DC/DC Converters for Electric Vehicles

International audienceThe large number of automobiles in use around the world has caused and continues to cause serious problems of environment and human life. Air pollution, global warming, and the rapid depletion of the earth’s petroleum resources are now serious problems. Electric Vehicles (EVs), Hybrid Electric Vehicles (HEVs) and Fuel Cell Electric Vehicles (FCEVs) have been typically proposed to replace conventional vehicles in the near future. Most electric and hybrid electric configurations use two energy storage devices, one with high energy storage capability, called the “main energy system” (MES), and the other with high power capability and reversibility, called the “rechargeable energy storage system” (RESS). MES provides extended driving range, and RESS provides good acceleration and regenerative braking. Energy storage or supply devices vary their output voltage with load or state of charge and the high voltage of the DC-link create major challenges for vehicle designers when integrating energy storage / supply devices with a traction drive. DC-DC converters can be used to interface the elements in the electric power train by boosting or chopping the voltage levels. Due to the automotive constraints, the power converter structure has to be reliable, lightweight, small volume, with high efficiency, low electromagnetic interference and low current/voltage ripple. Thus, in this chapter, a comparative study on three DC/DC converters topologies (Conventional step-up dc-dc converter, interleaved 4-channels step-up dc-dc converter with independent inductors and Full-Bridge step-up dc-dc converter) is carried out. The modeling and the control of each topology are presented. Simulations of 30KW DC/DC converter are carried out for each topology. This study takes into account the weight, volume, current and voltage ripples, Electromagnetic Interference (EMI) and the efficiency of each converter topology

Reducing Conducted Emissions at the Output of Full-Bridge DCDC Converters with High Voltage Steps

In this work, we analyze the impact of output filter design techniques aimed to reduce conducted emissions at the output of a DCDC power converter. A thorough analysis, based on high-frequency circuit models of the converter, is performed to assess expected improvements offered by different design strategies. This analysis is then confronted with measurements of conducted emissions at the output of a 300 W 48 V to 12 V Phase Shift Full Bridge (PSFB) prototype. Those experimental results demonstrate that a symmetric arrangement of the output LC filter and a direct bonding of the return output terminal of the converter to chassis are effective to reduce common mode conducted emissions at the output. Those results also demonstrate that the symmetry of the output LC filter can reduce conducted emissions in differential mode at high frequencies, where common mode to differential mode conversion is the predominant contribution to differential mode noise. However, direct bonding to chassis of the return output terminal may be ineffective at high frequencies due to the parasitic inductance associated with this connection. Main conclusions drawn for this analysis are applicable in general for isolated converters with a high voltage step between high and low voltage sides. Since the techniques of reduction of conducted emissions studied here do not increase the number of filter components, they are especially suitable for applications where high power density is an important requirement, e.g., aerospace or automotive applications.Ministerio de Economía y Competitividad de España TEC2014-54097-RUnión Europea H2020-EU.3.4.5.6

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics

Development of a Supercapacitor based Surge Resistant Uninterruptible Power Supply

Uninterruptible Power Supplies (UPSs) provide short-term power back-up to sensitive electronic and electrical equipments, where an unexpected power loss could lead to undesirable outcomes. They usually bridge the connected equipment between the utility mains power and other long term back-up power systems like generators. A UPS also provides a “clean” source of power, meaning they filter the connected equipment from distortions in electrical parameters of the mains power like noise, harmonics, surges, sags and spikes. A surge resistant UPS or SRUPS is one that has the capability to withstand surges, which are momentary or sustained increases in the mains voltage, and react quickly enough to offer protection to the connected equipment from the same. Usually UPSs run off battery power when the utility mains power is absent. But the SRUPS developed in this design project uses super capacitors instead of battery packs. The reason for this is that the high energy-densities and medium power-densities offered by super capacitors allow for it to serve two purposes. One is to provide the DC power to operate the UPS in the absence of mains power, as an alternative to batteries. Secondly, super capacitors can withstand heavy momentary high current/voltage surges due to its high energy-density characteristics. Also as the life-time of super capacitors is much higher than that of conventional batteries and as they do not need regular topping-up or inspection, the end result is a truly maintenance-free UPS. Most commercial UPSs do not have inherent surge protection capabilities. The UPS is one entity while a discrete surge protection module is inserted between the utility mains and the UPS to provide for transient surge suppression. In the proposed SRUPS, the super capacitor, because of their inherent capability to absorb transient surges, forms a protective front end to the actual UPS rather than needing to have the involvement of discrete protection devices

Conducted EMI Mitigation in Power Converters using Active EMI Filters

Wide bandgap devices enable high power density power converters. Despite the advantages of increased switching frequency, the passive components are still a major bottleneck towards enabling high power density. Among the passive components in the converter, the passive EMI filters are unavoidable to ensure compliance with conducted EMI standards. Active EMI filters help reduce the volume of the passive components and have been around for three decades now. Firstly, this work presents a summary of all the different active EMI filters based on the type of noise-sensing, noise-processing, the type of active circuits used and the type of control methods. This is followed by modeling, design and stability analysis of three different active EMI filters for DM noise attenuation. The first active EMI filter is a conventional active EMI filter. The key bottlenecks to improving performance of the conventional active EMI filter are identified while still achieving volume reduction of passive components. Following this two novel active EMI filters are presented that overcome the bottlenecks of conventional active EMI filter. The second active EMI filter is based on a analog twin-circuit. This novel filter uses a twin-circuit which enables the use of low-voltage surface-mount components for compensation. The third active EMI filter uses zero-phase filtering implemented in an FPGA. While all the filters are demonstrated for differential-mode noise, their use can be extended for common-mode noise attenuation

Switching Trajectory Control for High Voltage Silicon Carbide Power Devices with Novel Active Gate Drivers

The penetration of silicon carbide (SiC) semiconductor devices is increasing in the power industry due to their lower parasitics, higher blocking voltage, and higher thermal conductivity over their silicon (Si) counterparts. Applications of high voltage SiC power devices, generally 10 kV or higher, can significantly reduce the amount of the cascaded levels of converters in the distributed system, simplify the system by reducing the number of the semiconductor devices, and increase the system reliability. However, the gate drivers for high voltage SiC devices are not available on the market. Also, the characteristics of the third generation 10 kV SiC MOSFETs with XHV-6 package which are developed by CREE are approaching those of an ideal switch with high dv/dt and di/dt. The fast switching speed of SiC devices introduces challenges for the application since electromagnetic interference (EMI) noise and overshoot voltage can be serious. Also, the insulation should be carefully designed to prevent partial discharge. To address the aforementioned issues, this work investigates the switching behaviors of SiC power MOSFETs with mathematic models and the formation of EMI noise in a power converter. Based on the theoretical analysis, a model-based switching trajectory optimizing three-level active gate driver (AGD) is proposed. The proposed AGD has five operation modes, i.e., faster/normal/slower for the turn-on process and slower/normal for the turn-off process. The availability of multiple operation modes offers an extra degree of freedom to improve the switching performance for a particular application and enables it to be more versatile. The proposed AGD can provide higher switching speed adjustment resolution than the other AGDs, and this feature will allow the proposed AGD to fine tune the switching speed of SiC power devices. In addition, a novel model-based trajectory optimization strategy is proposed to determine the optimal gate driver output voltage by trading the EMI noise against the switching energy losses. For the 10 kV SiC power MOSFET, the detailed design considerations of the proposed AGD are demonstrated in this dissertation. The functionalities of the 3-L AGD are validated through the double pulse tests results with 1.2 kV and 10 kV SiC power MOSFETs