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H-bridge-based single-phase applications have second-order harmonics on the dc-link voltage. Conventionally, the second-order harmonics are filtered by bulky dc capacitors to maintain the constant dc-link voltage, which results in poor power density and low reliability. However, in applications, such as the solid-state variable capacitor (SSVC), the constant dc-link voltage is unnecessary since the dc link is disconnected from the load or source. This article proposes a dc capacitor-less SSVC, which removes the dc capacitors from the topology. The dc voltage is supported by the ac-side voltage directly. Only a 0.03 per unit (p.u.) capacitor is needed to filter the switching-frequency harmonics. This enables the proposed SSVC to use the snubber capacitors to achieve the function of the 0.03-p.u. filtering capacitor. Other capacitors can be removed from the dc-link busbar. The modulation, modeling, and control strategy of the proposed dc capacitor-less SSVC are provided in this article. The proposed dc capacitor-less SSVC is validated by the experiment. [ABSTRACT FROM AUTHOR]

Traditional load regulation methods for a resonant converter mainly rely on frequency modulation. It is always a tradeoff between the design of the resonant network and the range of load. Especially for wireless power transfer (WPT) systems, the resonant network usually has a high quality factor. Small variation on frequency leads to huge drop in gain and efficiency. Due to this problem, many WPT systems are unregulated and they need one or two more front-end stages to regulate the dc bus voltage and perform power factor correction (PFC). In order to lower the cost and complexity of two- or three-stages structure, a single-stage solution with a silicon carbide (SiC) based Z-source resonant converter (ZSRC) was recently proposed. The Z-source network provides high reliability as being immune to shoot-through problems. Additionally, a ZSRC can boost the dc bus voltage while the traditional voltage-source inverter can only produce a lower voltage. However, the load regulation of this new topology has not been addressed. Two effective load regulation methods with constant frequency are presented for this SiC-based ZSRC specifically. Operation principle of the two load regulation methods are described in this paper. Experimental results based on a 200-W scale-down prototype with a full-bridge series resonant dc–dc converter are presented to illustrate the mechanism of these two methods. [ABSTRACT FROM AUTHOR]

This letter generalizes the fundamental limit theory in switched-capacitor (SC) converters. The fundamental limit theory proposed in 1995 sets the voltage-gain-ratio (VCR) boundaries for a specific number of $k$ flying capacitors in the SC converter. Although this limit is valid for the positive VCR, another condition must be satisfied for the negative VCR. Moreover, the fundamental limit is only proved using single-input single-output SC converters, whereas multiple-input multiple-output (MIMO) SC converter implementation is desirable in some applications. Therefore, this letter extends the fundamental limit theory to include the negative VCR and the MIMO SC converter implementation. [ABSTRACT FROM PUBLISHER]

SUMMARY Current balancer-based phase leg paralleling provides a preponderant technology for the grid-tie inverter to extend current rating when transporting high wind power to the grid. However, the existing technology used one current balancer per phase output (one core per phase), so that three current balancers (three separate cores) were required for the three-phase system, which caused redundant large size. Also, the low-frequency circulating current components have to be controlled in order to avoid saturation of the current balancer designed for minimizing the switching frequency components of circulating current. This paper contributes in three aspects: (i) two multiphase coupling current balancers are proposed for two parallel configurations, only one single core is employed for the three-phase system, and the compactness and light weight are achieved with a very high permeability magnetic core and no air gap. (ii) The detailed current balancer design methods are proposed for both configurations, and the designed two prototypes compare two current balancers for application to two inverter configurations. (iii) A current closed-loop control is proposed to minimize the circulating current, which is verified by the simulated results. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The conventional current-source inverter has two major problems: unidirectional power flow and voltage boost operation, which make it impossible to be used in many applications, such as hybrid electric vehicles and general-purpose variable-speed motor drives. Z-source inverters (ZSIs) can solve both problems. Quasi-ZSIs (qZSIs) were recently proposed as an important improvement to traditional ZSIs. Besides the advantages inherited from ZSIs, qZSIs also have several of their own merits. This paper presents a comprehensive study on the new features of current-fed qZSI, including the advantageous buck–boost function, improved reliability, reduced passive component ratings, and unique regeneration capability. The current-fed qZSIs are bidirectional with an additional diode, unlike the voltage-fed ZSI that needs a switch to achieve bidirectional power flow. A modified space vector pulse-width-modulation method is proposed, and the available operating regions for motoring and regeneration operation are analyzed in this paper. Since the current-fed qZSI has the same operation as the current-fed ZSI, many results of this paper are also applicable to the current-fed ZSI. A reverse-blocking insulated-gate bipolar-transistor-based current-fed qZSI prototype was developed in the laboratory. Simulation and experimental results are shown to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a novel control method to lower the harmonic components of the conventional voltage balancing control for the multilevel converters. The harmonic components in the voltage balancing control theory are analyzed in detail. A revised control method based on the line-line voltage redundancy of the three-phase inverter is proposed to lower the harmonic components of both the converter and inverter side. The proposed method can significantly reduce the harmonic components while keeping the switching frequency nearly the same. Simulation and experimental results are provided to show the validity of the theory. [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]

Power flow control is important in power systems and recently becomes more urgent because of the deregulation and 2003 blackout. This paper presents a novel configuration of unified power flow controller. The proposed configuration has several unique features and advantages over the conventional configuration. As a result, cascade multilevel inverter can be used in the new configuration to lower the cost, volume, and increase the reliability of the system. Analysis and simulation results will be presented. [ABSTRACT FROM AUTHOR]

This paper presents a regenerative passive snubber circuit for pulse-width modulation (PWM) inverters to achieve soft-switching purposes without significant cost and reliability penalties. This passive soft-switching snubber (PSSS) employs a diode/capacitor snubber circuit for each switching device in an inverter to provide low dv/dt and low switching losses to the device. The PSSS further was a transformer-based energy regenerative circuit to recover the energy captured in the snubber capacitors. All components in the PSSS circuit are passive, thus leading to reliable and low-cost advantages over those soft-switching schemes relying on additional active switches. The snubber has been incorporated into a 150 kVA PWM inverter. Simulation and experimental results are given to demonstrate the validity and features of the snubber circuit. [ABSTRACT FROM AUTHOR]

A dual half-bridge (DHB) bidirectional dc-dc converter is a new proposed topology that has the advantages of decreased number of devices, soft-switching implementation, low cost, and high efficiency. Typical applications of this converter are the auxiliary power supply in fuel cell vehicles and battery charging and discharging systems where the power density- cost, weight, and reliability are critical factors. A switching-frequency-dependent state-space averaged model of the converter is developed here for either direction of power flow. This averaged model can be used to derive the steady-state characteristics and small signal dynamics of the proposed topology. It also provides a fast simulation tool to investigate the transient response of the converter. The simulated waveforms of the mathematical model are compared with the detailed circuit simulation to verify the accuracy of the modeling. [ABSTRACT FROM AUTHOR]

This paper presents a new zero-voltage-switching (ZVS) bidirectional dc-dc converter. Compared to the traditional full and half bridge bidirectional dc-dc converters for the similar applications, the new topology has the advantages of simple circuit topology with no total device rating (TDR) penalty, soft-switching implementation without additional devices, high efficiency and simple control. These advantages make the new converter promising for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required. The operating principle, theoretical analysis, and design guidelines are provided in this paper. The simulation and the experimental verifications are also presented. [ABSTRACT FROM AUTHOR]

The overvoltage caused by reflected wave phenomenon in motor drives becomes worse with the application of SiC devices due to the significantly higher $dv/dt$ compared with that of Si devices. This letter presents a low-loss and compact active reflected wave canceller (ARWC) to suppress the overvoltage at the motor terminal. The proposed ARWC circuit uses low current devices to break the rising and falling edges of the pulsewidth modulation voltage waveforms to two steps, whereas the second step cancels the first step reflection. In addition, the ARWC circuit does not require an additional dc power supply that allows the ARWC self-sustained. The experimental results on one phase 6 kVA application with and without proposed ARWC are provided and compared to verify the validity of proposed method. [ABSTRACT FROM AUTHOR]

Although gate-oxide degradation occurs in both silicon (Si) and silicon carbide (SiC) MOSFETs, it requires a special attention in SiC MOSFETs. This is because the gate oxide in SiC MOSFETs is comparatively thinner than the gate oxide in Si MOSFETs, and thus, a higher electric field that appears across it could push the gate oxide to its reliability limit. While several electrical parameters have been identified as precursors (indicators) for monitoring the gate-oxide degradation process in Si MOSFETs, very few have been identified for their SiC counterparts. The purpose of this article is twofold. The first objective is to demonstrate that the three gate-oxide degradation precursors identified for Si MOSFETs: 1) threshold voltage, 2) gate-plateau voltage, and 3) gate-plateau time can also be extended to SiC MOSFETs. The second objective is to demonstrate analytically and experimentally that all three precursors increase in a linear-with-log-stress-time manner during gate-oxide degradation in both planar and trench-gate SiC MOSFETs. The increasing trends of precursors and their associated logarithmic time responses were experimentally verified by inducing accelerated gate-oxide degradation in two different commercial SiC MOSFETs (650-V, 70-A trench-gate MOSFETs and 1200-V, 19-A planar MOSFETs) under high temperatures of 150 and 125 °C, respectively. [ABSTRACT FROM AUTHOR]

This article focuses on distributed power generation. The worldwide electric utility generation is estimated at over 3,000,000 installed megawatts (MW) and is growing by more than 80,000 MW per year. In the U.S. and many other parts of the world, retail competition is increasing and the power generation segment has been or is being deregulated and opened up to competition. Building new central generating plants is or will be a riskier proposition than it was for regulated utilities of the past. This new deregulated world has caused and will continue to cause the utility and new generating companies to seek opportunities for constructing smaller generating plants, closer to the customer, which reduce the risk and increase predictability of utilization.

Wireless power transfer (WPT) using only harmonic current for plug-in hybrid electric vehicle and electric vehicle is a fairly new concept. The frequency limitation of most high-voltage high-current IGBTs is around 20 kHz which also limits the system frequency of the transformer. The series resonant converter (SRC) is widely used in WPT application for its simplicity and high efficiency. Due to the bandpass filter characteristic of the resonant network, the SRC allows one frequency component to pass while the other frequency components are greatly attenuated. By deliberately selecting one harmonic current as the power carrier, the system frequency can be raised up to several times with the same switching frequency. Thus, a higher system frequency contributes to a more compact system. However, a high-order harmonic system results in high conduction loss on the switches, and it leads to a tradeoff between the system size and efficiency. This paper provides a theoretical and practical design for a system using harmonic current. Furthermore, a comprehensive comparison between different harmonic systems is carried out. A 1-kW SRC prototype with a 20-cm air gap is built to verify the proposed method. [ABSTRACT FROM AUTHOR]

This paper analyzes the stability problem of the grid-connected voltage-source inverter (VSI) with LC filters, which demonstrates that the possible grid-impedance variations have a significant influence on the system stability when conventional proportional-integrator (PI) controller is used for grid current control. As the grid inductive impedance increases, the low-frequency gain and bandwidth of the PI controller have to be decreased to keep the system stable, thus degrading the tracking performance and disturbance rejection capability. To deal with this stability problem, an H\infty controller with explicit robustness in terms of grid-impedance variations is proposed to incorporate the desired tracking performance and the stability margin. By properly selecting the weighting functions, the synthesized H\infty controller exhibits high gains at the vicinity of the line frequency, similar to the traditional proportional-resonant controller; meanwhile, it has enough high-frequency attenuation to keep the control loop stable. An inner inverter-output-current loop with high bandwidth is also designed to get better disturbance rejection capability. The selection of weighting functions, inner inverter-output-current loop design, and system disturbance rejection capability are discussed in detail in this paper. Both simulation and experimental results of the proposed H\infty controller as well as the conventional PI controller are given and compared, which validates the performance of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a Z-source inverter system for a split-phase grid-connected photovoitaic system. The operation principle, control method, and characteristics of the system are presented. A comparison between the new and traditional system configurations is performed. Simulation and experimental results are also shown to verify the proposed circuit and analysis. [ABSTRACT FROM AUTHOR]

The power transfer of a dual active bridge (DAB) dc–dc converter is not linearly proportional to the phase shift between the two active bridges. When the DAB converter controller receives the power reference, the phase shift needs to be obtained by either solving a quadratic equation online or looking up from a table. The online calculation method is computationally inefficient. The lookup table method has only limited operating points. In addition, when using interpolation to find missing operating points from the table, the control accuracy will be reduced. This letter proposes a simple phase-shift modulation using a parabolic carrier. The proposed method converts the power command into phase shift by modulation. Therefore, the solving of the quadratic equation can be eliminated. The Verilog results are provided to verify the proposed parabolic carrier. A case study of DAB with sinusoidal ripple current charging concept is provided to demonstrate the advantage of the proposed method. [ABSTRACT FROM AUTHOR]

High gain bidirectional dc–dc converter with high efficiency and high power density is a much desired circuit in any converter/inverter system. It is well known that switched capacitor circuits that are variants of the Dickson converter are suitable candidates for such a system. Modular design, absence of external magnetic components, and high efficiency are some of the features that make them suitable candidates. But, the inability to provide fractional and variable voltage gains at high efficiency during normal operation severely limits their application. It also leads to higher voltage stress in the overall system. The aim of this paper is twofold. First, a generalized modular switched capacitor converter, the “(n/m)X converter,” which is a variant of the original Dickson converter is introduced. Using this generalized configuration, the converter can be designed for a required fractional gain. Next, two different methods to enable dynamic variation in gain with high efficiency using the (n/m)X converter are proposed. Detailed analysis, design steps, equivalent circuits, and experimental results for a 1 kW prototype of a variable (4/0.5)X boost converter validate the proposed theory. A peak measured efficiency of over 95% is achieved for the prototype. The design framework and analysis in this paper can be extended to a generic (n/m)X converter. [ABSTRACT FROM AUTHOR]

An effective output voltage regulation method using harmonic burst control is presented. This method can greatly improve operating performance of the full-bridge series-resonant dc–dc converter (SRC) applied to electric vehicle (EV) battery charging. The proposed harmonic burst control not only provides load regulation, but it also achieves soft switching at both turn-ons and turn-offs under all load conditions. As a result, it improves the system efficiency over 10% for light-load conditions without any extra hardware, compared to that of the traditional frequency modulation method. Moreover, it has much smaller pulsed power over a wide range load compared to the traditional bang-bang burst control. Theoretical analysis of the series-resonant circuit and power loss analysis are discussed in detail in this paper. Experimental results based on a 1-kW prototype with 20-cm air gap between the primary and secondary sides of the series-resonant converter are presented to demonstrate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

In this paper, a modulation and control method for the new transformerless unified power flow controller (UPFC) is presented. As is well known, the conventional UPFC that consists of two back-to-back inverters requires bulky and often complicated zigzag transformers for isolation and reaching high power rating with desired voltage waveforms. To overcome this problem, a completely transformerless UPFC based on an innovative configuration of two cascade multilevel inverters has been proposed. The new UPFC offers several advantages over the traditional technology, such as transformerless, light weight, high efficiency, low cost and fast dynamic response. This paper focuses on the modulation and control for this new transformerless UPFC, including optimized fundamental frequency modulation for low total harmonic distortion and high efficiency, independent active and reactive power control over the transmission line, dc-link voltage balance control, etc. The new UPFC with proposed control method is verified by experiments based on 4160-V test setup. Both the steady-state and dynamic-response results will be shown in this paper. [ABSTRACT FROM PUBLISHER]

The major topology for wireless power transfer is resonant converters, which use fundamental harmonic approximation as a general analysis method. The accuracy of fundamental harmonic approximation (FHA) is unsatisfactory in some wireless power transfer applications, as the current has distortions due to the non-linear diode-bridge rectifier. Some frequency-domain models also consider harmonics beside fundamental component and indeed have a higher resolution. However, due to the difficulty of modeling the non-linear rectifier, most models are oversimplified by assuming a voltage source on the output to eliminate the rectifier. Moreover, the value of the voltage source is often treated as a fixed given number, which is not true for a resistive load. To cover a general case, this paper proposes a frequency-domain analytical model for resonant converters in continuous current mode (CCM) with the capability of considering any load and source situations in kHz frequency range. In terms of computation complexity, the proposed model only involves matrix operation (first-order). A simple algorithm has been chosen to demonstrate the fast convergency and high accuracy of the proposed model. The main findings are verified by the comparison between the theoretical calculation, time-domain simulation and experimental results, where the estimation of output power has 10% improvement than the FHA method. • Fundamental harmonic approximation is inaccurate in wireless power transfer. • Resonant converter models are limited on nonlinear diode-bridge rectifier. • An analytical model is developed for resonant converter in continuous conduction mode. • The analytical model has only one variable for fast computation of steady state. [ABSTRACT FROM AUTHOR]

Abstract: The quasi-Z-source inverter (qZSI) has some unique advantages and is suitable for photovoltaic (PV) system. This paper proposes a new topology—a qZSI with battery for PV power generation system. Battery is paralleled with one of the capacitors in quasi-Z-source (qZS) network, instead of an additional DC/DC converter. This system inherits all the advantages of qZSI. Besides, with a battery, the system can smooth the grid-injected power when PV power fluctuates. The operating principle of the new topology is analyzed and the design scheme of the qZS network is presented. And then, closed-loop control strategy for the proposed system is designed to manage the three power flows of PV panel, grid, and battery in the system. Maximum Power Point Tracking (MPPT) has been implemented in the qZSI with battery-based PV system by using the proposed control scheme. Different operating modes are simulated. A small-scale power prototype with a real PV panel is built to test the proposed system. The simulation results and experimental results verify the proposed circuit, theoretical analysis, and the control scheme. [Copyright &y& Elsevier]

This paper presents the design and development of a transformer isolated high-power dc-dc converter. There are several design issues and challenges. In this paper, we focus on three major issues in high-power dc-dc converters. 1) An energy recovery passive snubber circuit and the selection of pulsewidth modulation control methods are first introduced to reduce the voltage spike and power loss across switching devices. 2) Interleaved winding method is then employed to reduce proximity effect in the transformer winding. 3) The voltage oscillation problem in the secondary rectifier diode is addressed, and solutions are provided. [ABSTRACT FROM AUTHOR]

In this paper, three different inverters: conventional pulsewidth modulation (PWM) inverter, dc-dc boosted PWM inverter, and Z-source inverter were investigated and compared for fuel cell vehicle application. Total switching device power, passive components requirement, and constant power speed ratio of each of these inverters were calculated. For purposes of comparison, an example of the total switching device power, requirement of passive components, the constant power speed ratio, and the efficiencies of the different inverters for fuel cell vehicle powered by the same fuel cell were conducted. The comparisons show that the Z-source inverter is very promising in applications when the boost ratio is low (1–2). [ABSTRACT FROM AUTHOR]

This paper examines the demagnetization of a trapped magnetic field in a high TC superconducting (HTS) monolith using a single, short, high-amplitude field pulse. With a single optimized pulse, the peak trapped field can be reduced to one-third of the maximum saturated value. Alternatively, the spatial average of the trapped field could be fixed very close to zero. After demagnetization, the trapped field has both positive and negative values at various locations in the HTS monolith. Transient responses of the HTS to pulsed fields with different amplitudes are also reported and discussed. It does not appear that the residual trapped field can be reduced to zero throughout the monolith using pulsed field demagnetization methods in a fixed sample/coil geometry. Bean's critical state model is used to explain the measured equilibrium field distributions. Transient response of the HTS to an externally applied field is qualitatively explained by magnetic diffusion. Drive circuit characteristics and design feasibility issues are also addressed. [ABSTRACT FROM AUTHOR]

Compared with conventional field cooling (FC) and zero field cooling magnetization methods, pulsed field magnetization (PFM) is a promising way to magnetize high-temperature superconductors (HTS) with the advantage of dramatically decreasing the size and complexity of the electromagnetic charging system. The effects of the amplitude, width, and ramp rate of the pulsed current are reported. Transient responses of the HTS to pulsed magnetic fields are discussed and analyzed. A series of three pulses was found to be adequate to magnetize the HTS monolith with optimal trapped field if proper pulse amplitudes and widths are applied. Experiments verified that the trapped magnetic fields of HTS by PFM were comparable to those obtained by FC magnetization. [ABSTRACT FROM AUTHOR]