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In a dual active bridge (DAB) dc–dc converter, modulating the phase-shift ratios can suppress reactive power and increase the efficiency under non-unity voltage gain conditions. Derivation of the optimal phase-shift ratios to achieve the minimum reactive power is challenging because a DAB can operate in four different scenarios (forward/backward, buck/boost) and each scenario has five operating modes. This paper first introduces a transformation in which different DAB operating scenarios (forward/backward, buck/boost) can be equivalent to one another; then optimization of only one scenario (forward/buck) is required. Next, for the five modes in forward/buck scenario, based on a graphical method, this paper proves that each operating point of Modes 1, 2, and 5 can be mapped into that of Mode 3 with lower conduction losses, and only two modes require detailed analysis. The optimization process of these two modes are derived step-by-step. Global optimal phase-shift signals that minimize the reactive power under four different DAB operating scenarios (forward/backward, buck/boost) are presented. A simple table and control block diagram are presented for practical implementation of global reactive-power minimization control. Experimental comparison with other modulation schemes verifies the efficiency improvement of the proposed control method. [ABSTRACT FROM AUTHOR]

In this paper, a three-phase current-fed dual-active-bridge (DAB) bidirectional DC-DC converter is presented. Compared to the voltage source DAB converter, the proposed converter allows low RMS current and maintains zero voltage switching (ZVS) in the whole operating range by keeping the ratio between primary side and secondary side DC-link voltage constant, leading to high efficient energy conversion over a wide input voltage range. In addition, the ZVS conditions can be maintained using small DC inductors and the input current ripple still remains small because of high DC inductor current ripples being alleviated by three-phase interleaving structure. Furthermore, the proposed topology with Y-Y connected transformers is proven to have better current sharing capability compared with other three-phase topologies with different transformer connections. The operation mode analysis, soft switching conditions, and hardware design guidelines are derived in this paper. A 6-kW hardware prototype with input voltage range of 24~48 V and rated 288 V output voltage is developed and tested in the laboratory. The experimental results verified that the proposed converter could maintain high efficiency over a wide input voltage and power range. [ABSTRACT FROM AUTHOR]

The Energy Transfer Mode (ETM) in a Boost dc-dc converter is classified into two types, i.e., the Complete Inductor Supply Mode (CISM) and the Incomplete Inductor Supply Mode (IISM). The critical inductance and boundary condition of CISM and IISM are derived in the paper. Based on the classification, three operating modes are defined, and they are CISM, IISM in Continuous Conduction Mode (IISM-CCM) and IISM in Discontinuous Conduction Mode (IISM-DCM). Output voltage ripple (OVR) in three modes is analyzed, respectively. As for a Boost converter with certain load, output capacitance and switching frequency, the OVR in CISM is the lowest and independent of the inductance and OVR in IISM is higher and increases with the decrease of the inductance. It is concluded that the minimal inductance to guarantee the Maximum OVR (MOVR) to be the lowest is actually the critical inductance of CISM and IISM under the condition of the lowest input voltage and minimum load resistance. In addition, the lowest MOVR is independent of the inductance. The design method to find the minimal inductance is proposed in the paper. Experiment results are in positive to the analysis showing the feasibility of the proposed methods. [ABSTRACT FROM AUTHOR]

In this paper, the development of a low cost fuel cell inverter system is detailed. The approach consists of a three-terminal push-pull dc-dc converter to boost the fuel cell voltage (48 V) to ±200 VDC. A four switch [insulated gate bipolar transistor (IGET)] inverter is employed to produce 120-V/240-V, 60-Hz ac outputs. High performance, easy manufacturability, lower component count, safety and cost are addressed. Protection and diagnostic features form an important part of the design. Another highlight of the proposed design is the control strategy, which allows the inverter to adapt to the requirements of the load as well as the power source (fuel cell). A unique aspect of the design is the use of the TMS320LF2407 DSP to control the inverter. Two sets of lead-acid batteries are provided on the high voltage dc bus to supply sudden load demands. Efficient and smooth control of the power drawn from the fuel cell and the high voltage battery is achieved by controlling the front end dc-dc converter in current mode. The paper details extensive experimental results of the proposed design on Department of Energy (DoE) National Energy Technology Laboratory (NETL) fuel cell. [ABSTRACT FROM AUTHOR]

This paper proposes fault-tolerant (FT) operation of a single-switch dc-dc converter under a switch failure. In order to improve the reliability in critical applications, FT operation is mandatory to guarantee service continuity. The FT operation of a power system can be performed in three steps: fault diagnosis (detection and identification) and remedial actions. In the case of a switch failure, suitable fault detection is essential to avoid its propagation to the whole system. This study is based on a fast and efficient open- and short-circuit switch fault diagnosis. Both types of switch failure can be detected, identified, and handled in real time by implementing fault diagnosis and reconfiguration strategies on a field-programmable gate array target. No additional sensor is required to perform the fault detection. A redundant switch and a bidirectional switch are needed for converter reconfiguration in postfault operation. The results of hardware-in-the-loop and experimental tests, which all confirm the good performances of the proposed approach, are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, the general design of a battery buffer system (BBS) consisting of a dc/dc converter and electric double layer capacitors for an electric vehicle is presented. This is intended to save the regenerative braking energy and to support the battery during acceleration. The design of a multiphase converter in interleaved operation with nonideal coupled inductors is stated to minimize volume and power losses while maintaining given current ripple limitations. A reduced sensor current-sharing control method is developed and its correct choice of the sensor position is explained. The peak efficiency of the designed and built converter can be measured to nearly 99%. The corresponding BBS is implemented in a lead-acid battery powered electric lift truck propulsion system. The system operation with and without the BBS is compared to examine the behavior and the overall efficiency. It can be shown that the traction battery stress can be strictly reduced as well as the temperature rise in the battery. Furthermore, the efficiency can be increased in the range of 5-6%. The battery's lifetime improvement is estimated by means of the difference in the temperature rise to approximately 20%. [ABSTRACT FROM AUTHOR]

The paper discusses two approaches to multiphase nonisolated dc-dc converter design. An approach based on independent phases is directly compared to an approach using coupled phases. The comparison is performed through theoretical analysis of respective conversion functions, input and output filter requirements, and required input inductor size. Three-dimensional (3-D) high-power-density computer aided design (CAD) models and full-scale 56 kW prototypes based on both approaches were designed, built, and experimentally compared. As expected, the approach with independent phases has a considerable advantage regarding the low-power conversion efficiency where the efficiency can be up to 2% higher than with the coupled approach. On the other hand, the design with coupled inductors can reach power density as high as two times that of the independent phase design (87 kW/L versus 44.2 kW/L). Therefore, the use of coupled inductors may be very beneficial for space critical applications. In case of the electric vehicle power train, both factors may be very important and the suitable approach should be chosen based on system design priorities. [ABSTRACT FROM AUTHOR]

This paper presents an isolated on-board vehicular battery charger that utilizes silicon carbide (SiC) power devices to achieve high density and high efficiency for application in electric vehicles (EVs) and plug-in hybrid EVs (PHEVs). The proposed level 2 charger has a two-stage architecture where the first stage is a bridgeless boost ac-dc converter and the second stage is a phase-shifted full-bridge isolated dc-dc converter. The operation of both topologies is presented and the specific advantages gained through the use of SiC power devices are discussed. The design of power stage components, the packaging of the multichip power module, and the system-level packaging is presented with a primary focus on system density and a secondary focus on system efficiency. In this work, a hardware prototype is developed and a peak system efficiency of 95% is measured while operating both power stages with a switching frequency of 200 kHz. A maximum output power of 6.1 kW results in a volumetric power density of 5.0 kW/L and a gravimetric power density of 3.8 kW/kg when considering the volume and mass of the system including a case. [ABSTRACT FROM AUTHOR]

The electrical circuit and model of piezoelectric transformers (PTs) ELS-60 is developed. Rosen-type PT and many other nonisolated conversion circuits have the inherit problem of the common neutral between the input and output that make it difficult to connect the output in series like the magnetic transformer. A new method based on the bootstrap method is proposed to solve the aforementioned problem. A new circuit for output summation of voltage level in the output side of each PT is developed. The impact of load and output filter capacitor on the conversion ratio and resonant frequency is discussed. Experimental results based on one printed circuit board prototype of double-level PT and boost convertor validate the previous theoretical analysis and simulation results. The paper finally proposes a multilevel concept for many PT connected together for voltage summation. The method proposed can be applied to other multiple conversion circuits, which are based on common neutral between the input and output. [ABSTRACT FROM AUTHOR]

A dual-output dc-dc converter based on the complementary pulsewidth modulation is proposed to overcome the cross-regulation problem between the outputs. Using a special-connected two transformers cell, one operational period is divided into two complementary parts. One output branch gets the pulsewidth and is regulated by the duty cycle; the other output branch gets the complementary pulsewidth and is regulated by the PFM. Only one full bridge and several passive components are needed, but both the two outputs have the fully regulated abilities even in the no-load situation. Moreover, a full zero-voltage-switching (ZVS) range is achieved in all the switches without auxiliary circuits. Therefore, the proposed topology has compact structure, high switching frequency, high-power density, and high efficiency. The operation principle, ZVS conditions, and design considerations are presented in the paper. The analysis is verified by a 300 V input, and 24 V/10A and 48 V/5 A outputs prototype. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel approach to the modeling and controller design of the synchronous step-down dc-dc converter. We introduce a hybrid converter model that is valid for the whole operating regime and captures the different modes of operation. Based on this model, we formulate and solve a constrained optimal control problem. This allows a systematic controller design that achieves the regulation of the output voltage to its reference despite input voltage and output load variations while satisfying the constraints on the duty cycle and the inductor current. The resulting state-feedback control law is of piecewise affine form, which can be easily stored and implemented in a lookup table. A Kalman filter is added to account for unmeasured load variations and to achieve zero steady-state output voltage error. Experimental results demonstrate the potential advantages of the proposed control methodology. [ABSTRACT FROM AUTHOR]

A complete equivalent model and analysis of high-efficiency charge-pump gain-increase (PGI) circuits with resistive loads are proposed. Based on this simple analytical model, the characteristics of PGI circuits can be approximately predicted and several handy equations, which are useful for pencil-and-paper design, can also be found for planning the desired circuit to achieve good enough performance with an acceptable accuracy tolerance in the steady state. In addition, an optimized design method for PGI circuits with resistive loads is developed in terms of the total number of gain stages in the design and the ratio between pump capacitors. For 1.5 V supply voltage operation, reliability and accuracy are demonstrated by comparisons between SPICE simulations of the PGI circuit and the results from the equivalent model. The model also has been validated by means of measurements taken from a test chip and typically shows relative open-loop output voltage errors lower than 8%. Finally, although the derivation of the model was based on a PGI circuit, it is shown that the design strategy can also be applied to other charge pump designs that have no voltage drop between the inner stages and the output stage. [ABSTRACT FROM AUTHOR]

Fuel cell systems have not significantly penetrated the low-power (< 50 W) portable energy source market, largely due to complexity of control and the balance-of-plant systems required. Even though the fuel cell and fuel container may scale down well, the pumps, blowers, and power converters required may dominate the system mass. This paper focuses on the tradeoff between efficiency and converter mass, and achieving the design objective of minimum mass of both converter and fuel. The effect of desired run-time, or mission duration, on the optimal dc-dc converter design was explored in detail. The effort focused on boost converters; however, the methodology can be applied to any converter topology. In an example case, at a mission length of 100 h, the optimized converter saved 91 g of system mass when compared to an off-the-shelf dc-dc converter. [ABSTRACT FROM AUTHOR]

Single-ended and two-ended bidirectional capacitor multipliers for providing on-chip compensation, soft-start, and fast transient mechanisms are proposed in this paper. The bidirectional current mode capacitor multiplier technique can effectively move the crossover frequency toward to the origin in the start-up period for a smoothly rising of the output voltage. Besides, the small time constant is set by the fast transient control circuit in order to get a higher crossover frequency. Thus, the output voltage can be regulated to its stable value as fast as it can when large load current changes. A test chip fabricated by the Taiwan Semiconductor Manufacturing Corporation (TSMC) 0.35-μm process verifies the correctness of the bidirectional current mode capacitor multiplier technique. Experimental results demonstrate the transient speed by our proposed technique is faster than that by conventional control by about 2 times, and there is only about 76% dropout voltage of the conventional design with off-chip compensation. The proposed circuits consume more quiescent current about 10 μA in single-ended capacitor multiplier and 20 μA in two-ended capacitor multiplier. With the proposed bidirectional current mode capacitor multiplier technique, the performance of dc-dc converters is improved significantly and the external pins and footprint area are minimized. [ABSTRACT FROM AUTHOR]

This paper presents the theoretical analysis of the three-phase zero voltage switching pulsewidth modulation dc-dc converter associated with a double Wye connected rectifier, delta primary, using a special switching scheme in order to maintain equilibrium among the currents through the output filters. The operating stages are described and the simulation and experimental results of a 6-kW prototype are presented. [ABSTRACT FROM AUTHOR]

In this paper, an averaged model for a recently pro- posed novel three-phase transformer-isolated phase-shift dc-dc converter is derived. Fuel cell static and dynamic characteristics are used for the converter power stage design consideration. The controller is then designed based upon the power stage parameters and system dynamic requirements. The entire system has been designed, fabricated, and tested using a commercial 1.2-kW proton exchange membrane fuel cell. The experimental results match the simulation results fairly well on both fuel cell source dynamic and step load transient responses. [ABSTRACT FROM AUTHOR]

The aim of this paper is to introduce a dc-dc converter that can be used in an online uninterruptible power supply (UPS). The proposed converter provides uninterrupted, reliable power and voltage regulation for critical loads, as well as power factor correction in supply systems. Operating principles, theoretical analysis, and control strategy are described. Digital simulation and experimental results are included, supporting the validity of the concept. [ABSTRACT FROM AUTHOR]

The high installation cost is the major obstacle of the commercialization of the solid oxide fuel cell for distributed power generation. This paper presents a new low cost 10-kW converter system to overcome this obstacle. The proposed system consists of an isolated dc-dc converter to boost the fuel cell voltage to 400 V dc and a pulse-width modulated inverter with filter to convert the dc voltage to two split-phase 120-V ac. The dc-dc converter uses phase shifting to control power flow through a transformer with a metal oxide semiconductor field effect transistor full bridge on the low voltage side and a voltage doubler on the high voltage side. One IPM is used to realize the voltage doubler and the dc-ac inverter. Compared to the existing fuel cell converter systems, the proposed circuit has low cost, less component count, smaller size, and reduced dc-dc converter peak current. Simulation and experimental results are demonstrated. [ABSTRACT FROM AUTHOR]