The trend of electrification in transportation applications has led to the fast development of high-power-density power electronics converters. High-switching-frequency and high-temperature operations are the two key factors towards this target. Both requirements, however, are challenging the fundamental limit of silicon (Si) based devices. The emerging wide-bandgap, silicon carbide (SiC) power devices have become the promising solution to meet these requirements. With these advanced devices, the technology barrier has now moved to the compatible integration technology that can make the best of device capabilities in high-power-density converters. Many challenges are present, and some of the most important issues are explored in this dissertation. First of all, the high-temperature performances of the commercial SiC MOSFET are evaluated extensively up to 200 degree C. The static and switching characterizations show that the device has superior electrical performances under elevated temperatures. Meanwhile, the gate oxide stability of the device - a known issue to SiC MOSFETs in general - is also evaluated through both high-temperature gate biasing and gate switching tests. Device degradations are observed from these tests, and a design trade-off between the performance and reliability of the SiC MOSFET is concluded. To understand the interactions between devices and circuit parasitics, an experimental parametric study is performed to investigate the influences of stray inductances on the MOSFETs switching waveforms. A small-signal model is then developed to explain the parasitic ringing in the frequency domain. From this angle, the ringing mechanism can be understood more easily and deeply. With the use of this model, the effects of DC decoupling capacitors in suppressing the ringing can be further explained in a more straightforward way than the traditional time-domain analysis. A rule of thumb regarding the capacitance selection is also derived. A Power Electronics Building Block (PEBB) module is then developed with discrete SiC MOSFETs. Integrating the power stage together with the peripheral functions such as gate drive and protection, the PEBB concept allows the converter to be built quickly and reliably by simply connecting several PEBB modules. The high-speed gate drive and power stage layout designs are presented to enable fast and safe switching of the SiC MOSFET. Based on the PEBB platform, the state-of-the-art Si and SiC power MOSFETs are also compared in the device characteristics, temperature influences, and loss distributions in a high-frequency converter, so that special design considerations can be concluded for the SiC MOSFET. Towards high-temperature, high-frequency and high-power operations, integrated wire-bond phase-leg modules are also developed with SiC MOSFET bare dice. High-temperature packaging materials are carefully selected based on an extensive literature survey. The design considerations of improved substrate layout, laminated bus bars, and embedded decoupling capacitors are all discussed in detail, and are verified through a modeling and simulation approach in the design stage. The 200 degree C, 100 kHz continuous operation is demonstrated on the fabricated module. Through the comparison with a commercial SiC phase-leg module designed in the traditional way, it is also shown that the design considerations proposed in this work allow the SiC devices in the wire-bond structure to be switched twice as fast with only one-third of the parasitic ringing. To further push the performance of SiC power modules, a novel hybrid packaging technology is developed which combines the small parasitics and footprint of a planar module with the easy fabrication of a wire-bond module. The original concept is demonstrated on a high-temperature rectifier module with SiC JFET. A modified structure is then proposed to further improve design flexibility and simplify module fabrication. The SiC MOSFET phase-leg module built in this structure successfully reaches the switching speed limit of the device almost without any parasitic ringing. Finally, a new switching loop snubber circuit is proposed to damp the parasitic ringing through magnetic coupling without affecting either conduction or switching losses of the device. The concept is analyzed theoretically and verified experimentally. The initial integration of such a circuit into the power module is presented, and possible improvements are proposed. / Ph. D.

Le but de cette thèse est de concevoirun chargeur de véhicule électrique avec une fortedensité de puissance car il doit être embarqué dansle véhicule. La thèse se focalise sur le deuxièmeétage du chargeur qui comporte un transformateur.Cet élément représente une part importante du volumetotal du convertisseur.Pour réaliser cela, une nouvelle technologie de transistorsest utilisée : les transistors GaN. Ces composantsinduisent des pertes par commutation plusfaibles que les transistors classiquement utilisés cequi permet d’augmenter la fréquence de découpage.Cette fréquence est un levier pour améliorer la densitéde puissance des convertisseurs. Cependant lafréquence est également responsable de pertes dansd’autres composants comme le transformateur et lesinductances. Pour augmenter efficacement cette densité, la topologie du convertisseur doit être conçuepour réduire les contraintes sur ces composants.La thèse comporte trois parties. Tout d’abord, lecomportement des transistors GaN est évalué etdifférentes topologies sont analysées pour en déduireune structure de chargeur qui minimise les pertesdans le transformateur. Ensuite, un dimensionnementcompact de transformateur est réalisé à l’aide d’uneétude paramétrique et des simulations par élémentsfinis. Enfin, un prototype de ce deuxième étage duchargeur est réalisé et testé pour évaluer ses performanceset son volume / Improvement of power density is a bigchallenge for embedded electric vehicle chargers.Goal of the study is to reduce the volume of the DCDCcharger which contains a bulky transformer. Thekey point is to use wide band gap transistors (GaN) toincrease the charger switching frequency. High switchingfrequency can improve power density but theinconvenient is the increase of switching and transformerlosses. The PhD dissertation is organized inthree steps. First step is the definition of a charger topology.This topology is optimized to reduce transformerlosses. Second part of the study is the theoreticaldesign of a high power density transformer. A completetransformer parametric model is presented withFinite Element Analysis. Third part present the prototypeand test results of the charger DC-DC. Electricalbehavior, volume and efficiency results are discussedin this part.Universit ´

The trend towards more and all-electric apparatuses and more electrification will lead to higher electrical demand. Increases in electrical power demand can be provided by either higher currents or higher voltages. Due to "weight" and "voltage" drop, a raise in the current is not preferred; so, "higher voltages" are being considered. Another trend is to reduce the size and weight of apparatuses. Combined, these two trends result in the high voltage, high power density concept. It is expected that by 2030, 80% of all electric power will flow through "power electronics systems". In regards to the high voltage, high power density concept described above, "wide bandgap (WBG) power modules" made from materials such as "SiC and GaN (and, soon, Ga2O3 and diamond)", which can endure "higher voltages" and "currents" rather than "Si-based modules", are considered to be the most promising solution to reducing the size and weight of "power conversion systems". In addition to the trend towards higher "blocking voltage", volume reduction has been targeted for WBG devices. The blocking voltage is the breakdown voltage capability of the device, and volume reduction translates into power density increase. This leads to extremely high electric field stress, E, of extremely nonuniform type within the module, leading to a higher possibility of "partial discharge (PD)" and, in turn, insulation degradation and, eventually, breakdown of the module. Unless the discussed high E issue is satisfactorily addressed and solved, realizing next-generation high power density WBG power modules that can properly operate will not be possible. Contributions and innovations of this Ph.D. work are as follows. i) Novel electric field grading techniques including (a) various geometrical techniques, (b) applying "nonlinear field-dependent conductivity (FDC) materials" to high E regions, and (c) combination of (a) and (b), are developed; ii) A criterion for the electric stress intensity based upon accurate dimensions of a power device package and its "PD measurement" is presented; iii) Guidelines for the electrical insulation design of next-generation high voltage (up to 30 kV), high power density "WBG power modules" as both the "one-minute insulation" and PD tests according to the standard IEC 61287-1 are introduced; iv) Influence of temperature up to 250°C and frequency up to 1 MHz on E distribution and electric field grading methods mentioned in i) is studied; and v) A coupled thermal and electrical (electrothermal) model is developed to obtain thermal distribution within the module precisely. All models and simulations are developed and carried out in COMSOL Multiphysics. / Doctor of Philosophy / In power engineering, power conversion term means converting electric energy from one form to another such as converting between AC and DC, changing the magnitude or frequency of AC or DC voltage or current, or some combination of these. The main components of a power electronic conversion system are power semiconductor devices acted as switches. A power module provides the physical containment and package for several power semiconductor devices. There is a trend towards the manufacturing of electrification apparatuses with higher power density, which means handling higher power per unit volume, leading to less weight and size of apparatuses for a given power. This is the case for power modules as well. Conventional "silicon (Si)-based semiconductor technology" cannot handle the power levels and switching frequencies required by "next-generation" utility applications. In this regard, "wide bandgap (WBG) semiconductor materials", such as "silicon carbide (SiC)"," gallium nitride (GaN)", and, soon, "gallium oxide" and "diamond" are capable of higher switching frequencies and higher voltages, while providing for lower switching losses, better thermal conductivities, and the ability to withstand higher operating temperatures. Regarding the high power density concept mentioned above, the challenge here, now and in the future, is to design compact WBG-based modules. To this end, the extremely nonuniform high electric field stress within the power module caused by the aforementioned trend and emerging WBG semiconductor switches should be graded and mitigated to prevent partial discharges that can eventually lead to breakdown of the module. In this Ph.D. work, new electric field grading methods including various geometrical techniques combined with applying nonlinear field-dependent conductivity (FDC) materials to high field regions are introduced and developed through simulation results obtained from the models developed in this thesis.

In order to increase the power density, the discontinuous conducting mode (DCM) and small inductance is adopted for high power bidirectional dc-dc converter. The DCM related current ripple is minimized with multiphase interleaved operation. The turn-off loss caused by the DCM induced high peak current is reduced by snubber capacitor. The energy stored in the capacitor needs to be discharged before device is turned on. A complementary gating signal control scheme is employed to turn on the non-active switch helping discharge the capacitor and diverting the current into the anti-paralleled diode of the active switch. This realizes the zero voltage resonant transition (ZVRT) of main switches. This scheme also eliminates the parasitic ringing in inductor current. This work proposes an inductance and snubber capacitor optimization methodology. The inductor volume index and the inductor valley current are suggested as the optimization method for small volume and the realization of ZVRT. The proposed capacitance optimization method is based on a series of experiments for minimum overall switching loss. According to the suggested design optimization, a high power density hardware prototype is constructed and tested. The experimental results are provided, and the proposed design approach is verified. In this dissertation, a general-purposed power stage model is proposed based on complementary gating signal control scheme and derived with space-state averaging method. The model features a third-order system, from which a second-order model with resistive load on one side can be derived and a first-order model with a voltage source on both sides can be derived. This model sets up a basis for the unified controller design and optimization. The Δ-type model of coupled inductor is introduced and simplified to provide a more clearly physical meaning for design and dynamic analysis. These models have been validated by the Simplis ac analysis simulation. For power flow control, a unified controller concept is proposed based on the derived general-purposed power stage model. The proposed unified controller enables smooth bidirectional current flow. Controller is implemented with digital signal processing (DSP) for experimental verification. The inductor current is selected as feedback signal in resistive load, and the output current is selected as feedback signal in battery load. Load step and power flow step control tests are conducted for resistive load and battery load separately. The results indicate that the selected sensing signal can produce an accurate and fast enough feedback signal. Experimental results show that the transition between charging and discharging is very smooth, and there is no overshoot or undershoot transient. It presents a seamless transition for bidirectional current flow. The smooth transition should be attributed to the use of the complementary gating signal control scheme and the proposed unified controller. System simulations are made, and the results are provided. The test results have a good agreement with system simulation results, and the unified controller performs as expected. / Ph. D.

The demand for high power density keeps driving the development of electromagnetic integration technologies in the field of power electronics. Based on planar homogeneous integrated structures, the mechanism of the electromagnetic integration of passives has been investigated with distributed-parameter models. High order modeling of integrated passives has been developed to investigate the electromagnetic performance. The design algorithm combining electromagnetic design and loss models has been developed to optimize and evaluate the spiral winding structure. High power density of 480 W/in3 has been obtained on the prototype. Due to the structural limitation, the currently applied planar spiral winding structure does not sufficiently utilize the space, and the structure is mechanically vulnerable. The improvement on structures is necessary for further application of integrated passives. The goal of this research is to investigate and evaluate alternative structures for high-power-density integrated passives. The research covers electromagnetic modeling, constructional study, design algorithm, loss modeling, thermal management and implementation technology The symmetric single layer structure and the stacked structure are proposed to overcome the disadvantages of the currently applied planar spiral winding structure. Because of the potential of high power density and low power loss, the stacked structure is selected for further research. The structural characteristics and the processing technologies are addressed. By taking an integrated LLCT module as the study case, the general design algorithm is developed to find out a set of feasible designs. The obtained design maps are used to evaluate the constraints from spatial, materials and processing technologies for the stacked structure. Based on the assumption of one-dimensional magnetic filed on the cross-section and linear current distribution along the longitudinal direction of the stacked structure, the electromagnetic field distribution is analyzed and the loss modeling is made. The experimental method is proposed to measure the loss and to verify the calculation. The power loss in the module leads to thermal issues, which limit the processed power of power electronics modules and thus limit the power density. To further improve the power handling ability of the module, the thermal management is made based on loss estimation. The heat extraction technology is developed to improve the heat removal ability and further improve the power density of integrated passives. The experimental results verify the power density improvement from the proposed stacked structure and the applied heat extraction technology. The power density of 1147 W/in3 (70 W/cm3) is achieved in the implemented LLCT module with the efficiency of 97.8% at output power of 1008W. / Ph. D.

With the development of information technology, the market for power management of telecom and computing equipment keeps increasing. Distributed power systems are widely adopted in the telecom and computing applications for the reason of high performance and high reliability. Recently industry brought out aggressively high efficiency requirements for a wide load range for power management in telecom and computing equipment. High efficiency over a wide load range is now a requirement. On the other hand, power density is still a big challenge for front-end AC/DC converters. For DPS systems, front-end AC/DC converters are under the pressure of continuous increasing power density requirement. Although increasing switching frequency can dramatically reduce the passive component size, its effectiveness is limited by the converter efficiency and thermal management. Technologies to further increase the power density without compromising the efficiency need to be studied. The industry today is also at the beginning of transferring their design from analog control to full digital control strategy. Although issues are still exist, reducing components count, reducing the development cycle time, increasing the reliability, enhancing the circuit noise immunity and reducing the cost, all of these benefits indicate a great potential of the digital control. This thesis is focusing on how to improve the efficiency and power density by taking the advantages of the digital control. A novel Ï /2 phase shift two Channel interleaving PFC is developed to shrink the EMI filter size while maintain a good efficiency. A sophisticated power management strategy that associates with phase shedding and adaptive phase angle control is also discussed to increase the efficient for the entire load range without compromising the EMI filter size. The method of current sampling is proposed for Ï /2 phase shift two Channel interleaving PFC and multi-channel adaptive phase angle shift PFC is proposed to accurately extract the average total current information. A noise free current sampling strategy is also proposed that adjusting the sampling edge according to duty cycle information. An isolated ZVS dual boost converter is proposed to be the DC/DC stage of the front-end converter. This PWM converter has similar performance as the LLC resonant converter. It has hold up time extension capability without compromising the normal operation efficiency. It can achieve ZVS for all the switches. The current limit and SR implementation is much easier than LLC. State plane method, which potentially can be extent to other complex topologies, is used to fully study this circuit. All the operation modes are understood through the state plane method. The best operation mode is discovered for the front end applications. Light load efficiency is improved by the proposed pulse skipping method to guarantee the ZVS operation meanwhile reduce the switching frequency. Current limit operation is also proposed to restrict a best operation mode by fully taking the advantage of digital control that precisely control the circuit under the over current condition. High efficiency high power density is achieved by new topology, innovative interleaving, and the sophisticated digital control method. / Master of Science

Over the past ten years, there has been increased use of electronic power processing in alternative, sustainable, and distributed energy sources, as well as energy storage systems, transportation systems, and the power grid. Three-phase voltage source converters (VSCs) have become the converter of choice in many ac medium- and high-power applications due to their many advantages, such as high efficiency and fast response. For transportation applications, high power density is the key design target, since increasing power density can reduce fuel consumption and increase the total system efficiency. While power electronics devices have greatly improved the efficiency, overall performance and power density of power converters, using power electronic devices also introduces EMI issues to the system, which means filters are inevitable in those systems, and they make up a significant portion of the total system size and cost. Thus, designing for high power density for both power converters and passive components, especially filters, becomes the key issue for three-phase converters. This dissertation explores two different approaches to reducing the EMI filter size. One approach focuses on the EMI filters itself, including using advanced EMI filter structures to improve filter performance and modifying the EMI filter design method to avoid overdesign. The second approach focuses on reducing the EMI noise generated from the converter using a three-level and/or interleaving topology and changing the modulation and control methods to reduce the noise source and reduce the weight and size of the filters. This dissertation is divided into five chapters. Chapter 1 describes the motivations and objectives of this research. After an examination of the surveyed results from the literature, the challenges in this research area are addressed. Chapter 2 studies system-level EMI modeling and EMI filter design methods for voltage source converters. Filter-design-oriented EMI modeling methods are proposed to predict the EMI noise analytically. Based on these models, filter design procedures are improved to avoid overdesign using in-circuit attenuation (ICA) of the filters. The noise propagation path impedance is taken into consideration as part of a detailed discussion of the interaction between EMI filters, and the key design constraints of inductor implementation are presented. Based on the modeling, design and implementation methods, the impact of the switching frequency on EMI filter weight design is also examined. A two-level dc-fed motor drive system is used as an example, but the modeling and design methods can also be applied to other power converter systems. Chapter 3 presents the impact of the interleaving technique on reducing the system passive weight. Taking into consideration the system propagation path impedance, small-angle interleaving is studied, and an analytical calculation method is proposed to minimize the inductor value for interleaved systems. The design and integration of interphase inductors are also analyzed, and the analysis and design methods are verified on a 2 kW interleaved two-level (2L) motor drive system. Chapter 4 studies noise reduction techniques in multi-level converters. Nearest three space vector (NTSV) modulation, common-mode reduction (CMR) modulation, and common-mode elimination (CME) modulation are studied and compared in terms of EMI performance, neutral point voltage balancing, and semiconductor losses. In order to reduce the impact of dead time on CME modulation, the two solutions of improving CME modulation and compensating dead time are proposed. To verify the validity of the proposed methods for high-power applications, a 100 kW dc-fed motor drive system with EMI filters for both the AC and DC sides is designed, implemented and tested. This topology gains benefits from both interleaving and multilevel topologies, which can reduce the noise and filter size significantly. The trade-offs of system passive component design are discussed, and a detailed implementation method and real system full-power test results are presented to verify the validity of this study in higher-power converter systems. Finally, Chapter 5 summarizes the contributions of this dissertation and discusses some potential improvements for future work. / Ph. D.

With the development of solar energy, power conversion systems responsible for energy delivering from photovoltaic (PV) modules to ac or dc grid attract wide attentions and have significantly increased installations worldwide. Modular power conversion system has the highest efficiency of maximum power point tacking (MPPT), which can transfer more solar power to electricity. However, this system suffers the drawbacks of low power conversion efficiency and high cost due to a large number of power electronics converters. High-power density can provide potentials to reduce cost through the reduction of components and potting materials. Nowadays, the power electronics converters with the conventional silicon (Si) based power semiconductor devices are developed maturely and have limited improvements regarding in power conversion efficiency and power density. With the availability of wide bandgap devices, the power electronics converters have extended opportunities to achieve higher efficiency and higher power density due to the desirable features of wide bandgap devices, such as low on-state resistance, small junction capacitance and high switching speed. This dissertation focuses on the application of wide bandgap devices to the dc-dc power conversion for the modular PV applications in an effort to improve the power conversion efficiency and power density. Firstly, the structure of gallium-nitride (GaN) device is studied theoretically and characteristics of GaN device are evaluated under testing with both hard-switching and soft-switching conditions. The device performance during steady-state and transitions are explored under different power level conditions and compared with Si based devices. Secondly, an isolated high-efficiency GaN-based dc-dc converter with capability of wide range regulation is proposed for modular PV applications. The circuit configuration of secondary side is a proposed active-boost-rectifier, which merges a Boost circuit and a voltage-doubler rectifier. With implementation of the proposed double-pulse duty cycle modulation method, the active-boost-rectifier can not only serve for synchronous rectification but also achieve the voltage boost function. The proposed converter can achieve zero-voltage-switching (ZVS) of primary side switches and zero-current-switching (ZCS) of secondary side switches regardless of the input voltages or output power levels. Therefore, the proposed converter not only keeps the benefits of highly-efficient series resonant converter (SRC) but also achieves a higher voltage gain than SRC and a wide range regulation ability without adding additional switches while operating under the fixed-frequency condition. GaN devices are utilized in both primary and secondary sides. A 300-W hardware prototype is built to achieve a peak efficiency of 98.9% and a California Energy Commission (CEC) weighted efficiency of 98.7% under nominal input voltage condition. Finally, the proposed converter is designed and optimized at 1-MHz switching frequency to pursue the feature of high-power density. Considering the ac effects under high frequency, the magnetic components and PCB structure are optimized with finite element method (FEM) simulations. Compared with 140-kHz design, the volume of 1-MHz design can reduce more than 70%, while the CEC efficiency only drops 0.8% at nominal input voltage condition. There are also key findings on circuit design techniques to reduce parasitic effects. The parasitic inductances induced from PCB layout of primary side circuit can cause the unbalanced resonant current between positive and negative half cycles if the power loops of two half cycles have asymmetrical parasitic inductances. Moreover, these parasitic inductances reflecting to secondary side should be considered into the design of resonant inductance. The parasitic capacitances of secondary side could affect ZVS transitions and increase the required magnetizing current. Because of large parasitic capacitances, the dead-time period occupies a large percentage of entire switching period in MHz operations, which should be taken into consideration when designing the resonant frequency of resonant network. / Doctor of Philosophy / Solar energy is one of the most promising renewable energies to replace the conventional fossils. Power electronics converters are necessary to transfer power from solar panels to dc or ac grid. Since the output of solar panel is low voltage with a wide range and the grid side is high voltage, this power converter should meet the basic requirements of high step up and wide range regulation. Additionally, high power conversion efficiency is an important design purpose in order to save energy. The existing solutions have limitations of narrow regulating range, low efficiency or complicated circuit structure. Recently, the third-generation power semiconductors attract more and more attentions who can help to reduce the power loss. They are named as wide band gap devices. This dissertation proposed a wide band gap devices based power converter with ability of wide regulating range, high power conversion efficiency and simple circuit structure. Moreover, this proposed converter is further designed for high power density, which reduces more than 70% of volume. In this way, small power converter can merge into the junction box of solar panel, which can reduce cost and be convenient for installations.

The Martin Aircraft Company Limited has been developing the Martin Jetpack for over 25 years. The recent worldwide launch of the Jetpack has enabled the company to step up its research and development programme. The goal of this project was to determine the feasibility of an electrically powered version of the Martin Jetpack. The feasibility of the Electric Jetpack was determined by researching energy storage technologies, researching power cable technologies, simulations of flight times, surveys of electric motors, and the development of a simulation program which was used to optimise some preliminary custom motor designs. The overall conclusion of this project was that the Electric Jetpack was feasible only when it was powered through a tethered power cable, and on-board energy storage was not used. An investigation into current energy storage technologies showed that the Electric Jetpack is not considered feasible when using on-board energy storage, however it is possible to obtain flight for a very short time. The energy storage technologies studied were batteries, fuel cells, and ultra-capacitors. It was found that the best performing technology was the lithium iron nano-phosphate battery. A simulation of flight time showed that this battery type would be able to provide flight for approximately 3.6 minutes. Future trends indicated that the Electric Jetpack with on-board energy storage may eventually be feasible when using a lithium-ion based battery due to improvements being made in energy density and power density. By using a tethered power cable, the weight of the on-board energy storage could be eliminated. This was shown to be a feasible method for powering the Electric Jetpack for applications where the Jetpack needs to only be operated in a small area. The best cable type to use was a multi-stranded flexible cable operating at a high DC bus voltage. The weight of a 5 meter power cable using a 1000 V bus voltage was shown to be 4.9 kg. Potential applications for this kind of Jetpack could include thrill rides and rescue operations from multi-storied buildings. A cable made from carbon nanotubes was shown to be a future technology that could offer a lighter cable. A survey of currently available electric motors showed that none met both the power density and speed required by the Electric Jetpack, even when using a tethered power cable to eliminate the energy storage weight. Because of this, a custom motor design was needed. Research into motor technologies showed that the permanent magnet brushless DC (PMBLDC) motor was the most suited type for the Electric Jetpack. The permanent magnet brushless AC (PMBLAC) motor was also suitable. A PMBLDC motor simulation program was developed using MATLAB which could be used to optimise preliminary custom designs. A characterisation of allowable motor time constants for the PMBLDC motor type was made in order to speed up the simulation time. The optimisation results showed that a power density of 5.41 kW/kg was achievable for the motor when it was located inside the ducted fan tubes, and a power density of 6.56 kW/kg was achievable when the motor was located outside the ducted fans and operated at a higher speed. The motor designs were shown to be within the expected torque per unit rotor volume (TRV) range for aerospace machines. The best power density figures would leave between 37 kg and 42 kg of weight for the motor driver/controller, cable weight, and miscellaneous motor parts. This was considered to be feasible. An FEM simulation was made on one of the optimised motor designs. The FEM results agreed with the parametric results within reasonable accuracy. The parametric back-EMF waveform over-estimated the effects of slotting.

Enhancing performance of power electronics converters has always been an interesting topic in the power electronics community. Over the years, researchers and engineers are developing new high performance component, novel converter topologies, smart control methods and optimal design procedures to improve the efficiency, power density, reliability and reducing the cost. Besides pursuing high performance, researchers and engineers are striving to modularize the power electronics converters, which provides redundancy, flexibility and standardization to the end users. The trend of modularization has been seen in photovoltaic inverters, telecommunication power supplies, and recently, HVDC applications. A systematic optimal design approach for modular power converters is developed in this dissertation. The converters are developed for aerospace applications where there are stringent requirement on converter form factor, loss dissipation, thermal management and electromagnetic interference (EMI) performance. This work proposed an optimal design approach to maximize the nominal power of the power converters considering all the constraints, which fully reveals the power processing potential. Specifically, this work studied three-phase active front-end converter, three-phase isolated ac/dc converter and inverter. The key models (with special attention paid to semiconductor switching loss model), detailed design procedures and key design considerations are elaborated. With the proposed design framework, influence of key design variables, e.g. converter topology, switching frequency, etc. is thoroughly studied. Besides optimal design procedure, control issues in paralleling modular converters are discussed. A master-slave control architecture is used. The slave controllers not only follow the command broadcasted by the master controller, but also synchronize the high frequency clock to the master controller. The control architecture eliminates the communication between the slave controllers but keeps paralleled modules well synchronized, enabling a fully modularized design. Furthermore, the implementation issues of modularity are discussed. Although modularizing converters under form factor constraints adds flexibility to the system, it limits the design space by forbidding oversized components. This work studies the influence of the form factor by exploring the maximal nominal power of a double-sized converter module and comparing it with that of two paralleled modules. The tradeoff between modularity and performance is revealed by this study. Another implementation issue is related to EMI. Scaling up system capacity by paralleling converter modules induces EMI issues in both signal level and system level. This work investigates the mechanisms and provides solutions to the EMI problems. / Ph. D. / As penetration of power electronics technologies in electric power delivery keeps increasing, performance of power electronics converters becomes a key factor in energy delivery efficacy and sustainability. Enhancing performance of power electronics converters reduces footprint, energy waste and delivery cost, and ultimately, promoting a sustainable energy use. Over the years, researchers and engineers are developing new technologies, including high performance component, novel converter topologies, smart control methods and optimal design procedures to improve the efficiency, power density, reliability and reducing the cost of power electronics converters. Besides pursuing high performance, researchers and engineers are striving to modularize the power electronics converters, enabling power electronics converters to be used in a “plug-and-play” fashion. Modularization provides redundancy, flexibility and standardization to the end users. The trend of modularization has been seen in applications that process electric power from several Watts to Megawatts. This dissertation discusses the design framework for incorporating modularization into existing converter design procedure, synergically achieving performance optimization and modularity. A systematic optimal design approach for modular power converters is developed in this dissertation. The converters are developed for aerospace applications where there is stringent v requirement on converter dimensions, loss dissipation, and thermal management. Besides, to ensure stable operation of the onboard power system, filters comprising of inductors and capacitors are necessary to reduce the electromagnetic interference (EMI). Owning to the considerable weight and size of the inductors and capacitors, filter design is one of the key component in converter design. This work proposed an optimal design approach that synergically optimizes performance and promotes modularity while complying with the entire aerospace requirement. Specifically, this work studied three-phase active front-end converter, three-phase isolated ac/dc converter and three-phase inverter. The key models, detailed design procedures and key design considerations are elaborated. Experimental results validate the design framework and key models, and demonstrates cutting-edge converter performance. To enable a fully modularized design, control of modular converters, with focus on synchronizing the modular converters, is discussed. This work proposed a communication structure that minimizes communication resources and achieves seamless synchronization among multiple modular converters that operate in parallel. The communication scheme is demonstrated by experiments. Besides, the implementation issues of modularity are discussed. Although modularizing converters under form factor constraints adds flexibility to the system, it limits the design space by forbidding oversized components. This work studies the impact of modularity by comparing performance of a double-sized converter module with two paralleled modules. The tradeoff between modularity and performance is revealed by this study.