distribution opens new possibilities for network development. Community DC microgrid is considered as an efficient solution for providing clean energy for residential areas. The connection of the DC microgrid to the AC utility grid would need a power electronic based rectifier. Voltage Source Rectifier (VSR) and Current Source Rectifier (CSR) are considered as the two options for such application. This study compares the two topologies based on their power density and efficiency. Silicon Carbide (SiC) switches are used for designing the rectifiers to get better power density and efficiency. The proximity of the rectifier to the residential area requires electromagnetic compatibility (EMC) of the rectifier with established standards such as IEC 61000-3-4 and FCC B. This analysis shows that CSR has higher efficiency and higher power density compared to VSR

Evaluation of Losses in HID Electronic Ballast Using Silicon Carbide MOSFETs

HID lamps are used in applications where high luminous intensity is desired. They are used in a wide range of applications from gymnasiums to movie theatres, from parking lots to indoor aquaria, from vehicle headlights to indoor gardening. They require ballasts during start-up and also during operation to regulate the voltage and current levels. Electronic ballasts have advantages of less weight, smooth operation, and less noisy over electromagnetic ballasts. A number of topologies are available for the electronic ballast where control of power electronic devices is exploited to achieve the performance of a ballast for lighting. A typical electronic ballast consists of a rectifier, power factor control unit, and the resonant converter unit. Power factor correction (PFC) was achieved using a boost converter topology and average current mode control for gate control of the boost MOSFET operating at a frequency of 70 kHz. The PFC was tested with Si and SiC MOSFET at 250 W resistive load for varying input from 90 V to 264 V. An efficiency as high as 97.4% was achieved by Si MOSFET based PFC unit. However, for SiC MOSFET, the efficiency decreased and was lower than expected. A maximum efficiency of 97.2% was achieved with the SiC based PFC. A simulation model was developed for both Si and SiC MOSFET based ballasts. The efficiency plots are presented. A faster gate drive for SiC MOSFET could improve the efficiency of the SiC based systems

Design Approaches to Enhance Power Density in Power Converters for Traction Applications

This dissertation presents a design strategy to increase the power density for automotive Power Conversion Units (PCUs) consisting of DC-DC and DC-AC stages. The strategy significantly improves the volumetric power density, as evident by a proposed PCU constructed and tested having 55.6 kW/L, representing an 11.2 % improvement on the Department of Energy’s 2025 goal of 50 kW/L for the same power electronics architecture. The dissertation begins with a custom magnetic design procedure, based on optimization of a predetermined C-core geometrical relationship and custom Litz wire. It accounts for electrical and thermal tradeoffs to produce a magnetic structure to best accomplish volume and thermal constraints. This work is coupled with a control strategy for the DC-DC converter whereby a variable-frequency Discontinuous Conduction Mode (DCM) control is used to further reduce the required values of the passive components, to provide an increase in power density and a large improvement of low-power-level efficiency, experimentally demonstrated at full power through an 80 kW Interleaved Boost Converter. Integration of this enhanced DC-DC stage to the DC-AC stage requires a DC-Link capacitor, which hinders achieving power density targets. Increasing the switching frequency is an established method of reducing the size of passives. However, it is the RMS current sizing requirements that diminishes any gains achieved by raising the switching frequency. A synchronous carrier phase shift-based control algorithm, that aligns the output current of the boost stage with the input current of an inverter, is proposed to reduce the RMS current in the DC-Link capacitor by up to 25% and an average 20% smaller capacitor volume. Lastly, a new electrothermal platform based on paralleled discrete devices is presented for a 50 kW traction inverter. Embedded capacitors within the vacant volume of the hybrid material thermal management structure enables higher power density (155 kW/L) and significantly reduces cost

Design Approaches to Enhance Power Density in Power Converters for Traction Applications

This dissertation presents a design strategy to increase the power density for automotive Power Conversion Units (PCUs) consisting of DC-DC and DC-AC stages. The strategy significantly improves the volumetric power density, as evident by a proposed PCU constructed and tested having 55.6 kW/L, representing an 11.2 % improvement on the Department of Energy’s 2025 goal of 50 kW/L for the same power electronics architecture. The dissertation begins with a custom magnetic design procedure, based on optimization of a predetermined C-core geometrical relationship and custom Litz wire. It accounts for electrical and thermal tradeoffs to produce a magnetic structure to best accomplish volume and thermal constraints. This work is coupled with a control strategy for the DC-DC converter whereby a variable-frequency Discontinuous Conduction Mode (DCM) control is used to further reduce the required values of the passive components, to provide an increase in power density and a large improvement of low-power-level efficiency, experimentally demonstrated at full power through an 80 kW Interleaved Boost Converter. Integration of this enhanced DC-DC stage to the DC-AC stage requires a DC-Link capacitor, which hinders achieving power density targets. Increasing the switching frequency is an established method of reducing the size of passives. However, it is the RMS current sizing requirements that diminishes any gains achieved by raising the switching frequency. A synchronous carrier phase shift-based control algorithm, that aligns the output current of the boost stage with the input current of an inverter, is proposed to reduce the RMS current in the DC-Link capacitor by up to 25% and an average 20% smaller capacitor volume. Lastly, a new electrothermal platform based on paralleled discrete devices is presented for a 50 kW traction inverter. Embedded capacitors within the vacant volume of the hybrid material thermal management structure enables higher power density (155 kW/L) and significantly reduces cost