A twin-buck converter with zero-voltage-transition (ZVT) is proposed in this thesis. The converter comprises two identical buck conversion units connected in parallel by an interleaved inductor. The ZVT is accomplished by the resonating the currents between the interleaved inductor and the parasitic capacitances of the power MOSFETs. The circuit efficiency can be further improved by introducing synchronous rectification to reduce the condition loss on the diodes. The detailed circuit analysis and operation characteristics are provided. A laboratory circuit rated at 300 W is designed and tested. Experimental results show that the switching losses can be effectively reduced by smoothly transiting the currents of the active power switches.

The purpose of this thesis is to design and implement a linear quadratic optimal controller for a twin-buck converter with zero-voltage-transition (ZVT). The controller calculates duty ratio every cycle based on voltage and current feedback, as well as estimates the time instances when the synchronous rectification power switch current is zero. These time instances are crucial for ZVT operation. Via frequency modulation, the controller is designed to automatically regulate the output voltage to a desired value under load and voltage source variation. Simulations indicate that the proposed control design works. The controller is implemented using a Field Programmable Gate Array (FPGA). The experimental results match the simulations, which further verifies the applicability of the proposed voltage regulation strategy.

This dissertation presents the systematic analysis and the critical assessment of the AC side soft-switching inverters in electric vehicle (EV) applications. Although numerous soft-switching inverter techniques were claimed to improve the inverter performance, compared with the conventional hard-switching inverter, there is the lack of comprehensive investigations of analyzing and evaluating the performance of soft-switching inverters. Starting with an efficiency comparison of a variety of the soft-switching inverters using analytical calculation, the dissertation first reveals the effects of the auxiliary circuit's operation and control on the loss reduction. Three types of soft-switching inverters realizing the zero-voltage-transition (ZVT) or zero-current-transition (ZCT) operation are identified to achieve high efficiency operation. Then one hard-switching inverter and the chosen soft-switching inverters are designed and implemented with the 55 kW power rating for the small duty EV application. The experimental evaluations on the dynamometer provide the accurate description of the performance of the soft-switching inverters in terms of the loss reductions, the electromagnetic interference (EMI) noise, the total harmonic distortion (THD) and the control complexity. An analysis of the harmonic distortion caused by short pulses is presented and a space vector modulation scheme is proposed to alleviate the effect. To effectively analyze the soft-switching inverters' performance, a simulation based electrical modeling methodology is developed. Not only it extends the EMI noise analysis to the higher frequency region, but also predicts the stress and the switching losses accurately. Three major modeling tasks are accomplished. First, to address the issues of complicated existing scheme, a new parameter extraction scheme is proposed to establish the physics-based IGBT model. Second, the impedance based measurement method is developed to derive the internal parasitic parameters of the half-bridge modules. Third, the finite element analysis software is used to develop the model for the laminated bus bar including the coupling effects of different phases. Experimental results from the single-leg operation and the three-phase inverter operation verify the effectiveness of the presented systematic electrical modeling approach. With the analytical tools verified by the testing results, the performance analysis is further extended to different power ratings and different bus voltage designs. / Ph. D.

The work in this dissertation presents the first attempt in the literature to propose the concept of "soft switch". The goal of "soft switch" is to develop a standard PWM switch cell with built-in adaptive soft switching capabilities. Just like a regular switch, only one PWM signal is needed to drive the soft switch under soft switching condition. The core technique in soft switch development is a built-in adaptive soft switching circuit with minimized circulation energy. The necessity of minimizing circulation energy is first analyzed. The design and implementation of a universal controller for implementation of variable timing control to minimize circulation energy is presented. The controller has been tested successfully with three different soft switching inverters for electric vehicles application in the Partnership for a New Generation Vehicles (PNGV) project. To simplify the control, several methods to achieve soft switching with fixed timing control are proposed by analyzing a family of zero-voltage switching converters. The driver based soft switch concept was originated from development of a base driver circuit for current driven bipolar junction transistor (BJT). A new insulated-gate-bipolar-transistor (IGBT) and power metal-oxide-semiconductor field-effect-transistor (MOSFET) gated transistor (IMGT) base drive structure was initially proposed for a high power SiC BJT. The proposed base drive method drives SiC BJTs in a way similar to a Darlington transistor. With some modification, a new base driver structure can adaptively achieve zero voltage turn-on for BJT at all load current range with one single gate. The proposed gate driver based soft switching method is verified by experimental test with both Si and SiC BJT. The idea is then broadened for "soft switch" implementation. The whole soft switched BJT (SSBJT) structure behaves like a voltage-driven soft switch. The new structure has potentially inherent soft transition property with reduced stress and switching loss. The basic concept of the current driven soft switch is then extended to a voltage-driven device such as IGBT and MOSFET. The key feature and requirement of the soft switch is outlined. A new coupled inductor based soft switching cell is proposed. The proposed zero-voltage-transition (ZVT) cell serves as a good candidate for the development of soft switch. The "Equivalent Inductor" and state plane based analysis method are used to simply the analysis of coupled inductor based zero-voltage switching scheme. With the proposed analysis method, the operational property of the ZVT cell can be identified without solving complicated differential equations. Detailed analysis and design is proposed for a 3kW boost converter example. With the proposed soft switch design, the boost converter can achieve up to 98.9% efficiency over a wide operation range with a single gate drive. A high power inverter with coupled inductor scheme is also designed with simple control compared to the earlier implementation. A family of soft-switching converters using the proposed "soft switch" cell can be developed by replacing the conventional PWM switch with the proposed soft switch. / Ph. D.

In the thesis, we apply the state average method to model the time-average linear dynamic equation, which is used to design a gain scheduled linear quadratic optimal controller. Because the standard modulation method of the twin-buck converter is PFM(Pulse-Frequency Modulation) and twin-buck converter owns the soft-switching characteristic, the voltage step-down ratio, that is, control force can not be lowered less than 0.5. For expanding the range of control force of converter, we modulate the converter by means of mixed modulation of PWM/PFM. With the former odulation method, we have to calculate the discharging time of synchronous switch taken by controller to achieve zero-voltage-transition (ZVT). In the last part of this thesis, we verify the practicability of the controller and modulation method through soft simulation coded by MATLAB and hardware implementation of FPGA driven by Verilog.

The main goal of this project was an optimization of DC-DC converter design from company Meatest with regards to its efficiency, minimalizing power loses and radiated electromagnetic inference, while maintaining its price on reasonable level. The first part of this paper is introduction to the most common converter topologies. In the second part, design and optimization of converter are discussed. The third part is about measurement automatization in Simple. Measurements of converter prototype can be found in fourth part.

Boost dc-to-dc converters have very good source interface properties. The input inductor makes the source current smooth and hence these converters provide very good EMI performance. On account of this good property, the boost converter is also the preferred converter for off-line UPF rectifiers. One of the issues of concern in these converters is the large size of the storage capacitor on the dc link. The boost converter suffers from the disadvantage of discontinuous current injected to the load. The size of the capacitor is therefore large. Further, the ripple current in the capacitor is as much as the load current; hence the ESR specification of the tank capacitor is quite demanding. This is specially so in the emerging application areas of automotive power conversion, where the input voltage is low (typically 12V) and large voltage boost (4 to 5) are desired. The first part of this thesis suggests multi-phase boost converter to overcome the disadvantages of large size storage capacitor in boost converter. Comparison between the specification of single stage and multi-stages is thoroughly examined. Besides the average small signal analysis of N converters in parallel and obtaining an equivalent second order system are discussed. By paralleling the converters the design of closed loop control is a demanding task. To achieve proper current sharing among the stages using current control method is inevitable. Design and implementation of closed loop control of multi-phase boost converter both in analog and digital is the topic of next part of the thesis. Comparison between these two approaches is presented in this part and it will be shown that digital control is more convenient for such a topology on account of the requirement of synchronization, phase shifted operation, current balancing and other desired functions, which will be discussed later in detail. A new direct digital control method, which is simple and fast, is developed. Two different realizations with DSP controller and FPGA controller are considered. In the last part of the thesis a novel soft switching circuit for boost converter is presented. It provides Zero Voltage Switching (ZVS) for the main switch and Zero Current Switching (ZCS) for the auxiliary switch. The paper presents the idealized analysis giving all the circuit intervals and the equations necessary for the design of such a circuit. The proposed soft switching circuit is particularly suited for the tapped-inductor boost circuit with a minimum number of extra components. Extension of the method to tapped inductor boost converter addresses the application of Zero Voltage Transition (ZVT) to high conversion ratio converters. Extension of the method to multiphase boost converter shows that with less number of auxiliary switches soft switching operation can be achieved for all interleaved switching devices. Several laboratory prototype boost converters have been built to confirm the theoretical results and design methods are matching with both simulation and experimental results.